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Specific association between bacteria and buoyant Microcystis colonies compared with other bulk bacterial communities in the eutrophic Lake Taihu, China
Environmental Microbiology Reports
Abstract
The diversity of buoyant Microcystis colony-associated, settling particle-associated and free-living freshwater bacteria in the eutrophic Lake Taihu in China was compared by the polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) of 16S rRNA genes and by clone library analysis. The cluster analysis of DGGE profiles revealed that the buoyant Microcystis colony associates collected in summer and winter were clustered together and were distinct from settling particle-associated and free-living bacteria. In contrast, the bacterial communities of the latter two populations collected in summer were clustered together and varied from those collected in winter. The diversity indices of the Microcystis-associated bacterial population were significantly lower than those of the other two bulk bacterial communities (P < 0.05). Clone library analysis revealed that no shared operational taxonomic units were found in the three populations. Phylogenetic analysis confirmed that buoyant Microcystis-associated bacteria were distinct from the other communities and that they were dominated by Alphaproteobacteria, Betaproteobacteria and Gammaproteobacteria. Proteobacteria, Bacteroidetes and Actinobacteria were prevalent in all three habitats. Other bacterial taxa such as Planctomycetes, Verrucomicrobia, Gemmatimonadetes and Acidobacteria were associated with settling particles and with the water column. Buoyant Microcystis colonies, settling particles and the water column in the eutrophic lake are thus inhabited by different bacterial flora. In addition, specific bacterial communities are associated with buoyant Microcystis colonies.
... In different water bodies suffering Microcystis blooms, the composition of major bacteria phyla in attached bacterial community existed similarity. Of these major phyla, Proteobacteria have always been found to dominate attached bacterial communities (Shi et al. 2012;Parveen et al. 2013;Wu et al. 2019). Proteobacteria includes five classes, Alpha-, Beta-, Gamma, Delta-and Epsilonproteobacteria (Gouma et al. 2006). ...
... Proteobacteria includes five classes, Alpha-, Beta-, Gamma, Delta-and Epsilonproteobacteria (Gouma et al. 2006). Alpha-, Beta-and Gammaproteobacteria were usually became the dominant classes in attached bacterial communities (Humbert et al. 2009;Shi et al. 2009Shi et al. , 2012. In Chentaizi River, only Alpha-and Gammaproteobacteria were detected in attached bacterial community. ...
... Attached bacteria live in a microhabitat distinct from the surrounding water (Worm & Sondergaard 1998). The phylum composition in attached bacteria communities differed clearly from that in free-living bacterial communities (Shi et al. 2012;Parveen et al. 2013). However, we found there was significantly positive relationship between free-living and attached bacterial densities in Chentaizi River. ...
To further understand the role of attached bacteria in the formation of Microcystis colonies, we conducted a field investigation in Chentaizi River, a river often suffers Microcystis blooms during summer in Tianjin, China. The results showed the average cell density of Microcystis was 2.31 × 107 cell/L from July 19 to July 27, 2021. Free-living and attached bacteria communities shared similar phylum diversity, but the abundance changed obviously. The colony size of Microcystis and attached bacterial number in the colony showed an increasing trend during the whole sampling period. There was a significant positive correlation between Microcystis colonial size and attached bacterial density (P < 0.01), indicating attached bacteria could contribute the colony formation of Microcystis. The genus composition in attached bacterial community varied in colonies of different sizes. The relative abundance of Acinetobacter, Cloacibacterium, Sphingobacterium, and Ralstonia in >90 μm colonies were significantly higher than those in 8–20 μm and 20–90 μm colonies (P < 0.05). These genera might have positive effects on the colony formation of Microcystis during sampling.
... Since bacterial composition strongly shapes the functional potential of microbiomes there has been a great interest in understanding the compositional diversity and dynamics of bacterial assemblages during Microcystis blooms. Earlier studies used PCR/DGGE (Riemann and Winding, 2001;Shi et al., 2009Shi et al., , 2012Shen et al., 2011;Dziallas and Grossart, 2012;Parveen et al., 2013), T-RFLP (Eiler and Bertilsson, 2004;Li et al., 2011) and FISH (Maruyama et al., 2003;Dziallas and Grossart, 2012) to assess Microcystis colony-associated microbiomes. In recent years, several studies have been using high-throughput sequencing approaches including next generation amplicon sequencing (Wilhelm et al., 2011;Cai et al., 2014;Louati et al., 2015), metagenomics (Li et al., 2018) and metatranscriptomics (Berg et al., 2018), providing a more comprehensive and high resolution understanding of bacterial communities. ...
... Differences have been observed between the Microcystis colony co-occurring and free-living consortia, with members of the α-, β-, and γ-proteobacteria, and Bacteroidetes often enriched within the colonies (Cai et al., 2014;Shao et al., 2014;Akins et al., 2018). However, to date few studies have investigated compositional differences of free-living and colony-associated bacteria in natural systems (Kapustina, 2006;Shi et al., 2012;Parveen et al., 2013), and those that have were often over limited spatial and/or temporal scales (Yang et al., 2017;Akins et al., 2018). Further, while there has been extensive research on the impacts of nutrient loading and climatic warming on cyanobacteria composition and proliferation, there remains a limited understanding of how these parameters shape the compositions of naturally occurring Microcystis-associated bacteria communities and their functional potential (Wilhelm et al., 2011;Dziallas and Grossart, 2012). ...
... Size fractionation explained the largest amount of variability in the composition of the bacterial communities, accounting for over a quarter of the variation among both lakes and up to 75% of the variation within individual lakes. Such dissimilarity is consistent with prior studies that have identified compositionally different free-living and cyanobacteria-associated bacteria assemblages in lake systems (Shi et al., 2012;Parveen et al., 2013;Akins et al., 2018). The present study, however, further demonstrates differences even between the whole bacterial community and colony-associated communities. ...
The toxic cyanobacterium Microcystis is one of the most pervasive harmful algal bloom (HAB) genera and naturally occurs in large colonies known to harbor diverse heterotrophic bacterial assemblages. While colony-associated microbiomes may influence Microcystis blooms, there remains a limited understanding of the structure and functional potential of these communities and how they may be shaped by changing environmental conditions. To address this gap, we compared the dynamics of Microcystis-attached (MCA), free-living (FL), and whole water (W) microbiomes during Microcystis blooms using next-generation amplicon sequencing (16S rRNA), a predictive metagenome software, and other bioinformatic approaches. Microbiomes were monitored through high resolution spatial-temporal surveys across two North American lakes, Lake Erie (LE) and Lake Agawam (LA; Long Island, NY, United States) in 2017, providing the largest dataset of these fractions to date. Sequencing of 126 samples generated 7,922,628 sequences that clustered into 7,447 amplicon sequence variants (ASVs) with 100% sequence identity. Across lakes, the MCA microbiomes were significantly different than the FL and W fractions being significantly enriched in Gemmatimonadetes, Burkholderiaceae, Rhizobiales, and Cytophagales and depleted of Actinobacteria. Further, although MCA communities harbored > 900 unique ASVs, they were significantly less diverse than the other fractions with diversity inversely related to bloom intensity, suggesting increased selection pressure on microbial communities as blooms intensified. Despite taxonomic differences between lakes, predicted metagenomes revealed conserved functional potential among MCA microbiomes. MCA communities were significantly enriched in pathways involved in N and P cycling and microcystin-degradation. Taxa potentially capable of N2-fixation were significantly enriched (p < 0.05) and up to four-fold more abundant within the MCA faction relative to other fractions, potentially aiding in the proliferation of Microcystis blooms during low N conditions. The MCA predicted metagenomes were conserved over 8 months of seasonal changes in temperature and N availability despite strong temporal succession in microbiome composition. Collectively, these findings indicate that Microcystis colonies harbor a statistically distinct microbiome with a conserved functional potential that may help facilitate bloom persistence under environmentally unfavorable conditions.
... Thus, ACC, BCC, and their interactions are important parts of community ecology in littoral zones. There have been some reports about the differences of ACC/BCC between different habitats (Grossart et al., 2003;He et al., 2014;Fan et al., 2016;Pang et al., 2016;Levi et al., 2017) and the correlations between ACC and BCC in a specific habitat (Kent et al., 2007;Niu et al., 2011;Shi et al., 2012) (For precise description, see Table 1). However, there is little information about the algal and bacterial community distributions and algae-bacterial correlations based on habitat species pools. ...
... Levi et al., 2017 Researches about correlations between ACC & BCC in a specific habitat In water column (in lakes) Variation trend of Shannon-Wiener diversity index in bacterioplankton community was similar to that of phytoplankton community. Temperature and phytoplankton played key roles in structuring BCC Niu et al., 2011 On the surface of algae (in lakes) Specific bacterial communities are associated with the dominant algae Shi et al., 2012 In water column (in lakes) Synchrony exists between phytoplankton and bacterioplankton community dynamics. Kent et al., 2007 highest relative abundance of Planctomycetes (19.16%) and Verrucomicrobia (18.72%); ...
... This could also explain the significant correlation between PA and PB in our study. In terms of the periphytic habitats, habitat specificities were found in both BCC and ACC in this study, and besides, host specificities were found in algae-and plant-attaching habitats in previous studies (Shi et al., 2012;Fan et al., 2016). However, the correlation of community distributions between algae and bacteria were not found in the periphytic habitats in this study. ...
Understanding of community ecology is scale dependent. When the scale definition changes from subjectively defined "regional species pools" to "habitat species pools", heterogeneity differences occur for microbial communities. However, given the environmental gradients differences among habitats, responses of other organisms and interspecific correlations to habitat species pools may also be heterogeneous. This hypothesis is supported by our research about algal and bacterial communities among four different habitats in littoral zones. In our results, both the algal and bacterial community compositions varied along habitat species pools. Furthermore, at community level, significant correlation was only found between bacterioplankton and phyto-plankton in pelagic habitat. And at individual level, the covariant trends between habitat generalists in algal and bacterial communities varied among habitats. Our results indicated that habitat-specific patterns can not only influence the habitat species pools, but also shape the interspecies interaction, and this should be considered in the further study of algae-bacterial correlation.
... Bacterial phylotypes belonging to Proteobacteria, Bacteroidetes and Actinobacteria are frequently detected in bacterial community associated with Microcystis spp. (Cai et al. 2014;Parveen et al. 2013;Shi et al. 2009Shi et al. , 2012. Species-specific associations between Microcystis species and its associated bacteria have been found in culture and natural environments (Shi et al. , 2010. ...
... Previous studies have reported the composition of bacterial community associated with Microcystis in natural freshwater ecosystems (Parveen et al. 2013;Shi et al. 2012). However, the natural samples may include different Microcystis species and Microcystis cells of different growth phases. ...
... Because there is no interference from different Microcystis species, cyanobacterial cells of different growth phases or environmental factors, our investigation in this study could provide a valuable reference about the research on community composition of Microcystis-associated bacteria. Consistent with the reports on a Chinese lake (Lake Taihu) and a French lake (the Villerest reservoir) (Parveen et al. 2013;Shi et al. 2012), Proteobacteria and Bacteroidetes were present in both the Microcystis colony-attached and free-living bacterial communities, and Proteobacteria was the most dominant phylum in the colony-attached bacterial communities (Fig. 1). Consistent with the report on the Villerest reservoir (Parveen et al. 2013), Proteobacteria was the most dominant phylum in the free-living bacterial communities in the stationary growth phase of Microcystis (Fig. 1). ...
A better understanding of the distribution pattern of bacterial community in the Microcystis phycosphere will aid in elucidating the role of bacteria in the formation of cyanobacterial bloom. In the present study, we aimed to compare community composition between Microcystis colony-attached and free-living bacteria, as well as among bacteria attached with Microcystis colonies of various sizes in culture. In the exponentially growing cyanobacterial cultures, Proteobacteria was the most dominant phylum in each colony-attached bacterial community, whereas Bacteroidetes was the most dominant phylum in each free-living bacterial community. The analysis using an indirect PCA model and Bray–Curtis dissimilarity index indicated that the dissimilarity between colony-attached and free-living bacterial communities was greater in the exponentially growing cyanobacterial cultures, and it became smaller in the stationary cultures of Microcystis. In the exponential growth phase of Microcystis, the relative abundance of Proteobacteria in colony-attached bacterial communities tended to decrease with decreasing colony size, whereas the relative abundance of Bacteroidetes in colony-attached bacterial communities tended to increase. In the exponential growth phase of Microcystis, the community composition dissimilarity among bacteria attached with Microcystis colonies of various sizes could be ranked in a descending order as follows: > 100 µm versus < 50 µm; 50–100 µm versus < 50 µm; and > 100 µm versus 50–100 µm. Our data indicated that the community composition of Microcystis colony-attached bacteria was different from that of free-living bacteria, and the colony size of Microcystis played an important role in structuring the community composition of Microcystis-attached bacteria.
... Thus, ACC, BCC, and their interactions are important parts of community ecology in littoral zones. There have been some reports about the differences of ACC/BCC between different habitats (Grossart et al., 2003;He et al., 2014;Fan et al., 2016;Pang et al., 2016;Levi et al., 2017) and the correlations between ACC and BCC in a specific habitat (Kent et al., 2007;Niu et al., 2011;Shi et al., 2012) (For precise description, see Table 1). However, there is little information about the algal and bacterial community distributions and algae-bacterial correlations based on habitat species pools. ...
... Levi et al., 2017 Researches about correlations between ACC & BCC in a specific habitat In water column (in lakes) Variation trend of Shannon-Wiener diversity index in bacterioplankton community was similar to that of phytoplankton community. Temperature and phytoplankton played key roles in structuring BCC Niu et al., 2011 On the surface of algae (in lakes) Specific bacterial communities are associated with the dominant algae Shi et al., 2012 In water column (in lakes) Synchrony exists between phytoplankton and bacterioplankton community dynamics. Kent et al., 2007 highest relative abundance of Planctomycetes (19.16%) and Verrucomicrobia (18.72%); ...
... This could also explain the significant correlation between PA and PB in our study. In terms of the periphytic habitats, habitat specificities were found in both BCC and ACC in this study, and besides, host specificities were found in algae-and plant-attaching habitats in previous studies (Shi et al., 2012;Fan et al., 2016). However, the correlation of community distributions between algae and bacteria were not found in the periphytic habitats in this study. ...
Understanding of community ecology is scale‐dependent. When the scale definition changes from subjectively defined “regional species pools” to “habitat species pools”, heterogeneity differences occur for microbial communities. However, given the environmental gradients differences among habitats, responses of other organisms and interspecific correlations to habitat species pools may also be heterogeneous. This hypothesis is supported by our research about algal and bacterial communities among 4 different habitats in littoral zones. In our results, both the algal and bacterial community compositions varied along habitat species pools. Furthermore, at community level, significant correlation was only found between bacterioplankton and phytoplankton in pelagic habitat. And at individual level, the covariant trends between habitat generalists in algal and bacterial communities varied among habitats. Our results indicated that habitat‐specific patterns can not only influence the habitat species pools, but also shape the interspecies interaction, and this should be considered in the further study of algae‐bacterial correlation.
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... Typically, bloom-forming cyanobacteria occur as colonies embedded in mucilaginous matrices or as filaments within mucilaginous sheaths. The surfaces of cyanobacteria and their surrounding mucilage form microenvironments that make up the phycosphere, a distinctive habitat which supports heterotrophic bacterial communities that generally differ from the surrounding bacterioplankton (Li et al. 2011;Louati et al. 2015;Niu et al. 2011;Parveen et al. 2013a, b;Shi et al. 2012). These microenvironments are protected from physicochemical fluctuations in the water column (Paerl 1996) and are rich in organic compounds, including polysaccharides (Parikh and Madamwar 2006;Pereira et al. 2009;Plude et al. 1991;Xu et al. 2013) and oligopeptides (such as microcystins and nodularins) that can be used as carbon sources by some bacteria (Imanishi et al. 2005;Jones et al. 1994;Maruyama et al. 2003). ...
... contains supplementary material, which is available to authorized users. Parveen et al. 2013a;Shi et al. 2012). Comparisons across multiple lakes are necessary to understand whether differences between FL and CA bacterial communities are attributable to innate selective properties imposed by the cyanobacteria-microhabitat. ...
... Composition of bacterial communities associated with mucilaginous cyanobacteria varies but often includes Bacteroidetes and Actinobacteria (Cai et al. 2014;Li et al. 2011;Louati et al. 2015;Niu et al. 2011;Parveen et al. 2013a;Shen et al. 2011;Shi et al. 2012). Actinobacteria tend to be predominantly free-living cells incidentally co-occurring with cyanobacteria (Louati et al. 2015;Parveen et al. 2013b), although some members of this phylum live within the mucilage . ...
Lakes undergoing cyanobacterial blooms often exhibit differences between free-living (FL) and cyanobacteria-associated (CA) bacterial assemblages, but previous studies have not compared distinct FL and CA communities across multiple lakes. This project investigated whether FL and CA communities differ from each other in consistent ways across lakes. FL and CA communities were collected from three Ohio (USA) lakes on two sampling dates during cyanobacterial blooms. High-throughput sequencing was used to characterize the communities, and comparisons were made of the composition and diversity of FL and CA communities within and across lakes. Diversity estimates did not vary significantly among lakes nor between CA and FL assemblages. The taxonomic composition of CA communities differed significantly from that of FL communities in Buckeye and Harsha Lakes and in Maumee Bay on one of two sampling dates. CA communities from Buckeye and Harsha Lakes were more similar to each other than to their respective FL communities. Community composition in Maumee Bay on August 18 did not differ between FL and CA habitats. As the bloom progressed, the FL community remained similar in composition to samples collected on August 18, while the CA community became significantly dissimilar. This study is the first cross-lake comparisons of CA and FL communities, uncovering the impacts of habitat type, lake, and sampling date in determining community composition.
... Typically, bloom-forming cyanobacteria occur as colonies embedded in mucilaginous matrices or as filaments within mucilaginous sheaths. The surfaces of cyanobacteria and their surrounding mucilage form microenvironments that make up the phycosphere, a distinctive habitat which supports heterotrophic bacterial communities that generally differ from the surrounding bacterioplankton (Li et al. 2011;Louati et al. 2015;Niu et al. 2011;Parveen et al. 2013a, b;Shi et al. 2012). These microenvironments are protected from physicochemical fluctuations in the water column (Paerl 1996) and are rich in organic compounds, including polysaccharides (Parikh and Madamwar 2006;Pereira et al. 2009;Plude et al. 1991;Xu et al. 2013) and oligopeptides (such as microcystins and nodularins) that can be used as carbon sources by some bacteria (Imanishi et al. 2005;Jones et al. 1994;Maruyama et al. 2003). ...
