The kinetics of transfer of nonconjugative plasmids by mobilizing conjugative factors

Abstract

SUMMARY: A mathematical model for the kinetics of transfer of non-selftransmissible (nonconjugative) plasmids by mobilizing conjugative factors is presented and methods to estimate its parameters described. Using batch and chemostat cultures ofEscherichia coliK-12 with the nonconjugative plasmid pCR1 and an F′ mobilizing factor, the parameters of this model were estimated. The observed changes in concentrations of the different parental and transconjugant cell types and the changes in these concentrations anticipated from the model are presented for two different ‘mating’ combinations in both exponentially growing and equilibrium chemostat populations ofE. coli. The results of these experiments are interpreted to suggest that for bacterial populations dividing at a constant rate in liquid culture, the kinetics of mobilization transfer of nonconjugative plasmids can be reasonably well described by a simple set of mass action differential equations. These results also suggest that the carriage of the nonconjugative plasmid pCR1 has little, if any, effect on the capacity of a host bacterium to donate or receive conjugativeF′plasmids.