The roles of SsrA–SsrB and OmpR–EnvZ in the regulation of genes encoding the Salmonella typhimurium SPI-2 type III secretion system

Microbiology ◽  
2003 ◽  
Vol 149 (9) ◽  
pp. 2385-2396 ◽  
Author(s):  
Junkal Garmendia ◽  
Carmen R. Beuzón ◽  
Javier Ruiz-Albert ◽  
David W. Holden
Keyword(s):  
Gene Expression ◽  
Salmonella Typhimurium ◽  
Type Iii Secretion ◽  
Type Iii Secretion System ◽  
Regulatory System ◽  
Secretion System ◽  
Host Cells ◽  
Environmental Signals ◽  
Type Iii ◽  
Two Component

The type III secretion system (TTSS) encoded by Salmonella typhimurium pathogenicity island 2 (SPI-2) is expressed after bacterial entry into host cells. The SPI-2 TTSS secretes the translocon components SseBCD, which translocate across the vacuolar membrane a number of effector proteins whose action is required for intracellular bacterial replication. Several of these effectors, including SifA and SifB, are encoded outside SPI-2. The two-component regulatory system SsrA–SsrB, encoded within SPI-2, controls the expression of components of the SPI-2 TTSS apparatus as well as its translocated effectors. The expression of SsrA–B is in turn regulated by the OmpR–EnvZ two-component system, by direct binding of OmpR to the ssrAB promoter. Several environmental signals have been shown to induce in vitro expression of genes regulated by the SsrA–B or OmpR–EnvZ systems. In this work, immunoblotting and flow cytometry were used to analyse the roles of SsrA–B and OmpR–EnvZ in coupling different environmental signals to changes in expression of a SPI-2 TTSS translocon component (SseB) and two effector genes (sifA and sifB). Using single and double mutant strains the relative contribution of each regulatory system to the response generated by low osmolarity, acidic pH or the absence of Ca2+ was determined. SsrA–B was found to be essential for the induction of SPI-2 gene expression in response to each of these individual signals. OmpR–EnvZ was found to play a minor role in sensing these signals and to require a functional SsrA–B system to mediate their effect on SPI-2 TTSS gene expression.

scholarly journals OmpR Regulates the Two-Component System SsrA-SsrB in Salmonella Pathogenicity Island 2

2000 ◽  
Vol 182 (3) ◽  
pp. 771-781 ◽  
Author(s):  
Anthea K. Lee ◽  
Corrella S. Detweiler ◽  
Stanley Falkow
Keyword(s):  
Type Iii Secretion ◽  
Type Iii Secretion System ◽  
Regulatory System ◽  
Systemic Infection ◽  
Pathogenicity Island ◽  
Secretion System ◽  
Host Cells ◽  
Type Iii ◽  
Two Component ◽  
Footprint Analysis

ABSTRACT Salmonella pathogenicity island 2 (SPI-2) encodes a putative, two-component regulatory system, SsrA-SsrB, which regulates a type III secretion system needed for replication inside macrophages and systemic infection in mice. The sensor and regulator homologs,ssrAB (spiR), and genes within the secretion system, including the structural gene ssaH, are transcribed after Salmonella enters host cells. We have studied the transcriptional regulation of ssrAB and the secretion system by using gfp fusions to the ssrA andssaH promoters. We found that early transcription ofssrA, after entry into macrophages, is most efficient in the presence of OmpR. An ompR mutant strain does not exhibit replication within cultured macrophages. Furthermore, footprint analysis shows that purified OmpR protein binds directly to thessrA promoter region. We also show that minimal medium, pH 4.5, induces SPI-2 gene expression in wild-type but notompR mutant strains. We conclude that the type III secretion system of SPI-2 is regulated by OmpR, which activates expression of ssrA soon after Salmonella enters the macrophage.

scholarly journals Control of Type III Secretion System Effector/Chaperone Ratio Fosters Pathogen Adaptation to Host-Adherent Lifestyle

mBio ◽  
2019 ◽  
Vol 10 (5) ◽  
Author(s):  
Netanel Elbaz ◽  
Yaakov Socol ◽  
Naama Katsowich ◽  
Ilan Rosenshine
Keyword(s):  
Gene Expression ◽  
Type Iii Secretion ◽  
Type Iii Secretion System ◽  
Secretion System ◽  
Effector Proteins ◽  
Host Cells ◽  
Host Colonization ◽  
Content Type ◽  
Type Iii ◽  
Attached State

