Sophorose biosynthesis with heterologous beta-glucosidases for cellulase production in Trichoderma reesei

Sophorose is a strong soluble inducer of cellulase biosynthesis in Trichoderma reesei, but its practical use remains limited by availability and cost. In this study, an integrated strategy was developed to improve cellulase production by combining sophorose biosynthesis, sophorose-based induction, and heterologous β-glucosidase expression. β-Glucosidases from T. reesei QM6a, Penicillium digitatum Pdw03, and Aspergillus niger CBS 513.88 were expressed in Escherichia coli BL21(DE3) and compared for sophorose formation. The A. niger-derived enzyme rAnCel1A showed the highest transglycosylation activity, producing 8.42 ± 0.21 g L-1 sophorose at 47°C and showing optimal performance at pH 3.2. In a 20-L bioreactor, an enzymatically synthesized sophorose-glucose mixture containing 12.7 ± 0.8 g L-1 sophorose triggered detectable cellulase production within 24 h after induction, whereas glucose-only feeding failed to initiate cellulase production despite comparable biomass formation. Heterologous expression of fungal cel1A genes in T. reesei Rut-C30 further increased β-glucosidase and filter paper activities. The An-cel1A advantage disappeared after gene-dosage normalization, suggesting higher expression. These results provide a feasible framework for coupling inducer biosynthesis with cellulase production in T. reesei.