In Helicobacter pylori auto-inducer-2, but not LuxS/MccAB catalysed reverse transsulphuration, regulates motility through modulation of flagellar gene transcription. BMC Microbiol. 2010;10:210. [PMID: 20691071 PMCID: PMC2923134 DOI: 10.1186/1471-2180-10-210]

Effects of the quorum sensing related luxS gene and lsr operon on Klebsiella michiganensis resisting copper stress

Industrial wastewater is a major environmental concern due to its high copper content, which poses significant toxicity to microbial life. Autoinducer-2 (AI-2) can participate in the inter- and intra-species communication and regulate the physiological functions of different bacterial species by producing AI-2 signal molecules. However, there are few research reports on the luxS gene and lsr operon functions for AI-2 in bacteria with a certain tolerance to copper. This study delves into the potential of quorum sensing mechanisms, particularly the AI-2 system, for enhancing microbial resistance to copper toxicity in Klebsiella michiganensis (KM). We detail the critical roles of the luxS gene in AI-2 synthesis and the lsr operon in AI-2 uptake, demonstrating their collective impact on enhancing copper resistance. Our findings show that mutations in the lsr operon, alongside the knockout of the luxS gene in KM strain (KMΔluxSΔlsr), significantly impair the strain's motility (p < 0.0001) and biofilm formation (p < 0.01), underscoring the operon's role in AI-2 transport. These genetic insights are pivotal for developing bioremediation strategies aimed at mitigating copper pollution in wastewater. By elucidating the mechanisms through which KM modulates copper resistance, this study highlights the broader ecological significance of leveraging microbial quorum sensing pathways for sustainable wastewater management.

Single-base resolution quantitative genome methylation analysis in the model bacterium Helicobacter pylori by enzymatic methyl sequencing (EM-Seq) reveals influence of strain, growth phase, and methyl homeostasis

BACKGROUND

Bacterial epigenetics is a rapidly expanding research field. DNA methylation by diverse bacterial methyltransferases (MTases) contributes to genomic integrity and replication, and many recent studies extended MTase function also to global transcript regulation and phenotypic variation. Helicobacter pylori is currently one of those bacterial species which possess the highest number and the most variably expressed set of DNA MTases. Next-generation sequencing technologies can directly detect DNA base methylation. However, they still have limitations in their quantitative and qualitative performance, in particular for cytosine methylation.

RESULTS

As a complementing approach, we used enzymatic methyl sequencing (EM-Seq), a technology recently established that has not yet been fully evaluated for bacteria. Thereby, we assessed quantitatively, at single-base resolution, whole genome cytosine methylation for all methylated cytosine motifs in two different H. pylori strains and isogenic MTase mutants. EM-Seq reliably detected both m5C and m4C methylation. We demonstrated that three different active cytosine MTases in H. pylori provide considerably different levels of average genome-wide single-base methylation, in contrast to isogenic mutants which completely lost specific motif methylation. We found that strain identity and changed environmental conditions, such as growth phase and interference with methyl donor homeostasis, significantly influenced quantitative global and local genome-wide methylation in H. pylori at specific motifs. We also identified significantly hyper- or hypo-methylated cytosines, partially linked to overlapping MTase target motifs. Notably, we revealed differentially methylated cytosines in genome-wide coding regions under conditions of methionine depletion, which can be linked to transcript regulation.

CONCLUSIONS

This study offers new knowledge on H. pylori global and local genome-wide methylation and establishes EM-Seq for quantitative single-site resolution analyses of bacterial cytosine methylation.

Nanomaterials Regulate Bacterial Quorum Sensing: Applications, Mechanisms, and Optimization Strategies

Anti-virulence therapy that interferes with bacterial communication, known as "quorum sensing (QS)", is a promising strategy for circumventing bacterial resistance. Using nanomaterials to regulate bacterial QS in anti-virulence therapy has attracted much attention, which is mainly attributed to unique physicochemical properties and excellent designability of nanomaterials. However, bacterial QS is a dynamic and multistep process, and there are significant differences in the specific regulatory mechanisms and related influencing factors of nanomaterials in different steps of the QS process. An in-depth understanding of the specific regulatory mechanisms and related influencing factors of nanomaterials in each step can significantly optimize QS regulatory activity and enhance the development of novel nanomaterials with better comprehensive performance. Therefore, this review focuses on the mechanisms by which nanomaterials regulate bacterial QS in the signal supply (including signal synthesis, secretion, and accumulation) and signal transduction cascade (including signal perception and response) processes. Moreover, based on the two key influencing factors (i.e., the nanomaterial itself and the environment), optimization strategies to enhance the QS regulatory activity are comprehensively summarized. Collectively, applying nanomaterials to regulate bacterial QS is a promising strategy for anti-virulence therapy. This review provides reference and inspiration for further research on the anti-virulence application of nanomaterials.

