Gamma-glutamyl transpeptidase has a role in the persistent colonization of the avian gut by Campylobacter jejuni

Phenotypic, genotypic and proteomic variations between poor and robust colonizing Campylobacter jejuni strains

Campylobacter jejuni is one of the major causes of bacterial gastrointestinal disease in humans worldwide. This foodborne pathogen colonizes the intestinal tracts of chickens, and consumption of chicken and poultry products is identified as a common route of transmission. We analyzed two C. jejuni strains after oral challenge with 105 CFU/ml of C. jejuni per chick; one strain was a robust colonizer (A74/C) and the other a poor colonizer (A74/O). We also found extensive phenotypic differences in growth rate, biofilm production, and in vitro adherence, invasion, intracellular survival, and transcytosis. Strains A74/C and A74/O were genotypically similar with respect to their whole genome alignment, core genome, and ribosomal MLST, MLST, flaA, porA, and PFGE typing. The global proteomes of the two congenic strains were quantitatively analyzed by ultra-high performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) and 618 and 453 proteins were identified from A74/C and A74/O isolates, respectively. Cluster of Orthologous Groups (COG) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses showed that carbon metabolism and motility proteins were distinctively overexpressed in strain A74/C. The robust colonizer also exhibited a unique proteome profile characterized by significantly increased expression of proteins linked to adhesion, invasion, chemotaxis, energy, protein synthesis, heat shock proteins, iron regulation, two-component regulatory systems, and multidrug efflux pump. Our study underlines phenotypic, genotypic, and proteomic variations of the poor and robust colonizing C. jejuni strains, suggesting that several factors may contribute to mediating the different colonization potentials of the isogenic isolates.

Effects of Hydroxytyrosol Supplementation on Performance, Fat and Blood Parameters of Broiler Chickens

The study aimed to evaluate the effects of dietary supplementation of hydroxytyrosol (HT) on performance, fat, and blood parameters of broilers. In total, 960 male chicks were distributed into four treatments groups with 12 replicates with 20 birds per pen, with varying HT levels (0, 5, 10, and 50 mg/kg of feed) added to the basal diet from 1 to 42 days old. Feed intake, body weight gain, and feed conversion ratio were evaluated. Enzymes related to liver injury were evaluated in blood. Fatty acid profile and malondialdehyde (MDA) concentration were determined in the breast meat. Dietary supplementation of HT did not improve broilers' performance (p > 0.05). Birds fed 50 mg HT/kg had lower AST, ALT, and GGT concentrations (p ≤ 0.05), whereas broilers fed 5, 10, and 50 mg HT/kg, had lower TBIL concentrations (p ≤ 0.05). Breast meat of broilers fed 50 mg HT/kg had lower lipid content, saturated fatty acid, unsaturated fatty acids, MDA concentrations (p ≤ 0.05), and polyunsaturated fatty acids (p < 0.0001). In summary, supplementation of 5, 10, and 50 mg HT/kg does not improve the performance of broilers, but the dose of 50 mg HT/kg helps the liver against inflammation and improves fat parameters.

The glutathione import system satisfies the Staphylococcus aureus nutrient sulfur requirement and promotes interspecies competition

Sulfur is an indispensable element for bacterial proliferation. Prior studies demonstrated that the human pathogen Staphylococcus aureus utilizes glutathione (GSH) as a source of nutrient sulfur; however, mechanisms of GSH acquisition are not defined. Here, we identify a five-gene locus comprising a putative ABC-transporter and predicted γ-glutamyl transpeptidase (ggt) that promotes S. aureus proliferation in medium supplemented with either reduced or oxidized GSH (GSSG) as the sole source of nutrient sulfur. Based on these phenotypes, we name this transporter operon the glutathione import system (gisABCD). Ggt is encoded within the gisBCD operon, and we show that the enzyme is capable of liberating glutamate using either GSH or GSSG as substrates, demonstrating it is a bona fide γ-glutamyl transpeptidase. We also determine that Ggt is expressed in the cytoplasm, representing only the second example of cytoplasmic Ggt localization, the other being Neisseria meningitidis. Bioinformatic analyses revealed that Staphylococcus species closely related to S. aureus encode GisABCD-Ggt homologs. However, homologous systems were not detected in Staphylococcus epidermidis. Consequently, we establish that GisABCD-Ggt provides a competitive advantage for S. aureus over S. epidermidis in a GSH- and GSSG-dependent manner. Overall, this study describes the discovery of a nutrient sulfur acquisition system in S. aureus that targets GSSG in addition to GSH and promotes competition against other staphylococci commonly associated with the human microbiota.

Investigation on the colonisation of Campylobacter strains in the pig intestine depending on available metabolites

Campylobacter (C.) spp. represent one of the most important causes for food-borne bacterial pathogen in humans worldwide. The aim of this study was to investigate metabolic requirements of two Campylobacter strains of different species based on substrate utilisation (in vitro). Based on these results, a correlation between the colonisation and the available substrates in different intestinal sections was recorded using an animal model. Campylobacter coli (ST-5777) and C. jejuni (ST-122) were used to inoculate 16 pigs, respectively, and one group of 16 pigs was used as control. The strains differed significantly in substrate utilisation - C. coli was able to metabolise various substrates (acetate, asparagine, serine, fucose, and propionate), while C. jejuni only utilised serine. Metabolomic analysis of intestinal content from different gut sections showed the presence of all previously tested metabolites, except for fucose. A significantly larger amount of glucose was found in the jejunum of those pigs infected with C. coli, while neither strain utilised it in vitro. The analysis of the intestinal contents revealed a very low proportion of Campylobacterales in the total microbiome, suggesting that the small percentage of the inoculated Campylobacter strains in the gut microflora of the animals is too low to cause differences between the control and infected groups in the composition of the metabolome. Nevertheless, knowledge of specific nutritional requirements of the pathogens combined with proof of different metabolites in the intestinal segments may provide clues about the site of colonisation in the host and improve our understanding of this zoonotic germ.

Insights into the Virulence of Campylobacter jejuni Associated with Two-Component Signal Transduction Systems and Single Regulators

Campylobacter jejuni is one of the major aetiologies of diarrhoea. Understanding the processes and virulence factors contributing to C. jejuni fitness is a cornerstone for developing mitigation strategies. Two-component signal transduction systems, known as two-component systems (TCSs), along with single regulators with no obvious cognate histidine kinase, help pathogens in interacting with their environments, but the available literature on C. jejuni is limited. A typical TCS possesses histidine kinase and response regulator proteins. The objective of this review was to provide insights into the virulence of C. jejuni associated with TCSs and single regulators. Despite limited research, TCSs are important contributors to the pathogenicity of C. jejuni by influencing motility (FlgSR), colonisation (DccRS), nutrient acquisition (PhosSR and BumSR), and stress response (RacRS). Of the single regulators, CbrR and CosR are involved in bile resistance and oxidative stress response, respectively. Cross-talks among TCSs complicate the full elucidation of their molecular mechanisms. Although progress has been made in characterising C. jejuni TCSs, shortfalls such as triggering signals, inability to induce mutations in some genes, or developing suitable in vivo models are still being encountered. Further research is expected to shed light on the unexplored sides of the C. jejuni TCSs, which may allow new drug discoveries and better control strategies.

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.

