Integrative mechanisms of Mn peroxidase-dominated fungal digestion and CaO depolymerization for synergistic enhancement of biomass saccharification towards distinct bioethanol and lactic acid conversions in desired Miscanthus

Crop straws represent the enormous biomass resources convertible for sustainable biofuels and valuable biochemicals, but lignocellulose recalcitrance basically necessitates highly-efficient biomass processes under green-like manner. By incubating desirable Miscanthus (Msa6) straw with two classic white-rot fungi strains, this study examined effective wall polymer extractions from fungal secretions of four major types of lignocellulose-degradation enzymes and cofactors along with distinct metabolisms. Notably, the Lentinula edodes incubation secreted manganese peroxidase at extremely high activity for dominating lignin-network deconstruction, whereas the Pleurotus ostreatus incubation produced laccase with high activity for contribution to polysaccharide depolymerization indirectly through lignin oxidation and synergistic action with hydrolytic enzymes. Furthermore, the integrative L. edodes and CaO pretreatments could mostly cause lignocellulose depolymerization accountable for much raised biomass porosity such as the specific surface area and pore volume raised by 47% and 44%, which resulted in a synergistically enhanced biomass enzymatic saccharification for the highest hexose yield raised by 33%, compared to the control (optimal CaO pretreatment with raw straw). Meanwhile, despite of relatively less hexose yield obtained, the integrated P. ostreatus and CaO pretreatments achieved the higher bioethanol and lactic acid yields than those of the controls by 40% and 41%, probably due to releasing the less toxic compounds that inhibit yeast and bacterial fermentations. Based on all major findings achieved, this study finally proposes a novel mechanism model to elucidate why synergistic lignocellulose depolymerization and modification are achieved from integration of two green-like pretreatments, thereby offering a selective strategy for enhancing hexoses, bioethanol and lactic acid productivity in bioenergy crops.