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ChIP-chip profiling of SsrB in Salmonella enterica sv. Typhimurium

ABSTRACT: We performed chromatin immunoprecipitation on microarray (ChIP-chip) transcriptional profiling of the SsrB regulator of Salmonella enterica Typhimurium to better characterize its regulon and to identify the DNA-recognition element coordinating its specific interaction at cis-regulatory sites. SsrB, the response regulator of the two component regulatory system SsrA-SsrB encoded within the Salmonella Pathogenicity Island (SPI-2), directs transcriptional activation of the closely associated type three secretion system (T3SS) also encoded at this locus. Immunoprecipitaiton of SsrB translationally fused to a C-terminal FLAG-tag from formaldehyde cross-linked genomic DNA was performed under SPI-2 activating and non-activating conditions. Downstream analysis and experimental work identified specific interactions within SPI-2 at the previously identified ssrA, ssaB, sseA, ssaG, ssaM promoters and identified an additional cryptic promoter driving expression upstream of ssaR. Additionally, a previously unknown SsrB interaction site within ssaE was shown to be the major contributor driving the expression of the downstream genes and not the previously identified interaction site within the intergenic region of ssaE-sseA. Interactions were also identified outside of SPI-2 upstream of other T3SS-associated genes encoded within other genomic islands, and for other uncharacterized genes. Integration of this data with transcriptional microarray work, previously published DNase I footprinting data, bacteria 1-hybrid investigations and comparative genomics analyses of cis-regulatory regions within the orthologous Sodalis symbiosis region 3 (SSR-3) of Sodalis glossinidius enabled identification of a conserved 18bp palindrome which was experimentally validated as being required for transcriptional activation of SsrB dependant genes.

ORGANISM(S): Salmonella enterica subsp. enterica serovar Typhimurium str. SL1344

PROVIDER: GSE20192 | GEO | 2010/02/08

SECONDARY ACCESSION(S): PRJNA125691

REPOSITORIES: GEO

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Project description:We performed chromatin immunoprecipitation on microarray (ChIP-chip) transcriptional profiling of the SsrB regulator of Salmonella enterica Typhimurium to better characterize its regulon and to identify the DNA-recognition element coordinating its specific interaction at cis-regulatory sites. SsrB, the response regulator of the two component regulatory system SsrA-SsrB encoded within the Salmonella Pathogenicity Island (SPI-2), directs transcriptional activation of the closely associated type three secretion system (T3SS) also encoded at this locus. Immunoprecipitaiton of SsrB translationally fused to a C-terminal FLAG-tag from formaldehyde cross-linked genomic DNA was performed under SPI-2 activating and non-activating conditions. Downstream analysis and experimental work identified specific interactions within SPI-2 at the previously identified ssrA, ssaB, sseA, ssaG, ssaM promoters and identified an additional cryptic promoter driving expression upstream of ssaR. Additionally, a previously unknown SsrB interaction site within ssaE was shown to be the major contributor driving the expression of the downstream genes and not the previously identified interaction site within the intergenic region of ssaE-sseA. Interactions were also identified outside of SPI-2 upstream of other T3SS-associated genes encoded within other genomic islands, and for other uncharacterized genes. Integration of this data with transcriptional microarray work, previously published DNase I footprinting data, bacteria 1-hybrid investigations and comparative genomics analyses of cis-regulatory regions within the orthologous Sodalis symbiosis region 3 (SSR-3) of Sodalis glossinidius enabled identification of a conserved 18bp palindrome which was experimentally validated as being required for transcriptional activation of SsrB dependant genes. SsrB-FLAG immunoprecipitations were performed under SsrB activating and non-activating conditions from formaldehyde cross-linked bacterial lysates. Nine immunoprecipitation reactions were pooled into three replicate samples for the activating condition and three reactions were pooled into one sample for the non-activating control condition. The immunoprecipitated DNA in addition to the non-immunoprecipitated control DNA for each of the four samples were labeled with Cy3 or Cy5 fluorophores respectively and were concurrently hybridized to four arrays on a single slide.

