Thermosipho affectus sp. nov., a thermophilic, anaerobic, cellulolytic bacterium isolated from a Mid-Atlantic Ridge hydrothermal vent

A novel obligately anaerobic, extremely thermophilic, organotrophic bacterium, strain ik275mar^T, was isolated from a Mid-Atlantic Ridge deep-sea hydrothermal vent. Cells were rods surrounded by a sheath-like structure (toga), 0.4-0.9 μm in width and 1.2-6.0 μm in length. Strain ik275mar^T grew at 37-75 °C, pH 5.6-8.2 and at NaCl concentrations of 10-55 g l^-1. Under optimum conditions (70 °C, pH 6.6, NaCl 20 g l^-1), doubling time was 32 min. The isolate was able to ferment carbohydrates including starch, cellulose and cellulose derivatives. Acetate, H₂ and CO₂ were the main products of glucose fermentation. G+C content of DNA was 27 mol%. Phylogenetic analysis of 16S rRNA gene sequences showed that strain ik275mar^T is a member of the genus Thermosipho. 16S rRNA gene sequence identity with the other species of the genus Thermosipho ranged from 93.7 to 94.5%. Based on the phylogenetic analysis and physiological properties of the novel isolate, we propose a novel species, Thermosipho affectus sp. nov., with type strain ik275mar^T (=DSM 23112^T =VKM B-2574^T).