Essential role of ferritin Pfr in Helicobacter pylori iron metabolism and gastric colonization

A Self-Assembling Pfs230D1-Ferritin Nanoparticle Vaccine Has Potent and Durable Malaria Transmission-Reducing Activity

Malaria is caused by eukaryotic protozoan parasites of the genus Plasmodium. There are 249 million new cases and 608,000 deaths annually, and new interventions are desperately needed. Malaria vaccines can be divided into three categories: liver stage, blood stage, or transmission-blocking vaccines. Transmission-blocking vaccines prevent the transmission of disease by the mosquito vector from one human to another. Pfs230 is one of the leading transmission-blocking vaccine antigens for malaria. Here, we describe the development of a 24-copy self-assembling nanoparticle vaccine comprising domain 1 of Pfs230 genetically fused to H. pylori ferritin. The single-component Pfs230D1-ferritin construct forms a stable and homogenous 24-copy nanoparticle with good production yields. The nanoparticle is highly immunogenic, as two low-dose vaccinations of New Zealand White rabbits elicited a potent and durable antibody response with high transmission-reducing activity when formulated in two distinct adjuvants suitable for translation to human use. This single-component 24-copy Pfs230D1-ferritin nanoparticle vaccine has the potential to improve production pipelines and the cost of manufacturing a potent and durable transmission-blocking vaccine for malaria control.

Profiling of the Helicobacter pylori redox switch HP1021 regulon using a multi-omics approach

The gastric human pathogen Helicobacter pylori has developed mechanisms to combat stress factors, including reactive oxygen species (ROS). Here, we present a comprehensive study on the redox switch protein HP1021 regulon combining transcriptomic, proteomic and DNA-protein interactions analyses. Our results indicate that HP1021 modulates H. pylori's response to oxidative stress. HP1021 controls the transcription of 497 genes, including 407 genes related to response to oxidative stress. 79 proteins are differently expressed in the HP1021 deletion mutant. HP1021 controls typical ROS response pathways (katA, rocF) and less canonical ones, particularly DNA uptake and central carbohydrate metabolism. HP1021 is a molecular regulator of competence in H. pylori, as HP1021-dependent repression of the comB DNA uptake genes is relieved under oxidative conditions, increasing natural competence. Furthermore, HP1021 controls glucose consumption by directly regulating the gluP transporter and has an important impact on maintaining the energetic balance in the cell.

Can Pyomelanin Produced by Pseudomonas aeruginosa Promote the Regeneration of Gastric Epithelial Cells and Enhance Helicobacter pylori Phagocytosis?

Helicobacter pylori (H. pylori) infection is the most common cause of chronic gastritis, peptic ulcers and gastric cancer. Successful colonization of the stomach by H. pylori is related to the complex interactions of these bacteria and its components with host cells. The growing antibiotic resistance of H. pylori and various mechanisms of evading the immune response have forced the search for new biologically active substances that exhibit antibacterial properties and limit the harmful effects of these bacteria on gastric epithelial cells and immune cells. In this study, the usefulness of pyomelanin (PyoM) produced by Pseudomonas aeruginosa for inhibiting the metabolic activity of H. pylori was evaluated using the resazurin reduction assay, as well as in vitro cell studies used to verify the cytoprotective, anti-apoptotic and pro-regenerative effects of PyoM in the H. pylori LPS environment. We have shown that both water-soluble (PyoMsol) and water-insoluble (PyoMinsol) PyoM exhibit similar antibacterial properties against selected reference and clinical strains of H. pylori. This study showed that PyoM at a 1 μg/mL concentration reduced H. pylori-driven apoptosis and reactive oxygen species (ROS) production in fibroblasts, monocytes or gastric epithelial cells. In addition, PyoM enhanced the phagocytosis of H. pylori. PyoMsol showed better pro-regenerative and immunomodulatory activities than PyoMinsol.

Comparative transcriptome analysis to investigate the mechanism of anti-Helicobacter pylori activity of zinc

As a potential anti-Helicobacter pylori agent, zinc causes impairment of Helicobacter pylori growth, and this property of zinc is of broad interest to biological investigators. However, little is known about the molecular mechanisms by which zinc inhibits the growth of Helicobacter pylori. Here, an in vitro experiment revealed that zinc at specific concentrations inhibits Helicobacter pylori growth. Furthermore, an RNA sequencing-based investigation of the global regulatory response to zinc revealed that exposure to zinc altered the Helicobacter pylori transcriptional profile in numerous ways. A high concentration of zinc induced the upregulation of genes related to ribosomal subunit, ribosome biosynthesis, chaperone and adhesins. However, flagellar assembly genes and some type IV secretion system genes were repressed. In addition, the expression levels of some genes that encode transporters of metal ions and that play key roles in Helicobacter pylori pathogenicity were altered under conditions of zinc-induced stress. In summary, high concentrations of zinc initiated antimicrobial activity to Helicobacter pylori under the combined effect of multiple repressed or altered pathogenetic genes and metabolic pathways associated with bacteria growth. This result has significant implications for understanding not only the antimicrobial activity mechanism of zinc but also the role of zinc-mediated homeostasis in Helicobacter pylori.

Agrobacterium tumefaciens ferritins play an important role in full virulence through regulating iron homeostasis and oxidative stress survival

Ferritins are a large family of iron storage proteins, which are used by bacteria and other organisms to avoid iron toxicity and as a safe iron source in the cytosol. Agrobacterium tumefaciens, a phytopathogen, has two ferritin-encoding genes: atu2771 and atu2477. Atu2771 is annotated as a Bfr-encoding gene (Bacterioferritin, Bfr) and atu2477 as a Dps-encoding gene (DNA binding protein from starved cells, Dps). Three deletion mutants (Δbfr, Δdps, and bfr-dps double-deletion mutant ΔbdF) of these two ferritin-encoding genes were constructed to investigate the effects of ferritin deficiency on the iron homeostasis, oxidative stress resistance, and pathogenicity of A. tumefaciens. Deficiency of two ferritins affects the growth of A. tumefaciens under iron starvation and excess. When supplied with moderate iron, the growth of A. tumefaciens is not affected by the deficiency of ferritin. Deficiency of ferritin significantly reduces iron accumulation in the cells of A. tumefaciens, but the effect of Bfr deficiency on iron accumulation is severer than Dps deficiency and the double mutant ΔbdF has the least intracellular iron content. All three ferritin-deficient mutants showed a decreased tolerance to 3 mM H2 O2 in comparison with the wild type. The tumour induced by each of three ferritin-deficient mutants is less than that of the wild type. Complementation reversed the effects of ferritin deficiency on the growth, iron homeostasis, oxidative stress resistance, and tumorigenicity of A. tumefaciens. Therefore, ferritin plays an important role in the pathogenesis of A. tumefaciens through regulating iron homeostasis and oxidative stress survival.

N4-cytosine DNA methylation regulates transcription and pathogenesis in Helicobacter pylori

Many bacterial genomes exclusively display an N⁴-methyl cytosine base (m4C), whose physiological significance is not yet clear. Helicobacter pylori is a carcinogenic bacterium and the leading cause of gastric cancer in humans. Helicobacter pylori strain 26695 harbors a single m4C cytosine methyltransferase, M2.HpyAII which recognizes 5′ TCTTC 3′ sequence and methylates the first cytosine residue. To understand the role of m4C modification, M2.hpyAII deletion strain was constructed. Deletion strain displayed lower adherence to host AGS cells and reduced potential to induce inflammation and apoptosis. M2.hpyAII gene deletion strain exhibited reduced capacity for natural transformation, which was rescued in the complemented strain carrying an active copy of M2.hpyAII gene in the genome. Genome-wide gene expression and proteomic analysis were carried out to discern the possible reasons behind the altered phenotype of the M2.hpyAII gene deletion strain. Upon the loss of m4C modification a total of 102 genes belonging to virulence, ribosome assembly and cellular components were differentially expressed. The present study adds a functional role for the presence of m4C modification in H. pylori and provides the first evidence that m4C signal acts as a global epigenetic regulator in H. pylori.

