[Show abstract][Hide abstract] ABSTRACT: Several assays for the detection of host-specific genetic markers of the order Bacteroidales have been developed and used for microbial source tracking (MST) in environmental waters. It is recognized that the source-sensitivity and source-specificity are unknown and variable when introducing these assays in new geographic regions, which reduces their reliability and use. A Bayesian approach was developed to incorporate expert judgments with regional assay sensitivity and specificity assessments in a utility evaluation of a human and a ruminant-specific qPCR assay for MST in a drinking water source. Water samples from Lake Rådasjön were analyzed for E. coli, intestinal enterococci and somatic coliphages through cultivation and for human (BacH) and ruminant-specific (BacR) markers through qPCR assays. Expert judgments were collected regarding the probability of human and ruminant fecal contamination based on fecal indicator organism data and subjective information. Using Bayes formula, the conditional probability of a true human or ruminant fecal contamination given the presence of BacH or BacR was determined stochastically from expert judgments and regional qPCR assay performance, using Beta distributions to represent uncertainties. A web-based computational tool was developed for the procedure, which provides a measure of confidence to findings of host-specific markers and demonstrates the information value from these assays.
[Show abstract][Hide abstract] ABSTRACT: Terminal restriction fragment length polymorphism (T-RFLP) analysis is a DNA-fingerprinting method that can be used for comparisons of the microbial community composition in a large number of samples. There is no consensus on how T-RFLP data should be treated and analyzed before comparisons between samples are made, and several different approaches have been proposed in the literature. The analysis of T-RFLP data can be cumbersome and time-consuming, and for large datasets manual data analysis is not feasible. The currently available tools for automated T-RFLP analysis, although valuable, offer little flexibility, and few, if any, options regarding what methods to use. To enable comparisons and combinations of different data treatment methods an analysis template and an extensive collection of macros for T-RFLP data analysis using Microsoft Excel were developed.
The Tools for T-RFLP data analysis template provides procedures for the analysis of large T-RFLP datasets including application of a noise baseline threshold and setting of the analysis range, normalization and alignment of replicate profiles, generation of consensus profiles, normalization and alignment of consensus profiles and final analysis of the samples including calculation of association coefficients and diversity index. The procedures are designed so that in all analysis steps, from the initial preparation of the data to the final comparison of the samples, there are various different options available. The parameters regarding analysis range, noise baseline, T-RF alignment and generation of consensus profiles are all given by the user and several different methods are available for normalization of the T-RF profiles. In each step, the user can also choose to base the calculations on either peak height data or peak area data.
The Tools for T-RFLP data analysis template enables an objective and flexible analysis of large T-RFLP datasets in a widely used spreadsheet application.
[Show abstract][Hide abstract] ABSTRACT: Background
Terminal restriction fragment length polymorphism (T-RFLP) analysis is a common DNA-fingerprinting technique used for comparisons of complex microbial communities. Although the technique is well established there is no consensus on how to treat T-RFLP data to achieve the highest possible accuracy and reproducibility. This study focused on two critical steps in the T-RFLP data treatment: the alignment of the terminal restriction fragments (T-RFs), which enables comparisons of samples, and the normalization of T-RF profiles, which adjusts for differences in signal strength, total fluorescence, between samples.ResultsVariations in the estimation of T-RF sizes were observed and these variations were found to affect the alignment of the T-RFs. A novel method was developed which improved the alignment by adjusting for systematic shifts in the T-RF size estimations between the T-RF profiles. Differences in total fluorescence were shown to be caused by differences in sample concentration and by the gel loading. Five normalization methods were evaluated and the total fluorescence normalization procedure based on peak height data was found to increase the similarity between replicate profiles the most. A high peak detection threshold, alignment correction, normalization and the use of consensus profiles instead of single profiles increased the similarity of replicate T-RF profiles, i.e. lead to an increased reproducibility. The impact of different treatment methods on the outcome of subsequent analyses of T-RFLP data was evaluated using a data set from a longitudinal study of the bacterial community in an activated sludge wastewater treatment plant. Whether the alignment was corrected or not and if and how the T-RF profiles were normalized had a substantial impact on ordination analyses, assessments of bacterial dynamics and analyses of correlations with environmental parameters.ConclusionsA novel method for the evaluation and correction of the alignment of T-RF profiles was shown to reduce the uncertainty and ambiguity in alignments of T-RF profiles. Large differences in the outcome of assessments of bacterial community structure and dynamics were observed between different alignment and normalization methods. The results of this study can therefore be of value when considering what methods to use in the analysis of T-RFLP data.