ABSTRACT The transition from a planktonic lifestyle to a host-attached state is often critical for bacterial virulence. Upon attachment to host cells, enteropathogenic Escherichia coli (EPEC) employs a type III secretion system (T3SS) to inject into the host cells ∼20 effector proteins, including Tir. CesT, which is encoded from the same operon downstream of tir, is a Tir-bound chaperone that facilitates Tir translocation. Upon Tir translocation, the liberated CesT remains in the bacterial cytoplasm and antagonizes the posttranscriptional regulator CsrA, thus eliciting global regulation in the infecting pathogen. Importantly, tight control of the Tir/CesT ratio is vital, since an uncontrolled surge in free CesT levels may repress CsrA in an untimely manner, thus abrogating colonization. We investigated how fluctuations in Tir translation affect the regulation of this ratio. By creating mutations that cause the premature termination of Tir translation, we revealed that the untranslated tir mRNA becomes highly unstable, resulting in a rapid drop in cesT mRNA levels and, thus, CesT levels. This mechanism couples Tir and CesT levels to ensure a stable Tir/CesT ratio. Our results expose an additional level of regulation that enhances the efficacy of the initial interaction of EPEC with the host cell, providing a better understanding of the bacterial switch from the planktonic to the cell-adherent lifestyle. IMPORTANCE Host colonization by extracellular pathogens often entails the transition from a planktonic lifestyle to a host-attached state. Enteropathogenic E. coli (EPEC), a Gram-negative pathogen, attaches to the intestinal epithelium of the host and employs a type III secretion system (T3SS) to inject effector proteins into the cytoplasm of infected cells. The most abundant effector protein injected is Tir, whose translocation is dependent on the Tir-bound chaperon CesT. Upon Tir injection, the liberated CesT binds to and inhibits the posttranscriptional regulator CsrA, resulting in reprogramming of gene expression in the host-attached bacteria. Thus, adaptation to the host-attached state involves dynamic remodeling of EPEC gene expression, which is mediated by the relative levels of Tir and CesT. Fluctuating from the optimal Tir/CesT ratio results in a decrease in EPEC virulence. Here we elucidate a posttranscriptional circuit that prevents sharp variations from this ratio, thus improving host colonization.

scholarly journals SseL Is a Salmonella-Specific Translocated Effector Integrated into the SsrB-Controlled Salmonella Pathogenicity Island 2 Type III Secretion System

2006 ◽  
Vol 75 (2) ◽  
pp. 574-580 ◽  
Author(s):  
Brian K. Coombes ◽  
Michael J. Lowden ◽  
Jennifer L. Bishop ◽  
Mark E. Wickham ◽  
Nat F. Brown ◽  
...  
Keyword(s):  
Virulence Factors ◽  
Type Iii Secretion ◽  
Type Iii Secretion System ◽  
Regulatory System ◽  
Pathogenicity Island ◽  
Secretion System ◽  
Host Cells ◽  
Dependent Manner ◽  
Host Colonization ◽  
Type Iii

ABSTRACT Bacterial pathogens use horizontal gene transfer to acquire virulence factors that influence host colonization, alter virulence traits, and ultimately shape the outcome of disease following infection. One hallmark of the host-pathogen interaction is the prokaryotic type III secretion system that translocates virulence factors into host cells during infection. Salmonella enterica possesses two type III secretion systems that are utilized during host colonization and intracellular replication. Salmonella pathogenicity island 2 (SPI2) is a genomic island containing approximately 30 contiguous genes required to assemble a functional secretion system including the two-component regulatory system called SsrA-SsrB that positively regulates transcription of the secretion apparatus. We used transcriptional profiling with DNA microarrays to search for genes that coregulate with the SPI2 type III secretion machinery in an SsrB-dependent manner. Here we report the identification of a Salmonella-specific translocated effector called SseL that is required for full virulence during murine typhoid-like disease. Analysis of infected macrophages using fluorescence-activated cell sorting revealed that sseL is induced inside cells and requires SsrB for expression. SseL is retained predominantly in the cytoplasm of infected cells following translocation by the type III system encoded in SPI2. Animal infection experiments with sseL mutant bacteria indicate that integration of SseL into the SsrB response regulatory system contributes to systemic virulence of this pathogen.

scholarly journals Pseudomonas aeruginosa Magnesium Transporter MgtE Inhibits Type III Secretion System Gene Expression by Stimulating rsmYZ Transcription

2017 ◽  
Vol 199 (23) ◽  
Author(s):  
Shubham Chakravarty ◽  
Cameron N. Melton ◽  
Adam Bailin ◽  
Timothy L. Yahr ◽  
Gregory G. Anderson
Keyword(s):  
Gene Expression ◽  
Pseudomonas Aeruginosa ◽  
Gene Transcription ◽  
Type Iii Secretion ◽  
Type Iii Secretion System ◽  
Secretion System ◽  
Host Cells ◽  
Content Type ◽  
Type Iii ◽  
Magnesium Transporter

