Molecular Basis for Safety Assessment of Microbial Pesticides

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Baculovirus and Bt (Bacillus thuringiensis) are used as microbial pesticides all over the world and the former also provide a most efficient foreign gene expression system in eukaryotes (baculovector system). We studied the molecular basis in the safety of these entomopathogenic microorganisms. Recent studies demonstrated that a baculovirus (AcMNPV) can enter the nucleus of mammalian cells independently of the cell cycle without multiplication and effectively express foreign genes without expressing its own genes, suggesting that the baculovirus can be used as a low risk viral vector in the field of gene therapy. Contrary to the general perception, we elucidated that AcMNPV expressed viral genes at least partly in mammalian cells through the usual infection pathway. In addition, the expression of cellular gene (at least β-actin) was upregulated in the mammalian cells inoculated with AcMNPV. However, the expression of viral genes was inhibited to low level in mammalian cells partly by histone deacetylation mechanism and further the transcription of some viral genes started at incorrect site(s).As for the B. thuringiensis (Bt) strains, we investigated mainly the mechanisms of Vero cell toxicity by non-hemolytic enterotoxin C (NheC) that was thought to be the most important enterotoxin causing food-poisoning. It was elucidated that NheC secreted from a clinical isolate of B. cereus (Bc) strain possessing Vero cell toxicity could attach to the surface of Vero cells through the N-terminal region of 30 amino acids. On the other hand, the corresponding N-terminal region was truncated possibly by post-translational cleavage in the NheC secreted from Bt strains used in the commercial products. In addition, the N-terminal truncated from of NheC didn't show Vero cell toxicity any more.