Multiomics reveals the mechanism of B. longum in promoting the formation of mixed-species biofilms

It has been found previously that Bifidobacterium longum, Bacteroides ovatus, Enterococcus faecalis, and Lactobacillus gasseri can form a biofilm better when co-cultured in vitro and B. longum is the core biofilm-formation-promoting strain in this community. B. longum is part of the core microbiota in the gut and is widely recognized as a probiotic. Therefore, it is necessary to explore its role in mixed-species biofilms through transcriptomics and metabolomics. Metabolomics showed that the increase in amino acid and purine content could promote biofilm formation. In transcriptomic analysis, many genes related to carbohydrate metabolism, amino acid metabolism, and environmental tolerance of B. longum were up-regulated. Combined with the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis and Gene Ontology (GO) analysis, the differentially expressed genes (DEGs) of B. longum in mixed-species biofilms were mainly correlated to "quorum sensing (QS)", "ABC transporters", "biosynthesis of amino acids", "microbial metabolism in different environments", "carbohydrate metabolism" and "two-component system". In addition, the rpl and rps gene families, which function in the metabolism of organic substances and the biosynthesis of amino acids, were the core DEGs according to the analysis of the protein-protein interaction (PPI) network. Finally, by combining metabolomics and quorum sensing mechanisms, it was found that the metabolism of autoinducer peptides (proliylglycine and glycylleucine), N-acyl homoserine lactone (N-(3-oxo hydroxy) homoserine lactone), and AI-2 can promote the formation of biofilms, both mono- and mixed-species biofilms composed of B. longum. Our research enabled us to understand the critical role of B. longum in mixed-species biofilms and the interactions between biofilm metabolism and gut health. In addition, the generated knowledge will be of great significance for us to develop biofilm products with beneficial functions in future.

AI-2 Induces Urease Expression Through Downregulation of Orphan Response Regulator HP1021 in Helicobacter pylori

Helicobacter pylori causes gastric infections in more than half of the world's population. The bacterium's survival in the stomach is mediated by the abundant production of urease to enable acid acclimation. In this study, our transcriptomic analysis demonstrated that the expression of urease structural proteins, UreA and UreB, is induced by the autoinducer AI-2 in H. pylori. We also found that the orphan response regulator HP1021 is downregulated by AI-2, resulting in the induction of urease expression. HP1021 represses the expression of urease by directly binding to the promoter region of ureAB, ranging from −47 to +3 with respect to the transcriptional start site. The study findings suggest that quorum sensing via AI-2 enhances acid acclimation when bacterial density increases, and might enable bacterial dispersal to other sites when entering gastric acid.

Hesperetin Inhibits Expression of Virulence Factors and Growth of Helicobacter pylori

Helicobacter pylori (H. pylori) is a bacterium known to infect the human stomach. It can cause various gastrointestinal diseases including gastritis and gastric cancer. Hesperetin is a major flavanone component contained in citrus fruits. It has been reported to possess antibacterial, antioxidant, and anticancer effects. However, the antibacterial mechanism of hesperetin against H. pylori has not been reported yet. Therefore, the objective of this study was to determine the inhibitory effects of hesperetin on H. pylori growth and its inhibitory mechanisms. The results of this study showed that hesperetin inhibits the growth of H. pylori reference strains and clinical isolates. Hesperetin inhibits the expression of genes in replication (dnaE, dnaN, dnaQ, and holB) and transcription (rpoA, rpoB, rpoD, and rpoN) machineries of H. pylori. Hesperetin also inhibits the expression of genes related to H. pylori motility (flhA, flaA, and flgE) and adhesion (sabA, alpA, alpB, hpaA, and hopZ). It also inhibits the expression of urease. Hespereti n downregulates major virulence factors such as cytotoxin-associated antigen A (CagA) and vacuolating cytotoxin A (VacA) and decreases the translocation of CagA and VacA proteins into gastric adenocarcinoma (AGS) cells. These results might be due to decreased expression of the type IV secretion system (T4SS) and type V secretion system (T5SS) involved in translocation of CagA and VacA, respectively. The results of this study indicate that hesperetin has antibacterial effects against H. pylori. Thus, hesperetin might be an effective natural product for the eradication of H. pylori.

Lactobacillus rhamnosus JB3 inhibits Helicobacter pylori infection through multiple molecular actions

BACKGROUND

Eradication of Helicobacter pylori infection is the most direct and effective way for preventing gastric cancer. Lactic acid bacteria are considered as alternative therapeutic agents against H. pylori infection.

METHODS

Effects of Lactobacillus rhamnosus JB3 (LR-JB3) on the virulence gene expression of H. pylori and infection-induced cellular responses of AGS cells were investigated by co-cultivating infected AGS cells with different multiplicity of infections (MOIs) of LR-JB3.