ABSTRACT Pseudomonas aeruginosa causes numerous acute and chronic opportunistic infections in humans. One of its most formidable weapons is a type III secretion system (T3SS), which injects powerful toxins directly into host cells. The toxins lead to cell dysfunction and, ultimately, cell death. Identification of regulatory pathways that control T3SS gene expression may lead to the discovery of novel therapeutics to treat P. aeruginosa infections. In a previous study, we found that expression of the magnesium transporter gene mgtE inhibits T3SS gene transcription. MgtE-dependent inhibition appeared to interfere with the synthesis or function of the master T3SS transcriptional activator ExsA, although the exact mechanism was unclear. We now demonstrate that mgtE expression acts through the GacAS two-component system to activate rsmY and rsmZ transcription. This event ultimately leads to inhibition of exsA translation. This inhibitory effect is specific to exsA as translation of other genes in the exsCEBA operon is not inhibited by mgtE. Moreover, our data reveal that MgtE acts solely through this pathway to regulate T3SS gene transcription. Our study reveals an important mechanism that may allow P. aeruginosa to fine-tune T3SS activity in response to certain environmental stimuli. IMPORTANCE The type III secretion system (T3SS) is a critical virulence factor utilized by numerous Gram-negative bacteria, including Pseudomonas aeruginosa, to intoxicate and kill host cells. Elucidating T3SS regulatory mechanisms may uncover targets for novel anti-P. aeruginosa therapeutics and provide deeper understanding of bacterial pathogenesis. We previously found that the magnesium transporter MgtE inhibits T3SS gene transcription in P. aeruginosa. In this study, we describe the mechanism of MgtE-dependent inhibition of the T3SS. Our report also illustrates how MgtE might respond to environmental cues, such as magnesium levels, to fine-tune T3SS gene expression.

scholarly journals Chlamydial Lytic Exit from Host Cells Is Plasmid Regulated

mBio ◽  
2015 ◽  
Vol 6 (6) ◽  
Author(s):  
Chunfu Yang ◽  
Tregei Starr ◽  
Lihua Song ◽  
John H. Carlson ◽  
Gail L. Sturdevant ◽  
...  
Keyword(s):  
Type Iii Secretion ◽  
Actin Polymerization ◽  
Type Iii Secretion System ◽  
Secretion System ◽  
Cytoskeletal Proteins ◽  
Host Cells ◽  
Genetic Mechanism ◽  
Developmental Cycle ◽  
Obligate Intracellular ◽  
Type Iii

ABSTRACTChlamydia trachomatisis an obligate intracellular bacterium that is a globally important human pathogen. The chlamydial plasmid is an attenuating virulence factor, but the molecular basis for attenuation is not understood. Chlamydiae replicate within a membrane-bound vacuole termed an inclusion, where they undergo a biphasic developmental growth cycle and differentiate from noninfectious into infectious organisms. Late in the developmental cycle, the fragile chlamydia-laden inclusion retains its integrity by surrounding itself with scaffolds of host cytoskeletal proteins. The ability of chlamydiae to developmentally free themselves from this cytoskeleton network is a fundamental virulence trait of the pathogen. Here, we show that plasmidless chlamydiae are incapable of disrupting their cytoskeletal entrapment and remain intracellular as stable mature inclusions that support high numbers of infectious organisms. By using deletion mutants of the eight plasmid-carried genes (Δpgp1to Δpgp8), we show that Pgp4, a transcriptional regulator of multiple chromosomal genes, is required for exit. Exit of chlamydiae is dependent on protein synthesis and is inhibited by the compound C1, an inhibitor of the type III secretion system (T3S). Exit of plasmid-free and Δpgp4organisms, which failed to lyse infected cells, was rescued by latrunculin B, an inhibitor of actin polymerization. Our findings describe a genetic mechanism of chlamydial exit from host cells that is dependent on an unknownpgp4-regulated chromosomal T3S effector gene.IMPORTANCEChlamydia's obligate intracellular life style requires both entry into and exit from host cells. Virulence factors that function in exiting are unknown. The chlamydial inclusion is stabilized late in the infection cycle by F-actin. A prerequisite of chlamydial exit is its ability to disassemble actin from the inclusion. We show that chlamydial plasmid-free organisms, and also a plasmid gene protein 4 (pgp4) null mutant, do not disassociate actin from the inclusion and fail to exit cells. We further provide evidence that Pgp4-regulated exit is dependent on the chlamydial type III secretion system. This study is the first to define a genetic mechanism that functions in chlamydial lytic exit from host cells. The findings also have practical implications for understanding why plasmid-free chlamydiae are highly attenuated and have the ability to elicit robust protective immune responses.

