Biology subjects

Wuertz, S.

Publications and source records attributed to Wuertz, S..

36 records · Page 2Linked to original sources

bioRxiv2021

Global warming readiness: Feasibility of enhanced biological phosphorus removal from wastewater at 35oC

Recent research has shown enhanced biological phosphorus removal (EBPR) from municipal wastewater at warmer temperatures around 30{degrees}C to be stable in both laboratory-scale reactors and full-scale treatment plants. In the context of a changing climate, the feasibility of EBPR at even higher temperatures is of interest. We operated two lab-scale EBPR sequencing batch reactors with alternating anaerobic and aerobic phases for over 300 days at 30{degrees}C and 35{degrees}C, respectively, and followed the dynamics of the communities of phosphorus accumulating organisms (PAOs) and competing glycogen accumulating organisms (GAOs) using a combination of 16S rRNA gene metabarcoding, quantitative PCR and fluorescent in-situ hybridization analyses. Stable and nearly complete P removal was achieved at 30{degrees}C; similarly, long term P removal was stable at 35{degrees}C with effluent PO43--P concentrations < 0.5 mg/L on half of all monitored days. Diverse and abundant Ca. Accumulibacter amplicon sequence variants were closely related to those found in temperate environments, suggesting that EBPR at this temperature does not require a highly specialized PAO community. The slow-feeding strategy used effectively limited the carbon uptake rates of GAOs, allowing PAOs to outcompete GAOs at both temperatures. Candidatus Competibacter was the main GAO, along with cluster III Defluviicoccus members. These organisms withstood the slow-feeding regime, suggesting that their bioenergetic characteristics of carbon uptake differ from those of their tetrad-forming relatives. This specific lineage of GAOs warrants further study to establish how complete P removal can be maintained. Comparative cycle studies at two temperatures for each reactor revealed higher activity of Ca. Accumulibacter when the temperature was increased from 30{degrees}C to 35{degrees}C, suggesting that the stress was a result of the higher carbon (and/or P) metabolic rates of PAOs and GAOs, the resultant carbon deficiency, and additional community competition. An increase in the TOC to PO43--P ratio (from 25:1 to 40:1) effectively eased the carbon deficiency and benefited the proliferation of PAOs. In general, the slow-feeding strategy and sufficiently high carbon input benefited a high and stable EBPR at elevated temperature and represent basic conditions for full-scale applications.

microbiology↗

bioRxiv2020

Press xenobiotic disturbance favors deterministic assembly with a shift in function and structure of bacterial communities in sludge bioreactors

Disturbance is thought to affect community assembly mechanisms, which in turn shape community structure and the overall function of the ecosystem. Here, we tested the effect of a continuous (press) xenobiotic disturbance on the function, structure, and assembly of bacterial communities within a wastewater treatment system. Two sets of four-liter sequencing batch reactors were operated in triplicate with and without the addition of 3-chloroaniline for a period of 132 days, following 58 days of acclimation after inoculation with sludge from a full-scale treatment plant. Temporal dynamics of bacterial community structure were derived from 16S rRNA gene amplicon sequencing. Community function, structure and assembly differed between press disturbed and undisturbed reactors. Temporal partitioning of assembly mechanisms via phylogenetic and non-phylogenetic null modelling analysis revealed that deterministic assembly prevailed for disturbed bioreactors, while the role of stochastic assembly was stronger for undisturbed reactors. Our findings are relevant because research spanning various disturbance types, environments and spatiotemporal scales is needed for a comprehensive understanding of the effects of press disturbances on assembly mechanisms, structure, and function of microbial communities. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=110 SRC="FIGDIR/small/341966v1_ufig1.gif" ALT="Figure 1"> View larger version (42K): org.highwire.dtl.DTLVardef@115e7d3org.highwire.dtl.DTLVardef@126da82org.highwire.dtl.DTLVardef@1d3c4caorg.highwire.dtl.DTLVardef@1cb2ea_HPS_FORMAT_FIGEXP M_FIG C_FIG

microbiology↗

bioRxiv2020

A 180 My-old female-specific genome region in sturgeon reveals the oldest known vertebrate sex determining system with undifferentiated sex chromosomes

