Correlation of the aphicidal activity of Beauveria bassiana SFB-205 supernatant with enzymes

Abstract

The supernatant of Beauveria bassiana SFB-205 reduced the population of cotton aphid, Aphis gossypii Glover, with a dosage-dependent manner, which allowed a quality control (QC) factor to be determined for the evaluation of the supernatant as the first step of a development. Enzymes were assumed as possible QC factors based on 1) the comparable aphicidal activity of the supernatant protein pellet to the raw supernatant, 2) the supernatant-induced degradation of the insect cuticles, observed by transmission electron microscopy, and 3) the confirmation of enzymes related to the fungal penetration - chitinase, and the Pr1- and Pr2 proteases - in the supernatant. Finally, from the bioassay with the enzyme-inhibited supernatants processed by substrate inhibition one by one, decreased aphicidal activities were observed for all three enzyme-inhibited treatments. This phenomenon, furthermore, was more remarkable in the chitinase-inhibited supernatant. This finding provides that those enzymes (and most particularly the chitinase) in the supernatant were strongly involved in the aphicidal activity. Consequently, the amount of the chitinase may be used as one of the QC factors to determine the insecticidal activity of the supernatant of B. bassiana SFB-205 in the optimization of mass production.