Growth of methanogens on cyclopentanol/CO2and specificity of alcohol dehydrogenase

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.