Transducer like proteins of Campylobacter jejuni 81-176: role in chemotaxis and colonization of the chicken gastrointestinal tract

Identification of a dCache-type chemoreceptor in Campylobacter jejuni that specifically mediates chemotaxis towards methyl pyruvate

The foodborne pathogenic bacterium Campylobacter jejuni utilizes chemotaxis to assist in the colonization of host niches. A key to revealing the relationship among chemotaxis and pathogenicity is the discovery of signaling molecules perceived by the chemoreceptors. The C. jejuni chemoreceptor Tlp11 is encoded by the highly infective C. jejuni strains. In the present study, we report that the dCache-type ligand-binding domain (LBD) of C. jejuni ATCC 33560 Tlp11 binds directly to novel ligands methyl pyruvate, toluene, and quinoline using the same pocket. Methyl pyruvate elicits a strong chemoattractant response, while toluene and quinoline function as the antagonists without triggering chemotaxis. The sensory LBD was used to control heterologous proteins by constructing chimeras, indicating that the signal induced by methyl pyruvate is transmitted across the membrane. In addition, bioinformatics and experiments revealed that the dCache domains with methyl pyruvate-binding sites and ability are widely distributed in the order Campylobacterales. This is the first report to identify the class of dCache chemoreceptors that bind to attractant methyl pyruvate and antagonists toluene and quinoline. Our research provides a foundation for understanding the chemotaxis and virulence of C. jejuni and lays a basis for the control of this foodborne pathogen.

Bacterial envelope stress responses: Essential adaptors and attractive targets

Millions of deaths a year across the globe are linked to antimicrobial resistant infections. The need to develop new treatments and repurpose of existing antibiotics grows more pressing as the growing antimicrobial resistance pandemic advances. In this review article, we propose that envelope stress responses, the signaling pathways bacteria use to recognize and adapt to damage to the most vulnerable outer compartments of the microbial cell, are attractive targets. Envelope stress responses (ESRs) support colonization and infection by responding to a plethora of toxic envelope stresses encountered throughout the body; they have been co-opted into virulence networks where they work like global positioning systems to coordinate adhesion, invasion, microbial warfare, and biofilm formation. We highlight progress in the development of therapeutic strategies that target ESR signaling proteins and adaptive networks and posit that further characterization of the molecular mechanisms governing these essential niche adaptation machineries will be important for sparking new therapeutic approaches aimed at short-circuiting bacterial adaptation.

Effect of Probiotic E. coli Nissle 1917 Supplementation on the Growth Performance, Immune Responses, Intestinal Morphology, and Gut Microbes of Campylobacter jejuni Infected Chickens

Campylobacter jejuni is the most common cause of bacterial foodborne gastroenteritis and holds significant public health importance. The continuing increase of antibiotic-resistant Campylobacter necessitates the development of antibiotic-alternative approaches to control infections in poultry and in humans. Here, we assessed the ability of E. coli Nissle 1917 (EcN; free and chitosan-alginate microencapsulated) to reduce C. jejuni colonization in chickens and measured the effect of EcN on the immune responses, intestinal morphology, and gut microbes of chickens. Our results showed that the supplementation of 3-week-old chickens daily with free EcN in drinking water resulted in a 2.0 log reduction of C. jejuni colonization in the cecum, whereas supplementing EcN orally three times a week, either free or microencapsulated, resulted in 2.0 and 2.5 log reductions of C. jejuni colonization, respectively. Gavaged free and microencapsulated EcN did not have an impact on the evenness or the richness of the cecal microbiota, but it did increase the villous height (VH), crypt depth (CD), and VH:CD ratio in the jejunum and ileum of chickens. Further, the supplementation of EcN (all types) increased C. jejuni-specific and total IgA and IgY antibodies in chicken’s serum. Microencapsulated EcN induced the expression of several cytokines and chemokines (1.6 to 4.3-fold), which activate the Th1, Th2, and Th17 pathways. Overall, microencapsulated EcN displayed promising effects as a potential nonantibiotic strategy to control C. jejuni colonization in chickens. Future studies on testing microencapsulated EcN in the feed and water of chickens raised on built-up floor litter would facilitate the development of EcN for industrial applications to control Campylobacter infections in poultry.

A Review of the Advantages, Disadvantages and Limitations of Chemotaxis Assays for Campylobacter spp

Reproducible qualitative and quantitative assessment of bacterial chemotactic motility, particularly in response to chemorepellent effectors, is experimentally challenging. Here we compare several established chemotaxis assays currently used to investigate Campylobacter jejuni chemotaxis, with the aim of improving the correlation between different studies and establishing the best practices. We compare the methodologies of capillary, agar, and chamber-based assays, and discuss critical technical points, in terms of reproducibility, accuracy, and the advantages and limitations of each.

