High Recombinant Frequency in Extraintestinal Pathogenic Escherichia coli Strains

Area of Science:

• Microbiology
• Evolutionary Biology
• Genetics

Background:

• Homologous recombination (HR) is a key driver of genetic diversity, essential for pathogen adaptation.
• Pathogens face intense selective pressures from host defenses, potentially favoring higher recombination rates.
• Previous methods for estimating recombination rates were confounded by factors like DNA transfer and selection.

Purpose of the Study:

• To test the hypothesis that pathogens exhibit higher recombination rates than commensals.
• To develop a method for accurately measuring recombination rates independent of other evolutionary forces.
• To investigate the relationship between recombination frequency, lifestyle, and virulence in Escherichia coli.

Main Methods:

• Development of a novel plasmid-based system to quantify homologous recombination rates.
• Analysis of 160 isolates of human commensal and extraintestinal pathogenic Escherichia coli (ExPEC).
• Assessment of recombination frequency under different growth conditions, including simulated host environments (urine).

Main Results:

• Recombination frequencies varied dramatically across isolates (9 orders of magnitude) and were highly plastic, influenced by growth in urine.
• ExPEC isolates demonstrated significantly higher recombination rates compared to commensal E. coli.
• The presence of virulence factors was positively correlated with increased recombination frequencies.

Conclusions:

• Findings support the hypothesis that selection favors higher homologous recombination capacity in pathogens.
• Increased recombination likely contributes to enhanced evolvability and adaptation in pathogenic strains.
• This study provides a robust method for studying recombination dynamics in bacterial populations.