Unraveling the factors and mechanism involved in persistence: Host-pathogen interactions in Helicobacter pylori

Helicobacter pylori and humans have one of the most complex relationships in nature. How a bacterium manages to live in one of the harshest and hostile environments is a topic of unraveling mysteries. H. pylori is a prevalent species and it colonizes the human gut of more than 50% of the world population. It infects the epithelial region of antrum and persists there for a long period. Over the time of evolution, H. pylori has developed complex strategies to extend the degree of inflammation in gastric mucosa. H. pylori needs specific adaptations for initial colonization into the host environment like helical shape, flagellar movement, chemotaxis, and the production of urease enzyme that neutralizes acidic environment of the stomach. There are several factors from the bacterium as well as from the host that participate in these complex interactions. On the other hand, to establish the persistent infection, H. pylori escapes the immune system by mimicking the host antigens. This pathogen has the ability to dodge the immune system and then persist there in the form of host cell, which leads to immune tolerance. H. pylori has an ability to manipulate its own pathogen-associated molecular patterns, which leads to an inhibition in the binding with specific pattern recognition receptors of the host to avoid immune cell detection. Also, it manipulates the host metabolic homeostasis in the gastric epithelium. Besides, it has several genes, which may get involved in the acquisition of nutrition from the host to survive longer in the host. Due to the persistence of H. pylori, it causes chronic inflammation and raises the chances of gastric cancer. This review highlights the important elements, which are certainly responsible for the persistence of H. pylori in the human host.

Multi-omics and temporal dynamics profiling reveal disruption of central metabolism in Helicobacter pylori on bismuth treatment

Integration of multi-omics enables uncovering cellular responses to stimuli or the mechanism of action of a drug at a system level. Bismuth drugs have long been used for the treatment of Helicobacter pylori infection and their antimicrobial activity was attributed to dysfunction of multiple proteins based on previous proteome-wide studies. Herein, we investigated the response of H. pylori to a bismuth drug at transcriptome and metabolome levels. Our multi-omics data together with bioassays comprehensively reveal the impact of bismuth on a diverse array of intracellular pathways, in particular, disruption of central carbon metabolism is systematically evaluated as a primary bismuth-targeting system in H. pylori. Through temporal dynamics profiling, we demonstrate that bismuth initially perturbs the TCA cycle and then urease activity, followed by the induction of oxidative stress and inhibition of energy production, and in the meantime, induces extensive down-regulation in H. pylori metabolome. The present study thus expands our knowledge on the inhibitory actions of bismuth and provides a novel systematic perspective of H. pylori in response to a clinical drug that sheds light on enhanced therapeutic methodologies.

The Irr and RirA Proteins Participate in a Complex Regulatory Circuit and Act in Concert To Modulate Bacterioferritin Expression in Ensifer meliloti 1021

In this work we found that the bfr gene of the rhizobial species Ensifer meliloti, encoding a bacterioferritin iron storage protein, is involved in iron homeostasis and the oxidative stress response. This gene is located downstream of and overlapping the smc03787 open reading frame (ORF). No well-predicted RirA or Irr boxes were found in the region immediately upstream of the bfr gene although two presumptive RirA boxes and one presumptive Irr box were present in the putative promoter of smc03787 We demonstrate that bfr gene expression is enhanced under iron-sufficient conditions and that Irr and RirA modulate this expression. The pattern of bfr gene expression as well as the response to Irr and RirA is inversely correlated to that of smc03787 Moreover, our results suggest that the small RNA SmelC759 participates in RirA- and Irr-mediated regulation of bfr expression and that additional unknown factors are involved in iron-dependent regulation.IMPORTANCEE. meliloti belongs to the Alphaproteobacteria, a group of bacteria that includes several species able to associate with eukaryotic hosts, from mammals to plants, in a symbiotic or pathogenic manner. Regulation of iron homeostasis in this group of bacteria differs from that found in the well-studied Gammaproteobacteria In this work we analyzed the effect of rirA and irr mutations on bfr gene expression. We demonstrate the effect of an irr mutation on iron homeostasis in this bacterial genus. Moreover, results obtained indicate a complex regulatory circuit where multiple regulators, including RirA, Irr, the small RNA SmelC759, and still unknown factors, act in concert to balance bfr gene expression.

Metal homeostasis and resistance in bacteria

Metal ions are essential for many reactions, but excess metals can be toxic. In bacteria, metal limitation activates pathways that are involved in the import and mobilization of metals, whereas excess metals induce efflux and storage. In this Review, we highlight recent insights into metal homeostasis, including protein-based and RNA-based sensors that interact directly with metals or metal-containing cofactors. The resulting transcriptional response to metal stress takes place in a stepwise manner and is reinforced by post-transcriptional regulatory systems. Metal limitation and intoxication by the host are evolutionarily ancient strategies for limiting bacterial growth. The details of the resulting growth restriction are beginning to be understood and seem to be organism-specific.

Folate and Inflammatory Markers Moderate the Association Between Helicobacter pylori Exposure and Cognitive Function in US Adults

BACKGROUND

Helicobacter pylori (H. pylori) infection is associated with cognitive deficits in humans, an association potentially mediated or moderated by folate concentration or inflammation.

MATERIALS AND METHODS

We used the National Health and Nutrition Examination Survey (NHANES) datasets to examine whether folate concentration or inflammation mediates or moderates the relationship between H. pylori and cognitive function. Models were performed using linear, Poisson, and zero-inflated Poisson regression, and we performed separate analyses for groups aged 20-59 and 60-90 years with sample sizes ranging from 700 to 1700.

RESULTS

We did not find evidence of mediation in either age group. In the 20- to 59-year group, interactions between H. pylori and ferritin (p values ranging from .004 to .039) were associated with worse processing speed, better working memory, and worse reaction time. Interactions between H. pylori and fibrinogen (p values ranging from .023 to .045), C-reactive protein (CRP) (p = .023), and the inflammatory index (p = .045) were associated with worse processing speed. In 60- to 90-year-olds, H. pylori interacted with ferritin and the inflammatory index to predict fewer mathematical errors (p values of .036 and .023). Interactions with folate (p values of .016 and .006) and C-reactive protein (p values ranging from <.001 to .048) were inconsistent in directionality.

CONCLUSIONS

In this dataset, representative of the US population, inflammation and folate concentrations moderated but did not mediate the association between H. pylori seropositivity and cognition.

The Helicobacter pylori CZB Cytoplasmic Chemoreceptor TlpD Forms an Autonomous Polar Chemotaxis Signaling Complex That Mediates a Tactic Response to Oxidative Stress

Cytoplasmic chemoreceptors are widespread among prokaryotes but are far less understood than transmembrane chemoreceptors, despite being implicated in many processes. One such cytoplasmic chemoreceptor is Helicobacter pylori TlpD, which is required for stomach colonization and drives a chemotaxis response to cellular energy levels. Neither the signals sensed by TlpD nor its molecular mechanisms of action are known. We report here that TlpD functions independently of the other chemoreceptors. When TlpD is the sole chemoreceptor, it is able to localize to the pole and recruits CheW, CheA, and at least two CheV proteins to this location. It loses the normal membrane association that appears to be driven by interactions with other chemoreceptors and with CheW, CheV1, and CheA. These results suggest that TlpD can form an autonomous signaling unit. We further determined that TlpD mediates a repellent chemotaxis response to conditions that promote oxidative stress, including being in the presence of iron, hydrogen peroxide, paraquat, and metronidazole. Last, we found that all tested H. pylori strains express TlpD, whereas other chemoreceptors were present to various degrees. Our data suggest a model in which TlpD coordinates a signaling complex that responds to oxidative stress and may allow H. pylori to avoid areas of the stomach with high concentrations of reactive oxygen species.

