Hydrogenivirga caldilitoris gen. nov., sp. nov., a novel extremely thermophilic, hydrogen- and sulfur-oxidizing bacterium from a coastal hydrothermal field

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Abstract
A novel extremely thermophilic, hydrogen- and sulfur-oxidizing bacterium, designated strain IBSK3T, was isolated from a coastal hot spring in Ibusuki, Kagoshima Prefecture, Japan. The cells were motile, straight to slightly curved rods (1·2–3·0 μm long and 0·3–0·4 μm wide). Strain IBSK3T was an obligate chemolithoautotroph growing by respiratory nitrate reduction with H2, forming N2O as an end product. Low concentrations of O2 (0·4–7·7 %, v/v; optimum 2·0 %, v/v) could serve as an alternative electron acceptor to growth. In addition, strain IBSK3T was able to utilize elemental sulfur as a sole electron donor with either nitrate or low concentrations of O2 as an electron acceptor. Growth was observed between 55 and 77·5 °C (optimum 75 °C; 2 h doubling time), pH 5·5 and 8·3 (optimum pH 6·5–7·0), and in the presence of 0·5 and 4·0 % NaCl (optimum 2·0 %). The G+C content of the genomic DNA was 49·2 mol%. On the basis of 16S rRNA gene sequence analysis, strain IBSK3T belonged to the family Aquificaceae, but it only demonstrated a distant phylogenetic relationship with any recognized species within the family (sequence similarity was less than 92 %). On the basis of the physiological and molecular characteristics of the novel isolate, a new genus and novel species are proposed: the type strain of Hydrogenivirga caldilitoris gen. nov., sp. nov. is IBSK3T (=JCM 12173T=ATCC BAA-821T).