The Campylobacter jejuni Response Regulator and Cyclic-Di-GMP Binding CbrR Is a Novel Regulator of Flagellar Motility

A leading cause of bacterial gastroenteritis, Campylobacter jejuni is also associated with broad sequelae, including extragastrointestinal conditions such as reactive arthritis and Guillain-Barré Syndrome (GBS). CbrR is a C. jejuni response regulator that is annotated as a diguanylate cyclase (DGC), an enzyme that catalyzes the synthesis of c-di-GMP, a universal bacterial second messenger, from GTP. In C. jejuni DRH212, we constructed an unmarked deletion mutant, cbrR^-, and complemented mutant, cbrR⁺. Motility assays indicated a hyper-motile phenotype associated with cbrR^-, whereas motility was deficient in cbrR⁺. The overexpression of CbrR in cbrR⁺ was accompanied by a reduction in expression of FlaA, the major flagellin. Biofilm assays and scanning electron microscopy demonstrated similarities between DRH212 and cbrR^-; however, cbrR⁺ was unable to form significant biofilms. Transmission electron microscopy showed similar cell morphology between the three strains; however, cbrR⁺ cells lacked flagella. Differential radial capillary action of ligand assays (DRaCALA) showed that CbrR binds GTP and c-di-GMP. Liquid chromatography tandem mass spectrometry detected low levels of c-di-GMP in C. jejuni and in E. coli expressing CbrR. CbrR is therefore a negative regulator of FlaA expression and motility, a critical virulence factor in C. jejuni pathogenesis.

Virulence factors of foodborne pathogen Campylobacterjejuni

Campylobacter jejuni is a highly frequent cause of gastrointestinal foodborne disease in humans throughout the world. Disease outcomes vary from mild to severe diarrhea, and in rare cases the Guillain-Barré syndrome or reactive arthritis can develop as a post-infection complication. Transmission to humans usually occurs via the consumption of a range of foods, especially those associated with the consumption of raw or undercooked poultry meat, unpasteurized milk, and water-based environmental sources. When associated to food or water ingestion, the C. jejuni enters the human host intestine via the oral route and colonizes the distal ileum and colon. When it adheres and colonizes the intestinal cell surfaces, the C. jejuni is expected to express several putative virulence factors, which cause damage to the intestine either directly, by cell invasion and/or production of toxin(s), or indirectly, by triggering inflammatory responses. This review article highlights various C. jejuni characteristics - such as motility and chemotaxis - that contribute to the biological fitness of the pathogen, as well as factors involved in human host cell adhesion and invasion, and their potential role in the development of the disease. We have analyzed and critically discussed nearly 180 scientific articles covering the latest improvements in the field.

Inactivation of the core cheVAWY chemotaxis genes disrupts chemotactic motility and organised biofilm formation in Campylobacter jejuni

Flagellar motility plays a central role in the bacterial foodborne pathogen Campylobacter jejuni, as flagellar motility is required for reaching the intestinal epithelium and subsequent colonisation or disease. Flagellar proteins also contribute strongly to biofilm formation during transmission. Chemotaxis is the process directing flagellar motility in response to attractant and repellent stimuli, but its role in biofilm formation of C. jejuni is not well understood. Here we show that inactivation of the core chemotaxis genes cheVAWY in C. jejuni strain NCTC 11168 affects both chemotactic motility and biofilm formation. Inactivation of any of the core chemotaxis genes (cheA, cheY, cheV or cheW) impaired chemotactic motility but did not affect flagellar assembly or growth. The ∆cheY mutant swam in clockwise loops, while complementation restored normal motility. Inactivation of the core chemotaxis genes interfered with the ability to form a discrete biofilm at the air-media interface, and the ∆cheY mutant displayed reduced dispersal/shedding of bacteria into the planktonic fraction. This suggests that while the chemotaxis system is not required for biofilm formation per se, it is necessary for organized biofilm formation. Hence interference with the Campylobacter chemotaxis system at any level disrupts optimal chemotactic motility and transmission modes such as biofilm formation.

