Thermococcus thermotolerans sp. nov., a hyperthermophilic archaeon isolated from a chimney in the Southwest Indian Ocean

An anaerobic hyperthermophilic archaeon was isolated from a black smoker chimney with a snail attachment at a water depth of 2 739 m in the Southwest Indian Ocean. The sample was taken from the chimney exterior wall. The enrichment was conducted under a continuous culture with temperature fluctuation of 80-130 degrees C over 24 h for 42 days at 28 MPa. The isolation was performed at 90 degrees C at 0.1 MPa. Cells of the isolated strain 813A4T were irregular cocci. Strain 813A4T grew at 60-94 degrees C (optimal growth at 85 degrees C) at 0.1 MPa, and growth was detected at up to 99 degrees C at 28 MPa. At 85 degrees C, the strain was able to grow at pressures ranging from 0.1 to 110 MPa (optimal pressure, 0.1-40 MPa). At 85 degrees C, the cells of 813A4T grew at pH 5.5-9 (optimal, pH 7.0) and a NaCl concentration of 1.0-4.0 % (w/v; optimum concentration, 2.5 % NaCl). Strain 813A4T utilized yeast extract, tryptone and peptone as single carbon sources for growth. Elemental sulphur stimulated its growth. The G+C content of the complete genome was 53.48 mol%. Phylogenetic analysis based on 16S rRNA gene sequences revealed that strain 813A4T belonged to the genus Thermococcus, with the highest sequence similarity to Thermococcus barossii SHCK-94T (99.73 %). The average nucleotide identity between strains 813A4T and SHCK- 94T was 82.56 %. All these data indicated that strain 813A4T should be classified as representing a novel species of the genus Thermococcus, for which Thermococcus thermotolerans sp. nov. is proposed. The type strain is 813A4T (=JCM 39367T=MCCC M28628T).