Engineering for Hyperproduction of Cellulases on Glucose to Efficiently Saccharify Pretreated Corncobs.

The filamentous fungus (teleomorph ) is widely used as a cellulase producer in the industry. Herein, we describe the rational engineering of the publicly available QM9414 strain to achieve a remarkable high-level production of cellulase on glucose. Overexpression of the key cellulase regulator XYR1 by the copper-repressible promoter P was first implemented to achieve a full cellulase production in the context of catabolite repression (CCR) while eliminating the requirement of inducing sugars for enzyme production. The gene was further overexpressed to compensate for its low β-glucosidase activity on glucose. This overexpression resulted in a 102% increase in FPase activity compared with the CCR-released RUT-C30 strain cultured on Avicel. Moreover, the saccharification efficiency toward pretreated corncob residues by crude enzymes from the engineered strain on glucose increased by 85% compared with that treated by enzymes from RUT-C30 cultivated on Avicel. The engineered strain thus shows great potential as a viable alternative to deliver commercial cellulases after further optimization for efficient saccharification of agricultural waste.