Abstract

Three strains of CO(2)-reducing methanogens were isolated from marine sediments. Strain PL-15/H(P) was isolated from marine sediments of the Lipari Islands, near Sicily and the other two strains, Nankai-2 and Nankai-3(T), were isolated from deep marine sediments of the Nankai Trough, about 50 km from the coast of Japan. Analysis of the cellular proteins and 16S rRNA gene sequences indicated that these three strains represented a single novel species that formed a deep branch of the mesophilic methanococci. Phylogenetic analysis indicated that the three strains were most closely related to Methanothermococcus okinawensis (95 % 16S rRNA gene sequence similarity). However, strains PL-15/H(P), Nankai-2 and Nankai-3(T) grew at temperatures that were more similar to those of recognized species within the genus Methanococcus. Strain Nankai-3(T) grew fastest at 46 degrees C. Results of physiological and biochemical tests allowed the genotypic and phenotypic differentiation of strains PL-15/H(P), Nankai-2 and Nankai-3(T) from closely related species. The name Methanococcus aeolicus sp. nov. is proposed, with strain Nankai-3(T) (=OCM 812(T)=DSM 17508(T)) as the type strain.