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Cyanobacterial mats and stromatolites

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Abstract

Cyanobacteria are often the key organisms comprising microbial mats. They form dense micrometer-scale communities in which the full plethora of microbial metabolism can be present. Such mats are therefore excellent model systems and because of their analogy with Precambrian stromatolites they are also attractive subjects for evolutionary studies. Growth and metabolism of the oxygenic phototrophic cyanobacteria enrich the sediment with organic matter. However, in mature mats net growth of cyanobacteria appears to be of less importance. Most of the organic matter produced from photosynthetic CO2 fixation is liberated in the sediment by one of the following: fermentation, photorespiration, pouring out of solutes or secretion of mucus although grazing may also be important. This organic matter is degraded by chemotrophic microorganisms, among which sulphate-reducing bacteria are particularly prominent. The combined activities of the cyanobacteria and sulphate-reducing bacteria result in steep and fluctuating gradients of sulphide and oxygen. Cyanobacteria therefore have to cope with high concentrations of sulphide, oxygen supersaturated - and anoxic conditions. These physicochemical gradients force different functional groups of microorganisms to particular vertical stratified positions in the mat. This, and the fact that accretion of sediment fluctuates, gives rise to one of the most conspicuous properties of microbial mats namely their laminated structure. Modern microbial mats have this laminated structure in common with Precambrian stromatolites. Most modern mats do not lithify but this may also have been the case for Archean microbial mats. Only a few examples of modern calcifying stromatolithic microbial mats are known. A hypothesis has been developed which conceives a role for extracellular polysaccharides in calcification. Extracellular polysaccharides in cyanobacterial mats are often produced as the result of unbalanced growth caused by nitrogen deficiency. The mat organisms are embedded in the extensive polysaccharide matrix that inhibits calcification. All cyanobacterial mats can fix atmospheric dinitrogen, which covers part of their nitrogen demand, but the fluctuating physicochemical gradients limits the efficiency of this process. © 2012 Springer Science+Business Media B.V. All rights reserved.

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... Nutrient reductions are a key component to BCM mitigation strategies, and future research into how decreasing specific nutrient inputs into ecosystems with BCMs is key for potentially decreasing their spread and has been proposed in many studies (Brocke et al., 2015;Paerl et al., 1993;Pinckney et al., 2011;Wood et al., 2020). However, management strategies to decrease BCMs focused on bottom-up forces have not always been as successful as anticipated (Florida Keys National Marine Sanctuary, personal communication to S. McCoy, July 31, 2020), potentially due to mat nutrient recycling that sustains redox gradients even without external nutrient inputs, and is still not well understood (Bolhuis et al., 2014;Cissell, 2022;Stal, 2012;Stal et al., 2019). Therefore, we advocate for increased research into potential top-down management alternatives and further understanding of how resource partitioning and nutrient recycling sustain BCM proliferation. ...
... Benthic cyanobacterial mats cycle a variety of nutrients depending on their composition and environmental conditions. These include the cycling of carbon, nitrogen, sulfur, phosphorus, calcium, iron, other trace metals, and toxins, which all affect mat resource partitioning (e.g., Bolhuis et al., 2014;Stal, 2012;Stal et al., 2019). This geochemical cycling within mats is inextricably linked to mat community ecology. ...
... These forms of fixed nitrogen can also be taken up directly from the environment and are crucial in systems without light, such as in the deep sea (Baker et al., 2013). Nitrification, in which microbes convert these metabolites to nitrate and nitrite, is either spatially or temporally separated in BCMs as an aerobic process (Figure 3; Stal, 2012). Many different bacteria engage in nitrification, and the differences in these nitrifiers are affected by geochemical gradients and temporal and spatial niches, with differences driven by salinity, ammonium, and temperature (Fan et al., 2015b). ...
Article
Benthic cyanobacterial mats are increasing in abundance worldwide with the potential to degrade ecosystem structure and function. Understanding mat community dynamics is thus critical for predicting mat growth and proliferation and for mitigating any associated negative effects. Carbon, nitrogen, and sulfur cycling are the predominant forms of nutrient cycling discussed within the literature, while metabolic cooperation and viral interactions are understudied. Although many forms of nutrient cycling in mats have been assessed, the links between niche dynamics, microbial interactions, and nutrient cycling are not well described. Here, we present an updated review on how nutrient cycling and microbial community interactions in mats are structured by resource partitioning via spatial and temporal heterogeneity and succession. We assess community interactions and nutrient cycling at both intramat and metacommunity scales. Additionally, we present ideas and recommendations for research in this area, highlighting top‐down control, boundary layers, and metabolic cooperation as important future directions.
... Lamination results from the interaction among microbial consortia in thin (< mm) metabolically stratified benthic mats, ambient sediments, and the surrounding physical-chemical environment. It is preserved by penecontemporaneous lithification and subsequent diagenesis (Stal 2012, Bolhuis et al. 2014, Prieto-Barajas et al. 2018. Therefore, stromatolites only exist where physical and chemical conditions allow both their establishment and sustainment. ...
... Viruses may also occur among mat dwellers (Brüssow et al. 2004, Bolhuis et al. 2014. Once established, the mat becomes a self-sustaining ecosystem immersed in extracellular polymeric substances (EPS) (Bolhuis et al. 2014, Prieto-Barajas et al. 2018) and speckled by minerals, mainly carbonates and terrigenous grains (Stal 2012). The microbial mat organizes itself following several physicochemical gradients that will sustain and be sustained by the microbiota according to their physiology (Bolhuis et al. 2014), to light incidence and balance between O 2 and H 2 S (i.e. ...
... Although found worldwide in a wide range of sedimentary environments, three different modern microbial mats, which have been studied in detail, reveal important representative aspects of composition, diversity, molecular profile, and ecology of microbial mats: hypersaline environments, intertidal flats, and hot springs (Stal andCaumette 1994, Bolhuis et al. 2014). Cyanobacteria usually comprise the dominant forms, along with purple sulfur bacteria, followed by bacteroidetes and acidobacteria (Gobet et al. 2012, Burow et al. 2013, Bolhuis et al. 2014). ...
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Abstract Stromatolites are laminated biosedimentary structures of great importance for paleobiological, paleoecological, and paleoenvironmental analyses, mainly in Precambrian rocks. Their value is related to the glimpse of past life recorded in their lamination, fabric, and, eventually, due to the preservation of organic matter, including microfossils, and because their deposition is directly influenced by environmental conditions. Although stromatolites are widely described in microscopic scale, there is a lack of standardization of their nomenclature, precluding better paleoenvironmental and paleobiological interpretations. In this study, we propose a guide for the microscopic analysis of fossil stromatolites and, possibly, thrombolites, and provide a review of specialized literature and the bibliometric context of main terms. The goal is to contribute to the improvement of their application through systematization of microscopic data, in the face of novel paleoecological and paleobiological approaches and for astrobiological prospection for microbialites in therock record of Mars.
... They are common in almost all environments but their role in desert microbial consortia is especially significant. They can perform oxygenic photosynthesis, in high light and high UV intensity as well as low light conditions (Castenholz and Garcia-Pichel, 2012;Stal, 2012). In addition, many cyanobacteria can fix atmospheric nitrogen (N 2 ). ...
... As primary producers, cyanobacteria help diversify ecosystems and provide necessary conditions for the development of more complex communities (Hagemann et al., 2015). These communities can take the form of microbial mats -multilayered associations made of archaea, bacteria, eukaryotic algae, and other eukaryotes, for example diatoms, lichens, and mosses (Stal, 2012;Prieto-Barajas et al., 2018). Microbial mats grow on the borderline of terrestrial and aquatic environments, such as sediments of shallow pools, streams, and lake shores. ...
... Microbial mats grow on the borderline of terrestrial and aquatic environments, such as sediments of shallow pools, streams, and lake shores. Cyanobacteria are components of these communities and cannot be overestimated, as apart from carbon and nitrogen fixation they produce exopolysaccharides (EPS) that are essential for the functioning of mats, binding mat layers, providing structure and stability, as well as a medium for other bacteria (Stal, 2012;Bolhuis et al., 2014). Microbial mats are common in arid and semi-arid environments in which lakes with various salinity and turbidity levels and surrounding wetlands occur and are very important for the functioning of these fragile ecosystems (Vincent et al., 1993;Stal, 2012). ...
Article
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Introduction Microbial mats are complex communities of benthic microorganisms that occur at the soil-water interphase in lakes’ shores, streams, and ponds. In the cold, mountainous desert of Eastern Pamir (Tajikistan), where scarce water bodies are influenced by extreme environmental conditions, photosynthetic cyanobacteria form diverse mats. The mats are characterized by different morphology and thickness. Their habitats exhibit a wide range of conditions; from oligosaline to hypersaline, oligotrophic to hypertrophic, and from cold ponds to hot springs. The aim of the present study was to reveal the taxonomic composition and structure of these mats and to examine which environmental factors influence them. Methods Fifty-one mats were collected from small water bodies around Bulunkul, Karakul, and Rangkul Lakes in 2015 and 2017. The physical and chemical properties of the water were measured in situ, while the concentration of nutrients was analyzed ex-situ. To reveal the taxonomic composition of the mats, the hypervariable V3-V4 region of the 16S rRNA gene was examined using NGS technology. Results The results of bioinformatic analyses were compared with microscopic observations. They showed that Cyanobacteria was the dominant phylum, constituting on average 35% of bacterial ASVs, followed by Proteobacteria (28%), Bacteroidota (11%), and Firmicutes (9%). Synechococcales, Oscillatoriales, and Nostocales orders prevailed in Oxyphotobacteria, with a low contribution of Chroococcales, Gloeobacterales, and Chroococcidiopsidales. Occasionally the non-photosynthetic Vampirivibrionia (Melainabacteria) and Sericytochromatia from sister clades to Oxyphotobacteria were noted in the samples. Moreover, there was a high percentage of unidentified cyanobacterial sequences, as well as the recently described Hillbrichtia pamiria gen. et sp. nov., present in one of the samples. Salinity, followed by Na and K concentrations, correlated positively with the composition and structure of Oxyphotobacteria on different taxonomic levels and the abundance of all bacterial ASVs. Discussion The study suggests that the investigated communities possibly host more novel and endemic species. Among the environmental factors, salinity influenced the Oxyphotobacteria communities the most. Overall, the microenvironmental factors, i.e. the conditions in each of the reservoirs seemed to have a larger impact on the diversity of microbial mats in Pamir than the “subregional” factors, related to altitude, mean annual air temperature and distance between these subregions.
... Microbial mats are communities of benthic microorganisms with a laminated structure that develop on solid substrates at the interface with water. They are constituted by phototrophic (cyanobacteria, benthic diatoms, and bacteria) and heterotrophic microorganisms (Actinobacteria, Proteobacteria, and Bacteroidetes), embedded in a dense mucilaginous matrix of extracellular polymeric substances (EPS) of their own production (Bender et al., 1994;Prieto-Barajas et al., 2018;Stal, 2012). EPS are mainly composed of carbohydrates and other substances such as proteins, lipids, and lipopolysaccharides (Fernández et al., 2016;Stal, 2012). ...
