Isolation of a Trichoderma asperellum mutant with high-level β-glucosidase activity and application for...

The balanced hydrolase complexes are critical for efficient lignocellulose degradation, yet low β-glucosidase (BGL) activity is considered as the primary rate-limiting factor for cellulose hydrolysis by Trichoderma species. In this study, a dual-plate screening strategy with over 85 % positive mutation rate was designed, and a hypercellulolytic T. asperellum mutant ML02 was successfully isolated with approximately 2-fold increase of BGL activity after two rounds of ethyl methanesulfonate (EMS) mutagenesis. Phenotypic characterizations combined with genomic and transcriptomic analysis revealed that hyperbranching morphology, sporulation defects, and impaired cell wall integrity collectively contributed to the improved cellulase activity and cellulose degradation efficiency. Additionally, by constructing a microbial consortium composed of mutant ML02 and Lactobacillus paracasei, LA production from Avicel reached 72.65 g/L, with a cellulose degradation efficiency of 90 %. Besides, the LA yield from cellulose achieved 0.97 g/g, and over 87 % carbon flux from Avicel was channeled into LA synthesis. Importantly, the consortium also achieved an LA production of 60.74 g/L when used delignified rice straw as the sole carbon source, representing the highest reported performance for lignocellulosic LA production. These findings support that strain ML02 has strong potential to serve as an efficient microbial platform for cost-effective lignocellulose biorefining.