Plasmid transfer between the Bacillus thuringiensis subspecies kurstaki and tenebrionis in laboratory culture and soil and in lepidopteran and coleopteran larvae

Plasmid transfer between Bacillus thuringiensis subsp, kurstaki HD1 and B. thuringiensis subsp, tenebrionis donor strains and a streptomycin-resistant B. thuringiensis subsp, kurstaki recipient was studied under environmental ly relevant laboratory conditions in vitro, in soil, and in insects. Plasmi d transfer was detected in vitro at temperatures of 5 to 37 degrees C, at p H 5.9 to 9.0, and at water activities of 0.965 to 0.995, and the highest tr ansfer ratios (up to 10(-1) transconjugant/donor) were detected within 4 h, In contrast, no plasmid transfer was detected in nonsterile soil, and rapi d formation of spores by the introduced strains probably contributed most t o the lack of plasmid transfer observed. When a B. thuringiensis subsp. kur staki strain was used as the donor strain, plasmid transfer was detected in killed susceptible lepidopteran insect (Lacanobia oleracea) larvae but not in the nonsusceptible coleopteran insect Phaedon chocleriae, When a B, thu ringiensis subsp. tenerbrionis strain was used as the donor strain, no plas mid transfer was detected in either of these insects even when they were ki lled, These results show that in larger susceptible lepidopteran insects th ere is a greater opportunity for growth of B. thuringiensis strains, and th is finding, combined with decreased competition due to a low initial backgr ound bacterial population, can provide suitable conditions for efficient pl asmid transfer in the environment.