Estimation and sensitivity analysis of kinetic parameters for plasmid stability in continuous culture of a recombinant Escherichia coli harboring trp-operon plasmid

Abstract

A model equation to describe the plasmid instability in recombinant Escherichia coli fermentation is proposed. The equation allows one to estimate easily the two model parameters; (1) the difference in the specific growth rates between plasmid-free cells and plasmid-harboring cells (δ), and (2) the probability of plasmid loss by plasmid-harboring cells (ρ). The estimated values of δ and ρ were in the range of 0.02-0.07 and 10？3？10？5, respectively, and were strongly dependent on the dilution rate. As another parameter, the ratio of specific growth rates of plasmid-free cells and plasmid-harboring cells (\alha) was calculated and the result showed the highest value of 1.28 at the lowest dilution rate of 0.075 hr？l, examined in this work. By the sensitivity analyses on the estimates of δandρ, it was found that the growth rate difference (δ) affected the plasmid instability more seriously than the probability of plasmid loss (ρ). Furthermore, the profound instability of plasmid at low dilution rate could be explained by the high values of αandρ.