Identification, characterization, and spatial localization of two flagellin species in Helicobacter pylori flagella

Transcription Regulation of Flagellins: A Structural Perspective

Bacterial flagella are complex molecular motors that are essential for locomotion and host colonization. They consist of 30 different proteins expressed in varying stoichiometries. Their assembly and function are governed by a hierarchical transcriptional regulatory network with multiple checkpoints primarily regulated by sigma factors. Expression of late flagellar genes requires the complete assembly of the flagellar basal body and hook. The extracellular segment of the flagellum, termed filament, is composed of self-assembling flagellin subunits encoded by the fliC gene and harbors potent antigenic epitopes. Structural studies have illuminated the molecular mechanisms underlying its assembly and its regulation at the transcription level. σ28, a key subunit of the RNA polymerase complex, binds to specific promoter sequences to initiate transcription of late flagellar genes, while its activity is controlled by the antisigma factor FlgM. This review summarizes current insights into the structural characterization of flagellins across various bacterial species, their transcription by σ28, and the structural mechanism controlling σ28 activity through FlgM. Additionally, we highlight the regulation of flagellin gene expression via transcription factors and their post-transcriptional regulation, providing a comprehensive overview of the intricate mechanisms that support bacterial motility and adaptation.

How Long Will It Take to Launch an Effective Helicobacter pylori Vaccine for Humans?

Helicobacter pylori infection often occurs in early childhood, and can last a lifetime if not treated with medication. H. pylori infection can also cause a variety of stomach diseases, which can only be treated with a combination of antibiotics. Combinations of antibiotics can cure H. pylori infection, but it is easy to relapse and develop drug resistance. Therefore, a vaccine is a promising strategy for prevention and therapy for the infection of H. pylori. After decades of research and development, there has been no appearance of any H. pylori vaccine reaching the market, unfortunately. This review summarizes the aspects of candidate antigens, immunoadjuvants, and delivery systems in the long journey of H. pylori vaccine research, and also introduces some clinical trials that have displayed encouraging or depressing results. Possible reasons for the inability of an H. pylori vaccine to be available over the counter are cautiously discussed and some propositions for the future of H. pylori vaccines are outlined.

Transcriptional and functional characterizations of multiple flagellin genes in spirochetes

The flagellar filament is a helical propeller for bacterial locomotion. In external flagellates, the filaments are mostly homopolymers of a single flagellin protein. By contrast, the flagellar filaments of spirochetes are mostly heteropolymers of multiple flagellin proteins. This report seeks to investigate the role of multiple flagellin proteins using the oral spirochete Treponema denticola as a model. First, biochemical and genetic studies uncover that the flagellar filaments of T. denticola mainly comprise four proteins, FlaA, FlaB1, FlaB2, and FlaB3, in a defined stoichiometry. Second, transcriptional analyses reveal that the genes encoding these four proteins are regulated by two different transcriptional factors, sigma28 and sigma70 . Third, loss-of-function studies demonstrate that each individual flagellin protein contributes to spirochete motility, but none of them is absolutely required. Last, we provide genetic and structural evidence that FlaA forms a "seam"-like structure around the core and that deletion of individual flagellin protein alters the flagellar homeostasis. Collectively, these results demonstrate that T. denticola has evolved a unique mechanism to finely regulate its flagellar filament gene expression and assembly which renders the organelle with the right number, shape, strength, and structure for its distinct motility.

Molecular Characterization of Three Tandemly Located Flagellin Genes of Stenotrophomonas maltophilia

Stenotrophomonas maltophilia is a motile, opportunistic pathogen. The flagellum, which is involved in swimming, swarming, adhesion, and biofilm formation, is considered a virulence factor for motile pathogens. Three flagellin genes, fliC1, fliC2, and fliC3, were identified from the sequenced S. maltophilia genome. FliC1, fliC2, and fliC3 formed an operon, and their encoding proteins shared 67–82% identity. Members of the fliC1C2C3 operon were deleted individually or in combination to generate single mutants, double mutants, and a triple mutant. The contributions of the three flagellins to swimming, swarming, flagellum morphology, adhesion, and biofilm formation were assessed. The single mutants generally had a compromise in swimming and no significant defects in swarming, adhesion on biotic surfaces, and biofilm formation on abiotic surfaces. The double mutants displayed obvious defects in swimming and adhesion on abiotic and biotic surfaces. The flagellin-null mutant lost swimming ability and was compromised in adhesion and biofilm formation. All tested mutants demonstrated substantial but different flagellar morphologies, supporting that flagellin composition affects filament morphology. Bacterial swimming motility was significantly compromised under an oxidative stress condition, irrespective of flagellin composition. Collectively, the utilization of these three flagellins for filament assembly equips S. maltophilia with flagella adapted to provide better ability in swimming, adhesion, and biofilm formation for its pathogenesis.

Under the Radar: Strategies Used by Helicobacter pylori to Evade Host Responses

The body depends on its physical barriers and innate and adaptive immune responses to defend against the constant assault of potentially harmful microbes. In turn, successful pathogens have evolved unique mechanisms to adapt to the host environment and manipulate host defenses. Helicobacter pylori (Hp), a human gastric pathogen that is acquired in childhood and persists throughout life, is an example of a bacterium that is very successful at remodeling the host-pathogen interface to promote a long-term persistent infection. Using a combination of secreted virulence factors, immune subversion, and manipulation of cellular mechanisms, Hp can colonize and persist in the hostile environment of the human stomach. Here, we review the most recent and relevant information regarding how this successful pathogen overcomes gastric epithelial host defense responses to facilitate its own survival and establish a chronic infection. Expected final online publication date for the Annual Review of Physiology, Volume 84 is February 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Bacterial Flagellar Filament: A Supramolecular Multifunctional Nanostructure

The bacterial flagellum is a complex and dynamic nanomachine that propels bacteria through liquids. It consists of a basal body, a hook, and a long filament. The flagellar filament is composed of thousands of copies of the protein flagellin (FliC) arranged helically and ending with a filament cap composed of an oligomer of the protein FliD. The overall structure of the filament core is preserved across bacterial species, while the outer domains exhibit high variability, and in some cases are even completely absent. Flagellar assembly is a complex and energetically costly process triggered by environmental stimuli and, accordingly, highly regulated on transcriptional, translational and post-translational levels. Apart from its role in locomotion, the filament is critically important in several other aspects of bacterial survival, reproduction and pathogenicity, such as adhesion to surfaces, secretion of virulence factors and formation of biofilms. Additionally, due to its ability to provoke potent immune responses, flagellins have a role as adjuvants in vaccine development. In this review, we summarize the latest knowledge on the structure of flagellins, capping proteins and filaments, as well as their regulation and role during the colonization and infection of the host.