[Show abstract][Hide abstract] ABSTRACT: Biofilms are complex communities. Their growth and the presence of different bacterial populations can lead to physicochemical gradients in the biofilm. Those gradients could form microhabitats, allowing different bacterial populations to live in different parts of the biofilm.
One-stage partial nitritation-anammox biofilms, growing on carriers in Moving Bed Biofilm Reactors (MBBR) for nitrogen removal in wastewater treatment, is an example of a system with a strong spatial stratification. The layers facing the bulk water have access to oxygen and ammonium allowing the establishment of ammonia oxidizing bacteria (AOB). AOB in turn produce nitrite, and together with other bacteria, they create the anoxic condition that allows the establishment of anammox bacteria in deeper biofilm layers. MBBR biofilms are often several millimeters thick. These provide opportunities to studying large-scale process in biofilms.
We have studied biofilms from one-stage partial nitritation-anammox processes in MBBR. The biofilms are fixed and embedded in OCT, which allows lengthwise or crosswise cryosections of whole “wall-to wall” biofilms to be studied. Fluorescence in Situ Hybridization (FISH) and confocal laser scanning microscope (CLSM) together with novel imaging analyses tools are used to study population composition and biofilm positions of anammox and AOB, as well as eukaryotic predators.
After analyzing 16SrRNA gene clone library sequences we reported that Brocadia sp. 40 strongly dominated the anammox community in an MBBR biofilm. However, when studying “wall-to wall” biofilm cryosections with CLSM-FISH we observed that one of the minor members of the anammox community was present in the biofilm layers close to the bulk water, near the AOB. Thus, spatial distinct distribution between anammox populations may be due to their eco-physiological differences, just as we have shown earlier for AOB populations.
Biofilm structure and positioning of bacteria can be formed by gradients of electron donors and acceptors, but also by other forcing factors such as predation. We are using the same approach of combining cryosections and CLSM-FISH to study relationship between protozoa and bacteria in biofilms. We have shown that eukaryotic predators of different types are present at different depths in the biofilm. Preliminary result suggests the some predators penetrate into deeper biofilm parts and show evidence of grazing of anammox bacteria. Thus, neither the formation of microcolonies nor living deep within the biofilm can fully protect bacteria from predation. Little is known about bacterial predation in anammox biofilms. We discuss the importance of predation for the function of one stage MBBR nitrogen removal in wastewater.
Studies of bacterial activity in biofilms, using molecular methods, together with CLSM-FISH analyses of cryosections are underway and will be discussed in relation to electron donor and acceptor gradients and predation pressure.
The use of cryosections, combined with CLSM-FISH allows us to study large scale spatial patterns in biofilms. Together with techniques for cell activity it is possible to finally start seeing the big picture in biofilms, such as structures formed by limiting resources and predation.
[Show abstract][Hide abstract] ABSTRACT: The complete nucleotide sequence of plasmids pMCBF1 and pMCBF6 was determined and analyzed. pMCBF1 and pMCBF6 form a novel clade within the IncP-1 plasmid family designated IncP-1 ς. The plasmids were exogenously isolated earlier from a marine biofilm. pMCBF1 (62 689 base pairs; bp) and pMCBF6 (66 729 bp) have identical backbones, but differ in their mercury resistance transposons. pMCBF1 carries Tn5053 and pMCBF6 carries Tn5058. Both are flanked by 5 bp direct repeats, typical of replicative transposition. Both insertions are in the vicinity of a resolvase gene in the backbone, supporting the idea that both transposons are "res-site hunters" that preferably insert close to and use external resolvase functions. The similarity of the backbones indicates recent insertion of the two transposons and the ongoing dynamics of plasmid evolution in marine biofilms. Both plasmids also carry the insertion sequence ISPst1, albeit without flanking repeats. ISPs1is located in an unusual site within the control region of the plasmid. In contrast to most known IncP-1 plasmids the pMCBF1/pMCBF6 backbone has no insert between the replication initiation gene (trfA) and the vegetative replication origin (oriV). One pMCBF1/pMCBF6 block of about 2.5 kilo bases (kb) has no similarity with known sequences in the databases. Furthermore, insertion of three genes with similarity to the multidrug efflux pump operon mexEF and a gene from the NodT family of the tripartite multi-drug resistance-nodulation-division (RND) system in Pseudomonas aeruginosa was found. They do not seem to confer antibiotic resistance to the hosts of pMCBF1/pMCBF6, but the presence of RND on promiscuous plasmids may have serious implications for the spread of antibiotic multi-resistance.
