Monday, May 2, 2011
Grand Ballroom C-D, 2nd fl (Sheraton Seattle)
Trichoderma reesei is generally considered as the most efficient organism for the production of cellulolytic enzymes, mainly thanks to its high secretion capacity. The produced enzymatic cocktail contains three important enzymes: endoglucanases (EG), cellobiohydrolases (CBH) and beta-glucosidase (BGL1). The latter one is very poorly secreted by Trichoderma reesei strains and a complete hydrolysis of cellulose often requires supplementation with extra beta-glucosidase, especially to prevent inhibition of CBHs by cellobiose. In order to optimize the produced cocktail, a more efficient beta-glucosidase was cloned into T. reesei CL847 strain which is an industrial cellulase production strain. The improved beta-glucosidase was evolved by several rounds of L-shuffling, a specific directed evolution method, starting from 3 parental proteins. T. reesei CL847 TR3002 suitably expressing the evolved beta-glucosidase was selected for cellulase production in lab-scale reactors. The kinetics of growth and cellulase production of the new strain were characterized using fed-batch and chemostat modes under different culture conditions. In addition to the determination of cellulase and hemicellulase activities, hydrolysis of a steam exploded wheat straw was performed, and demonstrated that the new enzyme mixture led to a 4 fold decrease in cellulase loading without any loss in hydrolysis performance. An important reduction in the enzyme loading for the hydrolysis makes the process of bioethanol production from lignocellulosic materials profitable