... contains supplementary material, which is available to authorized users. Parveen et al. 2013a;Shi et al. 2012). Comparisons across multiple lakes are necessary to understand whether differences between FL and CA bacterial communities are attributable to innate selective properties imposed by the cyanobacteria-microhabitat. ...
... Composition of bacterial communities associated with mucilaginous cyanobacteria varies but often includes Bacteroidetes and Actinobacteria (Cai et al. 2014;Li et al. 2011;Louati et al. 2015;Niu et al. 2011;Parveen et al. 2013a;Shen et al. 2011;Shi et al. 2012). Actinobacteria tend to be predominantly free-living cells incidentally co-occurring with cyanobacteria (Louati et al. 2015;Parveen et al. 2013b), although some members of this phylum live within the mucilage . ...
... The bacteria attached to medium-and small-sized cyanobacterial aggregates during August and September were clustered, whereas large-and medium-sized aggregate communities in the October sample were grouped together and appeared distinct from the small-sized aggregate community (Cai, Jiang, Krumholz, & Yang, 2014;Cai, Yan, Wang, Krumholz, & Jiang, 2013). Different bacteria attached to Microcystis colonies from freeliving bacteria for several months were also documented (Parveen et al., 2013;Shi, Cai, Kong, & Yu, 2012). However, bacteria involved in three habitats, including large buoyant cyanobacterial colonies, small particles, and free-living bacteria in the water column, have yet to be compared in a duration of 1 year. ...
... Moreover, a lower diversity of bacterial communities was observed in LA than in FL, which has lower diversity than SA. Consistent with our previous observation, the bacterial communities attached to buoyant Microcystis colonies had lower diversity compared with other bulk bacteria (Shi et al., 2012). These results indicated that LA was different from regular large particles, which may also harbor different communities compared with FL but had selectivity for the attached bacteria. ...
... Interestingly, proportions of Planctomycetaceae were significantly higher in SA than that in LA. This result was consistent with our previous observation that Planctomycetaceae were few in buoyant Microcystis colonies (Shi et al., 2012). Although close associations between Planctomycetes and cyanobacterial colonies were observed (Cai et al., 2013;Tang et al., 2010), free-living Planctomycetes were also observed in hypoxic zone induced by Microcystis blooms (Li, Xing, & Wu, 2012). ...
Worldwide cyanobacterial blooms greatly impair ecosystems in many eutrophic lakes and impact the microbial environment. In particular, large cyanobacterial colonies that are buoyant on the water surface may provide a distinct habitat for bacteria from other small particles that are suspended stably in the water column. To test this hypothesis, bacterial communities (excluding cyanobacteria) attached to large particles dominated by cyanobacterial colonies (>120 μm, LA), small particles (3–36 μm, SA), and free‐living bacteria (0.2–3 μm, FL) were investigated monthly for a year in Lake Taihu, China. Results confirmed that the Shannon diversity index of LA was significantly lower than that of FL, which was lower than that of SA. Cytophagia and Alphaproteobacteria were specially enriched in LA. Although samples in each habitat collected during high‐ (May to November) and low‐bloom seasons (December to April) were separated, all samples in LA were clustered and separated from SA and FL, which were also clustered during the same sampling seasons. In addition, the bacterial communities in LA were correlated with nitrate level, whereas FL and SA were correlated with nitrate level and temperature. Mantel analysis revealed that bacterial composition significantly correlated with the cyanobacterial composition in LA and FL but not in SA. These results indicate that LA provides distinct niches to bacteria, whereas the differentiation of bacterial communities in FL and SA is seasonally dependent.
... Several studies have indicated that the Microcystis-adhered microbiome displays considerably less diversity of bacterial taxon than is found associated with free-living bacterioplankton. For example, association of members of rather limited taxonomic groups like Rhodobacterales, Sphingomonadales, Burkholderiales and Xanthomonadaceae was reported for Microcystis colonies (Shi et al. 2012). In contrast, much diverse taxa were prevalent in other habitats, and some of them could also be equally dominant in the cyanosphere. ...
... In contrast, much diverse taxa were prevalent in other habitats, and some of them could also be equally dominant in the cyanosphere. Furthermore, lack of Actinobacteria and dominance of Gammaproteobacteria are other characteristic features of cyanosphere communities (Shi et al. 2012;Parveen et al. 2013). More recently, it was reported that each Microcystis colony represent an oligotype comprised of same genotype of cells, which may differ from other colonies with respect to the 16S rRNA gene sequence (variable region; Smith et al. 2021). ...
The study was undertaken to size-fractionate the bacterial population associated with Microcystis blooms of an eutrophic lake. Two bacterial cultures were isolated from the particulate-bound fraction, and biochemical tests, phylogenetic analysis and homology of 16S rRNA gene sequences revealed their high similarity with Aeromonas veronii and Shigella flexneri. Another isolate with characteristics resembling Escherichia fergusonii was obtained in phytoplankton-free water samples. Since these three cultures were enriched on chitin-selective medium, their capability to utilize chitin as a sole C source was examined. The in vivo chitinase activity (as µg N‑acetyglucosamine produced min–1 mL–1 culture) was 82.1, 28.5 and 18.5 for A. veronii, S. flexneri and E. fergusonii, respectively. The corresponding N‑acetylglucosamine accumulation in medium was 421, 288 and 122 µg mL–1. There was also a gradation in growth indices in the three bacteria, which corresponded to their chitin utilization ability. Notwithstanding differences in chitinase activity, the three strains utilized almost equally the exogenous N‑acetylglucosamine. We propose that chitinase activity may have a role in affinity of the particular bacterial cell to phytoplankton extracellular polymeric substances and therefore, adherence ability.
... The families Xanthomonadaceae and Alcaligenaceae were be considered species-specific bacteria for Microcystis and Psephonema in Lake Erhai. The highly significant positive correlation between dominant algae and their species-specific bacteria in aquatic ecosystems suggests an important relationship between algal and bacterial communities (Niu et al. 2011;Shi et al. 2012). Our results show that the variation in bacterial community composition correlated with phytoplankton succession, particularly the variation in attached bacterial communities. ...
... The similarities of Microcystis-associated, settling particle-associated and free-living bacteria Shi et al. (2012) Lake Erie, USA Bacterial abundance (OTU richness) Chl a, pH, temperature Berry et al. (2017) Two north temperate humic lakes in Vilas County, Wisconsin ...
Bacterial communities are an important part of biological diversity and biogeochemical cycling in aquatic ecosystems. In this study, the relationship amongst the phytoplankton species composition and abiotic environmental factors on seasonal changes in the community composition of free-living and attached bacteria in Lake Erhai were studied. Using Illumina high-throughput sequencing, we found that the impact of environmental factors on both the free-living and attached bacterial community composition was greater than that of the phytoplankton community , amongst which total phosphorus, Secchi disk, water temperature, dissolved oxygen and conductivity strongly influenced bacterial community composition. Microcystis blooms associated with subdominant Psephonema occurred during the summer and autumn, and Fragilaria, Melosira and Mougeotia were found at high densities in the other seasons. Only small numbers of algal species-specific bacteria, including Xanthomonadaceae (Proteobacteria) and Alcaligenaceae (Betaproteobacteria), were tightly coupled to Microcystis and Psephonema during Microcystis blooms. Redundancy analysis showed that although the composition of the bacterial communities was controlled by species composition mediated by changes in phytoplankton communities and abiotic environmental factors, the impact of the abiotic environment on both free-living and attached bacterial community compositions were greater than the impact of the phytoplankton community. These results suggest that the species composition of both free-living and attached bacterial communities are affected by abiotic environmental factors, even when under strong control by biotic factors, particularly dominant genera of Microcystis and Psephonema during algal blooms.
... As phototrophic organisms, cyanobacteria release extracellular organic chemicals, primarily proteins and polysaccharides, which support the survival of associated microbes (Liang et al., 2021). In this symbiosis, attached bacteria supply essential nutrients like nitrogen and phosphorus that support cyanobacterial growth (Shi et al., 2012). ...
Cyanobacterial harmful algal blooms (CyanoHABs) represent a significant threat to freshwater ecosystems globally. To investigate the bacterial communities associated with these blooms, we conducted a metabarcoding analysis of water samples collected during the blooming events in various freshwater reservoirs, including Veeranam, Wellington, Perumal lake at Cuddalore and Trichy Kottapattu Pond, Tamil Nadu, India. Utilizing Metabarcoding of 16S rRNA amplicon sequencing, we characterized the taxonomic composition of bacterial communities in freshwater reservoirs. Our study revealed the dominance of key phyla such as Proteobacteria, Bacteroidetes, Firmicutes, and Actinobacteria across all four freshwater reservoirs. Predominantly, the abundance of cyanobacterial genera, notably toxin-producing Microcystis sp. and Nostoc sp., were identified, which played a crucial role in driving cyanobacterial bloom formation. Multifaceted interactions between bacteria and cyanobacteria, including core microbiomes and beta diversity patterns, shed light on the microbial dynamics underlying CyanoHABs. This provides a comprehensive understanding of freshwater reservoir Cyanobacterial dynamics, highlighting the bacterial communities involved in bloom events. These findings are crucial for protecting freshwater ecosystems and public health from the harmful effects of cyanobacterial blooms.
... In previous studies on the composition of the free-living bacterial community from various French lakes, Actinobacteria accounted for 20-60 % of the sequences (Boucher et al., 2006;Debroas et al., 2009;Humbert et al., 2009;Parveen et al., 2013), and similar findings were obtained in other countries (e.g. Sekar et al., 2003;Shi et al., 2012;Warnecke et al., 2004). While Actinobacteria are more abundant in pelagic freshwater habitats (Allgaier and Grossart, 2006;Glöckner et al., 2000;Sekar et al., 2003;Warnecke et al., 2005) than pelagic marine environments (Pommier et al., 2007), they remain significant members of the autochthonous estuarine community (e.g. in the central Baltic Sea proper (Riemann et al., 2008) or in the Delaware Estuary (Kirchman et al., 2005), displaying adaptability to estuarine gradients (Kirchman et al., 2005;Langenheder et al., 2003;Stevens et al., 2007). ...
Due to climate changes and eutrophication, blooms of predominantly toxic freshwater cyanobacteria are
intensifying and are likely to colonize estuaries, thus impacting benthic organisms and shellfish farming representing
a major ecological, health and economic risk. In the natural environment, Microcystis form large
mucilaginous colonies that influence the development of both cyanobacterial and embedded bacterial communities.
However, little is known about the fate of natural colonies of Microcystis by salinity increase. In this study,
we monitored the fate of a Microcystis dominated bloom and its microbiome along a French freshwater-marine
gradient at different phases of a bloom. We demonstrated changes in the cyanobacterial genotypic composition,
in the production of specific metabolites (toxins and compatible solutes) and in the heterotrophic bacteria
structure in response to the salinity increase. In particular M. aeruginosa and M. wesenbergii survived salinities up
to 20. Based on microcystin gene abundance, the cyanobacteria became more toxic during their estuarine
transfer but with no selection of specific microcystin variants. An increase in compatible solutes occurred along
the continuum with extensive trehalose and betaine accumulations. Salinity structured most the heterotrophic
bacteria community, with an increased in the richness and diversity along the continuum. A core microbiome in
the mucilage-associated attached fraction was highly abundant suggesting a strong interaction between Microcystis
and its microbiome and a likely protecting role of the mucilage against an osmotic shock. These results
underline the need to better determine the interactions between the Microcystis colonies and their microbiome as
a likely key to their widespread success and adaptation to various environmental conditions.
... Overall, these functions underlined the ability of these orders to degrades complex compounds. Given these biological functions, these orders, abundant during phytoplanktonic blooms [29][30][31], can directly and indirectly affect bloom development. ...
Global change severely increases the recurrence of freshwater cyanobacterial proliferations, with known deleterious consequences for ecosystem structure and functioning. A few studies highlighted the existence of bacterial communities associated to cyanobacteria (i.e., Cyanosphere), comparable to the well-known phycosphere. While phycosphere in general is expected to exchange nutrients with their associated phytoplankton communities, specific functions and dynamic of the cyanosphere remain unknown. Here, based on metabarcoding approaches, we showed that during bloom episodes, cyanosphere accounts for up to 30% of total bacterial abundance. More importantly, we demonstrated for the first-time the dynamics aspect of cyanosphere community composition at crucial bloom phases. In our study, these community changes imply variations in cyanosphere ecological functions over time. Our results highlight the ability of cyanosphere to regulate nutrient and energy exchange with cyanobacteria during the entire bloom period, modulating bloom intensity and dynamics. In the latter bloom phases, cyanosphere additionally tends to create microhabitats favoring cyanobacterial persistence in deleterious environmental conditions. At wider scale, as blooms constitute major turnovers of matter and energy in aquatic ecosystems, we argue that cyanosphere can have an important, yet underestimated, role in mediating C and nutrient cycles in environments.
... with Microcystis spp. (Cai et al., 2014;Parveen et al., 2013;Shi et al., 2012Shi et al., , 2009). ...
The presence of taste and odour compounds (T&O) in drinking water lead to numerous complaints to water companies worldwide. Geosmin and 2-MIB are common T&O compounds, with Cyanobacteria being the primary biological source in drinking water reservoirs. Both compounds have low odour thresholds in humans and require expensive additional treatment. This thesis used molecular and statistical analysis of water from Welsh Water reservoirs, to provide a framework for predicting and monitoring T&O events and understanding their causes.
Elevated T&O concentrations were confined to warmer months, except for a one geosmin event in winter 2019. There was no correlation between cyanobacterial abundance and T&O concentrations, but qPCR analysis based on eDNA sampling demonstrated that geosmin synthase (geoA) was a suitable proxy for predicting geosmin concentrations. Abundances of geoA and 2-MIB cyclase (mic) were significantly non-linearly associated with high ammonium-to-nitrate ratios, identifying thresholds for heightened T&O risk. The ratio of total inorganic nitrogen to total phosphorous was significantly non-linearly associated with increases in geoA. Increased geoA was also significantly negatively associated with temperature and dissolved reactive silicate in all reservoirs. Next-generation sequencing of bacterial and algal communities showed that community compositions clustered according to T&O concentrations. Bacterial and algal co-occurrence networks uncovered significant positive and negative associations, highlighting cyanospheres in all reservoirs. Random Forest models were developed for geosmin (Alaw) and 2-MIB (Pentwyn) using significantly co-occurring taxa exposing indicative T&O taxa and the probable Cyanobacteria causing the T&O. Cyanobacteria had more negative than positive associations in their cyanospheres.
This thesis illustrates the importance of nutrient ratios in triggering potential geosmin and 2-MIB events. It also indicates that Cyanobacteria subjected to environmental stress (negative biotic interactions and low temperatures) increase their T&O-production. These findings provide a useful framework for water monitoring to enable the prediction and possible prevention of T&O events.
... Upon the rapid development of genomics, metagenomics, and metabolomics, a growing number of studies have been focused on the interrelation between cyanobacteria and the attached bacteria, including the community succession dynamics, co-metabolic pathways, material exchanges and signal transmission [60][61][62]. In this symbiosis system, cyanobacteria could provide energy for their neighboring heterotrophic bacteria, whereas the attached bacteria in turn supply nitrogen and phosphorous for cyanobacteria [63,64]. The cyanobacteria Synechococcus and heterotrophic bacteria could survive permanently without the supply of external nutrients, after changing their relationship from antagonism to mutualism during long-term cocultivation [62]. ...
Background
Along with the fast development and urbanization in developing countries, the waterbodies aside the growing cities become heavily polluted and highly eutrophic, thus leading to the seasonal outbreak of cyanobacterial bloom. Systematic isolation and characterization of freshwater cyanophages might provide a biological solution to control the awful blooms. However, genomic sequences and related investigations on the freshwater cyanophages remain very limited to date.
Results
Following our recently reported five cyanophages Pam1~Pam5 from Lake Chaohu in China, here we isolated another five cyanophages, termed Pan1~Pan5, which infect the cyanobacterium Pseudanabaena sp. Chao 1811. Whole-genome sequencing showed that they all contain a double-stranded DNA genome of 37.2 to 72.0 kb in length, with less than half of the putative open reading frames annotated with known functions. Remarkably, the siphophage Pan1 encodes an auxiliary metabolic gene phoH and constitutes, together with the host, a complete queuosine modification pathway. Proteomic analyses revealed that although Pan1~Pan5 are distinct from each other in evolution, Pan1 and Pan3 are somewhat similar to our previously identified cyanophages Pam3 and Pam1 at the genomic level, respectively. Moreover, phylogenetic analyses suggested that Pan1 resembles the α -proteobacterial phage vB_DshS-R5C, revealing direct evidence for phage-mediated horizontal gene transfer between cyanobacteria and α -proteobacteria.
Conclusion
In addition to the previous reports of Pam1~Pam5, the present findings on Pan1~Pan5 largely enrich the library of reference freshwater cyanophages. The abundant genomic information provides a pool to identify novel genes and proteins of unknown function. Moreover, we found for the first time the evolutionary traces in the cyanophage that horizontal gene transfer might occur at the level of not only inter-species, but even inter-phylum. It indicates that the bacteriophage or cyanophage could be developed as a powerful tool for gene manipulation among various species or phyla.
... Although negative correlations between Gammaproteobacteria (Xanthomonadales) and the cyanobacterial bloom-forming OTUs were not statistically significant, references report Xanthomonadales to be associated with blooms of Microcystis spp. [100] but also with blooms of Planktothrix spp. or co-dominated by strains of Microcystis, Dolichospermum, Cylindrospermopsis and Synechococcus [119]. Moreover, Gammaproteobacteria comprise many pathogens, and can potentially increase health risks during cyanobacterial blooms [120][121][122]. ...
Climate change is enhancing the frequency of cyanobacterial blooms not only during summer but also in spring and autumn, leading to increased ecological impacts. The bacterioplankton community composition (BCC), in particular, is deeply affected by these blooms, although at the same time BCC can also play important roles in blooms’ dynamics. However, more information is still needed regarding BCC during species-specific cyanobacterial blooms. The goal of this study was to assess BCC succession in a hypereutrophic shallow lake (Vela Lake, Portugal) during a warm spring using a metagenomic approach to provide a glimpse of the changes these communities experience during the dominance of Aphanizomenon-like bloom-forming species. BCC shifts were studied using 16S rRNA gene metabarcoding and multivariate analyses. A total of 875 operational taxonomic units (OTUs) were retrieved from samples. In early spring, the dominant taxa belonged to Proteobacteria (mainly Alphaproteobacteria—Rickettsiales) and Bacteroidetes (Saprospirales, Flavobacteriales and Sphingobacteriales). However, at the end of May, a bloom co-dominated by cyanobacterial populations of Aphanizomenon gracile, Sphaerospermopsis aphanizomenoides and Synechococcus sp. developed and persisted until the end of spring. This led to a major BCC shift favouring the prevalence of Alphaproteobacteria (Rickettsiales and also Rhizobiales, Caulobacteriales and Rhodospirillales) and Bacteroidetes (Saprospirales, followed by Flavobacteriales and Sphingobacteriales). These results contribute to the knowledge of BCC dynamics during species-specific cyanobacterial blooms, showing that BCC is strongly affected (directly or indirectly) by Aphanizomenon-Sphaerospermopsis blooms.
