Antimony (Sb) is an industrially significant metalloid that has been exploited by humans for the last 3,000 years. Although Sb is more toxic than its well-known group 15 neighbor, arsenic, relatively little is known about the fate and transport of Sb in the environment, especially with respect to the involvement of microorganisms in mediating redox transformations. The isolation and description of the first microorganism capable of using antimonate [Sb(V)] as a terminal electron acceptor to support growth was accomplished. The microorganism, designated Desulfuribacillus stibiiarsenatis MLFW-2T, was an obligately anaerobic member of the order Bacillales of the phylum Firmicutes. It was isolated from anoxic sediments collected from the drainage area of a geothermal spring near the southern shore of alkaline, hypersaline Mono Lake, CA. MLFW-2T was capable of using formate, lactate, pyruvate, or H2 as electron donors with nitrate, nitrite, dimethyl sulfoxide (DMSO), selenate [Se(VI)], selenite [Se(IV)], arsenate [As(V)], or Sb(V) as electron acceptors. Consistent with the environment from which it was isolated, MLFW-2T was found to be mesophilic, slightly alkaliphilic, and halotolerant. Dissimilatory Sb(V) reduction by MLFW-2T was accompanied by the precipitation of antimonite [Sb(III)] as microcrystals of antimony trioxide. The draft genome of MLFW-2T contains 14 genes that encode the catalytic subunits of anaerobic respiratory reductases of the DMSO reductase (DMSOR) family of complex iron-sulfur molybdoenzymes. The involvement of each of these genes in the anaerobic respiratory chain of MLFW-2T was evaluated by monitoring their relative expression during growth on nitrate, Se(VI), As(V), and Sb(V) using reverse transcription-quantitative polymerase chain reaction (RT-qPCR). The analyses identified the most probable terminal reductase for each of the oxyanions tested. Homologs of an operon encoding the putative terminal Sb(V) reductase were found to occur in microorganisms belonging to six described phyla and two candidate phyla across both prokaryotic domains of life. Lastly, the physiological response of MLFW-2T to growth on Sb(V) and As(V) was examined using RNA sequencing. Sb was found to elicit a stronger oxidative stress response in comparison to As, with DNA, proteins, cofactors, and components of the cell envelope as the primary targets of damage.