Molecular Mechanisms of Campylobacter Biofilm Formation and Quorum Sensing

Even though Campylobacter spp. are known to be fastidious organisms, they can survive within the natural environment. One mechanism to withstand unfavourable conditions is the formation of biofilms, a multicellular structure composed of different bacterial and other microbial species which are embedded in an extracellular matrix. High oxygen levels, low substrate concentrations and the presence of external DNA stimulate the biofilm formation by C. jejuni. These external factors trigger internal adaptation processes, e.g. via regulating the expression of genes encoding proteins required for surface structure formation, as well as motility, stress response and antimicrobial resistance. Known genes impacting biofilm formation will be summarized in this review. The formation of biofilms as well as the expression of virulence genes is often regulated in a cell density depending manner by quorum sensing, which is mediated via small signalling molecules termed autoinducers. Even though quorum sensing mechanisms of other bacteria are well understood, knowledge on the role of these mechanisms in C. jejuni biofilm formation is still scarce. The LuxS enzyme involved in generation of autoinducer-2 is present in C. jejuni, but autoinducer receptors have not been identified so far. Phenotypes of C. jejuni strains lacking a functional luxS like reduced growth, motility, oxygen stress tolerance, biofilm formation, adhesion, invasion and colonization are also summarized within this chapter. However, these phenotypes are highly variable in distinct C. jejuni strains and depend on the culture conditions applied.

cheA, cheB, cheR, cheV, and cheY Are Involved in Regulating the Adhesion of Vibrio harveyi

Diseases caused by Vibrio harveyi lead to severe economic losses in the aquaculture industry. Adhesion is an important disease-causing factor observed in bacteria with chemotactic activity. In our study, we measured the adhesion of V. harveyi by subjecting the bacteria to stress using Cu²⁺, Pb²⁺, Hg²⁺, and Zn²⁺. The genes responsible for chemotaxis (cheA, cheB, cheR, cheV, and cheY), which are also crucial for adhesion, were identified and silenced via RNAi. We observed that a decrease in chemotactic gene expression reduced the ability of the organism to demonstrate adhesion, motility, chemotaxis, and biofilm formation. Upon comparing the cheA-RNAi bacteria to the wild-type strain, we observed that the transcriptome of V. harveyi was significantly altered. Additionally, the expression of key genes and the adhesion ability were affected by the pH (pH of 5, 6, 7, 8, and 9), salinity (NaCl at concentrations of 0.8, 1.5, 2.5, 3.5, or 4.5%), and temperature (4, 15, 28, 37, and 44°C) of the medium. Based on these results, the following conclusions were made: (1) The chemotactic genes cheA, cheB, cheR, cheV, and cheY may regulate the adhesion ability of V. harveyi by affecting bacterial motility, and participate in the regulation of adhesion at different temperatures, salinities, and pH values; (2) stable silencing of cheA could alter the transcriptional landscape of V. harveyi and regulate the expression of genes associated with its adhesion mechanisms.

The Campylobacter jejuni chemoreceptor Tlp10 has a bimodal ligand-binding domain and specificity for multiple classes of chemoeffectors

Campylobacter jejuni is a bacterial pathogen that is a common cause of enteritis in humans. We identified a previously uncharacterized type of sensory domain in the periplasmic region of the C. jejuni chemoreceptor Tlp10, termed the DAHL domain, that is predicted to have a bimodular helical architecture. Through two independent ligand-binding sites in this domain, Tlp10 responded to molecular aspartate, isoleucine, fumarate, malate, fucose, and mannose as attractants and to arginine, galactose, and thiamine as repellents. Tlp10 also recognized glycan ligands when present as terminal and intermediate residues of complex structures, such as the fucosylated human ganglioside GM1 and Lewis^a antigen. A tlp10 mutant strain lacking the ligand-binding sites was attenuated in its ability to colonize avian caeca and to adhere to cultured human intestinal cells, indicating the potential involvement of the DAHL domain in host colonization and disease. The Tlp10 intracellular signaling domain interacted with the scaffolding proteins CheV and CheW, which couple chemoreceptors to intracellular signaling machinery, and with the signaling domains of other chemoreceptors, suggesting a key role for Tlp10 in signal transduction and incorporation into sensory arrays. We identified the DAHL domain in other bacterial signal transduction proteins, including the essential virulence induction protein VirA from the plant pathogen Agrobacterium tumefaciens Together, these results suggest a potential link between Tlp10 and C. jejuni virulence.

Membrane Proteocomplexome of Campylobacter jejuni Using 2-D Blue Native/SDS-PAGE Combined to Bioinformatics Analysis