Identification and characterization of the proteolytic flagellin from the common freshwater bacterium Hylemonella gracilis

Flagellins are the protein components of bacterial flagella and assemble in up to 20,000 copies to form extracellular flagellar filaments. An unusual family of flagellins was recently discovered that contains a unique metalloprotease domain within its surface-exposed hypervariable region. To date, these proteolytic flagellins (also termed flagellinolysins) have only been characterized in the Gram-positive organism Clostridium haemolyticum, where flagellinolysin was shown to be proteolytically active and capable of cleaving extracellular protein substrates. The biological function of flagellinolysin and its activity in other organisms, however, remain unclear. Here, using molecular biochemistry and proteomics, we have performed an initial characterization of a novel flagellinolysin identified from Hylemonella gracilis, a Gram-negative organism originally isolated from pond water. We demonstrate that H. gracilis flagellinolysin (HgrFlaMP) is an active calcium-dependent zinc metallopeptidase and characterize its cleavage specificity profile using both trypsin and GluC-derived peptide libraries and protein substrates. Based on high-throughput degradomic assays, HgrFlaMP cleaved 784 unique peptides and displayed a cleavage site specificity similar to flagellinolysin from C. haemolyticum. Additionally, by using a set of six protein substrates, we identified 206 protein-embedded cleavage sites, further refining the substrate preference of HgrFlaMP, which is dominated by large hydrophobic amino acids in P1', and small hydrophobic or medium-sized polar residues on the amino-terminal side of the scissile bond. Intriguingly, recombinant HgrFlaMP was also capable of cleaving full-length flagellins from another species, suggesting its potential involvement in interbacterial interactions. Our study reports the first experimentally characterized proteolytic flagellin in a Gram-negative organism, and provides new insights into flagellum-mediated enzymatic activity.

Specificity in glycosylation of multiple flagellins by the modular and cell cycle regulated glycosyltransferase FlmG

How specificity is programmed into post-translational modification of proteins by glycosylation is poorly understood, especially for O-linked glycosylation systems. Here we reconstitute and dissect the substrate specificity underpinning the cytoplasmic O-glycosylation pathway that modifies all six flagellins, five structural and one regulatory paralog, in Caulobacter crescentus, a monopolarly flagellated alpha-proteobacterium. We characterize the biosynthetic pathway for the sialic acid-like sugar pseudaminic acid and show its requirement for flagellation, flagellin modification and efficient export. The cognate NeuB enzyme that condenses phosphoenolpyruvate with a hexose into pseudaminic acid is functionally interchangeable with other pseudaminic acid synthases. The previously unknown and cell cycle-regulated FlmG protein, a defining member of a new class of cytoplasmic O-glycosyltransferases, is required and sufficient for flagellin modification. The substrate specificity of FlmG is conferred by its N-terminal flagellin-binding domain. FlmG accumulates before the FlaF secretion chaperone, potentially timing flagellin modification, export, and assembly during the cell division cycle.

Propulsive nanomachines: the convergent evolution of archaella, flagella and cilia

Echoing the repeated convergent evolution of flight and vision in large eukaryotes, propulsive swimming motility has evolved independently in microbes in each of the three domains of life. Filamentous appendages – archaella in Archaea, flagella in Bacteria and cilia in Eukaryotes – wave, whip or rotate to propel microbes, overcoming diffusion and enabling colonization of new environments. The implementations of the three propulsive nanomachines are distinct, however: archaella and flagella rotate, while cilia beat or wave; flagella and cilia assemble at their tips, while archaella assemble at their base; archaella and cilia use ATP for motility, while flagella use ion-motive force. These underlying differences reflect the tinkering required to evolve a molecular machine, in which pre-existing machines in the appropriate contexts were iteratively co-opted for new functions and whose origins are reflected in their resultant mechanisms. Contemporary homologies suggest that archaella evolved from a non-rotary pilus, flagella from a non-rotary appendage or secretion system, and cilia from a passive sensory structure. Here, we review the structure, assembly, mechanism and homologies of the three distinct solutions as a foundation to better understand how propulsive nanomachines evolved three times independently and to highlight principles of molecular evolution.

Spatial arrangement of several flagellins within bacterial flagella improves motility in different environments

Bacterial flagella are helical proteinaceous fibers, composed of the protein flagellin, that confer motility to many bacterial species. The genomes of about half of all flagellated species include more than one flagellin gene, for reasons mostly unknown. Here we show that two flagellins (FlaA and FlaB) are spatially arranged in the polar flagellum of Shewanella putrefaciens, with FlaA being more abundant close to the motor and FlaB in the remainder of the flagellar filament. Observations of swimming trajectories and numerical simulations demonstrate that this segmentation improves motility in a range of environmental conditions, compared to mutants with single-flagellin filaments. In particular, it facilitates screw-like motility, which enhances cellular spreading through obstructed environments. Similar mechanisms may apply to other bacterial species and may explain the maintenance of multiple flagellins to form the flagellar filament.

Cross-kymography analysis to simultaneously quantify the function and morphology of the archaellum

In many microorganisms helical structures are important for motility, e.g., bacterial flagella and kink propagation in Spiroplasma eriocheiris. Motile archaea also form a helical-shaped filament called the ‘archaellum’ that is functionally equivalent to the bacterial flagellum, but structurally resembles type IV pili. The archaellum motor consists of 6–8 proteins called fla accessory genes, and the filament assembly is driven by ATP hydrolysis at catalytic sites in FlaI. Remarkably, previous research using a dark-field microscopy showed that right-handed filaments propelled archaeal cells forwards or backwards by clockwise or counterclockwise rotation, respectively. However, the shape and rotational rate of the archaellum during swimming remained unclear, due to the low signal and lack of temporal resolution. Additionally, the structure and the motor properties of the archaellum and bacterial flagellum have not been precisely determined during swimming because they move freely in three-dimensional space. Recently, we developed an advanced method called “cross-kymography analysis”, which enables us to be a long-term observation and simultaneously quantify the function and morphology of helical structures using a total internal reflection fluorescence microscope. In this review, we introduce the basic idea of this analysis, and summarize the latest information in structural and functional characterization of the archaellum motor.

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

BACKGROUND

Flagellar motility of Helicobacter pylori has been shown to be important for the bacteria to establish initial colonization. The ferric uptake regulator (Fur) is a global regulator that has been identified in H. pylori which is involved in the processes of iron uptake and establishing colonization. However, the role of Fur in H. pylori motility is still unclear.

MATERIALS AND METHODS

Motility of the wild-type, fur mutant, and fur revertant J99 were determined by a soft-agar motility assay and direct video observation. The bacterial shape and flagellar structure were evaluated by transmission electron microscopy. Single bacterial motility and flagellar switching were observed by phase-contrast microscopy. Autoinducer-2 (AI-2) production in bacterial culture supernatant was analyzed by a bioluminescence assay.

RESULTS

The fur mutant showed impaired motility in the soft-agar assay compared with the wild-type J99 and fur revertant. The numbers and lengths of flagellar filaments on the fur mutant cells were similar to those of the wild-type and revertant cells. Phenotypic characterization showed similar swimming speed but reduction in switching rate in the fur mutant. The AI-2 production of the fur mutant was dramatically reduced compared with wild-type J99 in log-phase culture medium.

CONCLUSIONS

These results indicate that Fur positively modulates H. pylori J99 motility through interfering with bacterial flagellar switching.

