Sulfurivirga caldicuralii gen. nov., sp. nov., a novel microaerobic, thermophilic, thiosulfate-oxidizing chemolithoautotroph, isolated from a shallow marine hydrothermal system occurring in a coral reef, Japan Ken Takai, 1 Masayuki Miyazaki, 1 Takuro Nunoura, 1 Hisako Hirayama, 1 Hanako Oida, 1 Yasuo Furushima, 2 Hiroyuki Yamamoto 2 and Koki Horikoshi 1 Correspondence Ken Takai kent@jamstec.go.jp 1,2 Subground Animalcule Retrieval (SUGAR) Program 1 and Marine Biology and Ecology Program 2 , Japan Agency for Marine-Earth Science and Technology (JAMSTEC), 2-15 Natsushima-cho, Yokosuka 237-0061, Japan Novel thermophilic bacteria, designated strains VW1 and MM1 T , were isolated from hydrothermal fluid and microbial mat samples, respectively, collected from a shallow marine hydrothermal system (water depth 22 m) occurring in coral reefs off Taketomi Island, Okinawa, Japan. Cells of the two novel strains were motile rods with a single polar flagellum in the exponential growth phase. In a medium that included elemental sulfur, cells of the two strains became non-motile with oval to spherical cell shapes. For both strains, growth occurred at between 30 and 60 6C (optimum temperature of 50–55 6C; 60–80 min doubling time) and between pH 5?5 and 7?1 (optimum pH 6?0). The isolates were microaerobic chemolithoautotrophs capable of using thiosulfate or tetrathionate as the sole energy source, O 2 as the sole electron acceptor and CO 2 as the sole carbon source. Organic substrates, such as yeast extract and tryptone, inhibited growth of both strains. The G+C contents of genomic DNA were 51?3 and 49?5 mol% for strains VW1 and MM1 T , respectively. Phylogenetic analysis based on 16S rRNA gene sequences indicated that the two strains were closely related to each other (99?9 % sequence similarity) and were distantly related to other previously described genera within the Gammaproteobacteria. The novel isolates could also be differentiated from other gammaproteobacterial genera on the basis of their physiological properties. It is suggested that the novel isolates represent the type species of a new genus, for which the name Sulfurivirga caldicuralii gen. nov., sp. nov. (type strain MM1 T =JCM 13439 T =DSM 17737 T ) is proposed. The occurrence of thermophilic, sulfur-oxidizing, chemo- lithoautotrophic bacteria is at present confined to a relatively narrow spectrum of taxa such as the Aquificae, Betaproteobacteria, Gammaproteobacteria and Epsilonproteo- bacteria (Garrity et al., 2005a, b, c; Reysenbach, 2001). Iso- lates from marine environments are further restricted to within the Aquificae and Epsilonproteobacteria (Go ¨tz et al., 2002; Huber et al., 1992; Nakagawa et al., 2004, 2005; Nakagawa & Takai, 2006; Reysenbach et al., 2000; Takai et al., 2003a). Several strains of thermophilic sulfur-oxidizing chemolithoautotrophs are known within the Gammaproteo- bacteria such as Acidithiobacillus caldus KU T (Hallberg & Lindstro ¨m, 1994; Kelly & Wood, 2000, 2005) and Ther- mithiobacillus tepidarius DSM 3134 T (Kelly & Wood, 2000; Wood & Kelly, 1985), both of which were isolated from terrestrial, acidic sulfide springs and metal sulfide ore biota. In contrast, a great diversity of mesophilic sulfur-oxidizing members of the Gammaproteobacteria have been found in a variety of marine environments, such as deep-sea and shallow marine hydrothermal systems and oceanic and coas- tal oxic–anoxic interfaces of sediments and water columns (Brinkhoff et al., 2005; Dando et al., 1998; Imhoff, 2005a, b; Jørgensen et al., 2005; Kuenen, 2005; Kuenen & Dubinina, 2005; Nishihara et al., 1991; Strohl, 2005; Schulz et al., 1999; Schulz & Jørgensen; 2005; Takai et al., 2004). Abbreviation: ORP, oxidation–reduction potential. The GenBank/EMBL/DDBJ accession numbers for the 16S rRNA gene sequences of strains MM1 T and VW1 are AB245479 and AB245480, respectively. Graphs showing the effects of temperature, pH and NaCl concentration on the growth of strains MM1 T and VW1 in MMJS medium are available as a supplementary figure in IJSEM Online. 64297 G 2006 IUMS Printed in Great Britain 1921 International Journal of Systematic and Evolutionary Microbiology (2006), 56, 1921–1929 DOI 10.1099/ijs.0.64297-0