Engineered Bacillus thuringiensis GO33A with broad insecticidal activity against lepidopteran and coleopteran pests

A recombinant plasmid pSTK-3A containing cry3Aa7 gene encoding a coleopteran-specific insecticidal protein was constructed and introduced into wild Bacillus thuringiensis subsp. aizawai G03, which contained cry1Aa, cry1Ac, cry1Ca, and cry2Ab genes and was highly toxic to lepidopteran insect pests. The genetically engineered strain were named G033A. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis and Western blot analysis demonstrated that the cry3Aa7 gene was expressed normally and produced a 67 kDa protein in G033A, and the flat rectangular crystals of Cry3Aa7 toxin protein was observed under scanning electron microscope. The recombinant plasmid was maintained in bacteria cultured for 180 generations in culture media containing no antibiotics. Synthesis of the Cry3Aa7 toxin conferred high and broad toxicity to the recombinant strain G033A against coleopteran order, elm leaf beetle (Pyrrhalta aenescens) (LC₅₀ 0.35 mg/ml), for which the parental strain G03 was not toxic. Both the parental strain G03 and recombinant strain G033A showed strong insecticidal activity to lepidopteran pests, beet armyworm (Spodoptera exigua), diamondback moth (Plutella xylostella), and cotton bollworm (Helicoverpa amigera), respectively. The lethal concentration 50% (LC₅₀) of G033A against S. exigua, P. xylostella, and H. amigera was 4.26, 0.86, and 1.76 μg/ml, respectively.