Sulfurifustis variabilis gen. nov., sp. nov., a sulfur oxidizer isolated from a lake, and proposal of Acidiferrobacteraceae fam. nov. and Acidiferrobacterales ord. nov.

A novel autotrophic bacterium, strain skN76 T , was isolated from sediment of a lake in Japan. As sole electron donor to support chemolithoautotrophic growth, the strain oxidized thiosulfate, tetrathionate and elemental sulfur. For growth, the optimum temperature was 42–45 °C and the optimum pH was 6.8–8.2. The cells were Gram-stain-negative, catalase-positive and oxidase-positive. The strain exhibited changes in morphology depending on growth temperature. Cells grown at the optimum temperature were rod-shaped (0.9–3.0 μm long and 0.3–0.5 μm wide), whereas a filamentous form was observed when the strain was cultured at the lowest permissive growth temperatures. The G+C content of genomic DNA was 69 mol%. The major components in the fatty acid profile were C 16 : 0 , summed feature 3 (C 16 : 1 ω7 c and/or C 16 : 1 ω6 c ) and summed feature 9 (iso-C 17 : 1 ω9 c and/or 10-methyl C 16 : 0 ). Phylogenetic analysis based on 16S rRNA gene sequences indicated that the closest cultivated relative of strain skN76 T was Acidiferrobacter thiooxydans m-1 T , with sequence similarity of 93 %. On the basis of its phylogenetic and phenotypic properties, strain skN76 T ( = DSM 100313 T = NBRC 110942 T ) is proposed as the type strain of a novel species of a novel genus, Sulfurifustis variabilis gen. nov., sp. nov. Novel taxa, Acidiferrobacteraceae fam. nov. and Acidiferrobacterales ord. nov., are also proposed to accommodate the genera Acidiferrobacter and Sulfurifustis gen. nov.