Kae Kyoung Kwon

A strictly anaerobic hyperthermophilic archaeon, designated strain IOH2 T , was isolated from a deep-sea hydrothermal vent (Onnuri vent field) area on the Central Indian Ocean Ridge. Strain IOH2 T showed high 16S rRNA gene sequence similarity to Thermococcus sibiricus MM 739 T (99.42 %), Thermococcus alcaliphilus DSM 10322 T (99.28 %), Thermococcus aegaeus P5 T (99.21 %), Thermococcus litoralis DSM 5473 T (99.13 %), ‘ Thermococcus bergensis’ T7324 T (99.13 %), Thermococcus aggregans TY T (98.92 %) and Thermococcus prieurii Bio-pl-0405IT2 T (98.01 %), with all other strains showing lower than 98 % similarity. The average nucleotide identity and in silico DNA–DNA hybridization values were highest between strain IOH2 T and T. sibiricus MM 739 T (79.33 and 15.00 %, respectively); these values are much lower than the species delineation cut-offs. Cells of strain IOH2 T were coccoid, 1.0–1.2 µm in diameter and had no flagella. Growth ranges were 60–85 °C (optimum at 80 °C), pH 4.5–8.5 (optimum at pH 6.3) and 2.0–6.0 % (optimum at 4.0 %) NaCl. Growth of strain IOH2 T was enhanced by starch, glucose, maltodextrin and pyruvate as a carbon source, and elemental sulphur as an electron acceptor. Through genome analysis of strain IOH2 T , arginine biosynthesis related genes were predicted, and growt