CHITINOLYTIC ACTIVITY OF THE ACAROPATHOGENIC FUNGI HIRSUTELLA-THOMPSONII AND HIRSUTELLA-NECATRIX

Two isolates of the acaropathogenic fungus Hirsutella thompsonii (Nos. 255 and 414), and Hirsutella necatrix, were able to produce and excre te chitinolytic enzymes. A chitobiase of >205 kDa was excreted by all fungi and a chitobiase of 112 kDa only by isolate 414. An endochitinas e of 162 kDa was excreted by isolate 414 and two endochitinases of 66 and 38 kDa were excreted by isolate 255. Both H. thompsonii isolates p roduced chitinolytic enzymes only under inducible conditions, in the p resence of colloidal chitin as the sole source of carbon. Hirsutella n ecatrix produced a chitobiase constitutively when grown in the presenc e of glucose. In addition to chitinolytic enzymes, the H. thompsonii i solates excreted proteolytic activities, including elastase, as well a s alpha-esterase and alpha-amylase activities. Hirsutella necatrix was unable to use casein, milk powder, or elastin as the sole carbon sour ce. The acaropathogenicity of these isolates was assayed on the carmin e spider mite (Tetranychus cinnabarinus). Isolates 414 and 255 and H. necatrix killed ca. 80, 35, and 15%, respectively, of the infected mit es. The role of chitinolytic and other enzymatic activities in the aca ropathogenicity of these fungi is discussed.