... Serious cyanobacterial blooms, mainly caused by Microcystis aeruginosa (Ma) [1], occurred almost every year from 1990 to 2005 in this lake mainly because of the dumping of agricultural, domestic and industrial waste [2]. Cells of Microcystis were often covered by mucilages, which provide a special ecological niche for attached bacteria [3][4][5]. Interactions between the cyanobacteria and these bacteria are extremely complex. The interactions are categorized into nutrient exchange, signal transduction, and gene transfer, of which nutrient exchange has been considered as the most common type of interactions [6] and frequently the basis of cyanobacterial-bacterial mutualism [7]. ...
A Gram-stain positive, aerobic, rod-shaped actinobacterial strain designated as JXJ CY 27-2T was isolated from the culture of Microcystis aeruginosa FACHB-905 (Maf) collected from Lake Kunming, southwest China. The isolate was catalase positive, oxidase negative, and able to grow at 10.0-44.0 °C, pH 5.0-10.0 and 0–5.0% NaCl. Based on the 16S rRNA gene sequences, JXJ CY 27-2T showed high similarities of 98.54–98.55% with Microbacterium invictum DSM 19600T, Microbacterium saccharophilum DSM 28107T, and Microbacterium aoyamense DSM 19461T, and less than 98.47% similarities with other members of the genus. Its major cellular fatty acids were anteiso-C17:0 and anteiso-C15:0. The predominant menaquinones were MK-11 and MK-12. The diagnostic diamino acid in the cell wall peptidoglycan was lysine. Whole cell sugars contained mannose, ribose, galactose, rhamnose and arabinose. The polar lipids were diphosphatidylglycerol, phosphatidylglycerol, two unidentified glycolipids, and an unidentified lipid. The DNA G + C content was 69.8%. The digital DNA-DNA hybridization and average nucleotide identity values between strain JXJ CY 27-2T and its three closest similar strains were 18.4–20.3% and 74.9–75.7%, respectively. Based on the above data, strain JXJ CY 27-2T was identified as a new species of the genus Microbacterium, for which the name Microbacterium kunmingensis sp. nov. is proposed. The type strain is JXJ CY 27-2T (=CGMCC 1.17506T = KCTC 49382T). Strain JXJ CY 27-2T could promote the growth of Maf by providing it with available phosphorus, nitrogen and probably other nutrients such as vitamins and indole-3-acetate.
... The interactions between freshwater cyanobacterial blooms and their associated bacteria play an important role in the regulation of cyanobacterial growth (Paerl, 1996;Rashidan & Bird, 2001;Eiler et al., 2006). Shi et al. (2012) have reported distinct changes in the structure and composition of freeliving and attached bacterial communities associated with cyanobacterial blooms. Daft & Stewart (1971) reported cyanolytic bacteria as a commonly found group in aquatic environments with a high primary productivity. ...
Outbreaks of cyanobacterial blooms in freshwaters have been increasingly reported worldwide during the last few decades. One of the major problems with cyanobacterial blooms is that some species can be toxic. Their toxins (cyanotoxins) can have mild to serious health effects on humans and animals due to direct contact or ingestion with drinking water and food. Due to the unavailability of efficient testing methods for cyanotoxins especially in developing countries, people may consume toxin contaminated water and foods. Non-toxic cyanobacterial blooms may cause other ecological and socioeconomic impacts. Therefore, physical and chemical control
methods are currently being employed as direct control or removal of cyanobacterial blooms. However, due to some intrinsic adverse consequences of physical and chemical control of blooms on the ecosystem and high operational cost, biological control has gained attention as an alternative sustainable bloom management strategy. A diverse array of control agents such as viruses, bacteria, fungi, actinomycetes, protozoa, flagellates, and macrophytes with the potential to terminate or suppress the growth of cyanobacteria have been isolated and identified from freshwater bodies in different parts of the world. Among the controlling agents, heterotrophic bacteria in the aquatic environment are of high interest owing to their high specificity on the targeted cyanobacteria and high survival ability during non-bloom conditions. Heterotrophic bacteria antagonize cyanobacteria either through direct contact or indirectly by the secretion of allelopathic compounds. The mechanisms of antagonism are known to be physiological and metabolic dysfunctions and
transcriptional regulation of genes. In addition, there are some evidence to show regulation of antagonism through cell density-dependent quorum-sensing (QS) mechanisms. In response, cyanobacteria induce defensive mechanisms such as alteration of colony morphology and activation of chemical defences against microbial antagonists. This review article aimed to encompass the current status of knowledge on the biological control of freshwater cyanobacterial blooms and to highlight the existing knowledge gap in the available literature. We highlight that although a large number of microbial antagonists have been isolated, identified, and demonstrated their cyanobacteria lytic activity in the laboratory, their field application is still challenging. Understanding the spatial and temporal variations in antagonists and cyanobacteria in a particular
aquatic ecosystem is essential for planning an effective bloom management strategy. We also highlight the necessity in expanding research focus towards novel strategies to enhance application
potential and overcome existing challenges.
Keywords: Biological control, cyanobacterial blooms, microbial antagonists, antagonistic
mechanisms
... Cyanobacterial Aggregate (CA), the basic unit wherein cyanobacteria and bacteria coexist in close contact, is the primary form of cyanobacteria during blooms. As autotrophic organisms, cyanobacteria provide food for their attached microbes by excreting rich extracellular organic matters, and in return, attached bacteria supply nitrogen, phosphorous, sulfur, and trace elements to the cyanobacteria ( Grant et al., 2014 ;Shi et al., 2012 ). Metagenomics studies focused on CA-attached bacteria have brought important insights into CA's bacterial community structure with its seasonal variation and spatial distribution ( Tang et al., 2015 ;Zhu et al., 2019b ). ...
Freshwater lakes are threatened by harmful cyanobacterial blooms, whose basic unit is Cyanobacterial Aggregate (CA). CA-attached bacteria play a significant role through different blooming stages with substantial variation of their taxonomic structure. However, little is known about their functional variations and functional links with cyanobacteria due to the lack of reference genomes. In this longitudinal study, we collected 16 CA samples from Lake Taihu, one of China's largest freshwater lakes, from April 2015 to February 2016, and sequenced their V4 region of 16S rRNA genes, full metagenomes (MG), and metatranscriptomes (MT). The analysis of these data revealed the dynamics of microbial taxonomic and functional structure in CAs, influenced by both external environmental factors and internal metabolism. 55 OTUs, 456 genes, and 37 transcripts showed significantly differential abundance across the early, middle, and late blooming stages (ANOVA test, P<0.05). Total nitrogen and total phosphorus were proved to be the most important environmental drivers of microbial taxonomic and functional variations in CAs (Mantel's r>0.25, P<0.05). We constructed 161 high-quality metagenome-assembled genomes (MAGs), out of which 22 were cyanobacterial strains with diverse energy pathways, transporters and prokaryotic defense systems. Based on these MAGs, we constructed a cyanobacteria-bacteria co-nitrogen-pathway and a cyanobacteria-bacteria co-phosphorus-pathway, by which we demonstrated how nitrogen and phosphorus influence the dynamics of the microbial structure to a certain extent by affecting these co-pathways. Overall, these results characterized the taxonomic, functional, and transcriptional variations of microbes in CAs through different blooming stages. Genome assembly and metabolic analysis of cyanobacteria and their attached bacteria suggested that the material exchange and signal transduction do, indeed, exist among them. Our understanding of the underlying molecular pathways for cyanobacterial blooms could lead to the control of blooms by interventional strategies to disrupt critical microbes' expression.
... Moreover, we found significantly lower diversity ( Figure 3A) and significantly different BCS ( Figure 4A) in samples detained on 20 µm filters compared with other treatments, which was consistent with other studies on Microcystis colony-associated bacteria (Shi et al., 2012;Parveen et al., 2013;Shi et al., 2018). The increased species diversity associated with decreasing pore size of filters (from 20 µm to 3.0 µm, Figure 3A) confirmed that most heterotrophic bacteria in Lake Taihu were attached to small particles . ...
Particles are hotspots of bacterial growth and nutrient recycling in aquatic ecosystems. In the study of particle-attached (PA) and/or free-living (FL) microbial assemblages, the first step is to separate particles from their surrounding water columns. Widely used collection techniques are filtration using different pore size filters, and centrifugation; however, it is unclear how the bacterial diversity, bacterial community structure (BCS) and taxonomic composition of PA assemblages are affected by different particle collection methods. To address this knowledge gap, we collected planktonic particles from eutrophic Lake Taihu, mesotrophic Lake Tianmu, and oligotrophic Lake Fuxian in China, using filtration with five pore size of filters (20, 10, 8.0, 5.0, and 3.0 μm), and centrifugation. Bacterial communities were then analyzed using Illumina MiSeq sequencing of the 16S rRNA gene. We found that PA collection method affected BCS significantly in all lakes. Centrifugation yielded the highest species diversity and lowest mean percentage of photoautotrophic Cyanobacteria in Lake Taihu, but not in the other two lakes, thus highlighting the potential compatibility of this method in the study of PA assemblage in eutrophic lakes. The high bacterial diversity and low relative percentage of Cyanobacteria was in samples retained on 5.0 μm filters in all lakes. These results suggest that collecting PA samples in lakes using filters with 5.0 μm pore size is the preferred protocol, if species diversity and heterotrophic bacteria are the top research priorities, when comparing bacterial communities in different trophic lakes at the same time. The present study offers the possibility of collecting PA samples using unified methods in oligotrophic to eutrophic lakes.
... As autotrophic organisms, cyanobacteria can provide food for their attached microbes by excreting rich extracellular organic matters. In turn, attached bacteria may supply nitrogen, phosphorous, sulfur and trace elements to the cyanobacteria [6,7]. Metagenomics studies focused on CA-attached bacteria have given us important insights into the bacterial community structure in CA with reporting their seasonal variation and spatial distribution [8,9]. ...
Background
Freshwater lakes are threatened by harmful cyanobacterial blooms; whose basic unit is Cyanobacterial Aggregate (CA). Community variations of CA-attached bacteria are substantial during different blooming stages. However, little is known about their transcriptional and metabolic variations. Most bacterial genomes in CA were not constructed in existing database, which limits our understanding of the bacterial variations as responses to cyanobacterial blooms. ResultsIn this longitudinal study, 16 CA samples were collected from Lake Taihu, one of the largest freshwater lakes in China, from April of 2015 to February of 2016. By sequencing the V4 region of 16S rRNA genes, full metagenomes (MG) and metatranscriptomes (MT), we generated 424 Mb of 16S rRNA gene data, 122 Gb of high-quality MG data and 160 Gb of high-quality MT data. We analyzed the taxonomic, functional and transcriptional variations of microbes in CAs along three blooming stages, and constructed metagenome-assembled genomes (MAGs) by binning analysis. First, 55 OTUs, 456 genes and 37 transcripts mainly associated with pathways of transporters, photosystem and energy metabolism showed significantly different abundance among the three stages. Second, 161 high-quality MAGs in CAs were achieved, with 19 of which significantly shifted in relative abundance among three stages. The most abundant MAGs have gene capacities to synthesize flagella and divers of transporters, and participate in metabolic pathways of nitrogen, phosphorus and sulfur. Finally, 22 high-quality cyanobacterial MAGs were constructed and can be divided into four functional clusters, which showed significant differences on the energy pathways, transporters and prokaryotic defense system.Conclusion
Overall, these results demonstrated the taxonomic, functional and transcriptional variations of microbes in CAs among three different blooming stages. Genome construction and metabolic analysis of cyanobacteria and their attached bacteria suggested that the material exchange and signal transmission do, indeed, exist among them. Our understanding of the underlying molecular pathways for cyanobacterial blooms could potentially lead to the control of blooms by interventional strategies to disrupt the expression of critical microbes.
... The phyla Proteobacteria and Bacteroidetes dominated the three membranes (63-65%) and unclassified bacteria ranged from 3% to 4% (Fig. 4). Particularly, Proteobacteria has been identified in early-stage biofilms developed in aquatic systems (Nagaraj et al., 2017;Rehman et al., 2020) and has been associated with MCproducing Microcystis (Briand et al., 2016;Parveen et al., 2013;Shi et al., 2012). The detection of the mcyE gene in all biofilms (Fig. S3 in Supplementary material) and the identification of Microcystis in BWt-NF (Fig. S2 in Supplementary material) confirmed the potential toxicity of the cyanobacterial bloom occurred during membrane exposure at the reservoir. ...
Microcystins (MC) are highly toxic secondary metabolites produced by cyanobacterial blooms in many freshwater ecosystems used for recreational and drinking water purposes. So far, biological processes remain to be optimized for an efficient cyanotoxin removal, and new approaches are necessary to compete with physical-chemical treatments. In previous studies we provided a new concept of membrane biofilm reactor made of recycled material, in which a single MC-degrading bacterial strain was inoculated. The present study evaluates the capacity of bacterial consortia associated with freshwater cyanobacterial blooms to form biofilms on recycled membranes and remove MC. Three different discarded reverse osmosis (RO) membranes, previously used in desalination plants after treating brackish water (BWd), seawater (SWd) and brackish water but transformed into nanofiltration (BWt-NF), were exposed to a cyanobacterial bloom in San Juan reservoir (central Spain). Results showed that the three recycled membranes developed a bacterial community with MC removal capacity. Little differences in bacterial coverage and MC removal efficiency between membranes were observed after their exposure in the reservoir. High-throughput sequencing of 16S rRNA gene analysis showed similar bacterial community composition at the phylum level but dissimilar at the order level between the three membranes. This suggests possible surface selectivity on the attached bacterial community. The mlr⁻ candidates such as Burkholderiales and Methylophilales were highly abundant in BWt-NF and BWd, respectively, while mlr⁺ candidates (e.g. Sphingomonadales) were low abundant in all membranes. Analysis of mlrA and mlrB genes used as markers for MC degradation following mlr-pathway confirmed the presence of this pathway in all membranes. These results suggest the co-existence of both genotypes in membrane-attached native biofilms. Therefore, this study confirms that recycled membranes are suitable support for many MC-degrading bacteria, thus giving value to discarded membranes for eco-friendly and low-cost biological filters.
... Thus, taken together with these studies, we speculated that species-specific relationships might exist in colonial Microcystis formation and their bacteria. Shi et al. (2012) also found a specific relationship between colonial Microcystis and their assoicated bacteria living in the mucilage. In addition, Parveen et al. (2013) showed a clear distinction between Microcystis-attached and freeliving bacterial communities. ...
Microcystis, a genus of cyanobacteria that is dominant in eutrophic lakes, occurs mainly as colonial morphs under natural conditions but as single cells in laboratory cultures. Recent studies have suggested that Microcystis-bacteria interactions significantly influence Microcystis morphology, but the underlying mechanism remains unclear. In this study, a total of 48 strains of heterotrophic bacteria were purified from Microcystis mucilage. Five bacteria, Aeromonas veronii, Enterobacter aerogenes, Exiguobacterium acetylicum, Bacil-lus cereus and Shewanella putrefaciens, can induce unicellu-lar Microcystis to form colonies. Heterotrophic bacteria stimulated Microcystis growth and induced the production of ex-tracellular polymeric substances in coculture treatments. Ex-tracellular polymeric substances, such as extracellular poly-saccharides (EPS), were responsible for the mucilage formation in colonial Microcystis. We analysed extracellular metabolic compounds produced by Microcystis aeruginosa and Microcystis wesenbergii using gas chromatography mass spectrometry. Filtrate extracts from coculture treatments indicated that some compounds, such as 2-dodecen-1-yl(-) s u c c i n i c a n h y d r i d e a n d b e n z o i c a c i d , 2 , 3-bis[(trimethylsilyl)oxy]-, trimethylsilyl ester, might play a significant role in colonial M. aeruginosa or M. wesenbergii formation. Our data suggested that the interaction of Microcystis and heterotrophic bacteria was crucial for the formation of Microcystis colony and outbreak of Microcystis blooms.
... The families Xanthomonadaceae and Alcaligenaceae were be considered species-specific bacteria for Microcystis and Psephonema in Lake Erhai. The highly significant positive correlation between dominant algae and their species-specific bacteria in aquatic ecosystems suggests an important relationship between algal and bacterial communities (Niu et al. 2011;Shi et al. 2012). Our results show that the variation in bacterial community composition correlated with phytoplankton succession, particularly the variation in attached bacterial communities. ...
Bacterial communities are an important part of biological diversity and biogeochemical cycling in aquatic ecosystems. In this study, the relationship amongst the phytoplankton species composition and abiotic environmental factors on seasonal changes in the community composition of free-living and attached bacteria in Lake Erhai were studied. Using Illumina high-throughput sequencing, we found that the impact of environmental factors on both the free-living and attached bacterial community composition was greater than that of the phytoplankton community, amongst which total phosphorus, Secchi disk, water temperature, dissolved oxygen and conductivity strongly influenced bacterial community composition. Microcystis blooms associated with subdominant Psephonema occurred during the summer and autumn, and Fragilaria, Melosira and Mougeotia were found at high densities in the other seasons. Only small numbers of algal species-specific bacteria, including Xanthomonadaceae (Proteobacteria) and Alcaligenaceae (Betaproteobacteria), were tightly coupled to Microcystis and Psephonema during Microcystis blooms. Redundancy analysis showed that although the composition of the bacterial communities was controlled by species composition mediated by changes in phytoplankton communities and abiotic environmental factors, the impact of the abiotic environment on both free-living and attached bacterial community compositions were greater than the impact of the phytoplankton community. These results suggest that the species composition of both free-living and attached bacterial communities are affected by abiotic environmental factors, even when under strong control by biotic factors, particularly dominant genera of Microcystis and Psephonema during algal blooms.
... Group 8 from Gemmatimonas was the lowest abundant population among the eight assembled genomes. Gemmatimonas is frequently associated with cyanobacterial colonies [43,44]. ...
