Skip to main page content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

Https

The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
. 2015 Mar;83(3):978-85.
doi: 10.1128/IAI.02506-14. Epub 2014 Dec 29.

Two-component regulators control hilA expression by controlling fimZ and hilE expression within Salmonella enterica serovar Typhimurium

M Aaron Baxter  1 , Bradley D Jones  2
Affiliations

Two-component regulators control hilA expression by controlling fimZ and hilE expression within Salmonella enterica serovar Typhimurium

M Aaron Baxter et al. Infect Immun. 2015 Mar.

Abstract

Salmonellae initiate disease through the invasion of host cells within the intestine. This ability to invade requires the coordinated action of numerous genes, many of which are found within Salmonella pathogenicity island 1 (SPI-1). The key to this process is the ability of the bacteria to respond to the environment, thereby upregulating the necessary genes under optimal conditions. Central to the control of SPI-1 is the transcriptional activator hilA. Work has identified at least 10 different activators and 8 different repressors responsible for the control of hilA. We have previously shown that hilE is a Salmonella-specific negative regulator that is able to repress hilA expression and invasion. Additionally, fimZ, a transcriptional activator responsible for the expression of type I fimbriae as well as flagellar genes, has also been implicated in this process. fimZ is homologous to response regulators from other two-component regulatory systems, although a sensor for the system has not been identified. The phoPQ and phoBR regulons are both two-component systems that negatively affect hilA expression, although the mechanism of action has not been determined. Our results show that PhoBR is capable of inducing fimZ expression, whereas PhoPQ does not affect fimZ expression but does upregulate hilE in an FimZ-dependent manner. Therefore, phosphate (sensed by PhoBR) and magnesium (sensed by PhoPQ) levels are important in controlling hilA expression levels when Salmonella is in the intestinal environment.

