Model for the Dynamics of Colicin Plasmids in Continuous Culture

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Abstract
Bacteriocin plasmids may be useful in preventing plasmid instability because the bacteriocin they produce selectively kills otherwise identical bacterial cells lacking the plasmid. This capability may allow plasmid-bearing cells to persist despite the problems of growth-rate depression and segregational plasmid loss that often lead to displacement by plasmid-free cells. In order to determine the conditions under which bacteriocin plasmids can prevent instability, we have developed and analyzed a mathematical model for the growth of colicin plasmid-bearing E. coli in continuous culture. Model behavior compares successfully with experimental results of Adams et al. Dependence of the system dynamic behavior on key parameters has been elucidated and a simple parameter criterion for prevention of plasmid instability has been derived. The possibility of instability prevention was found to be extremely sensitive to dilution rate.