Cooperative interactions between invader and resident microbial community members weaken the negative diversity-invasion relationship.

The negative diversity-invasion relationship observed in microbial invasion studies is commonly explained by competition between the invader and resident populations. However, whether this relationship is affected by invader-resident cooperative interactions is unknown. Using ecological and mathematical approaches, we examined the survival and functionality of Aminobacter niigataensis MSH1 to mineralize 2,6-dichlorobenzamide (BAM), a groundwater micropollutant affecting drinking water production, in sand microcosms when inoculated together with synthetic assemblies of resident bacteria. The assemblies varied in richness and in strains that interacted pairwise with MSH1, including cooperative and competitive interactions. While overall, the negative diversity-invasion relationship was retained, residents engaging in cooperative interactions with the invader had a positive impact on MSH1 survival and functionality, highlighting the dependency of invasion success on community composition. No correlation existed between community richness and the delay in BAM mineralization by MSH1. The findings suggest that the presence of cooperative residents can alleviate the negative diversity-invasion relationship.

Interspecies Interactions of the 2,6-Dichlorobenzamide Degrading Aminobacter sp. MSH1 with Resident Sand Filter Bacteria: Indications for Mutual Cooperative Interactions That Improve BAM Mineralization Activity.

Bioaugmentation often involves an invasion process requiring the establishment and activity of a foreign microbe in the resident community of the target environment. Interactions with resident micro-organisms, either antagonistic or cooperative, are believed to impact invasion. However, few studies have examined the variability of interactions between an invader and resident species of its target environment, and none of them considered a bioremediation context. Aminobacter sp. MSH1 mineralizing the groundwater micropollutant 2,6-dichlorobenzamide (BAM), is proposed for bioaugmentation of sand filters used in drinking water production to avert BAM contamination. We examined the nature of the interactions between MSH1 and 13 sand filter resident bacteria in dual and triple species assemblies in sand microcosms. The residents affected MSH1-mediated BAM mineralization without always impacting MSH1 cell densities, indicating effects on cell physiology rather than on cell number. Exploitative competition explained most of the effects (70%), but indications of interference competition were also found. Two residents improved BAM mineralization in dual species assemblies, apparently in a mutual cooperation, and overruled negative effects by others in triple species systems. The results suggest that sand filter communities contain species that increase MSH1 fitness. This opens doors for assisting bioaugmentation through co-inoculation with "helper" bacteria originating from and adapted to the target environment.

The pesticide mineralization capacity in sand filter units of drinking water treatment plants (DWTP): Consistency in time and relationship with intake water and sand filter characteristics.

Sand filters (SFs) are commonly applied in drinking water treatment plants (DWTPs) for removal of iron and manganese but also show potential for microbial degradation of pesticide residues. The latter is advantageous in case the intake water contains pesticide residues. However, whether this involves mineralization suggesting no generation of harmful transformation products, its consistency over time, and how this ability relates to physicochemical and biological characteristics of the DWTP intake water and the SFs is unknown. The capacity to mineralize the herbicides bentazon and 2-methyl-4-chlorophenoxyacetic acid (MCPA) was examined in SF samples from 11 DWTPs differing in operation, intake water composition and pesticide contamination level. MCPA was mineralized in all biologically active SFs while mineralization of bentazon occurred rarely. Mineralization of both compounds was consistent in time and across samples taken from different SF units of the same DWTP. Kinetic modelling of mineralization curves suggested the occurrence of growth linked bentazon and MCPA mineralization in several SF samples. Multivariate analysis correlating intake water/SF characteristics with pesticide mineralization indicated that pesticide mineralization capacity depended on a range of intake water characteristics, but was not necessarily explained by the presence of the pesticide in the intake water and hence the in situ exposure of the SF community to the pesticide. This was supported by testing a sample from DWTP Kluizen for its capacity to mineralize 5 other pesticides including pesticides not present or occasionally present in the intake water. All of those pesticides were mineralized as well.

Isolation and identification of culturable bacteria, capable of heterotrophic growth, from rapid sand filters of drinking water treatment plants.

The microbial community in sand filters (SFs) of drinking water treatment plants (DWTPs) likely contributes to SF functionalities, such as organic carbon removal through heterotrophic metabolism. However, the dynamics and functionality of the SF microbiome and microbial communities in oligotrophic freshwater environments in general, are poorly understood. Therefore, the availability of bacterial strains from these oligotrophic environments is of great interest, but such organisms are currently underrepresented in culture collections. Focusing on heterotrophic carbon metabolism, bacteria were isolated from SFs using conventional media and media that contained SF extracts to mimic the SF environment. The majority of isolates belonged to Betaproteobacteria, more specifically to the families Comamonadaceae (genera Acidovorax, Curvibacter, Hydrogenophaga, Simplicispira, Paucibacter, Pelomonas, Piscinibacter and Rhodoferax) and Oxalobacteraceae (Undibacterium). Additionally, members of Alphaproteobacteria (Mesorhizobium), Gammaproteobacteria (Aeromonas and Perlucidibaca) and Actinobacteria (Rhodococcus and Brachybacterium) were isolated. Several of those genera have only rarely been described, but appear typical inhabitants of oligotrophic freshwater environments. In this regard, the Comamonadaceae isolates are of particular interest. Our study shows that bacteria representative of oligotrophic environments can be isolated using simple isolation procedures. The isolates provide a microbial framework for extending our knowledge of the taxonomy, physiology and functionality of oligotrophic freshwater microbiomes and their interactions with possible invaders.

