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Analysis of virulence plasmid gene expression defines three classes of effectors in the type III secretion system of

Tony Le Gall1,2, Maria Mavris3, Maria Celeste Martino4

  • 1Laboratoire de Bactériologie, Faculté de Médecine de Brest, F-29285 Brest Cedex, France.

Microbiology (Reading, England)
|March 11, 2005
PubMed

Insights

Shigella flexneri virulence plasmid gene expression is regulated by temperature and transcriptional regulators VirF, VirB, and MxiE. This study reveals three categories of type III secretion substrates based on their regulation by these factors.

Area of Science:

  • Microbiology
  • Molecular Biology
  • Genetics

Background:

  • Shigella flexneri utilizes a 200 kb virulence plasmid to encode proteins essential for epithelial cell entry and dissemination.
  • A 30-kb entry region on this plasmid contains components of a type III secretion (TTS) apparatus, its substrates, and chaperones.
  • TTS gene expression is induced at 37°C, with the apparatus assembled but inactive until bacterial contact with host cells.

Purpose of the Study:

  • To delineate virulence plasmid genes regulated by growth temperature.
  • To identify genes controlled by the transcriptional regulators VirF, VirB, MxiE, and Orf81.
  • To understand gene regulation influenced by the activity of the type III secretion apparatus.

Main Methods:

  • Macroarray analysis was employed to compare expression profiles of 71 plasmid genes.
  • Gene expression was analyzed in wild-type Shigella flexneri at 37°C and 30°C.
  • Expression was also assessed in various mutants (virF, virB, mxiE, ipaB, ipaB mxiE, orf81) at 37°C.

Main Results:

  • Many virulence genes are controlled by VirB and indirectly by VirF.
  • No expression changes were observed in the orf81 mutant.
  • Thirteen genes showed increased expression in the ipaB mutant, dependent on MxiE, indicating MxiE's role in regulating secretion-induced genes.
  • TTS substrates were categorized into three groups based on regulation by VirB, MxiE, or both.

Conclusions:

  • Virulence gene expression in Shigella flexneri is intricately regulated by temperature and specific transcriptional regulators.
  • The type III secretion apparatus activity influences the expression of its substrates in a differential manner.
  • This differential regulation suggests distinct roles for various TTS effectors during different stages of host cell interaction.

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