EXPRESSION OF THE CRYSTAL PROTEIN GENE UNDER THE CONTROL OF THE ALPHA-AMYLASE PROMOTER IN BACILLUS-THURINGIENSIS STRAINS

The expression of an insecticidal crystal protein gene of Bacillus thu ringiensis under the control of the alpha-amylase gene promoter was in vestigated. The cryIC gene, which encodes a protein known to have a un ique activity against Spodoptera (armyworm) species, was used in this investigation. The cryIC gene was placed, along with the alpha-amylase promoter from B. subtilis, in a B. thuringiensis-derived cloning vect or, generating a pair of recombinant plasmids, pSB744 and pSB745. The cloning vector that contains the minimal replicon of B. thuringiensis subsp. kurstaki HD73 is stably maintained in a variety of B. thuringie nsis strains, as previously reported by Gamel and Plot (Gene 120:17-26 , 1992). The present study confirmed that the recombinant plasmids are also stably maintained in B. thuringiensis subsp. kurstaki Cry(-)B an d HD73 growing in media without selection pressure for at least 48 h. The cryIC gene on the recombinant plasmids were notably expressed at h igh levels in both recombinant strains. Expression of the introduced c ryIC gene on the recombinant plasmid in B. thuringiensis subsp. Kursta ki HD73 did not impair expression of the resident cryIA(c) gene. The C ryIA(c) protein is known to have a high level of activity against loop ers such as Trichoplusia ni (the cabbage looper). As a result of coexp ression of the introduced cryIC gene and the resident cryIA(c) gene, r ecombinant strain HD73 acquired an additional insecticidal activity ag ainst Spodoptera exigua (the beet armyworm) whereas the original activ ity level against T. ni was maintained.