Oxidation of arsenite by Thiomonas strains and characterization of Thiomonas arsenivorans sp. nov.

A novel bacterium, strain b6T (T=type strain), was isolated from a disused mine site by growth using arsenite [As(III)] as energy source in a simple mineral medium. Cells of strain b6T were rod-shaped, Gram-negative, non-sporulating and motile. Optimum growth occurred at temperatures between 20 and 30 °C, and at pH between 4.0 and 7.5. Strain b6T grew chemoautotrophically on As(III), sulphur and thiosulphate, and also heterotrophically on yeast extract and a variety of defined organic compounds. Several other Thiomonas strains, including the type species Thiomonas (Tm.) intermedia, were able to oxidize As(III), though only strain b6T and strain NO115 could grow using As(III) as sole energy source in the absence of any organic compound. The G+C content of the DNA of strain b6T was 65.1 mol %. Comparative small subunit (SSU) ribosomal RNA (rRNA) analysis indicated that strain b6T belongs to the genus Thiomonas in the β-subdivision of the Proteobacteria. It was closely related to an unnamed Thiomonas strain (NO115) isolated from a Norwegian mining site, though sequence identities between strain b6T and characterized Thiomonas species were less than 95%. DNA–DNA hybridization between strain b6T and the type species of the genus Tm. intermedia showed less than 50% homology. On the basis of phylogenetic and phenotypic characteristics, strain b6T (DSM 16361T, LMG 22795T) is proposed as the type strain of the new species Thiomonas arsenivorans, sp. nov.