Several hypotheses explain the prevalence of undifferentiated sex chromosomes in poikilothermic vertebrates. Turnovers change the master sex determination gene, the sex chromosome or the sex determination system (e.g. XY to WZ). Jumping master genes stay main triggers but translocate to other chromosomes. Occasional recombination (e.g. in sex-reversed females) prevents sex chromosome degeneration. Recent research has uncovered conserved heteromorphic or even homomorphic sex chromosomes in several clades of non-avian and non-mammalian vertebrates. Sex determination in sturgeons (Acipenseridae) has been a long-standing basic biological question, linked to economical demands by the caviar-producing aquaculture. Here, we report the discovery of a sex-specific sequence from sterlet (Acipenser ruthenus). Using chromosome-scale assemblies and pool-sequencing, we first identified a ~16 kb female-specific region. We developed a PCR-genotyping test, yielding female-specific products in six species, spanning the entire phylogeny with the most divergent extant lineages (A. sturio, A. oxyrinchus vs. A. ruthenus, Huso huso), stemming from an ancient tetraploidization. Similar results were obtained in two octoploid species (A. gueldenstaedtii, A. baerii). Conservation of a female-specific sequence for a long period, representing 180 My of sturgeon evolution, and across at least one polyploidization event, raises many interesting biological questions. We discuss a conserved undifferentiated sex chromosome system with a ZZ/ZW-mode of sex determination and potential alternatives.

evolutionary biology↗

bioRxiv2020

Integrative systems approach reveals dynamics of microbiome-metal-ion axis in mesocosms representing tropical urban freshwater canal ecosystem

Freshwater ecosystems of tropical urban canals systems (TrUCS), are highly dynamic and experience constant pressures from interspersed effects of land-use and rain. The dynamic nature of TrUCS ecosystems presents a unique opportunity to unravel the signature interactions between the macro-organisms (top-down), sedimentary microbial communities (SedMICs), their functioning and the geochemical environment (bottom-up). A systems level understanding of the molecular and mechanistic basis of the highly dynamic behaviour that leads to specific ecosystem outcomes, is currently lacking. Therefore, a research framework to identify the direct link between top-down and bottom-up ecological effects on SedMICs in a highly dynamic urban canal sedimentary system is needed. Here, we present a framework of integrated multi-dimensional data across system-level biotic and abiotic ecological descriptors, such as environmental variables and active SedMICs. We followed the ecosystem shifts after a natural disturbance (rain) in two different anthropogenic disturbance (land-use) regimes. Shifts in profiles of metabolically active community were conserved across different land-use types, indicating resilience to perturbation is an intrinsic property of the TrUCs ecosystem. Three distinct phases, which were dominated sequentially by autotrophy, anoxic-heterotrophy and oxic-heterotrophy, were identified within these shifts. The first two phases were influenced by the bottom-up effects of specific metal-ion combinations of nitrates and sulfates with magnesium, aluminum and iron, and the third phase was triggered by top-down influences of bioturbation. This generalized systems-level approach, which provides an ecosystem-centric understanding of TrUCS and integrates them in sustainable management practices, can also be extended to other freshwater ecosystems.

ecology↗

bioRxiv2020

Denitrification kinetics indicates nitrous oxide uptake is unaffected by electron competition in Accumulibacter

