Distinct Bacterial Consortia Established in ETBE-Degrading Enrichments from a Polluted Aquifer

Abstract

Ethyl tert-butyl ether (ETBE) is a gasoline additive that became an important aquifer pollutant. The information about natural bacterial consortia with a capacity for complete ETBE degradation is limited. Here we assess the taxonomical composition of bacterial communities and diversity of the ethB gene (involved in ETBE biodegradation) in ETBE-enrichment cultures that were established from a gasoline-polluted aquifer, either from anoxic ETBE-polluted plume water (PW), or from an upstream non-polluted water (UW). We used a 16S rRNA microarray, and 16S rRNA and ethB gene sequencing. Despite the dissimilar initial chemical conditions and microbial composition, ETBE-degrading consortia were obtained from both PW and UW. The composition of ETBE-enrichment cultures was distinct from their initial water samples, reflecting the importance of the rare biosphere as a reservoir of potential ETBE degraders. No convergence was observed between the enrichment cultures originating from UW and PW, which were dominated by Mesorhizobium and Hydrogenophaga, respectively, indicating that distinct consortia with the same functional properties may be present at one site. Conserved ethB genes were evidenced in both PW and UW ETBE-enrichment cultures and in PW water. Our results suggest that the presence of ethB genes rather than the taxonomical composition of in situ bacterial communities indicate the potential for the ETBE degradation at a given site.

Distribution of ETBE-degrading microorganisms and functional capability in groundwater, and implications for characterising aquifer ETBE biodegradation potential

“…The detection of the ethB gene in aquifer samples can provide additional microbiological-based evidence to support the hydrochemical assessment, complementing other molecular tools which may be deployed to evaluate GEO biodegradation (e.g. Fayolle-Guichard et al 2012 ; van der Waals et al 2018 ; Kucharzyka et al 2019 ; Kyselková et al 2019 ). This is site specific and may be appropriate in cases where the hydrochemical assessment suggests that conditions are favourable for ETBE biodegradation but this is not observed, or the hydrochemical data is unclear, for example due to releases of multiple GEO.…”

“…Hence, the taxonomic composition of the microbial community may not indicate ETBE biodegradation potential. This has been attributed to the functional redundancy of ETBE-degrading consortia, in that the distribution of the ethB gene within the microbial community may be independent of its taxonomic composition (Kyselková et al 2019 ). It implies that many bacterial species in a consortium could facilitate ETBE biodegradation, according to their functional capability.…”

“…In the case of ETBE the eth operon is flanked by two identical transposons and is readily lost under non-selective conditions (Chauvaux et al 2001 ). Therefore, close proximity of microbes in a biofilm could facilitate the horizontal transfer of the eth gene cluster between different bacterial species within the attached microbial community (Singh et al 2006 ; Kyselková et al 2019 ).…”

“…It should be noted that the presence of the ethB gene in an aquifer is evidence for ETBE biodegradation potential. However, the absence of this gene does not imply the absence of this potential, as ETBE b io degrad ation cou ld occur v ia other uncharacterised routes (Kyselková et al 2019).…”

“…Transcriptional investigations revealed that this gene is upregulated in the presence of ETBE (Malandain et al 2010). Therefore, the detection of the ethB gene in aquifer microorganisms demonstrates the presence of aerobic ETBE biodegradation potential in groundwater at an ETBE-release site (Fayolle-Guichard et al 2012;Kucharzyka et al 2019;Kyselková et al 2019). While ETBE biodegradation facilitated by ethB is the best characterised route for aerobic biodegradation, other biodegradation pathways have been proposed, although the genes involved have not been identified (Rosell et al 2012;Le Digabel et al 2013;Gunasekaran et al 2014).…”