•Iron acquisition and storage is controlled by Fur and iron-responsive sRNAs (RyhB).•Fur and RyhB are involved in the virulence of pathogenic bacteria.•Fur and RyhB regulate many virulence ...factors.•Fur and RyhB regulate directly or indirectly their targets.•Fur and RyhB mutants should be considered for vaccine development.
In bacteria–host interactions, competition for iron is critical for the outcome of the infection. As a result of its redox properties, this metal is essential for the growth and proliferation of most living organisms, including pathogenic bacteria. This metal is also potentially toxic, making the precise maintenance of iron homeostasis necessary for survival. Iron acquisition and storage control is mediated in most bacteria by the global ferric uptake regulator (Fur) and iron-responsive small regulatory non-coding RNAs (RyhB in the model organism Escherichia coli). While the role of these regulators in iron homeostasis is well documented in both pathogenic and non-pathogenic bacteria, many recent studies also demonstrate that these regulators are involved in the virulence of pathogenic bacteria. By sensing iron availability in the environment, Fur and RyhB are able to regulate, either directly or indirectly via other transcriptional regulators or modulation of intracellular iron concentration, many virulence determinants of pathogenic bacteria. Iron is thus both a nutritional and regulatory element, allowing bacteria to adapt to various host environments by adjusting expression of virulence factors. In this review, we present evidences that Fur and RyhB are the major regulators of this adaptation, as they are involved in diverse functions ranging from iron homeostasis to regulation of virulence by mediating key pathogen responses such as invasion of eukaryotic cells, toxin production, motility, quorum sensing, stress resistance or biofilm formation. Therefore, Fur and RyhB play a major role in regulating an adaptative response during bacterial infections, making them important targets in the fight against pathogenic bacteria.
Highlights • Successful colonization requires competition for nutrients in the host environment. • Metabolism and bacterial virulence are tightly and inextricably linked. • This link is achieved by ...transcriptional and post-transcriptional regulators. • sRNAs are key elements to respond to environmental nutrients and control virulence. • Approaches to target nutrient availability and/or bacterial sensing could reduce infections.
In Escherichia coli, the small regulatory noncoding RNA (sRNA) RyhB and the global ferric uptake regulator (Fur) mediate iron acquisition and storage control. Iron is both essential and potentially ...toxic for most living organisms, making the precise maintenance of iron homeostasis necessary for survival. While the roles of these regulators in iron homeostasis have been well studied in a nonpathogenic E. coli strain, their impact on the production of virulence-associated factors is still unknown for a pathogenic E. coli strain. We thus investigated the roles of RyhB and Fur in iron homeostasis and virulence of the uropathogenic E. coli (UPEC) strain CFT073. In a murine model of urinary tract infection (UTI), deletion of fur alone did not attenuate virulence, whereas a ΔryhB mutant and a Δfur ΔryhB double mutant showed significantly reduced bladder colonization. The Δfur mutant was more sensitive to oxidative stress and produced more of the siderophores enterobactin, salmochelins, and aerobactin than the wild-type strain. In contrast, while RyhB was not implicated in oxidative stress resistance, the ΔryhB mutant produced lower levels of siderophores. This decrease was correlated with the downregulation of shiA (encoding a transporter of shikimate, a precursor of enterobactin and salmochelin biosynthesis) and iucD (involved in aerobactin biosynthesis) in this mutant grown in minimal medium or in human urine. iucD was also downregulated in bladders infected with the ΔryhB mutant compared to those infected with the wild-type strain. Our results thus demonstrate that the sRNA RyhB is involved in production of iron acquisition systems and colonization of the urinary tract by pathogenic E. coli.
The
gene cluster encodes the phosphate-specific transport (Pst) system. Inactivation of the Pst system constitutively activates the two-component regulatory system PhoBR and attenuates the virulence ...of pathogenic bacteria. In uropathogenic
strain CFT073, attenuation by inactivation of
is predominantly attributed to the decreased expression of type 1 fimbriae. However, the molecular mechanisms connecting the Pst system and type 1 fimbriae are unknown. To address this, a transposon library was constructed in the
mutant, and clones were tested for a regain in type 1 fimbrial production. Among them, the diguanylate cyclase encoded by
(
in
) was identified to connect the Pst system and type 1 fimbrial expression. In the
mutant, the decreased expression of type 1 fimbriae is connected by the induction of
This is predominantly due to altered expression of the FimBE-like recombinase genes
and
, affecting at the same time the inversion of the
promoter switch (
). In the
mutant, inactivation of
restored
-dependent adhesion to bladder cells and virulence. Interestingly, the expression of
was activated by PhoB, since transcription of
was linked to the PhoB-dependent
operon. As YaiC is involved in cyclic di-GMP (c-di-GMP) biosynthesis, an increased accumulation of c-di-GMP was observed in the
mutant. Hence, the results suggest that one mechanism by which deletion of the Pst system reduces the expression of type 1 fimbriae is through PhoBR-mediated activation of
, which in turn increases the accumulation of c-di-GMP, represses the
operon, and, consequently, attenuates virulence in the mouse urinary tract infection model.
