Reformulating the Hydrolytic Enzyme Cocktail of <i>Trichoderma reesei</i> by Combining XYR1 Overexpression and Elimination of Four Major Cellulases to Improve Saccharification of Corn Fiber

Abstract

The industrial fungus <i>Trichoderma reesei</i> has an outstanding capability of secreting an enzyme cocktail comprising multiple plant biomass-degrading enzymes. Herein, the overexpression of XYR1, the master transactivator controlling (hemi)cellulase gene expression, was performed in <i>T. reesei</i> lacking four main cellulase-encoding genes. The resultant strain Δ4<i>cel</i>OE<i>xyr</i>1 was able to produce a dramatically different profile of secretory proteins on soluble glucose or lactose compared with that of the wild-type <i>T. reesei</i>. The Δ4<i>cel</i>OE<i>xyr</i>1 secretome included cellulases EGIII and BGLI as well as several hemicellulases and nonhydrolytic cellulose degradation-associated proteins that are not preferentially induced in the wild-type <i>T. reesei</i> strain. Δ4<i>cel</i>OE<i>xyr</i>1 produced a significant amount of α-arabinofuranosidase I on lactose, and the crude enzyme cocktail of Δ4<i>cel</i>OE<i>xyr</i>1 not only released a considerable quantity of glucose but also exhibited remarkable performance in the hydrolytic release of xylose, arabinose, and mannose from un-pretreated corn fiber. These results showed that the engineered <i>T. reesei</i> strain holds great potential for improving the saccharification efficiency of the hemicellulosic constituents within corn fiber.