Natural DNA uptake by Escherichia coli

Area of Science:

• Microbiology
• Bacteriology
• Genetics

Background:

• Escherichia coli possesses genes homologous to those involved in natural competence and DNA transformation in other bacteria.
• Despite these homologous genes, natural competence and transformation have not been previously detected in E. coli.
• The competence regulator Sxy induces these genes in other gamma-proteobacteria, but natural induction conditions for sxy expression in E. coli are unknown.

Purpose of the Study:

• To investigate whether E. coli's competence gene homologues encode a functional DNA uptake machinery.
• To determine if DNA uptake, induced by Sxy expression, leads to recombination in E. coli.
• To assess the impact of plasmid-borne sxy expression on natural competence across diverse E. coli strains.

Main Methods:

• Investigated the effects of constitutive plasmid-borne sxy expression on natural competence in various E. coli strains.
• Varied transforming DNA type, concentration, and incubation conditions.
• Measured radiolabeled DNA uptake directly.
• Assessed transformation frequency with and without co-provided lambda Red recombinase.

Main Results:

• High- and low-level sxy expression alone did not induce transformation in any tested E. coli strains.
• Direct measurements of radiolabeled DNA uptake were below detection limits.
• Transformants were detected when lambda Red recombinase was provided, indicating functional DNA uptake machinery.
• This study provides the first evidence that E. coli sxy expression can induce natural DNA uptake.

Conclusions:

• E. coli possesses a functional DNA uptake machinery encoded by its competence genes.
• Sxy regulator expression can induce natural DNA uptake in E. coli.
• Transformation efficiency is limited by low levels of DNA uptake and inefficient DNA processing/recombination.