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Acidic pH sensing in the bacterial cytoplasm is required for Salmonella virulence.

ABSTRACT: pH regulates gene expression, biochemical activities and cellular behaviors. A mildly acidic pH activates the master virulence regulatory system PhoP/PhoQ in the facultative intracellular pathogen Salmonella enterica serovar Typhimurium. The sensor PhoQ harbors an extracytoplasmic domain implicated in signal sensing, and a cytoplasmic domain controlling activation of the regulator PhoP. We now report that, surprisingly, a decrease in Salmonella's own cytoplasmic pH induces transcription of PhoP-activated genes even when the extracytoplasmic pH remains neutral. Amino acid substitutions in PhoQ's cytoplasmic domain hindered activation by acidic pH and attenuated virulence in mice, but did not abolish activation by low Mg(2+) or the antimicrobial peptide C18G. Conversely, removal of PhoQ's extracytoplasmic domains prevented the response to the latter PhoQ-activating signals but not to acidic pH. PhoP-dependent genes were minimally induced by acidic pH in the non-pathogenic species Salmonella bongori but were activated by low Mg(2+) and C18G as in pathogenic S. enterica. Our findings indicate that the sensor PhoQ enables S. enterica to respond to both host- and bacterial-derived signals that alter its cytoplasmic pH.

SUBMITTER: Choi J

PROVIDER: S-EPMC5015592 | biostudies-literature | 2016 Sep

REPOSITORIES: biostudies-literature

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Acidic pH sensing in the bacterial cytoplasm is required for Salmonella virulence.

Choi Jeongjoon J Groisman Eduardo A EA

Molecular microbiology 20160708 6

pH regulates gene expression, biochemical activities and cellular behaviors. A mildly acidic pH activates the master virulence regulatory system PhoP/PhoQ in the facultative intracellular pathogen Salmonella enterica serovar Typhimurium. The sensor PhoQ harbors an extracytoplasmic domain implicated in signal sensing, and a cytoplasmic domain controlling activation of the regulator PhoP. We now report that, surprisingly, a decrease in Salmonella's own cytoplasmic pH induces transcription of PhoP- ...[more]

PMID: 27282333

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Project description:Bacteria have evolved many different signal transduction systems to sense and respond to changing environmental conditions. Signal integration is mainly achieved by signal recognition at extracytosolic ligand-binding domains (LBDs) of receptors. Hundreds of different LBDs have been reported, and our understanding of their sensing properties is growing. Receptors must function over a range of environmental pH values, but there is little information available on the robustness of sensing as a function of pH. Here, we have used isothermal titration calorimetry to determine the pH dependence of ligand recognition by nine LBDs that cover all major LBD superfamilies, of periplasmic solute-binding proteins, and cytosolic LBDs. We show that periplasmic LBDs recognize ligands over a very broad pH range, frequently stretching over eight pH units. This wide pH range contrasts with a much narrower pH response range of the cytosolic LBDs analyzed. Many LBDs must be dimeric to bind ligands, and analytical ultracentrifugation studies showed that the LBD of the Tar chemoreceptor forms dimers over the entire pH range tested. The pH dependences of Pseudomonas aeruginosa motility and chemotaxis were bell-shaped and centered at pH 7.0. Evidence for pH robustness of signaling in vivo was obtained by Förster Resonance Energy Transfer (FRET) measurements of the chemotaxis pathway responses in Escherichia coli. Bacteria have evolved several strategies to cope with extreme pH, such as periplasmic chaperones for protein refolding. The intrinsic pH resistance of periplasmic LBDs appears to be another strategy that permits bacteria to survive under adverse conditions. IMPORTANCE Demonstration of the pH robustness of extracytoplasmic sensing reveals a previously undescribed evolutionary mechanism that enables bacteria to monitor environmental changes under changing conditions. This mechanism includes the maintenance of the dimeric state of four-helixbundle ligand-binding domains (LBDs). The construction of biosensors is a rapidly growing field of research, and their use to monitor the progression of the COVID-19 pandemic has impressively demonstrated their usefulness. LBDs represent an enormous reservoir of binding modules that can be used to create novel biosensors. Among ligands recognized by LBDs are neurotransmitters, hormones, and quorum-sensing signals. The demonstration that extracytosolic LBDs bind their signals over a wide range of pH values will facilitate the design of biosensors that function under highly variable conditions of acidity and alkalinity.

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Acidic pH sensing in the bacterial cytoplasm is required for Salmonella virulence.

Publications

Acidic pH sensing in the bacterial cytoplasm is required for Salmonella virulence.

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