Diversity of locations for Bacillus thuringiensis crystal protein genes

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Abstract
The location of crystal protein genes in 22 crystalliferous B. thuringiensis strains representing 14 subspecies was investigated by hybridization of an intragenic restriction fragment from a cloned crystal protein gene to whole plasmid preparations. Hybridization was found to a single plasmid in 8 strains, to more than 1 plasmid in 7 strains and to 1 or both of 2 large, unresolved plasmids in 2 strains. The sizes of the hybridized plasmids ranged from 33 to over 150 megadaltons. In 1 additional subspecies, hybridization was only to linear DNA fragments, suggesting a chromosomal crystal protein gene, and for 4 other subspecies, not reported to be toxic to lepidopteran insects, no hybridization was found to either plasmids or to total cell DNA. Hybridization to restriction digests of plasmids and total cell DNA of several strains of subspecies thuringiensis [B. t] and [B. t.] kurstaki revealed that all homology to the cloned crystal protein gene was plasmid associated and that several of these strains contained multiple regions of homology, implying the presence of multiple crystal protein genes.