Effects of wheat straw solid contents in fermentation media on utilization of soluble/insoluble nutrient, fungal growth and laccase production.

The objective of the work was to study the effect of agri-residue solid contents (2-20% w v-1) in fermentation medium on fungal growth, soluble and insoluble nutrient consumption and laccase production. Fungal strain Ganoderma lucidium and wheat straw substrate was screened for maximum laccase production. At low solid content submerged fermentation (SmF), fungus utilized mainly soluble nutrient and was unable to access the insoluble nutrient in media due to lack of contact with solid. At high solid content solid-state fermentation (SF), fungi grew on solid surface with dense and thin hyphae, utilized mainly insoluble nutrient. At medium solid content (8% w v-1) semi-solid fermentation (sSF), fungi grew on solid substrates with network of thick intercrossed hyphae, utilized both soluble and insoluble nutrients optimally resulting in highest fungal growth and laccase activity (~ 3.5 folds than in SmF and ~ 2.5 folds than in SF). Importance of soluble and insoluble nutrients was also established after isolation of their individual effects. Morphology of fungal growth (SEM), composition, thermal analysis (TGA/DTG) of substrates confirmed the results. sSF showed potential for the production of enzymes through utilization of agricultural residues as substrate.