Biology subjects

Seviour, T. W.

Publications and source records attributed to Seviour, T. W..

4 recordsLinked to original sources

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

Isolation of a putative S-layer protein from anammox biofilm extracellular matrix using ionic liquid extraction

Anaerobic ammonium oxidation (anammox) performing bacteria self-assemble into compact biofilms by expressing extracellular polymeric substances (EPS). Anammox EPS are poorly characterized, largely due to their low solubility in typical aqueous solvents. Pronase digestion achieved 19.5 {+/-} 0.9 and 41.4 {+/-} 1.4% (w/w) more solubilization of Candidatus Brocadia sinica-enriched anammox granules than DNase and amylase respectively. Nuclear magnetic resonance profiling of the granules confirmed that proteins were dominant. We applied ionic liquid (IL) 1-ethyl-3-methylimidazolium acetate and N,N- dimethylacetamide (EMIM-Ac/DMAc) mixture to extract the major structural proteins. Further treatment by anion exchange chromatography isolated homologous S/T-rich proteins BROSI_A1236 and UZ01_01563, which were major components of the extracted proteins and sequentially highly similar to putative anammox surface-layer (S-layer) protein KUSTD1514. EMIM-Ac/DMAc extraction enriched for these putative S-layer proteins against all other major proteins, along with six monosaccharides (i.e. arabinose, xylose, rhamnose, fucose, galactose and mannose). The sugars, however, contributed <0.5% (w/w) of total granular biomass, and were likely co-enriched as glycoprotein appendages. This study demonstrates that S-layer proteins are major constituents of anammox biofilms and can be isolated from the matrix using an ionic liquid-based solvent.

bioengineering↗

bioRxiv2019

The biofilm matrix scaffold of Pseudomonas species consists of non-canonically base paired extracellular DNA and RNA

While extracellular DNA (eDNA) is recognized as a critical biofilm matrix component, it is not understood how it contributes to biofilm function. Here we isolate eDNA from Pseudomonas biofilms using ionic liquids, and discover that its key biophysical signatures, i.e. fluid viscoelasticity, nucleic acid conformation, and temperature and pH dependencies of gel to solution transitions, are maintained. Solid-state analysis of isolated eDNA, as a proxy for eDNA structure in biofilms, revealed non-canonical Hoogsteen base pairs, triads or tetrads involving guanine and thymine or uracil. These were less abundant in chromosomal DNA and undetected as eDNA underwent gel-sol transition. Purine-rich RNA was present in the eDNA network, which potentially enables eDNA to be the main cross-linking exopolymer in the matrix through non-canonical nucleobase interactions. Our study suggests that Pseudomonas assemble extracellular DNA and RNA into a network with viscoelastic properties, which underpin their persistence and spreading, and may aid the development of more effective controls for biofilm-associated infections.

biochemistry↗

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↗