Fur Represses Adhesion to, Invasion of, and Intracellular Bacterial Community Formation within Bladder Epithelial Cells and Motility in Uropathogenic Escherichia coli

Abstract

Uropathogenic Escherichia coli (UPEC) is a major pathogen that causes urinary tract infections (UTIs). This bacterium adheres to and invades the host cells in the bladder, where it forms biofilm-like polymicrobial structures termed intracellular bacterial communities (IBCs) that protect UPEC from antimicrobial agents and the host immune systems. Using genetic screening, we found that deletion of the fur gene, which encodes an iron-binding transcriptional repressor for iron uptake systems, elevated the expression of type I fimbriae and motility when UPEC was grown under iron-rich conditions, and it led to an increased number of UPEC cells adhering to and internalized in bladder epithelial cells. Consequently, the IBC colonies that the fur mutant formed in host cells were denser and larger than those formed by the wild-type parent strain. Fur is inactivated under iron-restricted conditions. When iron was depleted from the bacterial cultures, wild-type UPEC adhesion, invasion, and motility increased, similar to the case with the fur mutant. The purified Fur protein bound to regions upstream of fimA and flhD, which encode type I fimbriae and an activator of flagellar expression that contributes to motility, respectively. These results suggest that Fur is a repressor of fimA and flhD and that its repression is abolished under iron-depleted conditions. Based on our in vitro experiments, we conclude that UPEC adhesion, invasion, IBC formation, and motility are suppressed by Fur under iron-rich conditions but derepressed under iron-restricted conditions, such as in patients with UTIs.

Tailoring a Global Iron Regulon to a Uropathogen

“…Indeed, many of the genes encoding components of the ferrous iron or heme uptake systems, components of the three siderophore biosynthetic pathways, various outer membrane siderophore receptors, and the TonB-ExbD system are upregulated when UPEC strains are grown in urine or in mouse models of urinary tract infections (18, 21, 57-59) (see Table S6 in the supplemental material). While in some cases the individual role of Fur or RyhB in controlling gene expression had been demonstrated or inferred (27,43,60), our global approaches of ChIP-seq, RNA-seq, and proteomics, allowed us to confirm predictions, distinguish between positive or negative impacts of Fur and RyhB, and identify new roles for these iron-responsive regulators on a genome-wide scale. Additional direct targets for Fur regulation within known pathogenicity islands were identified, such as a member of the major facilitator transport superfamily (ShiF), microcin H47 maturation enzymes (MchBCDEF), two predicted TonB dependent ironsiderophore receptors (Iha and IreA), a second system for ferric siderophore uptake referred to as the Fit pathway (c3771-3775) (41), an alternate isozyme (c1220) for synthesis of shikimate, an intermediate of aromatic amino acids, enterobactin and salmochelin synthesis.…”

Inactivation of ferric uptake regulator (Fur) attenuates Helicobacter pylori J99 motility by disturbing the flagellar motor switch and autoinducer‐2 production

“…Fur regulates genes involved in iron uptake, acid acclimation, and oxidative response and has been shown to be important for colonization of H. pylori in both murine and Mongolian gerbil models of infection. 23,34 Moreover, several genes involved in motility and chemotaxis, including flgL, fliY, flgK, cheA, and flaB, are Fur-dependent and positively regulated in H. pylori G27. 23 In this study, the fur mutant was flagellated and the expression of selected flagella-related genes in the fur mutant was similar to that of the wild-type J99 in iron-rich conditions ( Figure 3).…”

The high-pathogenicity island (HPI) promotes flagellum-mediated motility in extraintestinal pathogenic Escherichia coli

“…In the case of Vibrio parahaemolyticus , it is known that iron depletion is an essential signal for swarmer cell differentiation [ 34 ]. A relevant role of iron homeostasis for motility has also been reported in UPEC [ 35 ]. The iron master regulator Fur represses iron uptake systems by binding to specific Fur binding-sites, so called Fur boxes, in complex with ferrous iron under iron abundance.…”