Thermosipho activus sp. nov., a thermophilic, anaerobic, hydrolytic bacterium isolated from a deep-sea sample

A novel obligately anaerobic, extremely thermophilic, organotrophic bacterium, strain Rift-s3^T, was isolated from a deep-sea sample containing Riftia pachyptila sheath from Guaymas Basin, Gulf of California. Cells of the novel isolate were rods, 0.3-0.8 µmm in width and 1.5-10 µmm in length, surrounded by a sheath-like structure (toga). Strain Rift-s3^T grew at temperatures ranging from 44 to 75 °C, at pH 5.5 to 8.0, and with NaCl concentrations of 3 to 60 g l^-1. Under optimum conditions (65 °C, pH 6.0, NaCl 25 g l^-1), the doubling time was 30 min. The isolate was able to ferment mono-, oligo-and polysaccharides including cellulose, chitin, xylan and pectin, and proteins including β-keratins, casein and gelatin. Acetate, hydrogen and carbon dioxide were the main products of glucose fermentation. The G+C content of the DNA was 30 mol%. Phylogenetic analysis of 16S rRNA gene sequences showed the affiliation of strain Rift-s3^T with the genus Thermosipho, with Thermosipho atlanticus Ob7^T as the closest relative (96.5% 16S rRNA gene sequence similarity). Based on the phylogenetic analysis and physiological properties of the novel isolate we propose a novel species of the genus Thermosipho, Thermosipho activus sp. nov., with Rift-s3^T (=DSM 26467^T=VKM B-2803^T) as the type strain.