The abilities of isolates of saprophytes (), an opportunistic human pathogen (), an opportunistic insect pathogen (), plant pathogens (), a mushroom pathogen () and entomopathogens () to utilize plant cell walls and insect cuticle components in different nutrient media were compared. The pathogens showed enzymic adaptation to the polymers present in the integuments of their particular hosts. Thus, the plant pathogens produced high levels of enzymes capable of degrading pectic polysaccharides, cellulose and xylan, as well as a cutinase substrate, but secreted little or no chitinase and showed no proteolytic activity against elastin and mucin. The entomopathogens and degraded a broad spectrum of proteins (including elastin and mucin) but, except for chitinase, cellulase ( and only) and cutinase ( only), produced very low levels of polysaccharidases. The saprophytes ( and ) and the opportunistic pathogens ( and ) produced the broadest spectrum of protein and polysaccharide degrading enzymes, indicative of their less specialized nutritional status. and were compared in more detail to identify factors that distinguish plant and insect pathogens. but not grew well on different plant cell wall components. The major class of proteases produced in different media by isolates of and were broad spectrum basic (pl > 10) trypsins which degrade Z-AA-AA-Arg-NA substrates (Z, benzoyl; AA, various amino acids; NA, nitroanilide), hide protein azure and insect () cuticles. Analogous peptidases were produced by isolates of and but they were specific for Z-Phe-Val-Arg-NA. and also produced low levels of neutral (pl ca 7) and basic (pl ca 9.5) subtilisin-like proteases active against a chymotrypsin substrate (Succinyl-Ala2-Pro-Phe-NA) and insect cuticle. In contrast, subtilisins comprised the major protease component secreted by and Both and produced the highest levels of subtilisin and trypsin-like activities during growth on collagen or insect cuticle. Results are discussed in terms of the adaptation of fungi to the requirements of their ecological niches


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