Desulfotomaculum thermosubterraneum sp. nov., a thermophilic sulfate-reducer isolated from an underground mine located in a geothermally active area

A thermophilic, Gram-positive, endospore-forming, sulfate-reducing bacterium was isolated from an underground mine in a geothermally active area in Japan. Cells of this strain, designated RL50JIII^T, were rod-shaped and motile. The temperature range for growth was 5072 °C (optimum growth at 6166 °C) and the pH range was 6.47.8 (optimum at pH 7.27.4). Strain RL50JIII^T tolerated up to 1.5 % NaCl, but optimum growth occurred in the presence of 01 % NaCl. Electron acceptors utilized were sulfate, sulfite, thiosulfate and elemental sulfur. Electron donors utilized were H₂ in the presence of CO₂, alanine, various carboxylic acids and alcohols. Fermentative growth occurred on lactate and pyruvate. The cell wall contained mesodiaminopimelic acid and the major respiratory isoprenoid quinone was menaquinone 7 (MK-7). Major whole-cell fatty acids were iso-C_{15 : 0}, iso-C_{17 : 0} DMA (dimethyl acetal), iso-C_{15 : 0} DMA and iso-C_{17 : 0}. Phylogenetic analysis based on 16S rRNA gene sequence comparisons revealed 98.7 % similarity with Desulfotomaculum solfataricum DSM 14956^T. However, DNADNA hybridization experiments with Desulfotomaculum kuznetsovii, Desulfotomaculum luciae and D. solfataricum and the G+C content of the DNA (54.4 mol%) allowed the differentiation of strain RL50JIII^T from the recognized species of the genus Desulfotomaculum. Strain RL50JIII^T therefore represents a novel species, for which the name Desulfotomaculum thermosubterraneum sp. nov. is proposed. The type strain is RL50JIII^T (=DSM 16057^T=JCM 13837^T).