The Outer Membrane Protein TolC Is Required for Phytoalexin Resistance and Virulence of the Fire Blight Pathogen Erwinia Amylovora

Microb Biotechnol. 2009 Jul;2(4):465-75. doi: 10.1111/j.1751-7915.2009.00095.x. Epub 2009 Feb 17.


Erwinia amylovora causes fire blight on several plant species such as apple and pear, which produce diverse phytoalexins as defence mechanisms. An evolutionary successful pathogen thus must develop resistance mechanisms towards these toxic compounds. The E. amylovora outer membrane protein, TolC, might mediate phytoalexin resistance through its interaction with the multidrug efflux pump, AcrAB. To prove this, a tolC mutant and an acrB/tolC double mutant were constructed. The minimal inhibitory concentrations of diverse antimicrobials and phytoalexins were determined for these mutants and compared with that of a previously generated acrB mutant. The tolC and arcB/tolC mutants were considerably more susceptible than the wild type but showed similar levels as the acrB mutant. The results clearly indicated that neither TolC nor AcrAB significantly interacted with other transport systems during the efflux of the tested toxic compounds. Survival and virulence assays on inoculated apple plants showed that pathogenicity and the ability of E. amylovora to colonize plant tissue were equally impaired by mutations of tolC and acrB/tolC. Our results allowed the conclusion that TolC plays an important role as a virulence and fitness factor of E. amylovora by mediating resistance towards phytoalexins through its exclusive interaction with AcrAB.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Anti-Bacterial Agents / metabolism
  • Anti-Bacterial Agents / toxicity
  • Bacterial Outer Membrane Proteins / genetics
  • Bacterial Outer Membrane Proteins / metabolism*
  • DNA, Bacterial / chemistry
  • DNA, Bacterial / genetics
  • Drug Resistance, Bacterial*
  • Erwinia amylovora / drug effects*
  • Erwinia amylovora / pathogenicity
  • Gene Deletion
  • Malus / microbiology
  • Membrane Transport Proteins / genetics
  • Membrane Transport Proteins / metabolism*
  • Microbial Sensitivity Tests
  • Microbial Viability / drug effects
  • Molecular Sequence Data
  • Plant Diseases / microbiology*
  • Pyrus / microbiology
  • Sequence Analysis, DNA
  • Sesquiterpenes / metabolism
  • Sesquiterpenes / toxicity*
  • Virulence
  • Virulence Factors / genetics
  • Virulence Factors / metabolism*


  • Anti-Bacterial Agents
  • Bacterial Outer Membrane Proteins
  • DNA, Bacterial
  • Membrane Transport Proteins
  • Sesquiterpenes
  • Virulence Factors
  • phytoalexins

Associated data

  • GENBANK/FJ462442