Increased antifungal activity of Trichoderma harzianum transformants that overexpress a 33-kDa chitinase

Transformants of the biocontrol agent Trichoderma harzianum strain CECT 241 3 that overexpressed a 33-kDa chitinase (Chit33) were obtained and characte rized. Strain CECT 2413 was cotransformed with the amdS gene and its own ch it33 gene under the control of the pki constitutive promoter from T. reesei . Southern blotting indicated that the chit33 gene was integrated ectopical ly, mostly in tandem. Some transformants showed the same restriction patter n, indicating preferable sites of integration. There was no correlation bet ween the number of integrated copies and the level of expression of the chi t33 gene in the transformants. When grown in glucose, the extracellular chi tinase activity of the transformants was up to 200-fold greater than that o f the wild type, whereas in chitin, the activity of both the transformants and the wild type was similar. Under both conditions, the transformants wer e more effective in inhibiting the growth of Rhizoctonia solani as compared with the wild type. Similar results were obtained when culture supernatant s from the transformants and the wild type were tested against R. solani.