PubMed Disclaimer

Figures

FIG 1
FIG 1
The effects of constitutive phoQ expression on hilA are reduced by deletion of the Salmonella hilE gene. Strains were grown with shaking in LB broth to late stationary phase. The wild-type strain is S. enterica serovar Typhimurium LT2 strain EE251 carrying the hilA::lacZY plasmid reporter pLS31. The TA2367 strain contains the phoQc mutation and the hilA::lacZY reporter plasmid pLS31. BJ3106 is the TA2367 strain containing a defined hilE::cam mutation and the hilA::lacZY reporter plasmid pLS31. Expression levels were determined by lacZ output as measured by β-galactosidase activity. The experiment is representative of an assay which was repeated in triplicate on three separate days.
FIG 2
FIG 2
The effect of constitutive phoQ expression on hilE and hilA expression is mediated through fimZ. Strains were grown with shaking in LB broth to late stationary phase. The wild-type strain is S. enterica serovar Typhimurium LT2 strain EE251 carrying either the hilA::lacZY plasmid reporter pLS31 or the hilE::lacZY plasmid reporter pMAB69. The strain TA2367 contains the phoQc mutation and either the hilA::lacZY reporter plasmid pLS31 or the hilE::lacZY plasmid reporter pMAB69. BJ3179 is the TA2367 strain containing a defined fimZ::cam mutation and carries the hilE::lacZY reporter pMAB69. BJ3185 is the TA2367 strain containing a defined fimZ::cam mutation and carries the hilA::lacZY reporter pLS31. Expression levels were determined by lacZ output as measured by β-galactosidase activity. The experiment is representative of an assay which was repeated in triplicate on three separate days.
FIG 3
FIG 3
Various magnesium concentrations will alter the levels of hilA expression independently of hilE. Strains were grown with shaking in LB broth to late stationary phase. The wild-type S. enterica serovar Typhimurium strain SL1344 containing the hilA::lacZY reporter plasmid pLS31 was compared to the BJ2462 strain, which is an SL1344 strain containing an hilE::cam deletion and carries the same reporter plasmid. Expression levels were determined by lacZ output as measured by β-galactosidase activity. The experiment is representative of an assay which was repeated in triplicate on three separate days. High magnesium was at a concentration of 10 mM, whereas low magnesium was at 8 μM.
FIG 4
FIG 4
Overexpression of phoB leads to the activation of hilE. The wild-type strain is S. enterica serovar Typhimurium SL1344. The mutant tested is the SL1344 strain RL291, which contains a pstS deletion leading to the constitutive activation of phoB. Each strain contained the hilE::lacZY reporter plasmid pMAB69. The strains were grown in LB overnight with shaking, and expression levels were determined by measuring lacZ output as measured by β-galactosidase activity. The experiment is representative of an assay which was repeated in triplicate on three separate days.
FIG 5
FIG 5
The deletion of hilE reverses the repression of hilA in a constitutive phoB-expressing strain. The wild-type strain is S. enterica serovar Typhimurium SL1344. RL291 is an SL1344 derivative that contains a pstS mutation. BJ3100 is an RL291 strain containing a defined hilE::cam mutation within the chromosome. Each strain contained the hilA::lacZY reporter pLS31. The strains were grown in LB overnight with shaking, and expression levels were determined by measuring lacZ output as measured by β-galactosidase activity.
FIG 6
FIG 6
Overexpression of phoB increases the level of fimZ expression. The strains were shaken overnight in LB growing at 37°C. The wild-type bacterium is S. enterica serovar Typhimurium strain SL1344. RL291 is an SL1344 derivative that contains a pstS mutation that causes the overexpression of phoB. The BJ3184 strain is the RL291 strain containing a defined fimZ::cam mutation. Each strain tested contained the fimZ::lacZY reporter plasmid pISF239. The strains were grown in LB overnight with shaking, and expression levels were determined by measuring lacZ output as measured by β-galactosidase activity. The experiment is representative of an assay which was repeated in triplicate on three separate days.
FIG 7
FIG 7
Model of the regulatory cascade that transfers environmental signals into changes in Salmonella gene expression. Environmental signals such as magnesium or phosphate concentration increase or decrease fimZ expression. Under conditions of low magnesium concentration, the PhoPQ regulon is activated, leading to the phosphorylation of FimZ with the subsequent increase in hilE expression. Under conditions of low phosphate, PhoBR is activated, which increases fimZ expression, which upregulates hilE expression. A FimZ-activating signal additionally leads to increased type 1 fimbrial expression by direct binding of the FimZ activator to the type 1 fimbrial gene operon. Increased fimZ expression also decreases expression of the flhDC master regulatory proteins for the flagellar regulon by an unknown mechanism. Other regulatory signals generated from the cross talk between the flagellar system or other environmental signals may further influence the expression of fimZ. The increase in FimZ leads to the subsequent increase in HilE protein levels, which limits the availability of HilD to activate the hilA promoter due to HilE-HilD binding. A FimZ-deactivating signal would have the opposite effects. Collectively, these regulatory pathways control hilA expression and downstream expression of SPI-1 (22). In addition, it is likely that there are FimZ-independent signals that affect the expression and cross talk between all the systems described (motility, adherence, and invasion), which allows Salmonella to dynamically control when these various systems respond (60).
See this image and copyright information in PMC

Similar articles

See all similar articles

Cited by

See all "Cited by" articles

References

    1. Mead PS, Slutsker L, Dietz V, McCaig LF, Bresee JS, Shapiro C, Griffin PM, Tauxe RV. 1999. Food-related illness and death in the United States. Emerg Infect Dis 5:607–625. doi:10.3201/eid0505.990502. - DOI - PMC - PubMed
    1. CDC. 2010. Salmonella. Centers for Disease Control and Prevention, Atlanta, GA: http://www.cdc.gov/salmonella/index.html.
    1. Collazo CM, Galan JE. 1997. The invasion-associated type III system of Salmonella Typhimurium directs the translocation of Sip proteins into the host cell. Mol Microbiol 24:747–756. doi:10.1046/j.1365-2958.1997.3781740.x. - DOI - PubMed
    1. Darwin KH, Miller VL. 1999. Molecular basis of the interaction of Salmonella with the intestinal mucosa. Clin Microbiol Rev 12:405–428. - PMC - PubMed
    1. Bajaj V, Hwang C, Lee CA. 1995. hilA is a novel ompR/toxR family member that activates the expression of Salmonella Typhimurium invasion genes. Mol Microbiol 18:715–727. doi:10.1111/j.1365-2958.1995.mmi_18040715.x. - DOI - PubMed

Publication types

MeSH terms

LinkOut - more resources