Arsenite oxidation by a facultative chemolithoautotrophic Sinorhizobium sp. KGO-5 isolated from arsenic-contaminated soil.

A chemolithoautotrophic arsenite-oxidizing bacterium, designated strain KGO-5, was isolated from arsenic-contaminated industrial soil. Strain KGO-5 was phylogenetically closely related with Sinorhizobium meliloti with 16S rRNA gene similarity of more than 99%, and oxidized 5 mM arsenite under autotrophic condition within 60 h with a doubling time of 3.0 h. Additions of 0.01-0.1% yeast extract enhanced the growth significantly, and the strain still oxidized arsenite efficiently with much lower doubling times of approximately 1.0 h. Arsenite-oxidizing capacities (11.2-54.1 μmol h(-1) mg dry cells(-1)) as well as arsenite oxidase (Aio) activities (1.76-10.0 mU mg protein(-1)) were found in the cells grown with arsenite, but neither could be detected in the cells grown without arsenite. Strain KGO-5 possessed putative aioA gene, which is closely related with AioA of Ensifer adhaerens. These results suggest that strain KGO-5 is a facultative chemolithoautotrophic arsenite oxidizer, and its Aio is induced by arsenic.