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Biochemical and Pathological Characters of Different Bt Cry Toxins
An entomopathogenic bacterium, Bacillus thuringiensis (Bt), is Gram-positive and undergoes sporulation along with the production of the insecticidal crystal toxins in a paraspore form. This study investigated the biochemical and insecticidal activities of Cry toxins of various Bt strains of Bt aizawai, Bt kurstaki, Bt tenebrionis, and Bt israelensis. Bt aizawai for a Cry1C (135 kDa), Bt kurstaki for a Cry1A (133 kDa), Bt tenebrionis for a Cry3 (73 kDa), Bt israelensis for a Cry4A (134 kDa) and Cry4B (128 kDa). To look for insect pest spectra of these four Cry toxins against four different insects, Cry1A was the most potent to Plutella xylostella, Cry1C to Spodoptera exigua, Cry3 to Tribolium castaneum, and Cry4A to Drosophila melanogaster. To further analyze the differential insecticidal activities of Cry toxins, two Cry toxin genes were expressed using baculovirus expression system. Both Cry1Ac and Cry1Ca toxins significantly enhanced the baculoviral pathogenicity against P. xylostella and S. exigua. However, the synergistic effects were different depending on the type of Cry toxins. These results suggest that the different insecticidal spectra of different Bts are explained by the different Cry toxins produced by the bacteria.
