Characterization and nutritional properties of Methanothrix concilii sp. nov., a mesophilic, aceticlastic methanogen

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Abstract
A nonmotile, rod-shaped, nonspore-forming, mesophilic methanogenic bacterium was isolated from sewage sludge. The cells stained Gram negative. In the presence of CO2, the isolate was able to grow and produce significant amounts of methane from acetic acid. No growth or methane formation was observed when H2, methanol, pyruvate, propionate, butyrate, formate, or trimethylamine were provided as substrates in the presence of CO2. About 0.95 mol of CH4 was produced per mole of acetic acid consumed. The optimum pH and temperature for growth were 7.1–7.5 and 35–40 °C, respectively. The mass doubling time was about 24 h under optimum growth conditions. The almost complete inhibition of methane formation by 10 μM 2-bromoethanesulfonic acid (2-BES) was reversed in the presence of 50 μM 2-mercaptoethanesulfonic acid (HS-CoM). D-Cycloserine at 0.1 mg/mL concentration caused complete inhibition of growth. Sludge fluid enhanced the rate of methane formation, whereas 0.5% (w/v) yeast extract was inhibitory. The optimum initial CO2 (added as NaHCO3) for growth on acetic acid was 1.8 mM. The DNA base composition was 61.25 ± 0.60 mol% G + C. On the basis of its characteristics, this isolate is classified as Methanothrix concilii sp. nov. and the type strain is GP6 (=NRC 2989).