Denitrifying phosphorus removal is a cost and energy efficient treatment technology that relies on polyphosphate accumulating organisms (DPAOs) utilizing nitrate or nitrite as terminal electron acceptor. Denitrification is a multistep process and many organisms do not possess the complete pathway, leading to the accumulation of intermediates such as nitrous oxide (N2O), a potent greenhouse gas and ozone depleting substance. Candidatus Accumulibacter organisms are prevalent in denitrifying phosphorus removal processes and, according to genomic analyses, appear to vary in their denitrification abilities based on their lineage. Yet, denitrification kinetics and nitrous oxide accumulation by Accumulibacter after long-term exposure to either nitrate or nitrite as electron acceptor have never been compared. We investigated the preferential use of the nitrogen oxides involved in denitrification and nitrous oxide accumulation in two enrichments of Accumulibacter and a competitor - the glycogen accumulating organism Candidatus Competibacter. A metabolic model was modified to predict phosphorus removal and denitrification rates when nitrate, nitrite or N2O were added as electron acceptors in different combinations. Unlike previous studies, no N2O accumulation was observed for Accumulibacter in the presence of multiple electron acceptors. Electron competition did not affect denitrification kinetics or N2O accumulation in Accumulibacter or Competibacter. Despite the presence of sufficient internal storage polymers (polyhydroxyalkanoates, or PHA) as energy source for each denitrification step, the extent of denitrification observed was dependent on the dominant organism in the enrichment. Accumulibacter showed complete denitrification and N2O utilization, whereas for Competibacter denitrification was limited to reduction of nitrate to nitrite. These findings indicate that DPAOs can contribute to lowering N2O emissions in the presence of multiple electron acceptors under partial nitritation conditions.

bioengineering↗

bioRxiv2020

Analysis procedures for assessing recovery of high quality, complete, closed genomes from Nanopore long read metagenome sequencing

New long read sequencing technologies offer huge potential for effective recovery of complete, closed genomes from complex microbial communities. Using long read (MinION) obtained from an ensemble of activated sludge enrichment bioreactors, we 1) describe new methods for validating long read assembled genomes using their counterpart short read metagenome assembled genomes; 2) assess the influence of different correction procedures on genome quality and predicted gene quality and 3) contribute 21 new closed or complete genomes of community members, including several species known to play key functional roles in wastewater bioprocesses: specifically microbes known to exhibit the polyphosphate- and glycogen-accumulating organism phenotypes (namely Accumulibacter and Dechloromonas, and Micropruina and Defluviicoccus, respectively), and filamentous bacteria (Thiothrix) associated with the formation and stability of activated sludge flocs. Our findings further establish the feasibility of long read metagenome-assembled genome recovery, and demonstrate the utility of parallel sampling of moderately complex enrichments communities for recovery of genomes of key functional species relevant for the study of complex wastewater treatment bioprocesses.

bioinformatics↗

bioRxiv2020

Species level enrichment of AnAOB and associated growth morphology under the effect of key metabolites

Nineteen anaerobic ammonium oxidizing bacteria (AnAOB) species have been identified, yet the environmental factors that select for each species within a specialized ecological niche have not been described. We enriched AnAOB from a single inoculum under standard enrichment conditions (reactor R1) with stepwise increase in nitrite and ammonia concentration, nitric oxide (NO) supplementation (reactor R2), or with complex organic carbon using wastewater collected from mainstream wastewater treatment facility (reactor R3). AnAOB were enriched up to 80%, 90% and 50% relative abundance in R1, R2 and R3 respectively. Candidatus Brocadia caroliniensis predominated in all reactors, but a shift towards Ca. Brocadia sinica was consistently observed with increasing ammonium and nitrite concentrations beyond 270 mg NH4-N L-1 and 340 mg NO2-N L-1, respectively. In the presence of NO, growth of heterotrophs were inhibited, and Ca. Jettenia could coexist with Ca. B. caroliniensis before diminishing when nitrite increased to 160 mg NO2-N L-1. In contrast, supplementation of organic carbon led to the emergence of heterotrophic communities that coevolved with Ca. B. caroliniensis. Ca. B. caroliniensis and Ca. Jettenia preferentially form biofilms on reactor surfaces, whereas Ca. Brocadia sinica forms granules in suspension. Our results thus indicate that multiple AnAOB species co-exist and occupy sub-niches in anaerobic ammonium oxidation reactors, that the dominant population can be reversibly shifted by, for example, changing the nitrogen load (i.e. high nitrite concentration favors Ca. Brocadia caroliniensis), and that speciation has implications for wastewater process design, with the optimum cell immobilization strategy (i.e. carriers vs granules) dependent on which species dominates. IMPORTANCEThis study demonstrates how to reversibly and predictably shift dominant anammox population using operating parameters (e.g. high nitrite concentration favours Ca. Brocadia sinica), and that species selection has implications for wastewater process design, illustrated here in terms of dependence of optimum cell immobilization strategy (i.e. carriers vs granules) on which species dominates. The research informs the characterization of AnAOBs at species level as well process design and control strategies targeting Anammox species population dynamics in full scale waste water treatment systems.

