Variable response of arsenic contaminated groundwater microbial community to electron acceptor regime revealed by microcosm based high-throughput sequencing approach

Arsenic (As) mobilization in alluvial aquifers is facilitated by microbially catalyzed redox transformations that depend on the availability of electron acceptors (EAs). In this study, the response of an As-contaminated groundwater microbial community from West Bengal, India towards varied EAs was elucidated through microcosm based 16S rRNA gene amplicon sequencing. <i>Acinetobacter, Deinococcus, Nocardioides,</i> etc., and several unclassified bacteria (<i>Ignavibacteria</i>) and archaea (<i>Bathyarchaeia, Micrarchaeia</i>) previously not reported from As-contaminated groundwater of West Bengal, characterized the groundwater community. Distinct shifts in community composition were observed in response to various EAs. Enrichment of operational taxonomic units (OTUs) affiliated to <i>Denitratisoma</i> (NO₃ˉ)<i>, Spirochaetaceae</i> (Mn⁴⁺), <i>Deinococcus</i> (As⁵⁺), <i>Ruminiclostridium</i> (Fe³⁺), <i>Macellibacteroides</i> (SO₄²ˉ), <i>Holophagae</i>-<i>Subgroup 7</i> (HCO₃ˉ), <i>Dechloromonas</i> and <i>Geobacter</i> (EA mixture) was noted. Alternatively, As³⁺ amendment as electron donor allowed predominance of <i>Rhizobium</i>. Taxonomy based functional profiling highlighted the role of chemoorganoheterotrophs capable of concurrent reduction of NO₃ˉ, Fe³⁺, SO₄²ˉ, and As biotransformation in As-contaminated groundwater of West Bengal. Our analysis revealed two major aspects of the community, (a) taxa selective toward responding to the EAs, and (b) multifaceted nature of taxa appearing in abundance in response to multiple substrates. Thus, the results emphasized the potential of microbial community members to influence the biogeochemical cycling of As and other dominant anions/cations.