Recipient competence in F'lac matings of Escherichia coli K-12.

We studied recipient mating ability in the presence of excess F'lac donors. Ninety-five percent of recipients were able to receive F'lac in 30-min matings. Competition between an F'-lac donor and an F'lac traI donor, which mobilized a ColE1 derivative (pML2), showed that each recipient mated with an average of two to three donors in 30 min. Experiments in which the competing donor was added at different times showed that some competition occurred throughout the 30-min mating period, which suggested that aggregate formation was spread over this time.