Transduction of R Factors by a Proteus mirabilis Bacteriophage

Abstract

A transducing phage, designated φm, 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 ° of 29 which corresponds to a molecular weight of 24 × 10 6 daltons. The base composition of φm DNA was estimated to be 40% guanine plus cytosine on the basis of the buoyant density of the DNA. φm carries out generalized transduction of chromosomal genes in P. mirabilis at a frequency of 5 × 10 −8 to 2 × 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 × 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 φm 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.