Campylobacter is the leading cause of the human bacterial foodborne infections in the developed countries. The perception cues from biotic or abiotic environments by the bacteria are often related to bacterial surface and membrane proteins that mediate the cellular response for the adaptation of Campylobacter jejuni to the environment. These proteins function rarely as a unique entity, they are often organized in functional complexes. In C. jejuni, these complexes are not fully identified and some of them remain unknown. To identify putative functional multi-subunit entities at the membrane subproteome level of C. jejuni, a holistic non a priori method was addressed using two-dimensional blue native/Sodium dodecyl sulfate (SDS) polyacrylamide gel electrophoresis (PAGE) in strain C. jejuni 81-176. Couples of acrylamide gradient/migration-time, membrane detergent concentration and hand-made strips were optimized to obtain reproducible extraction and separation of intact membrane protein complexes (MPCs). The MPCs were subsequently denatured using SDS-PAGE and each spot from each MPCs was identified by mass spectrometry. Altogether, 21 MPCs could be detected including multi homo-oligomeric and multi hetero-oligomeric complexes distributed in both inner and outer membranes. The function, the conservation and the regulation of the MPCs across C. jejuni strains were inspected by functional and genomic comparison analyses. In this study, relatedness between subunits of two efflux pumps, CmeABC and MacABputC was observed. In addition, a consensus sequence CosR-binding box in promoter regions of MacABputC was present in C. jejuni but not in Campylobacter coli. The MPCs identified in C. jejuni 81-176 membrane are involved in protein folding, molecule trafficking, oxidative phosphorylation, membrane structuration, peptidoglycan biosynthesis, motility and chemotaxis, stress signaling, efflux pumps and virulence.

Assigning a role for chemosensory signal transduction in Campylobacter jejuni biofilms using a combined omics approach

Biofilms of the gastroenteric pathogen C. jejuni may serve an important role in the transmission of infection from reservoirs of infection to humans. Herein, we undertook a combinatorial approach examining differential gene expression and protein abundance during biofilm formation in C. jejuni. Biofilms induced a substantial rearrangement of the C. jejuni transcriptome and proteome, with ~600 genes differentially expressed when compared to planktonic cells. Genes and proteins induced in biofilms were involved in iron metabolism and acquisition, cell division, glycan production and attachment, while those repressed were associated with metabolism, amino acid usage, and large tracts of the chemotaxis pathway. We further examined the role of chemotaxis in C. jejuni biofilm formation by examining isogenic strains with deletions of the cheV and cheW signal transduction genes. Both ∆cheV and ∆cheW exhibited a significant decrease in directed motility when compared to wild-type C. jejuni as well as demonstrating an increase in autoagglutination ability and biofilm formation. A subtle difference was also observed between the phenotypes of ∆cheV and ∆cheW mutants, both in motility and biofilm formation. This suggests roles for CheV and CheW and may present signal transduction as a potential method for modulating C. jejuni biofilm formation.

Bridging the Gap: A Role for Campylobacter jejuni Biofilms

Campylobacter jejuni is the leading cause of bacterial gastroenteritis in the developed world. Cases of Campylobacteriosis are common, as the organism is an avian commensal and is passed on to humans through contaminated poultry meat, water, and food preparation areas. Although typically a fastidious organism, C. jejuni can survive outside the avian intestinal tract until it is able to reach a human host. It has long been considered that biofilms play a key role in transmission of this pathogen. The aim of this review is to examine factors that trigger biofilm formation in C. jejuni. A range of environmental elements have been shown to initiate biofilm formation, which are then affected by a suite of intrinsic factors. We also aim to further investigate the role that biofilms may play in the life cycle of this organism.

Campylobacter jejuni Demonstrates Conserved Proteomic and Transcriptomic Responses When Co-cultured With Human INT 407 and Caco-2 Epithelial Cells

Major foodborne bacterial pathogens, such as Campylobacter jejuni, have devised complex strategies to establish and foster intestinal infections. For more than two decades, researchers have used immortalized cell lines derived from human intestinal tissue to dissect C. jejuni-host cell interactions. Known from these studies is that C. jejuni virulence is multifactorial, requiring a coordinated response to produce virulence factors that facilitate host cell interactions. This study was initiated to identify C. jejuni proteins that contribute to adaptation to the host cell environment and cellular invasion. We demonstrated that C. jejuni responds to INT 407 and Caco-2 cells in a similar fashion at the cellular and molecular levels. Active protein synthesis was found to be required for C. jejuni to maximally invade these host cells. Proteomic and transcriptomic approaches were then used to define the protein and gene expression profiles of C. jejuni co-cultured with cells. By focusing on those genes showing increased expression by C. jejuni when co-cultured with epithelial cells, we discovered that C. jejuni quickly adapts to co-culture with epithelial cells by synthesizing gene products that enable it to acquire specific amino acids for growth, scavenge for inorganic molecules including iron, resist reactive oxygen/nitrogen species, and promote host cell interactions. Based on these findings, we selected a subset of the genes involved in chemotaxis and the regulation of flagellar assembly and generated C. jejuni deletion mutants for phenotypic analysis. Binding and internalization assays revealed significant differences in the interaction of C. jejuni chemotaxis and flagellar regulatory mutants. The identification of genes involved in C. jejuni adaptation to culture with host cells provides new insights into the infection process.