RESULTS

LR-JB3, specifically at a MOI of 25, suppressed the association ability of H. pylori and its induced IL-8 levels, as well as the mRNA levels of vacA, sabA, and fucT of H. pylori, infection-induced Lewis (Le)^x antigen and Toll-like receptor 4 (TLR4) expressions in AGS cells. However, the apoptosis mediated by infection was inhibited by LR-JB3 in a dose-dependent manner. In addition, autoinducer (AI)-2 was observed to have increased the association ability and fucT expression of H. pylori, and Le^x antigen and TLR4 expression of AGS cells. Interestingly, an unknown bioactive cue was hypothesized to have been secreted from LR-JB3 at a MOI of 25 to act as an antagonist of AI-2.

CONCLUSIONS

LR-JB3 possesses various means to interfere with H. pylori pathogenesis and infection-induced cellular responses of AGS cells to fight against infection.

AI-2 represses CagA expression and bacterial adhesion, attenuating the Helicobacter pylori-induced inflammatory response of gastric epithelial cells

BACKGROUND

Helicobacter pylori (H. pylori) infection of gastric epithelial cells induces inflammatory response. Outer membrane proteins (OMPs), Type 4 secretion system (T4SS) encoded by cagPAI, and the effector protein CagA are involved in the pathogenesis of H. pylori. H. pylori possesses a gene encoding LuxS which synthesizes AI-2, a quorum sensing signal molecule. The aim of this study was to investigate the role of AI-2 in the expression of virulence factors and the inflammatory response of gastric epithelial (AGS) cells induced by H. pylori.

MATERIALS AND METHODS

H. pylori ΔluxS mutant was constructed, and AI-2 activity was measured with Vibrio harveyi BB170. NF-κB activation, IL-8 production, expression of OMPs (outer membrane proteins), CagA, and T4SS encoded by cagPAI were investigated in H. pylori wild type, and ΔluxS with or without supplementation of AI-2.

RESULTS

H. pylori produced approximately 7 μM of AI-2 in the medium. AI-2 inhibited expression and translocation of CagA after infection of AGS cells. AI-2 upregulated the expression of CagM, CagE, and CagX, while had no effect to the interaction between T4SS and α5β1 integrin. AI-2 also reduced expression of adhesins and bacterial adhesion to AGS cells. Finally, AI-2 reduced the activation of NF-κB and expression of IL-8 in H. pylori-infected AGS.

CONCLUSIONS

AI-2 plays an important role in the pathogenesis of H. pylori. AI-2 inhibits the bacterial adhesion, expression, and translocation of CagA, and attenuates the inflammatory response of AGS cells induced by H. pylori.

Modulation of quorum sensing-associated virulence in bacteria: carbohydrate as a key factor

Quorum sensing (QS) is a method of inter-cellular communication that permits bacteria to dispense information about cell density and to synchronize the gene expression accordingly. Gram-positive and Gram-negative bacteria utilize distinct quorum sensing mechanisms for effective pathogenesis. Virulence factor production by pathogenic bacteria is one of the important traits that is under the control of QS. A growing body of evidence has indicated the role of the nutritional environment notably by carbohydrates in dictating the QS-associated virulence gene regulation. The modulation of QS by carbohydrates mitigates the survival and establishment of the pathogen within its host which in turn leads to an increase in morbidity and mortality. This mini-review throws light on the predilection of pathogenic bacteria to rapidly regulate its QS-linked virulence gene expression based on the changing nutrient levels that assist them in prospering within diverse niches.

Biofilm Formation as a Complex Result of Virulence and Adaptive Responses of Helicobacter pylori

Helicobacter pylori is a bacterium that is capable of colonizing a host for many years, often for a lifetime. The survival in the gastric environment is enabled by the production of numerous virulence factors conditioning adhesion to the mucosa surface, acquisition of nutrients, and neutralization of the immune system activity. It is increasingly recognized, however, that the adaptive mechanisms of H. pylori in the stomach may also be linked to the ability of this pathogen to form biofilms. Initially, biofilms produced by H. pylori were strongly associated by scientists with water distribution systems and considered as a survival mechanism outside the host and a source of fecal-oral infections. In the course of the last 20 years, however, this trend has changed and now the most attention is focused on the biomedical aspect of this structure and its potential contribution to the therapeutic difficulties of H. pylori. Taking into account this fact, the aim of the current review is to discuss the phenomenon of H. pylori biofilm formation and present this mechanism as a resultant of the virulence and adaptive responses of H. pylori, including morphological transformation, membrane vesicles secretion, matrix production, efflux pump activity, and intermicrobial communication. These mechanisms will be considered in the context of transcriptomic and proteomic changes in H. pylori biofilms and their modulating effect on the development of this complex structure.

