A stable cellulose-degrading microflora enriched from composting materials has been analyzed in our laboratory. Cellulose-degrading efficiency of an anaerobic cellulolytic isolate, Clostridium straminisolvens CSK1, was remarkably lower than that of the original microflora. We successfully constructed bacterial communities with effective cellulose degradation by mixing C. straminisolvens CSK1 with aerobic non-cellulolytic bacteria isolated from the original microflora. Comparison of the cellulose degradation processes of the pure culture of C. straminisolvens CSK1 and the mixed-culture indicated that non-cellulolytic bacteria essentially contribute to cellulose degradation by supplying anaerobic environment, consuming metabolites, which otherwise deteriorate the cellulolytic activity, and by neutralizing pH.

A novel anaerobic, thermophilic and cellulolytic bacterium (strain CSK1^T) was isolated from a cellulose-degrading bacterial community. On the basis of 16S rRNA gene sequence similarity, strain CSK1^T was mapped to cluster III of the genus Clostridium. Strain CSK1^T is closely related to Clostridium thermocellum (96·2 %) and Clostridium aldrichii (95·1 %). Strain CSK1^T is a non-motile, spore-forming, straight or slightly curved rod. The optimum temperature and initial pH for its growth and cellulose degradation are 50–55 °C and pH 7·5. Strain CSK1^T grew under a gas phase containing up to 4 % O₂. Phylogenetic and phenotypic analyses support the differentiation of strain CSK1^T from its closest relatives. Strain CSK1^T therefore represents a novel species, for which the name Clostridium straminisolvens sp. nov. is proposed, with CSK1^T (=DSM 16021^T=IAM 15070^T) as the type strain.