Proteomics Reveals Multiple Phenotypes Associated with N-linked Glycosylation in Campylobacter jejuni

Campylobacter jejuni is a major gastrointestinal pathogen generally acquired via consumption of poorly prepared poultry. N-linked protein glycosylation encoded by the pgl gene cluster targets >80 membrane proteins and is required for both nonsymptomatic chicken colonization and full human virulence. Despite this, the biological functions of N-glycosylation remain unknown. We examined the effects of pgl gene deletion on the C. jejuni proteome using label-based liquid chromatography/tandem mass spectrometry (LC-MS/MS) and validation using data independent acquisition (DIA-SWATH-MS). We quantified 1359 proteins corresponding to ∼84% of the C. jejuni NCTC 11168 genome, and 1080 of these were validated by DIA-SWATH-MS. Deletion of the pglB oligosaccharyltransferase (ΔpglB) resulted in a significant change in abundance of 185 proteins, 137 of which were restored to their wild-type levels by reintroduction of pglB (Δaaz.batpglB::ΔpglB). Deletion of pglB was associated with significantly reduced abundances of pgl targets and increased stress-related proteins, including ClpB, GroEL, GroES, GrpE and DnaK. pglB mutants demonstrated reduced survival following temperature (4 °C and 46 °C) and osmotic (150 mm NaCl) shock and altered biofilm phenotypes compared with wild-type C. jejuni Targeted metabolomics established that pgl negative C. jejuni switched from aspartate (Asp) to proline (Pro) uptake and accumulated intracellular succinate related to proteome changes including elevated PutP/PutA (proline transport and utilization), and reduced DctA/DcuB (aspartate import and succinate export, respectively). ΔpglB chemotaxis to some substrates (Asp, glutamate, succinate and α-ketoglutarate) was reduced and associated with altered abundance of transducer-like (Tlp) proteins. Glycosylation negative C. jejuni were depleted of all respiration-associated proteins that allow the use of alternative electron acceptors under low oxygen. We demonstrate for the first time that N-glycosylation is required for a specific enzyme activity (Nap nitrate reductase) that is associated with reduced abundance of the NapAB glycoproteins. These data indicate a multifactorial role for N-glycosylation in C. jejuni physiology.

The role of chemotaxis during Campylobacter jejuni colonisation and pathogenesis

Campylobacter jejuni is a ubiquitous gastrointestinal pathogen, transmitted to humans from birds and animals, where C. jejuni is part of normal intestinal flora. In C. jejuni, similar to other motile bacteria, chemotaxis pathway and the array of chemosensors sense and respond to external stimuli with unique precision and sensitivity and are considered to be critical for bacterial colonisation and pathogenicity. Disruption of any component of the signal transduction pathway consisting of receptor-CheA/CheW-CheY-flagella cascade, the signal adaptation system, and even a loss of a single chemosensory receptor, dramatically reduce the ability of C. jejuni to colonise various animal hosts and to cause disease.

Transcriptomic analysis of Campylobacter jejuni grown in a medium containing serine as the main energy source

Campylobacter jejuni is one of the most important causes of food-borne diseases in industrialized countries. Amino acids are an important nutrient source for this pathogen because it lacks enzymes related to glycolysis. However, the metabolic characteristics of C. jejuni grown in a nutrient-restricted medium with specific amino acids have not been fully elucidated. This study shows that C. jejuni NCTC 11168 grows well in a nutrient-restricted medium containing serine, aspartate, glutamate, and proline. Subtracting serine significantly reduced growth, but the removal of the three other amino acids did not, suggesting that serine is a priority among the four amino acids. A transcriptomic analysis of C. jejuni NCTC 11168 grown in a medium with serine as the main energy source was then performed. Serine seemed to be sensed by some chemoreceptors, and C. jejuni reached an adaptation stage with active growth in which the expression of flagellar assembly components was downregulated and the biosyntheses of multiple amino acids and nucleotide sugars were upregulated. These data suggest that C. jejuni NCTC 11168 requires serine as a nutrient.

Transducer-Like Protein in Campylobacter jejuni With a Role in Mediating Chemotaxis to Iron and Phosphate

Chemotaxis-mediated motility enables Campylobacter jejuni to navigate through complex environmental gradients and colonize diverse niches. C. jejuni is known to possess several methyl accepting chemotaxis proteins (MCPs), also called transducer-like proteins (Tlps). While the role of some of the Tlps in chemotaxis has been identified, their regulation and role in virulence is still not very clear. Here, we investigated the contribution of Tlp2 to C. jejuni chemotaxis, stress survival and colonization of the chicken gastrointestinal tract. The Δtlp2 deletion mutant showed decreased chemotaxis toward aspartate, pyruvate, inorganic phosphate (Pi), and iron (FeSO4). Transcriptional analysis of tlp2 with a promoter fusion reporter assay revealed that the tlp2 promoter (P tlp2 ) was induced by Pi and iron, both in the ferrous (Fe2+) and ferric form (Fe3+). RT-PCR analysis using overlapping primers indicated that the phoX gene, located immediately downstream of tlp2, is co-transcribed with tlp2. A transcription start site was identified at 53 bp upstream of the tlp2 start codon. The Δtlp2 mutant showed decreased colonization of the chicken gastrointestinal tract. Collectively, our findings revealed that the tlp2 plays a role in C. jejuni pathogenesis and colonization in the chicken host and its expression is regulated by iron.

