Development of the cellulolytic fungus Trichoderma reesei strain with enhanced β-glucosidase and filter paper activity using strong artifical cellobiohydrolase 1 promoter

To improve the β-glucosidase yield and total cellulase activity of Trichoderma reesei, extracellular β-glucosidase (BGLI) was overexpressed under the control of the modified four-copy cbh1 promoter. Three transformants B2, B12 and B15 with successful integration of the bgl1 gene expression cassette were obtained, which exhibited 3.7-, 2.0- and 1.8-fold increase in β-glucosidase activity than the parental strain RUT C30, respectively. The filter paper activities of the productive transformants B12 and B15 were improved by up to 130% and 55%, respectively. Saccharification of corncob residue with the crude enzyme dosages showed that the reducing sugar yields of B12 (5.59 mg/ml) and B15 (4.80 mg/ml) were 29% and 11% higher than that of RUT C30 (4.34 mg/ml), respectively. The present results proved that the modified four-copy cbh1 promoter was a useful tool for improving the cellulase activity of T. reesei, and the engineering strains developed in this study could be potentially used as promising cell factories for β-glucosidase or cellulase production.