Methanofervidicoccus abyssi gen. nov., sp. nov., a hydrogenotrophic methanogen, isolated from a hydrothermal vent chimney in the Mid-Cayman Spreading Center, the Caribbean Sea

A novel hydrogenotrophic methanogen, strain HHB T , was isolated from a deep-sea hydrothermal vent chimney sample collected from Beebe Vent Field at the Mid-Cayman Spreading Center, Caribbean Sea. The cells were non-motile regular to irregular cocci possessing several flagella. The novel isolate grew at 60–80 °C, pH 5.0–7.4 and with 1–4 % of NaCl (w/v). The isolate utilized H 2 /CO 2 as the only substrates for growth and methane production. The results of phylogenetic analyses of both 16S rRNA and mcrA gene sequences and comparative genome analysis indicated that HHB T represented a member of the order Methanococcales , and was closely related to the members of the genera Methanothermococcus and Methanotorris . The most closely related species were Methanothermococcus okinawensis IH1 T and Methanotorris igneus Kol 5 T in comparison of 16S rRNA gene sequences (each with 93 % identity), and Methanotorris formicicus Mc-S-70 T in the case of deduced amino acid sequence similarity of mcrA genes (92 % similarity). The ANI and AAI values between HHB T and the members of the genera Methanothermococcus and Methanotorris were 69–72 % and 66–70 %, respectively. Although many of the morphological and physiological characteristics were quite similar between HHB T and the species of the genera Methanothermococcus and Methanotorris , they were distinguishable by the differences in susceptibility to antibiotics, formate utilization, growth temperature and NaCl ranges. On the basis of these phenotypic, phylogenetic and genomic properties, we propose that strain HHB T represents a novel species, of a novel genus, Methanofervidicoccus abyssi gen. nov., sp. nov. The type strain is HHB T (=JCM 32161 T =DSM 105918 T ).