Two strains of the mesophilic anaerobic bacterium Sporacetigenium mesophilum (Class Clostridia) were isolated from an anaerobic sludge digester treating municipal waste. Unusually, optimal hydrogen production was detected at pH 8.8,with a moderate yield of 1.4 mol H 2 .mol–1 glucose and the major metabolic end products were acetate, ethanol, and CO 2 , typical for a clostridial-type fermentation [60].