... They are constituted by phototrophic (cyanobacteria, benthic diatoms, and bacteria) and heterotrophic microorganisms (Actinobacteria, Proteobacteria, and Bacteroidetes), embedded in a dense mucilaginous matrix of extracellular polymeric substances (EPS) of their own production (Bender et al., 1994;Prieto-Barajas et al., 2018;Stal, 2012). EPS are mainly composed of carbohydrates and other substances such as proteins, lipids, and lipopolysaccharides (Fernández et al., 2016;Stal, 2012). ...
... Furthermore, an increase in the concentration of phaeopigments may indicate that chlorophyll a is being damaged since they are products of its degradation (Sanmartín et al., 2011); however, in our experiment, there were no changes in their concentration. Perhaps it could be due to the high concentration of oxidized iron and sulphide naturally present in the microbial mats (Stal, 2012), which can be involved in the reduction of Cr into a less toxic form for cells (Cr (III)) (Gheju et al., 2016;Gorny et al., 2016). Among the microorganisms of microbial mats, iron-reducing bacteria are responsible for the immobilization of metals as Cr (Drewniak et al., 2016). ...
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Microbial mats have a special role in the removal of metals in marine environment. This study aimed to experimentally determine the efficiency of Cr removal from seawater by microbial mats. The effect of Cr on the microphytobenthic community and the influence of an aerated condition on the removal of metal and microorganisms were also considered. Hence, microbial mat samples were subdivided in 4 groups: submerged in Cr (chromium 2 mg/L without aeration), Cr + O2 (chromium 2 mg/L with aeration), SW + O2 (filtered seawater with aeration), and a control: SW (filtered seawater with neither chromium nor aeration). Water and microbial mat subsamples were used to determine Cr concentrations, organic matter content, granulometry, physicochemical parameters, chlorophyll a, phaeopigments, and quantitative analysis of the microphytobenthic community. Cr removal efficiency from seawater was 95% for the Cr treatment and 99% for the Cr + O2 treatment. The abundance of cyanobacteria tended to decrease between the initial and final days of the assay, whereas the opposite trend was observed for diatoms. Two aspects are worth noting in the paper: microbial mats efficiently removed Cr from seawater at a concentration of 2 mg Cr/L and the removal of Cr by microbial mats was more efficient with water aeration.
... In addition to light, physical and chemical conditions influence the abundance and activities of microbes in mat systems (Dillon et al., 2020a;Stal, 2012). Sulfide concentration and temperature are key factors in determining the relative abundance of primary producers, which can include cyanobacteria, diatoms, and anoxygenic phototrophs (Camacho et al., 2005;Cohen et al., 1975). ...
... The copyright holder for this preprint this version posted January 30, 2023. ; https://doi.org/10.1101/2023.01.30.526236 doi: bioRxiv preprint rRNA gene time series showed correlated relative abundances of Beggiatoa and Desulfonema, the most abundant SRB we observed, likely reflecting a metabolic interaction in which sulfide produced through sulfate reduction by Desulfonema is used by Beggiatoa as an electron donor, as observed in other cyanobacterial mats (Klatt et al., 2020;Stal, 2012). The higher overall abundance of deltaproteobacterial SRB in summer and autumn (Table S6) is consistent with higher sulfide availability in the mat and sediment later in the year (Kinsman-Costello et al., 2017). ...
... In addition to sulfate reduction, Desulfocapsa may grow through inorganic sulfur disproportionation (Finster et al., 2013;Janssen et al., 1996), and at up to 3.0% relative abundance may play important roles in cycling elemental sulfur, thiosulfate, and sulfite in MIS mats. Sulfur reduction and disproportionation strongly influence photosynthesis and the distribution of cyanobacteria and SOBs in other mat systems (Dick et al., 2018;Klatt et al., 2020;Stal, 2012). ...
Preprint
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Seasonal changes in light and physicochemical conditions have strong impacts on cyanobacteria, but how they affect community structure, metabolism, and biogeochemistry of cyanobacterial mats remains unclear. Light may be particularly influential for cyanobacterial mats exposed to sulfide by altering the balance of oxygenic photosynthesis and sulfide-driven anoxygenic photosynthesis. We studied temporal shifts in irradiance, water chemistry, and community structure and function of microbial mats in Middle Island Sinkhole (MIS), where anoxic and sulfate-rich groundwater provides habitat for cyanobacteria that conduct both oxygenic and anoxygenic photosynthesis. Seasonal changes in light and groundwater chemistry were accompanied by shifts in bacterial community composition, with a succession of dominant cyanobacteria from Phormidium to Planktothrix, and an increase in diatoms, sulfur-oxidizing bacteria, and sulfate-reducing bacteria from summer to autumn. Differential abundance of cyanobacterial light harvesting proteins likely reflects a physiological response of cyanobacteria to light level. Beggiatoa sulfur oxidation proteins were more abundant in autumn. Correlated abundances of taxa through time suggest interactions between sulfur oxidizers and sulfate reducers, sulfate reducers and heterotrophs, and cyanobacteria and heterotrophs. These results support the conclusion that seasonal change, including light availability, has a strong influence on community composition and biogeochemical cycling of sulfur and O 2 in cyanobacterial mats. Originality-Significance Statement Cyanobacterial mats are found in terrestrial and aquatic environments on modern Earth and their fossil remains are present throughout the geologic record. They are biogeochemical oases that underpin diverse metabolic interactions, transform key nutrients and fix carbon, and can thrive in extreme environments. Mat-forming cyanobacteria can be metabolically versatile and conduct both oxygenic and anoxygenic photosynthesis using sulfide (OP and AP), thereby participating in both oxygen and sulfur cycling. The effect of seasonality on ecological factors constraining photosynthetic production and geochemical cycling in extreme cyanobacterial mats is not well known. In this study, we surveyed the mat community composition via bacterial 16S rRNA genes, microbial activity via metaproteomics, and water physico- and geochemistry over multiple seasons and years of the cyanobacterial mat in Middle Island Sinkhole, an O 2 -poor benthic sinkhole in Lake Huron, Michigan. We found that higher availability of sulfate-rich groundwater, together with higher light intensity, coincided with dominance of the metabolically flexible cyanobacterium Phormidium during the summer. Diverse sulfur cycling bacteria were more successful in other seasons when the mat experienced lower light and sulfate availability. These results provide insights into how seasonal environmental dynamics can shape the community structure and metabolisms of microbial mats, ultimately controlling biogeochemical cycling in these ecological hotspots.
... For starters, they are considered to be formed by the action or influence of microbes, with extracellular polymeric substances (EPSs) forming multiple biofilms within a microbial mat (Gerdes 2010;Mei 2011a;Flemming et al. 2016). Second, cyanobacteria are thought to be one of the most important builders of carbonate microbialites (Stal 2012). ...
... The microstromatolites around the possible lithified burrow (Fig. 6A), sponge mummy (Fig. 5A), and Renalcids (fossilized biofilm clusters) (Fig. 5B), clearly demonstrate the sophisticated calcification of EPSs to form multiple microbial biofilms in relatively thick cyanobacterial microbial mats (Gerdes 2010;Reitner 2011aReitner , 2011bArp et al. 2012;Stal 2012;Flemming et al. 2016). A clear sponge mummy (Fig. 5A) coated by microstromatolites reflects a harmonious intergrowth between microbe and metazoan. ...
Article
Based on their mesostructures, carbonate microbialites are divided into four major groups: laminated stromatolite, clotted thrombolites, structureless leiolites, and dendritic dendrolite. Among the various types of microbialites, leiolites, also known as “cryptomicrobial deposits,” are uncommon in the stratigraphic records. This is exacerbated by leiolites relatively structureless and aphanitic structure, making their identification and characterization more challenging. Previous studies have revealed that leiolites have contrasting fabrics at different scale, heterogeneous microscopic fabrics and structureless mesoscopic to macroscopic fabrics. While it is widely assumed that cyanobacteria play a significant role in the formation of carbonate microbialites in marine environments, the origin and controlling mechanisms of variations in leiolites microstructures and macrostructures remain enigmatic. In the central part of the North China Platform, two excellent exposures of massive, structureless Cambrian bioherms (Furongian) dominated by leiolites were observed (Qijayu section). The Qijayu-section leiolites offer a unique opportunity to investigate the role of cyanobacterial input in governing the formation and textural heterogeneities of such microbialites. In addition, the significance of the Furongian leiolites stems from their association with a period of global development of microbial-dominated carbonate platforms. Our findings suggest that these Furongian leiolites developed during the forced-regressive systems tract. At the microscopic level, these Furongian leiolites exhibit a high degree of heterogeneity which is controlled by the presence of various types of cyanobacteria (Hedstroemia, Subtifioria, Girvanella), sponge mummy, and benthic ooids. The Hedstroemia, Subtifioria and Girvanella excreted extracellular polymeric substances that form multiple biofilms in cyanobacterial microbial mats where Furongian leiolites grew. The role of cyanobacteria in the microscale heterogeneity of Cambrian leiolites is evident, and this provides new insights into the development of microbial-dominated carbonate platforms in similar settings elsewhere. As a result, this study provides not only a reference example for global correlation but also some solid clues for further understanding the growth style of leiolites in the geologic record.
... Comme nous l'avons souligné plus haut, il semble que la biocalcification bactérienne n'ait pas de fonction aussi spécifique que celle rencontrée chez les macroorganismes (ossature, carapace, oeufs, …). Le CaCO 3 formé pourrait conférer des avantages sélectifs aux cyanobactéries en fournissant un bouclier protecteur contre l'exposition à une lumière intense, en offrant un moyen d'améliorer l'absorption des nutriments ou en jouant le rôle de tampon contre l'augmentation du pH dans un environnement alcalin [36][37][38]. En cas de surconcentration intracellulaire en Ca 2+ , la précipitation de CaCO 3 diminuerait la concentration de l'environnement de la cellule en Ca 2+ et permettrait également à la bactérie de l'excréter afin d'éviter d'atteindre des niveaux toxiques de calcium intracellulaire [37]. La précipitation bactérienne de CaCO 3 est biologiquement induite et fait intervenir une ou plusieurs activités métaboliques [22,39]. ...
... Le CaCO 3 formé pourrait conférer des avantages sélectifs aux cyanobactéries en fournissant un bouclier protecteur contre l'exposition à une lumière intense, en offrant un moyen d'améliorer l'absorption des nutriments ou en jouant le rôle de tampon contre l'augmentation du pH dans un environnement alcalin [36][37][38]. En cas de surconcentration intracellulaire en Ca 2+ , la précipitation de CaCO 3 diminuerait la concentration de l'environnement de la cellule en Ca 2+ et permettrait également à la bactérie de l'excréter afin d'éviter d'atteindre des niveaux toxiques de calcium intracellulaire [37]. La précipitation bactérienne de CaCO 3 est biologiquement induite et fait intervenir une ou plusieurs activités métaboliques [22,39]. ...