The Helicobacter pylori J99 jhp0106 Gene, under the Control of the CsrA/RpoN Regulatory System, Modulates Flagella Formation and Motility

CsrA has been shown to positively control the expression of flagella-related genes, including flaA and flaB, through regulating expression of an alternative sigma factor RpoN in Helicobacter pylori J99. Here, we aimed to characterize the CsrA regulatory system by comparative transcriptomic analysis carried out with RNA-seq on strain J99 and a csrA mutant. Fifty-three genes in the csrA mutant were found to be differentially expressed compared with the wild-type. Among CsrA-regulated genes, jhp0106, with unclear function, was found located downstream of flaB in the J99 genome. We hypothesized that flaB-jhp0106 is in an operon under the control of RpoN binding to the flaB promoter. The RT-qPCR results showed the expression of jhp0106 was decreased 76 and 92% in the csrA and rpoN mutants, respectively, compared to the wild-type. Moreover, mutations of the RpoN binding site in the flaB promoter region resulted in decreased expression of flaB and jhp0106 and deficient motility. Three-dimensional structure modeling results suggested that Jhp0106 was a glycosyltransferase. The role of jhp0106 in H. pylori was further investigated by constructing the jhp0106 mutant and revertant strains. A soft-agar motility assay and transmission electron microscope were used to determine the motility and flagellar structure of examined strains, and the results showed the loss of motility and flagellar structure in jhp0106 mutant J99. In conclusion, we found jhp0106, under the control of the CsrA/RpoN regulatory system, plays a critical role in H. pylori flagella formation.

The Cell Shape-determining Csd6 Protein from Helicobacter pylori Constitutes a New Family of L,D-Carboxypeptidase

Helicobacter pylori causes gastrointestinal diseases, including gastric cancer. Its high motility in the viscous gastric mucosa facilitates colonization of the human stomach and depends on the helical cell shape and the flagella. In H. pylori, Csd6 is one of the cell shape-determining proteins that play key roles in alteration of cross-linking or by trimming of peptidoglycan muropeptides. Csd6 is also involved in deglycosylation of the flagellar protein FlaA. To better understand its function, biochemical, biophysical, and structural characterizations were carried out. We show that Csd6 has a three-domain architecture and exists as a dimer in solution. The N-terminal domain plays a key role in dimerization. The middle catalytic domain resembles those of l,d-transpeptidases, but its pocket-shaped active site is uniquely defined by the four loops I to IV, among which loops I and III show the most distinct variations from the known l,d-transpeptidases. Mass analyses confirm that Csd6 functions only as an l,d-carboxypeptidase and not as an l,d-transpeptidase. The d-Ala-complexed structure suggests possible binding modes of both the substrate and product to the catalytic domain. The C-terminal nuclear transport factor 2-like domain possesses a deep pocket for possible binding of pseudaminic acid, and in silico docking supports its role in deglycosylation of flagellin. On the basis of these findings, it is proposed that H. pylori Csd6 and its homologs constitute a new family of l,d-carboxypeptidase. This work provides insights into the function of Csd6 in regulating the helical cell shape and motility of H. pylori.

CsrA regulates Helicobacter pylori J99 motility and adhesion by controlling flagella formation

BACKGROUND

Motility mediated by the flagella of Helicobacter pylori has been shown to be required for normal colonization and is thought to be important for the bacteria to move toward the gastric mucus in niches adjacent to the epithelium. Barnard et al. showed that CsrA appears to be necessary for full motility and the ability to infect mice, but its mechanism of regulation is still unclear.

METHODS

Motility and cell adhesion ability were determined in wild-type, csrA mutant, and revertant J99 strains. The bacterial shape and flagellar structure were evaluated by transmission electron microscopy. The expression of two major flagellins, flaA/flaB, and the alternative sigma factor rpoN (σ(54)) were determined by real-time quantitative RT-PCR and Western blot.

RESULTS

The csrA mutant showed loss of motility and lower adhesion ability compared with the wild-type and revertant J99 strains. The csrA mutant was not flagellated. Transcription of flaA and flaB mRNA decreased to only 40% and 16%, respectively, in the csrA mutant compared with the wild-type J99 (p = .006 and <.0001, respectively), and Western blot analysis showed dramatically reduced FlaA/FlaB proteins in a csrA mutant. The disruption of csrA also decreased expression of rpoN to 48% in the csrA mutant, but the degradation rate of rpoN mRNA was not changed.

CONCLUSION

These results suggest that CsrA regulates H. pylori J99 flagella formation and thereby affects bacterial motility.

Isolation and characterization of flagellar filaments from Bacillus cereus ATCC 14579

Isolated flagellar filaments from the type strain of Bacillus cereus, ATCC 14579, were shown to consist of 34, 32 and 31 kDa proteins in similar proportions as judged by band intensities on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The N-terminal amino acid sequences of these three proteins of strain ATCC 14579 were identical with the deduced sequences of three flagellin genes BC1657, BC1658 and BC1659 in the whole genome sequence. Strain ATCC 14579 was classified into serotype T2 by a flagellar serotyping scheme for B. cereus strains that are untypeable into known flagellar serotypes H1 to H23. Flagellar filaments from a reference strain of serotype T2 contained two protein bands at 34 and 32 kDa, but a single protein band at 39 kDa was detected in flagellar filaments of a reference strain of serotype H1. Two murine monoclonal antibodies, 1A5 and 2A5, which recognize both the 34 and 32 kDa flagellins and a single flagellin of 32 kDa, respectively, were specifically reactive with B. cereus strains ATCC 14579 and serotype T2 in whole-cell ELISA and bacterial motility inhibition tests. In immunoelectron microscopy with monoclonal antibodies 1A5 and 2A5, colloidal gold spheres were shown to localize almost evenly over the entire part of flagellar filaments. Since strain ATCC 14579, and presumably strain serotype T2, are unusual among B. cereus strains in possessing multiple genes that encode flagellin subunits, a possible unique mechanism may contribute to assembly of multiple flagellin subunits into the filament over its entire length.

The renaissance of bacillosamine and its derivatives: pathway characterization and implications in pathogenicity

Prokaryote-specific sugars, including N,N′-diacetylbacillosamine (diNAcBac) and pseudaminic acid, have experienced a renaissance in the past decade because of their discovery in glycans related to microbial pathogenicity. DiNAcBac is found at the reducing end of oligosaccharides of N- and O-linked bacterial protein glycosylation pathways of Gram-negative pathogens, including Campylobacter jejuni and Neisseria gonorrhoeae. Further derivatization of diNAcBac results in the nonulosonic acid known as legionaminic acid, which was first characterized in the O-antigen of the lipopolysaccharide (LPS) in Legionella pneumophila. Pseudaminic acid, an isomer of legionaminic acid, is also important in pathogenic bacteria such as Helicobacter pylori because of its occurrence in O-linked glycosylation of flagellin proteins, which plays an important role in flagellar assembly and motility. Here, we present recent advances in the characterization of the biosynthetic pathways leading to these highly modified sugars and investigation of the roles that each plays in bacterial fitness and pathogenicity.

Flagellar localization of a Helicobacter pylori autotransporter protein

Helicobacter pylori contains four genes that are predicted to encode proteins secreted by the autotransporter (type V) pathway. One of these, the pore-forming toxin VacA, has been studied in great detail, but thus far there has been very little investigation of three VacA-like proteins. We show here that all three VacA-like proteins are >250 kDa in mass and localized on the surface of H. pylori. The expression of the three vacA-like genes is upregulated during H. pylori colonization of the mouse stomach compared to H. pylori growth in vitro, and a wild-type H. pylori strain outcompeted each of the three corresponding isogenic mutant strains in its ability to colonize the mouse stomach. One of the VacA-like proteins localizes to a sheath that overlies the flagellar filament and bulb, and therefore, we designate it FaaA (flagella-associated autotransporter A). In comparison to a wild-type H. pylori strain, an isogenic faaA mutant strain exhibits decreased motility, decreased flagellar stability, and an increased proportion of flagella in a nonpolar site. The flagellar localization of FaaA differs markedly from the localization of other known autotransporters, and the current results reveal an important role of FaaA in flagellar localization and motility.

