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Porins facilitate nitric oxide-mediated killing of mycobacteria

Daniela Leite Fabrino1, Christopher K E Bleck, Elsa Anes

  • 1European Molecular Biology Laboratory, Postfach 102209, 69117 Heidelberg, Germany.

Microbes and Infection
|May 23, 2009
PubMed

Insights

Porins make Mycobacterium smegmatis vulnerable to macrophage killing. Deleting these porins enhances bacterial survival by increasing resistance to nitric oxide (NO) within phagosomes.

Area of Science:

  • Microbiology
  • Immunology
  • Cell Biology

Background:

  • Non-pathogenic mycobacteria like Mycobacterium smegmatis are phagocytosed by macrophages and killed through fusion with late endocytic/lysosomal compartments.
  • Porins are outer membrane proteins facilitating hydrophilic molecule influx in mycobacteria.
  • Previous studies showed deletion of MspA, MspC, and MspD porins increased M. smegmatis survival in macrophages, but the mechanism was unclear.

Purpose of the Study:

  • To investigate the mechanism by which porin deletion enhances Mycobacterium smegmatis survival within macrophages.
  • To determine if porins influence mycobacterial susceptibility to macrophage-mediated killing mechanisms, specifically nitric oxide (NO).

Main Methods:

  • Compared internalization and phagosome-lysosome fusion of wild-type M. smegmatis (SMR5) and a porin triple mutant (ML16) in J774 macrophages.
  • Assessed nitric oxide (NO) generation in macrophages infected with SMR5 or ML16.
  • Evaluated the in vitro susceptibility of SMR5 and ML16 to NO.

Main Results:

  • Internalization and phagosome trafficking of the porin mutant (ML16) were identical to wild-type M. smegmatis (SMR5).
  • Nitric oxide (NO) generation in infected macrophages was similar for both strains.
  • The porin mutant (ML16) exhibited significantly greater resistance to NO in vitro compared to the wild-type (SMR5).

Conclusions:

  • Porins render Mycobacterium smegmatis vulnerable to killing by reactive nitrogen intermediates within macrophage phagosomes.
  • This vulnerability is likely due to porins facilitating the uptake of nitric oxide (NO) across the mycobacterial outer membrane.
  • Porin deletion enhances M. smegmatis survival by increasing resistance to NO-mediated killing.

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