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DNA methylation-dependent regulation of pef expression in Salmonella typhimurium

B Nicholson1, D Low

  • 1Department of Pathology, University of Utah Health Sciences Center, Salt Lake City, UT 84132, USA.

Molecular Microbiology
|February 26, 2000
PubMed

Insights

Salmonella typhimurium

Area of Science:

  • Microbiology
  • Molecular Biology
  • Genetics

Background:

  • Plasmid-encoded fimbriae (Pef) in Salmonella typhimurium are crucial for adhesion to the intestinal epithelium.
  • The pef operon shares regulatory similarities with the Escherichia coli pyelonephritis-associated pilus (pap) operon, suggesting potential methylation-dependent control.
  • Pef fimbriae expression is restricted to specific conditions, unlike other fimbriae, indicating unique regulatory mechanisms.

Purpose of the Study:

  • To investigate the regulatory mechanisms governing Pef fimbriae production in Salmonella typhimurium.
  • To determine the role of DNA methylation in the transcriptional regulation of the pef operon.
  • To identify key regulatory proteins involved in Pef expression.

Main Methods:

  • Analysis of S. typhimurium grown under specific acidic, rich broth conditions.
  • Investigation of phase variation mechanisms controlling fimbrial expression.
  • Assays to determine the requirement of regulatory proteins (Lrp, Dam, H-NS, RpoS) and DNA methylation sites (GATC I, II, X) for pef transcription.

Main Results:

  • Pef production is regulated by phase variation, with populations existing in expression (ON) and non-expression (OFF) states.
  • Leucine-responsive regulatory protein (Lrp) and DNA adenine methylase (Dam) are essential for pef transcription.
  • Histone-like protein (H-NS) and stationary-phase sigma factor (RpoS) repress pef transcription.
  • Methylation of the pef GATC II site is crucial for fimbrial expression.
  • Under inducing acidic conditions, GATC I sites are non-methylated, while GATC II and X sites are methylated.
  • Lrp influences methylation protection at GATC I and GATC II sites, modulated by PefI.

Conclusions:

  • Pef fimbriae production in Salmonella typhimurium is regulated by DNA methylation.
  • This study presents the first evidence of methylation-dependent gene regulation outside of Escherichia coli.
  • The findings elucidate a novel regulatory pathway for bacterial adhesion factors.

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