Improvement of the capacity to hydrolyze corncob residues through deciphering the lignocellulolytic enzyme system of a hyper-cellulolytic mutant strain Trichoderma reesei CU7-4.

BACKGROUND: The degradation of agricultural wastes is crucial for sustainable economic and environmental development, necessitating efficient cellulolytic enzymes to enable high-value bioconversion. The filamentous fungus Trichoderma reesei is a widely used cellulase producer for deconstructing agricultural wastes in biomass conversion. However, its enzyme system remains suboptimal and requires further refinement to achieve economical bioconversion of agricultural wastes. RESULTS: Herein, a hyper-cellulolytic T. reesei mutant strain CU7-4 derived from the industrial strain RUT-C30 was obtained by UV mutagenesis. When degrading the different pretreated corncob residues, CU7-4 exhibited a 20% improvement in saccharification efficiency compared to the parental strain RUT-C30. Furthermore, comparative proteomics was employed to decipher the variation between the secretomes of CU7-4 and RUT-C30. It was found that the discrepancy of the protein proportion between the secretomes may enable the changed saccharification efficiency towards the pretreated corncob residues. Then, three small secreted proteins (SSP1, EPL1, CUT1) and two β-glucosidases (Cel3H, Cel3F) were identified through the significant differences analysis in protein abundance between CU7-4 and RUT-C30, combined with responding to the essential transcriptional regulator Xyr1. Further investigation of these five proteins was conducted. Deletion of SSP1 and EPL1 was certified to facilitate degrading corncob residues and corn stover. Overexpression of Cel3F improved the activities of cellobiohydrolase and β-glucosidase, and the in vitro addition of Cel3F significantly promoted the saccharification efficiency of RUT-C30 toward corncob residues. CONCLUSIONS: This study not only expands the protein functions for deciphering the mechanism of lignocellulose degradation, but also provides valuable protein targets for engineering the robust and powerful lignocellulolytic enzyme system, thereby facilitating the efficient degradation of agricultural wastes.