Urinary tract infections (UTIs) are common bacterial infections in humans. They are mainly caused by uropathogenic
(UPEC). We previously showed that interference with phosphate homeostasis decreases the expression of type 1 fimbriae and attenuates UPEC virulence. Herein, we identified that alteration of the phosphate metabolism increases production of the signaling molecule c-di-GMP, which in turn decreases the expression of type 1 fimbriae. We also determine the regulatory cascade leading to the accumulation of c-di-GMP and identify the Pho regulon as new players in c-di-GMP-mediated cell signaling. By understanding the molecular mechanisms leading to the expression of virulence factors, we will be in a better position to develop new therapeutics.
Extra-intestinal pathogenic Escherichia coli (ExPEC) strains cause many diseases in humans and animals. While remaining asymptomatic, they can colonize the intestine for subsequent extra-intestinal ...infection and dissemination in the environment. We have previously identified the fos locus, a gene cluster within a pathogenicity island of the avian ExPEC strain BEN2908, involved in the metabolism of short-chain fructooligosaccharides (scFOS). It is assumed that these sugars are metabolized by the probiotic bacteria of the microbiota present in the intestine, leading to a decrease in the pathogenic bacterial population. However, we have previously shown that scFOS metabolism helps BEN2908 to colonize the intestine, its reservoir. As the fos locus is located on a pathogenicity island, one aim of this study was to investigate a possible role of this locus in the virulence of the strain for chicken. We thus analysed fos gene expression in extracts of target organs of avian colibacillosis and performed a virulence assay in chickens. Moreover, in order to understand the involvement of the fos locus in intestinal colonization, we monitored the expression of fos genes and their implication in the growth ability of the strain in intestinal extracts of chicken. We also performed intestinal colonization assays in axenic and Specific Pathogen-Free (SPF) chickens. We demonstrated that the fos locus is not involved in the virulence of BEN2908 for chickens and is strongly involved in axenic chicken cecal colonization both in vitro and in vivo. However, even if the presence of a microbiota does not inhibit the growth advantage of BEN2908 in ceca in vitro, overall, growth of the strain is not favoured in the ceca of SPF chickens. These findings indicate that scFOS metabolism by an ExPEC strain can contribute to its fitness in ceca but this benefit is fully dependent on the bacteria present in the microbiota.
Extra-intestinal pathogenic
Escherichia coli (ExPEC) strains are responsible for a wide range of diseases in humans and animals. Using
in vitro invasion assays and transmission electron microscopy, ...we showed that BEN2908, an ExPEC strain of avian origin (also termed APEC for Avian Pathogenic
E. coli), is able to usurp cellular endocytic pathways to invade A549 human type II pneumocytes and LMH avian hepatocytes where it is able to survive over several days. Although type 1 fimbriae are the major adhesin of BEN2908, proportions of adherent fimbriated or afimbriated bacteria that entered cells were comparable. Internalization of BEN2908 into human pneumocytes reinforces previous studies indicating that APEC strains could represent a zoonotic risk.
Summary
A gene cluster involved in the metabolism of prebiotic short‐chain fructooligosaccharides (scFOS) has recently been identified in the extra‐intestinal avian pathogenic Escherichia coli strain ...BEN2908. This gene cluster, called the fos locus, plays a major role in the initiation stage of chicken intestinal colonization. This locus is composed of six genes organized as an operon encoding a sugar transporter and enzymes involved in scFOS metabolism, and of a divergently transcribed gene encoding a transcriptional regulator, FosR, belonging to the LacI/GalR family. To decipher the regulation of scFOS metabolism, we monitored the fos operon promoter activity using a luciferase reporter gene assay. We demonstrated that the expression of fos genes is repressed by FosR, controlled by catabolite repression and induced in the presence of scFOS. Using electrophoretic mobility shift assays and surface plasmon resonance experiments, we showed that FosR binds to two operator sequences of the fos operon promoter region. This binding to DNA was inhibited in the presence of scFOS, especially by GF2. We then propose a model of scFOS metabolism regulation in a pathogenic bacterium, which will help to identify the environmental conditions required for fos gene expression and to understand the role of this locus in intestinal colonization.
Abstract
The yicJI operon of the common genetic backbone of Escherichia coli codes an α-xylosidase and a transporter of the galactosides–pentoses–hexuronides:cation symporter family. In the ...extraintestinal pathogenic E. coli strain BEN2908, a metabolic operon (frz) of seven genes is found downstream of the yicI gene. It was proved that frz promotes bacterial fitness under stressful conditions. During this work, we identified a motif containing a palindromic sequence in the promoter region of both the frz and the yicJI operons. We then showed that these two operons are cotranscribed, suggesting a functional relationship. The phenotypes of frz and yicJI deletion mutants were compared. Our results showed that although the yicJI operon is not essential for the life of E. coli, it is necessary for its fitness under all the growth conditions tested.
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