Transduction of R Factors by a Proteus mirabilis Bacteriophage

A transducing phage, designated phim, was isolated from a lysogenic strain of Proteus mirabilis and was characterized with respect to its physical and genetic properties. The phage contains double-stranded deoxyribonucleic acid (DNA) with an S(20,w) degrees of 29 which corresponds to a molecular weight of 24 x 10(6) daltons. The base composition of phim DNA was estimated to be 40% guanine plus cytosine on the basis of the buoyant density of the DNA. phim carries out generalized transduction of chromosomal genes in P. mirabilis at a frequency of 5 x 10(-8) to 2 x 10(-6) per adsorbed phage. To obtain R-factor transduction, it was necessary to have a resident R factor in the recipient cells. In these experiments, different combinations of genetically distinguishable R factors were used in the donor and recipient cells. The frequencies of R-factor transduction were 10(-9) to 2 x 10(-8). The transduction of R factors using an R(-) recipient could not be detected. Transductant R factors were usually recombinant between donor and resident R factors. All of the transduced R factors were transferable by conjugation. A plausible explanation for the requirement for a resident R factor in the recipient cells is that phim transduces only a portion of the R-factor genome and therefore requires a resident R factor for genetic recombination. The reason for the low frequencies of R-factor transduction is not known, but some possible interpretations have been discussed.