Production of β-Glucosidase in Aspergillus Terreus ATG-5

Abstract

β-Glucosidase is an important component of the complex of cellulolytic enzymes converting cellobiose, a repressor of endo- and exo-β-glucanase, to the final product — glucose. Trichoderma reesei, one of the best producers of cellulases used in a pilot plant production of these enzymes, produces β-glucosidase exhibiting a low activity and this low activity is a limiting factor of hydrolysis of the cellulose substrate. For the commercial utilization of cellulolytic enzymes it is thus necessary to overcome some problems concerned with β-glucosidase (Woodward and Wiseman, 1982). These involve: 1. A low activity of extracellular β-glucosidase in culture filtrates of T. viride or T. reesei. 2. Inhibition of β-glucosidase by glucose, the final product of cellulolysis. The accumulated cellobiose then strongly inhibits endo- and exo-β-glucanases and thus the cellulolysis as a whole. 3. Heat inactivation of β-glucosidase during hydrolysis of cellulose. These problems can be solved in several ways such as: 1. Isolation of T. reesei producing higher amounts of ß-glucosidase, 2. Selection and isolation of other producers with a high production of β-glucosidase. Their ß-glucosidase would then be used in mixed enzyme preparations or, in its immobilized form, it would degrade cellobiose in cellulose hydrolyzates and thus increase the rate of hydrolysis. 3. Conversion of cellulolytic products to fructose which is only a weak inhibitor of β-glucosidase in T. reesei mutants. 4. Selection and isolation of producers forming β-glucosidase with altered properties, i.e. with an increased thermostability or decreased sensitivity of β-glucosidase against inhibition by the final product — glucose.