Desulfotomaculum tongense sp. nov., a moderately thermophilic sulfate-reducing bacterium isolated from a hydrothermal vent sediment collected from the Tofua Arc in the Tonga Trench

A novel, strictly anaerobic, moderately thermophilic, endospore-forming, sulfate-reducing bacterium, designated TGB60-1^T, was isolated from a hydrothermal sediment vent collected from the Tofua Arc in the Tonga Trench. The strain was characterized phenotypically and phylogenetically. The isolated strain was observed to be Gram-positive, with slightly curved rod-shaped cells and a polar flagellum. Strain TGB60-1^T was found to grow anaerobically at 37–60 °C (optimum, 50 °C), at pH 6.0–8.5 (optimum, pH 7.0) and with 1.0–4.0 % (w/v) NaCl (optimum, 3.0 %). The electron acceptors utilised were determined to be sulfate, sulfite, and thiosulfate. Strain TGB60-1^T was found to utilise pyruvate and H₂ as electron donors. Strain TGB60-1^T was determined to be related to representatives of the genus Desulfotomaculum and the closest relatives within this genus were identified as Desulfotomaculum halophilum SEBR 3139^T, Desulfotomaculum alkaliphilum S1^T and Desulfotomaculum peckii LINDBHT1^T (92.7, 92.1, and 91.8 % 16S rRNA gene sequence similarity, respectively). The major fatty acids (>20 %) were identified as C_16:0 and C_18:1 ω7c. The G+C content of the genomic DNA of this novel bacterium was determined to be 53.9 mol%. Based on this polyphasic taxonomic study, strain TGB60-1^T is considered to represent a novel species in the genus Desulfotomaculum, for which the name Desulfotomaculum tongense sp. nov. is proposed. The type strain of D. tongense is strain TGB60-1^T (= KTCT 4534^T = JCM 18733^T).