Sunday, August 1, 2010
Pacific Concourse (Hyatt Regency San Francisco)
An anaerobic, thermophilic, and cellulolytic bacterium, Clostridium thermocellum, produces a large extracellular polysaccharolytic multicomponent enzyme complex called the cellulosome, in which several cellulases are tightly bound to a scaffolding protein called CipA. The C. thermocellum strain S14 (NITE P-627), which was originally isolated from bagasse paper sludge in Thailand, produces the cellulosome with strong cellulolytic activity. To bring out the cellulolytic abilities of the cellulosome, it is required to eliminate inhibition toward cellulosome by the major end product, cellobiose. Combining recombinant b-glucosidase from Thermoanaerobacter brockii with the cellulosome from C. thermocellum S14, accumulated cellobiose was hydrolyzed thereby resulting in significant enhancement of microcrystalline cellulose degradation. On the other hand, when rice straw treated by soaking in aqueous ammonia (28 %) for 1 week at 60°C was hydrolyzed by the combination of β-glucosidase of 10 units and cellulosome loading of 2 mg protein/g glucan, approximately 91% of glucan existing in rice straw was hydrolyzed. The rice straw hydrolysates were fermented to ethanol by the yeast Saccharomyces cerevisiae without any inhibitions and in 95% of theoretical yield. These results suggest that the combination of β-glucosidase and cellulosome has great potential as an effective lignocellulose degradation system.