A STUDY OF LIGNOCELLULOLYTIC ENZYMES PRODUCED BY VOLVARIELLA VOLVACEA, THE EDIBLE STRAW MUSHROOM

Lignocellulose containing cellulose, hemicellulose, and lignin occurs as the structural element of plants. It is a major component in agricultural, forestry and municipal waste and is the earth's most abundant renewable resource. Unfortunately man and most animals can not digest cellulose directly. It must be converted into other usable forms such as glucose, ethanol, methane or other feedstocks. There are generally two main obstacles hindering efficient transformation of cellulose: (1) the highly ordered cellulose structure and (2) usually a lignin seal surrounding cellulose fibers. Microorganisms capable of degrading lignin and crystalline cellulose should be selected to solve both problems simutaneously. Volvariella volvacea, commonly known as the straw mushroom, an edible fungus cultivatable on cotton waste, a relatively crystalline cellulose, was chosen for this study. The final products of cultivation of V. volvacea on lignocellulose are mushrooms that are highly acceptable food and the enzymes remaining in the spent bed which can be used to hydrolyze lignocellulose to yield glucose.; Studies in shake flasks were carried out to determine the conditions for maximal biomass production and cellulase synthesis. V. volvacea had the following growth characteristics: minimal temperature, 25(DEGREES)C; optimal temperature, 37(DEGREES)C; maximal temperature 40(DEGREES)C; pH optimum 6.0. Optimal pH for cellulase production was 5.5. The optimal initial pH for cellulase production and mycelial growth was found to be pH 6.0. Biomass and enzyme yields were doubled when modified Mandels and Reese cellulose basal medium was supplemented with 0.1% yeast extract. A cellulose concentration of 1% was optimum for cellulase and biomass production. The addition of Tween 80 to the culture resulted in a two-fold increase in cell production and a ten to fifteen-fold increase in yields of cellulase. The pH and temperature optima for cellulolytic activity were 5.0 and 50(DEGREES)C, respectively.; In shake flask fermentation, the exponential phase extended between 48 to 72 hours. An exoglucanase activity of 1.16 u mole glucose produced per ml filtrate per day and an endoglucanase activity of 2.5 u mole glucose produced per ml filtrate per min. were obtained within five days. The filter paper activity was 3.48 mg glucose produced per hour per ml enzyme broth. The beta-glucosidase was present in low level. Cellulase activity was closely correlated with the amount of soluble protein in the culture filtrate. Reducing sugar was not detected in the culture.; Various carbon sources were examined as possible cellulase inducers. Highest cellulase yield was obtained when the organism was grown on insoluble microcrystalline cellulose. Carboxymethylcellulose, a soluble cellulose derivative, was less effective as an inducer. Weak cellulase activity was detected when cells were grown on cellobiose or lactose. Glucose repressed cellulase formation.; The cellulases were found to be partly cell-free and partly cell-bound during growth on microcystalline cellulose. The endoglucanase activity was primarily extracellular and beta-glucosidase activity was found exclusively extracellular. Sugar yield from saccharification of dry mushroom beds in buffer was low (5% w/w in 24 hours).; V. volvacea could not digest the lignin portion of newspaper in submerged shake flask cultivation. Growth with lignin as a sole carbon source was negligible. Phenol oxidase, a key enzyme in lignin biodegradation was also lacking in cell free filtrate. However, the organism oxidized phenolic compounds in the agar plate suggesting that it might have the capability of degrading lignin in the stationary solid state culture.