Biocarriers Improve Bioaugmentation Efficiency of a Rapid Sand Filter for the Treatment of 2,6-Dichlorobenzamide-Contaminated Drinking Water.

Aminobacter sp. MSH1 immobilized in an alginate matrix in porous stones was tested in a pilot system as an alternative inoculation strategy to the use of free suspended cells for biological removal of micropollutant concentrations of 2,6-dichlorobenzamide (BAM) in drinking water treatment plants (DWTPs). BAM removal rates and MSH1 cell numbers were recorded during operation and assessed with specific BAM degradation rates obtained in lab conditions using either freshly grown cells or starved cells to explain reactor performance. Both reactors inoculated with either suspended or immobilized cells showed immediate BAM removal under the threshold of 0.1 µg/L, but the duration of sufficient BAM removal was 2-fold (44 days) longer for immobilized cells. The longer sufficient BAM removal in case of immobilized cells compared to suspended cells was mainly explained by a lower initial loss of MSH1 cells at operational start due to volume replacement and shear. Overall loss of activity in the reactors though was due to starvation, and final removal rates did not differ between reactors inoculated with immobilized and suspended cells. Management of assimilable organic carbon, in addition to cell immobilization, appears crucial for guaranteeing long-term BAM degradation activity of MSH1 in DWTP units.

Draft Genome Sequence of Aeromonas sp. Strain EERV15.

We report here the draft genome sequence of Aeromonas sp. strain EERV15 isolated from sand filter. The organism most closely related to Aeromonas sp. EERV15 is Aeromonas veronii B565, with an average 83% amino acid sequence similarity of putatively encoded protein open reading frames.

Mineralization of the Common Groundwater Pollutant 2,6-Dichlorobenzamide (BAM) and its Metabolite 2,6-Dichlorobenzoic Acid (2,6-DCBA) in Sand Filter Units of Drinking Water Treatment Plants.

The intrinsic capacity to mineralize the groundwater pollutant 2,6-dichlorobenzamide (BAM) and its metabolite 2,6-dichlorobenzoic acid (2,6-DCBA) was evaluated in samples from sand filters (SFs) of drinking water treatment plants (DWTPs). Whereas BAM mineralization occurred rarely and only in SFs exposed to BAM, 2,6-DCBA mineralization was common in SFs, including those treating uncontaminated water. Nevertheless, SFs treating BAM contaminated water showed the highest 2,6-DCBA mineralization rates. For comparison, 2,6-DCBA and BAM mineralization were determined in various topsoil samples. As in SF samples, BAM mineralization was rare, whereas 2,6-DCBA mineralization capacity appeared widespread, with high mineralization rates found especially in forest soils. Multivariate analysis showed that in both SF and soil samples, high 2,6-DCBA mineralization correlated with high organic carbon content. Adding a 2,6-DCBA degradation deficient mutant of the BAM mineralizing Aminobacter sp. MSH1 confirmed that 2,6-DCBA produced from BAM is rapidly mineralized by the endogenous microbial community in SFs showing intrinsic 2,6-DCBA mineralization. This study demonstrates that (i) 2,6-DCBA mineralization is widely established in SFs of DWTPs, allowing the mineralization of 2,6-DCBA produced during BAM degradation and (ii) the first metabolic step in BAM mineralization is rare in microbial communities, rather than its further degradation beyond 2,6-DCBA.

Application of biodegradation in mitigating and remediating pesticide contamination of freshwater resources: state of the art and challenges for optimization.

In recent years, the application of pesticide biodegradation in remediation of pesticide-contaminated matrices moved from remediating bulk soil to remediating and mitigating pesticide pollution of groundwater and surface water bodies. Specialized pesticide-degrading microbial populations are used, which can be endogenous to the ecosystem of interest or introduced by means of bioaugmentation. It involves (semi-)natural ecosystems like agricultural fields, vegetated filter strips, and riparian wetlands and man-made ecosystems like on-farm biopurification systems, groundwater treatment systems, and dedicated modules in drinking water treatment. Those ecosystems and applications impose challenges which are often different from those associated with bulk soil remediation. These include high or extreme low pesticide concentrations, mixed contamination, the presence of alternative carbon sources, specific hydraulic conditions, and spatial and temporal variation. Moreover, for various indicated ecosystems, limited knowledge exists about the microbiota present and their physiology and about the in situ degradation kinetics. This review reports on the current knowledge on applications of biodegradation in mitigating and remediating freshwater pesticide contamination. Attention is paid to the challenges involved and current knowledge gaps for improving those applications.

