Abstract
A genetically-engineered Bacillus thuringiensis (Bt) strain, 3A-HBF, with a broad insecticidal spectrum was constructed by introducing the recombinant plasmid pSTK-3A containing cry3Aa7 into the wild-type Bt strain HBF-1 containing the cry8Ca2 gene. The Cry3Aa7 protein produced by strain 3A-HBF was verified by SDS-PAGE and Western blotting. Flat rectangular crystals of Cry3Aa7 protein were observed besides spherical crystals (Cry8Ca2). The plasmid pSTK-3A was stable when strain 3A-HBF was grown in medium without antibiotics. The growth rate of 3A-HBF was not significantly different from that of the recipient strain, HBF-1. Strain 3A-HBF showed toxicity against two families of pests, Scarabaeidae and Chrysomelidae pests, which are susceptible to Cry8Ca (Anomala corpulenta) and Cry3Aa (Leptinotarsa decemlineata and Colaphellus bowringi). The 50% lethal concentrations of 3A-HBF against A. corpulenta, L. decemlineata and C. bowringi were 0.730 x 10(8) c.f.u./g dry soil, 1.74 microg/ml and 1.15 microg/ml, respectively.
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