FIG. 1.

Minimum cell densities are required for mating. Donor and recipient bacteria at ratios of 1:1 were mated on filters at increasing total cell densities as described in the text. Transfer frequencies are expressed as transconjugants recovered per input donor, and culture densities are expressed as CFU per square centimeter. Each mating was quantified in triplicate, with less-than-10% differences in colony counts. The experiment was repeated two times. Although the actual frequencies of transfer differed between the three experiments, the patterns were identical. The results from a representative experiment are presented.