Article
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La précipitation du carbonate de calcium (CaCO 3 ) biologiquement induite en milieu marin joue un rôle important dans le cycle biogéochimique du carbone. Cette biocalcification est gouvernée par quatre facteurs clés : le taux de carbone inorganique dissous dont dépend le taux de carbonates (CO 3 ²⁻ ) dans le système, le taux d’ions calciques (Ca ²⁺ ), le pH et la disponibilité des sites de nucléation c’est-à-dire des zones de cristallisation primaire de la phase solide du minéral. Les bactéries impliquées dans la biocalcification marine vont alors agir sur un ou plusieurs de ces facteurs. Ce processus naturel, qui se produit dans divers contextes géologiques, peut être imité afin de développer un certain nombre de technologies permettant la séquestration des métaux lourds, la protection des métaux contre la corrosion, la restauration et le renforcement de matériaux préexistants et la consolidation de matériaux granulaires. Cette étude passe en revue les différentes activités métaboliques microbiennes menant à la précipitation du CaCO 3 ainsi que leurs applications potentielles en milieu marin.
... Cyanobacterial mats developed early in life history, representing among the oldest sedimentological fossils on Earth [4,5], and persist until today. They occur in a variety of habitats in marine and freshwater ecosystems [6], including extreme environments such as hypersaline lakes [7] and hot springs [8]. Unique geochemical changes in the geologic record have been linked to the intricate advent of cyanobacteria, like the "Great Oxidation Event" in the Paleoproterozoic [9] and even today, they are still important for ecosystem productivity. ...
... Sodalinema stali, formerly known as Microcoleus/Coleofascicculus chthonoplastes [34], globally dominates cyanobacterial mats in marine, hypersaline, as well as terrestrial habitats [6] and can therefore be considered a model organism for cyanobacterial mats. The marine, non-axenic Sodalinema stali strain 31.92 ...
Article
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Cyanobacterial mats inhabit a variety of aquatic habitats, including the most extreme environments on Earth. They can thrive in a wide range of phosphorus (P) levels and are thus important players for ecosystem primary production and P cycling at the sediment-water interface. Polyphosphate (polyP), the major microbial P storage molecule, is assigned a critical role in compensating for phosphate fluctuations in planktonic cyanobacteria, but little is known about potentially analogous mechanisms of mat-forming cyanobacteria. To investigate acclimation strategies of cyanobacterial mats to fluctuating phosphate concentrations, laboratory batch experiments were conducted, in which the cosmopolitan mat-forming, marine cyanobacterium Sodalinema stali was exposed to low dissolved P concentrations, followed by a P pulse. Our results show that the cyanobacteria dynamically adjusted cellular P content to ambient phosphate concentrations and that they had accumulated polyP during periods of high phosphate availability, which was subsequently recycled to sustain growth during phosphate scarcity. However, following the depletion of dispensable cellular P sources, including polyP, we observed a reallocation of P contained in DNA into polyP, accompanied by increasing alkaline phosphatase activity. This suggests a change of the metabolic focus from growth towards maintenance and the attempt to acquire organic P, which would be naturally contained in the sediment. P overplus uptake following a simulated P pulse further suggests that Sodalinema-dominated mats exhibit elaborated mechanisms to cope with severe P fluctuations to overcome unfavourable environmental conditions, and potentially modulate critical P fluxes in the aquatic cycle.
... Odors produced by decaying M. wollei growths on the shoreline of waterbodies are often immediately apparent. These odors are partially from communities of sulfate-reducing bacteria that often co-occur with cyanobacterial growths (Stal 2012). Additionally, M. wollei can produce the taste and odor compound geosmin, which is known for its earthy or musty odor and commonly causes customers to voice concerns about drinking water resources (Kutovaya and Watson 2014). ...
Technical Report
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Microseira wollei (formerly Lyngbya wollei) has grown to noxious densities within Lake St. Clair, located between Lake Erie and Lake Huron. De-spite the limited data on this cyanobacterium within Lake St. Clair, data exists for M. wollei within the Great Lakes region and in the southeastern United States, where water resource managers have been managing growths for decades. These data provide pertinent insights into the environmental distribution, environmental drivers, risks, and management of M. wollei, which is mainly distributed within eastern states and provinces in North America, from Canada to Florida. Environmental drivers may be site-specific and specific to the M. wollei population; therefore, the environmental drivers identified in this literature review are a starting point to inform further investigations. M. wollei within Lake St. Clair may pose risks to humans. Risks may originate from toxins, disinfection by-products, and, potentially, fecal indicator bacteria. M. wollei has the potential to produce a range of toxins; however, the most prevalent toxins are saxitoxins, a group of neurotoxins. This literature review will help the US Army Corps of Engineers Detroit District; Macomb County, Michigan; and other interested parties understand potential triggers for growth, communicate risks, and help develop an adaptive management framework.
... The transfer of microcystins from freshwater discharge to coastal environments has also been reported [13][14][15]. In most saline systems, however, photosynthetic benthic mats can be observed from sheltered coasts, estuarine habitats, salterns or hypersaline lagoons, and are usually composed of cyanobacteria, among other organisms [16,17]. Climate change will increase lagoon shallowness, which will favor not only the development of benthic communities, but also eutrophication levels to promote cyanobacterial growth [18]. ...
Article
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Cyanobacterial biodiversity and potential toxicity in coastal lagoons have barely been studied despite these transitional water systems being very important in conservation and for the preservation of economic resources. Most of these transitional systems have been affected by eutrophication, and climate change will severely affect them by promoting cyanobacteria growth, especially in Mediterranean areas. This study aims to characterize the diversity of epipelic and epiphytic cyanobacteria species in a Mediterranean coastal lagoon and their potential for toxins production (microcystins and saxitoxins). Strains were isolated and genetically identified. Toxins were extracted and quantified by LC/MS-MS. All the taxa belong to the former Oscillatoriales. The presence of Nodosilinea and Toxifilum is reported for the first time for Spanish waters, but Pseudanabaena, Phormidium, Geitlerinema and Synechococcus also formed part of benthic mats. All the strains contained Microcystin-YR (MC-YR), but saxitoxin (STX) was present only in the extracts of Nodosilinea and Pseudanabena. MC-LY, MC-LW and [D-Asp3] MC-LR were detected in the extracts of Synechococcus and MC-LF in Toxifilum, but at concentrations that did not permit quantification. Toxins production by epipelic and epiphytic strains in coastal lagoons may represent a hazard, but also an opportunity to obtain potentially interesting compounds that should be further studied.
... They produce numerous metabolites that are beneficial for them and for the whole community. Among them are scytonemin, a photoprotective pigment that screens the excess of UV radiation (Stal, 2012) or exopolysaccharides (EPS) that bind mat layers, providing stability, as well as a medium for other bacteria and eukaryotic algae to live in (Bolhuis et al., 2014). Benthic Cyanobacteria also produce cyanotoxins but in contrast to planktic environments in which microcystins are the most common toxins, they most commonly produce anatoxins Bauer et al., 2023. ...
... In the case of aquatic c y anobacteria, despite the increasing amount of information regarding their ecology, the biofilm con-cept is gener all y associated with benthic species, whic h form mats in se v er al aquatic ecosystems (Stal 2012 ). Among the planktonic groups we will focus on Microcystis spp., a complex of cyanobacteria from the Chroococcales order that live in freshwater and br ac kish waters . ...
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Species of the Microcystis genus are the most common bloom-forming toxic cyanobacteria worldwide. They belong to a clade of unicellular cyanobacteria whose ability to reach high biomasses during blooms is linked to the formation of colonies. Colonial lifestyle provides several advantages under stressing conditions of light intensity, ultraviolet light, toxic substances and grazing. The progression from a single-celled organism to multicellularity in Microcystis has usually been interpreted as individual phenotypic responses of the cyanobacterial cells to the environment. Here, we synthesize current knowledge about Microcystis colonial lifestyle and its role in the organism ecology. We then briefly review the available information on Microcystis microbiome and propose that changes leading from single cells to colonies are the consequence of specific and tightly regulated signals between the cyanobacterium and its microbiome through a biofilm-like mechanism. The resulting colony is a multi-specific community of interdependent microorganisms.
... These microalgae are one of the most abundant components of the epiphytic communities present on the thalli of macroalgae and the primary colonizers of marine surfaces, because they adhere to substrate through secretion of mucilage composed of extracellular polymeric substances (EPSs) (Cotiyane-Pondo and Bornman, 2021; Roubeix and Laviale, 2021). >90 % of the composition consists of polysaccharides (Stal, 2012) and, therefore, should have been degraded during digestion processes. However, they remained at- Forero-López et al. ...
Article
Marine microdebris (MDs, <5 mm) and mesodebris (MesDs, 5–25 mm), consist of various components, including microplastics (MPs), antifouling or anticorrosive paint particles (APPs), and metallic particles (Mmps), among others. The accumulation of these anthropogenic particles in macroalgae could have significant implications within coastal ecosystems because of the role of macroalgae as primary producers and their subsequent transfer within the trophic chain. Therefore, the objectives of this study were to determine the abundance of MDs and MesDs pollution in different species of macroalgae (P. morrowii, C. rubrum, Ulva spp., and B. minima) and in surface waters from the Southwest Atlantic coast of Argentina to evaluate the ecological damage. MDs and MesDs were chemically characterized using μ-FTIR and SEM/EDX to identify, and assess their environmental impact based on their composition and degree of pollution by MPs, calculating the Polymer Hazard Index (PHI). The prevalence of MDs was higher in foliose species, followed by filamentous and tubular ones, ranging from 0 to 1.22 items/g w.w. for MPs and 0 to 0.85 items/g w.w. for APPs. It was found that macroalgae accumulate a higher proportion of high-density polymers like PAN and PES, as well as APPs based on alkyd, PMMA, and PE resins, whereas a predominance of CE was observed in surrounding waters. Potentially toxic elements, such as Cr, Cu, and Ti, were detected in APPs and MPs, along with the presence of epiplastic communities on the surface of APPs. According to PHI, the presence of high-hazard score polymers, such as PAN and PA, increased the overall risk of MP pollution in macroalgae compared to surrounding waters. This study provided a baseline for MDs and MesDs abundance in macroalgae as well as understanding of the environmental impact of this debris and their bioaccumulation in the primary link of the coastal trophic chain.
... The colonization of siliciclastic sediments in hypersaline, evaporitic environments is dominated by photoautotrophic cyanobacteria and other types of bacteria (with aerobic and anaerobic tolerances; Farias et al., 2017;Pan, 2021). Several studies have determined that the development of microbial mats in siliciclastic environments depends mainly on light conditions, oxygen availability and redox potential, temperature, pH and salinity (Stal, 2010;Stal, 2012;Cuadrado et al., 2013;Pan et al., 2013aPan et al., , 2013bCardoso et al., 2019). Even if some references indicate that siliciclastic environments present lower dissolved inorganic nitrogen in comparison to carbonatic ones (Lapointe et al., 1992), nutrients seem not to be strong determinants for microbial mat development. ...
... As a by-product, they produce polymeric substances (Extracellular Polymeric Substances (EPS)), which bind sediment and minerals, providing physical protection and resistance to desiccation [16,17]. The diversity of the microbial mats is influenced by environmental stressors, such as salinity, seasonal desiccation, and high solar irradiance [18]. Thomas et al. [19] reported that salt-cyanobacteriota crusts north of the Ntwetwe Pan play a significant role in soil CO 2 efflux. ...
