Motility defects in Campylobacter jejuni defined gene deletion mutants caused by second-site mutations

Spatiotemporal variations in the occurrence of Campylobacter species in the Bloukrans and Swartkops rivers, Eastern Cape, South Africa

An increase in the incidence of Campylobacter species in rivers raises concerns on the safety of river water for humans who get exposed to river water. This study examines the spatiotemporal dynamics of Campylobacter species in the Bloukrans and Swartkops rivers, analysing patterns of its occurrence in relation to meteorological conditions, physicochemical parameters, seasons, and sampling sites. Physico-chemical parameters and meteorological conditions were measured during water sampling from various sites along the rivers over a year, while Polymerase Chain Reaction (PCR) was utilised to detect Campylobacter genus-specific genes and selected antibiotic-resistant genes. Campylobacter was detected in 66.67% (Bloukrans River) and 58.33% (Swartkops River). In the Bloukrans River, multi-drug resistance genes cmeA (20%), cmeB (65%), cmeC (10%), were detected while and tetO was detected at 70%. In the Swartkops River, the corresponding prevalence were 28%, 66.67%, 28.56%, and 76%. The study indicates that sampling season did not significantly impact Campylobacter prevalence. However, variation in Campylobacter occurrence exists among different sites along the rivers, reflecting the influence of site proximity to potential contamination sources. The study suggests that Campylobacter infection may be endemic in South Africa, with rivers serving as potential sources of exposure to humans, thereby contributing to the epidemiology of campylobacteriosis.

Identification of Campylobacter jejuni and Campylobacter coli genes contributing to oxidative stress response using TraDIS analysis

BACKGROUND

Campylobacter jejuni and Campylobacter coli are the major causative agents of bacterial gastroenteritis worldwide and are known obligate microaerophiles. Despite being sensitive to oxygen and its reduction products, both species are readily isolated from animal food products kept under atmospheric conditions where they face high oxygen tension levels.

RESULTS

In this study, Transposon Directed Insertion-site Sequencing (TraDIS) was used to investigate the ability of one C. jejuni strain and two C. coli strains to overcome oxidative stress, using H2O2 to mimic oxidative stress. Genes were identified that were required for oxidative stress resistance for each individual strain but also allowed a comparison across the three strains. Mutations in the perR and ahpC genes were found to increase Campylobacter tolerance to H2O2. The roles of these proteins in oxidative stress were previously known in C. jejuni, but this data indicates that they most likely play a similar role in C. coli. Mutation of czcD decreased Campylobacter tolerance to H2O2. The role of CzcD, which functions as a zinc exporter, has not previously been linked to oxidative stress. The TraDIS data was confirmed using defined deletions of perR and czcD in C. coli 15-537360.

CONCLUSIONS

This is the first study to investigate gene fitness in both C. jejuni and C. coli under oxidative stress conditions and highlights both similar roles for certain genes for both species and highlights other genes that have a role under oxidative stress.

Assessment of risk of exposure to Campylobacter species and their antibiotic-resistant genes from selected rivers in the Eastern Cape, South Africa

Contaminated rivers play a critical role in the transmission of Campylobacter and antibiotic-resistant genes (ARGs) in many parts of the world. South Africa is a water-scarce country which relies on its freshwater systems such as rivers for recreation, irrigation, and domestic activities. This study assesses the potential human exposure to Campylobacter and its ARGs from rivers through the ingestion route in two South African rivers. The concentration of viable Campylobacter and ARGs in selected rivers was determined using quantitative PCR. The concentrations were then used to estimate the number of gene copies a person could ingest after swimming in the contaminated water for 1 h (intake burden). The human intake burden of Campylobacter 16 S rRNA copies per 1-h swimming event ranged from 7.1 × 105-3.7 × 106 copies/h for the Bloukrans River, and 9.9 × 101-2.3 × 105 copies/h for the Swartkops River. The intake burden of Campylobacter ARGs ranged from 1.64 × 104-5.8 × 105 copies/h for cmeB; 1.0 × 103-5.7 × 104 copies/h for tetO for the Bloukrans River, and 3.6 × 102-1.551 × 105 copies/h (cmeB) and 9.98 × 102-5.7 × 104 copies/h (tetO) for the Swartkops River. Ingestion of water from contaminated rivers during recreation, cultural, or religious activities may lead to human exposure to ARGs, posing a health risk. In many communities in the world, rivers play an important role in the social and cultural lives of people, and so it is important to monitor the quality of river water. Studies such as these will help prevent the spread of antibiotic-resistant genes and waterborne diseases caused by pathogens such as Campylobacter.