Proteomics of Campylobacter jejuni Growth in Deoxycholate Reveals Cj0025c as a Cystine Transport Protein Required for Wild-type Human Infection Phenotypes

Campylobacter jejuni is a major cause of food-borne gastroenteritis. Proteomics by label-based two-dimensional liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS) identified proteins associated with growth in 0.1% sodium deoxycholate (DOC, a component of gut bile salts), and system-wide validation was performed by data-independent acquisition (DIA-SWATH-MS). LC-MS/MS quantified 1326 proteins (∼82% of the predicted C. jejuni proteome), of which 1104 were validated in additional biological replicates by DIA-SWATH-MS. DOC resulted in a profound proteome shift with 512 proteins showing significantly altered abundance. Induced proteins were associated with flagellar motility and antibiotic resistance; and these correlated with increased DOC motility and resistance to polymyxin B and ciprofloxacin. DOC also increased human Caco-2 cell adherence and invasion. Abundances of proteins involved in nutrient transport were altered by DOC and aligned with intracellular changes to their respective carbon sources. DOC increased intracellular levels of sulfur-containing amino acids (cysteine and methionine) and the dipeptide cystine (Cys-Cys), which also correlated with reduced resistance to oxidative stress. A DOC induced transport protein was Cj0025c, which has sequence similarity to bacterial Cys-Cys transporters. Deletion of cj0025c (Δcj0025c) resulted in proteome changes consistent with sulfur starvation, as well as attenuated invasion, reduced motility, atypical morphology, increased antimicrobial susceptibility and poor biofilm formation. Targeted metabolomics showed Δcj0025c could use known C. jejuni amino and organic acid substrates commensurate with wild-type. Medium Cys-Cys levels however, were maintained in Δcj0025c relative to wild-type. A toxic Cys-Cys mimic (selenocystine) inhibited wild-type growth, but not Δcj0025c Provision of an alternate sulfur source (2 mm thiosulfate) restored Δcj0025c motility. Our data confirm that Cj0025c is a Cys-Cys transporter that we have named TcyP consistent with the nomenclature of homologous proteins in other species.

Lsr operon is associated with AI-2 transfer and pathogenicity in avian pathogenic Escherichia coli

The function of Autoinducer-2 (AI-2) which acts as the signal molecule of LuxS-mediated quorum sensing, is regulated through the lsr operon (which includes eight genes: lsrK, lsrR, lsrA, lsrC, lsrD, lsrB, lsrF, and lsrG). However, the functions of the lsr operon remain unclear in avian pathogenic Escherichia coli (APEC), which causes severe respiratory and systemic diseases in poultry. In this study, the presence of the lsr operon in 60 APEC clinical strains (serotypes O1, O2, and O78) was investigated and found to be correlated with serotype and has the highest detection rate in O78. The AI-2 binding capacity of recombinant protein LsrB of APEC (APEC-LsrB) was verified and was found to bind to AI-2 in vitro. In addition, the lsr operon was mutated in an APEC strain (APEC94Δlsr(Cm)) and the mutant was found to be defective in motility and AI-2 uptake. Furthermore, deletion of the lsr operon attenuated the virulence of APEC, with the LD₅₀ of APEC94Δlsr(Cm) decreasing 294-fold compared with wild-type strain APEC94. The bacterial load in the blood, liver, spleen, and kidneys of ducks infected with APEC94Δlsr(Cm) decreased significantly (p < 0.0001). The results of transcriptional analysis showed that 62 genes were up-regulated and 415 genes were down-regulated in APEC94Δlsr(Cm) compared with the wild-type strain and some of the down-regulated genes were associated with the virulence of APEC. In conclusion, our study suggests that lsr operon plays a role in the pathogenesis of APEC.

Regulatory Mechanisms of the LuxS/AI-2 System and Bacterial Resistance

The quorum-sensing (QS) system is an intercellular cell-cell communication mechanism that controls the expression of genes involved in a variety of cellular processes and that plays critical roles in the adaption and survival of bacteria in their environment. The LuxS/AI-2 QS system, which uses AI-2 (autoinducer-2) as a signal molecule, has been identified in both Gram-negative and Gram-positive bacteria. As one of the important global regulatory networks in bacteria, it responds to fluctuations in the numbers of bacteria and regulates the expression of a number of genes, thus affecting cell behavior. We summarize here the known relationships between the LuxS/AI-2 system and drug resistance, discuss the inhibition of LuxS/AI-2 system as an approach to prevent bacterial resistance, and present new strategies for the treatment of drug-resistant pathogens.

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.

