ABSTRACT
Proteases produced by Metarhizium anisopliae (Metsch.) Sorokin are considered an important virulence factor, because they are fundamental in the process of penetration through the insect cuticle. The purpose of the present study was to verify the influence of different pH levels and concentrations of the substrates casein and cuticle of Mahanarva fimbriolata (Stål) (Hemiptera: Cercopidae) on the proteolytic activity of isolates of M. anisopliae. Casein and cuticle from adult M. fimbriolata, both in the concentrations of 1%, 2%, 3% and 4%, were added in minimum medium (MM) solid, without a carbon source. To verify pH influence on the proteolytic activity and possible pH change in the media, the media cited above were made with a pH indicator in the concentration that best influenced the proteolytic activity, with pH 5, 6, 7, 8, 9 and 10. The enzymatic activity was determined from the enzyme relation index (ERI). Isolates of M. anisopliae presented distinct optimum concentrations for each substrate, being 1% for casein and 2% for cuticle from Mahanarva fimbriolata. Regarding pH, it was verified that there was greater proteolytic activity in casein with pH 8 and 9 and cuticle from Mahanarva fimbriolata with pH 6, 7 and 8. Beginning at the 5th growth day of the isolates there occurred a pH color change in the medium casein 1% with pH initial 6 and 7 to pH 8. Therefore, the concentration of the substrates studied and the pH of the media had an influence on the proteolytic activity.
KEY WORDS
Biological control; fungus; proteases