Toxicity and receptor binding properties of a Bacillus thuringiensis CryIC toxin active against both lepidoptera and diptera.

This study describes an investigation into the relationship among toxicity, specificity, and binding of CryIC delta-endotoxin from Bacillus thuringiensis subspecies aizawai HD-229. In vivo bioassays of larvae using inclusions (Aedes aegypti) or solubilized toxin (Spodoptera littoralis, Spodoptera exigua, Spodoptera frugiperda, and Manduca sexta) revealed that CryIC was toxic to both dipteran and lepidopteran larvae. In vitro saturation binding assays with CryIC toxin labeled in vivo with [35S]methionine revealed specific and saturable binding to brush border membrane vesicles from both resistant and susceptible insect species. In contrast, dissociation binding experiments showed that the relative toxicities and specificities of CryIC to the insect species tested were correlated with the extent of irreversible binding to the insects' midgut brush border membrane vesicles.