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Estimating the rate of plasmid transfer: an end-point method
L Simonsen1, D M Gordon, F M Stewart
1Department of Zoology, University of Massachusetts, Amherst 01003.
Journal of General Microbiology
|November 1, 1990
Summary
This study introduces a new method to calculate the rate of conjugative plasmid transfer using bacterial densities and growth rates. This approach is robust against variations in cell density, donor:recipient ratio, and mating time, enabling environmental factor analysis.
Area of Science:
- Microbiology
- Molecular Biology
- Genetics
Background:
- Conjugative plasmid transfer is a key mechanism for bacterial evolution and antibiotic resistance.
- Accurate quantification of plasmid transfer rates is crucial for understanding bacterial population dynamics.
- Existing methods for estimating plasmid transfer rates can be complex and sensitive to experimental conditions.
Purpose of the Study:
- To develop and validate a novel, simplified method for determining the rate parameter of conjugative plasmid transfer.
- To assess the method's robustness against biological variabilities like growth rate differences and plasmid segregation.
- To enable the study of environmental influences on plasmid transfer rates, even when these factors affect bacterial growth.
Main Methods:
- Derivation of a formula for plasmid transfer rate (gamma) from a mathematical model of bacterial growth and plasmid transfer in batch culture.
- Utilizing single estimates of donor, recipient, and transconjugant densities, along with the exponential growth rate.
- Computer simulations to evaluate method sensitivity to biological factors; experimental validation using plasmid R1 in Escherichia coli K12.
Main Results:
- The developed method accurately estimates the plasmid transfer rate (gamma) using basic culture parameters.
- Simulations confirmed the method's resilience to variations in growth rates, plasmid segregation, and pilus synthesis.
- Experimental results showed that the estimated transfer rate (gamma) was independent of cell density, donor:recipient ratio, and mating duration.
Conclusions:
- The new method provides a reliable and straightforward way to quantify conjugative plasmid transfer rates.
- This technique overcomes limitations of previous methods, allowing for the investigation of environmental effects on plasmid transfer.
- The study successfully demonstrated the method's utility by examining the impact of temperature on plasmid transfer rates.