Solid-State Fermentation using a Strain of Trichoderma asperellum Improves the Saccharification of Rice Straw

Rice straw is a cheap and widely available agro-waste biomass that can be used to generate renewable biofuel. However, due to its composition, it is particularly recalcitrant to enzymatic degradation. Here, prior to enzymatic hydrolysis, biological pre-treatment of rice straw for saccharification by solid-state fermentation (SSF) was performed using a new isolate of Trichoderma asperellum called UNIPV1. More specifically, the study aimed to investigate the effect of adding the fungus to rice straw on the temporal activity of secreted enzymes, and reducing sugar formation. As excepted, under long-term solid-state fermentation (SSF), depolymerizing enzymes such as xylanases and exo/endo-cellulases were secreted by Trichoderma asperellum UNIPV1 during its growth. T. asperellum was an excellent producer of cellulolytic enzymes; a significant peak in reducing sugars occurred between 10-20 days. Trichoderma initially showed a high preference for the secretion of xylanases to degrade the linear polysaccharide beta-1,4-xylan into xylose. Afterwards, endoglucanase and exoglucanase enzymes were secreted to complete the hydrolytic activity on the substrate. This result is consistent with the trend of total protein accumulated in the secretome and the fungal metabolic activity measured by CO2 production. Overall, our findings suggest that a short fungal pre-treatment of rice straw might be useful to begin the degradation of cell-wall polymers, and can therefore effectively improve saccharification. That said, further work is required to improve the fungal pre-treatment, since alone does not entirely complete the degradation of lignocellulosic insoluble material.