A comparison of the kinetics of plasmid transfer in the conjugation systems encoded by the F plasmid from Escherichia coli and plasmid pCF10 from Enterococcus faecalis

Summary auto-generated

This study compared the kinetics of plasmid conjugation in three bacterial systems using mathematical models adapted from enzyme kinetics. The researchers analyzed the F plasmid from Escherichia coli and plasmid pCF10 from Enterococcus faecalis, comparing their results with previously characterized pXO16 from Bacillus thuringiensis. They measured conjugation rates by determining how many transconjugants (recipients receiving plasmids) were produced per donor cell per minute at varying recipient concentrations. The F plasmid system, which uses small cell aggregates connected by sex pili, achieved a maximal conjugation rate (Vmax) of approximately 0.15 transconjugants per donor per minute. The pheromone-induced pCF10 system in Enterococcus, which forms large aggregates, operated at 0.29 transconjugants per donor per minute. Despite mechanistic differences, both systems shared key characteristics: recipients required 40-80 minutes to mature into functional donors, and conjugation rates increased proportionally with recipient concentration until saturation. The Km values differed significantly between systems, reflecting differences in mating pair formation mechanisms. These findings provide quantitative parameters useful for understanding plasmid spread in natural environments and assessing risks of horizontal gene transfer.

Key findings

The F plasmid conjugation rate was 0.15 transconjugants per donor per minute, while pCF10 achieved 0.29 transconjugants per donor per minute, demonstrating different efficiencies despite both sustaining transfer in liquid medium.
Newly formed transconjugants required 40-80 minutes of maturation before functioning as competent donors across all three conjugation systems tested.
The Km values differed significantly between F plasmid (1.8×10⁷) and pCF10 (1.2×10⁸) systems, reflecting inherent differences in mating pair formation and transfer mechanisms.
Conjugation rates showed saturation kinetics similar to enzyme catalysis, with rates proportional to recipient concentration at lower densities but limited by donor capacity (Vmax) at higher densities.
Donors required recovery periods between successive rounds of plasmid transfer, with transconjugant maturation time being a major factor limiting secondary transfer rates.

This summary was generated automatically from the article PDF and is not part of the original publication. Refer to the PDF for the authoritative text.

Abstract

Quantitative measurements of horizontal DNA transfer are critical if one wishes to address questions relating to ecology, evolution and the safe use of recombinant bacteria. Traditionally, the efficiency of a conjugation system has been described by its transfer frequency. However, transfer frequencies can be determined in many ways and may be sensitive to physical, chemical and biological conditions. In this study the authors have used the mechanistic similarity between bacterial conjugation and simple enzyme catalysis in order to calculate the maximal conjugation rate (V_max) and the recipient concentration (K_m) at which the conjugation rate is half its maximal value, for two different conjugation systems: the F plasmid from Escherichia coli and plasmid pCF10 from Enterococcus faecalis. The results are compared with the data obtained from the aggregation-mediated conjugation system encoded on pXO16 from Bacillus thuringiensis. The conjugation systems analysed are fundamentally different; however, they have some characteristics in common: they are able to sustain conjugative transfer in liquid medium and the transfer efficiencies are very high. Conjugation encoded by the F plasmid in E. coli involves the formation of small aggregates (2-20 cells), established by sex pili, and the plasmid's maximal conjugation rate was estimated to be approximately 0·15 transconjugants per donor per minute. Pheromone-induced conjugation in Ent. faecalis, which involves the formation of large aggregates, was found to proceed at a maximal conjugation rate of 0·29 transconjugants per donor per minute. Also, the K_m value differed significantly between these conjugation systems; this may reflect the inherent differences in mating pair formation and transfer mechanisms. In these conjugation systems, the donors underwent a recovery period between rounds of conjugative transfer and newly formed transconjugants required a period of about 40-80 min to mature into proficient donors.