Cells of Microcystis are associated with heterotrophic bacteria and organized in colonies in natural environment, which are basic elements in the mass occurrence of cyanobacterial species. Analyzing these colonies by using metagenomics is helpful to understand species composition and relationship. Meanwhile, the difference in population abundance among Microcystis colonies could be used to recover genome bins from metagenome assemblies. Herein, we designed a pipeline to obtain high-quality genomes of mutualistic bacteria from single natural Microcystis colonies. Single colonies were lysed, and then amplified by using multiple displacement amplification to overcome the DNA quantity limit. A two-step assembly was performed after sequencing and scaffolds were grouped into putative bins based on their differential-coverage among species. We analyzed six natural colonies of three prevailing Microcystis species from Lake Taihu. Clustering results proved that colonies of the same species were similar in the microbial community composition. Eight putative population genome bins with wide bacterial diversity and different GC content were identified based on coverage difference among colonies. At the phylum level, proteobacteria was the most abundant besides cyanobacteria. Six of the population bins were further refined into nearly complete genomes (completeness > 90%).
... The dominant cyanobacterial genera in Lake Taihu were reported as Microcystis, Dolichospermum and Synechococcus (Chen et al., 2003b;Ye et al., 2011). However, only Microcystis and Dolichospermum formed large-size aggregates and blooms in Lake Taihu (Shi et al., 2012a;Wang et al., 2013;Ying et al., 2015), while Synechococcus exists as single cells (Callieri et al., 2011). Previous studies have shown that aggregates of Microcystis and Dolichospermum in Lake Taihu were generally larger than 50 μm (Brookes et al., 1999;Smith and Gilbert, 2010;Zhu et al., 2016). ...
... were also common to those found in other cyanobacterial associations. For example, in Microcystis, a bloom-forming genus that produce mucilaginous colonies, Porphyrobacter, Rhodobacterales, Sphingomonadales, and Burkholderiales are also typically associated (Shi et al., 2009(Shi et al., , 2012. Further, cyanobacterial associations with Flavobacterium and members of Sphingomonadaceae, Burkholderiales and Rhizobiales have been described from metagenomes of culture collections belonging to different cyanobacterial genera (Cornet et al., 2018). ...
Species of the genus Nostoc (Cyanobacteria) can form large colonies of up to several centimeters in diameter that may represent a unique habitat for bacteria in freshwaters. Bacteria inside the colony are probably segregated from the surrounding water and largely dependent on the metabolism of this primary producer. However, the existence of a specific bacterial community associated with free-living representatives of Nostoc from lakes and streams is unknown. Here, we studied large Nostoc spp. colonies (ca. 2–10 cm in diameter) from two adjacent, high altitude aquatic environments and assessed the diversity, and community composition of the bacterial community associated with the inner gelatinous matrix (GM). Further, we compared this community with that of the lake’s littoral zone where the colonies live or with the outer layer (OL) of the colony in samples collected from a stream. Alpha bacterial diversity in the inner GM of the colonies from both sites was lower than in the littoral zone or than in the OL. Significant differences in community composition were found between the inner and the OL, as well as between the inner GM, and the littoral zone. Further, these differences were supported by the putative metabolic processes of the bacterial communities. Our results indicate the existence of a specific bacterial community inside macrocolonies of Nostoc spp. and also imply that the inner environment exerts a strong selection. Finally, these large colonies represent not only a unique habitat, but probably also a hotspot of bacterial activity in an otherwise oligotrophic environment.
... Similar to Bacteroidetes, an inverse trend was observed for the temporal variations of Proteobacteria in 2016 and 2017 (Fig. 6E, F). In 2016, Proteobacteria accounted for a significant portion of the total bacterial community, which was consistent with previous studies on eutrophic lakes (Shi et al., 2012;Cai et al., 2013;Parulekar et al., 2017). Limnohabitans (Betaproteobacteria) was the predominant genus detected (Hahn et al., 2010). ...
The current study presents findings related to algal blooms in a fresh water lake, which has been experiencing severe cyanobacterial blooms (CyanoHABs). Primarily, picocyanobacteria belonging to the genus Synechococcus and filamentous cyanobacterial group belonging to Aphanizomenon and Dolichospermum dominated top water column during non-bloom and bloom periods respectively. The dominance of Synechococcus in early summer informs that blooming in Utah Lake starts in early summer and then later is taken over by other bloom-forming cyanobacteria, such as species belonging to the genus Aphanizomenon. A strong negative correlation (r = −0.9, p < 0.001) was found between the occurrence of Aphanizomenon and Synechococcus which correlates very well with the fact that the blooms of these two different cyanobacteria never coexisted. The predominance of cyanobacteria in 2017 was attributed more to temperature (r = 0.18, p < 0.001). The Actinobacteria was negatively correlated with primary production and high chlorophyll a concentration. Flavobacterium and Limnohabitans were the main phytoplankton colonizers and predators detected that could secrete extracellular enzymes to degrade algal exudates (such as proteins and polysaccharides). Additionally, cyanotoxins producers Microcystis aeruginosa and Planktothrix accounted for up to 12.43% and 7.04% of total cyanobacteria abundance during blooms. The relative abundance of chloroplast reads was overall lower than the cyanobacteria reads, except for the May 5th sampling in 2017. There was inter-annual variability in the bloom-associated heterotrophic bacterial populations, but these populations were consistent with bloom-associated bacterial populations found in other lakes. Community diversity analysis for both Shannon and Simpson indices indicated lower community diversity during the bloom period. The beta diversity conducted by PCoA and UPGMA trees suggested the significant temporal rather than spatial impacts on shaping the phytoplankton community structures during the summer season.
... From a general view, cyanobacteria off er a living habitat for heterotrophic bacteria; bacterial supersession could produce the source of nitrogen, phosphorus, sulfur, vitamin and carbon that cyanobacteria could utilize (Cai et al., 2013;Lee et al., 2014;Klawonn et al., 2015;Stuart et al., 2016;Xie et al., 2016). Some epiphytic bacteria are involved in complicated cyanobacterial life activities, which would contribute to cyanobacterial nutrition absorption, colony formation, and toxin degradation (Brunberg, 1999;Maruyama et al., 2003;Shi et al., 2010Shi et al., , 2012Shen et al., 2011). Diff erent cyanobacterial taxa with diff erent cellular/colonial surface structures and physiobiochemical features will form diff erently attached microbial communities (Parveen et al., 2013). ...
Harmful cyanobacterial blooms cause many ecological disasters worldwide. During the development of cyanobacterial blooms, the diversity and domination of cyanobacterial taxa are of a particular concern. In this study, the microbial community structure within a water system, such as in Yuqiao Reservoir and Haihe River in Tianjin City, China, was compared by using next-generation sequencing. A total of 5 001 operational taxonomic units were obtained and clustered from fi ltered 16S rDNA V3-V4 region sequences. The cyanobacterial and microbial structures greatly diff ered in these two water areas. Microcystis was dominant in Yuqiao, whereas Synechococcus was dominant in Haihe. Proteobacteria species were dominant among all detected samples. The relative abundances of Bacteroidetes and Planctomycetes were higher in Yuqiao Reservoir than in Haihe River, whereas Firmicutes and Verrucomicrobia were relatively abundant in Haihe River. Further analyses indicated that the domination of both cyanobacteria was strongly related to several environmental factors, such as total nitrogen, total phosphorus, and dissolved oxygen, refl ecting the role of trophic states in shaping the dominance of cyanobacterial taxa. The present study provided the example for Microcystis and Synechococcus dominance along a cyanobacterial bloom in north China. Applying high-throughput sequencing could off er a wide fi eld of vision in analyzing microbial community structures.
... Sphingomonadales, Xanthomonadaceae, and Burkholderiales were abundant bacterial groups in our Microcystis-epibiont communities, which were also commonly found in freshwater ecosystems (Berg et al., 2009;Limei et al., 2009;Dziallas and Grossart, 2011;Shen et al., 2011;Shi et al., 2012). Within the Alphaproteobacteria, Sphingomonadales species are capable of degrading polysaccharides, microcystins, hexachlorocyclohexane, and various other organic compounds (Valeria et al., 2006;Ho et al., 2007;Bala et al., 2010), and Rhodobacterales are involved in the degradation of aliphatic and aromatic hydrocarbons (Harwati et al., 2007;Brinkhoff et al., 2008). ...
Cyanobacterial blooms are worldwide issues of societal concern and scientific interest. Lake Taihu and Lake Dianchi, two of the largest lakes in China, have been suffering from annual Microcystis-based blooms over the past two decades. These two eutrophic lakes differ in both nutrient load and environmental parameters, where Microcystis microbiota consisting of different Microcystis morphospecies and associated bacteria (epibionts) have dominated. We conducted a comprehensive metagenomic study that analyzed species diversity, community structure, functional components, metabolic pathways and networks to investigate functional interactions among the members of six Microcystis-epibiont communities in these two lakes. Our integrated metagenomic pipeline consisted of efficient assembly, binning, annotation, and quality assurance methods that ensured high-quality genome reconstruction. This study provides a total of 68 reconstructed genomes including six complete Microcystis genomes and 28 high quality bacterial genomes of epibionts belonging to 14 distinct taxa. This metagenomic dataset constitutes the largest reference genome catalog available for genome-centric studies of the Microcystis microbiome. Epibiont community composition appears to be dynamic rather than fixed, and the functional profiles of communities were related to the environment of origin. This study demonstrates mutualistic interactions between Microcystis and epibionts at genetic and metabolic levels. Metabolic pathway reconstruction provided evidence for functional complementation in nitrogen and sulfur cycles, fatty acid catabolism, vitamin synthesis, and aromatic compound degradation among community members. Thus, bacterial social interactions within Microcystis-epibiont communities not only shape species composition, but also stabilize the communities functional profiles. These interactions appear to play an important role in environmental adaptation of Microcystis colonies.
... For instance, about 47% of the OTUs in the phylum of Planctomycetes were exclusively found in our PA samples, while only 10% OTUs were exclusively found in FL samples, suggesting adaption to PA lifestyle. This result is consistent with those found in recent studies (Shi et al. 2012;Parveen et al. 2013b;Louati et al. 2015), which showed that the phycosphere of cyanobacterial blooms harbors distinct bacterial communities including members of Planctomycetes. ...
In eutrophic lakes, heterotrophic bacteria are closely associated with algal detritus and play a crucial role in nutrient cycling. However, the seasonal and spatial dynamics of free-living (FL) and particle-attached (PA) bacteria and the environmental factors shaping this relationship remain poorly understood. To address this issue, we explored the spatiotemporal patterns of bacterial community composition (BCC) in Lake Taihu, China, using terminal restriction fragment length polymorphism (T-RFLP) and 454-tag pyrosequencing of 16S rRNA gene. We generated a total of 218,027 high quality non-cyanobacterial sequence reads that resulted in 4940 OTUs (97% cutoff), with Actinobacteria, β- and α-proteobacteria being the predominant taxa. Although PA communities contained significantly higher alpha-diversity than FL ones, we found that 59% of OTUs, that accounted for 96% of the total reads, were shared by both communities. The high degree of overlap between FL and PA communities indicates a high rate of dispersal potential, highlighting an underestimated connectivity and potentially similar ecological role for these two components. Distinct seasonal trends were recorded in both FL and PA communities, while spatial differences in BCC were small. In addition, both FL and PA bacterial communities exhibited similar patterns and synchrony, correlated to water temperature, nitrate and total suspended solids (TSS). Accordingly, the effects of eutrophication and hydrodynamics on the phylogenetic overlap and diversity between FL and PA communities were discussed.
... Comparable reports, suggesting that unique capabilities of these groups allow them to compete successfully in lakes with diverse trophic states have been published [70,86]. Proteobacteria represented a significant portion of the bacterial community, which is in agreement with other studies [74,87,88]. Many of the most prevalent and well-studied freshwater bacterial groups belong to Betaproteobacteria [66,89]. ...
Interactions between different phytoplankton taxa and heterotrophic bacterial communities within aquatic environments can differentially support growth of various heterotrophic bacterial species. In this study, phytoplankton diversity was studied using traditional microscopic techniques and the bacterial communities associated with phytoplankton bloom were studied using High Throughput Sequencing (HTS) analysis of 16S rRNA gene amplicons from the V1-V3 and V3-V4 hypervariable regions. Samples were collected from Lake Akersvannet, a eutrophic lake in South Norway, during the growth season from June to August 2013. Microscopic examination revealed that the phytoplankton community was mostly represented by Cyanobacteria and the dinoflagellate Ceratium hirundinella. The HTS results revealed that Proteobacteria (Alpha, Beta, and Gamma), Bacteriodetes, Cyanobacteria, Actinobacteria and Verrucomicrobia dominated the bacterial community, with varying relative abundances throughout the sampling season. Species level identification of Cyanobacteria showed a mixed population of Aphanizomenon flos-aquae, Microcystis aeruginosa and Woronichinia naegeliana. A significant proportion of the microbial community was composed of unclassified taxa which might represent locally adapted freshwater bacterial groups. Comparison of cyanobacterial species composition from HTS and microscopy revealed quantitative discrepancies, indicating a need for cross validation of results. To our knowledge, this is the first study that uses HTS methods for studying the bacterial community associated with phytoplankton blooms in a Norwegian lake. The study demonstrates the value of considering results from multiple methods when studying bacterial communities.
... Several publications have also evaluated the impact of cyanobacterial blooms on the structure and composition of BCs within the same ecosystems (e.g., Eiler and Bertilsson, 2004;Berg et al., 2009;Louati et al., 2015;Woodhouse et al., 2016). Microcystis sp., a toxic bloom-forming cyanobacteria, has been a specific focus given its high prevalence in many ecosystems around the world as well as its colonial organization, which offers a potential niche and physical support for direct interactions with heterotrophic prokaryotes (e.g., Shen et al., 2011;Li et al., 2012;Shi et al., 2012;Shao et al., 2014). ...
To overcome the limitations associated with studying the interactions between bacterial communities (BCs) and cyanobacteria in natural environments, we compared the structural and functional diversities of the BCs associated with 15 non-axenic cyanobacterial strains in culture and two natural BCs sampled during cyanobacterial blooms. No significant differences in richness and diversity were found between the natural and cultivated BCs, although some of the cyanobacterial strains had been isolated 11 years earlier. Moreover, these BCs shared some similar characteristics, such as a very low abundance of Actinobacteria, but they display significant differences at the operational taxonomic unit (OTU) level. Overall, our findings suggest that BCs associated with cyanobacteria in culture are good models to better understand the interactions between heterotrophic bacteria and cyanobacteria. Additionally, BCs associated with heterocystous cyanobacterial strains cultivated in Z8X culture medium without nitrate (Aphanizomenon–Dolichospermum) demonstrated significant differences compared to BCs associated with non-heterocystous strains cultivated in Z8 culture medium (Planktothrix–Microcystis) in terms of their composition and their ability to utilize different carbon sources, suggesting the potential influence of cyanobacterial metabolism and/or culture media on associated BCs. Finally, half of the dominant OTUs in these BCs were specifically associated with cyanobacteria or other phytoplankton, whereas the remaining OTUs were generally associated with ecosystems containing high organic matter content, such as sludge or intestines.
... 3 Mucilaginous investment of Microcystis provides an excellent ecological niches for many other bacteria, including Alphaproteobacteria, Betaproteobacteria, Gammaproteobacteria, Actinobacteria and Bacteroidetes. [4][5][6] Mutualism is one of the main reasons of this coexistence of Microcystis and bacteria, whereby the bacteria provide the raw materials to Microcystis and are replenished with nutrient and safer environments. [7][8][9][10][11][12] During a study of bacteria associated with mucilage released by M. aeruginosa FACHB-905 (MAF) collected from Lake Dianchi, a novel actinobacterium designated strain JXJ CY 01 T belonging to the genus Microbacterium was isolated. ...
A novel actinobacterium, designated strain JXJ CY 01T, was isolated from a mucilaginous sheath of Microcystis aeruginosa FACHB-905 collected from Lake Dianchi, south-west China. Taxonomic position of the isolate was determined by polyphasic approaches. Strain JXJ CY 01T shared 16S rRNA sequence similarities of 98.9 and 98.0% with Microbacterium marinilacus YM11-607T and Microbacterium paludicola US15T, and less than 98% with other members of the genus Microbacterium. The DNA–DNA relatedness values between strains JXJ CY 01T and M. marinilacus JCM 16546T and M. paludicola JCM 14308T were 53.5±1.4 and 53.8±2.1%, respectively. l-Ornithine was detected in the cell wall, and rhamnose, galactose, glucose, arabinose, fucose and mannose as signature sugars in the whole-cell hydrolysates. Other chemotaxonomic characteristics determined were MK-12 and MK-11 as predominant menaquinones, anteiso-C15:0, iso-C16:0, anteiso-C17:0 and iso-C17:0 as major cellular fatty acids (>10%), and diphosphatidylglycerol, phosphatidylglycerol, an unidentified glycolipid and two unidentified phospholipids as the polar lipids. The DNA G+C content was 70.4 mol%. On the basis of the above taxonomic data, strain JXJ CY 01T is determined to represent a novel species of the genus Microbacterium, for which the name Microbacterium lacusdiani sp. nov. is proposed. The type strain is JXJ CY 01T (= KCTC 29655T=DSM 29188T). The type strain JXJ CY 01T can solubilize both insoluble inorganic (calcium phosphate) and organic phosphate (l-α-phosphatidylcholine) and is possibly one of the mechanism for enhancement of growth of M. aeruginosa FACHB-905.
... The strong food preference for Microcystis cells as shown by light microscopy observations and small-scale feeding experiments (Van Wichelen, unpublished data) suggests that most of the amoebae are highly specialized (Angulamoeba micro cystivorans, Vannella planctonica, Korotnevella pel agolacustris, Copromyxa microcystidis). Others were found to be less preferential (Vexillifera westveldii) or unable to graze on Microcystis cells (Schoutedamoeba minuta) and thus may rather be more generalistic bacterivorous aggregate-dwelling amoebae scavenging the mucilage matrix containing a diverse community of heterotrophic bacteria (Worm and Søndergaard 1998, Brunberg 1999, Shi et al. 2012, Cai et al. 2014. A better understanding of the ecology and degree of specialization of these amoebae could be gained by investigating amoeba population dynamics in ponds throughout the year in both the benthic and planktonic environment together with (switches in) their feeding habits. ...