IMPORTANCE

Helicobacter pylori senses its environment with proteins called chemoreceptors. Chemoreceptors integrate this sensory information to affect flagellum-based motility in a process called chemotaxis. Chemotaxis is employed during infection and presumably aids H. pylori in encountering and colonizing preferred niches. A cytoplasmic chemoreceptor named TlpD is particularly important in this process, and we report here that this chemoreceptor is able to operate independently of other chemoreceptors to organize a chemotaxis signaling complex and mediate a repellent response to oxidative stress conditions. H. pylori encounters and must cope with oxidative stress during infection due to oxygen and reactive oxygen species produced by host cells. TlpD's repellent response may allow the bacteria to escape niches experiencing inflammation and elevated reactive oxygen species (ROS) production.

Helicobacter pylori adaptation in vivo in response to a high-salt diet

Helicobacter pylori exhibits a high level of intraspecies genetic diversity. In this study, we investigated whether the diversification of H. pylori is influenced by the composition of the diet. Specifically, we investigated the effect of a high-salt diet (a known risk factor for gastric adenocarcinoma) on H. pylori diversification within a host. We analyzed H. pylori strains isolated from Mongolian gerbils fed either a high-salt diet or a regular diet for 4 months by proteomic and whole-genome sequencing methods. Compared to the input strain and output strains from animals fed a regular diet, the output strains from animals fed a high-salt diet produced higher levels of proteins involved in iron acquisition and oxidative-stress resistance. Several of these changes were attributable to a nonsynonymous mutation in fur (fur-R88H). Further experiments indicated that this mutation conferred increased resistance to high-salt conditions and oxidative stress. We propose a model in which a high-salt diet leads to high levels of gastric inflammation and associated oxidative stress in H. pylori-infected animals and that these conditions, along with the high intraluminal concentrations of sodium chloride, lead to selection of H. pylori strains that are most fit for growth in this environment.

Roles of Agrobacterium tumefaciens membrane-bound ferritin (MbfA) in iron transport and resistance to iron under acidic conditions

Agrobacterium tumefaciens membrane-bound ferritin (MbfA) is a member of the erythrin (Er)-vacuolar iron transport family. The MbfA protein has an Er or ferritin-like domain at its N terminus and has been predicted to have five transmembrane segments in its C-terminal region. Analysis of protein localization using PhoA and LacZ reporter proteins supported the view that the N-terminal di-iron site is located in the cytoplasm whilst the C-terminal end faces the periplasm. An A. tumefaciens mbfA mutant strain had 1.5-fold higher total iron content than the WT strain. Furthermore, multi-copy expression of mbfA reduced total iron content two- and threefold in WT and mbfA mutant backgrounds, respectively. These results suggest that MbfA may function as an iron exporter rather than an iron storage protein. The mbfA mutant showed 10-fold increased sensitivity to the iron-activated antibiotic streptonigrin, implying that the mutant had increased accumulation of intracellular free iron. Growth of the mbfA mutant was reduced in the presence of high iron under acidic conditions. The expression of mbfA was induced highly in cells grown in iron-replete medium at pH 5.5, further supporting the view that mbfA is involved in the response to iron under acidic conditions. A. tumefaciens MbfA may play a protective role against increased free iron in the cytoplasm through iron binding and export, thus preventing iron-induced toxicity via the Fenton reaction.

Clinical proteomics identifies potential biomarkers in Helicobacter pylori for gastrointestinal diseases

The development of gastrointestinal diseases has been found to be associated with Helicobacter pylori (H. pylori) infection and various biochemical stresses in stomach and intestine. These stresses, such as oxidative, osmotic and acid stresses, may bring about bi-directional effects on both hosts and H. pylori, leading to changes of protein expression in their proteomes. Therefore, proteins differentially expressed in H. pylori under various stresses not only reflect gastrointestinal environment but also provide useful biomarkers for disease diagnosis and prognosis. In this regard, proteomic technology is an ideal tool to identify potential biomarkers as it can systematically monitor proteins and protein variation on a large scale of cell’s translational landscape, permitting in-depth analyses of host and pathogen interactions. By performing two-dimensional polyacrylamide gel electrophoresis (2-DE) followed by liquid chromatography-nanoESI-mass spectrometry (nanoLC-MS/MS), we have successfully pinpointed alkylhydroperoxide reductase (AhpC), neutrophil-activating protein and non-heme iron-binding ferritin as three prospective biomarkers showing up-regulation in H. pylori under oxidative, osmotic and acid stresses, respectively. Further biochemical characterization reveals that various environmental stresses can induce protein structure change and functional conversion in the identified biomarkers. Especially salient is the antioxidant enzyme AhpC, an abundant antioxidant protein present in H. pylori. It switches from a peroxide reductase of low-molecular-weight (LMW) oligomers to a molecular chaperone of high-molecular-weight (HMW) complexes under oxidative stress. Different seropositivy responses against LMW or HMW AhpC in H. pylori-infected patients faithfully match the disease progression from disease-free healthy persons to patients with gastric ulcer and cancer. These results has established AhpC of H. pylori as a promising diagnostic marker for gastrointestinal maladies, and highlight the utility of clinical proteomics for identifying disease biomarkers that can be uniquely applied to disease-oriented translational medicine.

The ferric uptake regulator of Helicobacter pylori: a critical player in the battle for iron and colonization of the stomach

Helicobacter pylori is arguably one of the most successful pathogens; it colonizes the stomachs of more than half of the human population. Colonization and persistence in such an inhospitable niche requires the presence of exquisite adaptive mechanisms. One of the proteins that contributes significantly to the remarkable adaptability of H. pylori is the ferric uptake regulator (Fur), which functions as a master regulator of gene expression. In addition to genes directly related to iron homeostasis, Fur controls expression of several enzymes that play a central role in metabolism and energy production. The absence of Fur leads to severe H. pylori colonization defects and, accordingly, several Fur-regulated genes have been shown to be essential for colonization. Moreover, proteins encoded by Fur-regulated genes have a strong impact on redox homeostasis in the stomach and are major determinants of inflammation. In this review, we discuss the main roles of Fur in the biology of H. pylori and highlight the importance of this regulatory protein in the infectious process.

Targeted identification of glycosylated proteins in the gastric pathogen Helicobacter pylori (Hp)

Virulence of the gastric pathogen Helicobacter pylori (Hp) is directly linked to the pathogen's ability to glycosylate proteins; for example, Hp flagellin proteins are heavily glycosylated with the unusual nine-carbon sugar pseudaminic acid, and this modification is absolutely essential for Hp to synthesize functional flagella and colonize the host's stomach. Although Hp's glycans are linked to pathogenesis, Hp's glycome remains poorly understood; only the two flagellin glycoproteins have been firmly characterized in Hp. Evidence from our laboratory suggests that Hp synthesizes a large number of as-yet unidentified glycoproteins. Here we set out to discover Hp's glycoproteins by coupling glycan metabolic labeling with mass spectrometry analysis. An assessment of the subcellular distribution of azide-labeled proteins by Western blot analysis indicated that glycoproteins are present throughout Hp and may therefore serve diverse functions. To identify these species, Hp's azide-labeled glycoproteins were tagged via Staudinger ligation, enriched by tandem affinity chromatography, and analyzed by multidimensional protein identification technology. Direct comparison of enriched azide-labeled glycoproteins with a mock-enriched control by both SDS-PAGE and mass spectrometry-based analyses confirmed the selective enrichment of azide-labeled glycoproteins. We identified 125 candidate glycoproteins with diverse biological functions, including those linked with pathogenesis. Mass spectrometry analyses of enriched azide-labeled glycoproteins before and after cleavage of O-linked glycans revealed the presence of Staudinger ligation-glycan adducts in samples only after beta-elimination, confirming the synthesis of O-linked glycoproteins in Hp. Finally, the secreted colonization factors urease alpha and urease beta were biochemically validated as glycosylated proteins via Western blot analysis as well as by mass spectrometry analysis of cleaved glycan products. These data set the stage for the development of glycosylation-based therapeutic strategies, such as new vaccines based on natively glycosylated Hp proteins, to eradicate Hp infection. Broadly, this report validates metabolic labeling as an effective and efficient approach for the identification of bacterial glycoproteins.

