Enrichment and characterization of a methanogenic bacterium from the oxic upper layer of the ocean

Enrichment cultures containing marine plankton from oxygenated coastal waters (50-108% saturated) with supersaturated levels of methane (> 700% saturated) yielded a strictly anaerobic methanogenic bacterium. Nonmotile, non-spore-forming, regular to slightly irregular cocci (0.5-0.8 mu m) were evident by phase contrast, epifluorescence, and scanning electron microscopies. The DNA base composition was 42 plus or minus 1% guanine plus cytosine. Serology suggested the isolate may be a new strain of Methanococcoides methylutens . Morphology, growth physiology, DNA base content and serology are all consistent with the type description of M. methylutens , a methylotrophic methanogen isolated from submarine sediments.