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The Makgadikgadi Salt Pans are the remnants of a mega paleo-lake system in the central Kalahari, Botswana. Today, the Makgadikgadi Basin is an arid to semi-arid area receiving water of meteoric origin during the short, wet season. Large microbial mats, which support primary production, are formed due to desiccation during the dry season. This study aimed to characterise the microbial diversity of the microbial mats and the underlying sediment. The focus was the Ntwetwe Pan, located west of the Makgadikgadi Basin. Metagenomic analyses demonstrated that the mats consisted of a high relative abundance of Cyanobacteriota (synonym Cyanobacteria) (20.50–41.47%), Pseudomonadota (synonym Proteobacteria) (15.71 to 32.18%), and Actinomycetota (synonym Actinobacteria) (8.53–32.56%). In the underlying sediments, Pseudomonadota, Actinomycetota, and Euryarchaeota represented over 70% of the community. Localised fluctuations in water content and pH did not significantly affect the microbial diversity of the sediment or the mats.
... The correlation coefficients and corresponding significance test p-values between PC concentrations and each meteorological factor were calculated (Fig. 12). TEMP was significantly and positively correlated with the mean PC concentration, and the highest correlation was found between the monthly TEMP and the monthly mean PC concentration (r = 0.43, p < 0.01), indicating that the growth and reproduction of cyanobacteria were closely related to the local temperature (Stal, 2000;Yang et al., 2020). Consistent conclusions were obtained by Chen et al. (2021) on the relationship between CBs area and temperature, which indicated that cyanobacterial blooms and expansion were closely related to local temperature . ...
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With the intensification of global warming, eutrophication in lakes at high latitudes of China has become increasingly severe, with the harm of blue-green algae blooms also on the rise. Therefore, it is urgent to conduct research on water quality of lakes in high latitudes. In this study, taking Lake Hulun as an example, a phyco-cyanin (PC) inversion model applicable to Sentinel-3 OLCI data was constructed and applied to the Sentinel-3 dataset from 2016 to 2022 to analyze the spatiotemporal variation characteristics of PC concentration. The driving mechanism of climate factors on PC concentration was explored, and the correlation between PC concentration and Cyanobacterial blooms (CBs) outbreak was analyzed. Results showed that the PC concentration inversion model based on XGBoost (XGB) has the highest accuracy (R 2 = 0.91, RMSE = 76.76 μg/L, and rRMSE = 0.54). Monthly average PC concentration is higher in July (44.52±64.85 μg/L) and lower in October (5.04 ±1.81 μg/L). From 2016 to 2022, the annual average concentration of PC in Hulun Lake in 2022 (38.82±63.34 μg/L) is higher than that in other years, while the annual average PC concentration in 2020 (4.60±1.76 μg/L) is lower. Temperature is the main impacting factor on PC concentration. The variation of PC concentration in Lake Hulun has high spatiotemporal consistency with the proportion of CBs area. In summary, using Sentinel-3 OLCI imagery for long-term remote sensing monitoring of spatiotemporal pattern changes of PC in Lake Hulun, and analyzing its changing characteristics and patterns, is of great significance for early warning of CBs.
... Calothrix-morphotypes were observed on all S. globiceps cores, as illustrated in the supplementary photographs ( Supplementary Fig. S5), however, these were not detected in the 16S rRNA barcoding. This is consistent with earlier findings of difficulties with DNA extraction and subsequent amplification for this filamentous cyanobacterial taxon (Nicholson and Clements 2023), possibly due to its thick extracellular polysaccharide sheath (Tillett and Neilan 2000;Garcia-Pichel et al. 2001;Sihvonen et al. 2007;Momper et al. 2015;Urrejola et al. 2019) or its unusual habit of precipitating calcium carbonate (Stal 2012;Pentecost and Whitton 2012;Komárek and Johansen 2015). The dominance of the Calothrix-morphotypes across both the outer-shelf and mid-shelf bite cores suggests that these biota are the most likely cyanobacteria targeted by the study parrotfish species. ...
... Calothrix-morphotypes were observed on all S. globiceps cores, as illustrated in the supplementary photographs ( Supplementary Fig. S5), however, these were not detected in the 16S rRNA barcoding. This is consistent with earlier findings of difficulties with DNA extraction and subsequent amplification for this filamentous cyanobacterial taxon (Nicholson and Clements 2023), possibly due to its thick extracellular polysaccharide sheath (Tillett and Neilan 2000;Garcia-Pichel et al. 2001;Sihvonen et al. 2007;Momper et al. 2015;Urrejola et al. 2019) or its unusual habit of precipitating calcium carbonate (Stal 2012;Pentecost and Whitton 2012;Komárek and Johansen 2015). The dominance of the Calothrix-morphotypes across both the outer-shelf and mid-shelf bite cores suggests that these biota are the most likely cyanobacteria targeted by the study parrotfish species. ...
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Diet in fish is influenced by multiple factors including nutritional requirements, trophic morphology and spatial and temporal variation in resource availability. We examined spatial variation in trophic resources on substrata grazed by scarinine parrotfishes by combining quantitative microhistology with 16S and 18S small subunit rRNA barcoding of feeding substrata in six parrotfish species on outer-shelf reefs of the Great Barrier Reef, Australia. We then compared four of these taxa with conspecific data from mid-shelf reefs differing in incident wave energy, parrotfish assemblage structure and benthic cover of hard corals, crustose coralline algae (CCA) and macroalgae. The dominant biota on outer-shelf feeding substrata in terms of both surface coverage and frequency of occurrence were filamentous cyanobacteria. The density of filamentous cyanobacteria on outer-shelf feeding substrata as measured by microscope did not differ either among the six parrotfish species or within-species cross-shelf. Endolithic and epilithic filamentous cyanobacteria from the order Nostocales were the most frequently observed filamentous cyanobacteria, suggesting that these represent a key feeding target for these parrotfishes. In addition to filamentous Nostocales cyanobacteria, taxa that were consistently present on both mid-shelf and outer-shelf feeding substrata were the euendolithic micro-chlorophytes Ostreobium and Phaeophila, diatoms, fungi, CCA, Peyssonnelia, dinoflagellates of the family Symbiodiniaceae, the sponge taxa Clionaida and Poecilosclerida and the filamentous algae Sphacelaria and Polysiphonia. Our results reveal key nutritional drivers underlying feeding by parrotfish on carbonate reefs and provide further support for the hypothesis that microscopic photoautotrophs are a major dietary target for grazing parrotfishes.
... Stromatolites are lithified microbial build-ups that are the result of the interaction between various microbial metabolic processes and their sedimentary environment (Dupraz & Visscher, 2005;Allwood et al. 2007;Sallstedt et al. 2018). Stromatolites in the fossil record have commonly been interpreted as products of cyanobacteria due to their remarkable similarity to modern cyanobacterial mats (Stal, 2012). A cyanobacterial origin has also been suggested for phosphatic stromatolites, occurring in shallow marine settings due to the presence of preserved oxygen gas bubbles (Bosak et al. 2009;Sallstedt et al. 2018), laminated fabrics related to trapping and binding mechanisms, stable isotope analyses, mineralogy, as well as facies analyses of the host sediments (Rao et al. 2000(Rao et al. , 2002Lundberg & McFarlane, 2011;Drummond et al. 2015;Caird et al. 2017;Sallstedt et al. 2018). ...
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The Drewer quarry located in the Rhenish Massif is a well-studied outcrop that comprises Upper Devonian (Famennian) to Lower Carboniferous (Viséan) strata. Within the Drewer deposits two black shale intervals have been described that are linked to two global oceanic anoxic events, the Hangenberg Event and the Lower Alum Shale Event. The black shales associated with the Middle Tournaisian Lower Alum Shale Event contain abundant phosphatic concretions, which were investigated using thin section petrography, powder X-ray diffraction, Fourier-transform infrared spectrometry and scanning electron microscopy. The concretions formed during several growth phases under anoxic and at least episodically sulphidic conditions within the sediment and served as a substrate for subsurface microbial mats that formed phosphatic microstromatolites. The microstromatolites occur either as partially branched columns of up to 600 µm in length attached to the phosphatic concretions or as smaller, bulbous aggregates surrounding the concretions. Element mapping identified the presence of pyrite and other metal sulphides within the phosphatic microstromatolites. The carbon and oxygen stable isotopic composition of phosphate-associated carbonate within the phosphatic microstromatolites suggests that the mat-forming microorganisms were probably anaerobic, chemotrophic microbial communities dwelling in the anoxic environment during the Lower Alum Shale Event. Such interpretation agrees with the deeper-water depositional setting of the Lower Alum Black Shale and its high content of organic matter, suggesting that chemotrophic microbial mats are potent agents of phosphogenesis in general, and of the formation of phosphatic stromatolites in particular.
... Microbial mats constituted by photosynthetic organisms dominated mainly by cyanobacterial species are commonly colonize shallow and intertidal marine to supratidal sediments (Noffke, 2010;Pan et al., 2019;Cuadrado, 2020). The cyanobacteria produce extracellular polymeric substances (EPS) that grow originally on the water-sediment interface as thin biofilms or a thick laminated layer forming a cohesive and leathery carpet that trap, bind and stabilize sediments (Gerdes et al., 2000;Stolz, 2000;Noffke, 2010;Stal, 2012;Pan et al., 2019). The EPS has a high water retention capacity that protects the mats from sever desiccation (Or et al., 2007;Decho, 2011). ...
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his study documents the occurrence of several MISS such as laminated microbial mats, biostabilized ripples, gas domes, mat folds, erosional pockets and remnants, microbial cracks, and gypsified mat chips in Salman hypersaline lagoon, north Jeddah city, Saudi Arabia. This study indicates that both microbial and physical processes are reponsible for sediments biostablization and formation of spits
... This group was long thought to be restricted to areas exposed or occasionally exposed to sunlight (Philippot et al. 2010). Today it is known that Cyanobacteria are very versatile microorganisms (Whitton and Potts 2012), and with the ability to generate energy independent of sunlight (Stal 2012). Several works have already reported the presence of cyanobacteria in deep subsurface samples (Thiel et al. 1990;Tang et al. 2014;Lindh et al. 2017), especially as discussed in detail by Hubalek et al. (2016). ...
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Microbial communities play a key role in the ocean, acting as primary producers, nutrient recyclers, and energy providers. The São Paulo Plateau is a region located on the southeastern coast of Brazil within economic importance, due to its oil and gas reservoirs. With this focus, this study examined the diversity and composition of microbial communities in marine sediments located at three oceanographic stations in the southern region of São Paulo Plateau using the HOV Shinkai 6500 in 2013. The 16S rRNA gene was sequenced using the universal primers (515F and 926R) by the Illumina Miseq platform. The taxonomic compositions of samples recovered from SP3 station were markedly distinct from those obtained from SP1 and SP2. Although all three stations exhibited a high abundance of Gammaproteobacteria (> 15%), this taxon dominated more than 90% of composition of the A and C sediment layers at SP3. The highest abundance of the archaeal class Nitrososphaeria was presented at SP1, mainly at layer C (~ 21%), being absent at SP3 station. The prediction of chemoheterotrophy and fermentation as important microbial functions was supported by the data. Additionally, other metabolic pathways related to the cycles of nitrogen, carbon and sulfur were also predicted. The core microbiome analysis comprised only two ASVs. Our study contributes to a better understanding of microbial communities in an economically important little-explored region. This is the third microbiological survey in plateau sediments and the first focused on the southern region.
