PARTIAL CHARACTERIZATION OF SPECIFIC INDUCERS OF A CUTICLE-DEGRADING PROTEASE FROM THE INSECT PATHOGENIC FUNGUS METARHIZIUM-ANISOPLIAE

The insect pathogenic fungus Metarhizium anisopliae produces several e xtracellular cuticle-degrading proteases and evidence is consistent wi th one of these, PR1, which is a chymoelastase, being a determinant of pathogenicity. We have shown previously that PR1 production is regula ted by both carbon catabolite and nitrogen metabolite repression and a lso by specific induction under derepressed conditions by insect cutic le. In the present work we have established that an enzymically releas ed proteinaceous component(s) of insect cuticle is capable of inducing PR1 (based on appearance of extracellular activity). Cuticle of the d esert locust Schistocerca gregaria treated with KOH to remove protein failed to induce PR1 production, whereas cuticle treated with either c hloroform or ether to remove lipids still induced PR1. Cuticle digeste d with either PR1 or the trypsin-like PR2 of M. anisopliae released pe ptides mainly in the range 150-2000 Da; addition of these peptides gen erated by PR1 or PR2 at 3 mu g alanine equivalents ml(-1) induced PR1 production to a level similar (75%) to that obtained with untreated in sect cuticle. Several amino acids and peptides which are abundant in i nsect cuticular protein (Ala, Gly, Ala-Ala, Ala-Ala-Ala, Ala-Pro and P ro-Ala) were tested at a range of concentrations and in restricted cul tures for their ability to induce PR1. None induced the protease to th e levels seen with cuticle or peptides enzymically released from cutic le. although some dimers and notably the monomers Ala and Gly gave 2-2 .7-fold enhanced PR1 activity above derepressed basal levels (up to 48 -57% of that achieved with induced synthesis on cuticle). There was ev idence for more efficient uptake and/or catabolism by M. anisopliae of alanine di- and tripeptides than of monomer amino acids.