The effect of bacterial chemotaxis on host infection and pathogenicity

Chemotaxis enables microorganisms to move according to chemical gradients. Although this process requires substantial cellular energy, it also affords key physiological benefits, including enhanced access to growth substrates. Another important implication of chemotaxis is that it also plays an important role in infection and disease, as chemotaxis signalling pathways are broadly distributed across a variety of pathogenic bacteria. Furthermore, current research indicates that chemotaxis is essential for the initial stages of infection in different human, animal and plant pathogens. This review focuses on recent findings that have identified specific bacterial chemoreceptors and corresponding chemoeffectors associated with pathogenicity. Pathogenicity-related chemoeffectors are either host and niche-specific signals or intermediates of the host general metabolism. Plant pathogens were found to contain an elevated number of chemotaxis signalling genes and functional studies demonstrate that these genes are critical for their ability to enter the host. The expanding body of knowledge of the mechanisms underlying chemotaxis in pathogens provides a foundation for the development of new therapeutic strategies capable of blocking infection and preventing disease by interfering with chemotactic signalling pathways.

The transducer-like protein Tlp12 of Campylobacter jejuni is involved in glutamate and pyruvate chemotaxis

BACKGROUND

Campylobacter jejuni is one of the most common bacterial causes of food-borne enteritis worldwide. Chemotaxis in C. jejuni is known to be critical for the successful colonization of the host and key for the adaptation of the microbial species to different host environments. In C. jejuni, chemotaxis is regulated by a complex interplay of 13 or even more different chemoreceptors, also known as transducer-like proteins (Tlps). Recently, a novel chemoreceptor gene, tlp12, was described and found to be present in 29.5% of the investigated C. jejuni strains.

RESULTS

In this study, we present a functional analysis of Tlp12 with the aid of a tlp12 knockout mutant of the C. jejuni strain A17. Substrate specificity was investigated by capillary chemotaxis assays and revealed that Tlp12 plays an important role in chemotaxis towards glutamate and pyruvate. Moreover, the Δtlp12 mutant shows increased swarming motility in soft agar assays, an enhanced invasion rate into Caco-2 cells and an increased autoagglutination rate. The growth rate was slightly reduced in the Δtlp12 mutant. The identified phenotypes were in partial restored by complementation with the wild type gene. Tlp12-harboring C. jejuni strains display a strong association with chicken, whose excreta are known to contain high glutamate levels.

CONCLUSIONS

TLP12 is a chemoreceptor for glutamate and pyruvate recognition. Deletion of tlp12 has an influence on distinct physiological features, such as growth rate, swarming motility, autoagglutination and invasiveness.

Chemotaxis of Escherichia coli to major hormones and polyamines present in human gut

The microorganisms in the gastrointestinal (GI) tract can influence the metabolism, immunity, and behavior of animal hosts. Increasing evidence suggests that communication between the host and the microbiome also occurs in the opposite direction, with hormones and other host-secreted compounds being sensed by microorganisms. Here, we addressed one key aspect of the host–microbe communication by studying chemotaxis of a model commensal bacterium, Escherichia coli, to several compounds present abundantly in the GI tract, namely catecholamines, thyroid hormones, and polyamines. Our results show that E. coli reacts to five out of ten analyzed chemicals, sensing melatonin, and spermidine as chemorepellents and showing mixed responses to dopamine, norepinephrine and 3,4-dihydroxymandelic acid. The strongest repellent response was observed for the polyamine spermidine, and we demonstrate that this response involves the low-abundance chemoreceptor Trg and the periplasmic binding protein PotD of the spermidine uptake system. The chemotactic effects of the tested compounds apparently correlate with their influence on growth and their stability in the GI tract, pointing to the specificity of the observed behavior. We hypothesize that the repellent responses observed at high concentrations of chemoeffective compounds might enable bacteria to avoid harmful levels of hormones and polyamines in the gut and, more generally, antimicrobial activities of the mucous layer.