PLoS ONE 03/2014; 9(3):e92321. DOI:10.1371/journal.pone.0092321 · 3.23 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Moving bed biofilm reactors (MBBRs) are increasingly used for nitrogen removal with nitritation-anaerobic ammonium oxidation (anammox) processes in wastewater treatment. Carriers provide protected surfaces where ammonia oxidizing bacteria (AOB) and anammox bacteria form complex biofilms. However, the knowledge about the organization of microbial communities in MBBR biofilms is sparse. We used new cryosectioning and imaging methods for fluorescence in situ hybridization (FISH) to study the structure of biofilms retrieved from carriers in a nitritation-anammox MBBR. The dimensions of the carrier compartments and the biofilm cryosections after FISH showed good correlation, indicating little disturbance of biofilm samples by the treatment. FISH showed that Nitrosomonas europaea/eutropha-related cells dominated the AOB and Candidatus Brocadia fulgida-related cells dominated the anammox guild. New carriers were initially colonized by AOB, followed by anammox bacteria proliferating in the deeper biofilm layers, probably in anaerobic microhabitats created by AOB activity. Mature biofilms showed a pronounced three-dimensional stratification where AOB dominated closer to the biofilm-water interface, whereas anammox were dominant deeper into the carrier space and towards the walls. Our results suggest that current mathematical models may be oversimplifying these three-dimensional systems and unless the multidimensionality of these systems is considered, models may result in suboptimal design of MBBR carriers.
International Journal of Molecular Sciences 02/2014; 15(2):2191-2206. DOI:10.3390/ijms15022191 · 2.86 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A simple and efficient principle for nanopatterning with wide applicability in the sub‐50 nanometer regime is chemisorption of nanoparticles; at homogeneous substrates, particles carrying surface charge may spontaneously self‐organize due to the electrostatic repulsion between adjacent particles. Guided by this principle, a method is presented to design, self‐assemble, and chemically functionalize gradient nanopatterns where the size of molecular domains can be tuned to match the level corresponding to single protein binding events. To modulate the binding of negatively charged gold nanoparticles both locally (100 μm) onto a single modified gold substrate, ion diffusion is used to achieve spatial control of the particles’ mutual electrostatic interactions. By subsequent tailoring of different molecules to surface‐immobilized particles and the void areas surrounding them, nanopatterns are obtained with variable chemical domains along the gradient surface. Fimbriated Escherichia coli bacteria are bound to gradient nanopatterns with similar molecular composition and macroscopic contact angle, but different sizes of nanoscopic presentation of adhesive (hydrophobic) and repellent poly(ethylene) glycol (PEG) domains. It is shown that small hydrophobic domains, similar in size to the diameter of the bacterial fimbriae, supported firmly attached bacteria resembling catch‐bond binding, whereas a high number of loosely adhered bacteria are observed on larger hydrophobic domains. Chemical gradients with the resolution needed to address complex biological binding events at the single protein level are prepared using surface‐deposited gold nanoparticles as a versatile template for orthogonal chemical modifications. The effect of hydrophobic domain arrangement on the sub‐50 nm scale is shown to influence binding of fimbriae carrying E. coli bacteria.
Particle and Particle Systems Characterization 02/2014; 31(2). DOI:10.1002/ppsc.201300154 · 0.54 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: It is a challenge to apply anaerobic ammonium oxidation (anammox) for nitrogen removal from wastewater at low temperatures. Maintenance of anammox- and aerobic ammonia oxidizing bacteria (AOB) and suppression of nitrite oxidizing bacteria (NOB) are key issues. In this work, a nitritation-anammox moving bed biofilm pilot reactor was operated at 19-10°C for 300d. Nitrogen removal was decreasing, but stable, at 19-13°C. At 10°C removal became unstable. Quantitative PCR, fluorescence in situ hybridization and gene sequencing showed that no major microbial community changes were observed with decreased temperature. Anammox bacteria dominated the biofilm (0.9-1.2×10(14) 16S rRNA copies m(-2)). Most anammox bacteria were similar to Brocadia sp. 40, but another smaller Brocadia population was present near the biofilm-water interface, where also the AOB community (Nitrosomonas) was concentrated in thin layers (1.8-5.3×10(12) amoA copies m(-2)). NOB (Nitrobacter, Nitrospira) were always present at low concentrations (<1.3×10(11) 16S rRNA copies m(-2)).
