Hydrogenimonas leucolamina sp. nov., a hydrogen- and sulphur-oxidizing mesophilic chemolithoautotroph isolated from a deep-sea hydrothermal vent chimney at the Suiyo Seamount in the Western Pacific Ocean

A novel mesophilic bacterium, strain SS33^T, was isolated from a deep-sea hydrothermal vent chimney at Suiyo Seamount, Izu-Bonin Arc, Western Pacific Ocean. The cells of strain SS33^T were motile short rods with a single polar flagellum. The growth of strain SS33^T was observed at the temperature range between 33 and 55 °C (optimum growth at 45 °C), at the pH range between 5.0 and 7.1 (optimum growth at pH 6.0) and in the presence of between 2.0 and 4.5% (w/v) NaCl [optimum growth at 3.5% (w/v)]. Strain SS33^T was a facultative anaerobic chemolithoautotroph using molecular hydrogen and elemental sulphur as the sole electron donor. Nitrate, nitrous oxide, sulphate, elemental sulphur and molecular oxygen were capable of serving as the sole electron acceptor. Phylogenetic analysis based on 16S rRNA gene sequences placed strain SS33^T in the genus <i>Hydrogenimonas</i> belonging to the class <i>Epsilonproteobacteria</i>. The closely related species of strain SS33^T were <i>Hydrogenimonas urashimensis</i> SSM-Sur55^T (95.96%), <i>Hydrogenimonas thermophila</i> EP1-55-1%^T (95.75%) and <i>Hydrogenimonas cancrithermarum</i> ISO32^T (95.24%). According to the taxonomic and physiological characteristics, it is proposed that strain SS33^T was classified into a novel species of genus <i>Hydrogenimonas</i>, <i>Hydrogenimonas leucolamina</i> sp. nov., with SS33^T (=JCM 39184^T =KCTC 25253^T) as the type strain. Furthermore, the genome comparison of <i>Epsilonproteobacteria</i> revealed that their [NiFe] hydrogenase genes belonging to Group 1b could be divided into two phylogenetic lineages and suggested that the reverse gyrase gene has been lost after division to the genus <i>Hydrogenimonas</i>.