Mycobacterium marinum MgtC plays a role in phagocytosis but is dispensable for intracellular multiplication

PLoS One. 2014 Dec 29;9(12):e116052. doi: 10.1371/journal.pone.0116052. eCollection 2014.

Abstract

MgtC is a virulence factor involved in intramacrophage growth that has been reported in several intracellular pathogens, including Mycobacterium tuberculosis and Salmonella enterica serovar Typhimurium. MgtC participates also in adaptation to Mg2+ deprivation. Herein, we have constructed a mgtC mutant in Mycobacterium marinum to further investigate the role of MgtC in mycobacteria. We show that the M. marinum mgtC gene (Mma mgtC) is strongly induced upon Mg2+ deprivation and is required for optimal growth in Mg2+-deprived medium. The behaviour of the Mma mgtC mutant has been investigated in the Danio rerio infection model using a transgenic reporter zebrafish line that specifically labels neutrophils. Although the mgtC mutant is not attenuated in the zebrafish embryo model based on survival curves, our results indicate that phagocytosis by neutrophils is enhanced with the mgtC mutant compared to the wild-type strain following subcutaneous injection. Increased phagocytosis of the mutant strain is also observed ex vivo with the murine J774 macrophage cell line. On the other hand, no difference was found between the mgtC mutant and the wild-type strain in bacterial adhesion to macrophages and in the internalization into epithelial cells. Unlike the role reported for MgtC in other intracellular pathogens, Mma MgtC does not contribute significantly to intramacrophage replication. Taken together, these results indicate an unanticipated function of Mma MgtC at early step of infection within phagocytic cells. Hence, our results indicate that although the MgtC function is conserved among pathogens regarding adaptation to Mg2+ deprivation, its role towards phagocytic cells can differ, possibly in relation with the specific pathogen's lifestyles.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Animals
  • Bacterial Proteins / genetics
  • Bacterial Proteins / metabolism*
  • Cell Line
  • Cell Membrane / drug effects
  • Cell Membrane / metabolism
  • Embryo, Nonmammalian / drug effects
  • Embryo, Nonmammalian / metabolism
  • Embryo, Nonmammalian / microbiology
  • Gene Expression Regulation, Bacterial / drug effects
  • Genes, Bacterial
  • HeLa Cells
  • Humans
  • Injections, Subcutaneous
  • Intracellular Space / drug effects
  • Intracellular Space / microbiology*
  • Magnesium / pharmacology
  • Molecular Sequence Data
  • Mutation
  • Mycobacterium marinum / drug effects
  • Mycobacterium marinum / genetics
  • Mycobacterium marinum / growth & development*
  • Mycobacterium marinum / metabolism*
  • Neutrophils / drug effects
  • Phagocytosis* / drug effects
  • Sequence Alignment
  • Zebrafish / embryology
  • Zebrafish / microbiology

Substances

  • Bacterial Proteins
  • Magnesium

Grant support

French National Agency (ANR ZebraFlam) and European Community's Seventh Framework Programme (FP7-PEOPLE-2011-ITN) under Grant Agreement PITN-GA-2011- 289209 for the Marie-Curie Initial Training Network FishForPharma. CB is supported by a MRT fellowship from the French Ministry of Research and the Fondation for Medical Research (FRM FDT20140930905). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.