Evidence for two different types of insecticidal P2 toxins with dual specificity in Bacillus thuringiensis subspecies

Analysis of polypeptides in the crystalline delta-endotoxins from different Bacillus thuringiensis strains revealed two antigenically similar forms of the P2 protein which differed in molecular mass, peptide profile, and amino acid sequence. Purified preparations of the two forms displayed the characteristic dual toxicity of the P2 protein towards members of the orders Lepidoptera and Diptera in vivo but differed markedly in potency for the insects tested. Both species of the P2 protoxin, solubilized and activated by sequential proteolysis with insect gut extract and alpha-chymotrypsin, retained activity in vivo and in vitro, despite the removal of 144 residues from the N terminus. For the low-molecular-mass form, the dual insecticidal activity was reproducible in the in vitro assays.