Rational Engineering A Xylanase Hyper-Producing System in Trichoderma Reesei for Efficient Biomass Degradation

Abstract Background: The degradation of lignocellulose needs the synergetic work of cellulase and xylanase. Filamentous fungi Trichoderma reesei has been widely used as a workhorse for cellulase and xylanase fermentation with great producing ability. Previous work for biomass saccharification mainly aims to improve the component and production of cellulase, however the low xylanase activity in T. reesei could not meet the needs of a high saccharification efficiency. Results: In this study, for the first time, a xylanase hyper-producing system in T. reesei was established by tailoring two transcription factors, XYR1 and ACE1, and homologous over-expression of the major xylanase XYNⅡ. The expression of key xylanolytic enzymes was significantly upregulated with an increase of 6.78- and 1.98-fold in the xylanase activity and pNPXase (β-xylosidase) activity compared to that of the parent, Rut-C30, respectively. Besides, 2310-3085 U/mL of xylanase activities were achieved using soluble lactose or glucose as sole carbon source, which was more efficient and economical than the traditional method of xylan induction. Treated with the crude xylanase cocktails as accessory enzymes, an increase of 39.7% in reducing sugar yield (31.3 mg/mL) in saccharification of alkali pretreated corn stover (5% w/v) was achieved compared to that of the parent. Conclusions: An efficient and economical xylanase hyper-producing platform was developed in T. reesei Rut-C30. The novel platform with outstanding ability for crude xylanase cocktails production would greatly fit in biomass degradation and give a new perspective of further engineering in T. reesei for industrial purposes.