Potential Role of Biofilm Formation in the Development of Digestive Tract Cancer With Special Reference to Helicobacter pylori Infection

Bacteria are highly social organisms that communicate via signaling molecules and can assume a multicellular lifestyle to build biofilm communities. Until recently, complications from biofilm-associated infection have been primarily ascribed to increased bacterial resistance to antibiotics and host immune evasion, leading to persistent infection. In this theory and hypothesis article we present a relatively new argument that biofilm formation has potential etiological role in the development of digestive tract cancer. First, we summarize recent new findings suggesting the potential link between bacterial biofilm and various types of cancer to build the foundation of our hypothesis. To date, evidence has been particularly convincing for colorectal cancer and its precursor, i.e., polyps, pointing to several key individual bacterial species, such as Bacteroides fragilis, Fusobacterium nucleatum, and Streptococcus gallolyticus subsp. Gallolyticus. Then, we further extend this hypothesis to one of the most common bacterial infection in humans, Helicobacter pylori (Hp), which is considered a major cause of gastric cancer. Thus far, there has been no direct evidence linking in vivo Hp gastric biofilm formation to gastric carcinogenesis. Yet, we synthesize the information to support an argument that biofilm associated-Hp is potentially more carcinogenic, summarizing biological characteristics of biofilm-associated bacteria. We also discuss mechanistic pathways as to how Hp or other biofilm-associated bacteria control biofilm formation and highlight recent findings on Hp genes that influence biofilm formation, which may lead to strain variability in biofilm formation. This knowledge may open a possibility of developing targeted intervention. We conclude, however, that this field is still in its infancy. To test the hypothesis rigorously and to link it ultimately to gastric pathologies (e.g., premalignant lesions and cancer), studies are needed to learn more about Hp biofilms, such as compositions and biological properties of extracellular polymeric substance (EPS), presence of non-Hp microbiome and geographical distribution of biofilms in relation to gastric gland types and structures. Identification of specific Hp strains with enhanced biofilm formation would be helpful not only for screening patients at high risk for sequelae from Hp infection, but also for development of new antibiotics to avoid resistance, regardless of its association with gastric cancer.

Mechanisms of Bacterial Tolerance and Persistence in the Gastrointestinal and Respiratory Environments

Pathogens that infect the gastrointestinal and respiratory tracts are subjected to intense pressure due to the environmental conditions of the surroundings. This pressure has led to the development of mechanisms of bacterial tolerance or persistence which enable microorganisms to survive in these locations. In this review, we analyze the general stress response (RpoS mediated), reactive oxygen species (ROS) tolerance, energy metabolism, drug efflux pumps, SOS response, quorum sensing (QS) bacterial communication, (p)ppGpp signaling, and toxin-antitoxin (TA) systems of pathogens, such as Escherichia coli, Salmonella spp., Vibrio spp., Helicobacter spp., Campylobacter jejuni, Enterococcus spp., Shigella spp., Yersinia spp., and Clostridium difficile, all of which inhabit the gastrointestinal tract. The following respiratory tract pathogens are also considered: Staphylococcus aureus, Pseudomonas aeruginosa, Acinetobacter baumannii, Burkholderia cenocepacia, and Mycobacterium tuberculosis Knowledge of the molecular mechanisms regulating the bacterial tolerance and persistence phenotypes is essential in the fight against multiresistant pathogens, as it will enable the identification of new targets for developing innovative anti-infective treatments.

The role of the ptsI gene on AI-2 internalization and pathogenesis of avian pathogenic Escherichia coli

The LuxS/AI-2 quorum sensing mechanism can regulate the physiological functions of avian pathogenic Escherichia coli (APEC) through internalization of the small molecule autoinducer-2 (AI-2). The ptsI gene encodes enzyme I, which participates in the phosphotransferase system (PTS) that regulates the virulence and AI-2 internalization of bacteria. The aim of the present study was to determine the effect of ptsI on AI-2 internalization and other pathogenesis process in APEC using a ptsI mutant of the APEC strain DE17 (serotype O2), namely DE17ΔptsI. The results showed that deletion of the ptsI gene changed the rdar (red dry and rough) morphotype and decreased motility and biofilm formation in APEC (p < 0.05). Furthermore, scanning electron microscopy showed that the biofilm structure of DE17ΔptsI became sparse and more extracellular, as compared with the wild-type strain DE17. Moreover, AI-2 assay showed that AI-2 was internalized by DE17ΔptsI, while the recombinant PtsI protein had no AI-2 binding activity. Furthermore, deletion of the ptsI gene in APEC significantly increased adherence to DF-1 cells (p < 0.05). The 50% lethal dose of DE17ΔptsI was decreased by 17.8-fold and the bacterial loads of DE17ΔptsI were decreased by 13600-, 68.5-, 131-, and 3600-fold in the blood, liver, spleen, and kidney, respectively, as compared to the DE17. Moreover, histopathological analysis showed that the mutant DE17ΔptsI was associated with reduced pathological changes in the heart, liver, spleen, and kidney of ducklings, respectively, as compared to the wild-type strain DE17. The results of this study will benefit further studies on the functions of the ptsI in APEC.

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.

