BASIC PROTEASES OF ENTOMOPATHOGENIC FUNGI DIFFER IN THEIR ADSORPTION PROPERTIES TO INSECT CUTICLE

The factors which are involved in the in vitro adsorption of Metarhizium anisopliae, Verticillium lecanii, and Beauveria bassiana proteases onto insect cuticle and the hydrolysis of cuticle proteins were investigated. Several proteases are produced by these fungi during growth in liquid media containing 1% (w/v) ground grasshopper cuticle, and the most basic of these proteases adsorb onto cuticle. Protease adsorption was maximum in a broad pH range from 4 to 7. Adsorption was also time dependent, with maximum adsorption occurring within 1 hr. Up to 50% of the adsorbed protease could be dissociated from the cuticle with 10 mM potassium phosphate (pH 7) but not with distilled water. Lysine and glutamic acid interfered with protease adsorption, while proline, alanine, and tyrosine did not. Modification of cuticle protein carboxyl groups by esterification or by carboxamidation resulted in a decrease of protease adsorption. Acetylation of the cuticle tyrosine hydroxyl groups resulted in decreased adsorption of M. anisopliae and V. lecanii protease but not B. bassiana protease. Phenylglyoxylation masked the amino groups with carboxyl groups and this resulted in increased protease adsorption. An increase in protease adsorption onto chemically modified cuticles was not necessarily correlated with increased hydrolysis. Results suggested that the proteases produced by M. anisopliae and V. lecanii were similar in their adsorption properties. All proteases required a carboxyl group for adsorption but M. anisopliae and V. lecanii proteases also required an unsubstituted hydroxyl group with a carboxyl group for maximum adsorption. (C) 1994 Academic Press, Inc.