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 enzyme activity were studied using p-nitro-phenyl-β-D-glucopyranoside as 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 β-glucosidase activity up to 47% while the reactives FeCl2, CuSO4, Cd(NO3)2 and cetyltrimethylammonium bromide inflicted a strong inhibitory effect. Glucose and cellobiose showed also an inhibitory effect on 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 up to date, in a basidiomycetous fungus.