Biofilm formation inhibition and dispersal of multi-species communities containing ammonia-oxidising bacteria.

Despite considerable research, the biofilm-forming capabilities of Nitrosomonas europaea are poorly understood for both mono and mixed-species communities. This study combined biofilm assays and molecular techniques to demonstrate that N. europaea makes very little biofilm on its own, and relies on the activity of associated heterotrophic bacteria to establish a biofilm. However, N. europaea has a vital role in the proliferation of mixed-species communities under carbon-limited conditions, such as in drinking water distribution systems, through the provision of organic carbon via ammonia oxidation. Results show that the addition of nitrification inhibitors to mixed-species nitrifying cultures under carbon-limited conditions disrupted biofilm formation and caused the dispersal of pre-formed biofilms. This dispersal effect was not observed when an organic carbon source, glucose, was included in the medium. Interestingly, inhibition of nitrification activity of these mixed-species biofilms in the presence of added glucose resulted in increased total biofilm formation compared to controls without the addition of nitrification inhibitors, or with only glucose added. This suggests that active AOB partially suppress or limit the overall growth of the heterotrophic bacteria. The experimental model developed here provides evidence that ammonia-oxidising bacteria (AOB) are involved in both the formation and maintenance of multi-species biofilm communities. The results demonstrate that the activity of the AOB not only support the growth and biofilm formation of heterotrophic bacteria by providing organic carbon, but also restrict and limit total biomass in mixed community systems

Predation by Bdellovibrio bacteriovorus significantly reduces viability and alters the microbial community composition of activated sludge flocs and granules

© FEMS 2017. All rights reserved. We recently isolated and characterised a predatory Bdellovibrio bacteriovorus strain from activated sludge (Ulu Pandan Water Reclamation Plant, Singapore), and this strain, B. bacteriovorus UP, was able to prey upon a broad spectrum of bacterial isolates from the activated sludge when grown as planktonic cells or as biofilms. Here, we have tested the effect of Bdellovibrio predation on floccular and granular sludge to determine if the spatial organisation, loosely or tightly aggregated communities, was protective from predation. The effect of predation was assessed using a combination of biomass quantification, cellular activity measurement and microscopic image analysis to determine community viability. Additionally, changes in the microbial communities due to predation by B. bacteriovorus UP were analysed through total RNA sequencing. Predation led to a significant reduction in microbial activity and total biomass for both floccular and granular sludge communities. Predation was also associated with significant changes in the microbial community composition in both communities, with > 90% of the community members reduced in relative abundance after 24 h. Of those community members, the dominant organisms, such as Proteobacteria and Bacteroidetes, were the most affected phylotypes. This suggests that predatory bacteria, which display indiscriminant feeding, could significantly shift the species composition and thus, may disturb the operational performance of wastewater treatment systems

Biofilm formation inhibition and dispersal of multi-species communities containing ammonia-oxidising bacteria

© 2019, The Author(s). Despite considerable research, the biofilm-forming capabilities of Nitrosomonas europaea are poorly understood for both mono and mixed-species communities. This study combined biofilm assays and molecular techniques to demonstrate that N. europaea makes very little biofilm on its own, and relies on the activity of associated heterotrophic bacteria to establish a biofilm. However, N. europaea has a vital role in the proliferation of mixed-species communities under carbon-limited conditions, such as in drinking water distribution systems, through the provision of organic carbon via ammonia oxidation. Results show that the addition of nitrification inhibitors to mixed-species nitrifying cultures under carbon-limited conditions disrupted biofilm formation and caused the dispersal of pre-formed biofilms. This dispersal effect was not observed when an organic carbon source, glucose, was included in the medium. Interestingly, inhibition of nitrification activity of these mixed-species biofilms in the presence of added glucose resulted in increased total biofilm formation compared to controls without the addition of nitrification inhibitors, or with only glucose added. This suggests that active AOB partially suppress or limit the overall growth of the heterotrophic bacteria. The experimental model developed here provides evidence that ammonia-oxidising bacteria (AOB) are involved in both the formation and maintenance of multi-species biofilm communities. The results demonstrate that the activity of the AOB not only support the growth and biofilm formation of heterotrophic bacteria by providing organic carbon, but also restrict and limit total biomass in mixed community systems

Loss of the acetate switch in <i>Vibrio vulnificus</i> enhances predation defence against <i>Tetrahymena pyriformis</i>.

