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Transduction of R Factors by a Proteus mirabilis Bacteriophage¹

^a Department of Biochemistry and Laboratory of Molecular Biology, University of Wisconsin, Madison, Wisconsin 53706

ABSTRACT

A transducing phage, designated m, 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 x 10⁶ daltons. The base composition of m DNA was estimated to be 40% guanine plus cytosine on the basis of the buoyant density of the DNA. m 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 m 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.

² On leave from the National Institute of Health, Tokyo, Japan. Present address: Department of Microbiology, Institute of Public Health, Shirokanedai, Minato-ku, Tokyo 108, Japan.

¹ Presented in part at the 68th Annual Meeting of the American Society for Microbiology, Detroit, Mich., 5-10 May, 1968.

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