Increased Antifungal Activity of Trichoderma harzianum Transformants That Overexpress a 33-kDa Chitinase.

ABSTRACT Transformants of the biocontrol agent Trichoderma harzianum strain CECT 2413 that overexpressed a 33-kDa chitinase (Chit33) were obtained and characterized. Strain CECT 2413 was cotransformed with the amdS gene and its own chit33 gene under the control of the pki constitutive promoter from T. reesei. Southern blotting indicated that the chit33 gene was integrated ectopically, mostly in tandem. Some transformants showed the same restriction pattern, indicating preferable sites of integration. There was no correlation between the number of integrated copies and the level of expression of the chit33 gene in the transformants. When grown in glucose, the extracellular chitinase activity of the transformants was up to 200-fold greater than that of the wild type, whereas in chitin, the activity of both the transformants and the wild type was similar. Under both conditions, the transformants were more effective in inhibiting the growth of Rhizoctonia solani as compared with the wild type. Similar results were obtained when culture supernatants from the transformants and the wild type were tested against R. solani.