The colonies of Microcystis, one of the most common bloom-forming cyanobacteria worldwide, harbor a diverse community of microorganisms. Among these, naked amoebae feeding on Microcystis cells can strongly influence natural Microcystis population dynamics. In this study, we investigated the species diversity of these amoebae based on 26 Microcystis-associated amoebae (MAA) strains from eutrophied water bodies in Belgium and elsewhere in western Europe. A detailed morphological characterization in combination with 18S
rDNA (SSU) phylogenies revealed the presence of no less than 10 species. Nine of these belonged to the known genera Vannella (2 species), Korotnevella (2), Copromyxa (2), Vexillifera (1), Cochliopodium (1) and the recently described Angulamoeba (1). Only two were previously described, the others were new to science. One taxon could not be assigned to a known genus and is here described as Schoutedamoeba gen.n., representing a new variosean lineage. The discovery of so many new species from only one very specific habitat (Microcystis colonies) from a rather restricted geographical area indicates that the diversity of planktonic naked amoebae is much higher than previously appreciated and that only a tiny fraction of the total diversity of naked amoebae is currently known.
... The algal blooms which predominantly occur in warm season are dominated by the genus Microcystis [1], of which the most common one is that of Microcystis aeruginosa [2,3]. The Microcystis mat is found to be associated with a host of other bacteria including those belonging to the phyla Alphaproteobacteria, Betaproteobacteria, Gammaproteobacteria, Actinobacteria and Bacteroidetes [4][5][6][7]. Co-existence between the two types of microorganisms is apparently maintained by the supply of growth factors, microelement [4], phosphate [8] and probably available carbon source (CO 2 ) [9] by the bacteria to Microcystis, which in turn, provide organic nutrients [4,[10][11][12] and safer growing environment [4,13] to the bacteria. ...
A novel actinobacterium, designated strain JXJ CY 19T, was isolated from a culture mat of Microcystis aeruginosa FACHB-905 collected from Dianchi Lake, South-west China. 16S rRNA gene sequences comparison of strain JXJ CY 19T and the available sequences in the GenBank database showed that the strain was closely related to Modestobacter marinus 42H12-1T (99.1% similarity) and Modestobacter roseus KLBMP 1279T (99.0%). The isolate had meso-diaminopimelic in the cell wall with whole-cell sugars of mannose, rhamnose, ribose, glucose, galactose, and arabinose. The menaquinone detected was MK-9(H4), while the major cellular fatty acids include C17:1 ω8c, C15:0 iso, C15:1 iso G and C16:0 iso. The polar lipids were diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylinositol, phosphatidylinositol mannoside and an unidentified phospholipid. The DNA-DNA hybridization values between strains JXJ CY 19T and the closely related type strains Modestobacter marinus CGMCC 4.5581T and Modestobacter roseus NBRC 108673T were determined to be 50.8 ± 0.8% and 44.1 ± 1.7%, respectively. The DNA G+C content was 71.9 mol%. On the basis of the above taxonomic data and differences in physiological characters from the closely related type strains, strain JXJ CY 19T was recognized as a novel species of the genus Modestobacter, for which the name Modestobacter lacusdianchii sp. nov. (JXJ CY 19T = KCTC 39600T = CPCC 204352T) is proposed. The type strain JXJ CY 19T can solubilize calcium phosphate tribasic (Ca3(PO4)2), phytin and L-α-phosphatidylcholine. The phosphate-solubilizing property of the novel actinobacterium could be a possible factor for the increase in growth of Microcystis aeruginosa FACHB-905 in ecosystem where the amount of available soluble phosphate is limited such as Dianchi Lake.
... A resulting effect is the occurrence of Microcystis blooms in Lake Dianchi during warm seasons (Liu et al. 2006). Microcystis can produce a mucilaginous sheath that can act as a habitat for many other bacteria including Alphaproteobacteria, Betaproteobacteria, Gammaproteobacteria, Actinobacteria and Bacteroidetes (Dziallas et al. 2011;Shi et al. 2012;Parveen et al. 2013). Mutualism is one of the main reasons of this co-existence of Microcystis with other bacteria. ...
A novel actinobacterium, designated strain JXJ CY 21T, was isolated from the culture mass of Microcystis sp. FACHB-905 collected from Lake Dianchi, South-west China. Polyphasic taxonomic study revealed that the isolate should be a member of the genus Citricoccus. Comparison of the 16S rRNA gene sequence of strain JXJ CY 21T with the available sequences in the GenBank database showed that the strain is closely related to Citricoccus zhacaiensis FS24T (97.8 % similarity), Citricoccus parietis 02-Je-010T (97.7 %), Citricoccus terreus V3M1T (97.6 %), Citricoccus nitrophenolicus PNP1T (97.2 %), Citricoccus alkalitolerans YIM 70010T (97.2 %) and Citricoccus muralis 4-0T (97.0 %). The DNA–DNA hybridization values between strain JXJ CY 21T and the related type strains C. zhacaiensis FS24T and C. parietis 02-Je-010T were 16.0 ± 2.6 and 5.4 ± 1.7 %, respectively. The peptidoglycan in the cell wall was A4α type containing lysine–glutamic acid–glycine. The major respiratory menaquinone was found to be MK-8 (H2) (98.5 %), while the major cellular fatty acids (>10 %) were anteiso-C15:0, iso-C16:0, iso-C15:0 and iso-C14:0. The polar lipids detected were diphosphatidylglycerol, phosphatidylinositol, phosphatidylglycerol, an unidentified phospholipid and an unidentified glycolipid. The DNA G + C content was determined to be 62.7 mol%. Strain JXJ CY 21T can solubilize both insoluble inorganic and organic phosphates up to 24.7 and 1.7 mg/l respectively. This property of the novel actinobacterium acts as a modulator for enhancement of growth of Microcystis sp. FACHB-905 in the lake ecosystem where the amount of soluble phosphate is limited. On the basis of the above taxonomic data, strain JXJ CY 21T represents a novel species of the genus Citricoccus, for which the name Citricoccus lacusdiani sp. nov. is proposed. The type strain is JXJ CY 21T (=KCTC 29653T = DSM 29160T).
A novel actinobacterial strain, designated as JXJ CY 30 T, was isolated from the phycosphere of Microcystis aeruginosa FACHB-905 (Maf) collected from Lake Dianchi, China. The strain was a Gram-stain-positive, aerobic and coccus-shaped actinobacterium. It had alanine, glutamic acid, aspartic acid, and lysine in the peptidoglycan, and mannose, ribose and arabinose in its cell wall sugars, anteiso-C15:0 and iso-C15:0 as the main cellular fatty acids, MK-7 and MK-8 as the major respiratory quinones, and phosphatidylglycerol, diphosphatidylglycerol, phosphatidylinositol, glycolipid, and an unidentified phospholipid as the polar lipids. The DNA G + C content was 73.08%. Its 16 S rRNA gene sequence shared 99.14%, and 98.75% similarities with Micrococcus flavus DSM 19079 T and M. porci KD337-16T, respectively, and ≤98.41% similarities with other type strains of the genus Micrococcus. It formed independent clade with M. flavus DSM 19079 T on the phylogenetic trees. The digital DNA-DNA hybridization and average nucleotide identity values between strain JXJ CY 30 T and M. flavus DSM 19079 T and M. porci KD337-16T were 48.0% and 92.1%, 25.5% and 83.2%, respectively. These data above indicated that strain JXJ CY 30 T represented a new species of the genus Micrococcus, and the species epithet is proposed as Micrococcus lacusdianchii sp. nov. (type strain JXJ CY 30 T = KCTC 49378 T = CGMCC 1.17508 T). Strain JXJ CY 30 T can potentially provide Maf with various nutrients such as available phosphorus and nitrogen, plant hormones, various vitamins and carotenoids for growth, while it was inhibited by metabolites from its symbiotic algae Maf.
The cyanobacteria-associated microbiome is constantly reshaped by bloom development. However, the synergistic-antagonistic nature of the relationships between Microcystis and its microbiome still remains unclear. Therefore, temporal changes of bacterioplankton communities and their functional potential through different developing stages of a Microcystis toxigenic bloom were investigated, considering bacterioplankton assemblages as particle-attached (PAB) and free-living (FLB) bacteria. 16S rRNA sequencing revealed that PAB were represented by Proteobacteria and Cyanobacteria, while FLB by Proteobacteria and Actinobacteria. Network and ordination analyses indicated that PAB inter-relationships were more complex—numerous connections between taxa with stronger correlations, than FLB—rather influenced by physico-chemical parameters. PAB in pre-summer was diverse with Proteobacteria containing potential taxa involved in nitrogen-transforming processes. In mid-summer, PAB presented a mix-bloom dominated by Snowella, Aphanizomenon, and Microcystis, which were succeeded by toxigenic Microcystis in post-summer. Both periods were associated to potential taxa with parasitic/predatory lifestyles against cyanobacteria. In post-summer, Sutterellaceae were recognized as poor water quality indicators, and their strong association with Microcystis could have represented an increased threat for that period. Microcystis was a major factor significantly reducing PAB diversity and evenness, suggesting that it negatively influenced bacterioplankton assemblages, probably also altering the overall community functional potential.
Large cyanobacterial colonies, which are unique niches for heterotrophic bacteria, are vital for blooming in eutrophic waters. However, the seasonal dynamics of molecular insights into microbes in these colonies remain unclear. Here, the community composition and metabolism pattern of microbes inhabiting large cyanobacterial colonies (> 120 µm, collected from Lake Taihu in China) were investigated monthly. The community structure of total microbes was mostly influenced by chlorophyll a (Chl a), total phosphorus (TP) concentration, dissolved oxygen, and temperature, whereas the colony-associated bacteria (excluding Cyanobacteria) were mostly influenced by total organic carbon, NO3⁻, and PO4³⁻ concentrations, indicating different response patterns of Cyanobacteria and the associated bacteria to water nutrient conditions. Metatranscriptomic data suggested that similar to that of Cyanobacteria, the gene expression patterns of the most active bacteria, such as Proteobacteria and Bacteroidetes, were not strictly dependent on season but separated by Chl a concentrations. Samples in July and September (high-bloom period) and February and March (non-bloom period) formed two distinct clusters, whereas those of other months (low-bloom period) clustered together. The accumulation of transcripts for pathways, such as phycobilisome from Cyanobacteria and bacterial chemotaxis and flagellum, phosphate metabolism, and sulfur oxidation from Proteobacteria, was enriched in high- and low-bloom periods than in non-bloom period. Network analyses revealed that Cyanobacteria and Proteobacteria exhibited coordinated transcriptional patterns in almost all divided modules. Modules had Cyanobacteria-dominated hub gene were positively correlated with temperature, Chl a, total dissolved phosphorus, and NH4⁺ and NO2⁻ concentrations, whereas modules had Proteobacteria-dominated hub gene were positively correlated with TP and PO4³⁻. These results indicated labor division might exist in the colonies. This study provided metabolic insights into microbes in large cyanobacterial colonies and would support the understanding and management of the year-round cyanobacterial blooms.
Microcystis spp., notorious bloom‐forming cyanobacteria, are often present in colony form in eutrophic lakes worldwide. Uncovering the mechanisms underlying Microcystis colony formation and maintenance is vital to control the blooms, but it has long been a challenge. Here, bacterial communities and gene expression patterns of colonial and unicellular forms of one non‐axenic strain of Microcystis aeruginosa isolated from Lake Taihu were compared. Evidently, different microbial communities between them were observed through 16S rDNA MiSeq sequencing. Metatranscriptome analyses revealed that transcripts for pathways involved in bacterial biofilm formation, such as biosynthesis of peptidoglycan and arginine by Bacteroidetes, methionine biosynthesis, alginate metabolism, flagellum, and motility, as well as widespread colonization islands by Proteobacteria, were highly enriched in the colonial form. Furthermore, transcripts for nitrogen fixation and denitrification pathways by Proteobacteria that usually occur in biofilms were significantly enriched in the colonial Microcystis. Results revealed that microbes associated with Microcystis colonies play important roles through regulation of biofilm‐related genes in colony formation and maintenance. Moreover, Microcystis colony represents a potential “buoyant particulate biofilm”, which is a good model for biofilm studies. The biofilm features of colonial Microcystis throw a new light on management and control of the ubiquitous blooms in eutrophic waters. This article is protected by copyright. All rights reserved.
Microalgal-bacterial consortium is an effective way to meet increasingly stringent standards in wastewater treatment. However, the mechanism of wastewater removal effect has not been properly explained in community structure by phycosphere. And little is known about that the concept of macroecology was introduced into phycosphere to explain the phenomenon. In the study, the algal–bacterial consortia with different ratios of algae and sludge were cultured in same aerobic wastewater within 48 h in photobioreactors (PSBRs). Community structure at start and end was texted by metagenomic analysis. Bray–Curtis similarities analysis based on microbial community showed that there was obvious convergent succession in all consortia, which is well known as “convergence” in macroecology. The result showed that Bray–Curtis similarities at End (overall above 0.88) were higher than these at Start (almost less than 0.66). In terms of community structure, the consortium with 5:1 ratio at Start are the more similar with the consortia at End by which the maximum removal of total dissolved nitrogen (TDN, 73.69%), total dissolved phosphorus (TDP, 94.40%) and NH3-N (93.26%) in wastewater treatment process and biomass production (98.2%) higher than other consortia, according with climax community in macroecology with the highest resource utilization than other communities. Therefore, the macroecology can be introduced into phycosphere to explain the consortium for advanced wastewater treatment and optimization community structure. And the study revealed a novel insight into treatment effect and community structure of algal–bacterial consortia for advanced wastewater treatment, a new idea for to shortening the culture time of consortium and optimize predicting their ecological community structure and predicting ecological community.
Cyanobacterial blooms are threatening our global freshwater ecosystem due to eutrophication and global warming. The heterotrophic Bacteria Associated with Cyanobacterial Aggregates (BACA) are known to provide adaptative support to cyanobacterial species which outcompete the microorganisms during the period of bloom formation. In this study, diversity, seasonal succession, spatial, and host specificity of BACA were explored by analyzing their diversity in time-series samples from a eutrophic freshwater lake, Lake Taihu. Diversity analysis using high-throughput sequencing of the samples investigated here revealed that four Microcystis species including Microcystis aeruginosa, Microcystis wesenbergii, Microcystis panniformis, and Microcystis flos-aquae tend to exhibit host specificity. However, no obvious differences between the BACA of floating and sinking samples were observed in this study. Water temperature was found as a key factor driving the succession of BACA in Taihu Lake. BACA was not only observed, exhibiting long term seasonal succession but intra-seasonal succession in response to steep environmental changes was also observed. This study provides detailed insights into the diversity, seasonal succession, spatial and host specificity of BACA in Lake Taihu.
Bacteria associated with Microcystis may play an important role in formation of Microcystis colonies and in development of cyanobacterial blooms. Adhesion to Microcystis cells is a requirement for colonization and long-term association of bacteria with Microcystis colonies. This study aimed to explore the relationship between autoaggregation ability and adhesion ability of Microcystis-associated bacteria, and to evaluate the effects of different environmental factors on their autoaggregation abilities. Twelve bacterial strains were isolated from colonies of three Microcystis morphospecies. All the bacterial isolates exhibited autoaggregation abilities. A positive correlation was found between autoaggregation ability and adhesion ability. Two selected bacterial isolates, HJX5 and HJX9, exhibited strong autoaggregation abilities at pH from 3 to 11. The laboratory experiment revealed the inhibitory effects of metal cations on the autoaggregation abilities of HJX5 and HJX9, but HJX5 and HJX9 could exhibit their autoaggregation abilities in the lake water. Extraction of exopolysaccharides (EPS) decreased significantly their autoaggregation abilities, indicating that EPS can play an important role in autoaggregation. The autoaggregation ability of Microcystis-associated bacteria may be an important trait contributing to their attachment into Microcystis colonies.
Many freshwater lakes undergo seasonal stratification, where the formation of phototrophic blooms in the epilimnion and subsequent sedimentation induces hypoxia/anoxia in the thermocline and hypolimnion. This autochthonously produced biomass represents a major seasonal organic input that impacts the entire ecosystem. While the limnological aspects of this process are fairly well documented, relatively little is known regarding the microbial community response to such events, especially in the deeper anoxic layers of the water column. Here, we conducted a spatiotemporal survey of the particle-associated and free-living microbial communities in a warm monomictic freshwater reservoir (Grand Lake O’ the Cherokees) in northeastern Oklahoma, USA. Pre-stratification samples (March) harbored a homogeneous community throughout the oxygenated water column dominated by typical oligotrophic aquatic lineages (acl clade within Actinobacteria, and Flavobacterium within the Bacteroidetes). The onset of phototrophic blooming in June induced the progression of this baseline community into two distinct trajectories. Within the oxic epilimnion, samples were characterized by the propagation of phototrophic (Prochlorococcus), and heterotrophic (Planctomycetes, Verrucomicrobia, and Beta-Proteobacteria) lineages. Within the oxygen-deficient thermocline and hypolimnion, the sedimentation of surface biomass induced the development of a highly diverse community, with the enrichment of Chloroflexi, “Latescibacteria”, Armatimonadetes, and Delta-Proteobacteria in the particle-associated fraction, and Gemmatimonadetes and “Omnitrophica” in the free-living fraction. Our work documents the development of multiple spatially and temporally distinct niches during lake stratification, and supports the enrichment of multiple yet-uncultured and poorly characterized lineages in the lake’s deeper oxygen-deficient layers, an ecologically relevant microbial niche that is often overlooked in lakes diversity surveys.
Epiphytic bacteria associated with colonial Microcystis may play an important role in the development of cyanobacterial bloom. However, information on characterization of Microcystis-associated bacteria is limited. In this study, eighteen Microcystis-associated bacteria which belonged to six bacterial groups: Alpha proteobacterium, Beta proteobacterium, Gamma proteobacterium, Actinobacteria, Cytophagia and Flavobacteriia, were isolated from four Microcystis species (M. wesenbergii, M. flos-aquae, M. firma and M. aeruginosa). Analysis by BIOLOG plate indicated that except for two isolates of Alpha proteobacterium and one isolate of Actinobacteria, the other isolates were capable of utilizing more than 10 carbon sources. Among 18 bacterial isolates, 12 isolates showed chemotaxis, 12 isolates displayed hydrophobicity, and 14 isolates exhibited autoaggregation ability. Except for Flavobacteriia, other five groups contained hydrophobic bacterial isolates. All six groups contained bacterial isolates with chemotaxis and autoaggregation ability. Most of bacterial isolates associated with each Microcystis species were capable of utilizing more than 10 carbon sources, and exhibited hydrophobicity. For each Microcystis species, there was at least one group of bacterial isolates exhibiting coaggregation ability. Except for M. flos-aquae, most of bacterial isolates associated with each of other three Microcystis species showed chemotaxis. The results indicated that active metabolic potential, chemotaxis, hydrophobicity, and the abilities of autoaggregation and coaggregation might help the bacteria colonize the Microcystis colonies.
