A cytolytic δ‐endotoxin from Bacillus thuringiensis var. israelensis forms cation‐selective channels in planar lipid bilayers

Abstract

In order to determine the mechanism of action of the 27 kDa mosquitocidal δ‐endotoxin of Bacillus thuringiensis var. israelensis we have studied its effects on the conductance of planar lipid bilayers. The toxin formed cation‐selective channels in the bilayers, permeable to K + and Na + but not to N ‐methylglucamine or Cl − , showing very fast, cooperative opening and closing. Channel opening was greatly reduced in the presence of divalent cations (Ca 2+ , Mg 2+ ) and the effect was reversed when these ions were removed. These results are consistent with our proposal that B. thuringiensis toxins act by a mechanism of colloid‐osmotic lysis.