Multi-omics reveal various potential antimonate reductases from phylogenetically diverse microorganisms

While previous work has demonstrated that antimonate (Sb(V)) can be bio-reduced with methane as the sole electron donor, the microorganisms responsible for Sb(V) reduction remain largely uncharacterized. Inspired by the recently reported Sb(V) reductase belonging to the dimethyl sulfoxide reductase (DMSOR) family, this study was undertaken to use metagenomics and metatranscriptomics to unravel whether any DMSOR family genes in the bioreactor had the potential for Sb(V) reduction. A search through metagenomic-assembled genomes recovered from the microbial community found that some DMSOR family genes, designated sbrA (Sb(V) reductase gene), were highly transcribed in four phylogenetically disparate assemblies. The putative catalytic subunits were found to be representatives of two distinct phylogenetic clades of reductases that were most closely related to periplasmic nitrate reductases and respiratory arsenate reductases, respectively. Putative operons containing sbrA possessed many other components, including genes encoding c-type cytochromes, response regulators, and ferredoxins, which together implement Sb(V) reduction. This predicted ability was confirmed by incubating the enrichment culture with ¹³C-labeled CH₄ and Sb(V) in serum bottles, where Sb(V) was reduced coincident with the production of ¹³C-labeled CO₂. Overall, these results increase our understanding of how Sb(V) can be bio-reduced in environments.