... Cyanobacteria are among the first biota to colonize grazed or scoured substrata and dead coral (Le Campion-Alsumard et al., 1995;Fine et al., 2006;Schroeder et al., 2008) and filamentous cyanobacteria are key components of many coral reef turf assemblages (Scott & Russ, 1987;Larkum et al., 1988;Bender et al., 2014;Harris et al., 2015;Nicholson & Clements, 2020;Arjunwadkar et al., 2022). Some cyanobacteria including Calothrix and Dichothrix (Nostocales) play a role in ocean calcification and reef biogenesis, precipitating calcium carbonate within their exopolysaccharide (EPS) sheaths (Littler & Littler, 1984;Dupraz & Visscher, 2005;Planavsky et al., 2009;Pentecost & Whitton, 2012;Stal, 2012;Komárek & Johansen, 2015). Some cyanobacteria, most notably Mastigocoleus testarum, are euendoliths (true-boring microflora) in dead coral and live crustose coralline algae and play a key role alongside the micro-Chlorophyte Ostreobium in calcium carbonate dissolution and sedimentation (Tribollet, 2008;Roush & Garcia-Pichel, 2020). ...
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Parrotfish are key agents of bioerosion and sediment production in coral reef ecosystems; however, their dietary targets and therefore potential sources of variation in carbonate cycling lack resolution. Here we address this knowledge shortfall in our current understanding of parrotfish diets by testing the concept that protein-rich micro-photoautotrophs are the target prey for many Scarinine parrotfishes. We focus at fine spatial scales on the feeding substrata of 12 syntopic Indo-Pacific parrotfish species at mid-shelf sites around Lizard Island, Great Barrier Reef, Australia. We followed individual parrotfish on snorkel until biting was observed, and then extracted a reef core around each bite. The surface of each bite core was scraped to ~1 mm for quantitative microscopic analysis (up to 630 × magnification) and for 16S and 18S rRNA metabarcoding. The most dominant photoautotrophic group in terms of surface cover was filamentous cyanobacteria, followed by crustose coralline algae. Epiphytic, epilithic, endophytic and endolithic filamentous cyanobacteria were consistent bite core biota. Although the density of filamentous cyanobacteria on bite cores was largely consistent among the 12 parrotfish species, the quantitative microscopic data and rRNA metabarcoding revealed distinct differences between parrotfish species in the taxonomic composition of core biota. Our data provide further evidence that these syntopic parrotfish species partition feeding resources.
... The uppermost layers are generally dominated by aerobic cyanobacteria, diatoms, and other oxygenic phototrophs, while the lowest layers are dominated by various anaerobic bacteria. Cyanobacterial mats occur in terrestrial and aquatic environments such as tidal sand flats, hypersaline ponds, hot springs, intertidal zones, and coral reefs [1][2][3] . The vertical distributions of bacteria can fluctuate daily 4 , and the mats can expand horizontally in radial directions 5 . ...
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Black band disease (BBD) in corals is characterized by a distinctive, band-like microbial mat, which spreads across the tissues and often kills infected colonies. The microbial mat is dominated by cyanobacteria but also commonly contains sulfide-oxidizing bacteria (SOB), sulfate-reducing bacteria (SRB), and other microbes. The migration rate in BBD varies across different environmental conditions, including temperature, light, and pH. However, whether variations in the migration rates reflect differences in the microbial consortium within the BBD mat remains unknown. Here, we show that the micro-scale surface structure, bacterial composition, and spatial distribution differed across BBD lesions with different migration rates. The migration rate was positively correlated with the relative abundance of potential SOBs belonging to Arcobacteraceae localized in the middle layer within the mat and negatively correlated with the relative abundance of other potential SOBs belonging to Rhodobacteraceae. Our study highlights the microbial composition in BBD as an important determinant of virulence.
... This pattern could also result from the successional stages of biofilm development in river ecosystems. Biofilm development generally starts with bacteria and diatoms (Azim and Asaeda, 2005;Stal, 1995Stal, , 2012, followed by filamentous algae, mostly Chlorophyta, as a late successional stage (Burns and Walker, 2000;Vadeboncoeur et al., 2021), which is consistent with our findings showing the growth of Chlorophyta and other algae overgrowing cyanobacteria in biofilms. ...
Article
The development of benthic cyanobacteria currently raises concern worldwide because of their potential to produce toxins. As a result, understanding which measures of biotic and abiotic parameters influence the development of cyanobacterial assemblages is of great importance to guide management actions. In this study, we investigate the relative contributions of abiotic and biotic parameters that may drive the development of cyanobacterial assemblages in river biofilms. First, a 2D hydrodynamic model allowed us to retrace changes in depths and velocities according to discharge at a 4 m2 resolution. From this model, we set up three hydraulic zones in each of the 4 reaches investigated along a 50-km-long river stretch. We further used univariate, multivariate and variance partitioning analyses to assess the contribution of past and present hydraulics, present physical and chemical parameters and algae to the temporal variability of cyanobacterial assemblage composition. The cyanobacterial assemblages were generally dominated by Phormidium sp., Lyngbya sp., Planktolyngbya sp. and Oscillatoria sp., four genera known to contain potentially toxic species. The highest biovolumes of cyanobacteria were present in low velocity zones in early summer and shifted to high velocity zones in late summer, highlighting the major influence of hydraulic parameters on benthic cyanobacteria settlement and development in rivers. Considering the identified genera, biofilms present a potentially high risk of toxin production. Relations between cyanobacterial development, toxin production and environmental parameters need to be further assessed to better estimate this risk.
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Microbial rhodopsins are prevalent in many cyanobacterial groups as a light-energy-harvesting system in addition to the photosynthetic system. It has been suggested that this dual system allows efficient capture of sunlight energy using complementary ranges of absorption wavelengths. However, the diversity of cyanobacterial rhodopsins, particularly in accumulated metagenomic data, remains underexplored. Here, we used a metagenomic mining approach, which led to the identification of a novel rhodopsin clade unique to cyanobacteria, cyanorhodopsin-II (CyR-II). CyR-IIs function as light-driven outward H+ pumps. CyR-IIs, together with previously identified cyanorhodopsins (CyRs) and cyanobacterial halorhodopsins (CyHRs), constitute cyanobacterial ion-pumping rhodopsins (CyipRs), a phylogenetically distinct family of rhodopsins. The CyR-II clade is further divided into two subclades, YCyR-II and GCyR-II, based on their specific absorption wavelength. YCyR-II absorbed yellow light (λmax = 570 nm), whereas GCyR-II absorbed green light (λmax = 550 nm). X-ray crystallography and mutational analysis revealed that the difference in absorption wavelengths is attributable to slight changes in the side chain structure near the retinal chromophore. The evolutionary trajectory of cyanobacterial rhodopsins suggests that the function and light-absorbing range of these rhodopsins have been adapted to a wide range of habitats with variable light and environmental conditions. Collectively, these findings shed light on the importance of rhodopsins in the evolution and environmental adaptation of cyanobacteria.
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Replicating or exceeding human intelligence, not just in particular domains but in general, has always been a major goal of Artificial Intelligence (AI). We argue here that “human intelligence” is not only ill-defined, but often conflated with broader aspects of human psychology. Standard arguments for replicating it are morally unacceptable. We then suggest a reframing: that the proper goal of AI is not to replicate humans, but to complement them by creating diverse intelligences capable of collaborating with humans. This goal renders issues of theory of mind, empathy, and caring, or community engagement, central to AI. It also challenges AI to better understand the circumstances in which human intelligence, including human moral intelligence, fails.
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https://authors.elsevier.com/a/1jIuC73N%7EEIZM ; Microbes, as essential components of any ecosystem for their metabolic capabilities of driving energy and matter cycles, must have been omnipresent in the earliest metazoan-dominated marine ecosystem that was initially established during the Ediacaran-Cambrian transition. However, contemporaneous microbial fossils and their ecological roles are rarely known. Here we report an exquisitely preserved microbial fossil assemblage from the ~535 million years old phosphorite of South China. Ten types of filamentous and spherical fossils have been identified and most are comparable to modern fungi, cyanobacteria, and microalgae at a cellular level. Particularly, mold- and yeast-like morphotypes that are interpreted as fungi provide potential fossil evidence for exploring the early evolution of fungi. This microbial assemblage including fungal and cyanobacterial analogues built symbiotic mats composed of decomposers and producers that were ecologically indispensable for early metazoans. A rapid phosphatization followed by silica-cementation is responsible for the high fidelity of fossil preservation, and hence is an ideal taphonomic window to explore the microbial world in geological past.
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Lake Untersee, a lake in Antarctica that is perennially covered with ice, is home to unique microbial structures that are not lithified. We have evaluated the structure of the community and its metabolic potential across the pigmented upper layers and the sediment‐enriched deeper layers in these pinnacle and cone‐shaped microbial structures using metagenomics. These microbial structures are inhabited by distinct communities. The upper layers of the cone‐shaped structures have a higher abundance of the cyanobacterial MAG Microcoleus , while the pinnacle‐shaped structures have a higher abundance of Elainellacea MAG. This suggests that cyanobacteria influence the morphologies of the mats. We identified stark contrasts in the composition of the community and its metabolic potential between the upper and lower layers of the mat. The upper layers of the mat, which receive light, have an increased abundance of photosynthetic pathways. In contrast, the lower layer has an increased abundance of heterotrophic pathways. Our results also showed that Lake Untersee is the first Antarctic lake with a substantial presence of ammonia‐oxidizing Nitrospiracea and amoA genes. The genomic capacity for recycling biological molecules was prevalent across metagenome‐assembled genomes (MAGs) that cover 19 phyla. This highlights the importance of nutrient scavenging in ultra‐oligotrophic environments. Overall, our study provides new insights into the formation of microbial structures and the potential metabolic complexity of Antarctic laminated microbial mats. These mats are important environments for biodiversity that drives biogeochemical cycling in polar deserts.
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A comprehensive study was conducted in the Cuatro Ciénegas Basin (CCB) in Coahuila, Mexico, which is known for its diversity of microorganisms and unique physicochemical properties. The study focused on the “Archaean Domes” (AD) site in the CCB, which is characterized by an abundance of hypersaline, non-lithifying microbial mats. In AD, we analyzed the small domes and circular structures using metagenome assembly genomes (MAGs) with the aim of expanding our understanding of the prokaryotic tree of life by uncovering previously unreported lineages, as well as analyzing the diversity of bacteria and archaea in the CCB. A total of 325 MAGs were identified, including 48 Archaea and 277 Bacteria. Remarkably, 22 archaea and 104 bacteria could not be classified even at the genus level, highlighting the remarkable novel diversity of the CCB. Besides, AD site exhibited significant diversity at the phylum level, with Proteobacteria being the most abundant, followed by Desulfobacteria, Spirochaetes, Bacteroidetes, Nanoarchaeota, Halobacteriota, Cyanobacteria, Planctomycetota, Verrucomicrobiota, Actinomycetes and Chloroflexi. In Archaea, the monophyletic groups of MAGs belonged to the Archaeoglobi, Aenigmarchaeota, Candidate Nanoarchaeota, and Halobacteriota. Among Bacteria, monophyletic groups were also identified, including Spirochaetes, Proteobacteria, Planctomycetes, Actinobacteria, Verrucomicrobia, Bacteroidetes, Candidate Bipolaricaulota, Desulfobacteria, and Cyanobacteria. These monophyletic groups were possibly influenced by geographic isolation, as well as the extreme and fluctuating environmental conditions in the pond AD, such as stoichiometric imbalance of C:N:P of 122:42:1, fluctuating pH (5–9.8) and high salinity (5.28% to saturation).
