[Instability study of Escherichia coli strains containing hybrid plasmids with threonine operon fragments]

The stability of Escherichia coli strains carrying hybrid plasmids which contain ColE1-like replicon and threonine operon genes was studied. It was shown that the main reason for instability is the loss of a plasmid. The second reason for instability is the rec-dependent recombination that leads to formation of new plasmids. All experiments where instability of strains was observed, can be quantitatively described by the model that presumes a random loss of plasmids in cell population with a frequency of about 7.10(-4), which results in diappearance of plasmid-borne cells due to their low growth rate. Instability increases during the stationary phase but it is not easy to quantitatively estimate this process.