Characterization and nutritional properties of <i>Methanothrix concilii</i> sp. nov., a mesophilic, aceticlastic methanogen

Abstract

A nonmotile, rod-shaped, nonspore-forming, mesophilic methanogenic bacterium was isolated from sewage sludge. The cells stained Gram negative. In the presence of CO 2 , the isolate was able to grow and produce significant amounts of methane from acetic acid. No growth or methane formation was observed when H 2 , methanol, pyruvate, propionate, butyrate, formate, or trimethylamine were provided as substrates in the presence of CO 2 . About 0.95 mol of CH 4 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 CO 2 (added as NaHCO 3 ) 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).