Desulfomicrobium thermophilum sp. nov., a novel thermophilic sulphate-reducing bacterium isolated from a terrestrial hot spring in Colombia

A moderately thermophilic, sulphate-reducing bacterium, designated strain P6-2^T, was isolated from a terrestrial hot spring located at a height of 2,500 m in the Andean region, Colombia (5°43′69″N, 73°6′10″W). Cells of strain P6-2^T were rod-shaped, stained Gram-negative and were motile by means of a single polar flagellum. The strain grew lithotrophically with H₂ as the electron donor and organotrophically on lactate, pyruvate, ethanol, malate, fumarate, n-propanol and succinate in the presence of sulphate as the terminal electron acceptor. Fumarate and pyruvate was fermented. Strain P6-2^T grew optimally at 55°C (range 37-60°C), pH 6.6 (range 5.8-8.8) in the presence of 0.5% NaCl (range 0-4.5%) with lactate and sulphate and produced acetate, CO ₂ and H₂S as the major end-products. Sulphate, sulphite and thiosulphate could be used as electron acceptors but not elemental sulphur or nitrate. The G + C content of the genomic DNA was 58.7 mol%. The 16S rRNA sequence analysis indicated that strain P6-2^T was a member of the class Deltaproteobacteria, domain Bacteria with Desulfomicrobium baculatum being the closest relative (similarity value of 94%). Phylogeny of genes encoding α- and β-subunits of the dissimilatory sulphite reductase (dsrAB genes) supported its affiliation to members of the genus Desulfomicrobium. On the basis of this evidence, we propose to assign strain P6-2^T as new species of the genus Desulfomicrobium, D. thermophilum sp. nov., with strain P6-2^T as the type strain (= DSM 16697^T = CCUG 49732 ^T).