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

In order to determine the mechanism of action of the 27 kDa mosquitocidal delta-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 (Ca2+, Mg2+) 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.