Crosstalk between Helicobacter pylori and gastric epithelial cells is impaired by docosahexaenoic acid

H. pylori colonizes half of the world's population leading to gastritis, ulcers and gastric cancer. H. pylori strains resistant to antibiotics are increasing which raises the need for alternative therapeutic approaches. Docosahexaenoic acid (DHA) has been shown to decrease H. pylori growth and its associated-inflammation through mechanisms poorly characterized. We aimed to explore DHA action on H. pylori-mediated inflammation and adhesion to gastric epithelial cells (AGS) and also to identify bacterial structures affected by DHA. H. pylori growth and metabolism was assessed in liquid cultures. Bacterial adhesion to AGS cells was visualized by transmission electron microscopy and quantified by an Enzyme Linked Immunosorbent Assay. Inflammatory proteins were assessed by immunoblotting in infected AGS cells, previously treated with DHA. Bacterial total and outer membrane protein composition was analyzed by 2-dimensional gel electrophoresis. Concentrations of 100 µM of DHA decreased H. pylori growth, whereas concentrations higher than 250 µM irreversibly inhibited bacteria survival. DHA reduced ATP production and adhesion to AGS cells. AGS cells infected with DHA pre-treated H. pylori showed a 3-fold reduction in Interleukin-8 (IL-8) production and a decrease of COX2 and iNOS. 2D electrophoresis analysis revealed that DHA changed the expression of H. pylori outer membrane proteins associated with stress response and metabolism and modified bacterial lipopolysaccharide phenotype. As conclusions our results show that DHA anti-H. pylori effects are associated with changes of bacteria morphology and metabolism, and with alteration of outer membrane proteins composition, that ultimately reduce the adhesion of bacteria and the burden of H. pylori-related inflammation.

Gastric Helicobacter infection induces iron deficiency in the INS-GAS mouse

There is increasing evidence from clinical and population studies for a role of H. pylori infection in the aetiology of iron deficiency. Rodent models of Helicobacter infection are helpful for investigating any causal links and mechanisms of iron deficiency in the host. The aim of this study was to investigate the effects of gastric Helicobacter infection on iron deficiency and host iron metabolism/transport gene expression in hypergastrinemic INS-GAS mice. INS-GAS mice were infected with Helicobacter felis for 3, 6 and 9 months. At post mortem, blood was taken for assessment of iron status and gastric mucosa for pathology, immunohistology and analysis of gene expression. Chronic Helicobacter infection of INS- GAS mice resulted in decreased serum iron, transferrin saturation and hypoferritinemia and increased Total iron binding capacity (TIBC). Decreased serum iron concentrations were associated with a concomitant reduction in the number of parietal cells, strengthening the association between hypochlorhydria and gastric Helicobacter-induced iron deficiency. Infection with H. felis for nine months was associated with decreased gastric expression of iron metabolism regulators hepcidin, Bmp4 and Bmp6 but increased expression of Ferroportin 1, the iron efflux protein, iron absorption genes such as Divalent metal transporter 1, Transferrin receptor 1 and also Lcn2 a siderophore-binding protein. The INS-GAS mouse is therefore a useful model for studying Helicobacter-induced iron deficiency. Furthermore, the marked changes in expression of gastric iron transporters following Helicobacter infection may be relevant to the more rapid development of carcinogenesis in the Helicobacter infected INS-GAS model.

A ferritin mutant of Mycobacterium tuberculosis is highly susceptible to killing by antibiotics and is unable to establish a chronic infection in mice

Iron is an essential, elusive, and potentially toxic nutrient for most pathogens, including Mycobacterium tuberculosis. Due to the poor solubility of ferric iron under aerobic conditions, free iron is not found in the host. M. tuberculosis requires specialized iron acquisition systems to replicate and cause disease. It also depends on a strict control of iron metabolism and intracellular iron levels to prevent iron-mediated toxicity. Under conditions of iron sufficiency, M. tuberculosis represses iron acquisition and induces iron storage, suggesting an important role for iron storage proteins in iron homeostasis. M. tuberculosis synthesizes two iron storage proteins, a ferritin (BfrB) and a bacterioferritin (BfrA). The individual contributions of these proteins to the adaptive response of M. tuberculosis to changes in iron availability are not clear. By generating individual knockout strains of bfrA and bfrB, the contribution of each one of these proteins to the maintenance of iron homeostasis was determined. The effect of altered iron homeostasis, resulting from impaired iron storage, on the resistance of M. tuberculosis to in vitro and in vivo stresses was examined. The results show that ferritin is required to maintain iron homeostasis, whereas bacterioferritin seems to be dispensable for this function. M. tuberculosis lacking ferritin suffers from iron-mediated toxicity, is unable to persist in mice, and, most importantly, is highly susceptible to killing by antibiotics, showing that endogenous oxidative stress can enhance the antibiotic killing of this important pathogen. These results are relevant for the design of new therapeutic strategies against M. tuberculosis.

Helicobacter pylori HP0876 is dispensable for heme-iron acquisition but attenuates bacterial adherence to gastric epithelial cells

Helicobacter pylori can efficiently capture iron either from free heme or heme-containing compounds in the iron-limited gastric mucosa. However, the heme iron utilization systems of H. pylori have not been fully described to date. To investigate the contribution of genes involved in heme-iron utilization, a gene homologous to frpB, encode by hp0876 in H. pylori ATCC 26695, was inactivated by homologous recombination. Δhp0876 showed no demonstrable growth defects in the presence of the various concentrations of free iron. Moreover, when hemoglobin or heme was supplied as the sole iron sources, Δhp0876 had growth curves similar to the wild-type strain. The growth competition experiments in vitro also showed that Δhp0876 retained the ability for iron acquisition. Furthermore, IL-8 production in human gastric epithelial cells co-cultured with Δhp0876 and wild-type strain was compared, and our results indicated that lack of HP0876 affected the IL-8 release. And Δhp0876 exhibited significantly increased adherence to gastric epithelial cells. Together, our data suggests that HP0876 is dispensable for H. pylori heme-iron uptake, but it may attenuate H. pylori adherence to gastric epithelial cells, which induced decreased production of H. pylori-induced IL-8 production in gastric epithelial cells.

Detailed analysis of Helicobacter pylori Fur-regulated promoters reveals a Fur box core sequence and novel Fur-regulated genes

In Helicobacter pylori, iron balance is controlled by the Ferric uptake regulator (Fur), an iron-sensing repressor protein that typically regulates expression of genes implicated in iron transport and storage. Herein, we carried out extensive analysis of Fur-regulated promoters and identified a 7-1-7 motif with dyad symmetry (5'-TAATAATnATTATTA-3'), which functions as the Fur box core sequence of H. pylori. Addition of this sequence to the promoter region of a typically non-Fur regulated gene was sufficient to impose Fur-dependent regulation in vivo. Moreover, mutation of this sequence within Fur-controlled promoters negated regulation. Analysis of the H. pylori chromosome for the occurrence of the Fur box established the existence of well-conserved Fur boxes in the promoters of numerous known Fur-regulated genes, and revealed novel putative Fur targets. Transcriptional analysis of the new candidate genes demonstrated Fur-dependent repression of HPG27_51, HPG27_52, HPG27_199, HPG27_445, HPG27_825 and HPG27_1063, as well as Fur-mediated activation of the cytotoxin associated gene A, cagA (HPG27_507). Furthermore, electrophoretic mobility shift assays confirmed specific binding of Fur to the promoters of each of these genes. Future experiments will determine whether loss of Fur regulation of any of these particular genes contributes to the defects in colonization exhibited by the H. pylori fur mutant.

