ADAPTATION OF PROTEASES AND CARBOHYDRASES OF SAPROPHYTIC, PHYTOPATHOGENIC AND ENTOMOPATHOGENIC FUNGI TO THE REQUIREMENTS OF THEIR ECOLOGICAL NICHES

The abilities of isolates of saprophytes (Neurospora crassa, Aspergill us nidulans), an opportunistic human pathogen (Aspergillus fumigatus), an opportunistic insect pathogen (Aspergillus flavus), plant pathogen s (Verticillium albo-atrum, Verticillium dahliae, Nectria haematococca ), a mushroom pathogen (Verticillium fungicola) and entomopathogens (V erticillium lecanii, Beauveria bassiana, Metarhizium anisopliae) to ut ilize plant cell walls and insect cuticle components in different nutr ient media were compared. The pathogens showed enzymic adaptation to t he polymers present in the integuments of their particular hosts. Thus , the plant pathogens produced high levels of enzymes capable of degra ding pectic polysaccharides, cellulose and xylan, as well as a cutinas e substrate, but secreted little or no chitinase and showed no proteol ytic activity against elastin and mucin. The entomopathogens and V. fu ngicola degraded a broad spectrum of proteins (including elastin and m ucin) but, except for chitinase, cellulase (V. lecanii and V. fungicol a only) and cutinase (B. bassiana only), produced very low levels of p olysaccharidases. The saprophytes (Neu. crassa and A. nidulans) and th e opportunistic pathogens (A. fumigatus and A. flavus) produced the br oadest spectrum of protein and polysaccharide degrading enzymes, indic ative of their less specialized nutritional status. V. lecanii and V. albo-atrum were compared in more detail to identify factors that disti nguish plant and insect pathogens. V. albo-atrum, but not V. lecanii, grew well on different plant cell wall components. The major class of proteases produced in different media by isolates of V. albo-atrum and V. dahliae were broad spectrum basic (pl > 10) trypsins which degrade Z-AA-AA-Arg-NA substrates (Z, benzoyl; AA, various amino acids; NA, n itroanilide), hide protein azure and insect (Manduca sexta) cuticles. Analogous peptidases were produced by isolates of V. lecanii and V. fu ngicola but they were specific for Z-Phe-Val-Arg-NA. V. albo-atrum and V. dahliae also produced low levels of neutral (pl ca 7) and basic (p l ca 9.5) subtilisin-like proteases active against a chymotrypsin subs trate (Succinyl-Ala(2). Pro-Phe-NA) and insect cuticle. In contrast, s ubtilisins comprised the major protease component secreted by V. lecan ii and V. fungicola. Both V. lecanii and V. albo-atrum produced the hi ghest levels of subtilisin and trypsin-like activities during growth o n collagen or insect cuticle. Results are discussed in terms of the ad aptation of fungi to the requirements of their ecological niches.