Identification of similar transcriptional regulatory mechanisms in multiple cry genes in Bacillus thuringiensis HD12

Bacillus thuringiensis subspecies morrisoni strain HD12, whose genome harbors multiple insecticidal protein-encoding genes, includes eight cry genes, as indicated by genome sequencing. This strain produces crystals that are toxic to lepidopteran species. These crystal inclusions were purified by sucrose gradients and sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE), followed by liquid chromatography-mass spectrometry, and found to contain five proteins (Cry1Da, Cry1Ae, Cry1Bb, Cry1Fb, and Cry1Ja). The transcriptional activities of the cry1Da, cry1Ae, cry1Bb, cry1Fb, and cry1Ja promoters indicated that transcription of cry1Da is controlled by SigE; however, the other four cry genes were found to be controlled by both SigE and SigK. The activities of the cry1Ja and cry1Fb promoters were the strongest among the five genes studied. These promoters were therefore used to direct the expression of the Cry1Ac- and Cry2Ab-encoding genes concurrently in a single strain. Our findings indicate that promoters with the same transcriptional profile may be used to direct the expression of different cry genes in one strain. Our results are expected to be valuable for the construction of strains with efficient expression of multiple cry genes in order to overcome current limitations associated with the application of B. thuringiensis-based insecticides.