Thermococcus argininiproducens sp. nov., an arginine biosynthesis archaeal species isolated from the Central Indian Ocean ridge

A strictly anaerobic hyperthermophilic archaeon, designated strain IOH2T, was isolated from a deep -sea hydrothermal vent (Onnuri vent field) area on the Central Indian Ocean Ridge. Strain IOH2T showed high 16S rRNA gene sequence similarity to Thermococcus sibiricus MM 739T (99.42%), Thermococcus alcaliphilus DSM 10322T (99.28%), Thermococcus aegaeus P5T (99.21 %), Thermococcus litoralis DSM 5473T (99.13 %), ' bergensis'Thermococcus T7324T (99.13 %), Thermococcus aggregans TYT (98.92 %) and Thermococcus prieurii Bio-pl-0405IT2T (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 IOH2T and T. sibiricus MM 739T (79.33 and 15.00 %, respectively); these values are much lower than the species delineation cut -offs. Cells of strain IOH2T were coccoid, 1.0-1.2 mu m in diameter and had no flagella. Growth ranges were 60-85 degrees C (optimum at 80 degrees C), pH 4.5-8.5 (optimum at pH 6.3) and 2.0-6.0 % (optimum at 4.0 %) NaCl. Growth of strain IOH2T was enhanced by starch, glucose, maltodextrin and pyru-vate as a carbon source, and elemental sulphur as an electron acceptor. Through genome analysis of strain IOH2T, arginine bio-synthesis related genes were predicted, and growth of strain IOH2T without arginine was confirmed. The genome of strain IOH2T was assembled as a circular chromosome of 1 946 249 bp and predicted 2096 genes. The DNA G+C content was 39.44 mol%. Based on the results of physiological and phylogenetic analyses, Thermococcus argininiproducens sp. nov. is proposed with type strain IOH2T (=MCCC 4K00089T=KCTC 25190T).