IscR Is Essential for Yersinia pseudotuberculosis Type III Secretion and Virulence

Abstract

Type III secretion systems (T3SS) are essential for virulence in dozens of pathogens, but are not required for growth outside the host. Therefore, the T3SS of many bacterial species are under tight regulatory control. To increase our understanding of the molecular mechanisms behind T3SS regulation, we performed a transposon screen to identify genes important for T3SS function in the food-borne pathogen Yersinia pseudotuberculosis. We identified two unique transposon insertions in YPTB2860, a gene that displays 79% identity with the E. coli iron-sulfur cluster regulator, IscR. A Y. pseudotuberculosis iscR in-frame deletion mutant (ΔiscR) was deficient in secretion of Ysc T3SS effector proteins and in targeting macrophages through the T3SS. To determine the mechanism behind IscR control of the Ysc T3SS, we carried out transcriptome and bioinformatic analysis to identify Y. pseudotuberculosis genes regulated by IscR. We discovered a putative IscR binding motif upstream of the Y. pseudotuberculosis yscW-lcrF operon. As LcrF controls transcription of a number of critical T3SS genes in Yersinia, we hypothesized that Yersinia IscR may control the Ysc T3SS through LcrF. Indeed, purified IscR bound to the identified yscW-lcrF promoter motif and mRNA levels of lcrF and 24 other T3SS genes were reduced in Y. pseudotuberculosis in the absence of IscR. Importantly, mice orally infected with the Y. pseudotuberculosis ΔiscR mutant displayed decreased bacterial burden in Peyer's patches, mesenteric lymph nodes, spleens, and livers, indicating an essential role for IscR in Y. pseudotuberculosis virulence. This study presents the first characterization of Yersinia IscR and provides evidence that IscR is critical for virulence and type III secretion through direct regulation of the T3SS master regulator, LcrF.

Characterization of the Vibrio vulnificus 1-Cys Peroxiredoxin Prx3 and Regulation of Its Expression by the Fe-S Cluster Regulator IscR in Response to Oxidative Stress and Iron Starvation

“…Therefore, V. vulnifcus could use IscR to activate prx3 upon exposure to low levels of ROS that are insufficient to oxidize OxyR. Second, the IscR regulon includes many genes seemingly related to the pathogenesis of bacteria (30,51). Accordingly, the iscR mutant of V. vulnificus is defective in motility, hemolytic activity, and adhesion to host cells, leading to attenuated virulence (30).…”

Yersinia Type III Secretion System Master Regulator LcrF

“…It is worth mentioning that we could not find LcrF binding sites upstream of two secreted effectors, yopJ and yopM, unless the threshold for motif calling was much lower (data not shown). Note also that yscC and yopK (from Y. enterocolitica and Y. pestis) do not seem to have a consensus TATA box following the TGANA motif, although these two genes are expressed under T3SS-inducing conditions (28). In contrast, the two LcrF binding sites upstream of virA and virB (Fig.…”

“…Therefore, it is possible that both the putative LcrF binding sites far upstream and those downstream of the yopE transcriptional start site are required for activation of the yopE promoter. Interestingly, yopE was reported to be transcribed strongly under T3SS-inducing conditions, while sycE was minimally transcribed (28). Because of this departure from the known characteristics of other LcrF binding sites, whether the putative LcrF binding sites within the yopE-sycE promoter regions are functional and, if so, how they function remain to be determined.…”

“…Nucleotides whose sequences are not identical are marked in red, while the conserved nucleotides are indicated by asterisks. The identified binding sequence for IscR is marked in purple, and critical residues required for IscR binding within this motif are in bold (28,64). The binding site for RcsB is marked in green (71).…”

Influence of chelation strength and bacterial uptake of gallium salicylidene acylhydrazide on biofilm formation and virulence of Pseudomonas aeruginosa

“…It may be speculated that Ga-related changes in metabolic status influence expression of T3SS, since the regulation of T3SS has been shown to also be subjected to metabolite control [38]. More specific mechanism of T3SS inhibition by Ga may be connected to T3SS control by IscR, a Fe containing transcription factor, shown to be important in Yersinia pseudotuberculosis and by analogy probably also in P. aeruginosa, since this transcription factor is well conserved between bacteria [39]. This could explain why the inhibitory effect on virulence was enhanced in presence of the Ga-ME0329 complex.…”