Bacillus thuringiensis conjugation under environmental conditions

A Bacillus thuringiensis plasmid carrying an insecticidal crystal protein gene (cry1Ac) was genetically marked with a gene conferring resistance to erythromycin. The conjugative transfer of this plasmid between B. thuringiensis strains was analyzed in broth culture, soil microcosms and infected larvae of the lepidopteran insect Anticarsia gemmatalis. Transconjugants appeared after 2 h in broth culture and after 4 h in soil systems. The lowest conjugation frequency was in soil (8.0×10−8–2.7×10−5) and the highest in infected larvae (1.0–8.4×10−1). Plasmid transfer was observed in non-supplemented soils originating from sites with and without different plant covers. Thus non-amended soil and insect larvae appear to be favorable environments for plasmid transfer by conjugation.