AN ANALYSIS OF THE INSTABILITY KINETICS OF PLASMID PHSG415 DURING CONTINUOUS-CULTURE OF ESCHERICHIA-COLI

The effect of dilution rate on the instability kinetics of Escherichia coli RV308(pHSG415) during glucose-limited continuous culture is exam ined. Two nonlinear models are fitted to the data, both of which chara cterize the plasmid-host system in terms of the rate parameters R (for the plasmid segregation rate) and d mu (for the specific growth rate difference between plasmid-free and plasmid-bearing single cells). In the first model, both R and d mu have constant values with respect to time. In the second, either R or d mu is represented as a time-depende nt function. Although both models fit the data equally well, it is dem onstrated that the constant rate parameter model gives results which a ppear to be misleading. a comparison is also made among some of the ma ny plasmid instability models (both mass-balance and segregated) which )rave appeared in the literature, It is found that all of these give i dentical trajectories and differ only in the definitions of the rate p arameters used.