Dissimilatory As(V)-respiring prokaryotes (DARPs) are recognized as having a crucial role in the formation of arsenic-contaminated groundwater. DARPs use dissolved organic carbon (DOC) as electron donor to directly reduce As(V) in solid phase to more mobile As(III). Therefore, DARPs are considered to be heterotrophic bacteria. However, these cannot explain why high concentrations of As(III) are produced in environments lacking DOC. We thus propose that reduced sulfur compounds may also be utilized by DARPs and affect the DARPs-mediated arsenic mobilization. This study sought to confirm this hypothesis. Metagenomic investigations on the DARP population derived from As-contaminated groundwater indicated that approximately 84 % of DARP MAGs possess the enzymes potentially catalyzing the oxidation of S^2-, S⁰, SO₃^2-, or S₂O₃^2-. Functional analysis of DARP population and cultivable strain suggested that DARPs, in addition to DOC, can effectively use sulfur compounds as electron donor to reduce As(V) to mobile As(III). Arsenic release experiments using DARP population and cultivable DARP strain showed that DARPs indeed utilized sulfur compounds as the sole electron donors under autotrophic and anoxic conditions to directly reduce adsorbed As(V) in the soil to mobile As(III). These findings provide new insights into the microbial mechanism responsible for the variation of As(III) concentration in contaminated groundwater.
 

As-contaminated groundwater,Sulfur compound,Soil microcosm,Metagenomic,As(V)-reducing microbes