Engineering Trichoderma reesei Rut-C30 with the overexpression of egl1 at the ace1 locus to relieve repression on cellulase production and to adjust the ratio of cellulolytic enzymes for more efficient hydrolysis of lignocellulosic biomass

Cellulose hydrolysis is a synergetic process performed sequentially by different cellulolytic enzymes including endoglucanases, exoglucanases and glucosidases. Trichoderma reesei has been acknowledged as the best cellulase producer, but cellulase production by T. reesei through submerged fermentation is costly due to intensive energy consumption associated with the process for mixing and aeration, since non-Newtonian fluid properties are developed with mycelial growth. Therefore, engineering the ratio of cellulolytic enzymes in the cocktail for more efficient cellulose hydrolysis is an alternative strategy for reducing cellulase dosage and thus saving cost in enzyme consumption for cellulose hydrolysis. In this study, T. reesei QS305 with high endoglucanase activity was developed from T. reesei Rut-C30 by replacing the transcription repressor gene ace1 with the coding region of endoglucanase gene egl1. Compared to T. reesei Rut-C30, T. reesei QS305 showed 90.0% and 132.7% increase in the activities of total cellulases and endoglucanases under flask culture conditions. When cellulase production by T. reesei QS305 was performed in the 5-L fermentor, cellulases activity of 10.7 FPU/mL was achieved at 108 h, 75.4% higher than that produced by T. reesei Rut-C30. Moreover, cellulases produced by T. reesei QS305 were more efficient for hydrolyzing pretreated corn stover and Jerusalem artichoke stalk.