Methanococcus vulcanius sp. nov., a novel hyperthermophilic methanogen isolated from East Pacific Rise, and identification of Methanococcus sp. DSM 4213(T) as Methanococcus fervens sp. nov.

An autotrophic, hyperthermophilic methanogen (M7(T)) was isolated from a de ep-sea hydrothermal chimney sample collected on the East Pacific Rise at a depth of 2600 m. The coccoid-shaped cells are flagellated and exhibit a sli ght tumbling motility. The temperature range for growth at pH 6.5 was 49-89 degrees C, with optimum growth at 80 degrees C. The optimum ph for growth was 6.5, and the optimum NaCl concentration for growth was around 25 g l(-1 ). The new isolate used H-2 and CO2 as the only substrates for growth and m ethane production. Tungsten, selenium and yeast extract stimulated growth s ignificantly. In the presence of CO2 and H-2, the organism reduced elementa l sulphur to hydrogen sulphide. Growth was inhibited by chloramphenicol and rifampicin, but not by ampicillin, kanamycin, penicillin and streptomycin. The G+C content of the genomic DNA was 31 mol%. As determined by 16S rDNA gene sequence analysis, this organism was closely related to Methanococcus jannaschii strain JAL-1(T). However, despite the high percentage of similar ity between their 16S rDNA sequences (97.1%), the DNA-DNA hybridization lev els between these strains were less than 5%. On the basis of these observat ions and physiological traits, it is proposed that this organism should be placed in a new species, Methanococcus vulcanius. The type strain is M7(T)( = DSM 12094(T)), During the course of this study, the 16S rDNA sequence ana lysis placed Methanococcus sp. strain AG86(T) (= DSM 4213(T)) as a close re lative of M, jannaschii strain JAL-1T. However, the weak level of DNA-DNA h ybridization with this strain (< 10%) allowed the proposal that strain AG86 (T) also constitutes a new species, Methanococcus fervens.