Thiobacter subterraneus gen. nov., sp nov., an obligately chemolithoautotrophic, thermophilic, sulfur-oxidizing bacterium from a subsurface hot aquifer

A novel, thermophilic, obligately chemolithoautotrophic, sulfur/thiosulfate-oxidizing bacterium was isolated from subsurface geothermal aquifer water (temperature approximately 70 degreesC) in the Hishikari gold mine, Japan. Cells of the isolate, designated strain C55(T), were motile, straight rods with a single polar flagellum. Growth was observed at temperatures between 35 and 62 degreesC (optimum 50-55 degreesC; 60 min doubling time) and pH between 5(.)2 and 7(.)7 (optimum pH 6(.)5-7(.)0). High growth rate of strain C55(T) was observed on either thiosulfate or elemental sulfur as a sole energy source, with molecular oxygen as the only electron acceptor. None of the organic compounds tested supported or stimulated growth of strain C55(T). The G+C content of the genomic DNA was 66(.)9 mol%. Phylogenetic analysis based on 16S rRNA gene sequences indicated that strain C55(T) was affiliated to the beta-Proteobacteria, but was distantly related to recognized genera. On the basis of its physiological and molecular properties, strain C55(T) (= JCM 12421(T) = DSM 16629(T) = ATCC BAA-941(T)) is proposed as the type strain of Thiobacter subterraneus gen. nov., sp. nov.