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Conjugational cotransfer of IncFI and IncI conjugative plasmids forming aggregate in a pathogenic Citrobacter
E Morzejko1, E Panek, S Cebrat
1Institute of Microbiology, Wrocław University, Poland.
Abstract:
Two plasmids, pEM4 (IncFI) determining virulence and pEM6 (IncI) determining colicine I production and resistance to tetracycline, have been found in a pathogenic strain of Citrobacter freundii. Even though pEM4 and pEM6 plasmids are conjugative and transfer themselves very efficiently during conjugation, a high cotransfer of both plasmids is observed--an unusually high fraction of transconjugants acquiring pEM6 acquires pEM4 and vice versa. The observed cotransfer of these plasmids is connected with their ability to complement their conjugational functions. An insertion mutant of pEM4 with decreased frequency of conjugational transfer has been isolated. This mutant (pEM44) lost its ability to mobilize nonconjugative plasmids. Its transfer is stimulated by pEM6 and it is transferred from (pEM44, pEM6) donors almost exclusively with pEM6 plasmid. The role of cotransfer and stimulation phenomena in spreading of plasmid aggregates in bacterial population is discussed.
Insights
Two plasmids, pEM4 and pEM6, in Citrobacter freundii show high cotransfer rates due to complementary functions. Plasmid pEM6 stimulates the transfer of a pEM4 mutant, influencing plasmid spread.
Area of Science:
- Microbiology
- Bacteriology
- Genetics
Background:
- Pathogenic Citrobacter freundii strains harbor multiple plasmids, including pEM4 (IncFI) for virulence and pEM6 (IncI) for colicin I production and tetracycline resistance.
- Both pEM4 and pEM6 are conjugative plasmids, capable of efficient self-transfer during bacterial conjugation.
Purpose of the Study:
- To investigate the unusually high cotransfer frequency observed between the pEM4 and pEM6 plasmids in Citrobacter freundii.
- To understand the underlying mechanisms, such as functional complementation, driving the cotransfer of these plasmids.
- To analyze the behavior of a pEM4 mutant (pEM44) and the influence of pEM6 on its conjugational transfer.
Main Methods:
- Conjugation experiments were performed to assess plasmid transfer and cotransfer frequencies.
- Isolation and characterization of an insertion mutant of the pEM4 plasmid (pEM44) with reduced conjugational transfer ability.
- Comparative analysis of plasmid transfer in the presence and absence of helper plasmids, specifically pEM6.
Main Results:
- A high frequency of cotransfer was observed between pEM4 and pEM6, with transconjugants frequently acquiring both plasmids.
- The cotransfer phenomenon was linked to the complementary conjugational functions of the two plasmids.
- A pEM4 mutant (pEM44) showed reduced mobilization of nonconjugative plasmids, but its transfer was significantly stimulated by the presence of pEM6, leading to exclusive cotransfer with pEM6.
Conclusions:
- The complementary functions of pEM4 and pEM6 contribute significantly to their high cotransfer rates in Citrobacter freundii.
- Plasmid pEM6 can stimulate the conjugational transfer of a defective pEM4 mutant, highlighting inter-plasmid interactions.
- These phenomena of cotransfer and stimulation play a crucial role in the dissemination and maintenance of plasmid aggregates within bacterial populations.