Production optimization of yellow laccase from Stropharia sp. ITCC 8422 and enzyme-mediated depolymerization and hydrolysis of lignocellulosic biomass for biorefinery application

Biological pretreatment plays a crucial role in utilization of copiously present lignocellulosic biomass in biorefinery. Thus, yellow laccase–producing strain Stropharia sp. ITCC 8422 was studied for its production, purification and integrated depolymerization and hydrolysis. Yellow laccase production optimization using CCD-RSM increased the activity from 160.9 to 323.2 U/L with 2-fold enhancement. Yellow laccase was partially purified using a single-step aqueous two-phase system (ATPS), and PEG 8000 (20%) and Na 2 SO 4 (30%) was the optimum system with activity recovery of 87.8% at the bottom phase of the PEG-salt system. The molecular weight of ATPS partially purified yellow laccase was approximately 100–135 kDa and exhibited stability towards alkaline pH (5 to 11) and temperature (30 to 50 °C) after 12 h of incubation. UV-visible spectra confirmed the production of yellow laccase whereas FTIR and XRD showed stronger intensity of α-helix as compared with β-sheet structure. The depolymerization ability of yellow laccase was determined using wheat straw (WS), rice straw (RS), sugarcane bagasse (SB) and Luffa cylindrica (LC). It effectively depolymerized lignin after 12 h of incubation and was confirmed by kappa number, Klason lignin FTIR and XRD. Later, integrated depolymerization and hydrolysis of lignocellulosic biomass were performed using three different laccase loads, keeping in-house-produced cellulase-xylanase load constant. The increase in laccase load enhanced sugar yield in all lignocellulosic biomass. Thus, one-step depolymerization and hydrolysis have an enormous value in terms of capital, at large-scale biorefinery concept, and enable its utility as a “green tool” and be a step towards “cleaner ecosystem and future”. Graphical abstract