Bacterial Gamma-Glutamyl Transpeptidase, an Emerging Biocatalyst: Insights Into Structure-Function Relationship and Its Biotechnological Applications

Gamma-glutamyl transpeptidase (GGT) enzyme is ubiquitously present in all life forms and plays a variety of roles in diverse organisms. Higher eukaryotes mainly utilize GGT for glutathione degradation, and mammalian GGTs have implications in many physiological disorders also. GGTs from unicellular prokaryotes serve different physiological functions in Gram-positive and Gram-negative bacteria. In the present review, the physiological significance of bacterial GGTs has been discussed categorizing GGTs from Gram-negative bacteria like Escherichia coli as glutathione degraders and from pathogenic species like Helicobacter pylori as virulence factors. Gram-positive bacilli, however, are considered separately as poly-γ-glutamic acid (PGA) degraders. The structure-function relationship of the GGT is also discussed mainly focusing on the crystallization of bacterial GGTs along with functional characterization of conserved regions by site-directed mutagenesis that unravels molecular aspects of autoprocessing and catalysis. Only a few crystal structures have been deciphered so far. Further, different reports on heterologous expression of bacterial GGTs in E. coli and Bacillus subtilis as hosts have been presented in a table pointing toward the lack of fermentation studies for large-scale production. Physicochemical properties of bacterial GGTs have also been described, followed by a detailed discussion on various applications of bacterial GGTs in different biotechnological sectors. This review emphasizes the potential of bacterial GGTs as an industrial biocatalyst relevant to the current switch toward green chemistry.

Foodborne pathogens in the omics era

Outbreaks and deaths related to Foodborne Diseases (FBD) occur constantly in the world, as a result of the consumption of contaminated foodstuffs with pathogens such as Listeria monocytogenes, Escherichia coli, Staphylococcus aureus, Salmonella spp, Clostridium spp. and Campylobacter spp. The purpose of this review is to discuss the main omic techniques applied in foodborne pathogen and to demonstrate their functionalities through the food chain and to guarantee the food safety. The main techniques presented are genomic, transcriptomic, secretomic, proteomic, and metabolomic, which together, in the field of food and nutrition, are known as "Foodomics." This review had highlighted the potential of omics to integrate variables that contribute to food safety and to enable us to understand their application on foodborne diseases. The appropriate use of these techniques had driven the definition of critical parameters to achieve successful results in the improvement of consumers health, costs and to obtain safe and high-quality products.

Antimicrobial Resistance Profiles, Virulence Genes, and Genetic Diversity of Thermophilic Campylobacter Species Isolated From a Layer Poultry Farm in Korea

Thermophilic Campylobacter species are among the major etiologies of bacterial enteritis globally. This study aimed at assessing the antimicrobial resistance (AMR) profiles, virulence genes, and genetic diversity of thermophilic Campylobacter species isolated from a layer poultry farm in South Korea. One hundred fifty-three chicken feces were collected from two layer poultry farms in Gangneung, South Korea. The Campylobacter species were isolated by cultural techniques, while PCR and sequencing were used for species confirmation. Antimicrobial susceptibility testing for six antimicrobials [ciprofloxacin (CIP), nalidixic acid (NAL), sitafloxacin (SIT), erythromycin (ERY), tetracycline (TET), and gentamicin (GEN)] was carried out by broth microdilution. Three AMR and nine virulence genes were screened by PCR. Genotyping was performed by flaA-restriction fragment length polymorphism (RFLP) and multilocus sequence typing (MLST). Of the 153 samples, Campylobacter spp. were detected in 55 (35.9%), with Campylobacter jejuni and Campylobacter coli being 49 (89.1%) and six (10.9%), respectively. High-level resistance was observed for CIP (100%), NAL (100%), and TET (C. jejuni, 93.9%; C. coli: 83.3%). No resistance was observed for SIT. The missense mutation (C257T) in gyrA gene was confirmed by sequencing, while the tet(O) gene was similar to known sequences in GenBank. The rate of multidrug-resistant (MDR) strains was 8.2%, and they all belonged to C. jejuni. All Campylobacter isolates possessed five virulence genes (cdtB, cstII, flaA, cadF, and dnaJ), but none possessed ggt, while the rates for other genes (csrA, ciaB, and pldA) ranged between 33.3 and 95.9%. The flaA-RFLP yielded 26 flaA types (C. jejuni: 21 and C. coli: five), while the MLST showed 10 sequence types (STs) for C. jejuni and three STs for C. coli, with CC-607 (STs 3611) and CC-460 (ST-460) being predominant. Among the 10 STs of C. jejuni, three were newly assigned. The findings of this study highlight the increased resistance to quinolones and TET, the virulence potential, and the diverse genotypes among Campylobacter strains isolated from the layer poultry farm.

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.

The function, biogenesis and regulation of the electron transport chains in Campylobacter jejuni: New insights into the bioenergetics of a major food-borne pathogen

Campylobacter jejuni is a zoonotic Epsilonproteobacterium that grows in the gastrointestinal tract of birds and mammals, and is the most frequent cause of food-borne bacterial gastroenteritis worldwide. As an oxygen-sensitive microaerophile, C. jejuni has to survive high environmental oxygen tensions, adapt to oxygen limitation in the host intestine and resist host oxidative attack. Despite its small genome size, C. jejuni is a versatile and metabolically active pathogen, with a complex and highly branched set of respiratory chains allowing the use of a wide range of electron donors and alternative electron acceptors in addition to oxygen, including fumarate, nitrate, nitrite, tetrathionate and N- or S-oxides. Several novel enzymes participate in these electron transport chains, including a tungsten containing formate dehydrogenase, a Complex I that uses flavodoxin and not NADH, a periplasmic facing fumarate reductase and a cytochrome c tetrathionate reductase. This review presents an updated description of the composition and bioenergetics of these various respiratory chains as they are currently understood, including recent work that gives new insights into energy conservation during electron transport to various alternative electron acceptors. The regulation of synthesis and assembly of the electron transport chains is also discussed. A deeper appreciation of the unique features of the respiratory systems of C. jejuni may be helpful in informing strategies to control this important pathogen.

Comparative genomics analysis to differentiate metabolic and virulence gene potential in gastric versus enterohepatic Helicobacter species

Background

The genus Helicobacter are gram-negative, microaerobic, flagellated, mucus-inhabiting bacteria associated with gastrointestinal inflammation and classified as gastric or enterohepatic Helicobacter species (EHS) according to host species and colonization niche. While there are over 30 official species, little is known about the physiology and pathogenic mechanisms of EHS, which account for most in the genus, as well as what genetic factors differentiate gastric versus EHS, given they inhabit different hosts and colonization niches. The objective of this study was to perform a whole-genus comparative analysis of over 100 gastric versus EHS genomes in order to identify genetic determinants that distinguish these Helicobacter species and provide insights about their evolution/adaptation to different hosts, colonization niches, and mechanisms of virulence.

Results

Whole-genome phylogeny organized Helicobacter species according to their presumed gastric or EHS classification. Analysis of orthologs revealed substantial heterogeneity in physiological and virulence-related genes between gastric and EHS genomes. Metabolic reconstruction predicted that unlike gastric species, EHS appear asaccharolytic and dependent on amino/organic acids to fuel metabolism. Additionally, gastric species lack de novo biosynthetic pathways for several amino acids and purines found in EHS and instead rely on environmental uptake/salvage pathways. Comparison of virulence factor genes between gastric and EHS genomes identified overlapping yet distinct profiles and included canonical cytotoxins, outer membrane proteins, secretion systems, and survival factors.

Conclusions

The major differences in predicted metabolic function suggest gastric species and EHS may have evolved for survival in the nutrient-rich stomach versus the nutrient-devoid environments, respectively. Contrasting virulence factor gene profiles indicate gastric species and EHS may utilize different pathogenic mechanisms to chronically infect hosts and cause inflammation and tissue damage. The findings from this study provide new insights into the genetic differences underlying gastric versus EHS and support the need for future experimental studies to characterize these pathogens.

Electronic supplementary material

The online version of this article (10.1186/s12864-018-5171-2) contains supplementary material, which is available to authorized users.

Gamma-glutamyltranspeptidase expression by Helicobacter saguini, an enterohepatic Helicobacter species isolated from cotton top tamarins with chronic colitis

BACKGROUND

Helicobacter saguini is a novel enterohepatic Helicobacter species isolated from captive cotton top tamarins with chronic colitis and colon cancer. Monoassociated H. saguini infection in gnotobiotic IL-10^-/- mice causes typhlocolitis and dysplasia; however, the virulent mechanisms of this species are unknown. Gamma-glutamyltranspeptidase (GGT) is an enzymatic virulence factor expressed by pathogenic Helicobacter and Campylobacter species that inhibits host cellular proliferation and promotes inflammatory-mediated gastrointestinal pathology. The aim of this study was to determine if H. saguini expresses an enzymatically active GGT homologue with virulence properties.