ecology↗

bioRxiv2019

Press disturbance unveils different community structure, function and assembly of bacterial taxa and functional genes in mesocosm-scale bioreactors

Sustained perturbations, or press disturbances, are of interest in microbial ecology as they can drive systems to alternative stable states. Here, we tested the effect of a sustained doubling of organic carbon loading on structure, assembly and function of bacterial communities. Two sets of replicate 5-liter sequencing batch reactors were operated at two different organic carbon loading levels (323 and 629 mg COD L-1) for a period of 74 days, following 53 days of acclimation after inoculation with sludge from a full-scale treatment plant. Temporal dynamics of community taxonomic and functional gene structure were derived from metagenomics and 16S rRNA gene metabarcoding data. Assembly mechanisms were assessed through a mathematical null model on the effective bacterial turnover expressed as a proportion of total bacterial diversity. Disturbed reactors exhibited different community function, structure and assembly compared to the undisturbed reactors. Bacterial taxa and functional genes showed dissimilar alpha-diversity and community assembly patterns. Deterministic assembly mechanisms were generally stronger in disturbed reactors, associated with common taxa. Stochastic assembly was more important for functional genes and was driven by rare genes. We urge caution when assessing microbial community assembly mechanisms, as results can vary depending on the approach.

microbiology↗

bioRxiv2019

Sustained organic loading perturbation inhibits nitrite oxidation in bioreactors, unveiling variable resistance and resilience of nitrification and nitrifiers

Sustained disturbances are relevant for environmental biotechnology as they can lead to alternative stable states in a system that may not be reversible. Here, we tested the effect of a sustained organic loading alteration (food-to-biomass ratio, F:M, and carbon-to-nitrogen ratio, C:N) on activated sludge bioreactors, focusing on the stability of nitrification and nitrifiers. Two sets of replicate 5-liter sequencing batch reactors were operated at different, low and high, F:M (0.19-0.36 mgCOD/mgTSS/d) and C:N (3.5-6.3 mgCOD/mgTKN) conditions for a period of 74 days, following 53 days of sludge acclimation. Recovery and resilience were tested during the last 14 days by operating all reactors at low F:M and C:N (henceforth termed F:M-C:N). Stable nitrite accumulation (77%) was achieved through high F:M-C:N loading with a concurrent reduction in the abundance of Nitrospira. Subsequently, only two of the three reactors experiencing a switch back from high to low F:M-C:N recovered the nitrite oxidation function, with an increase in Nitrobacter as the predominant NOB, without a recovery of Nitrospira. The AOB community was more diverse, resistant and resilient than the NOB community. We showed that functional recovery and resilience can vary across replicate reactors, and that nitrification recovery need not coincide with a return to the initial nitrifying community structure.

microbiology↗

bioRxiv2019

Evaluation of extraction solvents for untargeted metabolomics analysis of enrichment reactor cultures performing enhanced biological phosphorus removal (EBPR)

