gen. nov., sp. nov., a novel mesophilic, hydrogen-oxidizing, sulphate-reducing chemolithoautotroph isolated from a deep-sea hydrothermal vent chimney.

A novel mesophilic, strictly anaerobic, chemolithoautotrophic sulphate-reducing bacterium, designated strain KT2, was isolated from a deep-sea hydrothermal vent chimney at the Suiyo Seamount in the Izu-Bonin Arc. Strain KT2 grew at 25-40 °C (optimum 35 °C) and pH 5.5-7.0 (optimum 6.6) in the presence of 25-45 g l NaCl (optimum 30 g l). Growth occurred with molecular hydrogen as the electron donor and sulphate, thiosulphate, and sulphite as the electron acceptors. The isolate utilized CO as the sole carbon source for chemolithoautotrophic growth on H. Glycerol, succinate, fumarate, malate, glutamate, or casamino acids could serve as an alternative electron donor in the presence of CO. Malate, citrate, glutamate, and casamino acids were used as fermentative substrates for weak growth. The G+C content of genomic DNA was 46.1 %. Phylogenetic analysis of the 16S rRNA gene sequence indicated that strain KT2 is a member of the family , showing a sequence similarity of 94.3 % with . Phylogenomic analysis based on concatenated 156 single-copy marker genes confirmed the same topology as the 16S rRNA gene phylogeny. The ANI and AAI values between strain KT2 and related genera of the family were 65.6-68.6 % and 53.1-62.9 %. Based on the genomic, molecular, and physiological characteristics, strain KT2 represents a novel genus and species within the family , for which the name gen. nov., sp. nov. is proposed, with KT2 (=JCM 34118 = DSM 111364) as the type strain.