The pathogenesis of most bacterial infections is dependent on the actions of secreted proteins, and proteins secreted by the autotransporter pathway constitute the largest family of secreted proteins in pathogenic Gram-negative bacteria. In this study, we analyzed three autotransporter proteins (VacA-like proteins) produced by Helicobacter pylori, a Gram-negative bacterium that colonizes the human stomach and contributes to the pathogenesis of gastric cancer and peptic ulcer disease. We demonstrate that these three proteins each enhance the capacity of H. pylori to colonize the stomach. Unexpectedly, one of these proteins (FaaA) is localized to a sheath that overlies H. pylori flagella. The absence of FaaA results in decreased H. pylori motility as well as a reduction in flagellar stability and a change in flagellar localization. The atypical localization of FaaA reflects a specialized function of this autotransporter designed to optimize H. pylori colonization of the gastric niche.

Higher motility enhances bacterial density and inflammatory response in dyspeptic patients infected with Helicobacter pylori

BACKGROUND

Motility mediated by the flagella of Helicobacter pylori is important for the cells to move toward the gastric mucus in niches adjacent to the epithelium; then, H. pylori uses the adhesin SabA to interact with sialyl-Le(x) on inflammatory host cells for persistent infection. Here, we reveal the clinical association of bacterial motility, SabA expression, and pathological outcomes.

METHODS

Ninety-six clinical isolates were screened for bacterial motility, and the expression of SabA of each isolate was confirmed by Western blotting. H. pylori-infected patients were assessed for their bacterial density, sialyl-Le(x) expression, inflammatory scores, and clinical diseases.

RESULTS

The mean diameter in the motility assay was 17 mm, and eight (8.3%) of the strains had impaired motility, with a diameter <5 mm. H. pylori density in cardia, the acute inflammatory score in the body locus, and the prevalence rate of gastric atrophy were increased in patients infected with higher-motility strains (p = .023, <.001, or <.001, respectively). The total inflammatory scores (both acute and chronic) and bacterial density dramatically increased in patients expressing the sialyl-Le(x) antigen and infected with higher-motility, SabA-positive H. pylori (p = .016, .01, or .005, respectively).

CONCLUSION

These results suggest that the higher motility of H. pylori enhances pathological outcomes, and the SabA-sialyl-Le(x) interaction has a synergistic effect on virulence of the higher-motility strains.

Motility and chemotaxis in Campylobacter and Helicobacter

Flagellar motility of Campylobacter jejuni and Helicobacter pylori influences host colonization by promoting migration through viscous milieus such as gastrointestinal mucus. This review explores mechanisms C. jejuni and H. pylori employ to control flagellar biosynthesis and chemotactic responses. These microbes tightly control the activities of σ(54) and σ(28) to mediate ordered flagellar gene expression. In addition to phase-variable and posttranslational mechanisms, flagellar biosynthesis is regulated spatially and numerically so that only a certain number of organelles are placed at polar sites. To mediate chemotaxis, C. jejuni and H. pylori combine basic chemotaxis signal transduction components with several accessory proteins. H. pylori is unusual in that it lacks a methylation-based adaptation system and produces multiple CheV coupling proteins. Chemoreceptors in these bacteria contain nonconserved ligand binding domains, with several chemoreceptors matched to environmental signals. Together, these mechanisms allow for swimming motility that is essential for colonization.

Phasevarion mediated epigenetic gene regulation in Helicobacter pylori

Many host-adapted bacterial pathogens contain DNA methyltransferases (mod genes) that are subject to phase-variable expression (high-frequency reversible ON/OFF switching of gene expression). In Haemophilus influenzae and pathogenic Neisseria, the random switching of the modA gene, associated with a phase-variable type III restriction modification (R-M) system, controls expression of a phase-variable regulon of genes (a “phasevarion”), via differential methylation of the genome in the modA ON and OFF states. Phase-variable type III R-M systems are also found in Helicobacter pylori, suggesting that phasevarions may also exist in this key human pathogen. Phylogenetic studies on the phase-variable type III modH gene revealed that there are 17 distinct alleles in H. pylori, which differ only in their DNA recognition domain. One of the most commonly found alleles was modH5 (16% of isolates). Microarray analysis comparing the wild-type P12modH5 ON strain to a P12ΔmodH5 mutant revealed that six genes were either up- or down-regulated, and some were virulence-associated. These included flaA, which encodes a flagella protein important in motility and hopG, an outer membrane protein essential for colonization and associated with gastric cancer. This study provides the first evidence of this epigenetic mechanism of gene expression in H. pylori. Characterisation of H. pylori modH phasevarions to define stable immunological targets will be essential for vaccine development and may also contribute to understanding H. pylori pathogenesis.

Genetic and molecular characterization of flagellar assembly in Shewanella oneidensis

Shewanella oneidensis is a highly motile organism by virtue of a polar flagellum. Unlike most flagellated bacteria, it contains only one major chromosome segment encoding the components of the flagellum with the exception of the motor proteins. In this region, three genes encode flagellinsaccording to the original genome annotation. However, we find that only flaA and flaB encode functional filament subunits. Although these two genesare under the control of different promoters, they are actively transcribed and subsequently translated, producing a considerable number of flagellin proteins. Additionally, both flagellins are able to interact with their chaperon FliS and are subjected to feedback regulation. Furthermore, FlaA and FlaB are glycosylated by a pathwayinvolving a major glycosylating enzyme,PseB, in spite of the lack of the majority of theconsensus glycosylation sites. In conclusion, flagellar assembly in S. oneidensis has novel features despite the conservation of homologous genes across taxa.

Flagellin redundancy in Caulobacter crescentus and its implications for flagellar filament assembly

Bacterial flagella play key roles in surface attachment and host-bacterial interactions as well as driving motility. Here, we have investigated the ability of Caulobacter crescentus to assemble its flagellar filament from six flagellins: FljJ, FljK, FljL, FljM, FljN, and FljO. Flagellin gene deletion combinations exhibited a range of phenotypes from no motility or impaired motility to full motility. Characterization of the mutant collection showed the following: (i) that there is no strict requirement for any one of the six flagellins to assemble a filament; (ii) that there is a correlation between slower swimming speeds and shorter filament lengths in ΔfljK ΔfljM mutants; (iii) that the flagellins FljM to FljO are less stable than FljJ to FljL; and (iv) that the flagellins FljK, FljL, FljM, FljN, and FljO alone are able to assemble a filament.

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.