Biofilm Formation by Helicobacter pylori and Its Involvement for Antibiotic Resistance

Bacterial biofilms are communities of microorganisms attached to a surface. Biofilm formation is critical not only for environmental survival but also for successful infection. Helicobacter pylori is one of the most common causes of bacterial infection in humans. Some studies demonstrated that this microorganism has biofilm forming ability in the environment and on human gastric mucosa epithelium as well as on in vitro abiotic surfaces. In the environment, H. pylori could be embedded in drinking water biofilms through water distribution system in developed and developing countries so that the drinking water may serve as a reservoir for H. pylori infection. In the human stomach, H. pylori forms biofilms on the surface of gastric mucosa, suggesting one possible explanation for eradication therapy failure. Finally, based on the results of in vitro analyses, H. pylori biofilm formation can decrease susceptibility to antibiotics and H. pylori antibiotic resistance mutations are more frequently generated in biofilms than in planktonic cells. These observations indicated that H. pylori biofilm formation may play an important role in preventing and controlling H. pylori infections. Therefore, investigation of H. pylori biofilm formation could be effective in elucidating the detailed mechanisms of infection and colonization by this microorganism.

Inhibitory effect of piperine on Helicobacter pylori growth and adhesion to gastric adenocarcinoma cells

Background

Piperine is a compound comprising 5-9% of black pepper (Piper nigrum), which has a variety of biological roles related to anticancer activities. Helicobacter pylori has been classified as a gastric carcinogen, because it causes gastritis and gastric cancer by injecting the virulent toxin CagA and translocating VacA. The present study investigated the inhibitory action of piperine on H. pylori growth and adhesion.

Methods

Inhibition of H. pylori growth was determined by the broth macrodilution method, and adhesion to gastric adenocarcinoma cells validated by urease assay. Motility test was performed by motility agar and the expression of adhesion gene and flagellar gene in response to the piperine treatment was assessed by RT-PCR and immunoblotting.

Results

Administrated piperine suppressed the level of H. pylori adhesion to gastric adenocarcinoma cells in a dose dependent manner and the inhibition was statistically significant as determined by Student’s t-test. In addition, piperine treatment effects on the flagellar hook gene flgE and integral membrane component of the export apparatus gene flhA expression to be suppressed and piperine diminished the H. pylori motility.

Conclusions

flhA, encodes an integral membrane component of the export apparatus, which is also one of the regulatory protein in the class 2 genes expression and flgE is one of them that encodes hook part of the flagella. Suppression of both genes, leads to less motility results in the organism attracted less towards to the gastric epithelial cells might be the possible reason in the adhesion inhibition. To our knowledge, this is the first report published on the inhibitory effects of piperine against the adhesion of H. pylori to gastric adenocarcinoma cells.

From deep-sea volcanoes to human pathogens: a conserved quorum-sensing signal in Epsilonproteobacteria

Chemosynthetic Epsilonproteobacteria from deep-sea hydrothermal vents colonize substrates exposed to steep thermal and redox gradients. In many bacteria, substrate attachment, biofilm formation, expression of virulence genes and host colonization are partly controlled via a cell density-dependent mechanism involving signal molecules, known as quorum sensing. Within the Epsilonproteobacteria, quorum sensing has been investigated only in human pathogens that use the luxS/autoinducer-2 (AI-2) mechanism to control the expression of some of these functions. In this study we showed that luxS is conserved in Epsilonproteobacteria and that pathogenic and mesophilic members of this class inherited this gene from a thermophilic ancestor. Furthermore, we provide evidence that the luxS gene is expressed--and a quorum-sensing signal is produced--during growth of Sulfurovum lithotrophicum and Caminibacter mediatlanticus, two Epsilonproteobacteria from deep-sea hydrothermal vents. Finally, we detected luxS transcripts in Epsilonproteobacteria-dominated biofilm communities collected from deep-sea hydrothermal vents. Taken together, our findings indicate that the epsiloproteobacterial lineage of the LuxS enzyme originated in high-temperature geothermal environments and that, in vent Epsilonproteobacteria, luxS expression is linked to the production of AI-2 signals, which are likely produced in situ at deep-sea vents. We conclude that the luxS gene is part of the ancestral epsilonproteobacterial genome and represents an evolutionary link that connects thermophiles to human pathogens.

A repetitive DNA element regulates expression of the Helicobacter pylori sialic acid binding adhesin by a rheostat-like mechanism

During persistent infection, optimal expression of bacterial factors is required to match the ever-changing host environment. The gastric pathogen Helicobacter pylori has a large set of simple sequence repeats (SSR), which constitute contingency loci. Through a slipped strand mispairing mechanism, the SSRs generate heterogeneous populations that facilitate adaptation. Here, we present a model that explains, in molecular terms, how an intergenically located T-tract, via slipped strand mispairing, operates with a rheostat-like function, to fine-tune activity of the promoter that drives expression of the sialic acid binding adhesin, SabA. Using T-tract variants, in an isogenic strain background, we show that the length of the T-tract generates multiphasic output from the sabA promoter. Consequently, this alters the H. pylori binding to sialyl-Lewis x receptors on gastric mucosa. Fragment length analysis of post-infection isolated clones shows that the T-tract length is a highly variable feature in H. pylori. This mirrors the host-pathogen interplay, where the bacterium generates a set of clones from which the best-fit phenotypes are selected in the host. In silico and functional in vitro analyzes revealed that the length of the T-tract affects the local DNA structure and thereby binding of the RNA polymerase, through shifting of the axial alignment between the core promoter and UP-like elements. We identified additional genes in H. pylori, with T- or A-tracts positioned similar to that of sabA, and show that variations in the tract length likewise acted as rheostats to modulate cognate promoter output. Thus, we propose that this generally applicable mechanism, mediated by promoter-proximal SSRs, provides an alternative mechanism for transcriptional regulation in bacteria, such as H. pylori, which possesses a limited repertoire of classical trans-acting regulatory factors.