[Show abstract][Hide abstract] ABSTRACT: Assessments of bacterial community diversity and dynamics are fundamental for the understanding of microbial ecology as well as biotechnological applications. We show that the choice of PCR primers has great impact on the results of analyses of diversity and dynamics using gene libraries and DNA fingerprinting. Two universal primer pairs targeting the 16S rRNA gene, 27F&1492R and 63F&M1387R, were compared and evaluated by analyzing the bacterial community in the activated sludge of a large-scale wastewater treatment plant. The two primer pairs targeted distinct parts of the bacterial community, none encompassing the other, both with similar richness. Had only one primer pair been used, very different conclusions had been drawn regarding dominant phylogenetic and putative functional groups. With 27F&1492R, Betaproteobacteria would have been determined to be the dominating taxa while 63F&M1387R would have described Alphaproteobacteria as the most common taxa. Microscopy and fluorescence in situ hybridization analysis showed that both Alphaproteobacteria and Betaproteobacteria were abundant in the activated sludge, confirming that the two primer pairs target two different fractions of the bacterial community. Furthermore, terminal restriction fragment polymorphism analyses of a series of four activated sludge samples showed that the two primer pairs would have resulted in different conclusions about community stability and the factors contributing to changes in community composition. In conclusion, different PCR primer pairs, although considered universal, target different ranges of bacteria and will thus show the diversity and dynamics of different fractions of the bacterial community in the analyzed sample. We also show that while a database search can serve as an indicator of how universal a primer pair is, an experimental assessment is necessary to evaluate the suitability for a specific environmental sample.
PLoS ONE 10/2013; 8(10):e76431. DOI:10.1371/journal.pone.0076431 · 3.23 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The protection of drinking water from pathogens such as Cryptosporidium and Giardia requires an understanding of the short-term microbial release from faecal contamination sources in the catchment. Flow-weighted samples were collected during two rainfall events in a stream draining an area with on-site sewers and during two rainfall events in surface runoff from a bovine cattle pasture. Samples were analysed for human (BacH) and ruminant (BacR) Bacteroidales genetic markers through quantitative polymerase chain reaction (qPCR) and for sorbitol-fermenting bifidobacteria through culturing as a complement to traditional faecal indicator bacteria, somatic coliphages and the parasitic protozoa Cryptosporidium spp. and Giardia spp. analysed by standard methods. Significant positive correlations were observed between BacH, Escherichia coli, intestinal enterococci, sulphite-reducing Clostridia, turbidity, conductivity and UV254 in the stream contaminated by on-site sewers. For the cattle pasture, no correlation was found between any of the genetic markers and the other parameters. Although parasitic protozoa were not detected, the analysis for genetic markers provided baseline data on the short-term faecal contamination due to these potential sources of parasites. Background levels of BacH and BacR makers in soil emphasise the need to including soil reference samples in qPCR-based analyses for Bacteroidales genetic markers.
Journal of Water and Health 09/2013; 11(3):430-42. DOI:10.2166/wh.2013.226 · 1.46 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: To mitigate the faecal contamination of drinking water sources and, consequently, to prevent waterborne disease outbreaks, an estimation of the contribution from different sources to the total faecal contamination at the raw water intake of a drinking water treatment plant is needed. The aim of this article was to estimate how much different sources contributed to the faecal contamination at the water intake in a drinking water source, Lake Rådasjön in Sweden. For this purpose, the fate and transport of faecal indicator Escherichia coli within Lake Rådasjön were simulated by a three-dimensional hydrodynamic model. The calibrated hydrodynamic model described the measured data on vertical temperature distribution in the lake well (the Pearson correlation coefficient was 0.99). The data on the E. coli load from the identified contamination sources were gathered and the fate and transport of E. coli released from these sources within the lake were simulated using the developed hydrodynamic model, taking the decay of the E. coli into account. The obtained modelling results were compared to the observed E. coli concentrations at the water intake. The results illustrated that the sources that contributed the most to the faecal contamination at the water intake in Lake Rådasjön were the discharges from the on-site sewers and the main inflow to the lake – the river Mölndalsån. Based on the modelling results recommendations for water producers were formulated. The study demonstrated that this modelling approach is a useful tool for estimating the contribution from different sources to the faecal contamination at the water intake of a drinking water treatment plant and provided decision-support information for the reduction of risks posed to the drinking water source.
