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Methanocaldococcus indicus sp. nov., a novel hyperthermophilic methanogen isolated from the Central Indian Ridge

¹ UMR 6539, Centre National de la Recherche Scientifique, and Université de Bretagne Occidentale, Institut Universitaire Européen de la Mer, F-29280 Plouzané, France
² Portland State University, Department of Biology, Portland, OR 97201, USA
³ Zentrum für Ultrastrukturforschung und Ludwig Boltzmann-Institut für Molekulare Nanotechnologie, Universität für Bodenkultur, A-1180 Wien, Austria
⁴ DSMZ – German Collection of Microorganisms and Cell Cultures, Mascheroder Weg 1b, D-38124 Braunschweig, Germany

Correspondence
C. Jeanthon
jeanthon{at}univ-brest.fr

An autotrophic, hyperthermophilic methanogen, strain SL43^T, was isolated from a deep-sea hydrothermal chimney sample collected on the Central Indian Ridge at a depth of 2420 m. The coccoid, surface-layer-carrying, Gram-negative-staining cells were heavily flagellated and exhibited a slight tumbling motility. The temperature range for growth at pH 6·5 was 50–86 °C, with optimum growth at 85 °C. The optimum pH for growth was 6·6 and the optimum NaCl concentration for growth was 30 g l^-1. The novel isolate used H₂ and CO₂ as the only substrates for growth and produced methane. Selenium and yeast extract stimulated growth significantly. In the presence of CO₂ and H₂, the organism reduced elemental sulfur to hydrogen sulfide. Growth was inhibited by chloramphenicol and rifampicin, but not by ampicillin, kanamycin, penicillin or streptomycin. The G+C content of the genomic DNA was 30·7 mol%. On the basis of 16S rRNA gene sequence analysis, this organism was most closely related to Methanocaldococcus infernus ME^T (3·2 % distance). Its phylogenetic distinctiveness was confirmed by RFLP analysis of the 16S rDNA, a reliable tool for differentiating hyperthermophilic methanococci. On the basis of phylogenetic and physiological characteristics, it is proposed that strain SL43^T (=DSM 15027^T=JCM 11886^T) be designated as the type strain of a novel species, Methanocaldococcus indicus sp. nov.

The GenBank accession number for the 16S rDNA sequence of Methanocaldococcus indicus SL43^T is AF547621.

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