Microbially mediated sulfur oxidation coupled with arsenate reduction within oligotrophic mining-impacted habitats

Arsenate [As(V)] reduction is a major cause of arsenic (As) release from soils, which threatens more than 200 million people worldwide. While heterotrophic As(V) reduction has been investigated extensively, the mechanism of chemolithotrophic As(V) reduction is less studied. Since As is frequently found as a sulfidic mineral in the environment, microbial mediated sulfur oxidation coupled to As(V) reduction (SOAsR), a chemolithotrophic process, may be more favorable in sites impacted by oligotrophic mining (e.g. As-contaminated mine tailings). While SOAsR is thermodynamically favorable, knowledge regarding this biogeochemical process is still limited. The current study suggested that SOAsR was a more prevalent process than heterotrophic As(V) reduction in oligotrophic sites, such as mine tailings. The water-soluble reduced sulfur concentration was predicted to be one of the major geochemical parameters that had a substantial impact on SOAsR potentials. A combination of DNA stable isotope probing and metagenome binning revealed members of the genera Sulfuricella, Ramlibacter, and Sulfuritalea as sulfur oxidizing As(V)-reducing bacteria (SOAsRB) in mine tailings. Genome mining further expanded the list of potential SOAsRB to diverse phylogenetic lineages such as members associated with Burkholderiaceae and Rhodocyclaceae. Metagenome analysis using multiple tailing samples across southern China confirmed that the putative SOAsRB were the dominant As(V) reducers in these sites. Together, the current findings expand our knowledge regarding the chemolithotrophic As(V) reduction process, which may be harnessed to facilitate future remediation practices in mine tailings.