Secondary alcohols as hydrogen donors for CO2-reduction by methanogens

Out of 22 methanogens Methanobacterium formicicum, Methanobacterium bryantii M.o.H., Methanogenium marisnigri, Methanomicrobium paynteri, Methanocorpusculum parvum and the new coccoid methanogenic isolates GKZPZ and SZSXXZ were found to grow at the expense of 2-propanol and 2-butanol + CO₂. 2-Propanol was oxidized to acetone and 2-butanol was converted to 2-butanone during CO₂-reduction to methane. Growth was poor compared to that on H₂/CO₂, and in the presence of both, 2-propanol and H₂, molecular hydrogen was the preferred reductant. Acetone, formed during oxidation of 2-propanol in the absence of hydrogen, was reduced again to 2-propanol, when the culture was supplied with H₂/CO₂. Ethanol, 1-propanol, 1-butanol, 2-pentanol and cyclohexanol could not serve as hydrogen donors for methanogenesis.