Iron trafficking system in Helicobacter pylori

Helicobacter pylori infections are closely associated with peptic ulcers, gastric malignancy and iron deficiency anemia. Iron is essential for almost all living organisms and the investigation of iron uptake and trafficking system is thus important to understand the pathological roles of H. pylori. Up to now, the iron trafficking system of H. pylori is not yet fully clear and merits further efforts in this regards. The available information about iron uptake and regulation has been discussed in this concise review, such as FeoB in ferrous transportation, FrpB2 in hemoglobin uptake, HugZ in heme processing, virulence factors (VacA and CagA) in transferrin utilization, Pfr and NapA in iron storage and Fur in iron regulation. The identified iron trafficking system will help us to understand the pathological roles of H. pylori in the various gastric diseases and iron deficiency anemia and stimulates further development of effective anti-bacterial drugs.

Iron storage proteins are essential for the survival and pathogenesis of Mycobacterium tuberculosis in THP-1 macrophages and the guinea pig model of infection

Iron is one of the crucial elements required for the growth of Mycobacterium tuberculosis. However, excess free iron becomes toxic for the cells because it catalyzes the production of reactive oxygen radicals, leading to oxidative damage. Hence, it is essential for the pathogen to have the ability to store intracellular iron in an iron-rich environment and utilize it under iron depletion. M. tuberculosis has two iron storage proteins, namely BfrA (Rv1876; a bacterioferritin) and BfrB (Rv3841; a ferritin-like protein). However, the demonstration of biological significance requires the disruption of relevant genes and the evaluation of the resulting mutant for its ability to survive in the host and cause disease. In this study, we have disrupted bfrA and bfrB of M. tuberculosis and demonstrated that these genes are crucial for the storage and supply of iron for the growth of bacteria and to withstand oxidative stress in vitro. In addition, the bfrA bfrB double mutant (H37Rv ΔbfrA ΔbfrB) exhibited a marked reduction in its ability to survive inside human macrophages. Guinea pigs infected with H37Rv ΔbfrA ΔbfrB exhibited a marked diminution in the dissemination of the bacilli to spleen compared to that of the parental strain. Moreover, guinea pigs infected with H37Rv ΔbfrA ΔbfrB exhibited significantly reduced pathological damage in spleen and lungs compared to that of animals infected with the parental strain. Our study clearly demonstrates the importance of these iron storage proteins in the survival and pathogenesis of M. tuberculosis in the host and establishes them as attractive targets for the development of new inhibitors against mycobacterial infections.

Ulcerogenic Helicobacter pylori strains isolated from children: a contribution to get insight into the virulence of the bacteria

Infection with Helicobacter pylori is the major cause for the development of peptic ulcer disease (PUD). In children, with no other etiology for the disease, this rare event occurs shortly after infection. In these young patients, habits of smoking, diet, consumption of alcohol and non-steroid anti-inflammatory drugs and stress, in addition to the genetic susceptibility of the patient, represent a minor influence. Accordingly, the virulence of the implicated H. pylori strain should play a crucial role in the development of PUD. Corroborating this, our in vitro infection assays comparing a pool of five H. pylori strains isolated from children with PUD to a pool of five other pediatric clinical isolates associated with non-ulcer dyspepsia (NUD) showed the greater ability of PUD strains to induce a marked decrease in the viability of gastric cells and to cause severe damage in the cells cytoskeleton as well as an impairment in the production/secretion of mucins. To uncover virulence features, we compared the proteome of these two groups of H. pylori strains. Two-dimensional gel electrophoresis followed by mass-spectrometry allowed us to detect 27 differentially expressed proteins between them. In addition to the presence of genes encoding well established virulence factors, namely cagA, vacAs1, oipA “on” status, homB and jhp562 genes, the pediatric ulcerogenic strains shared a proteome profile characterized by changes in the abundance of: motility-associated proteins, accounting for higher motility; antioxidant proteins, which may confer increased resistance to inflammation; and enzymes involved in key steps in the metabolism of glucose, amino acids and urea, which may be advantageous to face fluctuations of nutrients. In conclusion, the enhanced virulence of the pediatric ulcerogenic H. pylori strains may result from a synergy between their natural ability to better adapt to the hostile human stomach and the expression of the established virulence factors.

Ferritin structure from Mycobacterium tuberculosis: comparative study with homologues identifies extended C-terminus involved in ferroxidase activity

Ferritins are recognized as key players in the iron storage and detoxification processes. Iron acquisition in the case of pathogenic bacteria has long been established as an important virulence mechanism. Here, we report a 3.0 Å crystal structure of a ferritin, annotated as Bacterioferritin B (BfrB), from Mycobacterium tuberculosis (Mtb), the causative agent of tuberculosis that continues to be one of the world's deadliest diseases. Similar to the other members of ferritin family, the Mtb BfrB subunit exhibits the characteristic fold of a four-helical bundle that possesses the ferroxidase catalytic centre. We compare the structure of Mtb BfrB with representatives of the ferritin family belonging to the archaea, eubacteria and eukarya. Unlike most other ferritins, Mtb BfrB has an extended C-terminus. To dissect the role of this extended C-terminus, truncated Mtb BfrB was purified and biochemical studies implicate this region in ferroxidase activity and iron release in addition to providing stability to the protein. Functionally important regions in a protein of known 3D-structure can be determined by estimating the degree of conservation of the amino-acid sites with its close homologues. Based on the comparative studies, we identify the slowly evolving conserved sites as well as the rapidly evolving variable sites and analyze their role in relation to structure and function of Mtb BfrB. Further, electrostatic computations demonstrate that although the electrostatic environment of catalytic residues is preserved within the family, extensive variability is exhibited by residues defining the channels and pores, in all likelihood keeping up with the diverse functions executed by these ferritins in varied environments.

Proteomannans in biofilm of Helicobacter pylori ATCC 43504

BACKGROUND

  The human bacterial pathogen Helicobacter pylori forms biofilms. However, the constituents of the biofilm have not been extensively investigated. In this study, we analyzed the carbohydrate and protein components of biofilm formed by H. pylori strain ATCC 43504 (NCTC 11637).

MATERIALS AND METHODS

  Development of H. pylori biofilm was analyzed using scanning electron microscopy (SEM) and quantified using crystal violet staining. The extracted extracellular polysaccharide (EPS) matrix was analyzed using GC-MS and nuclear magnetic resonance (NMR) analyses. Proteomic profiles of biofilms were examined by SDS-PAGE while deletion mutants of upregulated biofilm proteins were constructed and characterized.

RESULTS

  Formation of H. pylori biofilm is time dependent as shown by crystal violet staining assay and SEM. NMR reveals the prevalence of 1,4-mannosyl linkages in both developing and mature biofilms. Proteomic analysis of the biofilm indicates the upregulation of neutrophil-activating protein A (NapA) and several stress-induced proteins. Interestingly, the isogenic mutant napA revealed a different biofilm phenotype that showed reduced aggregated colonial structure when compared to the wild type.

