P76: Withdrawn: Novel Cellulase Recycling Method using Clostridium thermocellum Cellulosomes

Lignocellulosic plant biomass is difficult to hydrolyze because cellulose is surrounded by a lignin that has covalent associations with hemicellulose, and cellulose has a tightly packed crystalline structure. Among cellulolytic microorganisms, Clostridium thermocellum, an anaerobic thermophilic bacterium, is the most potent cellulose degrading bacterium known to produce the cellulosome. Recently, to isolate microorganisms that possess effective cellulose-degrading ability, new thermophilic cellulolytic strains were screened from agriculture residues in Thailand using microcrystalline cellulose as a carbon source. We isolated a new strain, C. thermocellum S14, which has higher cellulose-degrading ability than several type strains (1). When rice straw treated by soaking in aqueous ammonia was hydrolyzed by the combination of ß-glucosidase from Thermoanaerobacter brockii with the cellulosome from C. thermocellum S14, approximately 91% of glucan existing in the rice straw was hydrolyzed (2). On the other hand, enzyme recycling is desired to reduce costs of saccharification process. In order to recycle the combination, CBM from CipA was fused to the ß-glucosidase (3). When recycling tests were carried out against crystalline cellulose and ammonia-treated rice straw, combination of cellulosome and ß-glucosidase-fused CBM could recycle at least 5 and 3 rounds, respectively, consistent with high saccharification rates. These results indicated that the enzyme recycle using combination of cellulosomes and ß-glucosidase-fused CBM has great potential as an effective lignocellulose degradation system.

(1) Tachaapaikoon C, et al., (2012) Biodegradation. 23:57-68.

(2) Waeonukul R, et al., (2012) Bioresour Technol. 107:352-357.

(3) Waeonukul R, et al., (2013) Bioresour Technol. 130: 424-430.