A novel thermophilic, sulfur-reducing chemolithoautotroph, strain ABI70S6T, was isolated from a deep-sea hydrothermal field at the Yonaguni Knoll IV, Southern Okinawa Trough. Cells of strain ABI70S6T were motile rods, 0.9–2.0 μm in length and 0.4–0.8 μm in width. Strain ABI70S6T was an obligately anaerobic chemolithotroph, exhibiting hydrogen oxidation coupled with sulfur reduction. Growth was observed at 55–78 °C (optimum, 70 °C), pH 5.0–7.5 (optimum, pH 5.5–6.0) and 0.5–4.5 % NaCl (optimum, 3.0 % NaCl). H2 and elemental sulfur were utilized as electron donor and acceptor, respectively. The major fatty acids were C16 : 0 (40.0 %) and C20 : 1 (60.0 %). The G+C content of genomic DNA was 44.2 mol%. The physiological attributes of strain ABI70S6T are similar to those of species of genera within the family Desulfurobacteriaceae, most of which are thermophilic and chemolithoautotrophic sulfur reducers. However, 16S rRNA gene sequence similarities between the novel isolate and type strains of all species within the family Desulfurobacteriaceae were <87 %, which is close to the similarities found between the novel isolate and members of the family Thermodesulfobacteriaceae (<85 %). Based on physiological and phylogenetic features of the novel isolate, it is proposed that it represents a novel species in a novel genus, Thermosulfidibacter takaii gen. nov., sp. nov., within the phylum Aquificae. The type strain of T. takaii is ABI70S6T (=JCM 13301T=DSM 17441T).
A novel extremely thermophilic sulfur-oxidizing bacterium, strain LS12-2T, was isolated from a deep-sea hydrothermal field at the Yonaguni Knoll IV, Southern Okinawa Trough. Cells of strain LS12-2T were motile rods, 1.5–4.0 μm in length and 0.4–0.5 μm in width. Strain LS12-2T was an obligate chemolithoautotroph that could utilize elemental sulfur or thiosulfate as an electron donor and nitrate or oxygen as an electron acceptor. Growth was observed at 65–85 °C (optimum 70–75 °C), pH 5.8–8.3 (optimum pH 6.9–7.5), 1.0–4.0 % (w/v) NaCl (optimum 2.5 %) and 1.0–7.0 % O2 in the gas phase (optimum 3.0 %). Fatty acids detected were C16 : 0 (8.0 %), C18 : 0 (9.0 %), C18 : 1 (62.5 %) and C20 : 1 (20.5 %). The genomic DNA G+C content was 51.3 mol%. 16S rRNA gene sequence analysis indicated that strain LS12-2T belonged to the genus Hydrogenivirga. Based on physiological and phylogenetic characteristics of the isolate, it is proposed that this strain represents a novel species in the genus Hydrogenivirga, Hydrogenivirga okinawensis sp. nov. The type strain of Hydrogenivirga okinawensis is LS12-2T (=JCM 13302T=DSM 17378T).