Helicobacter pylori HP0518 affects flagellin glycosylation to alter bacterial motility

Helicobacter pylori is a human gastric pathogen associated with gastric and duodenal ulcers as well as gastric cancer. Mounting evidence suggests this pathogen's motility is prerequisite for successful colonization of human gastric tissues. Here, we isolated an H. pylori G27 HP0518 mutant exhibiting altered motility in comparison to its parental strain. We show that the mutant's modulated motility is linked to increased levels of O-linked glycosylation on flagellin A (FlaA) protein. Recombinant HP0518 protein decreased glycosylation levels of H. pylori flagellin in vitro, indicating that HP0518 functions in deglycosylation of FlaA protein. Furthermore, mass spectrometric analysis revealed increased glycosylation of HP0518 FlaA was due to a change in pseudaminic acid (Pse) levels on FlaA; HP0518 mutant-derived flagellin contained approximately threefold more Pse than the parental strain. Further phenotypic and molecular characterization demonstrated that the hyper-motile HP0518 mutant exhibits superior colonization capabilities and subsequently triggers enhanced CagA phosphorylation and NF-κB activation in AGS cells. Our study shows that HP0518 is involved in the deglycosylation of flagellin, thereby regulating pathogen motility. These findings corroborate the prominent function of H. pylori flagella in pathogen-host cell interactions and modulation of host cell responses, likely influencing the pathogenesis process.

The antibody titers to Helicobacter pylori in 7 - 12 year old iron deficiency anemic children, in Ilam

BACKGROUND

It has recently been revealed that H. pylori infection is one the most important causes of anemia inhibiting iron uptake. The current study was designed to evaluate the correlation between the iron deficiency anemia and IgG to H. pylori in anemic children.

METHODS

In this analytical study, 100 anemic children were analyzed using total Iron, Ferritin, TIBC and H. pylori IgG assay. Data were collected using a questionnaire including parameters of age, blood group, infancy nutrition, iron consumption, fatigue, weakness, height, weight, gastrointestinal infectious, parasitic and blood diseases, parent literacy, income, inhabitation, etc. Data were analyzed using Multivariate Regression Analysis Models, Pearson Correlation- test and Kolmogrov Smirnov.

RESULTS

The most prevalent blood group detected in the study sample was group O (62%); 79% were breastfed, 9% were bottle- fed, 12% were both breastfed and bottle- fed. The history of gastrointestinal disorders was mentioned amongst 91% of the patients' family members. A significant relationship was observed between the iron level with serum, ferritin, level of TIBC and elevated level of IgG titer to H. pylori (p < 0.001). There was a significant association between the shared dishes, GI disorders, fatigue and weakness and level of TIBC, ferritin, Iron and IgG (p < 0.001).

CONCLUSIONS

The significant relationship between the iron level, IgG titer and H. pylori infection rate can be referred to as important factors influencing the anemia rate. Therefore, H. pylori IgG test can be checked for anemia together with the other routine tests.

Helicobacter pylori colonization of the human gastric epithelium: a bug's first step is a novel target for us

After Helicobacter pylori enters the stomach, three steps are vital for infection: (i) establishing colonization; (ii) evading host immunity; and (iii) invading gastric mucosa; the last step is what is associated with diverse outcomes. Urease activity and motility mediated by the flagella of H. pylori are important in harboring colonies beneath the gastric mucus in niches adjacent to the epithelium. Several putative adhesins attach the organism to the gastric epithelium and prompt the succeeding processes for evading host immunity and invading the mucosa. Successful colonization is thus the leading and critical step. From another point of view, this can be a novel target to control this common and important infection. This review summarizes the putative adhesins that influence the evasion of host immunity, and how these could determine different clinico-pathologic outcomes. The putative adhesins include the interplay between bacterial and host Lewis antigens (type I: Le(a) and Le(b); type II: Le(x) and Le(y)), the dominant pathway between BabA and Le(b), the SabA adhesin binding to sialylated Le(x) that is upregulated in inflamed gastric tissue or those with weak-Le(b), the CagL apparatus to adapt with the alpha5beta1 integrin to mediate a type IV secretory system for CagA translocation into the epithelium; and other outer membrane proteins as HopZ, AlpA/AlpB, or OipA, without known corresponding receptors. This review implicates the adhesins vital for bugs that could be alternatively provided as novel targets for us to overcome the colonization.

Pyrazolopyrimidinediones are selective agents for Helicobacter pylori that suppress growth through inhibition of glutamate racemase (MurI)

Pyrazolopyrimidinediones are a novel series of compounds that inhibit growth of Helicobacter pylori specifically. Using a variety of methods, advanced analogues were shown to suppress the growth of H. pylori through the inhibition of glutamate racemase, an essential enzyme in peptidoglycan biosynthesis. The high degree of selectivity of the series for H. pylori makes these compounds attractive candidates for novel H. pylori-selective therapy.

Capillary electropherograms for restriction fragment length polymorphism of Helicobacter pylori

Rapid identification of Helicobacter pylori strains is of importance for diagnosis and then treatment of duodenal and gastric ulcers. We developed a CE approach for the analysis of RFLP of the PCR products of urease (UreAB) gene and flagellin A (FlaA) gene fragments. Prior to CE analysis, the 2.4-kbp UreAB and 1.5-kbp FlaA PCR products were digested with the restriction enzymes HaeIII and HhaI, respectively. The DNA fragments were then separated by CE in conjunction with laser-induced fluorescence detection using poly(ethylene oxide) in the presence of electroosmotic flow. The DNA fragments range in sizes 259-1831 bp and 12-827 bp for UreAB and FlaA restriction fragments, respectively. Of 27 samples, the CE approach provided five and ten different RFLP patterns of the HaeIII and HhaI digests. The RFLP of PCR products of the two genes allow great sensitivity of identification of H. pylori strains. When compared with slab gel electrophoresis, the present CE approach provides advantages of rapidity (within 6 min per run), simplicity, and automation. The preliminary results have shown great practicality of the CE approach for screening H. pylori strains.

The 3'-to-5' exoribonuclease (encoded by HP1248) of Helicobacter pylori regulates motility and apoptosis-inducing genes

The human gastric pathogen Helicobacter pylori has many virulence factors involved in pathogenesis, but the mechanisms regulating these virulence factors are not yet fully understood. In this study, we cloned HP1248, which is similar in sequence to Escherichia coli vacB, which was previously shown to be associated with the expression of virulence in Shigella and enteroinvasive E. coli. E. coli vacB encodes RNase R. RNase R is involved in the posttranscriptional regulation of mRNA stability. By global transcriptional microarray profiling of an H. pylori HP1248 deletion mutant, we defined six virulence-related genes which were posttranscriptionally downregulated by HP1248, including the motility-related genes HP1192 and flaB, the chemotaxis-related gene cheY, and the apoptosis-inducing genes HP0175, cagA, and gtt. In this study, recombinant HP1248 protein expressed in E. coli showed 3'-to-5' exoribonuclease activity. Motility and apoptosis induction were increased in the H. pylori HP1248 deletion mutant. We also showed that HP1192 is associated with H. pylori motility, possibly through HP1248 regulation. Further, we suggested and studied the possible mechanisms of this specific regulation of virulent genes by HP1248. In addition, the expression level of HP1248 mRNA changed dramatically in response to a variety of altered environmental conditions, including pH and temperature. Hence, HP1248 in H. pylori seems to play a role in environmental sensing and in regulation of virulent phenotypes, such as motility and host apoptosis induction.