Stimulus sensing and signal processing in bacterial chemotaxis

Motile bacteria use chemotaxis to migrate towards environments that are favorable for growth and survival. The signaling pathway that mediates this behavior is largely conserved among prokaryotes, with Escherichia coli chemotaxis system being one of the simplest and the best studied. At the core of this pathway are the arrays of clustered chemoreceptors that detect, amplify and integrate various stimuli. Recent work provided deeper understanding of spatial organization and signal processing by these clusters and uncovered the variety of sensory mechanisms used to detect environmental stimuli. Moreover, studies of bacteria with different lifestyles have led to new insights into the diversity and evolutionary conservation of the chemotaxis pathway, as well as the physiological relevance of chemotactic behavior in different environments.

New approach to distinguishing chemoattractants, chemorepellents and catabolised chemoeffectors for Campylobacter jejuni

Chemotactic behaviour is an important part of the lifestyle of motile bacteria and enables cells to respond to various environmental stimuli. The Hard Agar Plug (HAP) method is used to study the chemotactic behaviour of bacteria, including the fastidious microaerophile Campylobacter jejuni, an intestinal pathogen of humans. However, the traditional HAP assay is not quantitative, is unsuitable for chemotaxis observation over short time periods and for the investigation of repellent taxis, and is prone to false-positive and -negative results. Here we report an accurate, rapid, and quantitative HAP-based chemotaxis assay, tHAP, for the investigation of bacterial chemotactic responses. The critical component of the new assay is the addition of triphenyltetrazolium chloride (TTC). Enzymatic reduction of TTC to TFP-Red (1, 3, 5-Triphenylformazan) enables colourimetric detection of actively metabolising bacterial cells. Quantitative assessment of chemotaxis is achieved by colourimetric measurement or viability count over a period of 10 min to 3 h. Using the tHAP assay, we observed the dose-responsive chemotactic motility of C. jejuni cells along different concentrations of attractants aspartate and serine. Importantly, we have also designed a competitive tHAP assay to differentiate between repellents and attractants and to identify chemoeffectors that do not activate metabolism.

IMPORTANCE

The modified tHAP assay described here enables the exploration of the chemoresponse of Campylobacter jejuni towards chemorepellents, and catabolizable and non-catabolizable chemoattractants.

The activity of the C4-dicarboxylic acid chemoreceptor of Pseudomonas aeruginosa is controlled by chemoattractants and antagonists

Chemotaxis toward organic acids has been associated with colonization fitness and virulence and the opportunistic pathogen Pseudomonas aeruginosa exhibits taxis toward several tricarboxylic acid intermediates. In this study, we used high-throughput ligand screening and isothermal titration calorimetry to demonstrate that the ligand binding domain (LBD) of the chemoreceptor PA2652 directly recognizes five C4-dicarboxylic acids with K_D values ranging from 23 µM to 1.24 mM. In vivo experimentation showed that three of the identified ligands act as chemoattractants whereas two of them behave as antagonists by inhibiting the downstream chemotaxis signalling cascade. In vitro and in vivo competition assays showed that antagonists compete with chemoattractants for binding to PA2652-LBD, thereby decreasing the affinity for chemoattractants and the subsequent chemotactic response. Two chemosensory pathways encoded in the genome of P. aeruginosa, che and che2, have been associated to chemotaxis but we found that only the che pathway is involved in PA2652-mediated taxis. The receptor PA2652 is predicted to contain a sCACHE LBD and analytical ultracentrifugation analyses showed that PA2652-LBD is dimeric in the presence and the absence of ligands. Our results indicate the feasibility of using antagonists to interfere specifically with chemotaxis, which may be an alternative strategy to fight bacterial pathogens.

mcp, aer, cheB, and cheV contribute to the regulation of Vibrio alginolyticus (ND-01) adhesion under gradients of environmental factors

Adhesion is a key virulence factor of pathogens and can be affected by the environment. Our previously research with RNA-seq indicated that mcp, aer, cheB, and cheV might play roles in the regulation of adhesion in Vibrio alginolyticus (ND-01). In order to determine whether and how environmental factors affect adhesion through these genes, gene silencing was performed followed by quantitative real-time PCR (qRT-PCR), RNAi, transmission electron microscopy, and adhesion, capillary, and motility assays to verify how these genes influence adhesion. Silencing these genes led to deficiencies in adhesion, chemotaxis, flagellar assembly, and motility. The expression levels of cheA, cheW, and cheY, which are important genes closely related to the functions of mcp, aer, cheV, and cheB, were significantly downregulated in all of the RNAi groups. The expression of mcp, aer, cheV, and cheB under different gradients of temperature, pH, and salinity and after starvation for various durations was also detected, which showed that these genes were sensitive to certain environmental stresses, particularly pH and starvation. Our results indicated that mcp, aer, cheB, and cheV: (1) are necessary for ND-01 adhesion; (2) play key roles in the bacterial chemotaxis pathway by controlling the expression of downstream genes; (3) might affect adhesion by impacting motility, though motility is not the only route through which adhesion is affected; and (4) contribute to the regulation of ND-01 adhesion in natural environments with different temperatures, pH levels, and salinities as well as after various starvation periods.