Project description:Salmonella Typhimurium is an enteric food-borne pathogen responsible for causing salmonellosis associated with acute diarrhea. The bacterial invasion initially requires flagellar motility to reach the intestinal lumen and to cross the mucus layer of the intestinal epithelia and subsequent adhesion to the host cell, mainly mediated by fimbriae .The key genes involved in the pathogenic process are encoded within highly conserved regions of the bacterial genome called Salmonella Pathogenicity Islands (SPIs). The key regulator HilA, which is positively regulated by HilC and HilD, is located in SPI-1;however, other virulence-related regulators, such as RtsA, are encoded outside this island . During the invasion, proteins encoded by the prgHIJK, spaMNOPQRS, and invABCEFGH SPI-1 operons constitute a Type-3 Secretion System. Effector proteins,such as SipA and SipC (encoded in SPI-1) and SigD/SopB (encoded in SPI-5), translocate to the host cytosol through this system causing intracellular changes and inducing the immune response . The survival and replication of intracellular Salmonella inside Salmonella-containing vacuoles (SCVs) is mainly mediated by the genes located in SPI-2. The immune response is activated through the recognition of pathogen-associated molecular patterns (PAMPs) by specific receptors expressed on the surface and/or inside different cell types. The most important PAMPs are flagellin (monomers comprising the flagella filaments), particularly the FliC subunit, which is highly expressed on the bacterial surface, and lipopolysaccharide (LPS).Oxygen availability is limited in the inflamed gut whereas other compounds, such as hydrogen sulfide (H2S) and H2 are abundantly produced by the colonic bacteria. In addition, nutrients are also limited inside the SCV, while reactive oxygen as wellas nitrogen species may be found . In anaerobic conditions, Salmonella is able to survive by using alternative energy sources, such as nitrate or fumarate, through the use of specific enzymes: nitrate and nitrite reductases, fumarate reductase , DMSO reductase and respiratory hydrogenases.In a previous study, we compared transcriptomes of a clinical isolate of S. Typhimurium (strain 50-wt) and its derivative-multidrug-resistant mutant (strain 50-64) using microarrays . In addition to showing antimicrobial resistance, strain was also less invasive. In the present study, we focused on the genes of unknown function that showed impaired expression. We further selected those genes with a putative role in the acquired resistance phenotype or in the observed repressed virulence observed. Here, 4 putative membrane proteins and the yedF of unknown function were investigated to evaluate their involvement inthese two phenotypes.

Project description:Salmonella enterica Serovar Typhimurium (S. Typhimurium) causes enterocolitis in humans and calves characterized by diarrhea and polymorphonuclear cell (PMN) influx to the intestinal mucosa. The Salmonella Type III Secretion System encoded at Pathogenicity Island I (SPI-1) translocates the Salmonella effector proteins SipA, SopA, SopB, SopD, and SopE2 into the host epithelial cell cytoplasm. These five effector proteins act in concert to induce fluid secretion and transcription of C-X-C chemokines, which serve to recruit PMNs to the intestine. While the individual molecular interactions of these Salmonella proteins with cultured host cells have been extensively characterized, their combined role in the generation of fluid secretion and inflammation is less well understood. A bovine ligated ileal loop model was used in conjunction with a custom bovine microarray to determine intestinal response to acute S. Typhimurium infection in the calf. Gene expression responses to both wild type S. Typhimurium a delta sipA, sopABDE2 mutant were measured at seven times during the initial 12 hours of infection. Microarray analysis confirmed increased expression of genes encoding proteins previously associated with immune response to Salmonella spp. infection. Gene expression changes were mapped to molecular interaction pathways and changes in expression of mechanistic genes, which are defined as perturbed genes identified by Bayesian genetic network modeling, were strongly involved in the mechanisms of the host immune response. In addition to correctly identifying known effects of wild type S. Typhimurium on host (bovine) gene expression, Bayesian genetic network modeling identified novel effects of S. Typhimurium on several molecular interaction pathways. Novel effects impacted gene regulation in the following pathways: adipocytokine signaling, insulin signaling, complement and coagulation cascades, axon guidance, gap junction, neuroactive ligand-receptor interaction, long-term depression, long-term potentiation, melanogenesis, and natural killer cell mediated cytotoxicity. Known effects were observed in the following pathways: regulation of actin cytoskeleton, apoptosis, cytokine-cytokine receptor interaction, cell adhesion molecules (CAMs), MAPK signaling, calcium signaling, Jak-STAT signaling, leukocyte transendothelial migration, adherens junction, tight junction, and ECM-receptor interactions, phosphatidylinositol signaling system, and antigen processing and presentation. Quantitative real-time PCR was used to verify the expression of some of these mechanistic genes. Microarrays were used to examine the transcriptional profiles of bovine intestinal epithelia infected with wild type Salmonella enterica serotype Typhimurium (control and wild type or delta sipA sopABDE2 mutant infected) across seven time points (15 min, 30 min, 1, 2, 4, 8, and 12 hours). Experiments were performed in quadruplicate (bovine ligated ileal loops surgeries were performed with four calves), generateing a total of 84 arrays.

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ChIP-chip profiling of SsrB in Salmonella enterica sv. Typhimurium

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