Arcobacter spp. possess two very short flagellins of which FlaA is essential for motility

Like Campylobacter and Helicobacter spp., Arcobacter spp. possess two flagellin genes (flaA and flaB) located adjacent to each other. The aim of this study was to characterize the flagellin proteins of Arcobacter spp., because these proteins are known virulence factors in the Epsilonproteobacteria, to which these three species belong. With the exception of Arcobacter nitrofigilis, Arcobacter flagellins are almost half the size of those in other Epsilonproteobacteria. Arcobacter flagellin proteins lack a large part of the variable central region. The low homology observed among flagellins of different Arcobacter species indicates genetic heterology between the members of this genus. Unlike in other Epsilonproteobacteria, the transcription of flagellin genes is not regulated by sigma 28- or sigma 54-dependent promoters, which suggests that transcription must be regulated in a different way in Arcobacter spp. Mutational studies revealed that only FlaA is needed for the motility of Arcobacter spp. Quantitative PCR analysis showed that transcription of flaB is higher at 30 degrees C than at 37 degrees C. Mutation of flaB had no effect on motility or on flaA transcription while mutation of flaA abolished motility and increased the transcription of flaB. These results underline that the genus Arcobacter is an unusual taxon in the epsilon subdivision of the Proteobacteria.

Helicobacter pylori flagella: antigenic profile and protective immunity

Reproducible induction of sterilizing immunity, essential for an effective Helicobacter pylori vaccine, remains elusive. As motility is essential for gastric colonization by Helicobacter, we evaluated whether a vaccine targeting flagella induces improved protection. Mice immunized with a vaccine enriched for H. pylori flagella sheath proteins exhibited significantly reduced colonization, equivalent to that observed in mice immunized with whole-cell lysate. Two-dimensional profiles indicated that flagella contain proteins not evident in whole-cell lysate. Moreover, comparison of Western blot profiles using whole-cell lysate antisera revealed striking differences in antigenicity.

Identification of unusual bacterial glycosylation by tandem mass spectrometry analyses of intact proteins

The characterization of protein glycosylation can be a complex and time-consuming procedure, especially for prokaryote O-linked glycoproteins, which often comprise unusual oligosaccharide structures with no known glycosylation motif. In this report, we describe a "top-down" approach that provides information on the extent of glycosylation, the molecular masses, and the structure of oligosaccharide residues on bacterial flagella, important structural proteins involved in the motility of pathogenic bacteria. Flagella from four bacterial pathogens, namely, Campylobacter jejuni, Helicobacter pylori, Aeromonas caviae, and Listeria monocytogenes, were analyzed by this top-down mass spectrometry approach. The approach needs minimal sample preparation and can be performed within a few minutes compared to the tedious and often time-consuming "bottom-up" approach involving proteolytic digestion and LC-MS-MS analyses of the suspected glycopeptides. Multiply protonated protein precursor ions subjected to low-energy collisional activation in a quadrupole time-of-flight instrument showed extensive and specific gas-phase deglycosylation resulting in the formation of abundant oxonium ions with very few fragment ions from peptidic bond cleavages. Structural information on individual carbohydrate residues is obtained using a second-generation product ion scan of oxonium ions formed by collisional activation of the intact protein ions in the source region. The four bacterial flagella examined differed not only by the extent of glycosylation but also by the nature of carbohydrate substituents. For example, the flagellin from the Gram-positive bacterium, L. monocytogenes showed O-linked GlcNAc residues at up to 6 sites/protein monomer. In contrast, the three Gram-negative bacterial pathogens C. jejuni, H. pylori and A. caviae displayed up to 19 Ser/Thr O-linked sites modified with residues structurally related to N-acetylpseudaminic acid (Pse5Ac7Ac) and in the case of Campylobacter include a novel N-acetylglutamine substituent on Pse5Am7Ac.

Characterization of flgK gene and FlgK protein required for H pylori Colonization-from cloning to clinical relevance

AIM: To characterize the role of flgK and its protein product in H pylori colonization.

METHODS: The PCR cloning method identified the flgK gene. An isogenic flgK mutant was constructed by gene replacement and confirmed by Southern blot analysis and PCR analysis. The recombinant FlgK protein (r-FlgK) was purified. Electron microscopy (EM) was applied to demonstrate the flagella of H pylori. An in vitro motility test was assessed in semisolid medium. The densities of H pylori colonization with either the wild-type strain or its flgK mutant were compared among BALB/c mice with or without pre-immunization with r-FlgK. The serological responses to r-FlgK were analyzed for 70 clinical patients with different densities of H pylori colonization.

RESULTS: From a duodenal ulcer strain, the flgK gene was cloned and it contained 1821 bp, with a 95.7% identity to the published sequences. No flagella were observed under EM for the mutant strain, which had a loss of motility. H pylori density was lower in the BALB/c mice inoculated by the mutant or with pre-immunization with r-FlgK compared to unimmunized mice or mice inoculated by the wild-type strain (P < 0.05). In the H pylori-infected patients, the serological responses to r-FlgK were uniformly low in titer.

CONCLUSION: FlgK encoded by flgK is important for flagella formation and H pylori motility. Deficiency in FlgK or an enhanced serological response to r-FlgK can interfere with H pylori colonization. FlgK of H pylori could be a novel target for vaccination.

The Gaggle: an open-source software system for integrating bioinformatics software and data sources

Background

Systems biologists work with many kinds of data, from many different sources, using a variety of software tools. Each of these tools typically excels at one type of analysis, such as of microarrays, of metabolic networks and of predicted protein structure. A crucial challenge is to combine the capabilities of these (and other forthcoming) data resources and tools to create a data exploration and analysis environment that does justice to the variety and complexity of systems biology data sets. A solution to this problem should recognize that data types, formats and software in this high throughput age of biology are constantly changing.

Results

In this paper we describe the Gaggle -a simple, open-source Java software environment that helps to solve the problem of software and database integration. Guided by the classic software engineering strategy of separation of concerns and a policy of semantic flexibility, it integrates existing popular programs and web resources into a user-friendly, easily-extended environment.

We demonstrate that four simple data types (names, matrices, networks, and associative arrays) are sufficient to bring together diverse databases and software. We highlight some capabilities of the Gaggle with an exploration of Helicobacter pylori pathogenesis genes, in which we identify a putative ricin-like protein -a discovery made possible by simultaneous data exploration using a wide range of publicly available data and a variety of popular bioinformatics software tools.

Conclusion

We have integrated diverse databases (for example, KEGG, BioCyc, String) and software (Cytoscape, DataMatrixViewer, R statistical environment, and TIGR Microarray Expression Viewer). Through this loose coupling of diverse software and databases the Gaggle enables simultaneous exploration of experimental data (mRNA and protein abundance, protein-protein and protein-DNA interactions), functional associations (operon, chromosomal proximity, phylogenetic pattern), metabolic pathways (KEGG) and Pubmed abstracts (STRING web resource), creating an exploratory environment useful to 'web browser and spreadsheet biologists', to statistically savvy computational biologists, and those in between. The Gaggle uses Java RMI and Java Web Start technologies and can be found at .