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In the 21st century, glaciers are percepted as a distinct biome that has taken on special significance in today’s world of retreating ice. Here we review the results of recent studies of organomineral formations on glaciers, their diversity, processes, functioning and the role in the biosphere. The question is raised about the possibility of involving supraglacial organomineral formations in the range of objects of soil science. We review the supraglacial zone as an area of soils and soil-like bodies, which biogeochemical processes affect the glacial biome and its surrounding landscapes. Interpretation of supraglacial organomineral formations from a soil scientist point of view revealed the following processes: accumulation and stabilization of organic matter (OM), its heterotrophic transformation, formation of dark-colored humified OM and accumulation of residual solid-phase products of functioning in situ, fine earth aggregation, and biochemical weathering. Among supraglacial formations, we distinguish pre-soils and soil-like bodies in ice and snow, metastable soil-like bodies on cryoconite and soils with microprofiles under moss communities on ice, as well as relatively stable soils with macroprofiles on fine-earth-detrital deposits with underlying glaciers and dead ice. Labile water-soluble OM, accumulated and transformed in supraglacial soils and soil-like bodies, has a significant impact on the periglacial zone, leading to the reservoir and priming effects. The studies of supraglacial organomineral systems are of fundamental importance for understanding the evolution of ecosystems on Earth as well as for modeling supraglacial formations of extraterrestrial bodies with a vast cryosphere. Supraglacial soil formation is also a model object for studying common soils under conditions of a constant external input of organic and mineral components, which contribution outside the glaciers is no less significant, but is masked by the polymineral substrate of soils and parent rocks.
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Microbial community assembly results from the interaction between biotic and abiotic factors. However, environmental selection is thought to predominantly shape communities in extreme ecosystems. Salar de Huasco, situated in the high-altitude Andean Altiplano, represents a poly-extreme ecosystem displaying spatial gradients of physicochemical conditions. To disentangle the influence of abiotic and biotic factors, we studied prokaryotic and eukaryotic communities from microbial mats and underlying sediments across contrasting areas of this athalassohaline ecosystem. The prokaryotic communities were primarily composed of bacteria, notably including a significant proportion of photosynthetic organisms like Cyanobacteria and anoxygenic photosynthetic members of Alpha- and Gammaproteobacteria and Chloroflexi. Additionally, Bacteroidetes, Verrucomicrobia, and Deltaproteobacteria were abundantly represented. Among eukaryotes, photosynthetic organisms (Ochrophyta and Archaeplastida) were predominant, alongside relatively abundant ciliates, cercozoans, and flagellated fungi. Salinity emerged as a key driver for the assembly of prokaryotic communities. Collectively, abiotic factors influenced both prokaryotic and eukaryotic communities, particularly those of algae. However, prokaryotic communities strongly correlated with photosynthetic eukaryotes, suggesting a pivotal role of biotic interactions in shaping these communities. Co-occurrence networks suggested potential interactions between different organisms, such as diatoms with specific photosynthetic and heterotrophic bacteria or with protist predators, indicating influences beyond environmental selection. While some associations may be explained by environmental preferences, the robust biotic correlations, alongside insights from other ecosystems and experimental studies, suggest that symbiotic and trophic interactions significantly shape microbial mat and sediment microbial communities in this athalassohaline ecosystem. IMPORTANCE How biotic and abiotic factors influence microbial community assembly is still poorly defined. Here, we explore their influence on prokaryotic and eukaryotic community assembly within microbial mats and sediments of an Andean high-altitude polyextreme wetland system. We show that, in addition to abiotic elements, mutual interactions exist between prokaryotic and eukaryotic communities. Notably, photosynthetic eukaryotes exhibit a strong correlation with prokaryotic communities, specifically diatoms with certain bacteria and other protists. Our findings underscore the significance of biotic interactions in community assembly and emphasize the necessity of considering the complete microbial community.
Chapter
Dating back to the earliest period of geological time (Archean), cyanobacteria are the oldest known photoautotrophic organisms that release oxygen during their photosynthesis (= oxygenic photosynthesis).
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This study addresses the limited understanding of chromium-microbial mat interactions in estuarine tidal flats. The aims were to evaluate (1) the efficiency of the microbial consortium in Cr(III) removal from seawater; (2) the elemental and mineralogical composition of the microbial mat as a natural system in the Cr removal, (3) the effects of metal on microphytobenthos, and (4) possible interactions of Cr with other metals present in the consortium. Microbial mats were exposed to Cr(III) solutions at different concentrations (2–30 mg Cr/L). Analysis such as metal concentration, organic matter content, chlorophyll a and phaeopigment concentrations, abundance of diatoms and cyanobacteria, SEM-EDS, and XRD were performed. Most of the Cr(III) was deposited, as chromium oxide/hydroxide, on the surface of all microbial mat components. The complete microbial mat, comprising sediments, detritus, EPS, and diverse microorganism communities, exhibited a remarkable capacity to accumulate Cr(III), retaining over 87% in the solution.
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Numerous biodiversity–ecosystem functioning (BEF) experiments have shown that plant community productivity typically increases with species diversity. In these studies, diversity is generally quantified using metrics of taxonomic, phylogenetic, or functional differences among community members. Research has also shown that the relationships between species diversity and functioning depends on the spatial scale considered, primarily because larger areas may contain different ecosystem types and span gradients in environmental conditions, which result in a turnover of the species set present locally. A fact that has received little attention, however, is that ecological systems are hierarchically structured, from genes to individuals to communities to entire landscapes, and that additional biological variation occurs at levels of organization above and below those typically considered in BEF research. Here, we present cases of diversity effects at different hierarchical levels of organization and compare these to the species‐diversity effects traditionally studied. We argue that when this evidence is combined across levels, a general framework emerges that allows the transfer of insights and concepts between traditionally disparate disciplines. Such a framework presents an important step towards a better understanding of the functional importance of diversity in complex, real‐world systems.
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Chapter
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Benthic microbial mats dominated by Cyanobacteria are important features of polar lakes. Although culture-independent studies have provided important insights into their diversity, only a handful of genomes of polar Cyanobacteria have been sequenced to date. Here, we applied a genome-resolved metagenomics approach to data obtained from Arctic, sub-Antarctic, and Antarctic microbial mats. We recovered 22 unique metagenome-assembled genomes (MAGs) of Cyanobacteria, most of which are only distantly related to genomes that have been sequenced so far. These include i) lineages that are common in polar microbial mats such as the filamentous taxa Pseudanabaena, Leptolyngbya, Microcoleus/Tychonema , and Phormidium ; ii) the less common taxa Crinalium and Chamaesiphon ; iii) an enigmatic Chroococcales lineage only distantly related to Microcystis ; and iv) an early branching lineage in the order Gloeobacterales that is almost exclusively restricted to the cold biosphere, for which we propose the name Candidatus Sivonenia alaskensis. Our results show that genome-resolved metagenomics is a powerful tool for expanding our understanding of the diversity of Cyanobacteria, especially in understudied remote and extreme environments. Data summary The sequencing data generated in this study have been submitted to the European Nucleotide Archive (ENA) under the BioProject PRJEB59431. Individual accession numbers for raw reads and genomic bins are listed in Table S1 and Table S3 , respectively. Genomic bins can also be downloaded from doi.org/10.6084/m9.figshare.22003967. The commands used throughout this study are available in github.com/igorspp/polar-cyanobacteria-MAGs . Impact statement Cyanobacteria are photosynthetic microorganisms that play important roles in polar lacustrine ecosystems. Many Cyanobacteria are difficult to grow in the laboratory, particularly in isolation from other organisms, which makes it challenging to sequence their genomes. As such, considerably fewer genomes of Cyanobacteria have been sequenced so far compared to other bacteria. In this study, we used a metagenomics approach to recover novel genomes of Cyanobacteria from Arctic and Antarctic microbial mats without the need to isolate the organisms. The community DNA was extracted and sequenced, and the genomes of individual populations were separated using bioinformatics tools. We recovered 22 different genomes of Cyanobacteria, many of which have not been sequenced before. We describe in more detail an interesting lineage of ancestral Cyanobacteria in the order Gloeobacterales, for which we propose the name Candidatus Sivonenia alaskensis. Our study shows that genome-resolved metagenomics is a valuable approach for obtaining novel genomes of Cyanobacteria, which are needed to improve our understanding of life in the polar regions and the planet at large.
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Studies of the distribution of stable carbon isotopes within ecosystems frequently offer useful insights into the structure and function of those ecosystems. The isotopic composition of the organic matter in a community such as a microbial mat is controlled by those enzymes which create and subsequently alter organic compounds. The extent to which these enzymes can affect the isotopic composition of organics is influenced by the relative fluxes of carbon, both within a community and between the community and its environment. Because the isotopic composition of organic matter in sedimentary rocks resists thermal alteration better than organic molecular structures, isotopic studies of ancient rocks have been important for Precambrian paleobiology (Hayes et al. 1992; Des Marais et al. 1992a).
Chapter
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Stromatolites are products of benthic microbial communities composed predominantly of photosynthetic microorganisms, mainly cyanobacteria (blue-green algae), with occasional admixture of eukaryotic algae. The microbial communities (mats) may either act as traps for current-transported sediment particles, or they may induce in situ precipitation of minerals, mostly Ca and Mg carbonates. The in situ calcified, laminated microbial mats are classified as stromatolites whereas those characterized by clotted internal structures are termed thrombolites. Both structures can occur together in the same microbial sedimentary deposit and their clear-cut separation is often difficult (for review see: Kennard and James 1986; Burne and Moore 1987). The lamination in stromatolites may reflect diurnal, tidal, synodic, seasonal, annual or irregular growth increments which many produce by accretion in a great variety of macroscopic bodies grouped sometimes into large reefoid structures (e.g. Hofmann 1973; Monty 1973; Walter 1976). Both the trapping and mineralizing algal mats occur today, the former almost exclusively in marine environments, the latter in lagoonal, paralacustrine and lacustrine enviroments. This has not, however, been so in the geologic past: throughout most of the Precambrian stromatolites – the only large and widespread marine biological structures of that time – formed predominantly by in situ mineralization of cyanobacteria-like microbiota (e.g., Monty 1973, Serebryakov and Semikhatov 1974, Awramik 1982). It is still debated why stromatolites are so rare in modern seas and why marine cyanobacterial mats diminished their ability to calcify with the end of the Cretaceous. The present paper attempts to answer Monty’s (1972, p. 747) anxious question concerning the absence of in situ calcification in extant marine cyanobacteria.