IntroductionThe extraction solvent mixtures were optimized for untargeted metabolomics analysis of microbial communities from two laboratory scale activated sludge reactors performing enhanced biological phosphorus removal (EBPR).\n\nObjectiveTo develop a robust and simple analytical protocol to analyse microbial metabolomics from EBPR bioreactors.\n\nMethodsExtra- and intra-cellular metabolites were extracted using five methods and analysed by ultraperformance liquid chromatography mass spectrometry (UPLC-MS).\n\nResultsThe optimal extraction method was biomass specific and methanol:water (1:1 v/v) and methanol:chloroform:water (2:2:1 v/v) were chosen, respectively, for each of the two different bioreactors.\n\nConclusionOur approach provides direct surveys of the metabolic state of PAO-enriched EBPR communities, showing that extraction methods should be carefully tailored to the microbial community under study

systems biology↗

bioRxiv2019

Trait-based life-history strategies explain succession scenario for complex bacterial communities under varying disturbance

Trait-based approaches are increasingly gaining importance in community ecology, as a way of finding general rules for the mechanisms driving changes in community structure and function under the influence of perturbations. Frameworks for life-history strategies have been successfully applied to describe changes in plant and animal communities upon disturbance. To evaluate their applicability to complex bacterial communities, we operated replicated wastewater treatment bioreactors for 35 days and subjected them to eight different disturbance frequencies of a toxic pollutant (3-chloroaniline), starting with a mixed inoculum from a full-scale treatment plant. Relevant ecosystem functions were tracked and microbial communities assessed through metagenomics and 16S rRNA gene sequencing. Combining a series of ordination, statistical and network analysis methods, we associated different life-history strategies with microbial communities across the disturbance range. These strategies were evaluated using tradeoffs in community function and genotypic potential, and changes in bacterial genus composition. We further compared our findings with other ecological studies and adopted a semi-quantitative CSR (competitors, ruderals, stress-tolerants) classification. The framework reduces complex datasets of microbial traits, functions, and taxa into ecologically meaningful components to help understand the system response to disturbance, and hence represents a promising tool for managing microbial communities. Originality-Significance StatementThis study establishes, for the first time, CSR life-history strategies in the context of bacterial communities. This framework is explained using community aggregated traits in an environment other than soil, also a first, using a combination of ordination methods, network analysis, and genotypic information from shotgun metagenomics and 16S rRNA gene amplicon sequencing.

microbiology↗

bioRxiv2018

Environmental enrichment on neural plasticity in juvenile Baltic sturgeon (Acipenser oxyrinchus)

Conservation biologists have long emphasized the importance of environmental enrichment in hatcheries which main objective is restocking. In this study, we evaluated the impact that long-term exposure of environmental enrichment in an artificial river section (surface water, ambient light and temperature) has on neural plasticity in juvenile Baltic sturgeons (Acipenser oxyrinchus) in comparison to fish that were reared in glass-fiber tanks in a recirculation system (aquaculture control group) under constant light and temperature conditions and an intermediate group reared in glass-fiber tanks with ambient water and natural photoperiod and temperature fluctuation. All expositions were carried out in triplicate. From the three markers reported to indicate neural plasticity, only an up-regulation of neurod1 in the forebrain of Baltic sturgeon (A. oxyrinchus) reared in enriched environment was observed in comparison to the semi-natural group and to the aquaculture (control) group. The two other markers (brain-derived neurotropic factor (bdnf), and proliferating cell nuclear antigen (pcna) did not reveal any significant differences between the groups. In conclusion, only minor effects of environmental enrichment on neuroplasticity were observed here.

animal behavior and cognition↗

bioRxiv2018

Does juvenile Baltic sturgeon (Acipenser oxyrinchus) smell the enemy?