EXPERIMENTAL PROCEDURES

Two putative GGT paralogs (HSGGT1 and HSGGT2) identified in the H. saguini genome were bioinformatically analysed to predict enzymatic functionality and virulence potential. An isogenic knockout mutant strain and purified recombinant protein of HSGGT1 were created to study enzymatic activity and virulence properties by in vitro biochemical and cell culture experiments.

RESULTS

Bioinformatic analysis predicted that HSGGT1 has enzymatic functionality and is most similar to the virulent homologue expressed by Helicobacter bilis, whereas HSGGT2 contains putatively inactivating mutations. An isogenic knockout mutant strain and recombinant HSGGT1 protein were successfully created and demonstrated that H. saguini has GGT enzymatic activity. Recombinant HSGGT1 protein and sonicate from wild-type but not mutant H. saguini inhibited gastrointestinal epithelial and lymphocyte cell proliferation without evidence of cell death. The antiproliferative effect by H. saguini sonicate or recombinant HSGGT1 protein could be significantly prevented with glutamine supplementation or the GGT-selective inhibitor acivicin. Recombinant HSGGT1 protein also induced proinflammatory gene expression in colon epithelial cells.

CONCLUSIONS

This study shows that H. saguini may express GGT as a potential virulence factor and supports further in vitro and in vitro studies into how GGT expression by enterohepatic Helicobacter species influences the pathogenesis of gastrointestinal inflammatory diseases.

Unexpected differential metabolic responses of Campylobacter jejuni to the abundant presence of glutamate and fucose

INTRODUCTION

Campylobacter jejuni is the leading cause of foodborne bacterial enteritis in humans, and yet little is known in regard to how genetic diversity and metabolic capabilities among isolates affect their metabolic phenotype and pathogenicity.

OBJECTIVES

For instance, the C. jejuni 11168 strain can utilize both L-fucose and L-glutamate as a carbon source, which provides the strain with a competitive advantage in some environments and in this study we set out to assess the metabolic response of C. jejuni 11168 to the presence of L-fucose and L-glutamate in the growth medium.

METHODS

To achieve this, untargeted hydrophilic liquid chromatography coupled to mass spectrometry was used to obtain metabolite profiles of supernatant extracts obtained at three different time points up to 24 h.

RESULTS

This study identified both the depletion and the production and subsequent release of a multitude of expected and unexpected metabolites during the growth of C. jejuni 11168 under three different conditions. A large set of standards allowed identification of a number of metabolites. Further mass spectrometry fragmentation analysis allowed the additional annotation of substrate-specific metabolites. The results show that C. jejuni 11168 upon L-fucose addition indeed produces degradation products of the fucose pathway. Furthermore, methionine was faster depleted from the medium, consistent with previously-observed methionine auxotrophy.

CONCLUSIONS

Moreover, a multitude of not previously annotated metabolites in C. jejuni were found to be increased specifically upon L-fucose addition. These metabolites may well play a role in the pathogenicity of this C. jejuni strain.

Direct Manipulation of T Lymphocytes by Proteins of Gastrointestinal Bacterial Pathogens

Gastrointestinal bacterial infection represents a significant threat to human health, as well as a burden on food animal production and welfare. Although there is advanced knowledge about the molecular mechanisms underlying pathogenesis, including the development of immune responses to these pathogens, gaps in knowledge persist. It is well established that gastrointestinal bacterial pathogens produce a myriad of proteins that affect the development and effectiveness of innate immune responses. However, relatively few proteins that directly affect lymphocytes responsible for humoral or cell-mediated immunity and memory have been identified. Here, we review factors produced by gastrointestinal bacterial pathogens that have direct T cell interactions and what is known about their functions and mechanisms of action. T cell-interacting bacterial proteins that have been identified to date mainly target three major T cell responses: activation and expansion, chemotaxis, or apoptosis. Further, the requirement for more focused studies to identify and understand additional mechanisms used by bacteria to directly affect the T cell immune response and how these may contribute to pathogenesis is highlighted. Increased knowledge in this area will help to drive development of better interventions in prevention and treatment of gastrointestinal bacterial infection.

Molecular analyses of prostate tumors for diagnosis of malignancy on fine-needle aspiration biopsies

Prostate cancer (PCa) is a common cancer and remains the second-leading cause of cancer-associated mortality in men, but diagnosis of PCa remains a main clinical challenge. To investigate the involvement of differentially expressing genes in PCa with deregulated pathways to allow earlier diagnosis of the disease, transcriptomic analyses of differential expression genes in fine-needle aspiration (FNA) biopsies helped to discriminate PCa from benign prostatic hyperplasia (BPH). We identified 255 genes that were deregulated in prostate tumors compared with BPH tissues. qRT-PCR was conducted to examine the expression levels of the four genes in FNA biopsies and confirmed that ITGBL1 was significantly up-regulated and HOXA7, KRT15 and TGM4 were down-regulated in the PCa compared to the BPH, with a sensitivity of 87.1% and a specificity of 87.8%; the area under the receiver operating characteristic curve was estimated at 0.94, which was significantly improved compared with PSA alone (AUC = 0.82). Moreover, the increased expression of ITGBL1 correlated with total cholesterol, triglyceride and PSA. Our results demonstrated that transcriptomic analyses in FNA biopsies could facilitate rapid identification of potential targets for therapy and diagnosis of PCa.

Microbiota-Derived Short-Chain Fatty Acids Modulate Expression of Campylobacter jejuni Determinants Required for Commensalism and Virulence

Campylobacter jejuni promotes commensalism in the intestinal tracts of avian hosts and diarrheal disease in humans, yet components of intestinal environments recognized as spatial cues specific for different intestinal regions by the bacterium to initiate interactions in either host are mostly unknown. By analyzing a C. jejuni acetogenesis mutant defective in converting acetyl coenzyme A (Ac-CoA) to acetate and commensal colonization of young chicks, we discovered evidence for in vivo microbiota-derived short-chain fatty acids (SCFAs) and organic acids as cues recognized by C. jejuni that modulate expression of determinants required for commensalism. We identified a set of C. jejuni genes encoding catabolic enzymes and transport systems for amino acids required for in vivo growth whose expression was modulated by SCFAs. Transcription of these genes was reduced in the acetogenesis mutant but was restored upon supplementation with physiological concentrations of the SCFAs acetate and butyrate present in the lower intestinal tracts of avian and human hosts. Conversely, the organic acid lactate, which is abundant in the upper intestinal tract where C. jejuni colonizes less efficiently, reduced expression of these genes. We propose that microbiota-generated SCFAs and lactate are cues for C. jejuni to discriminate between different intestinal regions. Spatial gradients of these metabolites likely allow C. jejuni to locate preferred niches in the lower intestinal tract and induce expression of factors required for intestinal growth and commensal colonization. Our findings provide insights into the types of cues C. jejuni monitors in the avian host for commensalism and likely in humans to promote diarrheal disease.

Campylobacter jejuni is a commensal of the intestinal tracts of avian species and other animals and a leading cause of diarrheal disease in humans. The types of cues sensed by C. jejuni to influence responses to promote commensalism or infection are largely lacking. By analyzing a C. jejuni acetogenesis mutant, we discovered a set of genes whose expression is modulated by lactate and short-chain fatty acids produced by the microbiota in the intestinal tract. These genes include those encoding catabolic enzymes and transport systems for amino acids that are required by C. jejuni for in vivo growth and intestinal colonization. We propose that gradients of these microbiota-generated metabolites are cues for spatial discrimination between areas of the intestines so that the bacterium can locate niches in the lower intestinal tract for optimal growth for commensalism in avian species and possibly infection of human hosts leading to diarrheal disease.

