Genetic variation in the cuticle-degrading protease activity of the entomopathogen Metarhizium flavoviride

Extracellular proteases have been shown to be factors of virulence in fungal entomopathogenicity. We examined the production of the cuticle-degrading extracellular proteases chymoelastase (Pr1) and trypsin (Pr2) in isolates of the fungus Metarhizium flavoviride. Fungal growth was in a mineral medium (MM) containing nitrate, and in MM supplemented with either cuticle from Rhammatocerus schistocercoides or with the non-cuticular substrate casein. The substrates used for growth influenced the expression of both analyzed proteases, the highest protease activities of nearly all isolates having been observed in the medium containing insect cuticle, with more Pr1 than Pr2 being produced. There was a natural variability in the production of cuticle-degrading proteases among isolates, although this was less evident for Pr2. Our data support the hypothesis that the production of Pr1 on insect cuticle is a useful characteristic for the analysis of intraspecific variability of M. flavoviride isolates