Journal of Hydrology 08/2013; 497:15–23. DOI:10.1016/j.jhydrol.2013.05.044 · 3.05 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In biofilms, microbial activities form gradients of substrates and electron acceptors creating a complex landscape of microhabitats, often resulting in structured localization of the microbial populations present. To understand the dynamic interplay between and within these populations, quantitative measurements and statistical analysis of their localization patterns within the biofilms are necessary and adequate automated tools for such analyses are needed. We have designed and applied new methods for Fluorescence In Situ Hybridization (FISH) and digital image analysis on directionally dependent (anisotropic) multi-species biofilms. A sequential FISH approach allowed multiple populations to be detected in a biofilm sample. This was combined with an automated tool for vertical distribution analysis by generating in silico biofilm slices, and the recently developed Inflate algorithm for co-aggregation analysis of microbial populations in anisotropic biofilms. As a proof-of-principle, we show distinct stratification patterns of the ammonia-oxidizers Nitrosomonas oligotropha subclusters I and II and the nitrite-oxidizer Nitrospira sublineage I in three different types of wastewater biofilms, suggesting niche differentiation between the N. oligotropha subclusters, that could explain their coexistence in the same biofilms. Co-aggregation analysis showed that N. oligotropha subcluster II aggregated closer to Nitrospira than did N. oligotropha subcluster I in a pilot-plant nitrifying trickling filter (NTF) and a moving bed biofilm reactor (MBBR) but not in a full scale NTF, indicating important eco-physiological differences between these phylogenetically closely related subclusters. By using high-resolution quantitative methods, applicable to any multi-species biofilm in general, the ecological interactions of these complex ecosystems can be understood in more detail.
[Show abstract][Hide abstract] ABSTRACT: The faecal contamination of drinking water sources can lead to waterborne disease outbreaks. To estimate a potential risk for waterborne infections caused by faecal contamination of drinking water sources, knowledge of the pathogen concentrations in raw water is required. We suggest a novel approach to estimate pathogen concentrations in a drinking water source by using microbial source tracking data and fate and transport modelling. First, the pathogen (norovirus, Cryptosporidium, Escherichia coli O157/H7) concentrations in faecal contamination sources around the drinking water source Lake Rådasjön in Sweden were estimated for endemic and epidemic conditions using measured concentrations of faecal indicators (E. coli and Bacteroidales genetic markers). Afterwards, the fate and transport of pathogens within the lake were simulated using a three-dimensional coupled hydrodynamic and microbiological model. This approach provided information on the contribution from different contamination sources to the pathogen concentrations at the water intake of a drinking water treatment plant. This approach addresses the limitations of monitoring and provides data for quantitative microbial risk assessment (QMRA) and risk management in the context of faecal contamination of surface drinking water sources.
Journal of Water and Health 09/2012; 10(3):358-70. DOI:10.2166/wh.2012.183 · 1.46 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Background
The activated sludge process is one of the most widely used methods for treatment of wastewater and the microbial community composition in the sludge is important for the process operation. While the bacterial communities have been characterized in various activated sludge systems little is known about archaeal communities in activated sludge. The diversity and dynamics of the Archaea community in a full-scale activated sludge wastewater treatment plant were investigated by fluorescence in situ hybridization, terminal restriction fragment length polymorphism analysis and cloning and sequencing of 16S rRNA genes.
The Archaea community was dominated by Methanosaeta-like species. During a 15 month period major changes in the community composition were only observed twice despite seasonal variations in environmental and operating conditions. Water temperature appeared to be the process parameter that affected the community composition the most. Several terminal restriction fragments also showed strong correlations with sludge properties and effluent water properties. The Archaea were estimated to make up 1.6% of total cell numbers in the activated sludge and were present both as single cells and colonies of varying sizes.
The results presented here show that Archaea can constitute a constant and integral part of the activated sludge and that it can therefore be useful to include Archaea in future studies of microbial communities in activated sludge.