Comparison of enzymatic properties and small molecule inhibition of γ-glutamyltranspeptidases from pathogenic and commensal bacteria

Helicobacter pylori infects the stomach of 50% of the population worldwide, thus causing chronic gastritis. Although this infection can be cured by antibiotic treatment, therapeutic options are increasingly limited due to the development of resistances. The γ-glutamyl-transpeptidase (gGT) of H. pylori (HpgGT) is a virulence factor important for colonization and contributes to bacterial immune evasion. Therefore, this enzyme is a potential target for developing new anti-infectives. As species specificity of such compounds is required in order to avoid off-target or adverse effects, comparative analysis of the gGTs from different organisms is a prerequisite for drug development. To allow detailed biochemical and enzymatic characterization, recombinant gGTs from five different bacteria as well as Homo sapiens were characterized and compared. Investigation of the enzymatic activity, the binding modes of known inhibitors to the catalytic center, and a high resolution X-ray structure of the HpgGT provided a starting point for the identification of new inhibitory substances targeting HpgGT. Inhibitors with Ki values in the nm to mm range were identified and their binding modes were analyzed by mass spectrometry. The results of this study provide a basis for the development of species-specific lead compounds with anti-infective potential by effectively inhibiting HpgGT.

A novel phase variant of the cholera pathogen shows stress-adaptive cryptic transcriptomic signatures

Background

In a process known as phase variation, the marine bacterium and cholera pathogen Vibrio cholerae alternately expresses smooth or rugose colonial phenotypes, the latter being associated with advanced biofilm architecture and greater resistance to ecological stress. To define phase variation at the transcriptomic level in pandemic V. cholerae O1 El Tor strain N16961, we compared the RNA-seq-derived transcriptomes among the smooth parent N16961, its rugose derivative (N16961R) and a smooth form obtained directly from the rugose at high frequencies consistent with phase variation (N16961SD).

Results

Differentially regulated genes which clustered into co-expression groups were identified for specific cellular functions, including acetate metabolism, gluconeogenesis, and anaerobic respiration, suggesting an important link between these processes and biofilm formation in this species. Principal component analysis separated the transcriptome of N16961SD from the other phase variants. Although N16961SD was defective in biofilm formation, transcription of its biofilm-related vps and rbm gene clusters was nevertheless elevated as judged by both RNA-seq and RT-qPCR analyses. This transcriptome signature was shared with N16961R, as were others involving two-component signal transduction, chemotaxis, and c-di-GMP synthesis functions.

Conclusions

Precise turnarounds in gene expression did not accompany reversible phase transitions (i.e., smooth to rugose to smooth) in the cholera pathogen. Transcriptomic signatures consisting of up-regulated genes involved in biofilm formation, environmental sensing and persistence, chemotaxis, and signal transduction, which were shared by N16961R and N16961SD variants, may implicate a stress adaptation in the pathogen that facilitates transition of the N16961SD smooth form back to rugosity should environmental conditions dictate.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-016-3233-x) contains supplementary material, which is available to authorized users.

γ-Glutamyltranspeptidase is an endogenous activator of Toll-like receptor 4-mediated osteoclastogenesis

Chronic inflammation-associated bone destruction, which is observed in rheumatoid arthritis (RA) and periodontitis, is mediated by excessive osteoclastogenesis. We showed previously that γ-glutamyltranspeptidase (GGT), an enzyme involved in glutathione metabolism, acts as an endogenous activator of such pathological osteoclastogenesis, independent of its enzymatic activity. GGT accumulation is clinically observed in the joints of RA patients, and, in animals, the administration of recombinant GGT to the gingival sulcus as an in vivo periodontitis model induces an increase in the number of osteoclasts. However, the underlying mechanisms of this process remain unclear. Here, we report that Toll-like receptor 4 (TLR4) recognizes GGT to activate inflammation-associated osteoclastogenesis. Unlike lipopolysaccharide, GGT is sensitive to proteinase K treatment and insensitive to polymyxin B treatment. TLR4 deficiency abrogates GGT-induced osteoclastogenesis and activation of NF-κB and MAPK signaling in precursor cells. Additionally, GGT does not induce osteoclastogenesis in cells lacking the signaling adaptor MyD88. The administration of GGT to the gingival sulcus induces increased osteoclastogenesis in wild-type mice, but does not induce it in TLR4-deficient mice. Our findings elucidate a novel mechanism of inflammation-associated osteoclastogenesis, which involves TLR4 recognition of GGT and subsequent activation of MyD88-dependent signaling.

A transferable plasticity region in Campylobacter coli allows isolates of an otherwise non-glycolytic food-borne pathogen to catabolize glucose

Thermophilic Campylobacter species colonize the intestine of agricultural and domestic animals commensally but cause severe gastroenteritis in humans. In contrast to other enteropathogenic bacteria, Campylobacter has been considered to be non-glycolytic, a metabolic property originally used for their taxonomic classification. Contrary to this dogma, we demonstrate that several Campylobacter coli strains are able to utilize glucose as a growth substrate. Isotopologue profiling experiments with (13) C-labeled glucose suggested that these strains catabolize glucose via the pentose phosphate and Entner-Doudoroff (ED) pathways and use glucose efficiently for de novo synthesis of amino acids and cell surface carbohydrates. Whole genome sequencing of glycolytic C. coli isolates identified a genomic island located within a ribosomal RNA gene cluster that encodes for all ED pathway enzymes and a glucose permease. We could show in vitro that a non-glycolytic C. coli strain could acquire glycolytic activity through natural transformation with chromosomal DNA of C. coli and C. jejuni subsp. doylei strains possessing the ED pathway encoding plasticity region. These results reveal for the first time the ability of a Campylobacter species to catabolize glucose and provide new insights into how genetic macrodiversity through intra- and interspecies gene transfer expand the metabolic capacity of this food-borne pathogen.

The Campylobacter jejuni RacRS two-component system activates the glutamate synthesis by directly upregulating γ-glutamyltranspeptidase (GGT)

The highly conserved enzyme γ-glutamyltranspeptidase (GGT) plays an important role in metabolism of glutathione and glutamine. Yet, the regulation of ggt transcription in prokaryotes is poorly understood. In the human pathogen Campylobacter jejuni, GGT is important as it contributes to persistent colonization of the gut. Here we show that the GGT activity in C. jejuni is dependent on a functional RacRS (reduced ability to colonize) two-component system. Electrophoretic mobility shift and luciferase reporter assays indicate that the response regulator RacR binds to a promoter region ~80 bp upstream of the ggt transcriptional start site, which contains a recently identified RacR DNA binding consensus sequence. RacR needs to be phosphorylated to activate the transcription of the ggt gene, which is the case under low oxygen conditions in presence of alternative electron acceptors. A functional GGT and RacR are needed to allow C. jejuni to grow optimally on glutamine as sole carbon source under RacR inducing conditions. However, when additional carbon sources are present C. jejuni is capable of utilizing glutamine independently of GGT. RacR is the first prokaryotic transcription factor known to directly up-regulate both the cytoplasmic [glutamine-2-oxoglutarate aminotransferase (GOGAT)] as well as the periplasmic (GGT) production of glutamate.

Helicobacter, gamma-glutamyltransferase and cancer: Further intriguing connections

Virulence of Helicobacter pylori, Helicobacter suis and other bacteria appears to be partly mediated through a release of gamma-glutamyltransferase (GGT), an enzyme activity capable of promoting biochemical reactions ultimately resulting in damage to gastric epithelium and suppression of immune response. Recently published studies show that secretion of bacterial GGT occurs in the form of exosome-like vesicles. Very similar GGT-rich exosomes have been described to originate from human cancer cells, and the hypothesis is thus forwarded that in the resistant and invasive phenotype of malignant cells such vesicular/exosomal GGT may play roles akin to those described for Helicobacter infection, thus providing a significant contribution to the establishment of cancer metastases.

