Iron and pH Homeostasis Intersect at the Level of Fur Regulation in the Gastric Pathogen Helicobacter pylori

Abstract

Helicobacter pylori persistently colonizes the stomach of the majority of the world's population and is a tremendous medical burden due to its causal role in diverse gastric maladies. Since the stomach is a constantly changing environment, successful colonization of H. pylori within this niche requires regulation of bacterial gene expression to cope with the environmental fluctuations. In H. pylori, the ferric uptake regulator (Fur) has been shown to play an intricate role in adaptation of the bacterium to two conditions known to oscillate within the gastric mucosa: iron limitation and low pH. To extend our knowledge of the process of regulation and adaptation in H. pylori, we show that Fur is required for efficient colonization of the Mongolian gerbil: the mutant strain exhibits a 100-fold increase in the 50% infectious dose, as well as a 100-fold defect in competitive colonization, when coinfected with wild-type bacteria. Furthermore, we used DNA microarrays to identify genes whose expression was altered in a Fur-deficient strain. We show that the Fur regulon of H. pylori consists of approximately 30 genes, most of which have been previously annotated as acid stress associated. Finally, we investigate the role of Fur in acid-responsive modulation of gene expression and show that a large number of genes are aberrantly expressed in the Fur mutant specifically upon acid exposure. This fact likely explains the requirement for this regulator for growth and colonization in the stomach.

A Comparative Analysis of Perturbations Caused by a Gene Knock-out, a Dominant Negative Allele, and a Set of Peptide Aptamers

“…5A), thus confirming the identity of the samples, the proper expression of the transgenes, and the strong Fur basal activity under our experimental conditions. 75 of the 196 selected genes have already been identified in previous transcriptome studies as Fur-and/or iron-regulated genes in E. coli (17,42), Helicobacter pylori (38,(43)(44)(45), Neisseria meningitidis (46,47), Pseudomonas aeruginosa (48,49), Campylobacter jejuni (50), Shewanella oneidensis (51,52), and Pasteurella multicoda (53). Conversely we unveiled 121 genes that have not been reported by previous studies.…”

“…Virulence Assay in Animals-Fur has been shown to play an important role in the virulence of different pathogenic bacteria (18,38). We thus set out to determine whether Fur90 and the Fur-binding peptide aptamers affected the virulence of a pathogenic E. coli strain in an in vivo model system.…”

Identification of Campylobacter jejuni Genes Contributing to Acid Adaptation by Transcriptional Profiling and Genome-Wide Mutagenesis

“…Interestingly, the perR gene also was highly up-regulated in response to both in vitro and in vivo acid shock (71), further suggesting that the modulation of PerR levels is a general response to acid stress in C. jejuni. While there are no previous reports implicating PerR in bacterial acid stress responses, its homologue, the ferric uptake regulator Fur, is required for the induction of acid shock genes and proteins in H. pylori and S. enterica (30,32,36), and the mutation of fur in these bacteria renders cells acid sensitive (4,6,8,10,30,36). Studies of S. enterica suggest that the role of Fur in the acid stress response is independent of iron (36) and consequently is distinct from its role in mediating iron homeostasis.…”

Novel Insights into Fur Regulation in Helicobacter pylori

“…Previous transcriptional profiling studies using wildtype and fur mutant strains of H. pylori suggested that expression of oorD, oorA, and oorC were decreased in a fur mutant strain of H. pylori (67). At the chromosomal level, these genes appear to be encoded as part of an operon with oorB ( Figure 5A).…”

“…However, in many cases Fur also directly and indirectly regulates many other genes with diverse functions, including genes linked to colonization, virulence, and stress adaptation (58,67,72,108,128,134). Clearly, this regulatory protein plays in important role in the biology of many bacterial pathogens.…”