Proteolysis, Histopathological Effects, and Immunohistopathological Localization of δ-Endotoxins of Bacillus thuringiensis subsp. kurstaki in the Midgut of Lepidopteran Olive Tree Pathogenic Insect Prays oleae

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Considering the fact that Prays oleae is one of the most pathogenic insects to the olive tree in the Mediterranean basin, particularly in Tunisia, the mode of action of Cry insecticidal toxins of Bacillus thuringiensis kurstaki in Prays oleae midgut was investigated. The proteolysis of Bacillus thuringiensis δ-endotoxins in the midgut was a key step in determining their potency against Prays oleae. The latter's proteases activated the δ-endotoxins early, yielding stable toxins. The in vitro and in vivo binding of these toxins to Prays oleae larvae midgut was studied immunohistochemically, evidencing a midgut columnar cell vacuolization, microvilli damage, and then a pass of epithelium cell content into the larvae midgut. Moreover, Bacillus thuringiensis toxins were shown to bind to the apical microvilli of the midgut epithelial cells. The in vitro study of the interaction of Prays oleae midgut proteins with biotinylated Bacillus thuringiensis toxins allowed the prediction of four suitable receptor proteins in Prays oleae.

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