A mesophilic, Gram positive (Gram +ve), irregular coccoid methanogen, which showed close resemblance to a Methanosarcina sp., was isolated from swine manure. Acetate or methanol or H-2 + CO2 sewed as a substrate for methanogenesis in a mineral salt medium. The isolate did not use formate as a growth substrate. The organism had an optimum pH of 6.8 and an optimum temperature of 37 degrees C. The isolate used ammonia as a nitrogen source. The role of this methanogen in the swine manure is the terminal oxidation of simple organic compounds like acetate to CO2 and methane. In an earlier report, a sulfate-reducing bacterium (SRB) isolated from swine manure that converted phenol to acetic acid was described (Boopathy, 1995). The methanogen described in this paper was isolated from the same swine manure sample. In a microbial ecology scenario these two anaerobic bacteria (methanogen and SRB) could co-exist together and degrade phenol to CO2 and methane. (C) 1996 Published by Elsevier Science Ltd.