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Properties of R plasmid R772 and the corresponding pilus-specific phage PR772
Abstract:
R plasmid R772 was isolated from a strain of Proteus mirabilis and is a self-transmissible P-1 incompatibility group plasmid having a molecular weight of about 27 x 10(6). It renders bacterial hosts resistant to kanamycin. Phage PR772 was isolated as a phage dependent on the presence of R772 in bacterial hosts. It is hexagonal-shaped with a diameter of 53 nm, has a thick inner membrane and no tail. Vaguely defined appendages are sometimes apparent at some vertices and the phage possesses double-stranded DNA. The DNA has a guanine plus cytosine molar content of 48%. The phage is sensitive to chloroform and has a buoyant density of 1.26 g cm(-3). These observations suggested that the inner membrane of the phage could contain lipid. Phage PR772 differs in morphology from the double-stranded DNA plasmid-specific phages PR4 and PRR1 which adsorb to tips and sides, respectively, of sex pili coded for by P-1 incompatibility group plasmids. Phage PR772 formed clear plaques which varied in diameter. Serologically, phages PR772 and PR4 are possibly related though very distantly, but the two phages have identical host ranges. Phage PR772 adsorbed by one of its apices to tips of sex pili coded for by plasmid R772 in Escherichia coli. It also formed plaques on Salmonella typhimurium Proteus morganii and Providence strains harbouring this plasmid as well as strains of E. coli carrying plasmids of incompatibility groups N or W. The phage produced areas of partial clearing on lawns of P. mirabilis PM5006 harbouring plasmid R772, the P-1 incompatibility group plasmid RP4, the W group plasmid RSa or the N group plasmid N3, and on lawns of Providence strain P29 carrying plasmid RP4.
Insights
Researchers isolated R plasmid R772 and its dependent phage PR772. This phage specifically binds to sex pili of R772 plasmid hosts, impacting bacterial resistance.
Area of Science:
- Microbiology
- Molecular Biology
- Virology
Background:
- R plasmid R772, belonging to the P-1 incompatibility group, confers kanamycin resistance to bacterial hosts.
- Plasmid-dependent phages are crucial tools for studying plasmid biology and host-phage interactions.
- Understanding phage-host specificity is vital for microbial genetics and biotechnology applications.
Purpose of the Study:
- To characterize the novel phage PR772, dependent on the R772 plasmid.
- To investigate the morphology, DNA properties, and host interactions of phage PR772.
- To compare phage PR772 with other known plasmid-specific phages.
Main Methods:
- Isolation and characterization of plasmid R772 and phage PR772.
- Electron microscopy for phage morphology determination.
- DNA analysis including base composition and buoyant density.
- Plaque assays and host range determination on various bacterial strains.
- Adsorption studies to bacterial pili.
Main Results:
- Phage PR772 is hexagonal, 53 nm in diameter, with double-stranded DNA (48% G+C content) and a buoyant density of 1.26 g cm(-3), suggesting a lipid-containing membrane.
- Phage PR772 exhibits distinct morphology compared to other plasmid-specific phages like PR4 and PRR1.
- Phage PR772 specifically adsorbs to the tips of sex pili encoded by R772 and related plasmids in E. coli, forming plaques on various bacterial hosts carrying these plasmids.
Conclusions:
- Phage PR772 is a unique, double-stranded DNA phage dependent on the P-1 incompatibility group plasmid R772.
- Its specific adsorption mechanism to plasmid-encoded sex pili provides insights into phage-plasmid-host interactions.
- Phage PR772's distinct characteristics and host range offer potential for further research in microbial genetics.