HP0958 is an essential motility gene in Helicobacter pylori

Motility is an essential colonization factor for the human gastric pathogen Helicobacter pylori. The H. pylori genome encodes most known flagellar proteins, although a number of key transcription regulators, chaperones, and structural proteins have not yet been identified. Using recently published yeast two-hybrid data we identified HP0958 as a potential motility-associated protein due to its strong interactions with RpoN (sigma(54)) and FliH, a flagellar ATPase regulator. HP0958 exhibits no sequence similarity to any published flagellar genes but contains a carboxy-terminal zinc finger domain that could function in nucleic acid or protein binding. We created a HP0958 mutant by inserting a chloramphenicol resistance marker into the gene using a PCR-based allelic exchange method and the resultant mutant was non-motile as measured by a BacTracker instrument. Electron microscopic analysis revealed that the HP0958 mutant cells were aflagellate and Western blot analysis revealed a dramatic reduction in flagellin and hook protein production. The HP0958 mutant also showed decreased transcription of flgE, flaB and flaA as well as the checkpoint genes flhA and flhF. Expression of flgM was increased relative to the wild-type and both rpoN and fliA (sigma(28)) expression were unchanged. We conclude that HP0958 is essential for normal motility and flagella production, and represents a novel flagellar component in the epsilon proteobacteria.

Helicobacter pylori flagellar hook-filament transition is controlled by a FliK functional homolog encoded by the gene HP0906

Helicobacter pylori is a human gastric pathogen which is dependent on motility for infection. The H. pylori genome encodes a near-complete complement of flagellar proteins compared to model enteric bacteria. One of the few flagellar genes not annotated in H. pylori is that encoding FliK, a hook length control protein whose absence leads to a polyhook phenotype in Salmonella enterica. We investigated the role of the H. pylori gene HP0906 in flagellar biogenesis because of linkage to other flagellar genes, because of its transcriptional regulation pattern, and because of the properties of an ortholog in Campylobacter jejuni (N. Kamal and C. W. Penn, unpublished data). A nonpolar mutation of HP0906 in strain CCUG 17874 was generated by insertion of a chloramphenicol resistance marker. Cells of the mutant were almost completely nonmotile but produced sheathed, undulating polyhook structures at the cell pole. Expression of HP0906 in a Salmonella fliK mutant restored motility, confirming that HP0906 is the H. pylori fliK gene. Mutation of HP0906 caused a dramatic reduction in H. pylori flagellin protein production and a significant increase in production of the hook protein FlgE. The HP0906 mutant showed increased transcription of the flgE and flaB genes relative to the wild type, down-regulation of flaA transcription, and no significant change in transcription of the flagellar intermediate class genes flgM, fliD, and flhA. We conclude that the H. pylori HP0906 gene product is the hook length control protein FliK and that its function is required for turning off the sigma(54) regulon during progression of the flagellar gene expression cascade.

Clinical Relevance of the vacA, iceA, cagA, and flaA genes of Helicobacter pylori strains isolated in Eastern Taiwan

The genotypes of Helicobacter pylori flaA, cagA, vacA, and iceA were determined for DNA isolated from patients with chronic gastritis or peptic ulcer in eastern Taiwan. The vacA gene encoding the s1a subtype was found to predominate in peptic ulcer patients, and the iceA1 genotype was associated with chronic gastritis. cagA and flaA genes were not found to be associated with these types of disease.

Helicobacter pylori specific immune response induced by conservative flagellin linear B-cell epitope

AIM: To testify the immunogenicity of a conservative B-cell linear epitope of Helicobacter pylori (H pylori) flagellin A.

METHODS: Different programs were used to analyze the secondary structure, molecular hydropathy, and surface accessibility of H pylori flagellin A. Linear B-cell epitopes were estimated based on the structural and physiochemical information. Analysis of residue divergence was proposed to screen a conservative linear epitope. The 29-peptide (Pep29mer) synthesized by chemical method, including the predicted conservative B-cell epitope and a known K^2d compatible T-cell epitope, was used to immunize mice, and then H pylori-specific antibodies were detected by ELISA.

RESULTS: Based on the analyses of divergent amino acid residues, structural and physiochemical characteristics, it was strongly suggested that the short fragment NDSDGR was the core of a conservative linear epitope in flagellin A. Animals immunized by Pep29mer acquired efficient immune response. In detail, serum H pylori-specific IgA and IgG1 increased significantly in immunized group, while IgG2a only had an insignificant change. H pylori-specific IgA in gastrointestinal flushing fluid also increased significantly.

CONCLUSION: The conservative short fragment NDSDGR is the core of a linear B-cell epitope of flagellin A.

B-cell and T-cell immune responses to experimental Helicobacter pylori infection in humans

The acute antibody and T-cell immune response to Helicobacter pylori infection in humans has not been studied systematically. Serum from H. pylori-naive volunteers challenged with H. pylori and cured after 4 or 12 weeks was tested by enzyme-linked immunosorbent assays for anti-H. pylori-specific immunoglobulin M (IgM) and IgA established using bacterial lysates from homologous (the infecting strain) and heterologous H. pylori. Proteins recognized by IgM antibody were identified by mass spectrometry of immunoreactive bands separated by two-dimensional gel electrophoresis. Mucosal T-cell subsets (CD4, CD8, CD3, and CD30 cells) were assessed by immunohistochemistry. All 18 infected volunteers developed H. pylori-specific IgM responses to both homologous or heterologous H. pylori antigens. H. pylori antigens reacted with IgM antibody at 4 weeks postinfection. IgM Western blotting showed immunoreactivity of postinfection serum samples to multiple H. pylori proteins with molecular weights ranging between 9,000 (9K) to 150K with homologous strains but only a 70K band using heterologous antigens. Two-dimensional electrophoresis demonstrated that production of H. pylori-specific IgM antibodies was elicited by H. pylori flagellins A and B, urease B, ABC transporter binding protein, heat shock protein 70 (DnaK), and alkyl hydroperoxide reductase. Mucosal CD3, CD4, and CD8 T-cell numbers increased following infection. IgM antibody responses were detected to a range of homologous H. pylori antigens 2 to 4 weeks postchallenge. The majority of H. pylori proteins were those involved in motility and colonization and may represent targets for vaccine development.

Molecular biology of gastric cancer: Helicobacter infection and gastric adenocarcinoma: bacterial and host factors responsible for altered growth signaling

Gastric cancer remains the second most common cause of cancer-related mortality worldwide. The single most common cause of gastric cancer is chronic infection with the gram-negative microaerophilic spiral bacterium: Helicobacter pylori. Recent advances in this field have identified host factors which predispose to gastric cancer formation via modulation of the host immune response. In addition, recent work has explored bacterial virulence factors which may directly cause tissue damage, and lead to gastric carcinogenesis, as well as factors responsible for enhanced immune response. Environmental factors, long associated with a predilection for gastric cancer, are recognized as modifiers of key growth signalling pathways within the gastric mucosa and as such lead to growth alterations. This review focuses on exploring new advances in our understanding of bacterial factors, host genetic polymorphisms and the interaction between the bacterium and host at the level of the immune response and the regulation of proliferative and apoptotic signal transduction cascades. Modulation of the pivotal balance between cell growth and cell death leads to the formation of gastric adenocarcinoma.

Helicobacter pylori flagellins have very low intrinsic activity to stimulate human gastric epithelial cells via TLR5

Helicobacter pylori is a flagellated chronic pathogen, which colonizes the gastric mucus and mucosal cell surfaces. Flagella and motility are essential for the survival of this bacterium in the stomach environment. Flagellins of several bacterial species are potent activators of the human innate immune system by binding to TOLL-like receptor 5 (TLR5). The possible role of the two H. pylori flagellins FlaA and FlaB in stimulation of the innate immune system and induction of IL-8 release by human gastric epithelial cells was investigated in this study. Transcription and expression of TLR5 in three different human gastric epithelial cell lines was demonstrated. Salmonella enterica serovar Typhimurium FliC flagellin was able to activate human gastric epithelial cells. TLR5 transcription was modulated by H. pylori infection. However, both H. pylori flagellins appeared to possess no immunostimulatory potential on human gastric cells via TLR5, despite their extensive amino acid homology to stimulating flagellins of other bacterial species. The evolutionary development of such unique flagellins of low activating potential is proposed to be a novel mechanism of H. pylori to preserve the essential function of its flagella during chronic colonization of the stomach and to evade the deleterious host immune responses.

