Isolation and characterization of two thermophilic cellulolytic strains of Clostridium thermocellum from a compost sample.

AIMS: To isolate, identify and characterize new thermophilic cellulolytic bacterial strains from a compost sample. METHODS AND
RESULTS: Two thermophilic and cellulolytic bacterial strains were isolated via enrichment on cellulose (milled filter paper) and characterized. Both strains, CS7 and CS8, were rod-shaped, Gram-positive and spore-forming bacteria, sharing the same optimal temperature (60°C) and pH (7.0) for growth. Both were highly cellulolytic and produced ethanol and acetate as the major fermentation products, but lacked xylanase activity. They only grew on cellulose (both filter paper and crystalline cellulose) and cellobiose and produced yellow pigment, without growing on other substrates including glucose. Based on 16S rRNA gene sequence analysis, CS7 and CS8 are closely related (99% sequence identity) to Clostridium thermocellum ATCC 27405. However, they had significantly higher specific cellulase activities and ethanol/acetate ratios than Cl. thermocellum ATCC 27405.
CONCLUSIONS: CS7 and CS8 are two new highly cellulolytic and ethanologenic Cl. thermocellum strains. SIGNIFICANCE AND IMPACT OF THE STUDY: First report of applying the cloning-RFLP-sequencing approach for purity confirmation of the isolates beside conventional methods. Strains CS7 and CS8 might be of potential application in research and development of cellulosic bioconversion.