Caldimicrobium thiodismutans sp. nov., a sulfur-disproportionating bacterium isolated from a hot spring, and emended description of the genus Caldimicrobium.

A novel autotrophic, thermophilic bacterium, strain TF1T, was isolated from a hot spring in Japan. Cells of strain TF1T were motile, Gram-stain-negative, rod-shaped, 1.0-2.0 μm in length and 0.5-0.6 μm in width. Major components in the cellular fatty acid profile were C16:0, C18:0 and anteiso-C17:0. The temperature range for growth was 40-77 °C, and optimum temperature was 75 °C. The pH range for growth was 5.9-9.5, and the optimum pH was 7.5-8.8. Strain TF1T grew chemolithoautotrophically by disproportionation of sulfur, thiosulfate and sulfite. Phylogenetic analysis based on 16S rRNA gene sequences indicated that the strain belongs to the family Thermodesulfobacteriaceae. The closest cultivated relative was Caldimicrobium rimae DST, with highest 16S rRNA gene sequence similarity of 96%. The genome of strain TF1T consists of one circular chromosome, with a size of 1.8 Mbp and G+C content of 38.30 mol%. On the basis of its phylogenetic and phenotypic properties, strain TF1T (=DSM 29380T=NBRC 110713T) is proposed as the type strain of a novel species, Caldimicrobium thiodismutans sp. nov.