Dataset Information

Repression of Salmonella enterica phoP expression by small molecules from physiological bile.

ABSTRACT: Infection with Salmonella enterica serovar Typhi in humans causes the life-threatening disease typhoid fever. In the laboratory, typhoid fever can be modeled through the inoculation of susceptible mice with Salmonella enterica serovar Typhimurium. Using this murine model, we previously characterized the interactions between Salmonella Typhimurium and host cells in the gallbladder and showed that this pathogen can successfully invade gallbladder epithelial cells and proliferate. Additionally, we showed that Salmonella Typhimurium can use bile phospholipids to grow at high rates. These abilities are likely important for quick colonization of the gallbladder during typhoid fever and further pathogen dissemination through fecal shedding. To further characterize the interactions between Salmonella and the gallbladder environment, we compared the transcriptomes of Salmonella cultures grown in LB broth or physiological murine bile. Our data showed that many genes involved in bacterial central metabolism are affected by bile, with the citric acid cycle being repressed and alternative respiratory systems being activated. Additionally, our study revealed a new aspect of Salmonella interactions with bile through the identification of the global regulator phoP as a bile-responsive gene. Repression of phoP expression could also be achieved using physiological, but not commercial, bovine bile. The biological activity does not involve PhoPQ sensing of a bile component and is not caused by bile acids, the most abundant organic components of bile. Bioactivity-guided purification allowed the identification of a subset of small molecules from bile that can elicit full activity; however, a single compound with phoP inhibitory activity could not be isolated, suggesting that multiple molecules may act in synergy to achieve this effect. Due to the critical role of phoP in Salmonella virulence, further studies in this area will likely reveal aspects of the interaction between Salmonella and bile that are relevant to disease.

SUBMITTER: Antunes LC

PROVIDER: S-EPMC3347055 | biostudies-literature | 2012 May

REPOSITORIES: biostudies-literature

ACCESS DATA

Publications

Repression of Salmonella enterica phoP expression by small molecules from physiological bile.

Antunes L Caetano M LC Wang Melody M Andersen Sarah K SK Ferreira Rosana B R RB Kappelhoff Reinhild R Han Jun J Borchers Christoph H CH Finlay B Brett BB

Journal of bacteriology 20120224 9

Infection with Salmonella enterica serovar Typhi in humans causes the life-threatening disease typhoid fever. In the laboratory, typhoid fever can be modeled through the inoculation of susceptible mice with Salmonella enterica serovar Typhimurium. Using this murine model, we previously characterized the interactions between Salmonella Typhimurium and host cells in the gallbladder and showed that this pathogen can successfully invade gallbladder epithelial cells and proliferate. Additionally, we ...[more]

PMID: 22366421

Similar Datasets

Project description:Salmonella must rapidly adapt to various niches in the host during infection. Relevant virulence factors must be appropriately induced, and systems that are detrimental in a particular environment must be turned off. Salmonella infects intestinal epithelial cells using a type 3 secretion system (T3SS) encoded on Salmonella pathogenicity island 1 (SPI1). The system is controlled by three AraC-like regulators, HilD, HilC, and RtsA, which form a complex feed-forward loop to activate expression of hilA, encoding the main transcriptional regulator of T3SS structural genes. This system is tightly regulated, with many of the activating signals acting at the level of hilD translation or HilD protein activity. Once inside the phagosomes of epithelial cells, or in macrophages during systemic stages of disease, the SPI1 T3SS is no longer required or expressed. Here, we show that the PhoPQ two-component system, critical for intracellular survival, appears to be the primary mechanism by which Salmonella shuts down the SPI1 T3SS. PhoP negatively regulates hilA through multiple distinct mechanisms: direct transcriptional repression of the hilA promoter, indirect transcriptional repression of both the hilD and rtsA promoters, and activation of the small RNA (sRNA) PinT. Genetic analyses and electrophoretic mobility shift assays suggest that PhoP specifically binds the hilA promoter to block binding of activators HilD, HilC, and RtsA as a mechanism of repression.IMPORTANCESalmonella is one of the most common foodborne pathogens, causing an estimated 1.2 million illnesses per year in the United States. A key step in infection is the activation of the bacterial invasion machinery, which induces uptake of the bacterium into epithelial cells and leads to induction of inflammatory diarrhea. Upon entering the vacuolar compartments of host cells, Salmonella senses an environmental transition and represses the invasion machinery with a two-component system relevant for survival within the vacuole. This adaptation to specific host niches is an important example of how signals are integrated for survival of the pathogen.

