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Transduction of R factors by a Proteus mirabilis bacteriophage
Abstract:
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.
Insights
The transducing phage, phim, facilitates generalized transduction of chromosomal genes in Proteus mirabilis. R-factor transduction requires a resident R factor in recipient cells for recombination, with observed frequencies ranging from 10(-9) to 2 x 10(-8).
Area of Science:
- Microbiology
- Molecular Biology
- Genetics
Background:
- Phages are viruses that infect bacteria and can be used as tools in genetic research.
- Transduction is a process where bacterial DNA is transferred from one bacterium to another by a phage.
- R-factors are plasmids that confer antibiotic resistance to bacteria.
Purpose of the Study:
- To characterize the physical and genetic properties of the transducing phage phim.
- To investigate the transduction capabilities of phim for chromosomal genes and R-factors in Proteus mirabilis.
- To elucidate the mechanism and requirements for R-factor transduction by phim.
Main Methods:
- Isolation and characterization of the transducing phage phim from Proteus mirabilis.
- Determination of phage DNA properties (double-stranded DNA, molecular weight, base composition).
- Transduction experiments to assess chromosomal gene and R-factor transfer frequencies, including genetic recombination analysis.
Main Results:
- Phim possesses double-stranded DNA with a molecular weight of 24 x 10(6) daltons and 40% guanine-cytosine content.
- Phim mediates generalized transduction of chromosomal genes at frequencies of 5 x 10(-8) to 2 x 10(-6).
- R-factor transduction requires a resident R factor in recipient cells, with frequencies of 10(-9) to 2 x 10(-8); transductants are typically recombinant and conjugative.
Conclusions:
- Phim is a capable generalized transducing phage for Proteus mirabilis chromosomal genes.
- A resident R factor is essential for phim-mediated R-factor transduction, likely facilitating recombination of fragmented R-factor DNA.
- The low frequency of R-factor transduction warrants further investigation into the underlying mechanisms.