METHANOCOCCUS INFERNOS SP. NOV., A NOVEL HYPERTHERMOPHILIC LITHOTROPHIC METHANOGEN ISOLATED FROM A DEEP-SEA HYDROTHERMAL VENT

An autotrophic, extremely thermophilic methanogen (MET) was isolated f rom a deep-sea hydrothermal chimney sample collected on the Mid-Atlant ic Ridge at a depth of 3000 m. The heavily flagellated cells are motil e and coccoid shaped. The new strain grows between 55 and 91 degrees C , with an optimum growth temperature at 85 degrees C. The optimum pH f or growth is 6.5, and the optimum sea salt concentration for growth is around 25 g l(-1). The organism uses H-2 and CO2 as the only substrat e for growth and methane production. Tungsten, selenium and yeast extr act stimulate growth significantly. In the presence of CO2 and H-2, th e organism reduces elemental sulphur to hydrogen sulphide. The G+C con tent of the genomic DNA is 33 mol%. As determined by 16S gene sequence analysis, this organism is closely related to Methanococcus jannaschi i strain JAL-1(T). However, no significant homology was observed betwe en them with DNA-DNA hybridization. It is proposed that this organism should be placed in a new species, Methanococcus infernus. The type st rain is MET (= DSM 11812(T)).