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 RL50JIIIT, were rod-shaped and motile. The temperature range for growth was 50-72 degrees C (optimum growth at 61-66 degrees C) and the pH range was 6.4-7.8 (optimum at pH 7.2-7.4). Strain RL50JIIIT tolerated up to 1.5% NaCl, but optimum growth occurred in the presence of 0-1% 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-C15:0, iso-C17:0 DMA (dimethyl acetal), iso-C15:0 DMA and iso-C17:0. Phylogenetic analysis based on 16S rRNA gene sequence comparisons revealed 98.7% similarity with Desulfotomaculum solfataricum DSM 14956T. However, DNA-DNA 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 RL50JIIIT from the recognized species of the genus Desulfotomaculum. Strain RL50JIIIT therefore represents a novel species, for which the name Desulfotomaculum thermosubterraneum sp. nov. is proposed. The type strain is RL50JIIIT (=DSM 16057T=JCM 13837T).