Polyhedrosis Virus in Bacillus thuringiensis

This study was conducted to build a recombinant strain with highly insecticidal activity and a wide host range by using the cry 1 Ac and p74 gene. Firstly, the p74 gene was amplified from the genosome of Autographa californica multicapsid nucleopolyhedrovirus. The cry1Ac gene and the terminator gene of cry1Ac, named cry1Act, were amplified from the plasmid of Bt 4.0718 strain. Three T vectors, named pTp74, pT1Ac, and pT1Act which held the aimed gene p74, cry1Ac, and cry1Act, respectively, and two middle vectors, named pTp74Act and pT1Acp74 which held the aimed fusion gene p74-cry1Act and cry1Ac-p74, respectively, were built by using pMD18-T. Then pT1Acp74 and the shuttle plasmid were digested and linked and an expressing-vector pH1Acp74 was built. Finally, pH1Acp74 was transformed into the acrystalliferous strain XBU001 and the aimed recombinant strain XBU-H1Acp74 was obtained. The expression of Bt transformant XBU-H1Acp74 was analyzed by SDS-PAGE which showed XBU-H1Acp74 could produce 130 kDa Cry1Ac protein and 50 kDa P74 protein. The insecticidal activity of transformant against Spodoptera exigua was evaluated compared with the contrast strains HTX-42 (only cry1Ac gene was transformed into XBU001) after auto lysis. The LC50 of HTX-42 was higher than that of the XBU-H1Acp74's, which implied that P74 could increase the efficacy and range of Bt Cry toxins in insect control. The fusion gene of cry1Ac and p74 were constructed successfully which will be served as the foundation for constructing the fusion genes of Bt cry gene and other foreign genes.