Characterization of two acidic β-glucosidases and ethanol fermentation in the brown rot fungus Fomitopsis palustris

Two acidic beta-glucosidases (beta GI and beta GII) from the brown rot fungus Fomitopsis palustris were purified to homogeneity by several chromatographic steps. beta GI and beta GII had molecular weights of 130 and 213 kDa, respectively, and exhibited optimum activity at pH 2.5 and 55 degrees C. The K-m values of beta GI and beta GII for p-nitrophenyl-beta-D-glucopyranoside were 0.706 and 0.971 mM, respectively. Although the effect of metal ions and inhibitors differed between the two enzymes, both beta-glucosidases exhibited preferential glucose release during hydrolysis of cello-oligosaccharides, indicating that beta GI and beta GII possess effective exo-type activities. Notably, F. palustris was able to produce ethanol when cultured on medium containing 20 g/l of glucose, mannose, cellobiose, and maltose, in which the maximum ethanol concentrations measured were 9.2, 8.7, 9.0, and 8.9 g/l, corresponding to 90.2%, 85.3%, 88.2%, and 87.3% of the theoretical yield, respectively. These findings suggest that F. palustris has the ability not only to secrete beta-glucosidase enzymes effective at low pH, but also to function as a biocatalyst, which may be suitable for the conversion of lignocellulosic materials into ethanol. (C) 2010 Elsevier Inc. All rights reserved.