INSERTION-SEQUENCE ELEMENTS IN BACILLUS-THURINGIENSIS SUBSP DARMSTADIENSIS

Two variants of insertion sequence IS231G named IS231G and H, were iso lated from Bacillus thuringiensis subsp. darmstadiensis 73-E-10-2 (BTD 2), an isolate toxic to dipteran insects, and characterized by DNA seq uence analysis. They are encoded consecutively as direct repeats on an EcoRI fragment of 5.6 kilo base pairs. Direct tandem repeats of IS231 elements have not been previously reported. Both elements are closely related to other members of the IS231 family that have been isolated from B. thuringiensis strains toxic to lepidopteran as well as to dipt eran insects. A close correlation exists between the evolutionary rela tionships of the IS231 sequences determined to date and the toxicity s pectrum of the host cell. Probing of BTD2 DNA with a radiolabeled IS23 1G fragment demonstrated that IS231 elements are located on 55- and 34 -MDa plasmids as well as on chromosomal DNA. Chromosomal DNA, but not plasmids, from BTD2 also hybridizes to another, unrelated insertion se quence, IS240, from B. thuringiensis subsp. israelensis, an isolate to xic to dipteran insects. BTD2, therefore, contains IS elements once th ought to reside exclusively in either dipteran- or lepidopteran-specif ic subspecies of B. thuringiensis.