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Surface-localized spermidine protects the Pseudomonas aeruginosa outer membrane from antibiotic treatment and

Lori Johnson1, Heidi Mulcahy, Uliana Kanevets

  • 1Department of Microbiology, Immunology and Infectious Diseases, University of Calgary, Calgary, Alberta, Canada.

Journal of Bacteriology
|December 14, 2011
PubMed

Insights

Extracellular DNA triggers Pseudomonas aeruginosa to produce spermidine, a polyamine that protects the outer membrane from antibiotics and oxidative damage. This discovery reveals new roles for spermidine in bacterial defense mechanisms.

Area of Science:

  • Microbiology
  • Bacterial Physiology
  • Molecular Biology

Background:

  • Extracellular DNA influences bacterial gene expression, particularly concerning cation levels and antibiotic resistance.
  • Pseudomonas aeruginosa is a significant opportunistic pathogen where understanding resistance mechanisms is crucial.

Purpose of the Study:

  • To characterize novel DNA-induced genes in Pseudomonas aeruginosa.
  • To investigate the role of spermidine synthesis genes (speD and speE) in bacterial stress response.
  • To elucidate the function of cell surface polyamines in outer membrane integrity and resistance.

Main Methods:

  • Transcriptional lux fusions and quantitative RT-PCR to monitor gene expression.
  • Construction and analysis of gene mutants (PA4774).
  • Assays for outer membrane susceptibility to antibiotics (polymyxin B, CP10A, gentamicin) and oxidative stress (H2O2).
  • High-performance liquid chromatography (HPLC) and mass spectrometry (MS) for polyamine identification.

Main Results:

  • DNA and membrane-damaging antibiotics induced expression of PA4773-PA4775, homologs of spermidine synthesis genes.
  • A PA4774 mutant showed increased susceptibility to polymyxin B, CP10A, gentamicin, and oxidative damage.
  • Exogenous polyamines protected against DNA/peptide-mediated induction and rescued the mutant's resistance phenotypes.
  • The mutant failed to produce cell surface spermidine, which was restored by genetic complementation.

Conclusions:

  • Spermidine synthesis genes are induced by extracellular DNA and membrane stress in Pseudomonas aeruginosa.
  • Cell surface spermidine plays a critical role in stabilizing the outer membrane and conferring resistance to antibiotics and oxidative damage.
  • Polyamines are produced under magnesium-limiting conditions to protect the bacterial outer membrane by binding lipopolysaccharide (LPS).

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