title: Nitratiruptor tergarcus gen. nov., sp. nov. and Nitratifractor salsuginis gen. nov., sp. nov., nitrate-reducing chemolithoautotrophs of the epsilon-Proteobacteria isolated from a deep-sea hydrothermal system in the Mid-Okinawa Trough.
abstract: Two novel denitrifying bacteria, designated strains MI55-1(T) and E9I37-1(T), were isolated from deep-sea hydrothermal vent chimney structures at the Iheya North hydrothermal field in the Mid-Okinawa Trough, Japan. Both isolates were strict chemolithoautotrophs growing by respiratory nitrate reduction with H(2), forming N(2) as a metabolic product. Oxygen (at low concentrations) could serve as an alternative electron acceptor for growth of the isolates. Growth of strain MI55-1(T) was observed at temperatures between 40 and 57 degrees C (optimum, 55 degrees C; doubling time, 2 h), at pH values between 5.4 and 6.9 (optimum, pH 6.4) and in the presence of between 1.5 and 4.0 % (w/v) NaCl (optimum, 2.5 %). Growth of strain E9I37-1(T) was observed at temperatures between 28 and 40 degrees C (optimum, 37 degrees C; doubling time, 2.5 h), at pH values between 5.6 and 7.6 (optimum, pH 7.0) and in the presence of between 1.5 and 3.5 % (w/v) NaCl (optimum, 3.0 %). The G+C contents of the genomic DNA of strains MI55-1(T) and E9I37-1(T) were 29.6 and 35.5 mol%, respectively. Phylogenetic analysis based on 16S rRNA gene sequences indicated that strains MI55-1(T) and E9I37-1(T) belonged to groups A and F of the epsilon-Proteobacteria, but that they had distant phylogenetic relationships with any species, within the phylogenetic groups, that had validly published names (sequence similarities were less than 91 %). On the basis of the physiological and molecular characteristics of the novel isolates, it is proposed that they should each be classified in a novel genus: Nitratiruptor tergarcus gen. nov., sp. nov., with MI55-1(T) (=JCM 12459(T)=DSM 16512(T)) as the type strain, and Nitratifractor salsuginis gen. nov., sp. nov., with E9I37-1(T) (=JCM 12458(T)=DSM 16511(T)) as the type strain.
authors.affiliation: Laboratory of Marine Microbiology, Graduate School of Agriculture, Kyoto University, Kyoto 606-8502, Japan.
authors.forename: Satoshi
authors.initials: S
authors.lastname: Nakagawa
authors.affiliation: Subground Animalcule Retrieval (SUGAR) Project, Frontier Research System for Extremophiles, Japan Agency for Marine-Earth Science and Technology, 2-15 Natsushima-cho, Yokosuka 237-0061, Japan.
authors.forename: Ken
authors.initials: K
authors.lastname: Takai
authors.affiliation: Subground Animalcule Retrieval (SUGAR) Project, Frontier Research System for Extremophiles, Japan Agency for Marine-Earth Science and Technology, 2-15 Natsushima-cho, Yokosuka 237-0061, Japan.
authors.forename: Fumio
authors.initials: F
authors.lastname: Inagaki
authors.affiliation: Subground Animalcule Retrieval (SUGAR) Project, Frontier Research System for Extremophiles, Japan Agency for Marine-Earth Science and Technology, 2-15 Natsushima-cho, Yokosuka 237-0061, Japan.
authors.forename: Koki
authors.initials: K
authors.lastname: Horikoshi
authors.affiliation: Laboratory of Marine Microbiology, Graduate School of Agriculture, Kyoto University, Kyoto 606-8502, Japan.
authors.forename: Yoshihiko
authors.initials: Y
authors.lastname: Sako
mesh_terms: D015373:Bacterial Typing Techniques; D004269:DNA, Bacterial / Q000032:analysis; D004275:DNA, Ribosomal / Q000032:analysis; D020565:Epsilonproteobacteria / Q000145:classification* / Q000235:genetics / Q000254:growth & development / Q000302:isolation & purification; D006358:Hot Temperature; D007564:Japan; D008969:Molecular Sequence Data; D009566:Nitrates / Q000378:metabolism*; D010084:Oxidation-Reduction; D010802:Phylogeny; D012336:RNA, Ribosomal, 16S / Q000235:genetics; D012623:Seawater / Q000382:microbiology*; D017422:Sequence Analysis, DNA; D013045:Species Specificity
chemical_list: D004269:DNA, Bacterial; D004275:DNA, Ribosomal; D009566:Nitrates; D012336:RNA, Ribosomal, 16S