Methanococcus infernus sp. nov., a novel hyperthermophilic lithotrophic methanogen isolated from a deep-sea hydrothermal vent

An autotrophic, extremely thermophilic methanogen (ME(T)) was isolated from a deep-sea hydrothermal chimney sample collected on the Mid-Atlantic Ridge at a depth of 3000 m. The heavily flagellated cells are motile and coccoid shaped. The new strain growths between 55 and 91 degrees C, with an optimum growth temperature at 85 degree C. The optimum pH for growth is 6.5, and the optimum sea salt concentration for growth is around 25 g l-1. The organism uses H2 and CO2 as the only substrate for growth and methane production. Tungsten, selenium and yeast extract stimulate growth significantly. In the presence of CO2 and H2, the organism reduces elemental sulphur to hydrogen sulphide. The G+C content of the genomic DNA is 33 mol%. As determined by 16S gene sequence analysis, this organism is closely related to Methanococcus jannaschii strain JAL-1T. However, no significant homology was observed between them with DNA-DNA hybridization. It is proposed that this organism should be placed in a new species, Methanococcus infernus. The type strain is ME(T) (= DSM 11812T).