Simultaneous prevention of glutamine synthesis and high-affinity transport attenuates Salmonella typhimurium virulence

Karl E. Klose, John J. Mekalanos

Research output: Contribution to journalArticlepeer-review

86 Scopus citations


In Salmonella typhimurium, transcription of the glnA gene (encoding glutamine synthetase) is under the control of the nitrogen-regulatory (ntr) system comprising the alternate sigma factor σ54 (NtrA) and the two- component sensor-transcriptional activator pair NtrB and NtrC. The glnA, ntrB, and ntrC genes form an operon. We measured the virulence of S. typhimurium strains with nitrogen-regulatory mutations after intraperitoneal (i.p.) or oral inoculations of BALB/c mice. Strains with single mutations in glnA, ntrA, ntrB, or ntrC had i.p. 50% lethal doses (LD50s) of <10 bacteria, similar to the wild-type strain. However, a strain with a Δ(glnA- ntrC) operon deletion had an i.p. LD50 of > 105 bacteria, as did ΔglnA ntrA and ΔglnA ntrC strains, suggesting that glnA strains require an ntr- transcribed gene for full virulence. High-level transcription of the glutamine transport operon (glnHPQ) is dependent upon both ntrA and ntrC, as determined by glnHp-lacZ fusion measurements. Moreover, ΔglnA glnH and ΔglnA glnQ strains are attenuated, similar to ΔglnA ntrA and ΔglnA ntrC strains. These results reveal that access of S. typhimurium to host glutamine depends on the ntr system, which apparently is required for the transcription of the glutamine transport genes. The Δ(glnA-ntrC) strain exhibited a reduced ability to survive within the macrophage cell line J774, identifying a potential host environment with low levels of glutamine. Finally, the Δ(glnA-ntrC) strain, when inoculated at doses as low as 10 organisms, provided mice with protective immunity against challenge by the wild-type strain, demonstrating its potential use as a live vaccine.

Original languageEnglish (US)
Pages (from-to)587-596
Number of pages10
JournalInfection and immunity
Issue number2
StatePublished - Feb 1997
Externally publishedYes

ASJC Scopus subject areas

  • Parasitology
  • Microbiology
  • Immunology
  • Infectious Diseases


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