Physical assay of competence for specific mating-pair formation in Escherichia coli

The fractions of Escherichia coli female and male bacteria that are competent to form specific mating pairs at any time during normal exponential growth have been measured by a physical assay. The competencies of a Hayes- and a Cavali-type donor were 35 and 50%, respectively, in agreement with piliation assays reported by others. The competencies of two recipient strains, PA309 and P678, were found to be 33 and 29%, respectively.