The FlgS/FlgR two-component signal transduction system regulates the fla regulon in Campylobacter jejuni

The human pathogen Campylobacter jejuni is a highly motile organism that carries a flagellum on each pole. The flagellar motility is regarded as an important trait in C. jejuni colonization of the intestinal tract, however, the knowledge of the regulation of this important colonization factor is rudimentary. We demonstrate by phosphorylation assays that the sensor FlgS and the response regulator FlgR form a two-component system that is on the top of the Campylobacter flagellum hierarchy. Phosphorylated FlgR is needed to activate RpoN-dependent genes of which the products form the hook-basal body filament complex. By real-time reverse transcriptase-PCR we identified that FlgS, FlgR, RpoN, and FliA belong to the early flagellar genes and are regulated by sigma70. FliD and the putative anti-sigma-factor FlgM are regulated by a sigma54- and sigma28-dependent promoters. Activation of the fla regulon is growth phase-dependent, a 100-fold rpoN mRNA reduction is seen in the early stationary phase compared with the early logarithmic phase. Whereas flaB transcription decreases, flaA transcription increases in early stationary phase. Our data show that the C. jejuni flagellar hierarchy largely differs from that of other bacteria. Phenotypical analysis revealed that unflagellated C. jejuni mutants grow three times faster in broth medium compared with wild-type bacteria. In vivo the C. jejuni flagella are needed to pass the gastrointestinal tract of chickens, but not to colonize the ceaca of the chicken.

Growth phase-dependent response of Helicobacter pylori to iron starvation

Iron is an essential nutrient that is often found in extremely limited available quantities within eukaryotic hosts. Because of this, many pathogenic bacteria have developed regulated networks of genes important for iron uptake and storage. In addition, it has been shown that many bacteria use available iron concentrations as a signal to regulate virulence gene expression. We have utilized DNA microarray technology to identify genes of the human pathogen Helicobacter pylori that are differentially regulated on a growth-inhibiting shift to iron starvation conditions. In addition, the growth phase-dependent expression of these genes was investigated by examining both exponential and stationary growth phase cultures. We identified known iron-regulated genes, as well as a number of genes whose regulation by iron concentration was not previously appreciated. Included in the list of regulated factors were the known virulence genes cagA, vacA, and napA. We examined the effect of iron starvation on the motility of H. pylori and found that exponential- and stationary-phase cultures responded differently to the stress. We further found that while growing cells are rapidly killed by iron starvation, stationary-phase cells show a remarkable ability to survive iron depletion. Finally, bioinformatic analysis of the predicted promoter regions of the differentially regulated genes led to identification of several putative Fur boxes, suggesting a direct role for Fur in iron-dependent regulation of these genes.

pH-regulated gene expression of the gastric pathogen Helicobacter pylori

Colonization by the gastric pathogen Helicobacter pylori has been shown to be intricately linked to the development of gastritis, ulcers, and gastric malignancy. Little is known about mechanisms employed by the bacterium that help it adapt to the hostile environment of the human stomach. In an effort to extend our knowledge of these mechanisms, we utilized spotted-DNA microarrays to characterize the response of H. pylori to low pH. Expression of approximately 7% of the bacterial genome was reproducibly altered by shift to low pH. Analysis of the differentially expressed genes led to the discovery that acid exposure leads to profound changes in motility of H. pylori, as a larger percentage of acid-exposed bacterial cells displayed motility and moved at significantly higher speeds. In contrast to previous publications, we found that expression of the bacterial virulence gene cagA was strongly repressed by acid exposure. Furthermore, this transcriptional repression was reflected at the level of protein accumulation in the H. pylori cell.

Structural, genetic and functional characterization of the flagellin glycosylation process in Helicobacter pylori

Mass spectrometry analyses of the complex polar flagella from Helicobacter pylori demonstrated that both FlaA and FlaB proteins are post-translationally modified with pseudaminic acid (Pse5Ac7Ac, 5,7-diacetamido-3,5,7,9-tetradeoxy-l-glycero-l-manno -n o n-ulosonic acid). Unlike Campylobacter, flagellar glycosylation in Helicobacter displays little heterogeneity in isoform or glycoform distribution, although all glycosylation sites are located in the central core region of the protein monomer in a manner similar to that found in Campylobacter. Bioinformatic analysis revealed five genes (HP0840, HP0178, HP0326A, HP0326B, HP0114) homologous to other prokaryote genes previously reported to be involved in motility, flagellar glycosylation or polysaccharide biosynthesis. Insertional mutagenesis of four of these homologues in Helicobacter (HP0178, HP0326A, HP0326B, HP0114) resulted in a non-motile phenotype, no structural flagella filament and only minor amounts of flagellin protein detectable by Western immunoblot. However, mRNA levels for the flagellin structural genes remained unaffected by each mutation. In view of the combined bioinformatic and structural evidence indicating a role for these gene products in glycan biosynthesis, subsequent investigations focused on the functional characterization of the respective gene products. A novel approach was devised to identify biosynthetic sugar nucleotide precursors from intracellular metabolic pools of parent and isogenic mutants using capillary electrophoresis-electrospray mass spectrometry (CE-ESMS) and precursor ion scanning. HP0326A, HP0326B and the HP0178 gene products are directly involved in the biosynthesis of the nucleotide-activated form of Pse, CMP-Pse. Mass spectral analyses of the cytosolic extract from the HP0326A and HP0326B isogenic mutants revealed the accumulation of a mono- and a diacetamido trideoxyhexose UDP sugar nucleotide precursor.

Growth phase-dependent and differential transcriptional control of flagellar genes in Helicobacter pylori

Helicobacter pylori possesses two different flagellin genes, flaA and flaB, which are unlinked on the chromosome and transcribed from sigma(28) and sigma(54) promoters, respectively. Both flagellins are hypothesized to be present in varying amounts in the flagellum, to adapt the physical properties of the flagellar filament to different environmental conditions. The influence of growth phase and environmental conditions on the transcriptional regulation of both flagellin genes has not been investigated so far. Using three different reporter genes as well as Northern blot analyses and RT-PCR, it was determined that both flagellin genes are transcribed in a growth phase-dependent fashion. Growth phase dependency was also found for the flagellar basal body export apparatus gene flhA which is involved in the transcriptional regulation of both flagellin genes. Peak transcription of flaB and flhA occurred earlier during the growth phase than that of flaA, possibly consistent with a hook-proximal localization of the minor flagellin FlaB. Of the reporter gene systems, luciferase fusions reflected best the dynamic regulation patterns of H. pylori flagellin genes. Growth phase in vitro had the strongest influence on transcriptional control of H. pylori flaA and flaB, while differences in supplements to a rich culture medium had only a modest modulatory effect on flagellin gene transcription.