Francisella tularensis tmRNA system mutants are vulnerable to stress, avirulent in mice, and provide effective immune protection

Mol Microbiol. 2012 Jul;85(1):122-41. doi: 10.1111/j.1365-2958.2012.08093.x. Epub 2012 May 28.

Abstract

Through targeted inactivation of the ssrA and smpB genes, we establish that the trans-translation process is necessary for normal growth, adaptation to cellular stress and virulence by the bacterial pathogen Francisella tularensis. The mutant bacteria grow slower, have reduced resistance to heat and cold shocks, and are more sensitive to oxidative stress and sublethal concentrations of antibiotics. Modifications of the tmRNA tag and use of higher-resolution mass spectrometry approaches enabled the identification of a large number of native tmRNA substrates. Of particular significance to understanding the mechanism of trans-translation, we report the discovery of an extended tmRNA tag and extensive ladder-like pattern of endogenous protein-tagging events in F. tularensis that are likely to be a universal feature of tmRNA activity in eubacteria. Furthermore, the structural integrity and the proteolytic function of the tmRNA tag are both crucial for normal growth and virulence of F. tularensis. Significantly, trans-translation mutants of F. tularensis are impaired in replication within macrophages and are avirulent in mouse models of tularemia. By exploiting these attenuated phenotypes, we find that the mutant strains provide effective immune protection in mice against lethal intradermal, intraperitoneal and intranasal challenges with the fully virulent parental strain.

Publication types

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

MeSH terms

  • Amino Acid Sequence
  • Animals
  • Bacterial Vaccines / immunology
  • Base Sequence
  • Cells, Cultured
  • Female
  • Francisella tularensis / genetics
  • Francisella tularensis / pathogenicity*
  • Gene Targeting
  • Macrophages / microbiology*
  • Mice
  • Mice, Inbred C3H
  • Mice, Inbred C57BL
  • Microbial Sensitivity Tests
  • Molecular Sequence Data
  • Mutagenesis, Insertional
  • Nucleic Acid Conformation
  • Open Reading Frames
  • Phagosomes / microbiology
  • RNA, Bacterial / genetics*
  • Stress, Physiological
  • Tularemia / immunology
  • Tularemia / microbiology*
  • Vaccines, Attenuated / immunology
  • Virulence

Substances

  • Bacterial Vaccines
  • RNA, Bacterial
  • Vaccines, Attenuated
  • tmRNA