Vibrio vulnificus is an opportunistic human pathogen and autochthonous inhabitant of coastal marine environments, where the bacterium is under constant predation by heterotrophic protists or protozoans. As a result of this selection pressure, genetic variants with anti-predation mechanisms are selected for and persist in the environment. Such natural variants may also be pathogenic to animal or human hosts, making it important to understand these defence mechanisms. To identify anti-predator strategies, thirteen V. vulnificus strains of different genotypes isolated from diverse environments were exposed to predation by the ciliated protozoan, Tetrahymena pyriformis, and only strain ENV1 was resistant to predation. Further investigation of the cell-free supernatant showed that ENV1 acidifies the environment by the excretion of organic acids, which is toxic to T. pyriformis. As this predation resistance was dependent on the availability of iron, transcriptomes of V. vulnificus in iron-replete and iron-deplete conditions were compared. This analysis revealed that ENV1 ferments pyruvate and the resultant acetyl-CoA leads to acetate synthesis under aerobic conditions, a hallmark of overflow metabolism. The anaerobic respiration global regulator, arcA, was upregulated when iron was available. An ΔarcA deletion mutant of ENV1 accumulated less acetate and importantly, was sensitive to grazing by T. pyriformis. Based on the transcriptome response and quantification of metabolites, we conclude that ENV1 has adapted to overflow metabolism and has lost a control switch that shifts metabolism from acetate excretion to acetate assimilation, enabling it to excrete acetate continuously. We show that overflow metabolism and the acetate switch contribute to prey-predator interactions. Importance Bacteria in the environment, including Vibrio spp., interact with protozoan predators. To defend against predation, bacteria evolve anti-predator mechanisms ranging from changing morphology, biofilm formation and secretion of toxins or virulence factors. Some of these adaptations may result in strains that are pathogenic to humans. Therefore, it is important to study predator defence strategies of environmental bacteria. V. vulnificus thrives in coastal waters and infects humans. Very little is know about the defence mechanisms V. vulnificus expresses against predation. Here we show that a V. vulnificus strain (ENV1) has rewired the central carbon metabolism enabling the production of excess organic acid that is toxic to the protozoan predator, T. pyriformis. This is a previously unknown mechanism of predation defence that protects against protozoan predators

Fabrication of high aspect ratio tungsten nanostructures on ultrathin c-Si membranes for extreme UV applications

International audienc

Biofouling control in reverse osmosis by nitric oxide treatment and its impact on the bacterial community

© 2018 The Authors Recent discoveries regarding the regulation of the biofilm life cycle by bacterial signaling systems have identified novel strategies for manipulation of biofilm development to control the biofouling of membrane-based water purification systems. Nitric oxide (NO) signaling has been shown to induce dispersal of a wide range of single- and multi-species biofilms. However, the impact of NO-mediated biofilm dispersal on the taxa composition of natural communities as well as the potential selection for non-responding community members have rarely been addressed. Here, we investigated the effect of diethylenetriamine (DETA) NONOate, an NO donor with a long half-life, on biofilm dispersal of a bacterial community responsible for membrane biofouling to address this question. The biofilm of a complex community from a fouled industrial reverse osmosis (RO) membrane was dispersed over 50% by 500 μM of DETA NONOate treatment in a continuous flow system. Once-daily treatment with DETA NONOate in a laboratory-scale RO system demonstrated its anti-biofouling effect by delaying the transmembrane pressure increase during constant-flux filtration. Characterization of the bacterial communities of dispersed cells and remaining biofilm cells using a 16S Illumina MiSeq metabarcoding approach demonstrated that biofilm dispersal by DETA NONOate had no selection bias in the community

Metagenomic and metatranscriptomic analysis of saliva reveals disease-associated microbiota in patients with periodontitis and dental caries

Oral health: Signals from gene activity in saliva Genetic analysis of saliva reveals the activity of bacteria linked to gum disease and tooth decay and may prove useful in early diagnosis. Daniel Belstrøm and colleagues at the University of Copenhagen, Denmark, with co-workers at Nanyang Technological University in Singapore, analyzed saliva from 10 patients with periodontitis gum disease, 10 with dental caries and 10 with good oral health. DNA analysis revealed which bacteria were present, while examining RNA revealed which bacterial genes were most active. The procedure identified greater abundance and activity of bacteria linked to each specific oral condition in the oral disease groups, and also found distinctive bacterial activity in those people with good oral health. Further studies should investigate the possibility of testing bacterial gene activity in saliva to identify oral diseases before they become clinically evident

Onset of microbial influenced corrosion (MIC) in stainless steel exposed to mixed species biofilms from equatorial seawater

10.1149/2.0521709jesJournal of the Electrochemical Society1649C532-C53