sp. nov., a novel anaerobic bacterium isolated from a deep-sea hydrothermal vent.

A novel anaerobic heterotrophic bacterium, designated strain SWIR-1, was isolated from a deep-sea hydrothermal vent field sample collected from the Southwest Indian Ridge at a depth of 2700 m. Phylogenetic analysis indicated that strain SWIR-1 belongs to the genus , and the most closely related species are B1 (99.1 % 16S rRNA gene sequence similarity), DV1184 (94.6 %) and SC562 (93.9 %). Strain SWIR-1 shares 77.3-87.2 % average nucleotide identity and 21.5-35.7 % digital DNA-DNA hybridization values with the three type strains of species. Cells of strain SWIR-1 were Gram-stain-positive, motile, short straight rods. Endospores were observed in stationary-phase cells when grown on rich medium. Strain SWIR-1 grew at 15-45 °C (optimum, 30°C), at pH 5.5-8.0 (optimum, pH 7.0) and with 1.0-6.0 % (w/v) NaCl (optimum, 2.0 %). Substrates utilized by strain SWIR-1 included complex proteinaceous, chitin, starch, lactose, maltose, fructose, galactose, glucose, rhamnose, arabinose, ribose, alanine, glycine and glycerol. The major fermentation products from glucose were acetate, lactate, H and CO. Elemental sulphur, sulphate, thiosulphate, sulphite, fumarate, nitrate, nitrite and FeCl are not used as terminal electron acceptors. The main cellular fatty acids consisted of iso-C (28.4 %), C iso F (15.4 %) and C (9.8 %). The major polar lipids were phospholipids and glycolipids. No respiratory quinones were detected. Genomic comparison revealed a distinctive blended gene cluster comprising genes, which play a crucial role in the synthesis, maturation, activation and export of NiFe-hydrogenase. Based on the phylogenetic analysis, genomic, physiologic and chemotaxonomic characteristics, strain SWIR-1 is considered to represent a novel species within the genus , for which the name sp. nov. is proposed. The type strain is strain SWIR-1 (=DSM 113848=MCCC 1K07078).