Cloning and heterologous expression of an insecticidal delta-endotoxin gene from Bacillus thuringiensis var. aizawai IC1 toxic to both lepidoptera and diptera.

Bacillus thuringiensis var. aizawai IC1 synthesises an insecticidal protein delta-endotoxin (130-135 kDa) that is toxic to both lepidopteran and dipteran larvae, and cross-reacts immunologically with certain monospecific lepidopteran toxins. A 166-kb plasmid from this bacterium was found to hybridise with an intragenic probe derived from the clone B. thuringiensis var. sotto lepidopteran-specific delta-endotoxin gene. A strongly hybridising 5.2-kb SstI fragment from var. aizawai plasmid DNA was cloned in pUC18. After subcloning of this DNA in Escherichia coli, recombinants were obtained that synthesised large amounts of a 130-135-kDa protein. The protein was deposited in the cytoplasm as microscopically visible inclusion bodies and lysates of these cells were found to be toxic to both lepidopteran and dipteran larvae by comparison with controls. The structural basis for the dual specificity of this var. aizawai toxin is now amenable to further study.