Cyanobacterial blooms drastically influence carbon and nutrient cycling in eutrophic freshwater lakes. To understand the mineralization process of cyanobacteria-derived particulate organic matter (CyanPOM), the aerobic degradation of cyanobacterial blooms dominated by Microcystis sp. was investigated over a 95-day microcosm experiment. Approximately 91%, 95% and 83% of the initial particulate organic carbon (POC), particulate organic nitrogen (PON), and particulate organic phosphorus (POP) were decomposed, respectively. The POC:PON ratio gradually increased from 5.9 to 13.5, whereas the POC:POP ratio gradually decreased from 230.3 to 120. These results indicated that the coupling of POC, PON, and POP changed during the decomposition of CyanPOM. Moreover, approximately 29%, 51% and 46% of POC, PON, and POP were mineralized to dissolved organic carbon, NO3⁻, and PO43 −, respectively. Rhodospirillales (10.9%), Burkholderiales (16.5%), and Verrucomicrobiales (14.3%) dominated during the rapid phase (days 0–21), whereas Sphingomonadales (12.8%), Rhizobiales (11.8%), and Xanthomonadales (36.5%) dominated during the slow phase (days 21–50) of CyanPOM decomposition. Nitrospira (16.6%–32.9%) dominated and NO3⁻ increased during the refractory phase (days 50–95), thus suggesting the occurrence of nitrification. Redundancy analysis revealed that bacterial communities during rapid decomposition were distinct from those during the slow and refractory periods. POC:POP, NH4⁺, and NO3⁻ were the major driving factors for the patterns of bacterial communities. Furthermore, increase in nitrogen metabolism, methane metabolism, amino acid related enzymes and pyruvate metabolism characterized the functional variation of bacterial communities during degradation. Therefore, CyanPOM is an important nutrient source, and its decomposition level shapes bacterial communities.
The acidic heteropolysaccharide released by a water-bloom cyanobacterium Microcystis aeruginosa FACHB-912, which contained 8.3% protein, was used as the carbon source in stable enrichment cultures inoculated with natural aquatic microbial communities. The process of microbial breakdown of the exopolysaccharide and composition of the microbial community related to degrading exopolysaccharide were investigated. After inoculation of aquatic microbial community from Lake Taihu, enrichment cultures were obtained. In the enrichment culture, the exopolysaccharide was degraded immediately. The breakdown of the exopolysaccharide slowed markedly after about 18d, left a nondegraded fraction after 37d. The above data, together with comparison experiments on degradation capability of bacterial communities from various aquatic environments, indicated that the exopolysaccharide from M. Aeruginosa FACHB-912 could indeed be degraded by microorganisms coexisting only with the water bloom in nature. Denaturing gradient gel electrophoresis (DGGE) analysis showed composition of the microbial community did not change significantly during exopolysaccharide degradation. Phylogenetic analysis on DNA fragments, which were excised from DGGE gels, placed three degraders in Sphingomonas, one in Phaeospirillum, one in Pseudomonas, one in Rhodocyclaceae, one in Hylemonella, and one in Mycobacterium.
To investigate the intra-habitat heterogeneity of environmental factors that may have an impact on the bacterioplankton community composition (BCC), a 1 yr observation was done at 2 study sites in Lake Taihu, a large shallow eutrophic lake in China. One site was located at the center of Meiliang Bay, the other site was near the central region of the lake. Denaturing gradient gel electrophoresis (DGGE) of PCR-amplified partial 16S rRNA gene fragments was applied to analyze BCC. The unweighted pair group method with arithmetic mean (UPGMA) was used to investigate differences among BCC. Redundancy analyses (RDA) of the gel patterns, in relation to the physical, chemical, and biological factors of the 2 sites, were performed. Differences between the samples in Meiliang Bay and the lake center were evident during all periods. Four variables (the biomass of Microcystis spp., chl a, dissolved inorganic phosphorus [DIP], and water turbidity) were most strongly correlated with the bacterioplankton DGGE patterns. Particularly, significant intra-habitat heterogeneity of the environmental factors was detected. In Meiliang Bay, seasonal variations in DIP concentration had a profound impact on the composition of bacterioplankton communities, while in the lake center, wind-induced frequent sediment resuspension was an important reason for the variations in BCC. The inherent intra-habitat heterogeneity of environmental conditions is essential to maintain the heterogeneity of BCC at the 2 study sites.
The phylogenetic diversity and seasonal dynamics of free-living and particle-associated bacterial communities were investigated in the epilimnion of 4 lakes of the Mecklenburg Lake District, northeastern Germany. All lakes differed in their limnological features, ranging from oligotrophic to eutrophic and dystrophic. Bacterial community structure and seasonal dynamics were analyzed by denaturing gradient gel electrophoresis (DGGE) and clone libraries of 16S rRNA gene fragments. Communities of free-living and particle-associated bacteria greatly differed among the lakes. In addition, significant differences occurred between both bacterial fractions within each lake. Seasonal changes were more pronounced in free-living than in particle-associated bacterial communities. Non-metric multidimensional scaling (NMDS) analyses revealed several strong correlations between bacterial communities (both free-living and particle-associated) and environmental variables such as pH, dissolved organic carbon (DOC), phytoplankton biomasses, and primary production. Phylogenetically, all cloned and sequenced 16S rRNA gene fragments belonged to already known freshwater clusters. Clone libraries of free-living bacteria were dominated by sequences of Actinobacteria, Bacteroidetes, and Betaproteobacteria, whereas those of particle-associated bacteria predominantly consisted of Cyanobacteria and Bacteroidetes sequences. Other freshwater phyla such as Alpha- and Gammaproteobacteria, Verrucomicrobia, Planctomycetes, and members of Candidate Division OP10 were found in low proportions. These differences may indicate an adaptation of distinct bacterioplankton communities to the respective environmental conditions of each lake.
Phytoplankton blooms were created in freshwater enclosures to study the functional succession and diversification for attached (>10 mum size fraction) and free-living (<10 m size fraction) assemblages of bacteria, Bacterial dynamics in abundance, production and enzyme activity was monitored by standard methods. The functional diversity with respect to sole carbon source utilization was assessed with Biolog GN plates inoculated with bacteria from the 2 size fractions. Moreover, bacterial isolates were screened for enzyme activity involved in the degradation of carbohydrates, chitin, protein and lipid. As the bloom proceeded, the functional diversity of attached and free-living bacteria appeared to be very similar. Most functional groups present in the free-living bacterial assemblage were also recovered attached to particulate matter. Additionally, the distribution of bacterial isolates with enzyme expression was similar with respect to 6 enzymes (p > 0.07), whereas 3 glucoside-bond cleaving enzymes were more frequent among the free-living isolates (p < 0.02). These results indicate that attached and free-living bacteria were functionally closely related and that their succession tended to converge during the phytoplankton bloom. Hence, bacteria attached to particulate matter are not necessarily functionally distinct and specialized for polymer hydrolysis relative to the free-living assemblage, though they are often anticipated to be different due to their close association with particulate polymers.
The relationship between bacterial 16S rRNA gene composition and carbon metabolism was analyzed during an intense dinoflagellate bloom off the Southern California coast during the spring of 1997. Bacterial numbers and rate processes, chlorophyll a, and the dissolved and particulate organic matter pools were measured during the bloom to provide a framework within which to assess bacterial community composition. Free bacteria were numerically dominant, generally comprising >90% of the total, and were responsible for >70% of bacterial production. Attached bacteria had higher cell-specific growth rates than free bacteria (range = 0.5 to 15.1 and 0.7 to 2.5 d(-1), respectively) and had hydrolytic ectoenzyme activities at times more than an order of magnitude higher on a per cell basis. Denaturing gradient gel electrophoresis analysis of bacterial community composition indicated that: (1) the free and attached communities were distinct, and (2) marked shifts in bacterial community structure occurred concomitant with the peaks in attached enzyme activities, specific growth rates and DOC concentration. Of the 24 16S rDNA clones analyzed, 7 were related to the Cytophaga-like bacteria (CLB), 6 to the alpha -subclass and 5 to the gamma -subclass of the Proteobacteria; 3 were related to oxygenic phototrophs, 2 were heteroduplexes and 1 was a possible chimera. While the alpha- and gamma -Proteobacteria predominated in the <1.0 m fraction, CLB were identified in both the free and attached fractions as well as among bacteria cultured from the same water, without overlap among these groups. The observation that distinct Cytophaga group sequences were present in the free versus attached fractions is counter to the current understanding that these organisms occupy a principally 'particle-specialist' niche. Our results suggest that some CLB are also important in the decomposition of polymeric organic matter in the dissolved phase with implications for the accumulation of dissolved organic matter and pathways of carbon flow during phytoplankton blooms.
A freshwater gliding bacterium, Alcaligenes denitrificans, was isolated from a hypereutrophic pond in Japan. This bacterium caused cell lysis and death of some cyanobacterial species, but showed no algicidal effects on the species of chlorophyceae tested. Microcystis aeruginosa, M. viridis and M. wesenbergii were susceptible to the bacterial attack and the growth-inhibiting effect of the bacterium was significant on M. aeruginosa, particularly when the alga was in the exponential growth phase. When A. denitrificans was inoculated at low densities (10(3) cells ml(-1)) together with Microcystis species, the bacterium proliferated to 10(8) cells ml(-1) and caused algal cell lysis. M. aeruginosa died when A. denitrificans was added to the algal culture but not when only the filtrate from the bacterial culture was added. This suggests that extracellular products are not inhibitory to M. aeruginosa and that only direct contact between A. denitrificans and M. aeruginosa was lethal. Thus, we suggest that A. denitrificans plays an important role in influencing the growth of Microcystis spp. and contributes to the death of Microcystis spp. in freshwater environments.
We used denaturing gradient gel electrophoresis (DGGE) of 16S rDNA PCR amplicons to analyze the composition of Bacteria communities in samples collected during the summer, low flow season from northern San Francisco Bay, California. There were clear compositional differences in communities sampled at different locations in the Bay and at different times of the year. Particle-associated (attached) and free-living (free) bacteria in a given sample were generally more similar than communities in different samples. At times, the attached and free communities in a sample appeared identical, suggesting a fairly rapid exchange between them. The free-living community tended to be richer (more operational taxonomic units [OTU] per sample) than the attached community; however, the difference was not statistically significant. Richness declined through the summer. The richest samples were collected on the June cruise (51 OTU sample(-1)) while the least rich samples were collected on the September cruise (21 OTU sample(-1)). The number of distinct OTUs encountered in all samples from a cruise ranged from 61 (April) to 45 (October). The greatest number of unique OTUs (26) was found in April samples while the fewest (3) was found in September. There was no consistent hierarchy of richness between samples. Sample groups representing location and size fractions contained from 55 to 61 different OTUs and from 8 to 18 unique (found only once) OTUs. An average of 23 % of the OTUs from a given station and size fraction were unique while an average of 5.5% were found on all cruises. Ubiquitous OTUs (found at all stations) ranged from 34 % (free-living, June) to 7 % (free-living, August) of the distinct OTUs encountered on a given cruise. Our results suggest Little difference in the biogeochemical role played by attached versus free bacteria in San Francisco Bay, particularly in the estuarine turbidity maximum. These results are generally consistent with our analyses of the metabolic potential of these communities.
We studied the ecology of heterotrophic bacteria attached to the mucilaginous colonies of Microcystis spp. (Cyanobacteria) in the eutrophic lake Frederiksborg Slotsso, Denmark. The succession in bacterial abundance, production and potential aminopeptidase activity in 20 mu m fractionated samples was followed during periods in which Microcystis dominated the phytoplankton. We operationally defined that nets of 20 mu m mesh-width segregated bacteria associated with Microcystis (Microcystis-associated bacteria, MB; 120 mu m size fraction) from the mainly fsee-living bacteria in the filtrate (FB, <20 mu m size fraction). According to this definition, the contribution of MB during summer 1995 and autumn 1994, respectively, averaged 10 +/- 4 (+/- standard deviation) and 37 +/- 12% of total bacterial biomass and 25 +/- 13 and 43 +/- 16% of total bacterial production, as estimated from thymidine (TdR) incorporation. During summer, MB further contributed 55 +/- 18% of total leucine incorporation measured at 600 nM leucine and 53 +/- 12% of total potential aminopeptidase activity. Although 20 mu m mesh-width nets also retained particles other than Microcystis, our results indicate that Microcystis was a 'hotspot' for bacterial activity, comparable to larger aggregates known as marine or lake snow. During summer, growth rate and specific aminopeptidase activity of MB generally exceeded those of FB, which points to diversified microenvironments or species compositions. In order to balance gain and loss rates within the community of MB, we hypothesize that a large fraction of MB produced were exported from Microcystis to the surrounding water, only modified by the loss due to viral lysis. This idea arose from reported low loss rates of Microcystis and continuous measures indicating that a surplus of more than 70% of MB production (TdR) was not reflected as biomass increases within the community of MB. According to this hypothesis Microcystis may be considered as a bacterial 'incubator' for the surrounding water.
Water samples were collected in August 2001 and 2002 from the eutrophic Lake Joutikas during cyanobacterial blooms. DNA and RNA were isolated from size fractionated samples and the diversity of the bacteria present in each fraction was studied by PCR amplification of partial 16S rRNA and denaturing gradient gel electrophoresis (DGGE) fingerprinting. Major bands from the gels were sequenced for further identification. Cyanobacteria were also identified and counted under the rnicroscope. Anabaena/Aphanizomenon were the most abundant cyanobacteria in both years, although the dominant species was different each year. When comparing the 2 techniques, equal numbers of abundant Anabaena/Aphanizomen on morphotypes were detected by microscopy and phylotypes by DGGE. The genera Microcystis and Synechococcus appeared more abundant in the DGGE analysis than under the microscope. In the heterotrophic bacterial community variation was observed between the bloom samples from the 2 years. Verrucomicrobia was the most abundant group in both years in both DNA- and RNA-derived profiles. Otherwise the patterns based on DNA and RNA-derived DGGE-profiles differed, especially in 2002. The presence of Actinobacteria and Chloroflexi was less pronounced in RNA-based than in DNA-based analysis. This indicates that their relative biomass was smaller than estimated by DNA-analysis. It might also indicate that they were metabolically inactive. In contrast, in 2002, the CFB group (Cytophaga-Flavobacterium-Bacteroides) and delta-Proteobacteria were more prominent in the RNA-based than in the DNA-based profiles. Thus they probably formed a substantial fraction of biomass and/or were active members in the blooms.
The paradigm of the 'microbial loop' has became increasingly important for understanding the structure and function of aquatic ecosystems. Most of the microbial loop studies have focused on energy flow and nutrient cycling. Much less is known, however, about the importance of grazing as a force shaping the structure and community composition of planktonic bacteria. Theoretical considerations of predator-prey interactions suggest that predator evasion mechanisms should have evolved for bacteria in the same way as in other predator-prey systems (e.g. zooplankton-phytoplankton). Consistent with this hypothesis, field data show that bacteria are often the most stable component of planktonic communities. Refuges from grazing are one of the possible mechanisms buffering bacterioplankton against strong seasonal fluctuations in abundance. Substantial direct and indirect evidence exists for the occurrence of grazing-resistant bacteria (GRB) in both marine and freshwater habitats. We summarize the potential mechanisms for grazing resistance, including morphological, chemical and behavioral defenses as well as growth in spatial refuges. Cell size appears to be an important factor influencing susceptibility to grazing, with a refuge at the lower and upper ends of the bacterial size range. Thus, a relative grazing resistance can be assumed for the large number of ultramicrobacteria as well as for morphologically complex growth forms such as filaments and aggregates. Besides morphological features, resistance may be achieved by other mechanisms for which, however, much less information is available. We describe how GRB can be included in conceptual models of the interactions among metazooplankton, bacterivorous protozoans and bacteria. It is suggested that the relative importance of GRB increases with increasing grazing pressure exerted by protozoans, whereas it decreases with increasing top-down control of protozoans by metazooplankton. GRB may reduce the productivity of planktonic systems through decreased trophic transfer efficiencies and reduced regeneration of bacterially bound nutrients.
The dynamics of benthic colonies of Microcystis aeruginosa (cyanobacteria) play an important part in the formation of the summer bloom underlying many harmful effects. Became this benthic phase remains somewhat unknown, we developed an approach using flow cytometry to follow the esterase activity of this species in the Grangent reservoir. The esterase activity of benthic cyanobacteria extracted from two layers of sediment (0-2 cm and 2-4 cm deep) was measured weekly, as an indicator of viability, by flow cytometry with carbonyfluorescein diacetate. In parallel, the concentration of benthic cyanobacteria was estimated under epifluorescence microscopy and the water temperature and dissolved oxygen concentration were measured in the hypolimnion. Esterase activity increased gradually as spring temperatures increased. This metabolic reactivation allowed one part of the benthic cyanobacteria to regain the water column, entailing a simultaneous decrease of their number in the upper sediment (0-2 cm). Then, after a maximum in summer, esterase activity decreased while the number of colonies increased. This corresponded with the domination of the senescent planktonic form following the decline of the bloom.
Develops the notion of a 'phycosphere', with examination of: the size and abundance of planktonic bacteria and algae; associated species in the algal microenvironment; endosymbiotic bacteria; inhibition of algal growth by bacteria (eg. by modifying the environment, by lysis, by competing for limiting nutrients and by other forms of inhibition); stimulation of algal growth by bacteria (eg. by nutrient regeneration, vitamin production, and other stimulatory products); inhibition of bacterial growth by algae (eg. by production of antibiotics and alteration of the macroenvironment); and stimulation of bacteria by algae (eg. by decomposition, extracellular release, and growth of enteric and pathogenic organisms in algal organic matter). The appropriateness of considering ecological succession in the phycosphere is indicated.-P.J.Jarvis
The isolation of high-quality nucleic acids from cyanobacterial strains, in particular environmental isolates, has proven far from trivial. We present novel techniques for the extraction of high molecular weight DNA and RNA from a range of cultured and environmental cyanobacteria, including stains belonging to the genera Microcystis, Lyngbya, Pseudanabaena, Aphanizomenon, Nodularia, Anabaena, and Nostoc, based on the use of the nontoxic polysaccharide solubilizing compound xanthogenate. These methods are rapid, require no enzymatic or mechanical cell disruption, and have been used to isolate both DNA and RNA free of enzyme inhibitors or nucleases. In addition, these procedures have proven critical in the molecular analysis of bloom-forming and other environmental cyanobacterial isolates. Finally, these techniques are of general microbiological utility for a diverse range of noncyanobacterial microorganisms, including Gram-positive and Gram-negative bacteria and the Archea.
