Abstract |
The document describes a method for determining the rate parameter of conjugative plasmid transfer that is based on single estimates of donor, recipient and transconjugant densities and the growth rate in exponential phase of the mating culture. The formula for estimating the plasmid transfer rate, gamma, was derived from a mathematical model describing cell growth and plasmid transfer in batch culture. Computer simulations were used to explore the sensitivity of the method to the realities of bacterial life, such as growth rate differences, plasmid segregation and transitory derepression of pilus synthesis. As predicted by the theory, mating experiments with the plasmid R1 in Escherichia coli K12 demonstrated that the estimate gamma is unaffected by cell density, donor: recipient ratio and mating time. Unlike previous techniques, the method allows investigations into the effect of environmental factors on plasmid transfer rates when these factors also influence population growth rates. To illustrate this, the authors examined the effect of temperature on the rate of plasmid transfer. (Copyright (c) 1990 SGM.) |