Expression of cryIVA and cryIVB Genes, Independently or in Combination, in a Crystal-Negative Strain of Bacillus thuringiensis subsp. israelensis

Abstract

The cryIVA and cryIVB genes, encoding the 125- and 135-kDa proteins, respectively, of Bacillus thuringiensis subsp. israelensis , were cloned either alone or together into a shuttle vector and expressed in a nontoxic strain of B. thuringiensis subsp. israelensis . The CryIVB protein was produced at a high level during sporulation and accumulated as inclusions; in contrast, the CryIVA polypeptide did not form such structures unless it was cloned on a higher-copy-number plasmid. Transcriptional fusions between the cryIVA or cryIVB gene promoter and the lacZ gene were constructed. The poor synthesis of CryIVA was not due to a poor efficiency of transcription from the cryIVA gene promoter. Mosquitocidal assays performed with purified inclusions showed that CryIVA was toxic for larvae of the species Aedes aegypti, Anopheles stephensi , and Culex pipiens , whereas CryIVB displayed activity only toward Aedes aegypti and Anopheles stephensi . The activity of inclusions containing both polypeptides was higher than that of single-peptide inclusions but was not as high as that of the native crystals, which contain at least four polypeptides.