Toxicity and binding properties of the Bacillus thuringiensis delta-endotoxin Cry1C to cultured insect cells.

A better understanding of the mode of action of Bacillus thuringiensis delta-endotoxins is needed to develop strategies which may prevent or slow down selection for resistance. We studied the effect of Cry1C on several different cultured insect cell lines by means of toxicity assays, ligand blotting, and toxin binding studies. A clear difference in sensitivity toward Cry1C between the insect cell lines was observed. Spodoptera frugiperda cell line Sf9 was most sensitive, whereas Spodoptera exigua cell lines SeUCR and SelZD2109 showed intermediate sensitivity. Mamestra brassicae (Mb0503) and Drosophila melanogaster (Dm1) cells were the least sensitive as compared to Sf9 cells. Ligand blot analysis of SDS-PAGE size-separated proteins showed that Cry1C specifically binds to a 40-kDa protein in Sf9, SeUCR, and SelZD2109 cells. Cry1Ab does not bind to this protein. The Cry1C-binding protein was not observed in Mb0503 and Dm1 cells, suggesting that the presence of the 40-kDa Cry1C-binding protein is correlated with sensitivity toward Cry1C.