Multiple Factors Independently RegulatehilAand Invasion Gene Expression inSalmonella entericaSerovar Typhimurium

Abstract

HilA activates the expression of Salmonella enterica serovar Typhimurium invasion genes. To learn more about regulation of hilA, we isolated Tn5 mutants exhibiting reduced hilA and/or invasion gene expression. In addition to expected mutations, we identified Tn5 insertions in pstS, fadD, flhD, flhC, and fliA. Analysis of the pstS mutant indicates that hilA and invasion genes are repressed by the response regulator PhoB in the absence of the Pst high-affinity inorganic phosphate uptake system. This system is required for negative control of the PhoR-PhoB two-component regulatory system, suggesting that hilA expression may be repressed by PhoRPhoB under low extracellular inorganic phosphate conditions. FadD is required for uptake and degradation of long-chain fatty acids, and our analysis of the fadD mutant indicates that hilA is regulated by a FadDdependent, FadR-independent mechanism. Thus, fatty acid derivatives may act as intracellular signals to regulate hilA expression. flhDC and fliA encode transcription factors required for flagellum production, motility, and chemotaxis. Complementation studies with flhC and fliA mutants indicate that FliZ, which is encoded in an operon with fliA, activates expression of hilA, linking regulation of hilA with motility. Finally, epistasis tests showed that PhoB, FadD, FliZ, SirA, and EnvZ act independently to regulate hilA expression and invasion. In summary, our screen has identified several distinct pathways that can modulate S. enterica serovar Typhimurium's ability to express hilA and invade host cells. Integration of signals from these different pathways may help restrict invasion gene expression during infection.

DNA-Binding Activities of the HilC and HilD Virulence Regulatory Proteins ofSalmonella entericaSerovar Typhimurium

“…Analysis of hilA-lacZ transcriptional fusions by Lee and colleagues (30)(31)(32)42), among others, led to a model proposing that hilA transcription is repressed by a negative factor acting within the promoter region between positions Ϫ300 and Ϫ100. The HilD and perhaps the HilC proteins play central roles in controlling hilA transcription and may counteract this repressor activity.…”

“…4, lane 1) and from an isogenic mutant deleted for SPI1 (Fig. 4, lane 2) grown under inducing conditions for hilA expression, i.e., high salt and low aeration (32). A single SPI1-dependent transcript was detected for hilC and hilD.…”

“…Many regulatory proteins influence invasion gene expression (31,32), but the key regulator is the SPI1-encoded HilA protein, which can activate their transcription directly (1,4,28) or by increasing expression of the activator InvF (9). The N-terminal region of HilA carries a DNA-binding and transcription-activating helix-loop-helix motif typical of OmpR/ToxR family members (4).…”

Mathematical model of flagella gene expression dynamics in Salmonella enterica serovar typhimurium

“…Another insight from the model is the prediction that FliZ is the secretiondependent link between flagella and the SPI1 regulatory network. FliZ has been previously shown to be activator of SPI1 gene expression, and our model predicts that this happens post-secretion (Chubiz et al 2010;Iyoda et al 2001;Lucas et al 2000). Previous modeling efforts of the flagellar regulon have been limited to the FliA-FlgM interaction only (Kalir et al 2005;Saini et al 2011).…”

Characterization of a yjjQ mutant of avian pathogenic Escherichia coli (APEC)

“…In addition, Fur affects iron uptake by binding to the promoter region of ironregulated genes with ferrous iron as a cofactor, thus repressing the expression of these genes (Hantke, 2001). The virulence and pathogenesis of medically important organisms are also regulated by these regulators, and in recent years great progress has been made in identifying those that coordinate expression of virulence genes (Byrne & Swanson, 1998;Johnson et al, 2006a;Lucas et al, 2000;Mellies et al, 2006;Pizarro-Cerda & Tedin, 2004). Perhaps not surprisingly, such regulators are almost as numerous as the environmental signals to which virulence gene expression has been found to respond (Dong et al, 2005;Lucas & Lee, 2001;Sturme et al, 2005), and many of them remain to be identified.…”