Dynamics of plasmid transfer in bacteria

Bacteria can obtain DNA from other cells or directly from the environment. These genes can have positive effect on fitness, but most of the time the effect will be negative. They are often carried on plasmids (autonomous genetic elements). Once a cell is transformed with such genes, further transfer may be facilitated in the presence of plasmids carrying transfer functions. Moreover, some elements may not be compatible with one another, so presence of one may result in resistance to another. This results in a complex dynamics in which the effects of the cost to fitness associated with each element, the transfer efficiency, population size and structure may result their loss, complete establishment, or persistence but with wild fluctuations of the fraction of carriers. We plan to present an initial analysis of system dynamics using a model with 3 plasmids: (i) a plasmid carrying only deleterious genes, (ii) a plasmid that is not compatible with it (carrying "resistance" functions), and (iii) a plasmid which carries transfer functions. The first two plasmids can be transferred from one cell to another only in the presence of the third.