-Glucosidase and cellulase formation by a Trichoderma reesei mutant defective in constitutive -glucosidase formation

Abstract

A mutant of Trichoderma reesei QM 9414 - T. reesei M8 - was isolated after γ-irradiation. It did not form β-glucosidase during growth on glycerol or glucose, but secreted β-glucosidase upon growth on cellobiose. The mutant was also able to grow on cellulose and secrete β-glucosidase, but with a longer lag. β-Glucosidase activity could be induced in the mutant in a replacement medium by cellobiose and β-methyl d-glucoside. Mycelia lacking β-glucosidase were able to take up both these inducers immediately, indicating the presence of a constitutive permease. The mutant produced cellulases upon growth on lactose and - after a lag - on cellulose. Mycelia of T. reesei M8 pregrown on glycerol or cellobiose could be induced by sophorose to produce cellobiohydrolase I in a replacement system. The findings show that (i) cellobiose and other β-linked disaccharides can be taken up by T. reesei without prior hydrolysis, and (ii) that cellobiose most probably induces β-glucosidase formation during growth on cellulose.