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Unter geeigneten Bedingungen erhält man bei der Photosynthese von Chlorella eine dem Kohlensäureverbrauch äquivalente Menge an Glykolsäure.
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Natural genetic transformation is the active uptake of free DNA by bacterial cells and the heritable incorporation of its genetic information. Since the famous discovery of transformation in Streptococcus pneumoniae by Griffith in 1928 and the demonstration of DNA as the transforming principle by Avery and coworkers in 1944, cellular processes involved in transformation have been studied extensively by in vitro experimentation with a few transformable species. Only more recently has it been considered that transformation may be a powerful mechanism of horizontal gene transfer in natural bacterial populations. In this review the current understanding of the biology of transformation is summarized to provide the platform on which aspects of bacterial transformation in water, soil, and sediments and the habitat of pathogens are discussed. Direct and indirect evidence for gene transfer routes by transformation within species and between different species will be presented, along with data suggesting that plasmids as well as chromosomal DNA are subject to genetic exchange via transformation. Experiments exploring the prerequisites for transformation in the environment, including the production and persistence of free DNA and factors important for the uptake of DNA by cells, will be compiled, as well as possible natural barriers to transformation. The efficiency of gene transfer by transformation in bacterial habitats is possibly genetically adjusted to submaximal levels. The fact that natural transformation has been detected among bacteria from all trophic and taxonomic groups including archaebacteria suggests that transformability evolved early in phylogeny. Probable functions of DNA uptake other than gene acquisition will be discussed. The body of information presently available suggests that transformation has a great impact on bacterial population dynamics as well as on bacterial evolution and speciation.
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The oxidation of organic matter coupled to the reduction of Fe(III) or Mn(IV) is one of the most important biogeochemical reactions in aquatic sediments, soils, and groundwater. This process, which may have been the first globally significant mechanism for the oxidation of organic matter to carbon dioxide, plays an important role in the oxidation of natural and contaminant organic compounds in a variety of environments and contributes to other phenomena of widespread significance such as the release of metals and nutrients into water supplies, the magnetization of sediments, and the corrosion of metal. Until recently, much of the Fe(III) and Mn(IV) reduction in sedimentary environments was considered to be the result of nonenzymatic processes. However, microorganisms which can effectively couple the oxidation of organic compounds to the reduction of Fe(III) or Mn(IV) have recently been discovered. With Fe(III) or Mn(IV) as the sole electron acceptor, these organisms can completely oxidize fatty acids, hydrogen, or a variety of monoaromatic compounds. This metabolism provides energy to support growth. Sugars and amino acids can be completely oxidized by the cooperative activity of fermentative microorganisms and hydrogen- and fatty-acid-oxidizing Fe(III) and Mn(IV) reducers. This provides a microbial mechanism for the oxidation of the complex assemblage of sedimentary organic matter in Fe(III)- or Mn(IV)-reducing environments. The available evidence indicates that this enzymatic reduction of Fe(III) or Mn(IV) accounts for most of the oxidation of organic matter coupled to reduction of Fe(III) and Mn(IV) in sedimentary environments. Little is known about the diversity and ecology of the microorganisms responsible for Fe(III) and Mn(IV) reduction, and only preliminary studies have been conducted on the physiology and biochemistry of this process.
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The removal of cell-bound water through air drying and the addition of water to air-dried cells are forces that have played a pivotal role in the evolution of the prokaryotes. In bacterial cells that have been subjected to air drying, the evaporation of free cytoplasmic water (Vf) can be instantaneous, and an equilibrium between cell-bound water (Vb) and the environmental water (vapor) potential (psi wv) may be achieved rapidly. In the air-dried state some bacteria survive only for seconds whereas others can tolerate desiccation for thousands, perhaps millions, of years. The desiccated (anhydrobiotic) cell is characterized by its singular lack of water--with contents as low as 0.02 g of H2O g (dry weight)-1. At these levels the monolayer coverage by water of macromolecules, including DNA and proteins, is disturbed. As a consequence the mechanisms that confer desiccation tolerance upon air-dried bacteria are markedly different from those, such as the mechanism of preferential exclusion of compatible solutes, that preserve the integrity of salt-, osmotically, and freeze-thaw-stressed cells. Desiccation tolerance reflects a complex array of interactions at the structural, physiological, and molecular levels. Many of the mechanisms remain cryptic, but it is clear that they involve interactions, such as those between proteins and co-solvents, that derive from the unique properties of the water molecule. A water replacement hypothesis accounts for how the nonreducing disaccharides trehalose and sucrose preserve the integrity of membranes and proteins. Nevertheless, we have virtually no insight into the state of the cytoplasm of an air-dried cell. There is no evidence for any obvious adaptations of proteins that can counter the effects of air drying or for the occurrence of any proteins that provide a direct and a tangible contribution to cell stability. Among the prokaryotes that can exist as anhydrobiotic cells, the cyanobacteria have a marked capacity to do so. One form, Nostoc commune, encompasses a number of the features that appear to be critical to the withstanding of a long-term water deficit, including the elaboration of a conspicuous extracellular glycan, synthesis of abundant UV-absorbing pigments, and maintenance of protein stability and structural integrity. There are indications of a growing technology for air-dried cells and enzymes. Paradoxically, desiccation tolerance of bacteria has virtually been ignored for the past quarter century. The present review considers what is known, and what is not known, about desiccation, a phenomenon that impinges upon every facet of the distributions and activities of prokaryotic cells.
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The filamentous, non-heterocystous cyanobacterium Microcoleus chthonoplastes is a cosmopolitan organism, known to build microbial mats in a variety of different environments. Although most of these cyanobacterial mats are known for their capacity to fix dinitrogen, M. chthonoplastes has not been assigned as a diazotrophic organism. None of the strains that were correctly identified as M. chthonoplastes has been shown to fix dinitrogen and it has repeatedly been reported that these organisms lacked the cyanobacterial nifH, the structural gene for dinitrogenase reductase. In this study, we show that a complete nif-gene cluster is present in the genome of M. chthonoplastes PCC 7420 and that the three structural nitrogenase genes, nifHDK, are present in a collection of axenic strains of M. chthonoplastes from distant locations. Phylogenetic analysis of nifHDK revealed that they cluster with the Deltaproteobacteria and that they are closely related to Desulfovibrio. The nif operon is flanked by typical cyanobacterial genes, suggesting that it is an integral part of the M. chthonoplastes genome. In this study, we provide evidence that the nif operon of M. chthonoplastes is acquired through horizontal gene transfer. Moreover, the presence of the same nif-cluster in M. chthonoplastes isolates derived from various sites around the world suggests that this horizontal gene transfer event must have occurred early in the evolution of M. chthonoplastes. We have been unable to express nitrogenase in cultures of M. chthonoplastes, but we show that these genes were expressed under natural conditions in the field.
Chapter
Relative to biological demands, marine waters are often depleted in combined forms of nitrogen (Dugdale 1967). As such, the development of microbial mats in coastal marine environments is dependent on the fixation of atmospheric dinitrogen as the dominant source of biologically available N.
Article
Microbial mats arising in the sand flats of the Ebro Delta (Tarragona, Spain) were investigated during the summer season, when the community was highly developed. These mats are composed of three pigmented layers of phototrophic organisms, an upper brown layer mainly composed of Lyngbya aestuarii and diatoms, an intermediate green layer of the cyanobacterium Microcoleus chthonoplastes, and an underlying pink layer of a so-far unidentified purple sulfur bacterium. In the photic zone, oxygenic phototrophs constitute about 58% of total photosynthetic biomass, measured as biovolume, and anoxygenic phototrophs represent 42%. Diatoms constitute 11.8% of the oxygenic biomass, M chthonoplastes 61.2%, and L. aestuarii and coccoid cyanobacteria 20.6 and 6.4%, respectively. In this laminated community, organic matter has an autochthonous origin, and photosynthesis is the most important source of organic carbon. Oxygen production reaches up to 27.2 mmol O-2 m(-2) h(-1), measured at 1000 muE m(-2) s(-1) light intensity, whereas oxidation of sulfide in the light has been calculated to be 18.6 mmol S m(2) h(-1). This amount represents 26% of the total photosynthetic production in terms of photoassimilated carbon, demonstrating the important role of anoxygenic phototrophs as primary producers in the pink layer of Ebro Delta microbial mats.
Chapter
Light dependent movement of gliding cyanobacteria has been studied for more than a hundred years and several types of response to light have been observed (Häder 1987). The following concepts have been recommended by an ad hoc committee on behavioral terminology, (Diehn et al. 1979): Phototaxis: Orientation of movement with respect to a directional light field; photokinesis: by which the steady-state speed of movement is related to the total light intensity and a photophobic response: where the movement is altered by a spatial or temporal change in light intensity. Most photosynthetic organisms display one or more of these behaviours in their search of suitable light conditions (Castenholz 1982).
Chapter
Microbial mats are among the most productive aquatic ecosystems on Earth, yet, in many cases, the waters from which they grow are depleted in the basic nutrient elements. How, then, are nutrients cycled to allow for such high rates, and what ultimately controls these rates? To begin to address these issues, the cycling of carbon, oxygen, sulfur and nutrients has been explored over several years in Microcoleus chtholoplastes-dominated cyanobacterial mats from the hypersaline salt ponds in Guerrero Negro, Baja California Sur, Mexico (D’Amelio et al. 1989; Canfield and Des Marais 1993).
Chapter
Depth profiles of organic and inorganic sulfur compounds were measured in the top 50 mm of a mature marine microbial mat during three growth seasons. Similarly, the vertical distribution of sulfate-reducing bacteria, colorless sulfur bacteria, and anoxygenic phototrophic bacteria was also measured. In combination with profiles of important physico-chemical parameters, which define the mat environment, and laboratory studies, sources and sinks of volatile sulfur compounds were evaluated. Calculations show that consumption of dimethyl sulfide potentially can balance its production, minimizing the flux from the sediment to the atmosphere.
Article
The fate of representative fermentation products (acetate, propionate, butyrate, lactate, and ethanol) in hot spring cyanobacterial mats was investigated. The major fate during incubations in the light was photoassimilation by filamentous bacteria resembling Chloroflexus aurantiacus. Some metabolism of all compounds occurred under dark aerobic conditions. Under dark anaerobic conditions, only lactate was oxidized extensively to carbon dioxide. Extended preincubation under dark anaerobic conditions did not enhance anaerobic catabolism of acetate, propionate, or ethanol. Acetogenesis of butyrate was suggested by the hydrogen sensitivity of butyrate conversion to acetate and by the enrichment of butyrate-degrading acetogenic bacteria. Accumulation of fermentation products which were not catabolized under dark anaerobic conditions revealed their importance. Acetate and propionate were the major fermentation products which accumulated in samples collected at temperatures ranging from 50 to 70 degrees C. Other organic acids and alcohols accumulated to a much lesser extent. Fermentation occurred mainly in the top 4 mm of the mat. Exposure to light decreased the accumulation of acetate and presumably of other fermentation products. The importance of interspecies hydrogen transfer was investigated by comparing fermentation product accumulation at a 65 degrees C site, with naturally high hydrogen levels, and a 55 degrees C site, where active methanogenesis prevented significant hydrogen accumulation. There was a greater relative accumulation of reduced products, notably ethanol, in the 65 degrees C mat.