Defining the metabolic requirements for the growth and colonization capacity of Campylobacter jejuni

During the last decade Campylobacter jejuni has been recognized as the leading cause of bacterial gastroenteritis worldwide. This facultative intracellular pathogen is a member of the Epsilonproteobacteria and requires microaerobic atmosphere and nutrient rich media for efficient proliferation in vitro. Its catabolic capacity is highly restricted in contrast to Salmonella Typhimurium and other enteropathogenic bacteria because several common pathways for carbohydrate utilization are either missing or incomplete. Despite these metabolic limitations, C. jejuni efficiently colonizes various animal hosts as a commensal intestinal inhabitant. Moreover, C. jejuni is tremendously successful in competing with the human intestinal microbiota; an infectious dose of few hundreds bacteria is sufficient to overcome the colonization resistance of humans and can lead to campylobacteriosis. Besides the importance and clear clinical manifestation of this disease, the pathogenesis mechanisms of C. jejuni infections are still poorly understood. In recent years comparative genome sequence, transcriptome and metabolome analyses as well as mutagenesis studies combined with animal infection models have provided a new understanding of how the specific metabolic capacity of C. jejuni drives its persistence in the intestinal habitat of various hosts. Furthermore, new insights into the metabolic requirements that support the intracellular survival of C. jejuni were obtained. Because C. jejuni harbors distinct properties in establishing an infection in comparison to pathogenic Enterobacteriaceae, it represents an excellent organism for elucidating new aspects of the dynamic interaction and metabolic cross talk between a bacterial pathogen, the microbiota and the host.

Utilization of host-derived cysteine-containing peptides overcomes the restricted sulphur metabolism of Campylobacter jejuni

The non-glycolytic food-borne pathogen Campylobacter jejuni successfully colonizes the intestine of various hosts in spite of its restricted metabolic properties. While several amino acids are known to be used by C. jejuni as energy sources, none of these have been found to be essential for growth. Here we demonstrated through phenotype microarray analysis that cysteine utilization increases the metabolic activity of C. jejuni. Furthermore, cysteine was crucial for its growth as C. jejuni was unable to synthesize it from sulphate or methionine. Our study showed that C. jejuni compensates this limited anabolic capacity by utilizing sulphide, thiosulphate, glutathione and the dipeptides γGlu-Cys, Cys-Gly and Gly-Cys as sulphur sources and cysteine precursors. A panel of C. jejuni mutants in putative peptidases and peptide transporters were generated and tested for their participation in the catabolism of the cysteine-containing peptides, and the predicted transporter protein CJJ81176_0236 was discovered to facilitate the growth with the dipeptide Cys-Gly, Ile-Arg and Ile-Trp. It was named Campylobacter peptide transporter A (CptA) and is the first representative of the oligopeptide transporter OPT family demonstrated to participate in the glutathione-derivative Cys-Gly catabolism in prokaryotes. Our study provides new insights into how host- and microbiota-derived substrates like sulphide, thiosulphate and short peptides are used by C. jejuni to compensate its restricted metabolic capacities.

Proteomic and genomic analysis reveals novel Campylobacter jejuni outer membrane proteins and potential heterogeneity

Gram-negative bacterial outer membrane proteins play important roles in the interaction of bacteria with their environment including nutrient acquisition, adhesion and invasion, and antibiotic resistance. In this study we identified 47 proteins within the Sarkosyl-insoluble fraction of Campylobacter jejuni 81-176, using LC-ESI-MS/MS. Comparative analysis of outer membrane protein sequences was visualised to reveal protein distribution within a panel of Campylobacter spp., identifying several C. jejuni-specific proteins. Smith-Waterman analyses of C. jejuni homologues revealed high sequence conservation amongst a number of hypothetical proteins, sequence heterogeneity of other proteins and several proteins which are absent in a proportion of strains.

Role of Campylobacter jejuni gamma-glutamyl transpeptidase on epithelial cell apoptosis and lymphocyte proliferation

Background

A gamma-glutamyl transpeptidase (GGT) is produced by up to 31% of strains of Campylobacter jejuni isolates. C. jejuni GGT is close to Helicobacter pylori GGT suggesting a conserved activity but unlike the latter, C. jejuni GGT has not been studied extensively. In line with the data available for H. pylori, our objectives were to purify C. jejuni GGT from the bacteria, and to evaluate its inhibitory and proapoptotic activities on epithelial cells and human lymphocytes.

Methods

C. jejuni GGT was purified from culture supernatants by chromatography. After verification of the purity by using mass spectrometry of the purified enzyme, its action on two epithelial cell lines and human lymphocytes was investigated. Cell culture as well as flow cytometry experiments were developed for these purposes.

Results

This study demonstrated that C. jejuni GGT is related to Helicobacter GGTs and inhibits the proliferation of epithelial cells with no proapoptotic activity. C. jejuni GGT also inhibits lymphocyte proliferation by causing a cell cycle arrest in the G0/G1 phase. These effects are abolished in the presence of a specific pharmacological inhibitor of GGT.

Conclusion

C. jejuni GGT activity is comparable to that of other Epsilonproteobacteria GGTs and more generally to Helicobacter bilis (inhibition of epithelial cell and lymphocyte proliferation, however with no proapoptotic activity). It could therefore be considered as a pathogenicity factor and promote, via the inhibition of lymphocyte proliferation, the persistence of the bacteria in the host. These observations are consistent with a role of this enzyme in the pathophysiology of chronic infections associated with C. jejuni.

Identification of the main venom protein components of Aphidius ervi, a parasitoid wasp of the aphid model Acyrthosiphon pisum

Background

Endoparasitoid wasps are important natural enemies of the widely distributed aphid pests and are mainly used as biological control agents. However, despite the increased interest on aphid interaction networks, only sparse information is available on the factors used by parasitoids to modulate the aphid physiology. Our aim was here to identify the major protein components of the venom injected at oviposition by Aphidius ervi to ensure successful development in its aphid host, Acyrthosiphon pisum.

Results

A combined large-scale transcriptomic and proteomic approach allowed us to identify 16 putative venom proteins among which three γ-glutamyl transpeptidases (γ-GTs) were by far the most abundant. Two of the γ-GTs most likely correspond to alleles of the same gene, with one of these alleles previously described as involved in host castration. The third γ-GT was only distantly related to the others and may not be functional owing to the presence of mutations in the active site. Among the other abundant proteins in the venom, several were unique to A. ervi such as the molecular chaperone endoplasmin possibly involved in protecting proteins during their secretion and transport in the host. Abundant transcripts encoding three secreted cystein-rich toxin-like peptides whose function remains to be explored were also identified.

Conclusions

Our data further support the role of γ-GTs as key players in A. ervi success on aphid hosts. However, they also evidence that this wasp venom is a complex fluid that contains diverse, more or less specific, protein components. Their characterization will undoubtedly help deciphering parasitoid-aphid and parasitoid-aphid-symbiont interactions. Finally, this study also shed light on the quick evolution of venom components through processes such as duplication and convergent recruitment of virulence factors between unrelated organisms.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2164-15-342) contains supplementary material, which is available to authorized users.

Colonisation of a phage susceptible Campylobacter jejuni population in two phage positive broiler flocks

The pathogens Campylobacter jejuni and Campylobacter coli are commensals in the poultry intestine and campylobacteriosis is one of the most frequent foodborne diseases in developed and developing countries. Phages were identified to be effective in reducing intestinal Campylobacter load and this was evaluated, in the first field trials which were recently carried out. The aim of this study was to further investigate Campylobacter population dynamics during phage application on a commercial broiler farm. This study determines the superiority in colonisation of a Campylobacter type found in a field trial that was susceptible to phages in in vitro tests. The colonisation factors, i.e. motility and gamma glutamyl transferase activity, were increased in this type. The clustering in phylogenetic comparisons of MALDI-TOF spectra did not match the ST, biochemical phenotype and phage susceptibility. Occurrence of Campylobacter jejuni strains and phage susceptibility types with different colonisation potential seem to play a very important role in the success of phage therapy in commercial broiler houses. Thus, mechanisms of both, phage susceptibility and Campylobacter colonisation should be further investigated and considered when composing phage cocktails.

