RT Journal Article SR Electronic(1) A1 L'Haridon, S. A1 Reysenbach, A.-L. A1 Banta, A. A1 Messner, P. A1 Schumann, P. A1 Stackebrandt, E. A1 Jeanthon, C.YR 2003 T1 Methanocaldococcus indicus sp. nov., a novel hyperthermophilic methanogen isolated from the Central Indian Ridge JF International Journal of Systematic and Evolutionary Microbiology, VO 53 IS 6 SP 1931 OP 1935 DO https://doi.org/10.1099/ijs.0.02700-0 PB Microbiology Society, SN 1466-5034, AB An autotrophic, hyperthermophilic methanogen, strain SL43T, 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 MET (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 SL43T (=DSM 15027T=JCM 11886T) be designated as the type strain of a novel species, Methanocaldococcus indicus sp. nov., UL https://www.microbiologyresearch.org/content/journal/ijsem/10.1099/ijs.0.02700-0