Location of the crystal toxin gene ofBacillus thuringiensis var.aizawai

Mutants of two different isolates ofBacillus thuringiensis var.aizawai that are different from the parental strains in their plasmid profile were generated by plasmid curing experiments. Examination of these mutants by microscopy resulted in the identification of derivatives containing only the small crystal inclusions as well as those containing both the small and the large crystal inclusions. Acrystalliferous variants were also identified. Analysis of the plasmid profiles of these mutants along with the results from the bioassays seem to indicate that the spodopteran-active -endotoxin (i.e., small crystal inclusions) gene of theB. thuringiensis var.aizawai isolates used in this study is most likely located on the chromosome. The determinants of the large crystal inclusions (nontoxic toSpodopera exigua), however, appear to be located on either a plasmid (of 46 mega-Daltons in size) of one isolate or the chromosome of the other.