The Norepinephrine Metabolite 3,4-Dihydroxymandelic Acid Is Produced by the Commensal Microbiota and Promotes Chemotaxis and Virulence Gene Expression in Enterohemorrhagic Escherichia coli

Enterohemorrhagic Escherichia coli (EHEC) is a commonly occurring foodborne pathogen responsible for numerous multistate outbreaks in the United States. It is known to infect the host gastrointestinal tract, specifically, in locations associated with lymphoid tissue. These niches serve as sources of enteric neurotransmitters, such as epinephrine and norepinephrine, that are known to increase virulence in several pathogens, including enterohemorrhagic E. coli The mechanisms that allow pathogens to target these niches are poorly understood. We previously reported that 3,4-dihydroxymandelic acid (DHMA), a metabolite of norepinephrine produced by E. coli, is a chemoattractant for the nonpathogenic E. coli RP437 strain. Here we report that DHMA is also a chemoattractant for EHEC. In addition, DHMA induces the expression of EHEC virulence genes and increases attachment to intestinal epithelial cells in vitro in a QseC-dependent manner. We also show that DHMA is present in murine gut fecal contents and that its production requires the presence of the commensal microbiota. On the basis of its ability to both attract and induce virulence gene expression in EHEC, we propose that DHMA acts as a molecular beacon to target pathogens to their preferred sites of infection in vivo.

Campylobacter jejuni transducer like proteins: Chemotaxis and beyond

Chemotaxis, a process that mediates directional motility toward or away from chemical stimuli (chemoeffectors/ligands that can be attractants or repellents) in the environment, plays an important role in the adaptation of Campylobacter jejuni to disparate niches. The chemotaxis system consists of core signal transduction proteins and methyl-accepting-domain-containing Transducer like proteins (Tlps). Ligands binding to Tlps relay a signal to chemotaxis proteins in the cytoplasm which initiate a signal transduction cascade, culminating into a directional flagellar movement. Tlps facilitate substrate-specific chemotaxis in C. jejuni, which plays an important role in the pathogen's adaptation, pathobiology and colonization of the chicken gastrointestinal tract. However, the role of Tlps in C. jejuni's host tissue specific colonization, physiology and virulence remains not completely understood. Based on recent studies, it can be predicted that Tlps might be important targets for developing strategies to control C. jejuni via vaccines and antimicrobials.

cj0371: A Novel Virulence-Associated Gene of Campylobacter jejuni

Campylobacter jejuni is the major cause of human bacterial diarrhea worldwide. Its pathogenic mechanism remains poorly understood. cj0371 is a novel gene that was uncovered using immunoscreening. There have been no previous reports regarding its function. In this study, we constructed an insertion mutant and complement of this gene in C. jejuni and examined changes in virulence. We observed that the cj0371 mutant showed significantly increased invasion and colonization ability. We also investigated the role of cj0371 in motility, chemotaxis, and growth kinetics to further study its function. We found that the cj0371 mutant displays hypermotility, enhanced chemotaxis, and enhanced growth kinetics. In addition, we localized the Cj0371 protein at the poles of C. jejuni by fluorescence microscopy. We present data that collectively significantly proves our hypothesis that cj0371 is a new virulence-associated gene and through the influence of chemotaxis plays a negative role in C. jejuni pathogenicity.

Polyphosphate kinases modulate Campylobacter jejuni outer membrane constituents and alter its capacity to invade and survive in intestinal epithelial cells in vitro

Campylobacter jejuni is the most prevalent cause of bacterial gastroenteritis worldwide. Polyphosphate kinases 1 and 2 (PPK1 and PPK2) regulate several cellular processes, including the biosynthesis of the bacterial cell wall. Despite their importance, whether PPK1 and PPK2 modulate the composition of C. jejuni outer membrane constituents (OMCs) and consequently impact its interaction with host cells remains unknown. Our comparative analysis between C. jejuni wild type, Δppk1, and Δppk2 strains showed qualitative and quantitative differences in the total OMC composition among these strains. Importantly, these OMC variations observed on the C. jejuni polyphosphate kinase mutants are directly related to their capacity to invade, survive, and alter the immune response of intestinal epithelial cells in vitro. Specifically, sub-fractionation of the C. jejuni OMC indicated that OMC proteins are uniquely associated with bacterial invasion, whereas C. jejuni OMC proteins, lipids, and lipoglycans are all associated with C. jejuni intracellular survival. This study provides new insights regarding the function of polyphosphate kinases and their role in C. jejuni infection.