SvpA, a novel surface virulence-associated protein required for intracellular survival of Listeria monocytogenes.
A previously unknown protein, designated SvpA (surface virulence-associated protein) and implicated in the virulence of the intracellular pathogen Listeria monocytogenes, was identified. This 64 kDa protein, encoded by svpA, is both secreted in culture supernatants and surface-exposed, as shown by immunogold labelling of whole bacteria with an anti-SvpA antibody. Analysis of the peptide sequence revealed that SvpA contains a leader peptide, a predicted C-terminal transmembrane region and a positively charged tail resembling that of the surface protein ActA, suggesting that SvpA might partially reassociate with the bacterial surface by its C-terminal membrane anchor. An allelic mutant was constructed by disrupting svpA in the wild-type strain LO28. The virulence of this mutant was strongly attenuated in the mouse, with a 2 log decrease in the LD50 and restricted bacterial growth in organs as compared to the wild-type strain. This reduced virulence was not related either to a loss of adherence or to a lower expression of known virulence factors, which remained unaffected in the svpA mutant. It was caused by a restriction of intracellular growth of mutant bacteria. By following the intracellular behaviour of bacteria within bone-marrow-derived macrophages by confocal and electron microscopy studies, it was found that most svpA mutant bacteria remained confined within phagosomes, in contrast to wild-type bacteria which rapidly escaped to the cytoplasm. The regulation of svpA was independent of PrfA, the transcriptional activator of virulence genes in L. monocytogenes. In fact, SvpA was down-regulated by MecA, ClpC and ClpP, which are highly homologous to proteins of Bacillus subtilis forming a regulatory complex controlling the competence state of this saprophyte. The results indicate that: (i) SvpA is a novel factor involved in the virulence of L. monocytogenes, promoting bacterial escape from phagosomes of macrophages; (ii) SvpA is, at least partially, associated with the surface of bacteria; and (iii) SvpA is PrfA-independent and controlled by a MecA-dependent regulatory network.
Borezée
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Laboratoire de Microbiologie, Institut National de la Santé et de la Recherche Médicale U411, Faculté de Médecine Necker-Enfants Malades, 156 rue de Vaugirard, 75730 Paris Cedex 15, France.
Pellegrini
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E
Beretti
J L
JL
Berche
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P
D000595:Amino Acid Sequence; D000818:Animals; D001412:Bacillus subtilis / Q000235:genetics; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D003001:Cloning, Molecular; D015964:Gene Expression Regulation, Bacterial; D006360:Heat-Shock Proteins / Q000502:physiology; D008089:Listeria monocytogenes / Q000235:genetics / Q000472:pathogenicity / Q000502:physiology*; D008264:Macrophages / Q000276:immunology / Q000382:microbiology; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D051379:Mice; D008969:Molecular Sequence Data; D016296:Mutagenesis; D010454:Peptide Termination Factors; D010588:Phagosomes / Q000276:immunology / Q000382:microbiology; D010641:Phenotype; D015183:Restriction Mapping; D017384:Sequence Deletion; D015534:Trans-Activators / Q000502:physiology; D014774:Virulence
D001426:Bacterial Proteins; C087481:ClpC protein, Bacteria; D006360:Heat-Shock Proteins; D008565:Membrane Proteins; D010454:Peptide Termination Factors; C443120:SvpA protein, Listeria monocytogenes; D015534:Trans-Activators; C083616:mecA protein, Bacillus subtilis