Sporacetigenium mesophilum gen. nov., sp. nov., isolated from an anaerobic digester treating municipal solid waste and sewage

Two mesophilic, anaerobic bacterial strains (ZLJ115T and L4-2) were isolated from the sludge of an anaerobic digester treating municipal solid waste and sewage in Fujian province, China. The strains were Gram-positive, spore-forming, motile rods (0.9-1.0 x 3.6-7.3 microm). Growth of the strains was observed at 20-42 degrees C and pH 6.0-9.5. Both strains fermented several mono- and disaccharides. The main fermentation products from glucose were acetate, ethanol, hydrogen and carbon dioxide. Optimal hydrogen production by the new isolates was observed at pH 8.8 and 39 degrees C, and 1.4 mol H2 was detected from fermentation of 1 mol glucose. The DNA G+C contents of strains ZLJ115T and L4-2 were 53.9 and 54.3 mol%, respectively. Phylogenetic analysis based on 16S rRNA gene sequences revealed that the isolates represented a novel phyletic sublineage within cluster XI of the clostridia, clustering with four thermophilic species, with <93.8 % 16S rRNA gene sequence similarity to previously described species. Phenotypically, the new isolates were distinguished from their phylogenetic relatives by growing mesophilically and by fermenting a variety of pentoses, as well as their higher genome DNA G+C content. On the basis of polyphasic evidence from this study, a novel genus and species are proposed, Sporacetigenium mesophilum gen. nov., sp. nov.; strain ZLJ115T (=DSM 16796T = AS 1.5019T) is the type strain of Sporacetigenium mesophilum.