Lake Taihu is characterized by its shallowness (mean depth = 1.9 m) and large surface area (2,338 km2). Runoff sources are mostly from the mountainous west and southwest, and outflows are located throughout East Taihu. This
causes shorter retention times in the south. In contrast, urban pollutants discharge into northern Taihu and result in poor
water quality. Non-point pollution from rural areas and sewage wastewater is the primary pollution source. Water current velocity
ranges from 10–30 cm s−1, and surface currents normally follow wind direction. Bottom currents appear to be a compensation flow. Most wave heights
are less than 40 cm, and underwater irradiance correlates to seston in the water column. Lacustrine sediment is distributed
in littoral zones, mostly along the western shoreline, with almost no accumulation in the lake center. Intensive aquaculture
in East Taihu caused eutrophication and hampered water supply in surrounding areas. In addition, development of marshiness
in the eastern littoral zones and East Taihu has occurred. The function of flood discharging of East Taihu has been limited
by flourishing macrophytes. The problems facing in Lake Taihu will be alleviated by improving the management of nutrient sources
into the lake.
Phosphorus release from Microcystis aeruginosa and attached bacterium (Pseudomonas sp.) isolated from Lake Taihu was examined using a phosphorus isotope tracer in order to investigate the phosphorus transference
between the two species. Our results reveal that the amount of phosphorus released form 32P-saturated M. aeruginosa is determined by its growth phase and most of phosphorus is assimilated by Pseudomonas finally while the amount of phosphorus released from 32P-saturated Pseudomonas is also determined by the growth phase of M. aeruginosa and most of them are assimilated by M. aeruginosa. The results suggest that phosphorus transference occurs between M. aeruginosa and its attached Pseudomonas. This process makes microenvironment of mucilage of M. aeruginosa attached bacteria maintain relative high amounts of phosphorus. Attached bacteria may be a temporary phosphorus bank to the
growth of M. aeruginosa, and assimilation of phosphorus by M. aeruginosa becomes easy when M. aeruginosa is in lag growth phase. Thus, the phosphorus exchange between M. aeruginosa and attached Pseudomonas in microenvironment may be important to microfood web and cyanobacteria bloom.
Kinetics of glucose and amino acid uptake by attached and free-living bacteria were compared in the upper 70 m of the oligotrophic
north-western Mediterranean Sea. Potential uptake rates of amino acids were higher than those of glucose in all the samples
analysed. Cell-specific potential uptake rates of attached bacteria were up to two orders of magnitude higher than those of
total bacteria, both for amino acids and glucose (0.72–153 amol amino acids cell−1 h−1 and 0.05–58.42 amol glucose cell−1 h−1 for attached bacteria and 0.34–1.37 amol amino acids cell−1 h−1 and 0.07–0.22 amol glucose cell−1 h−1 for total bacteria). The apparent K
m values were also higher in attached bacteria than in total bacteria, both for amino acids and glucose. These results would
reflect the presence of different uptake systems in attached and free-living bacteria, which is in accordance with the different
nutrient characteristics of their microenvironments, ambient water and particles. Attached bacteria show transport systems
with low affinity, which characterise a bacterial community adapted to high concentration of substrates.
We investigated the molecular diversity of cyanobacteria and bacteria during a water bloom in a lake with a long history of
toxic cyanobacterial blooms (Lake Kastoria, Greece). We also tested the hypothesis whether bloom-forming cyanobacteria are
preserved in the lake’s sediment 2years after the bloom. The dominant cyanobacteria during the bloom included the potentially
toxin-producing Microcystis aeruginosa and several other Chroococcales forms closely related to the genus Microcystis. This suggests that the use of cyanobacterial-specific primers seems to be very informative in describing the cyanobacteria
during the water blooms. The bacterial community showed high diversity, consisting mostly of singleton and doubleton phylotypes.
The majority of the phylotypes were typical lake bacteria including some potential pathogens and toxin metabolising bacteria,
suggesting that the dominant toxic cyanobacteria did not have any significant effect on the bacterial community structure.
In the sediment, 2years after the water bloom, no bloom-forming cyanobacteria were retrieved, suggesting that they cannot
be preserved in the sediment. Similar to the water column, sediment bacterial diversity was also high, consisting mostly of
yet-uncultured bacteria that are related to environments where organic matter degradation takes place.
KeywordsCyanobacteria-Bacteria-16S rRNA-Water column-Sediment-Lake-Kastoria
The temporal variability of the abundance and the incorporation of 3H-thymidine and 14C-glucose by attached and free-living bacteria, as well as their relation with environmental factors, were analyzed in a coastal marine ecosystem during a year. Both communities were quantitatively very different. Attached bacteria represented only 6.8% of the total bacterial abundance, whereas free-living bacteria represented 93.2%. The environmental factors most closely linked to the abundance and activity of free-living bacteria were temperature and the concentration of dissolved nutrients. Moreover, the free-living community showed similar temporal variations in abundance and in activity, with lower values in the cold months (from October to May). The attached community did not present the same pattern of variation as the free-living one. The abundance of the attached bacteria was mainly correlated to the concentration of particulate material, whereas their activity was correlated to temperature. We did not find a significant correlation between the abundance and the activity of the attached community. On the other hand, the activity per cell of the two communities did not present a clear temporal variation. Attached bacteria were more active than free-living ones in the incorporation of radiolabeled substrates on a per cell basis (five times more in the case of glucose incorporation and twice as active in thymidine incorporation). However, both communities showed similar specific growth rates. The results suggest that the two aquatic bacterial communities must not be considered as being independent of each other. There appears to be a dynamic equilibrium between the two communities, regulated by the concentrations of particulate matter and nutrients and by other environmental factors.
Recently developed techniques for estimating bacterial biomass and productivity indicate that bacterial biomass in the sea is related to phytoplankton concentration and that bacteria utilise 10 to 50 % of carbon fixed by photosynthesis. Evidence is presented to suggest that numbers of free bacteria are controlled by nanoplankton~c heterotrophic flagellates which are ubiquitous in the marine water column. The flagellates in turn are preyed upon by microzooplankton. Heterotrophic flagellates and microzooplankton cover the same size range as the phytoplankton, thus providing the means for returning some energy from the 'microbial loop' to the conventional planktonic food chain.
Aggregation of algae, mainly diatoms, is an important process in marine systems leading to the settling of particulate organic carbon predominantly in the form of marine snow. Exudation products of phytoplankton form transparent exopolymer particles (TEP), which acts as the glue for particle aggregation. Heterotrophic bacteria interacting with phytoplankton may influence TEP formation and phytoplankton aggregation. This bacterial impact has not been explored in detail. We hypothesized that bacteria attaching to Thalassiosira weissflogii might interact in a yet-to-be determined manner, which could impact TEP formation and aggregate abundance. The role of individual T. weissflogii-attaching and free-living new bacterial isolates for TEP production and diatom aggregation was investigated in vitro. T. weissflogii did not aggregate in axenic culture, and striking differences in aggregation dynamics and TEP abundance were observed when diatom cultures were inoculated with either diatom-attaching or free-living bacteria. The data indicated that free-living bacteria might not influence aggregation whereas bacteria attaching to diatom cells may increase aggregate formation. Interestingly, photosynthetically inactivated T. weissflogii cells did not aggregate regardless of the presence of bacteria. Comparison of aggregate formation, TEP production, aggregate sinking velocity and solid hydrated density revealed remarkable differences. Both, photosynthetically active T. weissflogii and specific diatom-attaching bacteria were required for aggregation. It was concluded that interactions between heterotrophic bacteria and diatoms increased aggregate formation and particle sinking and thus may enhance the efficiency of the biological pump.
The biodiversity of a specific cyanobacterial mat associated to a thermomineral spring from the Western Plain of Romania was investigated. Light and electron microscopy, together with molecular tools (denaturing gradient gel electrophoresis-DGGE, automated ribosomal intergenic spacer analysis-ARISA and amplified ribosomal DNA restriction analysis-ARDRA), based on 16S rDNA and 16S-23S internal transcribed spacer markers were used. Based on the partial 16S rRNA fragments sequenced, eight cyanobacterial taxons were identified, all belonging to the Oscillatoriales order, Phormidium and Leptolyngbya being dominant. A significant difference was observed, in comparison with the morphological approach. In certain conditions, DGGE can provide misleading information due to multiple melting domains in the same sequence, to multiple rrn operons in the same genome and due to unspecific hybridization among closely related sequences. This can lead to an overestimated species abundance which can cause incorrect description of the microbial community investigated. Additional techniques, such as ARISA and ARDRA, can improve the microbial biodiversity studies, thus providing optimal results.
The effect of environmental temperature on the affinity of microorganisms for substrates is discussed in relation to measurements of affinity by either K(b) values or specific affinity (a(A)). It can be shown for psychrophiles, mesophiles and thermophiles that when a(A) is used as the measure of affinity, affinity decreases consistently as temperature drops below the optimum temperature for growth. This effect may be because of stiffening of the lipids of the membrane below the temperature optimum, leading to decreased efficiency of transport proteins embedded in the membrane. The lower temperature limit for growth is. therefore, that temperature at which an organism is no longer able to supply the maintenance requirement of the growth rate-limiting nutrient because of loss of affinity for that substrate. This linking of temperature and affinity for substrates taken up by active transport (a temperature-modulated substrate affinity model) includes uptake of both organic and inorganic substrates. This effect of decreased substrate affinity at low temperature may have profound implications on the availability of substrates in the natural environment as environmental temperatures change. At temperatures below their optimum for growth microorganisms will become increasingly unable to sequester substrates from their environment because of lowered affinity: exacerbating the anyway near-starvation conditions in many natural environments.
As has been pointed out in Chapter 1, the planktonic community is especially suitable for testing general ecological theories. Its spatial structure is relatively simple, and many species can be easily cultured and have short generation times. An experimental approach can be effective, particularly with those plankton showing the highest potential growth rates: the bacteria. Indeed, many important biotic interactions such as competition, commensalism, mutualism, predation, and parasitism have been studied using bacteria (Frederickson, 1977). In spite of this wealth of experimental data, however, there is no consensus regarding the control of planktonic bacterial succession. This lack of agreement is not surprising considering the inability of current methodologies to clearly distinguish different populations of bacteria. The information gained from microscopic examination of bacteria is limited, unlike the case for phyto- and zooplankton. Bacterial composition can at best be differentiated according to rough morphologic criteria such as length and width of cells, multicellular or single-celled growth, attachment to surfaces, etc. The indirect approach of analyzing the composition of colonies grown on agar plates is hindered by the large discrepancy between plate counts and direct microscopic counts (Staley and Konopka, 1985). As has been emphasized by Pedros-Alio (see Chapter 8), promising approaches based on species-specific biomolecular cues may improve this situation in the near future.
Six out of 23 genera of the family Xanthomonadaceae in the Gammaproteobacteria are involved directly or indirectly in oil or petroleum hydrocarbon degradation. In this chapter we discuss the taxonomy, physiology, and ecology of species of Hydrocarboniphaga, Pseudoxanthomonas, Rhodanobacter, Stenotrophomonas, Xanthomonas, and Xylella that are involved in oil degradation.
The structure and composition of the bacterial community associated with buoyant Microcystis colonies were monitored during the decline of a cyanobacterial bloom (from October 13, 2009 to January 27, 2010). When temperature decreased, the ratio between the colony-associated bacteria and the Microcystis gradually decreased as estimated by a quantitative real-time polymerase chain reaction (qRT-PCR)-based approach. Diversity of bacterial communities was determined through denaturing gradient gel electrophoresis (DGGE) of 16S rRNA gene fragments. Cluster analysis of the DGGE profiles showed that most of the bacterial communities associated with Microcystis colonies collected on the nearby dates were clustered together. The bacterial clones from four clone libraries in different months were classified into 5, 12, 6 and 12 operational taxonomic units, most of which were affiliated with Gammaproteobacteria, Alphaproteobacteria and Bacteroidetes. Shift in dominance from pathogenic Aeromonas sp. to Shewanella sp. capable of remineralization of many organic materials was observed, and both species seemed to be associated with Microcystis colonies along with the bloom decline. These results indicated that the potential harmful effects of the Microcystis bloom on the safety of lake water during the decline period should be taken into account.
It has been known for many years that filtrates from axenic algal cultures may be enriched with organic compounds. These materials, including simple amino acids and peptides, sugars, polyalcohols, and occasionally vitamins, enzymes, and toxins, are usually lumped under the term â€oe¿¿ extracellular products†• (Fogg, 1966). Studies using natural populations of phytoplankton have shown that extracellular products are not mere laboratory artifacts, and that, depending upon environmental conditions, they account for 1â€"20%of the total photoassimilated carbon (Helle bust, 1965; Nalewajko, 1966; Samuel, Shad and Fogg, 1971; Thomas, 1971). The potential significance of extracellular organic material in marine food chains is extremely interesting. Many authors (Fogg, 1966; Brock, 1966; Alexander, 1971; Whittaker and Feeney, 1971) have suggested that these products may play an important role in marine food chains, especially as potential nutrients for bac teria. However, to our knowledge, there is no direct evidence that this is so although the ability of bacteria to grow in algal cultures (Vela and Guerra, 1966; Berland, Bianchi and Maestrini, 1969) might be interpreted to support such conclusions. If, in fact, algal extracellular products are important contributors to bacterial food chains, it would seem possible to construct an aquatic counterpart of the well known â€oe¿¿ rhizosphere†• of terrestrial ecosystems (Rovira, 1965). A zone may exist, extending outward from an algal cell or colony for an undefined distance, in which bacterial growth is stimulated by extracellular products of the alga. For purposes of discussion in this paper, we will term this region the â€oe¿¿ phycosphere.†• Motile bacteria commonly exhibit chemotaxis to concentration gradients of or ganic material (Weibull, 1960; Adler, 1969). The ecology of chemotaxis by organotrophic bacteria has not been well studied, but highly species-specific re sponses to certain carbohydrates, amino acids, and nucleotide bases have been ob served (Fogel, Chet and Mitchell, 1971), and certain predatory microorganisms have been shown to be chemotactic to their prey (Chet, Fogel and Mitchell, 1971).
The realization that natural assemblages of planktonic bacteria may acquire a significant fraction of their nitrogen and phosphorus via the uptake of dissolved inorganic nutrients has modified our traditional view of these microorganisms as nutrient remineralizers in plankton communities. Bacterial uptake of inorganic nitrogen and phosphorus may place bacteria and phytoplankton in competition for growth-limiting nutrients, rather than in their traditional roles as the respective "source" and "sink" for these nutrients in the plankton. Bacterial nutrient uptake also implies that bacterivorous protozoa may play a pivotal role in the remineralization of these elements in the microbial loop. The overall contribution of bacterial utilization of inorganic nutrients to total nutrient uptake in the ocean is still poorly understood, but some generalizations are emerging with respect to the geographical areas and community physiological conditions that might elicit this behavior.
The phylogenetic diversity of macroaggregate-attached vs. free-living marine bacteria, co-occurring in the same water mass, was compared. Bacterial diversity and phylogcnetic identity were inferred by analyzing polymerase chain reaction (PCR) amplified, cloned ribosomal RNA (rRNA) genes. Ribosomal RNA genes from macroaggregatc-associated bacteria were fundamentally different from those of free-living bacterio- plankton. Most rRNA types recovered from the free-living bacterioplankton were closely related to a phenotypically undcscribcd (Y Proteobacteria group, previously detected in surface waters of North Pacific and Atlantic central ocean gyres. The results suggest that members of this phylogenetically distinct, (Y proteobacterial group are abundant free-living bactcrioplankters in coastal, as well as open-ocean habitats. In contrast, most macroaggregate-associated rRNA clones were closely related to Cytophuga, Plancto- myce.s, or y Proteobacteria, within the domain Bacteria. These data indicate that specific bacterial pop- ulations, different from those which predominate in free-living bacterioplankton, develop on marine phytodetrital aggregates. The inferred properties of attached bacterial assemblages have significant im- plications for models of microbially mediated transformation of particulate organic material.
Bacterivory on aggregates and bulk seawater by three nanoflagellates and a microciliate was investigated. A new approach to measure bacterivory on the attached bacterial community is proposed. Macroaggregates containing attached fluorescently labeled bacteria (FLB) were obtained by adding labeled planktonic bacteria to rolling tanks filled with natural seawater, and they were used to measure protistan grazing rates on the bacteria attached to aggregates. Protistan grazing on free-suspended bacteria was measured according to the monodispersed FLB uptake technique. The four protists showed low grazing rates when feeding on free-suspended bacteria at the low densities usually found in seawater. Surprisingly, the analyzed protists also showed low grazing rates when feeding on aggregates despite the very high bacterial densities inhabiting them. The analysis of the influence of prey density on bacterial grazing rates suggests that feeding on bacteria attached to aggregates involves a relevant additional effort when compared to feeding on free-suspended bacteria. The paradox between these results and the very high abundance of protistan communities usually found in aggregates is discussed attending to the view of aggregates as biological reactors. Therefore, marine macroaggregates can be considered as microniches able to support the maintenance of a protistan community without food limitation, as well as to attract protistan colonizers by generating a water layer enriched in organic matter and bacteria.
We studied the composition of free-living and particle-associated bacterial communities during the course of the phytoplankton succession in spring and early summer in the Wadden Sea, a tidal flat ecosystem in the southern North Sea. We applied the denaturing gradient gel electrophoresis (DGGE) approach based on PCR-amplified 16S rRNA gene fragments and, in addition to Bacteria specific primers, used primer sets targeting Alphaproteobacteria, the Roseobacter-clade and the Bacteroidetes phylum. Even though the application of the primer sets targeting Bacteria and Alphaproteobacteria detected some changes, they were most pronounced with those targeting the Roseobacter-clade and Bacteroidetes. The changes were supported by a correspondence analysis, which showed a statistically significant correlation of the DGGE banding patterns of the Roseobacter-specific PCR with the composition of the phytoplankton (p = 0.03). This indicates that changes in the phytoplankton composition in this habitat are not reflected by changes in the most abundant or most readily amplifiable phylotypes. The findings rather suggest that few, specialized, heterotrophic bacteria are most responsive to the organic matter supplied by distinct phytoplankton communities and that the main part of organic matter in the Wadden Sea is utilized by generalists. Sequence analyses of excised bands revealed a high diversity for the Bacteria- and Bacteroidetes-targeted approaches. The bacterial community detected by the primer set targeting Alphaproteobacteria, however, was mainly composed of bacteria affiliated to the Roseobacter-clade.
