Characterization of β-glucosidase produced by the white rot fungus Flammulina velutipes

Abstract

β-Glucosidase production by the white rot fungus Flammulina velutipes CFK 3111 was evaluated using different carbon and nitrogen sources under submerged fermentation. Maximal extracellular enzyme production was 1.6 U/ml, corresponding to a culture grown in sucrose 40 g/l and asparagine 10 g/l. High production yield was also obtained with glucose 10 g/l and asparagine 4 g/l medium (0.5 U/ml). Parameters affecting the enzyme activity were studied using p-nitrophenyl-β-D-glucopyranoside as the substrate. Optimal activity was found at 50°C and pHs 5.0 to 6.0. Under these conditions, β-glucosidase retained 25% of its initial activity after 12 h of incubation and exhibited a half-life of 5 h. The addition of MgCl2, urea, and ethanol enhanced the β-glucosidase activity up to 47%, whereas FeCl2, CuSO4, Cd(NO3)2, and cetyltrimethylammonium bromide inflicted a strong inhibitory effect. Glucose and cellobiose also showed an inhibitory effect on the β-glucosidase activity in a concentration-dependent manner. The enzyme had an estimated molecular mass of 75 kDa. To the best of our knowledge, F. velutipes CFK 3111 β-glucosidase production is amongst the highest reported to date, in a basidiomycetous fungus.