Prevalence of virulence genes in strains of Campylobacter jejuni isolated from human, bovine and broiler

Campylobacter jejuni isolates of different origins (bovine, broiler meat, human) were screened by polymerase chain reaction for the presence of 4 genes cdtB, cst-II, ggt, and virB11, previously linked to virulence such as adherence, invasion, colonization, molecular mimicry, and cytotoxin production. In addition, the isolates were screened for the presence of the global gene regulator csrA linked to oxidative stress responses, biofilms formation, and cell adhesion. All the C. jejuni isolates were positive for cdtB gene. The csrA gene was detected in 100% and 92% of C. jejuni isolates from human and animal origin and the virB11 gene was detected in 7.3% and 3.6% isolates from chicken and human respectively. All isolates from bovine were negative for the virB11 gene. The isolates showed a wide variation for the presence of the remaining genes. Of the C. jejuni recovered from human 83.6%, and 32.7% were positive for cst-II, and ggt respectively. Out of the isolates from chicken 40% and 5.5% isolates revealed the presence of cst-II, and ggt, respectively. Finally of the C. jejuni isolates from bovine, 97.7% and 22.7% were positive for cst-II, and ggt respectively. We conclude that the genes of this study circulate among humans and animals. These results led us to hypothesize that the isolates associated with enteritis (cdtB positives) are not selected by environmental or host-specific factors. On the other hand, the high frequencies of csrA gene in C. jejuni show that this gene is important for the survival of C. jejuni in animals and humans.

Comparative genomics of unintrogressed Campylobacter coli clades 2 and 3

BACKGROUND

Campylobacter jejuni and C. coli share a multitude of risk factors associated with human gastrointestinal disease, yet their phylogeny differs significantly. C. jejuni is scattered into several lineages, with no apparent linkage, whereas C. coli clusters into three distinct phylogenetic groups (clades) of which clade 1 has shown extensive genome-wide introgression with C. jejuni, yet the other two clades (2 and 3) have less than 2% of C. jejuni ancestry. We characterized a C. coli strain (76339) with four novel multilocus sequence type alleles (ST-5088) and having the capability to express gamma-glutamyltranspeptidase (GGT); an accessory feature in C. jejuni. Our aim was to further characterize unintrogressed C. coli clades 2 and 3, using comparative genomics and with additional genome sequences available, to investigate the impact of horizontal gene transfer in shaping the accessory and core gene pools in unintrogressed C. coli.

RESULTS

Here, we present the first fully closed C. coli clade 3 genome (76339). The phylogenomic analysis of strain 76339, revealed that it belonged to clade 3 of unintrogressed C. coli. A more extensive respiratory metabolism among unintrogressed C. coli strains was found compared to introgressed C. coli (clade 1). We also identified other genes, such as serine proteases and an active sialyltransferase in the lipooligosaccharide locus, not present in C. coli clade 1 and we further propose a unique scenario for the evolution of Campylobacter ggt.

CONCLUSIONS

We propose new insights into the evolution of the accessory genome of C. coli clade 3 and C. jejuni. Also, in silico analysis of the gene content revealed that C. coli clades 2 and 3 have genes associated with infection, suggesting they are a potent human pathogen, and may currently be underreported in human infections due to niche separation.

Complete genome analysis of a Haemophilus parasuis serovar 12 strain from China

Haemophilus parasuis is the etiological agent of Glässer's disease in pigs and 15 standard serovars were identified. The widespread disease causes great economic loss in the swine industry worldwide. Aiming to investigate the differences in genome composition and functions among various strains, a highly virulent strain ZJ0906 of H. parasuis serovar 12 from China was analyzed and compared with serovar 5 SH0165. Strain ZJ0906 genome is 2,324,740 base pairs with 40.06% genomic GC content. It contains 2,484 open reading frames (ORF) predicted by Glimmer 3.02, of which 2,352 (∼94.7%) were annotated by NCBI nr blast, 1,745 by COG database and 1,829 by KEGG database. 109 potential virulence factors were annotated in strain ZJ0906 and 3 of which are potentially related to antibiotic resistance. Strain ZJ0906 genome is ∼55 kilobases longer than SH0165 genome, with an extra 211 predicted ORFs. VFDB, ARDB, and PAIDB blast searches showed that ZJ0906 and SH0165 shared a nearly identical panel of potential virulence factors, drug resistant genes and four PAI-like regions which showed high homology to Enterococcus, Escherichia and Salmonella. Synteny analysis showed that gene rearrangements are frequent between the two strains, which may lead to variations in pathogenicity and cross-protection among serovars. KEGG pathway analyses showed strain ZJ0906 shared similar metabolic pathways to strain SH0165. Molecular identification of these genomic elements and potential virulence factors pave the way to the better understanding of mechanisms underlying metabolic capabilities and pathogenicity of H. parasuis and prospective vaccine targets besides the widely used method of inactivated bacteria.

Distribution of colonization and antimicrobial resistance genes in Campylobacter jejuni isolated from chicken

Campylobacter jejuni is an important worldwide foodborne pathogen commonly found as a commensal organism in poultry that can reach high numbers within the gut after colonization. Although information regarding some genes involved in colonization is available, little is known about their distribution in strains isolated specifically from chickens and whether there is a linkage between antimicrobial resistance (AMR) and colonization genes. To assess the distribution and relevance of genes associated with chicken colonization and AMR, a C. jejuni microarray was created to detect 254 genes of interest in colonization and AMR including variants. DNA derived from chicken-specific Campylobacter isolates collected in 2003 (n=29) and 2008 (n=28) was hybridized to the microarray and compared. Hybridization results showed variable colonization-associated gene presence. Acquired AMR genes were low in prevalence whereas chemotaxis receptors, arsenic resistance genes, as well as genes from the cell envelope and flagella functional groups were highly variable in their presence. Strains clustered into two groups, each linked to different control strains, 81116 and NCTC11168. Clustering was found to be independent of collection time. We also show that AMR weakly associated with the CJ0628 and arsR genes. Although other studies have implicated numerous genes associated with C. jejuni chicken colonization, our data on chicken-specific isolates suggest the opposite. The enormous variability in presumed colonization gene prevalence in our chicken isolates suggests that many are of lesser importance than previously thought. Alternatively, this also suggests that combinations of genes may be required for natural colonization of chicken intestines.

Contribution of amino acid catabolism to the tissue specific persistence of Campylobacter jejuni in a murine colonization model

Campylobacter jejuni is a major cause of food-borne disease in industrialized countries. Carbohydrate utilization by C. jejuni is severely restricted, and knowledge about which substrates fuel C. jejuni infection and growth is limited. Some amino acids have been shown to serve as carbon sources both in vitro and in vivo. In the present study we investigated the contribution of serine and proline catabolism to the invitro and invivo growth of C. jejuni 81-176. We confirmed that the serine transporter SdaC and the serine ammonia-lyase SdaA are required for serine utilization, and demonstrated that a predicted proline permease PutP and a bifunctional proline/delta-1-pyrroline-5-carboxylate dehydrogenase PutA are required for proline utilization by C. jejuni 81-176. C. jejuni 81-176 mutants unable to utilize serine were shown to be severely defective for colonization of the intestine and systemic tissues in a mouse model of infection. In contrast, C. jejuni 81-176 mutants unable to utilize proline were only defective for intestinal colonization. These results further emphasize the importance of amino acid utilization in C. jejuni colonization of various tissues.

γ-Glutamyltranspeptidases: sequence, structure, biochemical properties, and biotechnological applications

γ-Glutamyltranspeptidases (γ-GTs) are ubiquitous enzymes that catalyze the hydrolysis of γ-glutamyl bonds in glutathione and glutamine and the transfer of the released γ-glutamyl group to amino acids or short peptides. These enzymes are involved in glutathione metabolism and play critical roles in antioxidant defense, detoxification, and inflammation processes. Moreover, γ-GTs have been recently found to be involved in many physiological disorders, such as Parkinson's disease and diabetes. In this review, the main biochemical and structural properties of γ-GTs isolated from different sources, as well as their conformational stability and mechanism of catalysis, are described and examined with the aim of contributing to the discussion on their structure-function relationships. Possible applications of γ-glutamyltranspeptidases in different fields of biotechnology and medicine are also discussed.

