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The ESAT-6/CFP-10 secretion system of Mycobacterium marinum modulates phagosome maturation

Tracy Tan1, Warren L Lee, David C Alexander

  • 1Department of Medical Genetics and Microbiology, University of Toronto, 1 King's College Circle, Toronto, ON, M5S 1A8, Canada.

Cellular Microbiology
|August 23, 2006
PubMed

Insights

The ESAT-6/CFP-10 secretion system in pathogenic mycobacteria prevents phagolysosome fusion, a novel virulence mechanism. This system is crucial for bacterial survival within host cells, impacting mycobacterial pathogenesis.

Area of Science:

  • Microbiology
  • Cell Biology
  • Pathogenesis

Background:

  • Virulence of pathogenic mycobacteria, including Mycobacterium tuberculosis, depends on the secretion of early secretory antigenic 6 kDa (ESAT-6) and culture filtrate protein 10 (CFP-10).
  • These proteins are exported via an alternative secretion pathway encoded by the RD1 locus, but their specific functions remain unclear.
  • Mutations in ESAT-6 or CFP-10 secretion attenuate M. tuberculosis virulence in animal models.

Purpose of the Study:

  • To investigate the function of the ESAT-6/CFP-10 secretion system in host-pathogen interactions.
  • To elucidate the role of this secretion system in the survival of pathogenic mycobacteria within host cells.

Main Methods:

  • Isolation and characterization of a Mycobacterium marinum mutant defective in ESAT-6/CFP-10 secretion, with a mutation in the MM5446 gene (orthologous to Rv3871).
  • Analysis of bacterial replication within J774 macrophages and growth in 7H9 medium.
  • Confocal and electron microscopy to assess phagosome maturation and acidification in infected macrophages using LAMP-1, rhodamine-dextran, ferritin, and LysoTracker Red.

Main Results:

  • The MM5446 mutant exhibited impaired replication within macrophages compared to the parental strain, despite equivalent growth in culture medium.
  • Wild-type M. marinum predominantly resided in poorly acidified, non-lysosomal compartments.
  • A significantly higher percentage of MM5446 mutant bacteria were found in acidified compartments, indicating a defect in phagolysosome maturation/acidification.

Conclusions:

  • The ESAT-6/CFP-10 secretion system plays a critical role in preventing phagolysosomal fusion, a novel mechanism for bacterial survival within host cells.
  • This function of the ESAT-6/CFP-10 secretion system contributes to the virulence of pathogenic mycobacteria.
  • Understanding this pathway provides insights into mycobacterial pathogenesis and potential therapeutic targets.

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