[Show abstract][Hide abstract] ABSTRACT: Ammonia-oxidizing bacteria (AOB) are essential for the nitrification process in wastewater treatment. To retain these slow-growing bacteria in wastewater treatment plants (WWTPs), they are often grown as biofilms, e.g., on nitrifying trickling filters (NTFs) or on carriers in moving bed biofilm reactors (MBBRs). On NTFs, a decreasing ammonium gradient is formed because of the AOB activity, resulting in low ammonium concentrations at the bottom and reduced biomass with depth. To optimize the NTF process, different ammonium feed strategies may be designed. This, however, requires knowledge about AOB population dynamics. Using fluorescence in situ hybridization (FISH) and confocal laser scanning microscopy, we followed biomass changes during 6 months, of three AOB populations on biofilm carriers. These were immersed in aerated MBBR tanks in a pilot plant receiving full-scale wastewater. Tanks were arranged in series, forming a wastewater ammonium gradient mimicking an NTF ammonium gradient. The biomass of one of the dominating Nitrosomonas oligotropha-like populations increased after an ammonium upshift, reaching levels comparable to the high ammonium control in 28 days, whereas a Nitrosomonas europaea-like population increased relatively slowly. The MBBR results, together with competition studies in NTF systems fed with wastewater under controlled ammonium regimes, suggest a differentiation between the two N. oligotropha populations, which may be important for WWTP nitrification.
[Show abstract][Hide abstract] ABSTRACT: The implementation of microbial fecal source tracking (MST) methods in drinking water management is limited by the lack of knowledge on the transport and decay of host-specific genetic markers in water sources. To address these limitations, the decay and transport of human (BacH) and ruminant (BacR) fecal Bacteroidales 16S rRNA genetic markers in a drinking water source (Lake Rådasjön in Sweden) were simulated using a microbiological model coupled to a three-dimensional hydrodynamic model. The microbiological model was calibrated using data from outdoor microcosm trials performed in March, August, and November 2010 to determine the decay of BacH and BacR markers in relation to traditional fecal indicators. The microcosm trials indicated that the persistence of BacH and BacR in the microcosms was not significantly different from the persistence of traditional fecal indicators. The modeling of BacH and BacR transport within the lake illustrated that the highest levels of genetic markers at the raw water intakes were associated with human fecal sources (on-site sewers and emergency sewer overflow). This novel modeling approach improves the interpretation of MST data, especially when fecal pollution from the same host group is released into the water source from different sites in the catchment.
[Show abstract][Hide abstract] ABSTRACT: Bacteria associated with seaweeds can both harm and benefit their hosts. Many seaweed species are known to produce compounds that inhibit growth of bacterial isolates, but the ecological role of seaweed metabolites for the associated bacterial community structure is not well understood. In this study the response of a colonizing bacterial community to the secondary metabolite (1,1,3,3-tetrabromo-2-heptanone) from the red alga Bonnemaisonia hamifera was investigated by using field panels coated with the metabolite at a range of concentrations covering those measured at the algal surface. The seaweed metabolite has previously been shown to have antibacterial effects. The metabolite significantly affected the natural fouling community by (i) altering the composition, (ii) altering the diversity by increasing the evenness and (iii) decreasing the density, as measured by terminal restriction fragment length polymorphism in conjunction with clone libraries of the 16S rRNA genes and by bacterial enumeration. No single major bacterial taxon (phylum, class) was particularly affected by the metabolite. Instead changes in community composition were observed at a more detailed phylogenetic level. This indicates a broad specificity of the seaweed metabolite against bacterial colonization, which is supported by the observation that the bacterial density was significantly affected at a lower concentration (0.02 μg cm⁻²) than the composition (1-2.5 μg cm⁻²) and the evenness (5 μg cm⁻²) of the bacterial communities. Altogether, the results emphasize the role of secondary metabolites for control of the density and structure of seaweed-associated bacterial communities.
[Show abstract][Hide abstract] ABSTRACT: Nitrogen removal in wastewater treatment is energy consuming and often carried out in biofilm nitrifying trickling filters (NTFs). We investigated nitrification potential and population dynamics of nitrifying bacteria in pilot-plant NTFs fed with full-scale plant wastewater with high (8-9 mg NH(4)(+)l(-1)) or low (<0.5mg NH(4)(+)l(-1)) ammonium concentrations. After ammonium shifts, nitrification potentials stabilized after 10-43 days depending on feed regime. An NTF fed with 3 days of high, and 4 days of low load per week reached a high nitrification potential, whereas a high load for 1 day a week gave a low potential. Nitrosomonas oligotropha dominated the AOB and changes in nitrification potentials were not explained by large population shifts to other AOBs. Although nitrification potentials were generally correlated with the relative amounts of AOB and NOB, this was not always the case. Ammonium feed strategies can be used to optimize wastewater treatment performance.