CONCLUSIONS

  This in vitro study shows that mannose-related proteoglycans (proteomannans) are involved in the process of H. pylori biofilm formation while the presence of upregulated NapA in the biofilm implies the potency to increase adhesiveness of H. pylori biofilm. Being a complex matrix of proteins and carbohydrates, which are probably interdependent, the H. pylori biofilm could possibly offer a protective haven for the survival of this gastric bacterial pathogen in the extragastric environments.

Change is good: variations in common biological mechanisms in the epsilonproteobacterial genera Campylobacter and Helicobacter

Microbial evolution and subsequent species diversification enable bacterial organisms to perform common biological processes by a variety of means. The epsilonproteobacteria are a diverse class of prokaryotes that thrive in diverse habitats. Many of these environmental niches are labeled as extreme, whereas other niches include various sites within human, animal, and insect hosts. Some epsilonproteobacteria, such as Campylobacter jejuni and Helicobacter pylori, are common pathogens of humans that inhabit specific regions of the gastrointestinal tract. As such, the biological processes of pathogenic Campylobacter and Helicobacter spp. are often modeled after those of common enteric pathogens such as Salmonella spp. and Escherichia coli. While many exquisite biological mechanisms involving biochemical processes, genetic regulatory pathways, and pathogenesis of disease have been elucidated from studies of Salmonella spp. and E. coli, these paradigms often do not apply to the same processes in the epsilonproteobacteria. Instead, these bacteria often display extensive variation in common biological mechanisms relative to those of other prototypical bacteria. In this review, five biological processes of commonly studied model bacterial species are compared to those of the epsilonproteobacteria C. jejuni and H. pylori. Distinct differences in the processes of flagellar biosynthesis, DNA uptake and recombination, iron homeostasis, interaction with epithelial cells, and protein glycosylation are highlighted. Collectively, these studies support a broader view of the vast repertoire of biological mechanisms employed by bacteria and suggest that future studies of the epsilonproteobacteria will continue to provide novel and interesting information regarding prokaryotic cellular biology.

Detailed in vivo analysis of the role of Helicobacter pylori Fur in colonization and disease

Helicobacter pylori persistently colonizes the harsh and dynamic environment of the stomach in over one-half of the world's population and has been identified as a causal agent in a spectrum of pathologies that range from gastritis to invasive adenocarcinoma. The ferric uptake regulator (Fur) is one of the few regulatory proteins that has been identified in H. pylori. Fur regulates genes important for acid acclimation and oxidative stress and has been shown to be important for colonization of H. pylori in both murine and Mongolian gerbil models of infection. To more thoroughly define the role of Fur in vivo, we conducted an extensive temporal analysis of the location of, competitive ability of, and resultant pathology induced by a Deltafur strain in the Mongolian gerbil model of infection and compared the results to results for its wild-type parent. We found that at the earliest time points postinfection, significantly more Deltafur bacteria than wild-type bacteria were recovered. However, this trend was reversed by day 3, when there was significantly increased recovery of the wild-type strain. The increased recovery of the Deltafur strain at 1 day postinfection reflected increased recovery from both the corpus and the antrum of the stomach. When the wild-type strain was allowed to colonize first, the Deltafur strain was unable to compete for colonization at any time postinfection. However, when the Deltafur strain was allowed to colonize first, the wild type efficiently outcompeted the Deltafur strain only at early times postinfection. Finally, we demonstrated that there was a delay in the development and severity of inflammation and pathology of the Deltafur strain in the gastric mucosa even after comparable levels of colonization occurred. Together, these data indicate that H. pylori Fur is most important at early stages of infection and illustrate the importance of the ability of H. pylori to adapt to its constantly fluctuating environment when it is establishing infection, inflammation, and disease.

Iron core mineralisation in prokaryotic ferritins

BACKGROUND

To satisfy their requirement for iron while at the same time countering the toxicity of this highly reactive metal ion, prokaryotes have evolved proteins belonging to two distinct sub-families of the ferritin family: the bacterioferritins (BFRs) and the bacterial ferritins (Ftns). Recently, Ftn homologues have also been identified and characterised in archaeon species. All of these prokaryotic ferritins function by solubilising and storing large amounts of iron in the form of a safe but bio-available mineral.

SCOPE OF REVIEW

The mechanism(s) by which the iron mineral is formed by these proteins is the subject of much current interest. Here we review the available information on these proteins, with particular emphasis on significant advances resulting from recent structural, spectroscopic and kinetic studies.

MAJOR CONCLUSIONS

Current understanding indicates that at least two distinct mechanisms are in operation in prokaryotic ferritins. In one, the ferroxidase centre acts as a true catalytic centre in driving Fe(2+) oxidation in the cavity; in the other, the centre acts as a gated iron pore by oxidising Fe(2+) and transferring the resulting Fe(3+) into the central cavity.

GENERAL SIGNIFICANCE

The prokaryotic ferritins exhibit a wide variation in mechanisms of iron core mineralisation. The basis of these differences lies, at least in part, in structural differences at and around the catalytic centre. However, it appears that more subtle differences must also be important in controlling the iron chemistry of these remarkable proteins.

Proteomics of bacterial pathogenicity: therapeutic implications

Identification of the molecular mechanisms of host-pathogen interaction is becoming a key focus of proteomics. Analysis of these interactions holds promise for significant developments in the identification of new therapeutic strategies to combat infectious diseases, a process that will also benefit parallel improvements in molecular diagnostics, biomarker identification and drug discovery. This review highlights recent advances in functional proteomics initiatives in infectious disease with emphasis on studies undertaken within physiologically relevant parameters that enable identification of the infectious proteome rather than that of the vegetative state. Deciphering the molecular details of what constitutes physiologically relevant host-pathogen interactions remains an underdeveloped aspect of research into infectious disease. The magnitude of this deficit will be largely influenced by the ease with which model systems can be established to investigate such interactions. As the selective pressures exerted by the host on an infecting pathogen are numerous, the adequacy of certain model systems should be considered carefully.

Upregulation of a non-heme iron-containing ferritin with dual ferroxidase and DNA-binding activities in Helicobacter pylori under acid stress

Helicobacter pylori is a spiral Gram-negative microaerophilic bacterium. It is unique and distinctive among various bacterial pathogens for its ability to persist in the extreme acidic environment of human stomachs. To address and identify changes in the proteome of H. pylori in response to low pH, we have used a proteomic approach to study the protein expression of H. pylori under neutral (pH 7) and acidic (pH 5) conditions. Global protein-expression profiles of H. pylori under acid stress were analysed by two-dimensional polyacrylamide gel electrophoresis (2-DE) followed by liquid chromatography (LC)-nanoESI-mass spectrometry (MS)/MS and bioinformatics database analysis. Among the proteins differentially expressed under acidic condition, a non-heme iron-containing ferritin of H. pylori (HP-ferritin) was found to be consistently upregulated at pH 5 as compared to pH 7. It was also found that HP-ferritin can switch from an iron-storage protein with ferroxidase activity to a DNA-binding/protection function under in vitro conditions upon exposure to acidic environment. Prokaryotic ferritins, such as non-heme iron-binding HP-ferritin with dual functionality reported herein, may play a significant urease-independent role in the acid adaptation of H. pylori under physiological conditions in vivo.

Crystallization and preliminary X-ray diffraction analysis of the truncated cytosolic domain of the iron transporter FeoB

FeoB-family proteins are widely distributed in bacteria and archaea and are involved in high-affinity Fe(2+) uptake through the plasma membrane. FeoB consists of an N-terminal cytosolic region followed by a C-terminal transmembrane region. The cytosolic region contains small GTPase and GDP dissociation inhibitor-like domains, which serve a regulatory function. The truncated cytosolic region of the iron transporter FeoB from Thermotoga maritima was overexpressed, purified and crystallized. Four native or SeMet crystal forms in a nucleotide-free state or in complex with either GDP or GMPPNP diffracted to resolutions of between 1.5 and 2.1 A.

