Desulfosoma profundi sp. nov., a thermophilic sulfate-reducing bacterium isolated from a deep terrestrial geothermal spring in France

A novel strictly anaerobic bacterium designated SPDX02-08 T was isolated from a deep terrestrial geothermal spring located in southwest France. Cells (1–2 × 2–6 μm) were non-motile, non sporulating and stained Gram negative. Strain SPDX02-08 T grew at a temperature between 40 and 60°C (optimum 55°C), pH between 6.3 and 7.3 (optimum 7.2) and a NaCl concentration between 0 and 5 g/l (optimum 2 g/l). Sulfate, thiosulfate and sulfite were used as terminal electron acceptors, but not elemental sulfur, nitrate, nitrite, Fe (III) or fumarate. In the presence of sulfate, strain SPDX02-08 T completely oxidized pyruvate, propionate, butyrate, isobutyrate, valerate, isovalerate and hexadecanoate. Stoichiometric measurements revealed a complete oxidation of part of lactate (0.125 mol of acetate produced per mole lactate oxidized). Strain SPDX02-08 T required yeast extract to oxidize formate and H 2 but did not grow autotrophically on H 2 . Among the substrates tested, only pyruvate was fermented. The G+C content of the genomic DNA was 57.6 mol%. Major cellular fatty acids of strain SPDX02-08 T were iso-C 15:0 , C 15:0 , and C 16:0 . Phylogenetic analysis of the 16S small-subunit (SSU) ribosomal RNA gene sequence indicated that strain SPDX02-08 T belongs to the genus Desulfosoma , family Syntrophobacteraceae , having Desulfosoma caldarium as its closest phylogenetic relative (97.6% similarity). The mean DNA/DNA reassociation value between strain SPDX02-08 T and Desulfosoma caldarium was 16.9 ± 2.7%. Based on the polyphasic differences, strain SPDX02-08 T is proposed to be assigned as a new species of the genus Desulfosoma , Desulfosoma profundi sp. nov. (DSM 22937 T = JCM 16410 T ). GenBank accession number for the 16S rRNA gene sequence of strain SPDX02-08 T is HM056226.