The current knowledge of micro- and macroaggregates in running waters as well as an assessment of their importance will be given in this overview. Micro- and macroscopic aggregates are an abundant component of running waters, considering both rivers and estuaries. They are composed of different kinds of organic and inorganic matter and elements, mainly from the aquatic but also from the terres- trial environment. Their production is determined by natural and anthropogenically influenced abiotic and biotic factors. Aggregate abundance, size and composition vary greatly along the longitudinal pro- file of running waters. Aggregates are actively or passively colonized by bacteria, protozoa (amoebae, ciliates and flagellates) and metazoa (copepods, nematodes, rotifers, veliger larvae) and they show hig- her loads of nutrients and organisms compared to the surrounding water. Detritus in running waters has been examined over a period of 100 years but investigations of single aggregates began only in 1996, after pioneering works in the marine field and in lakes. Since then studies have been focused on sever- al aspects of aggregate formation, colonization, nutrient recycling and decomposition. Aggregates have been identified as foci of microbial activity. It has been shown that the significance of aggregate - asso- ciated organisms and processes varies both temporally and spatially and is also affected by the nutrient status of surrounding water. An important conclusion from recent studies is that the resuspension and sedimentation of aggregates connects pelagic and benthic food webs to an aquatic food web. It also underlines the importance of the microbial food web, with its fluxes among aggregate-associated pico- and nano-organisms, to organisms of higher trophic levels. Predators of higher trophic levels are only able to eat small-sized organisms if they are associated to aggregates.
Oceanic macroaggregates (marine snow and Rhizosolenia mats) sampled from the Sargasso Sea are associated with bacterial and protozoan populations up to four orders of magnitude
greater than those present in samples from the surrounding water. Filamentous, curved, and spiral bacteria constituted a higher
proportion of the bacteria associated with the particles than were found among bacteria in the surrounding water. Protozoan
populations were dominated numerically by heterotrophic microflagellates, but ciliates and amoebas were also observed. Macroaggregates
are highly enriched heterotrophic microenvironments in the oceans and may be significant for the cycling of particulate organic
matter in planktonic food chains.
1. Sediments from hypereutrophic Lake Vallentunasjön were enriched with Microcystis colonies from the lake water, thereby simulating the conditions after the autumn sedimentation. Release of phosphorus to the overlying lake water was followed during 2–3 weeks in the laboratory. X-ray microanalysis of individual Microcystis and bacterial cells, and chemical phosphorus fractionation, were used to assess the phosphorus pool size in different fractions of the sediment.
2. Benthic Microcystis colonies, most of these having survived within the sediment for 1 year or more, were less susceptible to decomposition, and the specific growth rate of bacteria in their mucilage was lower than for other sediment bacteria.
3. Pelagic Microcystis colonies from late August were resistant to decomposition, when placed on the sediments. When Microcystis colonies from a declining pelagic population in October were added to the sediments, however, a substantial fraction of these colonies was decomposed. The specific growth rate of mucilage bacteria was five times higher than for other sediment bacteria.
4. Release of molybdate-reactive phosphorus to the overlying lake water was larger from sediment cores enriched with Microcystis colonies than from control cores. Chemical phosphorus fractionation showed a decrease in organic-bound phosphorus (residual P).
5. X-ray microanalysis showed that the phosphorus bound in Microcystis cells decreased by -0.300 mg g−1 DW in the October experiment, due both to a decrease in biomass (i.e. mineralization) and to a decrease in phosphorus content in the remaining cells. Heterotrophic bacteria increased their cellular concentration of phosphorus. The net release of phosphorus from the Microcystis and bacterial pools corresponded to 74% of the decrease of organic-bound phosphorus in the chemical phosphorus fractionation, and to 65% of the decrease of total phosphorus in the upper 0–1 cm of the sediment.
6. Benthic bacteria and cyanobacteria may thus contribute significantly to changes in phosphorus content and turnover of the sediment by changes in their biomass, turnover rate and cellular phosphorus content.
The mucilage of cyanobacteria represents a unique habitat for both water column and sediment bacteria. In Lake Vallentunasjön, Sweden, the pelagic Microcystis-associated bacteria constituted 19–40% of the total bacterial abundance, and their contribution to the total bacterial production was 7–30%. In the sediment, the mucilage bacteria constituted only 1–5% of the total bacterial abundance, but contributed with 8–13% to the total bacterial production during the summer. Microcystis-associated bacteria thus were less active (bacterial production/cell) than ambient water column bacteria, while in the sediments the Microcystis colonies were ‘hot spots’ with enhanced bacterial activity as compared to other sediment bacteria.
1. To reveal the role of aquatic heterotrophic bacteria in the process of development of Microcystis blooms in natural waters, we cocultured unicellular Microcystis aeruginosa with a natural Microcystis-associated heterotrophic bacterial community.
2. Unicellular M. aeruginosa at different initial cell densities aggregated into colonies in the presence of heterotrophic bacteria, while axenic Microcystis continued to grow as single cells. The specific growth rate, the chl a content, the maximum electron transport rate (ETRmax) and the synthesis and secretion of extracellular polysaccharide (EPS) were higher in non-axenic M. aeruginosa than in axenic M. aeruginosa after cell aggregation, whereas axenic and non-axenic M. aeruginosa displayed the same physiological characteristic before aggregation.
3. Heterotrophic bacterial community composition was analysed by PCR–denaturing gradient gel electrophoresis (PCR–DGGE) fingerprinting. The biomass of heterotrophic bacteria strongly increased in the coinoculated cultures, but the DGGE banding patterns in coinoculated cultures were distinctly dissimilar to those in control cultures with only heterotrophic bacteria. Sequencing of DGGE bands suggested that Porphyrobacter, Flavobacteriaceae and one uncultured bacterium could be specialist bacteria responsible for the aggregation of M. aeruginosa.
4. The production of EPS in non-axenic M. aeruginosa created microenvironments that probably served to link both cyanobacterial cells and their associated bacterial cells into mutually beneficial colonies. Microcystis colony formation facilitates the maintenance of high biomass for a long time, and the growth of heterotrophic bacteria was enhanced by EPS secretion from M. aeruginosa.
5. The results from our study suggest that natural heterotrophic bacterial communities have a role in the development of Microcystis blooms in natural waters. The mechanisms behind the changes of the bacterial community and interaction between cyanobacteria and heterotrophic bacteria need further investigations.
Several dinoflagellate species have been shown to produce potent neurotoxins known as paralytic shellfish toxins. Evidence is also accumulating that marine bacteria associated with dinoflagellates play a role in the accumulation of paralytic shellfish toxins. In this study, the diversity of bacteria in cultures of both toxic and non-toxic dinoflagellates, Alexandrium spp. and Scrippsiella trochoidea, were compared using colony morphology, restriction fragment length polymorphisms, denaturing gradient gel electrophoresis of PCR-amplified 16S rRNA genes and, ultimately, sequence determination of the 16S rRNA genes. The results suggest that a number of different bacterial species are associated with dinoflagellates, some of which are common to each of the dinoflagellate cultures examined, whereas others appear to be unique to a particular dinoflagellate. The phylogenetic diversity of the bacteria observed was limited to two bacterial phyla, the Proteobacteria and the Cytophaga-Flavobacter-Bacteroides (CFB). Although phylum level diversity was limited, many distinct phylogenetic clades were recovered, including members of both the α- and γ-subclasses of the Proteobacteria. Additionally, several of the bacterial phylotypes isolated were not closely related to any published bacterial species but, rather, were identical to isolates characterised from Alexandrium cultures 4 years earlier. Finally, many of the bacteria isolated from the dinoflagellate cultures were related to microorganisms with known surface-associated life histories (e.g. the CFB phylum, Hyphomonas, Caulobacter and some members of the Roseobacter clade including Ruegeria algicola).
High molecular weight (HMW) DNA prepared from a toxic freshwater cyanobacterial bloom sample was used to construct a PCR-generated 75-clone, 16S rRNA gene library and a 2850-clone bacterial artificial chromosome (BAC) library. Phylogenetic analysis of the 16S rRNA gene library demonstrated that members of eight phyla of domain Bacteria, which included Cyanobacteria, Actinobacteria, Verrucomicrobium, Bacteriodetes, Planctomycetes, Chloroflexi, Candidate Division OP10 and Alpha-, Beta- and Gammaproteobacteria, were present in the bloom community. Diversity estimates determined from 16S rRNA gene analysis and direct cell counts and morphological identification of phytoplanktons suggested that the bloom community was dominated by members of the genera Aphanizomenon and Cylindrospermopsis, phylum Cyanobacteria. BAC-end sequencing of 37 randomly selected clones and subsequent sequence analysis provided a snapshot of the total bloom community putative metabolic activities. The sequencing of the entire inserts of seven clones (clones designated 578, 67, 142, 543, 905, 1664 and 2089) selected from BAC-end sequence studies resulted in the generation of a total of 144-kb sequence data and in the identification of 130 genes for putative proteins representing at least four phyla, Proteobacteria, Actinobacteria, Bacteroidetes and Cyanobacteria. This is the first report on a snapshot analysis of a limited metagenome of a toxic cyanobacterial freshwater bloom.
Twelve strains of algicidal bacteria were isolated from the surfacewater of the pond Shinobazu and the moat Ote-bori (Tokyo, Japan). Nine of thesestrains were considered to be in the Pseudomonas group byanalyses of 16S rDNA sequences. The methanol extract ofPseudomonas sp. K44-1 showed marked antialgal activity bythe paper disk method. Harmane (1-methyl--carboline) was isolated fromtheethyl acetate extract of the whole culture broth ofPseudomonas sp. K44-1 by using silica gel columnchromatography and high performance liquid chromatography (HPLC). Harmaneshowedantagonistic activities against several cyanobacterial strains at aconcentration of 30 g disk–1.
In the experiment with water from the hypereutrophic Lake Frederiksborg Slotso (Denmark) sampled during the autumn peak of
Microcystis growth, the quantity and production of free-living and cyanobacteria-associated heterotrophic bacteria were determined, as
well as the extracellular enzymatic (aminopeptidase) activity. The functional diversities of associated and free-living bacterial
communities were additionally compared using BIOLOG GN microplates to reveal the possible export of Microcystis-attached bacteria into ambient water. It has been shown that the cell size, production values, and growth rates of associated
bacteria were less than those of free-living bacteria. At the same time, the potential aminopeptidase activity of associated
bacteria was always higher than that of free-living bacteria. The experimental results have shown significant compositional
differences in the structure of bacterial communities from different habitats.
An aquatic bacterium capable of eliminating the cyanobacterium Microcystis aeruginosa was isolated from the sediment of an eutrophic lake (Lake Juam, Korea). On the basis of 16S rDNA sequences and biochemical and morphological characteristics, the isolate was determined to be Streptomyces neyagawaensis. It grew optimally at 40 °C and pH 7. In the presence of this bacterium, the biomass of cyanobacterium M. aeruginosa NIES-298 was strongly suppressed, by up to 84.5% in abundance compared to the control. The antialgal activity of S. neyagawaensis depended on the growth phase of the cyanobacterium, but not of the antialgal bacterium. The antialgal activity of S. neyagawaensis was effective against a wide range of algae, including the green alga Chlorella sp., the diatoms Aulacoseira granulata and Stephanodiscus hantzschii, and four cyanobacteria, M. aeruginosa NIES-44, Anabaena cylindrica, Anabaena flos-aquae, and Oscillatoria sancta. S. neyagawaensis indirectly attacked M. aeruginosa by secretion of extracellular antialgal substances that were localized in the bacterial periplasm and had a specific activity of 7.7 U/μg. These results suggest that indigenous bacteria isolated from sediments may have potential application in controlling harmful cyanobacterial blooms in freshwaters.
Several dinoflagellate species have been shown to produce potent neurotoxins known as paralytic shellfish toxins. Evidence is also accumulating that marine bacteria associated with dinoflagellates play a role in the accumulation of paralytic shellfish toxins. In this study, the diversity of bacteria in cultures of both toxic and non-toxic dinoflagellates, Alexandrium spp. and Scrippsiella trochoidea, were compared using colony morphology, restriction fragment length polymorphisms, denaturing gradient gel electrophoresis of PCR-amplified 16S rRNA genes and, ultimately, sequence determination of the 16S rRNA genes. The results suggest that a number of different bacterial species are associated with dinoflagellates, some of which are common to each of the dinoflagellate cultures examined, whereas others appear to be unique to a particular dinoflagellate. The phylogenetic diversity of the bacteria observed was limited to two bacterial phyla, the Proteobacteria and the Cytophaga-Flavobacter-Bacteroides (CFB). Although phylum level diversity was limited, many distinct phylogenetic clades were recovered, including members of both the α- and γ-subclasses of the Proteobacteria. Additionally, several of the bacterial phylotypes isolated were not closely related to any published bacterial species but, rather, were identical to isolates characterised from Alexandrium cultures 4 years earlier. Finally, many of the bacteria isolated from the dinoflagellate cultures were related to microorganisms with known surface-associated life histories (e.g. the CFB phylum, Hyphomonas, Caulobacter and some members of the Roseobacter clade including Ruegeria algicola).
PCR-denaturing gradient gel electrophoresis (DGGE) and canonical correspondence analysis (CCA) were used to explore the relationship between succession of phytoplankton community and temporal variation of bacterioplankton community composition (BCC) in the eutrophic Lake Taihu. Serious Microcystis bloom was observed in July-December 2008 and Bacillariophyta and Cryptophyta dominated in January-June 2009. BCC was characterized by DGGE of 16S rRNA gene with subsequent sequencing. The DGGE banding patterns revealed a remarkable seasonality which was closely related to phytoplankton community succession. Variation trend of Shannon-Wiener diversity index in bacterioplankton community was similar to that of phytoplankton community. CCA revealed that temperature and phytoplankton played key roles in structuring BCC. Sequencing of DGGE bands suggested that the majority of the sequences were affiliated with common phylogenetic groups in freshwater: Alphaproteobacteria, Betaproteobacteria, Bacteroidetes and Actinobacteria. The cluster STA2-30 (affiliated with Actinobacteria) was found almost across the sampling time at the two study sites. We observed that the family Flavobacteriaceae (affiliated with Bacteroidetes) tightly coupled to diatom bloom and the cluster ML-5-51.2 (affiliated with Actinobacteria) dominated the bacterioplankton communities during Microcystis bloom. These results were quite similar at the two sampling sites, indicating that BCC changes were not random but with fixed pattern. Our study showed insights into relationships between phytoplankton and bacterioplankton communities at species level, facilitating a better understanding of microbial loop and ecosystem functioning in the lake.
Cyanobacterial blooms represent a nutritious niche for associated bacteria including potential pathogens for humans as well as livestock. We investigated bacterial community composition associated with Microcystis sp. using different approaches: batch experiments on Microcystis sp. or its enriched exudates, field enclosures (dialysis bags) and field sampling during natural blooms in freshwaters. Bacterial community composition associated with Microcystis sp. differed significantly with temperature, bacterial source community and number of incubated cyanobacterial strains. Interestingly, Actinobacteria of the AcI cluster were only present in the 20°C treatments and disappeared at higher incubation temperatures. Moreover, Archaea were present in all field samples but did not show any regional patterns, which is consistent with bacteria. Absence of Archaea in the experimental treatments indicates reduced growth under experimental conditions. In contrast, members of the genus Sphingomonas (Alphaproteobacteria), which includes species known as human pathogens, occurred in almost all samples. Thus Sphingomonadales seem to be an integral element of Microcystis sp. blooms - even affecting concentrations of microcystins as a result of their breakdown of the toxins. Depending on environmental conditions such as temperature, light, currents and nutrients, the role of heterotrophic Bacteria associated with Cyanobacteria can greatly vary by either increasing (pathogens) or decreasing (breakdown of toxins) health risks caused by mass developments of potentially toxic Cyanobacteria.
Short-term bacterial community composition (BCC) dynamics in response to accumulation and breakdown of Microcystis blooms were examined by conducting in situ mesocosm experiments with varying levels of Microcystis sp. biomass, ranging from 15 to 3217 μg/L as measured by chlorophyll-a concentration in the freshwater water column. The BCC was assessed by means of terminal restriction fragment length polymorphism (T-RFLP) of 16S ribosomal RNA genes followed by cloning and sequencing of selected samples. The results showed that the composition of both free-living and particle-attached bacterial communities changed during the accumulation and breakdown phases of a Microcystis bloom, and differences were also evident with different levels of Microcystis biomass. The relative abundance of bacteria affiliated with Micrococcineae and Legionellales increased in general after amendment with Microcystis. Significant correlation between the relative abundance of Micrococcineae and breakdown of Microcystis biomass was also observed. Canonical correspondence analysis (CCA) showed that the changes in the free-living and particle-attached bacterial community were mostly related to the changes in the concentrations of chlorophyll-a, dissolved organic carbon (DOC), dissolved oxygen (DO) and pH, which were mainly induced by the breakdown of Microcystis biomass. Overall, our study revealed the following: i) accumulation of Microcystis blooms and their breakdown have strong impacts on bacterial community composition; ii) there might be saprophytic association between Micrococcineae and decomposition of Microcystis biomass; iii) it is necessary to reveal potential associations between Legionellales organisms and Microcystis blooms in eutrophic freshwater lakes.
Cyanobacterial strains isolated from terrestrial and freshwater habitats in Brazil were evaluated for their antimicrobial and siderophore activities. Metabolites of fifty isolates were extracted from the supernatant culture media and cells using ethyl acetate and methanol, respectively. The extracts of 24 isolates showed antimicrobial activity against several pathogenic bacteria and one yeast. These active extracts were characterized by Q-TOF/MS. The cyanobacterial strains Cylindrospermopsis raciborskii 339-T3, Synechococcus elongatus PCC7942, Microcystis aeruginosa NPCD-1, M. panniformis SCP702 and Fischerella sp. CENA19 provided the most active extracts. The 50 cyanobacterial strains were also screened for the presence of non-ribosomal peptide synthetase (NRPS) and polyketide synthase (PKS) genes and microcystin production. Putative fragment genes coding for NRPS adenylation domains and PKS keto-synthase domains were successfully PCR amplified from 92% and 80% of cyanobacterial strains, respectively. The potential therapeutical compounds siderophores were detected in five cyanobacterial isolates. Microcystin production was detected by ELISA test in 26% of the isolates. Further a protease inhibitor substance was detected by LC-MS/MS in the M. aeruginosa NPLJ-4 extract and the presence of aeruginosin and cyanopeptolin was confirmed by PCR amplification using specific primers, and sequenced. This screening study showed that Brazilian cyanobacterial isolates are a rich source of natural products with potential for pharmacological and biotechnological applications.