Synergistic effect of imp/ostA and msbA in hydrophobic drug resistance of Helicobacter pylori

Background

Contamination of endoscopy equipment by Helicobacter pylori (H. pylori) frequently occurs after endoscopic examination of H. pylori-infected patients. In the hospital, manual pre-cleaning and soaking in glutaraldehyde is an important process to disinfect endoscopes. However, this might not be sufficient to remove H. pylori completely, and some glutaraldehyde-resistant bacteria might survive and be passed to the next patient undergoing endoscopic examination through unidentified mechanisms. We identified an Imp/OstA protein associated with glutaraldehyde resistance in a clinical strain, NTUH-C1, from our previous study. To better understand and manage the problem of glutaraldehyde resistance, we further investigated its mechanism.

Results

The minimal inhibitory concentrations (MICs) of glutaraldehyde andexpression of imp/ostA RNA in 11 clinical isolates from the National Taiwan University Hospital were determined. After glutaraldehyde treatment, RNA expression in the strains with the MICs of 4–10 μg/ml was higher than that in strains with the MICs of 1–3 μg/ml. We examined the full-genome expression of strain NTUH-S1 after glutaraldehyde treatment using a microarray and found that 40 genes were upregulated and 31 genes were downregulated. Among the upregulated genes, imp/ostA and msbA, two putative lipopolysaccharide biogenesis genes, were selected for further characterization. The sensitivity to glutaraldehyde or hydrophobic drugs increased in both of imp/ostA and msbA single mutants. The imp/ostA and msbA double mutant was also hypersensitive to these chemicals. The lipopolysaccharide contents decreased in individual imp/ostA and msbA mutants and dramatically reduced in the imp/ostA and msbA double mutant. Outer membrane permeability assay demonstrated that the imp/ostA and msbA double mutation resulted in the increase of outer membrane permeability. Ethidium bromide accumulation assay demonstrated that MsbA was involved in efflux of hydrophobic drugs.

Conclusion

The expression levels of imp/ostA and msbA were correlated with glutaraldehyde resistance in clinical isolates after glutaraldehyde treatment. Imp/OstA and MsbA play a synergistic role in hydrophobic drugs resistance and lipopolysaccharide biogenesis in H. pylori.

orf4 of the Bacillus cereus sigB gene cluster encodes a general stress-inducible Dps-like bacterioferritin

The function of orf4 in the sigB cluster in Bacillus cereus ATCC 14579 remains to be explored. Amino-acid sequence analysis has revealed that Orf4 is homologous with bacterioferritins and Dps. In this study, we generated an orf4-null mutant and produced recombinant protein rOrf4 to establish the role of orf4. In vitro, the purified rOrf4 was found to exist in two distinct forms, a dimeric form and a polymer form, through size exclusion analysis. The latter form exhibited a unique filament structure, in contrast to the typical spherical tetracosamer structure of bacterioferritins; the former can be induced to form rOrf4 polymers immediately after the addition of FeCl(2). Catalysis of the oxidation of ferrous irons by ferroxidase activity was detected with rOrf4, and the mineralized irons were subsequently sequestered only in the rOrf4 polymer. Moreover, rOrf4 exerted DNA-protective activity against oxidative damage via DNA binding in a nonspecific manner, as is seen with Dps. In vivo, deletion of orf4 had no effect on activation of the alternative sigma factor sigma(B), and therefore, orf4 is not associated with sigma(B) regulation; however, orf4 can be significantly upregulated upon environmental stress but not H(2)O(2) treatment. B. cereus strains with constitutive Orf4 expression exhibited a viability higher than that of the orf4-null mutant, under specific oxidative stress or heat shock. Taken together, these results suggest that Orf4 functions as a Dps-like bacterioferritin in response to environmental stress and can provide cell protection from oxidative damage through iron sequestration and DNA binding.

The crystal structure of ferritin from Helicobacter pylori reveals unusual conformational changes for iron uptake

The crystal structure of recombinant ferritin from Helicobacter pylori has been determined in its apo, low-iron-bound, intermediate, and high-iron-bound states. Similar to other members of the ferritin family, the bacterial ferritin assembles as a spherical protein shell of 24 subunits, each of which folds into a four-alpha-helix bundle. Significant conformational changes were observed at the BC loop and the entrance of the 4-fold symmetry channel in the intermediate and high-iron-bound states, whereas no change was found in the apo and low-iron-bound states. The imidazole rings of His149 at the channel entrance undergo conformational changes that bear resemblance to heme configuration and are directly coupled to axial translocation of Fe ions through the 4-fold channel. Our results provide the first structural evidence of the translocation of Fe ions through the 4-fold channel in prokaryotes and the transition from a protein-dominated process to a mineral-surface-dominated process during biomineralization.

Controlled, household-randomized, open-label trial of the effect of treatment of Helicobacter pylori infection on iron deficiency among children in rural Alaska: results at 40 months

BACKGROUND

Helicobacter pylori infection treatment was found not to reduce the prevalence of iron deficiency or anemia among Alaska Native children at 14 months after treatment initiation. We hypothesized that 14 months was to early to resolve H. pylori-induced gastric damage. Consequently, we conducted a 40-month follow-up.

METHODS

We enrolled 219 children 7-11 years old who had H. pylori infection (as diagnosed by (13)C-labeled urea breath test) and iron deficiency (serum ferritin level, <22.47 pmol/L) in a controlled, household-randomized trial of the effect of treatment of H. pylori on iron deficiency and anemia (hemoglobin level, <115 g/L). At 40 months, 176 children were evaluated.

RESULTS

Forty-four (52%) of 85 children in the intervention group and 53 (58%) of 91 in the control group had iron deficiency (adjusted relative risk [ARR], 0.92 [95% confidence interval {CI}, 0.68-1.26]), versus 4 (5%) and 17(19%), respectively, with both iron deficiency and anemia (ARR, 0.25 [95% CI, 0.09-0.73]). Reinfection occurred among 33 (52%) of 64 children who had cleared their infection. H. pylori-negative children had lower prevalences of iron deficiency (ARR, 0.62 [95% CI, 0.38-1.01]) and iron deficiency and anemia (ARR, 0.22 [95% CI, 0.03-1.50]), compared with H. pylori -positive children.

CONCLUSIONS

The resolution of H. pylori infection for >14 months modestly reduced the prevalence of iron deficiency and substantially reduced the prevalence of iron deficiency and anemia. H. pylori likely plays a casual role in hematological outcomes for some children.

Functional identification of HugZ, a heme oxygenase from Helicobacter pylori

Background

Iron is recognized as an important trace element, essential for most organisms including pathogenic bacteria. HugZ, a protein related to heme iron utilization, is involved in bacterial acquisition of iron from the host. We previously observed that a hugZ homologue is correlated with the adaptive colonization of Helicobacter pylori (H. pylori), a major gastro-enteric pathogen. However, its exact physiological role remains unclear.

Results

A gene homologous to hugZ, designated hp0318, identified in H. pylori ATCC 26695, exhibits 66% similarity to cj1613c of Campylobacter jejuni NCTC 11168. Soluble 6 × His fused-HugZ protein was expressed in vitro. Hemin-agrose affinity analysis indicated that the recombinant HugZ protein can bind to hemin. Absorption spectroscopy at 411 nm further revealed a heme:HugZ binding ratio of 1:1. Enzymatic assays showed that purified recombinant HugZ protein can degrade hemin into biliverdin and carbon monoxide in the presence of either ascorbic acid or NADPH and cytochrome P450 reductase. The biochemical and enzymatic characteristics agreed closely with those of Campylobacter jejuni Cj1613c protein, implying that hp0318 is a functional member of the HugZ family. A hugZ deletion mutant was obtained by homologous recombination. This mutant strain showed poor growth when hemoglobin was provided as the source of iron, partly because of its failure to utilize hemoglobin efficiently. Real-time quantitative PCR also confirmed that the expression of hugZ was regulated by iron levels.

