Integrated lignocellulolytic enzyme production and pretreatment of wheat straw by fungal consortium

Abstract

ABSTRACT In nature, fungi play a leading role in the biodegradation of organic waste by secreting a broad spectrum of lignocellulolytic enzymes (cellulases, hemicellulases, and ligninases). Inspired by this natural ecological synergy, in the present study, two promising fungal isolates, Trichoderma sp. isolate HR27 and Ganoderma sp. isolate HR31, were isolated and assessed for biocompatibility. Subsequently, their consortium was utilized for single-factorial optimization of various parameters (inoculum size, incubation time, lignocellulosic substrate, temperature, moisture content, pH, surfactant, nitrogen source, co-substrate, and inducer) under solid-state fermentation (SSF) using lignocellulosic waste for enhanced lignocellulolytic enzyme production. The results revealed that a significant increase in enzyme yield was achieved by utilizing wheat straw as the substrate, supplemented with 1.5 g/L Tween 80 and 0.5 mM CuSO4 in Asther’s medium with an initial pH of 3.5 at 30˚C. Compared to unoptimized media, optimized media resulted in 5.99, 5.18, 1.13, 2.57, 4.97, and 2.68-fold increases in endoglucanase, exoglucanase, β-glucosidase, mannanase, xylanase, and laccase production, respectively, on the fourth day of fermentation. Compositional analysis revealed that enhanced enzyme production under optimized conditions resulted in 31.7% delignification of wheat straw; however, only 22.9% was observed under unoptimized conditions, compared to that of the raw substrate. The removal of lignin resulted in higher exposure of cellulose (43.25%) and hemicellulose (24.85%) contents in wheat straw under optimized conditions. These findings highlight the potential of the fungal consortium as an effective candidate for lignocellulolytic enzyme cocktail production for various industrial applications using agricultural waste with concurrent valorization of agro-waste. GRAPHICAL ABSTRACTA flowchart diagram of the research workflow from fungal isolation and compatibility study to solid-state fermentation optimization and biomass analysis.A flowchart diagram outlining the experimental workflow and sequential steps of a lignocellulolytic enzyme study using fungal isolates HR27 and HR31. The study initiated with fruiting bodies collected from decayed wood, which were processed for fungal isolation on a Malt Extract Agar (MEA) plate. The resulting isolates underwent primary screening for lignocellulolytic enzymes, identifying two distinct strains labeled HR 27 and HR 31. To verify their cooperative growth, both strains were subjected to a compatibility test on agar plate. The validated consortium was then combined with agricultural residues and a liquid moistening medium for optimization studies for enzyme production using fungal consortium HR 27 and HR 31 under SSF. Following the optimization phase, the process yielded biologically treated wheat straw and a harvested lignocellulolytic enzyme cocktail in a flask. The treated wheat straw was further analyzed for determination of biomass content, visualized by a stacked bar chart displaying the altered ratios of cellulose, hemicellulose, and lignin. Concurrently, branching directly downward from the optimization node, a clustered bar chart tracks the final enhanced lignocellulolytic enzyme production.