Methanogenium liminatans spec. nov., a new coccoid,mesophilic methanogen able to oxidize secondary alcohols

A new mesophilic, coccoid methanogen, assigned as Methanogenium liminatans spec. nov. strain DSM 4140, was isolated from effluent of a reactor for the anaerobic treatment of industrial waste water. Cells of M. Liminatans formed irregular cocci, about 1.5 m in size, and occurred singly. The cell envelope was an S-layer with hexagonally arranged glycoprotein subunits (M_r=118000). The center-to-center spacings were 15.4 nm. The polar lipid pattern was similar to that of Methanogenium tationis, the polyamine content similar to that found in several Methanogenium species. Strain DSM 4140 grew with H₂/CO₂, formate, 2-propanol/CO₂, 2-butanol/CO₂ and cyclopentanol/CO₂. For growth with the different substrates acetate was required as an additional carbon source. Growth on H₂/CO₂ was stimulated by the addition of tungstate. The optimal concentration was 1–2 M Na₂WO₄. ¹⁸⁵WO _inf4 ^sup2- was incorporated into cells. Growth was not influenced by 0–600 mM NaCl, but no growth occurred in the presence of 800 mM NaCl. Increasing concentrations of KCl up to 100 mM were slightly inhibitory for growth. The optimal growth temperature was around 40°C. The G+C content of the DNA was 59.3 mol% (T_m) or 60.5 mol% (HPLC).Abbreviations HPLC = high performance liquid chromatography - PAS = periodic acid-Schiff reagent - sADH = secondary alcohol dehydrogenase - F₄₂₀ = 7,8-didemethyl-8-hydroxy-5-deazariboflavin     

Growth of methanogens on cyclopentanol/CO2 and specificity of alcohol dehydrogenase

Abstract Growth of 5 strains of secondary alcohol-utilizing methanogens on cyclopentanol/CO₂ was demonstrated. Cultures reached only low optical densities, comparable to those observed during growth on 2-propanol/CO₂ or 2-butanol/CO₂. The conversion of cyclopentanol to cyclopentanone was reversible in the presence of hydrogen. The specificity of ADHs of nine secondary alcohol-utilizing methanogens for coenzyme requirement and substrates was tested using crude enzyme preparations. The ADH of Methanobacterium bryantii M.o.H.G, Methabobacterium palustre, Methanocorpusculum parvum and Methanocorpusculum bavaricum was only active with NADP⁺, the ADH of Methanomicrobium paynteri, Methanogenium marisnigri, Methanogenium bourgense , strain GKZPZ and strain INSLUZ with F₄₂₀ as electron carrier. FAD, FMN, methylene blue, benzyl viologen and tetrazolium, chloride could be used as electron carriers by the F₄₂₀-dependent ADHs if endogenous F₄₂₀ was introduced with the crude ADH preparation. No reaction with these electron carriers occurred if dialyzed extracts were used as a source of ADH. The ADH of all tested strains oxidized 2-propanol, 2-butanol, 2-pentanol and cyclopentanol, while the ADH of Mg. marisnigri and Mm. paynteri oxidized cyclohexanol, of Mb. palustre and Mcp. bavaricum cyclopentanol and 2,3-butanediol,and of Mcp. parvum cyclopentanol, 2,3-butanediol, ethanol and 1-propanol in addition.