scholarly journals Concomitant Regulation by a LacI-Type Transcriptional Repressor XylR on Genes Involved in Xylan and Xylose Metabolism and the Type III Secretion System in Rice Pathogen Xanthomonas oryzae pv. oryzae

2018 ◽  
Vol 31 (6) ◽  
pp. 605-613 ◽  
Author(s):  
Yumi Ikawa ◽  
Sayaka Ohnishi ◽  
Akiko Shoji ◽  
Ayako Furutani ◽  
Seiji Tsuge
Keyword(s):  
Gene Expression ◽  
Type Iii Secretion ◽  
Type Iii Secretion System ◽  
Xylose Isomerase ◽  
Secretion System ◽  
Xanthomonas Oryzae ◽  
Upstream Region ◽  
Xylose Metabolism ◽  
Type Iii ◽  
Hrp Genes

The hypersensitive response and pathogenicity (hrp) genes of Xanthomonas oryzae pv. oryzae, the causal agent of bacterial leaf blight of rice, encode components of the type III secretion system and are essential for virulence. Expression of hrp genes is regulated by two key hrp regulators, HrpG and HrpX; HrpG regulates hrpX and hrpA, and HrpX regulates the other hrp genes on hrpB-hrpF operons. We previously reported the sugar-dependent quantitative regulation of HrpX; the regulator highly accumulates in the presence of xylose, followed by high hrp gene expression. Here, we found that, in a mutant lacking the LacI-type transcriptional regulator XylR, HrpX accumulation and hrp gene expression were high even in the medium without xylose, reaching the similar levels present in the wild type incubated in the xylose-containing medium. XylR also negatively regulated one of two xylose isomerase genes (xylA2 but not xylA1) by binding to the motif sequence in the upstream region of the gene. Xylose isomerase is an essential enzyme in xylose metabolism and interconverts between xylose and xylulose. Our results suggest that, in the presence of xylose, inactivation of XylR leads to greater xylan and xylose utilization and, simultaneously, to higher accumulation of HrpX, followed by higher hrp gene expression in the bacterium.

scholarly journals Salmonella enterica subspecies enterica serovar Enteritidis Salmonella pathogenicity island 2 type III secretion system: role in intestinal colonization of chickens and systemic spread

Microbiology ◽  
2010 ◽  
Vol 156 (9) ◽  
pp. 2770-2781 ◽  
Author(s):  
Amanda L. S. Wisner ◽  
Taseen S. Desin ◽  
Birgit Koch ◽  
Po-King S. Lam ◽  
Emil M. Berberov ◽  
...  
Keyword(s):  
Type Iii Secretion ◽  
Salmonella Enterica ◽  
Type Strain ◽  
Wild Type Strain ◽  
Type Iii Secretion System ◽  
Secretion System ◽  
Host Cells ◽  
Wild Type ◽  
Type Iii ◽  
Systemic Spread

Salmonella enterica subspecies enterica serovar Enteritidis (S. Enteritidis) has been identified as a significant cause of salmonellosis in humans. Salmonella pathogenicity islands 1 and 2 (SPI-1 and SPI-2) each encode a specialized type III secretion system (T3SS) that enables Salmonella to manipulate host cells at various stages of the invasion/infection process. For the purposes of our studies we used a chicken isolate of S. Enteritidis (Sal18). In one study, we orally co-challenged 35-day-old specific pathogen-free (SPF) chickens with two bacterial strains per group. The control group received two versions of the wild-type strain Sal18: Sal18 attTn7 : : tet and Sal18 attTn7 : : cat, while the other two groups received the wild-type strain (Sal18 attTn7 : : tet) and one of two mutant strains. From this study, we concluded that S. Enteritidis strains deficient in the SPI-1 and SPI-2 systems were outcompeted by the wild-type strain. In a second study, groups of SPF chickens were challenged at 1 week of age with four different strains: the wild-type strain, and three other strains lacking either one or both of the SPI-1 and SPI-2 regions. On days 1 and 2 post-challenge, we observed a reduced systemic spread of the SPI-2 mutants, but by day 3, the systemic distribution levels of the mutants matched that of the wild-type strain. Based on these two studies, we conclude that the S. Enteritidis SPI-2 T3SS facilitates invasion and systemic spread in chickens, although alternative mechanisms for these processes appear to exist.

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