The aggregation-mediated conjugation system of Bacillus thuringiensis subsp. israelensis: Host range and kinetics of transfer

The aggregation-mediated conjugation system in Bacillus thuringiensis subsp. israelensis encoded on the plasmid pXO16 is characterized by the formation of aggregates when Agr(+) and Agr(-) cells are socialized in exponential growth. Using the aggregation phenotypes, we have identified potential recipients of the aggregation-plasmid pXO16 among Bacillus cereus, Bacillus subtilis, Bacillus megaterium Bacillus sphaericus, and 24 subspecies of B. thuringiensis. We found 14 Agr(-) strains, i.e., potential recipients of the aggregation system encoded by plasmid pXO16. Five strains contained a conjugative apparatus of their own and were excluded from further examinations. To monitor the transfer of plasmid pXO16, we constructed a transposon insertion of the plasmid with Tn5401. The study of the plasmid transfer of pX016::Tn5401 indicated the secretion of bacteriocins from both donor strain and recipient strains. Only one out of the nine strains examined was unable to receive the aggregation-plasmid pXO16 and express the aggregation phenotype and the conjugative abilities. It was found that the transfer of plasmid pX016 to Bacillus thuringiensis subsp. israelensis Agr(-) strains was 100%. All recipients had acquired the aggregation-plasmid pXO16 and converted to the Agr(+) phenotype.