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 excrete chitinolytic enzymes. A chitobiase of >205 kDa was excreted by all fungi and a chitobiase of 112 kDa only by isolate 414. An endochitinase 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 produced chitinolytic enzymes only under inducible conditions, in the presence of colloidal chitin as the sole source of carbon. Hirsutella necatrix produced a chitobiase constitutively when grown in the presence of glucose. In addition to chitinolytic enzymes, the H. thompsonii isolates excreted proteolytic activities, including elastase, as well as alpha-esterase and alpha-amylase activities. Hirsutella necatrix was unable to use casein, milk powder, or elastin as the sole carbon source. The acaropathogenicity of these isolates was assayed on the carmine spider mite (Tetranychus cinnabarinus). Isolates 414 and 255 and H. necatrix killed ca. 80, 35, and 15%, respectively, of the infected mites. The role of chitinolytic and other enzymatic activities in the acaropathogenicity of these fungi is discussed.