Factors that mediate colonization of the human stomach by Helicobacter pylori

Helicobacter pylori (H. pylori) colonizes the stomach of humans and causes chronic infection. The majority of bacteria live in the mucus layer overlying the gastric epithelial cells and only a small proportion of bacteria are found interacting with the epithelial cells. The bacteria living in the gastric mucus may act as a reservoir of infection for the underlying cells which is essential for the development of disease. Colonization of gastric mucus is likely to be key to the establishment of chronic infection. How H. pylori manages to colonise and survive in the hostile environment of the human stomach and avoid removal by mucus flow and killing by gastric acid is the subject of this review. We also discuss how bacterial and host factors may together go some way to explaining the susceptibility to colonization and the outcome of infection in different individuals. H. pylori infection of the gastric mucosa has become a paradigm for chronic infection. Understanding of why H. pylori is such a successful pathogen may help us understand how other bacterial species colonise mucosal surfaces and cause disease.

Phylogeographic origin of Helicobacter pylori determines host-adaptive responses upon coculture with gastric epithelial cells

While Helicobacter pylori infects over 50% of the world's population, the mechanisms involved in the development of gastric disease are not fully understood. Bacterial, host, and environmental factors play a role in disease outcome. To investigate the role of bacterial factors in H. pylori pathogenesis, global gene expression of six H. pylori isolates was analyzed during coculture with gastric epithelial cells. Clustering analysis of six Colombian clinical isolates from a region with low gastric cancer risk and a region with high gastric cancer risk segregated strains based on their phylogeographic origin. One hundred forty-six genes had increased expression in European strains, while 350 genes had increased expression in African strains. Differential expression was observed in genes associated with motility, pathogenicity, and other adaptations to the host environment. European strains had greater expression of the virulence factors cagA, vacA, and babB and were associated with increased gastric histologic lesions in patients. In AGS cells, European strains promoted significantly higher interleukin-8 (IL-8) expression than did African strains. African strains significantly induced apoptosis, whereas only one European strain significantly induced apoptosis. Our data suggest that gene expression profiles of clinical isolates can discriminate strains by phylogeographic origin and that these profiles are associated with changes in expression of the proinflammatory and protumorigenic cytokine IL-8 and levels of apoptosis in host epithelial cells. These findings support the hypothesis that bacterial factors determined by the phylogeographic origin of H. pylori strains may promote increased gastric disease.

Robustness of Helicobacter pylori infection conferred by context-variable redundancy among cysteine-rich paralogs

Deletion of single genes from expanded gene families in bacterial genomes often does not elicit a phenotype thus implying redundancy or functional non-essentiality of paralogous genes. The molecular mechanisms that facilitate evolutionary maintenance of such paralogs despite selective pressures against redundancy remain mostly unexplored. Here, we investigate the evolutionary, genetic, and functional interaction between the Helicobacter pylori cysteine-rich paralogs hcpG and hcpC in the context of H. pylori infection of cultured mammalian cells. We find that in natural H. pylori populations both hcpG and hcpC are maintained by positive selection in a dual genetic relationship that switches from complete redundancy during early infection, whereby ΔhcpC or ΔhcpG mutants themselves show no growth defect but a significant growth defect is seen in the ΔhcpC,ΔhcpG double mutant, to quantitative redundancy during late infection wherein the growth defect of the ΔhcpC mutant is exacerbated in the ΔhcpC,ΔhcpG double mutant although the ΔhcpG mutant itself shows no defect. Moreover, during early infection both hcpG and hcpC are essential for optimal translocation of the H. pylori HspB/GroEL chaperone, but during middle-to-late infection hcpC alone is necessary and sufficient for HspB/GroEL translocation thereby revealing the lack of functional compensation among paralogs. We propose that evolution of context-dependent differences in the nature of genetic redundancy, and function, between hcpG and hcpC may facilitate their maintenance in H. pylori genomes, and confer robustness to H. pylori growth during infection of cultured mammalian cells.