Atlantic sturgeon (Acipenser oxyrinchus), also known as Baltic sturgeon, is considered extinct in German waters. Fish-rearing for conservation purposes still relies on classical hatchery technology producing fish not well suited for facing life in the wild, lacking behavioural skills such as foraging or anti-predation. Predation is hence a major source of mortality in newly stocked individuals. The aim of this study was to evaluate if naive Baltic sturgeon juveniles were able to smell and recognize a common predator, sander (Sander lucioperca). Over a period of 30 days, three tanks from each group of Baltic sturgeon were attached to a rearing tank with sander (sander unit) and, as a control, carp (carp unit). Morphology of the dorsal scutes, distribution within the tank, stress (glucose, lactate and cortisol) and gene expression of brain plasticity and cognition were studied in comparison to the control group (carp unit). No significant differences were observed in any of the parameters measured. Thus, we conclude that naive Baltic sturgeon is not able to innately recognize potential predators and future studies should focus on implementing predator odour together with chemical alarm substances.

animal behavior and cognition↗

bioRxiv2018

How to improve foraging efficiency for restocking measures of juvenile Baltic sturgeon (Acipenser oxyrinchus)

Atlantic sturgeon (Acipenser oxyrinchus), also known as Baltic sturgeon, is considered missing or extinct in German waters. Current conservation efforts focus on re-stocking activities, but classical hatchery rearing may reduce the fitness of the respective juveniles. In this study, we evaluated if foraging efficiency can be improved by short term training. Over a period of 14 d, we kept individuals of the training group in a raceway and fed them chironomids buried in a small sand spot to stimulate benthic feeding behavior while fish of the control group were fed in tanks without substrate. Thereafter, each fish was transferred to a raceway entirely covered with sand. For feeding, chironomids were randomly buried in the sand. During the first 7 days, trained fish recovered the feed significantly faster than untrained fish of the control group. Gene expression revealed an up-regulation in neurod1 in all brain regions after 14 d of training. Thus, this study suggests that foraging efficiency can be improved through short-time training thus improve fitness upon restocking into the wild.

animal behavior and cognition↗

bioRxiv2018

Improving recovery of member genomes from enrichment reactor microbial communities using MinION--based long read metagenomics

New long read sequencing technologies offer huge potential for effective recovery of complete, closed genomes. While much progress has been made on cultured isolates, the ability of these methods to recover genomes of member taxa in complex microbial communities is less clear. Here we examine the ability of long read data to recover genomes from enrichment reactor metagenomes. Such modified communities offer a moderate level of complexity compared to the source communities and so are realistic, yet tractable, systems to use for this problem. We sampled an enrichment bioreactor designed to target anaerobic ammonium-oxidising bacteria (AnAOB) and sequenced genomic DNA using both short read (Illumina 301bp PE) and long read data (MinION Mk1B) from the same extraction aliquot. The community contained 23 members, of which 16 had genome bins defined from an assembly of the short read data. Two distinct AnAOB species from genus Candidatus Brocadia were present and had complete genomes, of which one was the most abundant member species in the community. We can recover a 4Mb genome, in 2 contigs, of long read assembled sequence that is unambiguously associated with the most abundant AnAOB member genome. We conclude that obtaining near closed, complete genomes of members of low-medium microbial communities using MinION long read sequence is feasible.

genomics↗

bioRxiv2018

Frequency of disturbance alters diversity, function, and underlying assembly mechanisms of complex bacterial communities

