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

A novel bacterium, strain b6^T (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 b6^T 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 b6^T 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 b6^T 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 b6^T was 65.1 mol %. Comparative small subunit (SSU) ribosomal RNA (rRNA) analysis indicated that strain b6^T 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 b6^T and characterized Thiomonas species were less than 95%. DNA–DNA hybridization between strain b6^T and the type species of the genus Tm. intermedia showed less than 50% homology. On the basis of phylogenetic and phenotypic characteristics, strain b6^T (DSM 16361^T, LMG 22795^T) is proposed as the type strain of the new species Thiomonas arsenivorans, sp. nov.