Degradation of Bacillus thuringiensis δ-endotoxin in host insect gut juice

When Bacillus thuringiensis subsp. kurstaki HD-1 and subsp. sotto F-endotoxins were activated from their protoxins in 50% Choristoneura fumiferana gut juice, the amount of 60-65-kDa toxin protein produced was much less than that produced in 1% gut juice. In bioassays against Bombyx mori larvae, the toxicity of activation mixtures with 50% C. fumiferana gut juice was less than activation mixtures with 1% gut juice. Differences between 50% and 1% B. mori gut juice in the amount of activated toxin produced from protoxin were much less pronounced. The present study may explain, in part, why B. thuringiensis subsp. kurstaki HD-1 is more toxic to B. mori than to C.fumiferana larvae, and suggests that the enhancement of B. thuringiensis delta-endotoxin insecticidal activity by protease inhibitors may be the result of reduced toxin degradation in the insect midgut. (C) 1998 Federation of European Microbiological Societies. Published by Elsevier Science B.V. All rights reserved.