Conclusion

These findings provide biochemical and genetic evidence that hugZ (hp0318) encodes a heme oxygenase involved in iron release/uptake in H. pylori.

Proteomic analysis of Helicobacter pylori cellular proteins fractionated by ammonium sulfate precipitation

Among 1590 ORFs in the Helicobacter pylori genome, >250 have been identified as authentic genes by proteomic analysis. Low-abundance proteins need to be enriched to a minimal amount for MALDI-TOF analysis and salt precipitation has generally been used for protein enrichment. Here, a whole-cell extract of H. pylori strain 26695 was subjected to protein fractionation with stepwise concentrations of ammonium sulfate and the proteins were displayed by 2-DE. The protein spots were quantified using PDQUEST software and identified by peptide fingerprinting. The 2-DE profiles and intensities of individual protein spots differed among the protein fractions. Out of the 98 identified proteins, 61 were found in the stepwise ammonium sulfate fractions but not in the whole-cell extract. Out of these, 37 proteins, including KdsA, were found exclusively in a single fraction. In contrast, GroEL, UreA, UreB, TrxA, NapA, and FldA were ubiquitously present in all fractions. Iron-containing proteins such as NapA, SodB, CeuE, and Pfr were found predominantly in the 100% saturated ammonium sulfate precipitate. Additionally, 29 proteins were newly identified in this study. These data will facilitate the preparation of significant H. pylori proteins, as well as provide information about low-abundance proteins.

The pathogenesis of Helicobacter pylori-induced gastro-duodenal diseases

Helicobacter pylori is the main cause of peptic ulceration, distal gastric adenocarcinoma, and gastric lymphoma. Only 15% of those colonized develop disease, and pathogenesis depends upon strain virulence, host genetic susceptibility, and environmental cofactors. Virulence factors include the cag pathogenicity island, which induces proinflammatory, pro-proliferative epithelial cell signaling; the cytotoxin VacA, which causes epithelial damage; and an adhesin, BabA. Host genetic polymorphisms that lead to high-level pro-inflammatory cytokine release in response to infection increase cancer risk. Pathogenesis is dependent upon inflammation, a Th-1 acquired immune response and hormonal changes including hypergastrinaemia. Antral-predominant inflammation leads to increased acid production from the uninflamed corpus and predisposes to duodenal ulceration; corpus-predominant gastritis leads to hypochlorhydria and predisposes to gastric ulceration and adenocarcinoma. Falling prevalence of H. pylori in developed countries has led to a falling incidence of associated diseases. However, whether there are disadvantages of an H. pylori-free stomach, for example increased risk of esosphageal adenocarcinoma, remains unclear.

Early influences and childhood development. Does helicobacter play a role?

In the late 1960s, Rene Dubos showed that a variety of nutritional stress in utero or in early infancy could have dramatic impact on childhood development that was irreversible. This included detectable changes in the brain. Since that time, iron deficiency anemia (IDA) has been identified as one of the major nutritional stresses that leads to permanent behavioral changes in both experimental animals and humans resulting in poorer cognitive, motor, and social-emotional function. It has been proposed that these changes play an important part in the inter-generational transmission of poverty. More recently, it is becoming clear that Helicobacter pylori causes IDA in populations on an iron-limiting diet. The main thesis of this article is that H. pylori infection may indeed have an impact on childhood development and that much more research is needed in this area as intervention via immunization or antimicrobial therapy in populations in the developing world may have major positive benefits via cure of IDA and prevention of brain damage in the young.

The role of ferritins in the physiology of Salmonella enterica sv. Typhimurium: a unique role for ferritin B in iron-sulphur cluster repair and virulence

Ferritins are ubiquitous iron (Fe) storage proteins that play a fundamental role in cellular Fe homeostasis. The enteric pathogen Salmonella enterica serovar Typhimurium possesses four ferritins: bacterioferritin, ferritin A, ferritin B and Dps. The haem-containing bacterioferritin (Bfr) accounts for the majority of stored Fe, followed by ferritin A (FtnA). Inactivation of bfr elevates the intracellular free Fe concentration and enhances susceptibility to H2O2 stress. The DNA-binding Dps protein provides protection from oxidative damage without affecting the steady-state intracellular free Fe concentration. FtnB appears to be particularly important for the repair of oxidatively damaged Fe-sulphur clusters of aconitase and, in contrast to Bfr and FtnA, is required for Salmonella virulence in mice. Moreover, ftnB and dps are repressed by the Fe-responsive regulator Fur and induced under conditions of Fe limitation, whereas bfr and ftnA are maximally expressed when Fe is abundant. The absence of a conserved ferroxidase domain and the potentiation of oxidative stress by FtnB in some strains lacking Dps suggest that FtnB serves as a facile cellular reservoir of Fe2+.

Agrobacterium tumefaciens fur has important physiological roles in iron and manganese homeostasis, the oxidative stress response, and full virulence

In Agrobacterium tumefaciens, the balance between acquiring enough iron and avoiding iron-induced toxicity is regulated in part by Fur (ferric uptake regulator). A fur mutant was constructed to address the physiological role of the regulator. Atypically, the mutant did not show alterations in the levels of siderophore biosynthesis and the expression of iron transport genes. However, the fur mutant was more sensitive than the wild type to an iron chelator, 2,2'-dipyridyl, and was also more resistant to an iron-activated antibiotic, streptonigrin, suggesting that Fur has a role in regulating iron concentrations. A. tumefaciens sitA, the periplasmic binding protein of a putative ABC-type iron and manganese transport system (sitABCD), was strongly repressed by Mn(2+) and, to a lesser extent, by Fe(2+), and this regulation was Fur dependent. Moreover, the fur mutant was more sensitive to manganese than the wild type. This was consistent with the fact that the fur mutant showed constitutive up-expression of the manganese uptake sit operon. Fur(At) showed a regulatory role under iron-limiting conditions. Furthermore, Fur has a role in determining oxidative resistance levels. The fur mutant was hypersensitive to hydrogen peroxide and had reduced catalase activity. The virulence assay showed that the fur mutant had a reduced ability to cause tumors on tobacco leaves compared to wild-type NTL4.

Potential role of thiol:disulfide oxidoreductases in the pathogenesis ofHelicobacter pylori

Helicobacter pylori infections are responsible for a sequence of molecular events which ultimately result in the development of gastric diseases. The pathogenesis of H. pylori has been studied extensively with strong focus on the identification of virulence factors. In contrast, the involvement of thiol:disulfide oxidoreductases in bacterial pathogenesis is less well understood. This paper provides a review of the current knowledge of H. pylori putative thiol:disulfide oxidoreductases, and their potential role in promoting virulence and colonization. Several bioinformatic analyses served to complete the information on these oxidoreductases of H. pylori.

Metal-responsive gene regulation and metal transport in Helicobacter species

Helicobacter species are among the most successful colonizers of the mammalian gastrointestinal and hepatobiliary tract. Colonization is usually lifelong, indicating that Helicobacter species have evolved intricate mechanisms of dealing with stresses encountered during colonization of host tissues, like restriction of essential metal ions. The recent availability of genome sequences of the human gastric pathogen Helicobacter pylori, the murine enterohepatic pathogen Helicobacter hepaticus and the unannotated genome sequence of the ferret gastric pathogen Helicobacter mustelae has allowed for comparative genome analyses. In this review we present such analyses for metal transporters, metal-storage and metal-responsive regulators in these three Helicobacter species, and discuss possible contributions of the differences in metal metabolism in adaptation to the gastric or enterohepatic niches occupied by Helicobacter species.