INHIBITION OF BEAUVERIA-BASSIANA PROTEASES AND FUNGAL DEVELOPMENT BY INDUCIBLE PROTEASE INHIBITORS IN THE HEMOLYMPH OF GALLERIA-MELLONELLA LARVAE

Injection of zymosan oi dead yeast cells enhanced the inhibitory activ ity against exocellular Beauveria bassiana proteases in rite cell-fee haemolymph of Galleria mellonella larvae. Pre-injected larvae exhibite d no decreased mortality after subsequent injection with living B. bas siana blastospores but survived for a prolonged time before death. Inc reased levels of protease inhibitors in the haemolymph were also obser ved after injection of B. bassiana proteases. In contrast, no enhanced inhibitory activity against B. bassiana proteases was detected in inf ected larvae when mycosis was initiated with conidia which enabled the fungus to invade host larvae through the integument in a natural mann er. B. bassiana proteases were not completely inhibited by the additio n of cell-free haemolymph. Protease inhibitors obtained after heat and trichloroacetic acid precipitation of cell-free haemolymph were added to the protein medium of B. bassiana to study the effect on its growt h in vitro. Enriched fractions from pre-injected larvae delayed fungal growth in comparison with fractions from untreated larvae, suggesting that delayed mortality of immunized G. mellonella larvae infected wit h B. bassiana is due to enhanced levels of protease inhibitors. A non- virulent form of the same strain exhibited reduced capacity to release proteases in vitro. The results strongly suggest that the capacity of insects to release inhibitors against fungal proteases influences the ir susceptibility against entomopathogenic fungi.