Formation of a novel surface structure encoded by Salmonella Pathogenicity Island 2

EMBO J. 2005 Jun 1;24(11):2043-52. doi: 10.1038/sj.emboj.7600676. Epub 2005 May 12.


The type III secretion system (T3SS) encoded by Salmonella Pathogenicity Island 2 (SPI2) is essential for virulence and intracellular proliferation of Salmonella enterica. We have previously identified SPI2-encoded proteins that are secreted and function as a translocon for the injection of effector proteins. Here, we describe the formation of a novel SPI2-dependent appendage structure in vitro as well as on the surface of bacteria that reside inside a vacuole of infected host cells. In contrast to the T3SS of other pathogens, the translocon encoded by SPI2 is only present singly or in few copies at one pole of the bacterial cell. Under in vitro conditions, appendages are composed of a filamentous needle-like structure with a diameter of 10 nm that was sheathed with secreted protein. The formation of the appendage in vitro is dependent on acidic media conditions. We analyzed SPI2-encoded appendages in infected cells and observed that acidic vacuolar pH was not required for induction of SPI2 gene expression, but was essential for the assembly of these structures and their function as translocon for delivery of effector proteins.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Bacterial Proteins / analysis
  • Bacterial Proteins / genetics*
  • Bacterial Proteins / metabolism
  • Bacterial Proteins / physiology
  • Cell Surface Extensions / genetics*
  • Cell Surface Extensions / physiology
  • Cell Surface Extensions / ultrastructure
  • Dimerization
  • Gene Expression Regulation, Bacterial
  • Hydrogen-Ion Concentration
  • Macrophages / microbiology
  • Macrophages / ultrastructure
  • Membrane Proteins / genetics*
  • Membrane Proteins / metabolism
  • Membrane Proteins / physiology
  • Mice
  • Microscopy, Electron, Scanning / methods
  • Molecular Chaperones / analysis
  • Molecular Chaperones / genetics
  • Molecular Chaperones / metabolism
  • Phagosomes / microbiology
  • Protein Transport
  • Salmonella typhimurium / genetics*
  • Salmonella typhimurium / pathogenicity
  • Salmonella typhimurium / ultrastructure
  • Vacuoles / microbiology
  • Virulence / genetics


  • Bacterial Proteins
  • Membrane Proteins
  • Molecular Chaperones
  • SPI-2 protein, Salmonella
  • SseB protein, Salmonella typhimurium
  • SseC protein, Salmonella typhimurium
  • SseD protein, Salmonella typhimurium