Bacillus thuringiensis var. israelensis crystal hemolysis as a possible basis for an assay of larval toxicity

Optimal conditions for the extraction of a hemolysin from crystals of Bacillus thurin-giensis var. israelensis (B.t.i.) have been described. Evidence is given that the mechanism of hemoly-sin release from crystals involves proteolytic en-zymes. The hemolysin extracted from B.t.i. crys-tals has been shown to be antigenically different from the hemolysin excreted by vegetative cells of the same strain. As there is good correlation be-tween the hemolytic and larvicidal properties of various B.t.i. preparations it is suggested that the hemolytic assay should be tried as a rapid assay for preliminary determinations of the activity of B.t.i. preparations.