Co-production of ligninolytic enzymes by Pleurotus pulmonarius on wheat bran solid state cultures

In this paper, the production of biomass and ligninolytic enzymes by the white-rot fungus Pleurotus pulmonarius (FR.) QUELET cultured on wheat bran at high initial moisture was evaluated. When the initial moisture was lower than 86%, the fungal hyphae penetrated into and bound tightly to the solid-substrate particles. When the moisture was equal or higher than 86%, the growth was characterized by formation of a large mycelial mass above the substrate (surface growth). In this case, the mycelial mass could be easily separated from the residual solid substrate and quantified by gravimetric analysis. The fungus produced 0.32 g of dry mycelial mass per g of dry substrate after 15 days of cultivation. Analysis of the residual substrate showed that growth was mainly due to the consumption of soluble proteins and carbohydrates. The condition of high initial moisture strongly promoted the expression of laccase (up to 24,000 U per g of substrate or 78,000 U per g of dry fungal biomass), while the production of manganese peroxidase was negatively affected. In fact, manganese peroxidase was maximally produced when the initial moisture was 75% (2,000 U per g of substrate). The production of other enzymes, such as polysaccharidases and proteases, was not significantly affected by the initial moisture.