A fungal lectin that reinforces the cell wall to enhance fermentation

The efficiency of filamentous fungi in industrial fermentations, particularly on lignocellulosic substrates, is often limited by hyphal integrity under stress. Enhancing cell wall robustness is a promising strategy for improving fungal performance. Transcriptomic analysis of Trichoderma harzianum under straw-based fermentation revealed significant upregulation of a novel fucose-specific lectin (FFSL). Molecular docking and isothermal titration calorimetry confirmed FFSL's high-affinity (K_d = 5.24 μM), entropy-driven binding to fucose. Exogenous FFSL application remodelled the hyphal cell wall, as evidenced by thermogravimetric analysis and solid-state NMR, which indicated increased chitin content (by 11.26 %), enhanced acetylation, and elevated levels of matrix components like mannose and galactose. This structural reinforcement resulted in superior thermostability and stress tolerance. Consequently, FFSL treatment significantly boosted fungal biomass by up to 35.3 % and 24.96 % in wild-type and engineered strains, respectively, on straw medium. Most notably, extracellular protein production was dramatically enhanced, with increases of up to 86.26 % in the engineered strain, highlighting a concurrent improvement in protein secretion efficiency. FFSL acts as a potent cell wall potentiator by binding to surface fucose and inducing structural reinforcement. This strategy effectively enhances the robustness and productivity of Trichoderma harzianum in biotechnological applications, offering a novel approach for optimizing fungal cell factories.