Fungal-integrated second-generation lignocellulosic biorefinery: utilization of agricultural biomass for co-production of lignocellulolytic enzymes, mushroom, fungal polysaccharides, and bioethanol

Ganoderma lucidum is a basidiomycetous fungus with enormous potential for the co-production of diverse extracellular ligninases, pharmaceutically important polysaccharides, and medicinal mushrooms. In the present study, G. lucidum MDU-7 was grown in laboratory-designed boxes, bucket, wood logs, and iron mesh–like structure for basidiocarp formation and laccase isozyme secretion. The maximum laccase production (5087.48 U/g ± 81.44 U/g) was observed after the 9th day of incubation at pH 6.5 from mixed agricultural biomass. The nutritional analysis of G. lucidum MDU-7 basidiocarp indicated pharmaceutical and therapeutical importance of the fungal culture. Compositional analysis of the residual biomass after mushroom cultivation revealed the degradation of lignin and phenols, i.e., 49.16 ± 2.79% and 58.66 ± 5.26%, respectively. Morphological and anatomical studies (SEM, FTIR, and XRD) of pretreated fungal biomass indicated significant structural changes in the biomass structure compared to untreated materials. Further, when saccharified with a customized cellulase consortium of Aspergillus flavus MDU-5 and Trichoderma citrinoviride MDU-1, the fungal pretreated biomass released 367.12 ± 4.12 mg/g sugars after 40 h of incubation, with notable hydrolysis yield (70.60 ± 4.68%). The enzymatic hydrolysates containing 10.34 ± 0.22 g/L sugars were fermented in a bench-top bioreactor using Saccharomyces cerevisiae NCIM-3640, and produced 6.24 ± 0.14 g/L ethanol with a high yield (89.11 ± 1.35% of the theoretical value). Our findings in the current report advocate that fungal-integrated biorefinery process is an environmentally suitable technology, which provides a promising strategy in the field of lignocellulose biotechnology.