[Stability and dynamics of R-plasmids in Escherichia coli populations in continuous cultivation]

The stability of the conjugative plasmid RP4 and the nonconjugative plasmid pBS94 in Escherichia coli C600 cells containing both plasmids was studied in continuous cultivation under chemostat and pH-stat conditions. The plasmids remained stable in the cells of the bacterial population for 100 generations, and no cells were found without the plasmids. The competition between strains with and without the plasmids in a mixed culture resulted in the removal of the plasmid-free strain from the population. In these experiments, conjugative transfer of plasmids into the plasmid-free strain was observed, and co-transfer of both plasmids was more effective under the pH-stat conditions.