Engineering of for enhanced degradation of lignocellulosic biomass by truncation of the cellulase activator ACE3.

Background: The filamentous fungus is a major workhorse employed to produce cellulase, which hydrolyzes lignocellulosic biomass for the production of cellulosic ethanol and bio-based products. However, the economic efficiency of biorefineries is still low.

Results: In this study, the truncation of cellulase activator ACE3 was identified and characterized in classical mutant NG14 and its direct descendants for the first time. We demonstrated that the truncated ACE3 is the crucial cause of cellulase hyper-production in NG14 branch. Replacing the native ACE3 with truncated ACE3 in other strains remarkably improves cellulase production. By truncating ACE3, we engineered a mutant, PC-3-7-A723, capable of producing more cellulase than other strains. In a 30-L fermenter, fed-batch fermentation with PC-3-7-A723 drastically increased the maximum cellulase titer (FPase) to 102.63 IU/mL at 240 h, which constitutes a 20-30% improvement to that of the parental strain PC-3-7.

Conclusions: This work characterized the function of truncated ACE3 and demonstrated that analysis of classical mutants allows rational engineering of mutant strains with improved cellulase production necessary to process lignocellulosic biomass. Our rational engineering strategy might be useful for enhancing the production of other bio-based products.