Geothermobacter hydrogeniphilus sp. nov., a mesophilic, iron(III)-reducing bacterium from seafloor/subseafloor environments in the Pacific Ocean, and emended description of the genus Geothermobacter

A novel mesophilic, anaerobic, mixotrophic bacterium, with designated strains EPR-MT and HR-1, was isolated from a semi-extinct hydrothermal vent at the East Pacific Rise and from an Fe-mat at Lo'ihi Seamount, respectively. The cells were Gram-negative, pleomorphic rods of about 2.0 mu m in length and 0.5 mu m in width. Strain EPR-MT grew between 25 and 45 degrees C (optimum, 37.5-40 degrees C), 10 and 50 g l(-1) NaCl (optimum, 15-20 g l(-1)) and pH 5.5 and 8.6 (optimum, pH 6.4). Strain HR-1 grew between 20 and 45 degrees C (optimum, 37.5-40 degrees C), 10 and 50 g l(-1) NaCl (optimum, 15-25 g l(-1)) and pH 5.5 and 8.6 (optimum, pH 6.4). Shortest generation times with H-2 as the primary electron donor, CO2 as the carbon source and ferric citrate as terminal electron acceptor were 6.7 and 5.5 h for EPR-M-T and HR-1, respectively. Fe(OH)(3), MnO2, AsO43-, SO42-, SeO42-, S2O32-, S-0 and NO3- were also used as terminal electron acceptors. Acetate, yeast extract, formate, lactate, tryptone and Casamino acids also served as both electron donors and carbon sources. G+C content of the genomic DNA was 59.4mol% for strain EPR-M-T and 59.2mol% for strain HR-1. Phylogenetic and phylogenomic analyses indicated that both strains were closely related to each other and to Geothermobacter ehrlichii, within the class delta-Proteobacteria (now within the class Desulfuromonadia). Based on phylogenetic and phylogenomic analyses in addition to physiological and biochemical characteristics, both strains were found to represent a novel species within the genus Geothermobacter, for which the name Geothermobacter hydrogeniphilus sp. nov. is proposed. Geothermobacter hydrogeniphilus is represented by type strain EPR-M-T (=JCM 32109(T)=KCTC 15831(T)=ATCC TSD-173(T)) and strain HR-1 (=JCM 32110=KCTC 15832).