To date, little information is available on the oxidation and reduction of Sb by bacteria. The biogeochemical effects of microorganisms on redox potential and mobility of Sb were investigated in this research. A dissimilatory Sb(V)-reducing bacterium was isolated from stream sediment samples (Sb 3,069 mg/kg) taken in the vicinity of an Sb oxide-producing factory in Korea. This anaerobic rod-shaped bacterium reduced Sb(V) and grew through respiration using 5 mM Sb(V) and 10 mM acetate under pH 7.7 and 30 oC. A part of Sb(III) which was produced in anoxic minimal medium precipitated as a biomineral which was likely Sb(OH)3. Based on the phylogenetics of 16s rRNA gene sequence and DNA G+C content, the bacterium appears to be a novel strain of the Sinorhizobium genus. The results suggest that microorganisms may play a significant role in changing the redox state of Sb and thus geochemical fates of Sb in geological media.
Twelve Sb-resistant bacteria were isolated from the same sediment samples, and eight of these strains were heterotrophic Sb(III)-oxidizing bacteria. Phylogenetic analyses showed that the Sb(III)-oxidizing bacteria fell within two subdivisions of Proteobacteria. Cupriavidus sp. NL4 and Comamonas sp. NL11 belong to the subdivision β-Proteobacteria. Acinetobacter sp. NL1, Acinetobacter sp. NL12, Pseudomonas sp. NL2, Pseudomonas sp. NL5, Pseudomonas sp. NL6, and Pseudomonas sp. NL10 are the members of the γ-subdivision of the Proteobacteria. Among them, Cupriavidus sp. NL4 completely oxidized 100 μmoles/L Sb(III) in 500 hours. The other strains could not oxidize all of the Sb(III) in the medium, even with longer incubation. The results imply that diverse bacterial lineages are able to detoxify sites polluted with Sb(III) by oxidizing it to Sb(V), and to contribute to antimony cycling in natural environments.