Disturbance is known to affect ecosystem structure, but predicting its outcomes remains elusive. Similarly, community diversity is believed to relate to ecosystem functions, yet the underlying mechanisms are poorly understood. Here, we tested the effect of disturbance on the structure, diversity, and ecosystem function of complex microbial communities within an engineered system. We carried out a microcosm experiment where activated sludge bioreactors were subjected to a range of disturbances in the form of a toxic pollutant, tracking changes in ecosystem function. Microbial communities were assessed by combining distance-based methods, general linear multivariate models, -diversity indices, and null model analyses on metagenomics and 16S rRNA gene amplicon data. A stronger temporal decrease in -diversity at the extreme, undisturbed and press-disturbed, ends of the disturbance range led to a hump-backed pattern, with the highest diversity found at intermediate levels of disturbance. Undisturbed and press-disturbed levels displayed the highest community and functional similarity across replicates, suggesting deterministic processes were dominating. The opposite was observed amongst intermediately disturbed levels, indicating stronger stochastic assembly mechanisms. Tradeoffs were observed in community function between organic carbon removal and both nitrification and biomass productivity, as well as between diversity and these functions. Hence, not every ecosystem function was favoured by higher community diversity. Our results show that the assessment of changes in diversity, along with the underlying stochastic-niche assembly processes, is essential to understanding the impact of disturbance in complex microbial communities.\n\nImportanceMicrobes drive the Earths biogeochemical cycles, yet how they respond to perturbations like anthropogenic pollutants is poorly understood. As human impact continues to increase worldwide, foreseeing how disturbances will affect microbial communities and the ecosystem services they provide is key for ecosystem management and conservation efforts. Employing laboratory-scale wastewater treatment bioreactors, this study shows that changes in community diversity accompany variations in the underlying deterministic-stochastic assembly mechanisms. Disturbances could promote stochastic community structuring, which despite harboring higher diversity could lead to variable overall function, possibly explaining why after similar perturbations the process outcome differs. A conceptual framework, termed the intermediate stochasticity hypothesis is proposed to theoretically predict bacterial community shifts in diversity and ecosystem function, given a range of possible disturbance types, in a well-replicated time-series experiment. Our findings are relevant for managing complex microbial systems, which could display similar responses to disturbance, like oceans, soils or the human gut.

microbiology↗

bioRxiv2018

Apparent oxygen half saturation constant for nitrifiers: genus specific, inherent physiological property, or artefact of colony morphology?

We report that a single Nitrospira sublineage I OTU performs nitrite oxidation in several full-scale domestic wastewater treatment plants (WWTPs) in the tropics (29-31 {degrees}C). Contrary to the prevailing theory for the relationship between nitrite oxidizing bacteria (NOB) and ammonia oxidizing bacteria (AOB), members of the Nitrospira sublineage I OTU had an apparent half saturation coefficient, Ks(app) lower than that of the full-scale domestic activated sludge cohabitant AOB (0.09 {+/-} 0.02 g O2 m-3 versus 0.3 {+/-} 0.03 g O2 m-3). Paradoxically, NOB may thus thrive under conditions of low oxygen supply. Low dissolved oxygen (DO) conditions could enrich for and high aeration inhibit the NOB in a long-term lab-scale reactor. The relative abundance of Nitrospira gradually decreased with increasing DO until it was washed out. Nitritation was sustained even after the DO was lowered subsequently. Based on 3D-fluorescence in situ hybridization (FISH) image analysis, the morphologies of AOB and NOB microcolonies responded to DO levels in accordance with their apparent oxygen half saturation constant Ks(app). When exposed to the same oxygenation level, NOB formed densely packed spherical clusters with a low surface area-to-volume ratio compared to the Nitrosomonas-like AOB clusters, which maintained a porous and non-spherical morphology. Microcolony morphology is thus a way for AOB and NOB to regulate oxygen exposure and sustain the mutualistic interaction. However, short-term high DO exposure can select for AOB and against NOB in full-scale domestic WWTPs and such population dynamics depend on which specific AOB and NOB species predominate under given environmental conditions.

systems biology↗

bioRxiv2017

Draft Genome Sequence Of A Candidatus Brocadia Bacterium Enriched From Tropical-Climate Activated Sludge

We present the draft genome of an anaerobic ammonium-oxidizing (anammox) bacterium, cluster III Candidatus Brocadia, which was enriched in an anammox reactor. A 3.2 Mb genome sequence comprising 168 contigs was assembled, in which 2,765 gene-coding regions, 47 tRNAs, and 5S, 16S and 23S ribosomal RNAs were annotated. No evidence for the presence of a nitric oxide-forming nitrite reductase was found.

microbiology↗