Microbiological Oxidation of Antimony(III) with Oxygen or Nitrate by Bacteria Isolated from Contaminated Mine Sediments

Bacterial oxidation of arsenite [As(III)] is a well-studied and important biogeochemical pathway that directly influences the mobility and toxicity of arsenic in the environment. In contrast, little is known about microbiological oxidation of the chemically similar anion antimonite [Sb(III)]. In this study, two bacterial strains, designated IDSBO-1 and IDSBO-4, which grow on tartrate compounds and oxidize Sb(III) using either oxygen or nitrate, respectively, as a terminal electron acceptor, were isolated from contaminated mine sediments. Both isolates belonged to theComamonadaceae family and were 99% similar to previously described species. We identify these novel strains asHydrogenophaga taeniospiralis strain IDSBO-1 andVariovorax paradoxus strain IDSBO-4. Both strains possess a gene with homology to theaioA gene, which encodes an As(III)-oxidase, and both oxidize As(III) aerobically, but only IDSBO-4 oxidized Sb(III) in the presence of air, while strain IDSBO-1 could achieve this via nitrate respiration. Our results suggest that expression ofaioA is not induced by Sb(III) but may be involved in Sb(III) oxidation along with an Sb(III)-specific pathway. Phylogenetic analysis of proteins encoded by theaioA genes revealed a close sequence similarity (90%) among the two isolates and other known As(III)-oxidizing bacteria, particularlyAcidovorax sp. strain NO1. Both isolates were capable of chemolithoautotrophic growth using As(III) as a primary electron donor, and strain IDSBO-4 exhibited incorporation of radiolabeled [14 C]bicarbonate while oxidizing Sb(III) from Sb(III)-tartrate, suggesting possible Sb(III)-dependent autotrophy. Enrichment cultures produced the Sb(V) oxide mineral mopungite and lesser amounts of Sb(III)-bearing senarmontite as precipitates.