The quantity and quality of dissolved organic matter as supplementary carbon source impacts the pesticide-degrading activity of a triple-species bacterial biofilm.

Effects of environmental dissolved organic matter (eDOM) that consists of various low concentration carbonic compounds on pollutant biodegradation by bacteria are poorly understood, especially when it concerns synergistic xenobiotic-degrading consortia where degradation depends on interspecies metabolic interactions. This study examines the impact of the quality and quantity of eDOM, supplied as secondary C-source, on the structure, composition and pesticide-degrading activity of a triple-species bacterial consortium in which the members synergistically degrade the phenylurea herbicide linuron, when grown as biofilms. Biofilms developing on 10 mg L⁻¹ linuron showed a steady-state linuron degradation efficiency of approximately 85 %. The three bacterial strains co-localized in the biofilms indicating syntrophic interactions. Subsequent feeding with eDOM or citrate in addition to linuron resulted into changes in linuron-degrading activity. A decrease in linuron-degrading activity was especially recorded in case of co-feeding with citrate and eDOM of high quality and was always associated with accumulation of the primary metabolite 3,4-dichloroaniline. Improvement of linuron degradation was especially observed with more recalcitrant eDOM. Addition of eDOM/citrate formulations altered biofilm architecture and species composition but without loss of any of the strains and of co-localization. Compositional shifts correlated with linuron degradation efficiencies. When the feed was restored to only linuron, the linuron-degrading activity rapidly changed to the level before the mixed-substrate feed. Meanwhile only minor changes in biofilm composition and structure were recorded, indicating that observed eDOM/citrate effects had been primarily due to repression/stimulation of linuron catabolic activity rather than to biofilm characteristics.

Variovorax sp.-mediated biodegradation of the phenyl urea herbicide linuron at micropollutant concentrations and effects of natural dissolved organic matter as supplementary carbon source.

In nature, pesticides are often present as micropollutants with concentrations too low for efficient biodegradation and growth of heterotrophic pollutant-degrading bacteria. Instead, organic carbon present in environmental dissolved organic matter (eDOM) constitutes the main carbon source in nature. Information on how natural organic carbon affects degradation of pollutants and micropollutants, in particular, is however poor. Linuron-degrading Variovorax sp. strains SRS16, WDL1, and PBLH6 and a triple-species bacterial consortium, from which WDL1 originated, were examined for their ability to degrade linuron at micropollutant concentrations and the effect hereon of different eDOM formulations of varying biodegradability as supplementary C-source was explored. Individual strains and the consortium degraded linuron at initial concentrations as low as 1 µg L(-1) till concentrations below 4 ng L(-1). Degradation kinetics differed among strains with rates that differed up to 70-fold at the lowest linuron concentrations and with lag phases ranging from 0 to 7 days. Linuron biodegradation by the individual strains was inhibited by an easily biodegradable compound such as citrate but stimulated by eDOM at a linuron concentration of 10 mg L(-1). Effects were strongly reduced or became non-existent at micropollutant linuron concentrations. Effects of eDOM on degradation at 10 mg L(-1) linuron by WDL1 were reduced when WDL1 was incubated together with its original consortium members. This is the first report on eDOM effects on degradation of pesticides at micropollutant concentrations and indicates these effects are limited and depend on linuron and eDOM concentrations, eDOM quality, and the bacterial culture.

Cooperative dissolved organic carbon assimilation by a linuron-degrading bacterial consortium.

Dissolved organic matter (DOM) is the primary environmental carbon source for heterotrophic bacteria and its quality and quantity have been shown to affect microbial community structure and functioning. In that context, it was examined whether a bacterial consortium synergistically degrading the herbicide linuron extends this synergism toward natural DOM degradation. Biodegradable dissolved organic carbon (BDOC) of DOM of various origins and concomitant growth was determined for the consortium members in isolation and in combination. BDOC decreased with increasing DOM aromaticity, which is a recalcitrance indicator. BDOC in DOM of low aromaticity was 40-50% for all inocula. For DOM with high aromaticity, BDOC decreased with increasing aromaticity and was inoculum dependent, that is, BDOC was > 23% for consortium members in combination compared with BDOC < 16% for isolated strains. The observed BDOC and growth indicated that synergism existed within the consortium for degradation of DOM of both low and high aromaticity. All members benefited from this synergism as growth of all strains increased when incubated in combination, but their relative growth benefit depended on DOM composition. These data suggest that consortia benefit more than individual pesticide degraders from environmental DOM due to cooperation. This is important to understand the effects of DOM on stability and activity of pollutant-degrading consortia.