CHARACTERIZATION OF PLASMID PAW63, A 2ND SELF-TRANSMISSIBLE PLASMID IN BACILLUS-THURINGIENSIS SUBSP KURSTAKI HD73

Bacillus thuringiensis subspecies kurstaki HD73, toxic for lepidoptera n larvae, contains two large self-transmissible plasmids of approximat ely 75 kb, pHT73 and pAW63. The conjugative plasmid pHT73 has been stu died extensively and has been shown to harbour the toxin gene cry1Ac, the transposon Tn4430 and several insertion sequences. In this study i t was demonstrated that the minor plasmid pAW63 is also self-transmiss ible and about 10-30 times more efficient in mobilizing plasmid pBC16. To facilitate direct selection for pAW63 transfer, the plasmid was ta gged with the tetracycline resistance transposon Tn5401 and in intrasp ecies matings it was found that after 2 h, all recipients had acquired a copy of the plasmid. Mating experiments demonstrated that pAW63 cou ld be transferred to Bacillus thuringiensis subsp. israelensis, Bacill us cereus, Bacillus licheniformis, Bacillus subtilis and Bacillus spha ericus, and that the conjugative functions were expressed in these hos ts. Hybridization studies showed that the replicons of pAW63 and pHT73 were distinct from one another. Sequences homologous to transposon Tn 4430 and several insertion sequences were, however, shown to reside on both plasmids.