Chitinolytic Enzymes Produced by Trichoderma harzianum: Antifungal Activity of Purified Endochitinase and Chitobiosidase

Abstract

Two chitinolytic enzymes from Trichoderma harzianum strain P1 were tested for their antifungal activity in bioassays against nine different fungal species. Spore germination (or cell replication) and germ tube elongation were inhibited for all chitin-containing fungi except T. harzianum strain P1. The degree of inhibition was proportional to the level of chitin in the cell wall of the target fungi. For most of the fungi tested, the ED50 values for the endochitinase and the chitobiosidase were 35-135 micrograms ml-1 and 62-180 micrograms ml-1, respectively. Complete inhibition occurred at 200-300 micrograms ml-1. Combining the two enzymes resulted in a synergistic increase of antifungal activity. The ED50 values for a 1:1 mixture of endochitinase and chitobiosidase were as low as 10 micrograms ml-1 for Botrytis cinerea, 34 micrograms ml-1 for Ustilago avenae, 13 micrograms ml-1 for Uncinula necator, and 30 micrograms ml-1 for Fusarium solani. T. harzianum strain P1 was resistant to its own chitinolytic enzymes up to 800 micrograms ml-1, with an ED50 value 1,000 micrograms ml-1. The chitinolytic enzymes from T. harzianum appeared to be biologically more active than enzymes from other sources and more effective against a wider range of fungi. The involvement of these chitinolytic enzymes in biocontrol is also discussed