Experimental evidence for the involvement of amino acid residue Glu398 in the autocatalytic processing of Bacillus licheniformis γ-glutamyltranspeptidase

The role of glutamate 398 in the autocatalytic processing of Bacillus licheniformis γ-glutamyltranspeptidase (BlGGT) was explored by site-directed mutagenesis. This glutamate was substituted by either alanine, aspartate, arginine or glutamine and the expressed mutant enzymes were purified to apparent homogeneity with metal-affinity chromatography. SDS–PAGE analysis showed that E398A, E398D and E398K were unable to process themselves into a large and a small subunit. However, E398Q was not only able to process itself, but also had a catalytic activity comparable to that of BlGGT. As compared with the wild-type enzyme, no significant change in circular dichroism spectra was observed for the mutant proteins. Thermal unfolding of BlGGT, E398A, E398D, E398K and E398Q followed the two-state unfolding process with a transition point (T_m) of 47.7–69.4 °C. Tryptophan fluorescence spectra of the mutant enzymes were different from the wild-type protein in terms of fluorescence intensity. Native BlGGT started to unfold beyond ∼1.92 M guanidine hydrochloride (GdnHCl) and reached an unfolded intermediate, [GdnHCl]_{0.5, N–U}, at 3.07 M equivalent to free energy change (Δ⁢GN−UH2⁢O) of 14.53 kcal/mol for the N → U process, whereas the denaturation midpoints for the mutant enzymes were 1.31–2.99 M equivalent to Δ⁢GN−UH2⁢O of 3.29–12.05 kcal/mol. Taken together, these results strongly suggest that the explored glutamate residue is indeed important for the autocatalytic processing of BlGGT.

Association of Campylobacter jejuni metabolic traits with multilocus sequence types

In this study, we describe the association of three Campylobacter jejuni metabolism-related traits, γ-glutamyl-transpeptidase (GGT), fucose permease (fucP), and secreted L-asparaginase [ansB(s)], with multilocus sequence types (STs). A total of 710 C. jejuni isolates with known STs were selected and originated from humans, poultry, bovines, and the environment. Among these isolates, we found 31.1% to produce GGT and 49.3% and 30.3% to be positive for ansB(s) and fucP, respectively. The combination of GGT production, the presence of ansB(s), and the absence of fucP was associated with ST-22, ST-586, and the ST-45 and ST-283 clonal complexes (CCs), which were the main STs and CCs found among the human and chicken isolates. The ST-21 CC was associated with the presence of fucP and was the major CC among the bovine isolates. Although the ST-61 CC was the second major CC among the bovine isolates, these isolates did not have any of the markers studied, making the role of fucP in bovine gut colonization questionable. The ST-45 CC was subdivided into three groups that were attributed solely to ST-45. One group showed a marker combination described previously, another group was found to be positive for ansB(s) only, and the third group did not have any of the markers studied. These results suggest that the host association of these markers seems to be indirect and may arise as a consequence of host-ST and -CC associations. Thus, a representative collection of STs should be tested to draw sensible conclusions in similar studies.

FdhTU-modulated formate dehydrogenase expression and electron donor availability enhance recovery of Campylobacter jejuni following host cell infection

Campylobacter jejuni is a food-borne bacterial pathogen that colonizes the intestinal tract and causes severe gastroenteritis. Interaction with host epithelial cells is thought to enhance severity of disease, and the ability of C. jejuni to modulate its metabolism in different in vivo and environmental niches contributes to its success as a pathogen. A C. jejuni operon comprising two genes that we designated fdhT (CJJ81176_1492) and fdhU (CJJ81176_1493) is conserved in many bacterial species. Deletion of fdhT or fdhU in C. jejuni resulted in apparent defects in adherence and/or invasion of Caco-2 epithelial cells when assessed by CFU enumeration on standard Mueller-Hinton agar. However, fluorescence microscopy indicated that each mutant invaded cells at wild-type levels, instead suggesting roles for FdhTU in either intracellular survival or postinvasion recovery. The loss of fdhU caused reduced mRNA levels of formate dehydrogenase (FDH) genes and a severe defect in FDH activity. Cell infection phenotypes of a mutant deleted for the FdhA subunit of FDH and an ΔfdhU ΔfdhA double mutant were similar to those of a ΔfdhU mutant, which likewise suggested that FdhU and FdhA function in the same pathway. Cell infection assays followed by CFU enumeration on plates supplemented with sodium sulfite abolished the ΔfdhU and ΔfdhA mutant defects and resulted in significantly enhanced recovery of all strains, including wild type, at the invasion and intracellular survival time points. Collectively, our data indicate that FdhTU and FDH are required for optimal recovery following cell infection and suggest that C. jejuni alters its metabolic potential in the intracellular environment.

Renal function at hospital admission and mortality due to acute kidney injury after myocardial infarction

BACKGROUND

The role of an impaired estimated glomerular filtration rate (eGFR) at hospital admission in the outcome of acute kidney injury (AKI) after acute myocardial infarction (AMI) has been underreported. The aim of this study was to assess the influence of an admission eGFR<60 mL/min/1.73 m(2) on the incidence and early and late mortality of AMI-associated AKI.

METHODS

A prospective study of 828 AMI patients was performed. AKI was defined as a serum creatinine increase of ≥ 50% from the time of admission (RIFLE criteria) in the first 7 days of hospitalization. Patients were divided into subgroups according to their eGFR upon hospital admission (MDRD formula, mL/min/1.73 m(2)) and the development of AKI: eGFR ≥ 60 without AKI, eGFR<60 without AKI, eGFR ≥ 60 with AKI and eGFR<60 with AKI.

RESULTS

Overall, 14.6% of the patients in this study developed AKI. The admission eGFR had no impact on the incidence of AKI. However, the admission eGFR was associated with the outcome of AMI-associated AKI. The adjusted hazard ratios (AHR, Cox multivariate analysis) for 30-day mortality were 2.00 (95% CI 1.11-3.61) for eGFR<60 without AKI, 4.76 (95% CI 2.45-9.26) for eGFR ≥ 60 with AKI and 6.27 (95% CI 3.20-12.29) for eGFR<60 with AKI. Only an admission eGFR of <60 with AKI was significantly associated with a 30-day to 1-year mortality hazard (AHR 3.05, 95% CI 1.50-6.19).

CONCLUSIONS

AKI development was associated with an increased early mortality hazard in AMI patients with either preserved or impaired admission eGFR. Only the association of impaired admission eGFR and AKI was associated with an increased hazard for late mortality among these patients.

Antimicrobial activities of isothiocyanates against Campylobacter jejuni isolates

Food-borne human infection with Campylobacter jejuni is a medical concern in both industrialized and developing countries. Efficient eradication of C. jejuni reservoirs within live animals and processed foods is limited by the development of antimicrobial resistances and by practical problems related to the use of conventional antibiotics in food processes. We have investigated the bacteriostatic and bactericidal activities of two phytochemicals, allyl-isothiocyanate (AITC), and benzyl isothiocyanate (BITC), against 24 C. jejuni isolates from chicken feces, human infections, and contaminated foods, as well as two reference strains NCTC11168 and 81-176. AITC and BITC displayed a potent antibacterial activity against C. jejuni. BITC showed a higher overall antibacterial effect (MIC of 1.25-5 μg mL(-1)) compared to AITC (MIC of 50-200 μg mL(-1)). Both compounds are bactericidal rather than bacteriostatic. The sensitivity levels of C. jejuni isolates against isothiocyanates were neither correlated with the presence of a GGT (γ-Glutamyl Transpeptidase) encoding gene in the genome, with antibiotic resistance nor with the origin of the biological sample. However the ggt mutant of C. jejuni 81-176 displayed a decreased survival rate compared to wild-type when exposed to ITC. This work determined the MIC of two ITC against a panel of C. jejuni isolates, showed that both compounds are bactericidal rather than bacteriostatic, and highlighted the role of GGT enzyme in the survival rate of C. jejuni exposed to ITC.