The luxS gene functions in the pathogenesis of avian pathogenic Escherichia coli

Avian pathogenic Escherichia coli (APEC) causes avian colibacillosis, the most significant infectious bacterial disease of poultry worldwide. LuxS, the product of the luxS gene, mediates the quorum sensing (QS) mechanism. This involves the production of autoinducer-2 (AI-2), which regulates important physiological traits and a variety of adaptive processes in different bacteria. In this study, a luxS gene deleted APEC mutant strain, ΔDE17, was constructed using strain DE17. Analysis of bioluminescence indicated that deletion of the luxS gene abolished the production of the QS signal AI-2 in the bacteria. Further studies showed that deletion of the luxS gene in DE17 reduced the bacterial virulence by 31.5-fold in ducklings, based on the measurement of the 50% lethal dose. The mutant strain reduced significantly the abilities of adherence and invasion, by 50.0% and 40.7% respectively, compared with the wild strain DE17. The mutant strain also showed reduced survival in vivo: the bacterial loads of the mutant strain in infected liver, spleen and blood were 46.4-fold, 5.2-fold, and 3.7-fold reduced, respectively, compared with the wild-type strain DE17. Real-time polymerase chain reaction (PCR) demonstrated further that the mRNA levels of the virulence-related genes iucD, fyuA, vat, ompA, iss, fimC and tsh were significantly decreased in the mutant strain ΔDE17, when compared with DE17 (p < 0.05). In addition, the deletion of the luxS gene reduced the motility of the bacterium. This study suggests that the luxS gene functions in the pathogenesis of diseases caused by avian pathogenic E. coli.

AI-2-mediated signalling in bacteria

Success in nature depends upon an ability to perceive and adapt to the surrounding environment. Bacteria are not an exception; they recognize and constantly adjust to changing situations by sensing environmental and self-produced signals, altering gene expression accordingly. Autoinducer-2 (AI-2) is a signal molecule produced by LuxS, an enzyme found in many bacterial species and thus proposed to enable interspecies communication. Two classes of AI-2 receptors and many layers and interactions involved in downstream signalling have been identified so far. Although AI-2 has been implicated in the regulation of numerous niche-specific behaviours across the bacterial kingdom, interpretation of these results is complicated by the dual role of LuxS in signalling and the activated methyl cycle, a crucial central metabolic pathway. In this article, we present a comprehensive review of the discovery and early characterization of AI-2, current developments in signal detection, transduction and regulation, and the major studies investigating the phenotypes regulated by this molecule. The development of novel tools should help to resolve many of the remaining questions in the field; we highlight how these advances might be exploited in AI-2 quorum quenching, treatment of diseases, and the manipulation of beneficial behaviours caused by polyspecies communities.

Quorum sensing dependent phenotypes and their molecular mechanisms in Campylobacterales

Quorum sensing comprises the mechanism of communication between numerous bacteria via small signalling molecules, termed autoinducers (AI). Using quorum sensing, bacteria can regulate the expression of multiple genes involved in virulence, toxin production, motility, chemotaxis and biofilm formation, thus contributing to adaptation as well as colonisation. The current understanding of the role of quorum sensing in the lifecycle of Campylobacterales is still incomplete. Campylobacterales belong to the class of Epsilonproteobacteria representing a physiologically and ecologically diverse group of bacteria that are rather distinct from the more commonly studied Proteobacteria, such as Escherichia and Salmonella. This review summarises the recent knowledge on distribution and production of AI molecules, as well as possible quorum sensing dependent regulation in the mostly investigated species within the Campylobacterales group: Campylobacter jejuni and Helicobacter pylori.

Helicobacter pylori perceives the quorum-sensing molecule AI-2 as a chemorepellent via the chemoreceptor TlpB

Helicobacter pylori moves in response to environmental chemical cues using a chemotaxis two-component signal-transduction system. Autoinducer-2 (AI-2) is a quorum-sensing signal produced by the LuxS protein that accumulates in the bacterial environment in a density-dependent manner. We showed previously that a H. pylori luxS mutant was defective in motility on soft agar plates. Here we report that deletion of the luxS gene resulted in swimming behaviour with a reduced frequency of stops as compared to the wild-type strain. Stopping frequency was restored to wild-type levels by genetic complementation of the luxS mutation or by addition of synthetic 4,5-dihydroxy-2,3-pentanedione (DPD), which cyclizes to form AI-2. Synthetic DPD also increased the frequency of stops in wild-type H. pylori, similar to the behaviour induced by the known chemorepellent HCl. We found that whereas mutants lacking the chemoreceptor genes tlpA, tlpC or tlpD responded to an exogenous source of synthetic DPD, the chemoreceptor mutant tlpB was non-responsive to a gradient or uniform distribution of the chemical. Furthermore, a double mutant lacking both tlpB and luxS exhibited chemotactic behaviour similar to the tlpB single mutant, whereas a double mutant lacking both tlpB and the chemotransduction gene cheA behaved like a nonchemotactic cheA single mutant, supporting the model that tlpB functions in a signalling pathway downstream of luxS and upstream of cheA. We conclude that H. pylori perceives LuxS-produced AI-2 as a chemorepellent via the chemoreceptor TlpB.