Project description:Infection with Salmonella enterica serovar Typhi in humans causes the systemic, life-threatening disease typhoid fever. In the laboratory, typhoid fever can be modeled through the inoculation of susceptible mice with Salmonella enterica serovar Typhimurium. The ensuing disease is characterized by systemic dissemination and colonization of many organs, including the liver, spleen and gallbladder. Using this murine model, we previously characterized the interactions between Salmonella Typhimurium and host cells in the gallbladder and showed that this pathogen can successfully invade gallbladder epithelial cells and proliferate. Additionally, we showed that Salmonella Typhimurium can use bile phospholipids to grow at high rates. These abilities are likely important for quick colonization of the gallbladder during typhoid fever and further pathogen dissemination through fecal shedding. To further characterize the interactions between Salmonella and the gallbladder environment we compared the transcriptome of Salmonella cultures grown in LB or physiological murine bile. Our data showed that many genes involved in bacterial central metabolism are affected by bile, with the citric acid cycle being repressed and alternative respiratory systems being activated. Additionally, our study revealed a new aspect of Salmonella interactions with bile through the identification of phoP as a bile-responsive gene. Repression of phoP expression does not involve PhoPQ sensing of a bile component. Due to its critical role in Salmonella virulence, further studies in this area will likely reveal aspects of the interaction between Salmonella and bile that are relevant to disease. Salmonella enterica serovar Typhimurium LT2 glass slide microarrays were obtained through the NIAID’s Pathogen Functional Genomics Resource Center, managed and funded by Division of Microbiology and Infectious Diseases, NIAID, NIH, DHHS and operated by the J. Craig Venter Institute. Two independent cultures of Salmonella enterica serovar Typhimurium SL1344 were grown overnight in Luria-Bertani (LB) broth with streptomycin (100 μg/mL) at 37oC with shaking (225 RPM). Cells were pelleted by centrifugation and resuspended in sterile Dulbecco’s phosphate-buffered saline (PBS). These suspensions were further diluted 1:50 in PBS and used to inoculate 70 μL of either LB or physiological murine bile (in 0.65-mL tubes) at a 1:100 dilution. Cultures were incubated for 24 hours at 37oC with agitation (225 RPM). Then, samples were diluted in PBS and serial dilutions were plated on LB plates containing 100 μg/mL of streptomycin and incubated overnight at 37oC for bacterial growth and enumeration by colony counting. The remaining cells were used in the subsequent steps, as described below. RNA isolation began with the addition of 2 volumes of RNAprotect Bacteria Reagent (Qiagen, Hilden, Germany) to the bacterial cultures and incubation at room temperature for approximately 5 minutes. Cells were pelleted by centrifugation and RNA was isolated using the RNeasy Mini Kit (Qiagen) with the on-column DNase digestion, according to the manufacturer’s recommendations. Synthesis of cDNA was performed as described herein. The entire RNA sample (≥3 μg) was mixed with 6 μg of Random Primers (Invitrogen, Burlington, Canada) and 40 units of RNaseOUT recombinant ribonuclease inhibitor (Invitrogen, Burlington, Canada) in a total volume of 18.5 μL and incubated at 70oC for 10 minutes. Samples were incubated on ice for 30 seconds, centrifuged to bring down condensation and incubated with the following components (final concentrations; Invitrogen): First Strand Buffer (1X), dithiothreitol (DTT; 10 mM), dNTPs (dATP, dCTP, dGTP, dTTP; 0.5 mM each) and 100 units of SuperScript II reverse transcriptase in a total volume of 30 μL. The mixture was incubated at 42oC overnight and the reaction was stopped and the RNA degraded through the addition of 0.5 M EDTA and 1 M sodium hydroxide (10 μL each) and incubation at 65oC for 15 minutes. Then, 25 μL of 1 M Tris (pH 7) was added to neutralize the pH of the cDNA solution. cDNA was purified using the MinElute PCR Purification Kit (Qiagen) according to the manufacturer’s recommendations, except that the Qiagen wash and elution buffers were substituted by phosphate buffers, according to the PFGRC microarray protocol. cDNA was then precipitated using ammonium acetate and ethanol and labeled with Cy3 (LB cultures) and Cy5 (bile cultures) using the ULS aRNA Fluorescent Labeling Kit (KREATECH Biotechnology, Amsterdam, The Netherlands) according to the manufacturer’s instructions. Samples were mixed, dried and saved at -80oC until used. Pre-hybridization, hybridization and washing steps were performed essentially as described in the PFGRC protocols, except that the hybridization buffer contained KREAblock blocking buffer (25%; KREATECH Biotechnology). After hybridization, slides were scanned using an Affymetrix 428 Array Scanner from Eurofins MWG Operon (Huntsville, USA).

Project description:Salmonella enterica serovar Typhimurium induces inflammatory diarrhea and bacterial uptake into intestinal epithelial cells using the Salmonella pathogenicity island 1 (SPI1) type III secretion system (T3SS). HilA activates transcription of the SPI1 structural components and effector proteins. Expression of hilA is activated by HilD, HilC, and RtsA, which act in a complex feed-forward regulatory loop. Many environmental signals and other regulators are integrated into this regulatory loop, primarily via HilD. After the invasion of Salmonella into host intestinal epithelial cells or during systemic replication in macrophages, the SPI T3SS is no longer required or expressed. We have shown that the two-component regulatory system PhoPQ, required for intracellular survival, represses the SPI1 T3SS mostly by controlling the transcription of hilA and hilD Here we show that PinT, one of the PhoPQ-regulated small RNAs (sRNAs), contributes to this regulation by repressing hilA and rtsA translation. PinT base pairs with both the hilA and rtsA mRNAs, resulting in translational inhibition of hilA, but also induces degradation of the rts transcript. PinT also indirectly represses expression of FliZ, a posttranslational regulator of HilD, and directly represses translation of ssrB, encoding the primary regulator of the SPI2 T3SS. Our in vivo mouse competition assays support the concept that PinT controls a series of virulence genes at the posttranscriptional level in order to adapt Salmonella from the invasion stage to intracellular survival.IMPORTANCE Salmonella is one of the most important food-borne pathogens, infecting over one million people in the United States every year. These bacteria use a needle-like device to interact with intestinal epithelial cells, leading to invasion of the cells and induction of inflammatory diarrhea. A complex regulatory network controls expression of the invasion system in response to numerous environmental signals. Here we explore the molecular mechanisms by which the small RNA PinT contributes to this regulation, facilitating inactivation of the system after invasion. PinT controls several important virulence systems in Salmonella, tuning the transition between different stages of infection.

Dataset Information

Repression of Salmonella enterica phoP expression by small molecules from physiological bile.

Publications

Repression of Salmonella enterica phoP expression by small molecules from physiological bile.

Similar Datasets

OmicsDI is part of the ELIXIR infrastructure

Tweets