The unique sugar conversion and complex CAZyme system of Trichoderma brev T069 during solid-state fermentation of cassava peel

Abstract

Cassava peel is a lignocellulose-based agricultural by-product that can be degraded into reducing sugars as a raw material for energy. However, chemical and enzymatic treatment processes of cell wall polymers are expensive. We found that the filamentous fungus Trichoderma brev T069 can grow in a cassava peel matrix without any additional nutrient and degrade macromolecular carbohydrates, producing high levels of glucose and valuable hydrolytic enzymes. Therefore, this paper investigated the utilization strategy of T. brev T069 on cassava peels by dynamically analyzing its growth and hydrolytic enzyme system during solid fermentation, degradation of cassava peel components, and changes in reducing sugars. Results showed that T. brev T069 uses a "borrow-return" method of reducing sugar conversion, first absorbing fructose for growth for 3 days and later releasing glucose (99.56 mg/g) and cellobiose (24.69 mg/g) via hydrolases and high levels of β-glucosidase (1196.05 IU/g). Scanning electron microscopy and Fourier transform infrared spectrometry revealed the compositional breakdown and decreased carbohydrate contents of the peels. Label-free proteomics identified 257 carbohydrate-active enzymes (CAZymes), and functional annotation indicated that hemicellulases, lignin-modifying enzymes, and pectinases were induced at early stages, whereas amylases and cellulases were induced at later stages. A protein–protein interaction network revealed that protein degradation-related proteases and α-mannosidases may be involved in the realignment of enzymatic degradation strategies. This study explored the hydrolytic enzymatic potential of the Trichoderma CAZyme system and provided a practical approach for the biotransformation of tropical agricultural wastes into value-added products.