Optimal ultrasound enhances T. reesei cellulases secretion for high biomass enzymatic saccharification by hyphal fragmentation

Although ultrasound technology has been broadly employed in diverse fields, its direct application during fungal incubation for production of lignocellulose-degrading enzymes is not implemented. Using sugarcane bagasse together with sugarcane juice, this study optimized T. reesei incubation condition for secretion of mixed-cellulases at high activities. The optimal ultrasound treatment was then explored to improve enzyme production during T. reesei incubation with the bagasse substrate for secretions of three major types of cellulases and xylanases. As a comparison, the secreted CBHI, EGII, β-glucosidase and xylanase activities were respectively increased by 48%, 10%, 147% and 74%, whereas the FPA was raised by 54% relative to the control (without ultrasound). Furthermore, those secreted enzymes were employed for biomass enzymatic saccharification in three representative bioenergy crops after mild alkali pretreatments, with raised hexose yields by 50%-64% and total sugar yields by 34%-43%. Notably, we observed the hyphal fragmentation at well distribution and the digested lignocelluloses at high homogeneity during a long-term T. reesei incubation after optimal ultrasound treatment. Meanwhile, untargeted metabolomic profiling revealed a distinctively altered metabolic remodeling in both fungal-secreted enzymes and all remaining fungal-lignocellulose residues under optimal ultrasound treatment. Based on all major findings achieved, a model is finally proposed about the distinct roles of optimal ultrasound treatment for improving T. reesei secretion of cellulases and xylanases at high-yield and high-activity by facilitating T. reesei interaction with bagasse substrate. Therefore, this study has demonstrated an advanced ultrasound technology to upgrade enzymes production from fungal-lignocellulose incubation for enhancing biomass enzymatic saccharification in bioenergy crops.