Donor/recipient interactions affecting plasmid transfer amongStreptomyces species: A conjugative plasmid will mobilize nontransferable plasmids in soil

Streptomyces parvulus was used as the recipient for plasmid pIJ303 and pIJ211, two conjugative plasmids derived from the self-transmissible plasmid pIJ101. One of the resulting transconjugantS. parvulus strains containing plasmid pIJ303 was used withS. lividans to evaluate the effects of the host strain on the frequency of pIJ303 transfer betweenStreptomyces species. Only 30% ofS. parvulus cells acquired plasmid pIJ303 in crosses in whichS. lividans was the donor, whereas 100% ofS. lividans cells acquired the plasmid whenS. parvulus was the donor. This indicates that the frequency of transfer of the conjugative plasmid was determined by the recipient. The other resulting transconjugantS. parvulus strain containing plasmid pIJ211 was evaluated for its ability to mobilize the nonconjugative plasmid pIJ702 fromS. lividans, on agar and in sterile soil. AfterS. lividans containing pIJ702 was crossed on agar and in sterile soil withS. parvulus containing pIJ211, recombinantS. parvulus colonies carrying pIJ702 and expressing pigments characteristic of both species were recovered, from both agar and soil. Although a large percentage ofS. parvulus transconjugants lost pIJ211 during incubation in soil, the mobilization of pIJ702 fromS. lividans intoS. parvulus still occurred. Plasmid integration into the chromosome of the donor and the transconjugant was evaluated by Southern blot hybridization. Hybridization of plasmid pIJ303, with chromosomal DNA fromS. lividans andS. parvulus transconjugants, using biotinylated DNA, indicated that no integration had occurred. Genetic exchange betweenStreptomyces species also occurred in a liquid medium. The finding of plasmid mobilization in soil is significant. It demonstrates that genetic exchange in the environment can occur between released genetically engineeredStreptomyces species and nativeStreptomyces species that contain conjugative plasmids.Paper of the Idaho Agricultural Experiment Station.