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The sensor kinase QseC regulates the unlinked PmrA response regulator and downstream gene expression in Francisella

ABSTRACT: The facultative intracellular bacterial pathogen Francisella tularensis is the causative agent of tularemia in humans and animals. Gram negative bacteria utilize two-component regulatory systems (TCS) to sense and respond to their changing environment. No classical, tandemly arranged sensor kinase and response regulator TCS genes exist in the human virulent Francisella tularensis subsp. tularensis, but orphaned members are present. PmrA is an orphan response regulator responsible for intramacrophage growth and virulence; however, the regulation of PmrA activity is not understood. We and others have shown that PmrA represses the expression of priM, described to encode an anti-virulence determinant. By screening a mutant library for increased priM promoter activity, we identified the sensor kinase homolog QseC as an upstream regulator of priM expression, and this regulation is in part, dependent upon the aspartate phosphorylation site of PmrA (D51). PmrA directly binds to the promoter of priM and a PmrAD51A mutation decreases binding. Several examined environmental signals including epinephrine, which is reported to activate QseC in other bacteria, do not affect priM expression in a manner dependent on PmrA. Intramacrophage survival assays also question the finding that PriM is an anti-virulence factor. Thus, these data suggest that the PmrA-regulated gene priM is regulated by an uncoupled TCS QseC-PmrA (QseB) in Francisella.

ORGANISM(S): Francisella tularensis Francisella tularensis subsp. novicida

PROVIDER: GSE154698 | GEO | 2020/07/20

REPOSITORIES: GEO

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Project description:Francisella tularensis is a Gram-negative bacterium that is highly virulent in humans, causing the disease tularemia. F. novicida is closely related to F. tularensis and exhibits high virulence in mice, but is avirulent in healthy humans. A F. novicida-specific gene cluster (FTN0451-FTN0456) encodes two proteins with diguanylate cyclase (DGC) and phosphodiesterase (PDE) domains that modulate synthesis and degradation of cyclic di-GMP (cdGMP). No DGC or PDE containing proteins are present in the F. tularensis genome. F. novicida strains lacking either the two DGC/PDE genes cdgA and cdgB or the entire gene cluster (KKF457) are defective for biofilm formation. In addition, expression of CdgB or a heterologous DGC in KKF457 stimulated F. novicida biofilms, even in a strain lacking the biofilm regulator QseB. Genetic evidence suggests that CdgA is predominantly a PDE, while CdgB is predominantly a DGC. The F. novicida qseB strain has reduced cdgA and cdgB transcript levels, demonstrating a F. novicida biofilm signaling cascade that controls cdGMP levels. Interestingly, KKF457 with elevated cdGMP levels exhibited a decrease in intramacrophage replication and virulence in mice, as well as increased growth yield and biofilm formation in vitro. Microarray analyses revealed that cdGMP stimulated the transcription of a chitinase (ChiB) known to contribute to biofilm formation. Our results indicate that elevated cdGMP in F. novicida stimulates biofilm formation and inhibits virulence. We suggest that differences in human virulence between F. novicida and F. tularensis may be due in part to the absence of cdGMP signaling in F. tularensis. A whole genome NibleGen microarray was developed for multiple Francisella subspecies, using shared probes for common genes as well as unique probes for subspecies-specific genes. Included were probes representing the F. novicida U112 genome, with a maximum of 6 probes/gene. RNA was isolated from bacteria and purified as described above. The double-strand cDNA was generated and labeled with Cy3 according to the NimbleGen Gene Expression Array protocol (www.nimblegen.com), using SuperScript Double-Stranded cDNA Synthesis Kit (Invitrogen) and the DNA Labeling Kit (NimbleGen). Microarray results were analyzed using the ArrayStar software (DNASTAR).

Project description:Raghunathan2010 - Genome-scale metabolic network of Francisella tularensis (iRS605) This model is described in the article: Systems approach to investigating host-pathogen interactions in infections with the biothreat agent Francisella. Constraints-based model of Francisella tularensis. Raghunathan A, Shin S, Daefler S. BMC Syst Biol 2010; 4: 118 Abstract: BACKGROUND: Francisella tularensis is a prototypic example of a pathogen for which few experimental datasets exist, but for which copious high-throughout data are becoming available because of its re-emerging significance as biothreat agent. The virulence of Francisella tularensis depends on its growth capabilities within a defined environmental niche of the host cell. RESULTS: We reconstructed the metabolism of Francisella as a stoichiometric matrix. This systems biology approach demonstrated that changes in carbohydrate utilization and amino acid metabolism play a pivotal role in growth, acid resistance, and energy homeostasis during infection with Francisella. We also show how varying the expression of certain metabolic genes in different environments efficiently controls the metabolic capacity of F. tularensis. Selective gene-expression analysis showed modulation of sugar catabolism by switching from oxidative metabolism (TCA cycle) in the initial stages of infection to fatty acid oxidation and gluconeogenesis later on. Computational analysis with constraints derived from experimental data revealed a limited set of metabolic genes that are operational during infection. CONCLUSIONS: This integrated systems approach provides an important tool to understand the pathogenesis of an ill-characterized biothreat agent and to identify potential novel drug targets when rapid target identification is required should such microbes be intentionally released or become epidemic. This model is hosted on BioModels Database and identified by: MODEL1507180003. To cite BioModels Database, please use: BioModels Database: An enhanced, curated and annotated resource for published quantitative kinetic models. To the extent possible under law, all copyright and related or neighbouring rights to this encoded model have been dedicated to the public domain worldwide. Please refer to CC0 Public Domain Dedication for more information.

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The sensor kinase QseC regulates the unlinked PmrA response regulator and downstream gene expression in Francisella

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