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Recombination between plasmids of incompatibility groups P-1 and P-2
Abstract:
R plasmids of incompatibility group P-2 are readily transmissible between Pseudomonas strains, but not to Escherichia coli or other enterobacteria, whereas those of group P-1 have a broad host range. Pseudomonas aeruginosa donor strains carrying both a P-1 plasmid (RP1, RP4, or R751) and a P-2 plasmid (pMG1, pMG2, pMG5, or RPL11) were mated with E. coli K-12, and selection was imposed for resistance markers on the P-2 plasmids. Transconjugants were obtained at a low frequency, in which P-2 markers were expressed and were serially transmissible in E. coli together with P-1 markers. These plasmids had P-1 incompatibility properties, conferred susceptibility to phages active on P-1 carrying strains, and behaved on sucrose gradient centrifugation as unimolecular species of higher molecular weights than the P-1 parent. Recombinant plasmid formation was independent of a functional Rec gene in both donor and recipient and, with R751, had a preferred site leading to loss of trimethoprim resistance. Interaction between insertion sequences may be involved. Thus, plasmids of group P-2 can recombine with R factors of another group quite separate in compatibility properties, host range, and pilus type. Formation of such recombinants provides one pathway by which the genetic diversity of plasmids may have evolved.
Insights
Plasmids of incompatibility group P-2, typically limited to Pseudomonas, can recombine with broad-host-range P-1 plasmids in Escherichia coli. This recombination facilitates gene transfer and enhances plasmid genetic diversity.
Area of Science:
- Molecular Biology
- Microbiology
- Genetics
Background:
- R plasmids are crucial for bacterial adaptation and antibiotic resistance.
- Incompatibility group P-2 plasmids are generally restricted to Pseudomonas hosts.
- Incompatibility group P-1 plasmids exhibit a broad host range, including Escherichia coli.
Purpose of the Study:
- To investigate the potential for recombination between P-1 and P-2 R plasmids.
- To determine if P-2 plasmids can be transferred and maintained in E. coli through recombination with P-1 plasmids.
Main Methods:
- Conjugation experiments were performed using Pseudomonas aeruginosa donor strains harboring both P-1 and P-2 plasmids and E. coli K-12 recipients.
- Selection for P-2 plasmid markers was applied to identify transconjugants.
- Characterization of transconjugant plasmids included assessing marker expression, transmissibility, incompatibility properties, phage susceptibility, and molecular weight via sucrose gradient centrifugation.
Main Results:
- P-2 plasmid markers were successfully transferred to E. coli at low frequencies when P-1 plasmids were present in the donor.
- Transconjugant plasmids expressed P-2 markers and were stably maintained and serially transmissible in E. coli, exhibiting P-1 incompatibility properties.
- Recombinant plasmids displayed characteristics of both P-1 and P-2 plasmids, including altered molecular weights and susceptibility to specific phages.
- Recombination occurred independently of the Rec gene in both donor and recipient, suggesting Rec-independent mechanisms like insertion sequence interactions.
Conclusions:
- Plasmids from different incompatibility groups, such as P-1 and P-2, can recombine, expanding their host range and genetic repertoire.
- This inter-group plasmid recombination is a significant mechanism contributing to the evolution of plasmid diversity and the spread of genetic traits, including antibiotic resistance.