microbiology, Vol 141, 63-70, Copyright © 1995 by Society for General Microbiology
An analysis of the instability kinetics of plasmid pHSG415 during continuous culture of Escherichia coli
A Dunn, AM Davidson, MJ Day and PF Randerson
School of Pure and Applied Biology, University of Wales College, Cardiff, UK.
The effect of dilution rate on the instability kinetics of Escherichia coli
RV308(pHSG415) during glucose-limited continuous culture is examined. Two
nonlinear models are fitted to the data, both of which characterize 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- dependent function. Although both models
fit the data equally well, it is demonstrated that the constant rate
parameter model gives results which appear to be misleading. A comparison
is also made among some of the many plasmid instability models (both
mass-balance and segregated) which have appeared in the literature. It is
found that all of these give identical trajectories and differ only in the
definitions of the rate parameters used.
