Type IV pili in Francisella tularensis: roles of pilF and pilT in fiber assembly, host cell adherence, and virulence

Infect Immun. 2008 Jul;76(7):2852-61. doi: 10.1128/IAI.01726-07. Epub 2008 Apr 21.


Francisella tularensis, a highly virulent facultative intracellular bacterium, is the causative agent of tularemia. Genome sequencing of all F. tularensis subspecies revealed the presence of genes that could encode type IV pili (Tfp). The live vaccine strain (LVS) expresses surface fibers resembling Tfp, but it was not established whether these fibers were indeed Tfp encoded by the pil genes. We show here that deletion of the pilF putative Tfp assembly ATPase in the LVS resulted in a complete loss of surface fibers. Disruption of the pilT putative disassembly ATPase also caused a complete loss of pili, indicating that pilT functions differently in F. tularensis than in model Tfp systems such as those found in Pseudomonas aeruginosa and Neisseria spp. The LVS pilF and pilT mutants were attenuated for virulence in a mouse model of tularemia by the intradermal route. Furthermore, although absence of pili had no effect on the ability of the LVS to replicate intracellularly, the pilF and pilT mutants were defective for adherence to macrophages, pneumocytes, and hepatocytes. This work confirms that the surface fibers expressed by the LVS are encoded by the pil genes and provides evidence that the Francisella pili contribute to host cell adhesion and virulence.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Adenosine Triphosphatases / chemistry
  • Adenosine Triphosphatases / genetics
  • Adenosine Triphosphatases / metabolism*
  • Amino Acid Sequence
  • Animals
  • Bacterial Adhesion*
  • Bacterial Proteins / chemistry
  • Bacterial Proteins / genetics
  • Bacterial Proteins / metabolism*
  • Bacterial Vaccines
  • Cells, Cultured
  • Fimbriae Proteins / chemistry
  • Fimbriae Proteins / genetics
  • Fimbriae Proteins / metabolism*
  • Fimbriae, Bacterial / metabolism*
  • Francisella tularensis / genetics
  • Francisella tularensis / metabolism
  • Francisella tularensis / pathogenicity*
  • Hepatocytes / microbiology
  • Macrophages / microbiology
  • Mice
  • Mice, Inbred C3H
  • Molecular Motor Proteins / chemistry
  • Molecular Motor Proteins / genetics
  • Molecular Motor Proteins / metabolism*
  • Molecular Sequence Data
  • Mutation
  • Oligonucleotide Array Sequence Analysis
  • Tularemia / microbiology
  • Tularemia / physiopathology*
  • Vaccines, Attenuated
  • Virulence


  • Bacterial Proteins
  • Bacterial Vaccines
  • Molecular Motor Proteins
  • Vaccines, Attenuated
  • Fimbriae Proteins
  • Adenosine Triphosphatases