Host epithelial cell invasion by Campylobacter jejuni: trigger or zipper mechanism?

Campylobacter jejuni, a spiral-shaped Gram-negative pathogen, is a highly frequent cause of gastrointestinal foodborne illness in humans worldwide. Clinical outcome of C. jejuni infections ranges from mild to severe diarrheal disease, and some other complications including reactive arthritis and Guillain–Barré syndrome. This review article highlights various C. jejuni pathogenicity factors, host cell determinants, and proposed signaling mechanisms involved in human host cell invasion and their potential role in the development of C. jejuni-mediated disease. A model is presented which outlines the various important interactions of C. jejuni with the intestinal epithelium, and we discuss the pro’s and con’s for the “zipper” over the “trigger” mechanism of invasion. Future work should clarify the contradictory role of some previously identified factors, and should identify and characterize novel virulence determinants, which are crucial to provide fresh insights into the diversity of strategies employed by this pathogen to cause disease.

How a sugary bug gets through the day: recent developments in understanding fundamental processes impacting Campylobacter jejuni pathogenesis

Campylobacter jejuni is a highly prevalent yet fastidious bacterial pathogen that poses a significant health burden worldwide. Lacking many hallmark virulence factors, it is becoming increasingly clear that C. jejuni pathogenesis involves different strategies compared with other well-characterized enteric organisms. This includes the involvement of basic biological processes and cell envelope glycans in a number of aspects related to pathogenesis. The past few years have seen significant progress in the understanding of these pathways and how they relate to C. jejuni fundamental biology, stress survival, colonization, and virulence attributes. This review focuses on recent studies in three general areas where "pathogenesis" and "basic biology" overlap: physiology, stress responses and glycobiology.

Evidence for conserved function of γ-glutamyltranspeptidase in Helicobacter genus

The confounding consequences of Helicobacter bilis infection in experimental mice populations are well recognized, but the role of this bacterium in human diseases is less known. Limited data are available on virulence determinants of this species. In Helicobacter pylori, γ-glutamyltranspeptidase (γGT) contributes to the colonization of the gastric mucosa and to the pathogenesis of peptic ulcer. The role of γGT in H. bilis infections remains unknown. The annotated genome sequence of H. bilis revealed two putative ggt genes and our aim was to characterize these H. bilis γGT paralogues. We performed a phylogenetic analysis to understand the evolution of Helicobacter γGTs and to predict functional activities of these two genes. In addition, both copies of H. bilis γGTs were expressed as recombinant proteins and their biochemical characteristics were analysed. Functional complementation of Esherichia coli deficient in γGT activity and deletion of γGT in H. bilis were performed. Finally, the inhibitory effect of T-cell and gastric cell proliferation by H. bilis γGT was assessed. Our results indicated that one gene is responsible for γGT activity, while the other showed no γGT activity due to lack of autoprocessing. Although both H. bilis and H. pylori γGTs exhibited a similar affinity to L-Glutamine and γ-Glutamyl-p-nitroanilide, the H. bilis γGT was significantly less active. Nevertheless, H. bilis γGT inhibited T-cell proliferation at a similar level to that observed for H. pylori. Finally, we showed a similar suppressive influence of both H. bilis and H. pylori γGTs on AGS cell proliferation mediated by an apoptosis-independent mechanism. Our data suggest a conserved function of γGT in the Helicobacter genus. Since γGT is present only in a few enterohepatic Helicobacter species, its expression appears not to be essential for colonization of the lower gastrointestinal tract, but it could provide metabolic advantages in colonization capability of different niches.

Nutrient acquisition and metabolism by Campylobacter jejuni

The gastrointestinal pathogen Campylobacter jejuni is able to colonize numerous different hosts and compete against the gut microbiota. To do this, it must be able to efficiently acquire sufficient nutrients from its environment to support its survival and rapid growth in the intestine. However, despite almost 50 years of research, many aspects as to how C. jejuni accomplishes this feat remain poorly understood. C. jejuni lacks many of the common metabolic pathways necessary for the use of glucose, galactose, or other carbohydrates upon which most other microbes thrive. It does however make efficient use of citric acid cycle intermediates and various amino acids. C. jejuni readily uses the amino acids aspartate, glutamate, serine, and proline, with certain strains also possessing additional pathways allowing for the use of glutamine and asparagine. More recent work has revealed that some C. jejuni strains can metabolize the sugar l-fucose. This finding has upset years of dogma that C. jejuni is an asaccharolytic organism. C. jejuni also possesses diverse mechanisms for the acquisition of various transition metals that are required for metabolic activities. In particular, iron acquisition is critical for the formation of iron–sulfur complexes. C. jejuni is also unique in possessing both molybdate and tungsten cofactored proteins and thus has an unusual regulatory scheme for these metals. Together these various metabolic and acquisition pathways help C. jejuni to compete and thrive in wide variety of hosts and environments.

Closely related Campylobacter jejuni strains from different sources reveal a generalist rather than a specialist lifestyle

Background

Campylobacter jejuni and Campylobacter coli are human intestinal pathogens of global importance. Zoonotic transmission from livestock animals or animal-derived food is the likely cause for most of these infections. However, little is known about their general and host-specific mechanisms of colonization, or virulence and pathogenicity factors. In certain hosts, Campylobacter species colonize persistently and do not cause disease, while they cause acute intestinal disease in humans.

Results

Here, we investigate putative host-specificity using phenotypic characterization and genome-wide analysis of genetically closely related C. jejuni strains from different sources. A collection of 473 fresh Campylobacter isolates from Germany was assembled between 2006 and 2010 and characterized using MLST. A subset of closely related C. jejuni strains of the highly prevalent sequence type ST-21 was selected from different hosts and isolation sources. PCR typing of strain-variable genes provided evidence that some genes differed between these strains. Furthermore, phenotypic variation of these strains was tested using the following criteria: metabolic variation, protein expression patterns, and eukaryotic cell interaction. The results demonstrated remarkable phenotypic diversity within the ST-21 group, which however did not correlate with isolation source. Whole genome sequencing was performed for five ST-21 strains from chicken, human, bovine, and food sources, in order to gain insight into ST-21 genome diversity. The comparisons showed extensive genomic diversity, primarily due to recombination and gain of phage-related genes. By contrast, no genomic features associated with isolation source or host were identified.

Conclusions

The genome information and phenotypic data obtained in vitro and in a chicken infection model provided little evidence of fixed adaptation to a specific host. Instead, the dominant C. jejuni ST-21 appeared to be characterized by phenotypic flexibility and high genetic microdiversity, revealing properties of a generalist. High genetic flexibility might allow generalist variants of C. jejuni to reversibly express diverse fitness factors in changing environments.

Protein domain of unknown function 3233 is a translocation domain of autotransporter secretory mechanism in gamma proteobacteria

Vibrio cholerae, the enteropathogenic gram negative bacteria is one of the main causative agents of waterborne diseases like cholera. About 1/3^rd of the organism's genome is uncharacterised with many protein coding genes lacking structure and functional information. These proteins form significant fraction of the genome and are crucial in understanding the organism's complete functional makeup. In this study we report the general structure and function of a family of hypothetical proteins, Domain of Unknown Function 3233 (DUF3233), which are conserved across gram negative gammaproteobacteria (especially in Vibrio sp. and similar bacteria). Profile and HMM based sequence search methods were used to screen homologues of DUF3233. The I-TASSER fold recognition method was used to build a three dimensional structural model of the domain. The structure resembles the transmembrane beta-barrel with an axial N-terminal helix and twelve antiparallel beta-strands. Using a combination of amphipathy and discrimination analysis we analysed the potential transmembrane beta-barrel forming properties of DUF3233. Sequence, structure and phylogenetic analysis of DUF3233 indicates that this gram negative bacterial hypothetical protein resembles the beta-barrel translocation unit of autotransporter Va secretory mechanism with a gene organisation that differs from the conventional Va system.