Electrochemical bioaugmentation as a new strategy for arsenic bioremediation in groundwater.

Arsenic (As) is a toxic metalloid that affects over 100 million people worldwide. Bioelectrochemical systems (BESs) offer a new opportunity to catalyze the biological oxidation of arsenite to arsenate, decreasing toxicity and improving subsequent physicochemical separation steps. However, research on arsenic-related electrochemically active microorganisms (As-EAMs) remains limited. This study electrochemically enriched As-EAMs from sediments of a hydrothermal source in northern Chile using a three-electrode cell. Chronoamperometry was run for 116 days at a poised potential of +0.3V (vs. Ag/AgCl) and under open-circuit potential (O.C.P.). Bacterial colonization over carbon cloth electrodes was examined by scanning electron microscopy and flow cytometry, while microbial communities were characterized via 16S rRNA gene sequencing (Illumina MiSeq). Our results indicated that Rhodococcus sp. was the most abundant genus in both conditions, representing over 90% of the relative abundance. Despite this shared dominance, the poised-potential assay showed 27% and 39% dissimilarity in attached and planktonic communities, respectively, relative to O.C.P. This compositional difference was associated with a higher As(III) oxidation rate: 20% under poised potential versus 5.5% for O.C.P. and less than 3.7% for abiotic controls (p < 0.05). This research improves our understanding of As-EAMs and supports the development of novel electro-biotransformation strategies.