Methanobacterium thermoflexum sp. nov. and Methanobacterium defluvii sp. nov., Thermophilic Rod-Shaped Methanogens Isolated from Anaerobic Digestor Sludge

Two new rod-shaped Gram-positive, autotrophic, thermophilic methanogens, strains ADZ and IDZ, were isolated from the anaerobic digestor sludge operating on waste waters containing methacrylates. The isolates use H2 + CO2 and formate as substrates for growth and methane production. Strain ADZ grows with a doubling time of 1.5 h under optimal conditions (60°C, pH 7.0, 25 mg/l Na2S, 0.8–20 g/l NaCl). The GC content of the DNA is 62.2 mol%. Strain IDZ grows with a doubling time of 3.5 h under optimal conditions (55°C, pH 7.9–8.2, 150 mg/l Na2S, 1–30 g/l NaCl). The GC content of the DNA for the strain IDZ is 55 mol%. The new isolates are closely related to the genus Methanobacterium, but differ from each other and from the members of the genus mentioned antigenically, in amino acid composition of cell walls, low DNA-DNA homology and the GC content of the DNA. Therefore, they are considered as a new species of the genus Methanobacterium, which we name Methanobacterium thermoflexum with type strain IDZ (VKM B-1963), and Methanobacterium defluvii with type strain ADZ (VKM B-1962).