Thermococcus indicus sp. nov., a Fe(III)-reducing hyperthermophilic archaeon isolated from the Onnuri Vent Field of the Central Indian Ocean ridge.

A strictly anaerobic, dissimilatory Fe(III)-reducing hyperthermophilic archaeon, designated as strain IOH1, was isolated from a new deep-sea hydrothermal vent (Onnuri Vent Field) area in the Central Indian Ocean ridge. Strain IOH1 showed > 99% 16S rRNA gene sequence similarity with Thermococcus celericrescens TS2 (99.4%) and T. siculi DSM 12349 (99.2%). Additional three species T. barossii SHCK-94 (99.0%), T. celer Vu13 (98.8%), and (98.6%) showed > 98.6% of 16S rRNA gene sequence similarity, however, the maximum OrthoANI value is 89.8% for the genome of T. celericrescens TS2. Strain IOH1 cells are coccoid, 1.2-1.8 μm in diameter, and motile by flagella. Growth was at 70-82°C (optimum 80°C), pH 5.4-8.0 (optimum pH 6.0) with 2-4% (optimum 3%) NaCl. Growth of strain IOH1T was enhanced by starch, pyruvate, D(+)-maltose and maltodextrin as a carbon sources, and elemental sulfur as an electron acceptor; clearly different from those of related species T. celecrescens DSM 17994 and T. siculi DSM 12349. Strain IOH1, T. celercrescence DSM 17994, and T. siculi DSM 12349 reduced soluble Fe(III)-citrate present in the medium, whereas the amount of total cellular proteins increased with the concomitant accumulation of Fe(II). We determined a circular chromosome of 2,234 kb with an extra-chromosomal archaeal plasmid, pTI1, of 7.7 kb and predicted 2,425 genes. The DNA G + C content was 54.9 mol%. Based on physiological properties, phylogenetic, and genome analysis, we proposed that strain IOH1 (= KCTC 15844 = JCM 39077) is assigned to a new species in the genus Thermococcus and named Thermococcus indicus sp. nov.