Article
Anoxic iron-rich sediment samples that had been stored in the light showed development of brown, rusty patches. Subcultures in defined mineral media with ferrous iron (10 mmol/liter, mostly precipitated as FeCO3) yielded enrichments of anoxygenic phototrophic bacteria which used ferrous iron as the sole electron donor for photosynthesis. Two different types of purple bacteria, represented by strains L7 and SW2, were isolated which oxidized colorless ferrous iron under anoxic conditions in the light to brown ferric iron. Strain L7 had rod-shaped, nonmotile cells (1.3 by 2 to 3 microns) which frequently formed gas vesicles. In addition to ferrous iron, strain L7 used H2 + CO2, acetate, pyruvate, and glucose as substrate for phototrophic growth. Strain SW2 had small rod-shaped, nonmotile cells (0.5 by 1 to 1.5 microns). Besides ferrous iron, strain SW2 utilized H2 + CO2, monocarboxylic acids, glucose, and fructose. Neither strain utilized free sulfide; however, both strains grew on black ferrous sulfide (FeS) which was converted to ferric iron and sulfate. Strains L7 and SW2 grown photoheterotrophically without ferrous iron were purple to brownish red and yellowish brown, respectively; absorption spectra revealed peaks characteristic of bacteriochlorophyll a. The closest phototrophic relatives of strains L7 and SW2 so far examined on the basis of 16S rRNA sequences were species of the genera Chromatium (gamma subclass of proteobacteria) and Rhodobacter (alpha subclass), respectively. In mineral medium, the new isolates formed 7.6 g of cell dry mass per mol of Fe(II) oxidized, which is in good agreement with a photoautotrophic utilization of ferrous iron as electron donor for CO2 fixation. Dependence of ferrous iron oxidation on light and CO2 was also demonstrated in dense cell suspensions. In media containing both ferrous iron and an organic substrate (e.g., acetate, glucose), strain L7 utilized ferrous iron and the organic compound simultaneously; in contrast, strain SW2 started to oxidize ferrous iron only after consumption of the organic electron donor. Ferrous iron oxidation by anoxygenic phototrophs is understandable in terms of energetics. In contrast to the Fe3+/Fe2+ pair (E0 = +0.77 V) existing in acidic solutions, the relevant redox pair at pH 7 in bicarbonate-containing environments, Fe(OH)3 + HCO3-/FeCO3, has an E0' of +0.2 V. Ferrous iron at pH 7 can therefore donate electrons to the photosystem of anoxygenic phototrophs, which in purple bacteria has a midpoint potential around +0.45 V. The existence of ferrous iron-oxidizing anoxygenic phototrophs may offer an explanation for the deposition of early banded-iron formations in an assumed anoxic biosphere in Archean times.
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We have conducted long-term studies of microbial mats of hot springs as model systems for investigating composition and structure of natural microbial communities and as modern analogs of stromatolites (Ward et al. 1984, 1987, 1989b). As recently as the last symposium on microbial mats our knowledge of the biodiversity within these communities was based solely on microbial species cultivated from such mat systems. The view has changed dramatically in the intervening years, because of the application of culture-independent techniques to recover and probe ribosomal RNAs (rRNAs) as biomarkers representing individual mat community members (Ward et al. 1992; Weller et al. 1992 and references cited therein), and more recently because of the renewed attempt to cultivate more relevant species. Here, we summarize what is currently known. The evidence suggests that the molecular methods we are using (Ward et al. 1992) may still not permit a complete understanding of the true complexity of the community. However, the approach does provide insight into understanding the basis behind this large biodiversity and into how more relevant species can be cultivated.
Chapter
Microbial mats develop in a wide variety of environments such as hot springs, hypersaline ponds, dry and hot deserts, alkaline lakes and coastal intertidal sediments (Cohen et al. 1984; Cohen and Rosenberg 1989). A noticeable similarity of these environments is their relative low species diversity. Particularly, multicellular organisms are excluded from such environments and it has been conceived that the absence or limited activity of grazing organisms is an important prerequisite for the development of microbial mats (Walter 1976). At first sight such conditions seem not to apply to coastal environments. However, intertidal sediments are alternatingly inundated and exposed to the atmosphere and this will cause fluctuations of water content, salinity and temperature. Fluctuations of environmental conditions are more extreme in the higher parts of the intertidal flats where microbial mats develop particularly well (Stal et al. 1985; Pierson et al. 1987).
Chapter
The shortest wavelengths of the solar spectrum reaching the ground, known as the solar ultraviolet (UV, 280–400 nm), amount to only a small percentage of the total incident irradiance (Table 1). However, they may produce disproportionately large biological effects because they activate many photochemical reactions involving molecules of central biological importance. The consequence of these photoreactions is usually detrimental to the cellular metabolism. Mutation and lethal DNA and RNA damage, lipid peroxidation, photoinhibition of photosynthesis and respiration, and specific enzyme inactivation can all be a result of exposure to UV (Jagger 1985). These physiological effects are not always a laboratory curiostity but have ecological implications under natural conditions: the solar UV has been recognized as an important environmental stress factor in a variety of microbially dominated ecosystems. UV has been shown to cause sustained inhibition of both primary productivity and bacterial production in planktonic communities and to drive marked changes in species composition in periphyton communities (see Worrest 1982), but not much is known about the significance of ultraviolet radiation in benthic ecosystems. We have gathered some direct experimental evidence, as well as strong indirect inference from ecophysiological studies in diverse mat communities, suggesting that UV may be of importance, at least for the top phototrophic layers.
Article
Enrichment and pure cultures of nitrate-reducing bacteria were shown to grow anaerobically with ferrous iron as the only electron donor or as the additional electron donor in the presence of acetate. The newly observed bacterial process may significantly contribute to ferric iron formation in the suboxic zone of aquatic sediments.
Article
Article
Prochlorococcus is the most abundant phytoplankter throughout the photic zone in stratified marine waters and experiences distinct gradients of light and nitrogen nutrition. Physiologically and genetically distinct Prochlorococcus ecotypes partition the water column: high-B/A (low-light adapted) ecotypes are generally restricted to the deep euphotic zone near or at the nitracline. Low-B/A (high-light adapted) ecotypes predominate in, but are not limited to, NO3--depleted surface waters, where they outnumber coexisting Synechococcus populations. The niche partitioning by different Prochlorococcus ecotypes begs the question of whether they also differ in their nitrogen (N) utilization physiology, especially with respect to NO3- utilization. To explore this possibility, we studied the capabilities of different Prochlorococcus and Synechococcus strains to grow on a variety of N sources. We found that all the isolates grew well on NH4- and all were capable of urea utilization, occasionally at a lower growth rate. None of the Prochlorococcus isolates were able to grow with NO3-. Four high-B/A Prochlorococcus isolates grew on NO2-, but all others did not. Whole genome analysis of the low-B/A Prochlorococcus MED4 revealed that the genes required for NO3- uptake and reduction were absent. The genome of the high-B/A Prochlorococcus MIT 9313 also lacked the NO3- utilization genes but has homologs of genes required for NO2- utilization consistent with its physiology and ecology. Thus, the utilization of different N sources in the marine environment is partitioned among closely related ecotypes, each with adaptations optimized for the environment where these sources are available.
Article
Iron-rich sediments have been deposited intermittently throughout earth history, but virtually all significant deposits of the cherty layered rock referred to as iron formation are of Precambrian age. Present evidence suggests three periods of peak deposition rate. This review deals only with those of the cherty oxide facies. Two distinct subtypes are recognized: well laminated cherty banded iron formation (BIF in this paper) and granule iron formation. Both are primary chemical precipitates, modified subsequently. The depositional basins of BIF showed unusual tectonic and environmental stability coupled with an absence of clastic contamination. The paleoenvironment of granule iron formation was, by contrast, a high-energy one in which the deposited material was subjected to para-depositional reworking. -from Author Precambrian chemical precipitates cherty oxide facies
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This chapter discusses open marine subtidal and intertidal stromatolites. The most important factors controlling the distribution and morphology of recent subtidal and intertidal stromatolites in open marine waters are: (1) the widespread distribution and high abundance of grazing and burrowing invertebrates, and (2) the lack of rapid cementation of organic and organosedimentary. Several types of algal sediments occur in the shallow subtidal zone. Their form, distribution and vertical or lateral sequences provides detailed information on depositional environments structures. Stromatolites occur in open marine subtidal environments in which, for various reasons, invertebrate grazers and burrowers are greatly reduced in numbers. Subsequently, stromatolite growth may begin on any surface irregularity (stabilized cipple, flat pebble of algally bound sediment, Thulussia rhizome, elevated reef or rock substrate) that elevates the surface above the surrounding matbound bottom. Maximum observed depths for subtidal stromatolite formation are 4-5m.
Chapter
The last decade has shown a great revival in the study of halophilic microorganisms. In part this interest has been caused by the discovery of properties interesting from a theoretical point of view, such as mechanisms of osmotic adjustment, the functioning of enzymes in the presence of high salt concentrations, and the possession of retinal pigments, such as bacteriorhodopsin and halorhodopsin in a number of Halobacterium strains, representing simple mechanisms of converting light energy into biologically available energy (Stoeckenius and Bogomolni, 1982). Moreover, accumulation of valuable products, such as glycerol and (in certain strains) β-carotene, in the halotolerant unicellular green alga Dunaliella has industrial potential (Ben-Amotz and Avron, 1983).
Article
A vegetation of non-aquatic and free-living (non-lichenized) algae exists in the Negev Desert of Israel. The following algal habitats are described: (A) soil algae, comprising (1) endedaphic algae (in soil), (2) epedaphic algae (on the surface of soil), and (3) hypolithic algae (on the lower surface of stones lying on soil); (B) rock algae (lithophytes) such as (4) chasmolithic algae (in rock fissures) and (5) endolithic algae (penetrating the rock tissue). The main water source of algae is thought to be dew. The floristic list comprises mainly green and blue-green algae.
Article
Hydrophobicity and pore clogging are suggested as two mechanisms responsible for generating runoff over microbiotic crusts overlying dune sand. Although natural microbiotic crusts in the Hallamish dune field (Negev Desert, Israel) did not show any hydrophobicity, that was not the case with natural crusts subjected to long periods of continuous wetness in the lab. Monoalgal crusts, grown in the lab, also showed high hydrophobicity when dry. The hydrophobicity vanished, however, once the surface was wetted. Runoff on monoalgal lab-grown crusts was obtained when (i) the dry crust exhibited hydrophobic properties and (ii) the wetted crust no longer showed water repellence. Although runoff generation caused by hydrophobicity is expected, it is suggested that runoff initiation when the crusts do not exhibit any hydrophobicity stems from the high water absorption and swelling of the exopolysaccharide cyanobacterial sheaths causing pore clogging. The multi-layered structure of the crust and filament migration to the surface may enhance pore clogging. The experiments and their interpretation are supported by reinterpretation of published data.