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

A novel anaerobic heterotrophic bacterium, designated strain SWIR-1(T), 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(T) belongs to the genus Tepidibacter, and the most closely related species are Tepidibacter mesophilus B1(T) (99.1 % 16S rRNA gene sequence similarity), Tepidibacter formicigenes DV1184(T) (94.6%) and Tepidibacter thalassicus SC562(T) (93.9 %). Strain SWIR-1T shares 77.3-87.2% average nucleotide identity and 21.5-35.7% digital DNA-DNA hybridization values with the three type strains of Tepidibacter species. Cells of strain SWIR-1(T) were Gram-stain- positive, motile, short straight rods. Endospores were observed in stationary-phase cells when grown on Thermococcales rich medium. Strain SWIR-1(T) grew at 15-45 degrees C (optimum, 30 degrees 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(T) 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-2 and CO2. Elemental sulphur, sulphate, thiosulphate, sulphite, fumarate, nitrate, nitrite and FeCl3 are not used as terminal electron acceptors. The main cellular fatty acids consisted of iso-C-15:0 (28.4%), C-15:1 iso F (15.4%) and C-16: 0 (9.8%). The major polar lipids were phospholipids and glycolipids. No respiratory quinones were detected. Genomic comparison revealed a distinctive blended gene cluster comprising hyb-tat- hyp 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-1T is considered to represent a novel species within the genus Tepidibacter, for which the name Tepidibacter hydrothermalis sp. nov. is proposed. The type strain is strain SWIR-1(T) (=DSM 113848(T)=MCCC 1K07078(T))