Isolation and Characterization of a Thermophilic Strain of Methanosarcina Unable to Use H 2 -CO 2 for Methanogenesis

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Abstract
A thermophilic strain of Methanosarcina, designated Methanosarcina strain TM-1, was isolated from a laboratory-scale 55°C anaerobic sludge digestor by the Hungate roll-tube technique. Penicillin and d -cycloserine, inhibitors of peptidoglycan synthesis, were used as selective agents to eliminate contaminating non-methanogens. Methanosarcina strain TM-1 had a temperature optimum for methanogenesis near 50°C and grew at 55°C but not at 60°C. Substrates used for methanogenesis and growth by Methanosarcina strain TM-1 were acetate (12-h doubling time), methanol (7- to 10-h doubling time), methanol-acetate mixtures (5-h doubling time), methylamine, and trimethylamine. When radioactively labeled acetate was the sole methanogenic substrate added to the growth medium, it was predominantly split to methane and carbon dioxide. When methanol was also present in the medium, the metabolism of acetate shifted to its oxidation and incorporation into cell material. Electrons derived from acetate oxidation apparently were used to reduce methanol. H 2 -CO 2 was not used for growth and methanogenesis by Methanosarcina strain TM-1. When presented with both H 2 -CO 2 and methanol, Methanosarcina strain TM-1 was capable of limited hydrogen metabolism during growth on methanol, but hydrogen metabolism ceased once the methanol was depleted. Methanosarcina strain TM-1 required a growth factor (or growth factors) present in the supernatant of anaerobic digestor sludge. Growth factor requirements and the inability to use H 2 -CO 2 are characteristics not found in other described Methanosarcina strains. The high numbers of Methanosarcina -like clumps in sludges from thermophilic digestors and the fast generation times reported here for Methanosarcina TM-1 indicate that Methanosarcina may play an important role in thermophilic methanogenesis.