Application of TraDIS to define the core essential genome of Campylobacter jejuni and Campylobacter coli

Campylobacter species are the major cause of bacterial gastroenteritis. As there is no effective vaccine, combined with the rapid increase in antimicrobial resistant strains, there is a need to identify new targets for intervention. Essential genes are those that are necessary for growth and/or survival, making these attractive targets. In this study, comprehensive transposon mutant libraries were created in six C. jejuni strains, four C. coli strains and one C. lari and C. hyointestinalis strain, allowing for those genes that cannot tolerate a transposon insertion being called as essential. Comparison of essential gene lists using core genome analysis can highlight those genes which are common across multiple strains and/or species. Comparison of C. jejuni and C. coli, the two species that cause the most disease, identified 316 essential genes. Genes of interest highlighted members of the purine pathway being essential for C. jejuni whilst also finding that a functional potassium uptake system is essential. Protein-protein interaction networks using these essential gene lists also highlighted proteins in the purine pathway being major 'hub' proteins which have a large number of interactors across the network. When adding in two more species (C. lari and C. hyointestinalis) the essential gene list reduces to 261. Within these 261 essential genes, there are many genes that have been found to be essential in other bacteria. These include htrB and PEB4, which have previously been found as core virulence genes across Campylobacter species in other studies. There were 21 genes which have no known function with eight of these being associated with the membrane. These surface-associated essential genes may provide attractive targets. The essential gene lists presented will help to prioritise targets for the development of novel therapeutic and preventative interventions.

Development and validation of a CRISPR interference system for gene regulation in Campylobacter jejuni

BACKGROUND

Campylobacter spp. are the leading cause of bacterial food-borne illness in humans worldwide, with Campylobacter jejuni responsible for 80% of these infections. There is an urgent need to understand fundamental C. jejuni biology for the development of new strategies to prevent and treat infections. The range of molecular tools available to regulate gene expression in C. jejuni is limited, which in turn constrains our ability to interrogate the function of essential and conditionally essential genes. We have addressed this by developing and utilising a CRISPR-based interference system known as CRISPRi in C. jejuni to control gene expression. To achieve this, a catalytically inactive ("dead") cas9 and sgRNA backbone from the Streptococcus pyogenes CRISPRi system was combined with C. jejuni-derived promoters of predetermined expression activities to develop a CRISPRi-based repression tool in C. jejuni strains M1Cam and 81-176.

RESULTS

The CRISPRi tool was validated through successful repression of the arylsulphatase-encoding gene astA using a range of sgRNA target sequences spanning the astA gene. The tool was also applied to target astA in an M1Cam CRISPR-Cas9 deletion strain, which showed that the presence of an endogenous CRISPR-Cas9 system did not affect the activity of the CRISPRi-based repression tool. The tool was further validated against the hippicurase-encoding gene hipO. Following this, the flagella genes flgR, flaA, flaB and both flaA and flaB were targeted for CRISPRi-based repression, which resulted in varying levels of motility reduction and flagella phenotypes as determined by phenotypical assays and transmission electron microscopy (TEM).

CONCLUSIONS

This is the first report of a CRISPRi-based tool in C. jejuni, which will provide a valuable resource to the Campylobacter community.

Experimental Evolution of Campylobacter jejuni Leads to Loss of Motility, rpoN (σ54) Deletion and Genome Reduction

Evolution experiments in the laboratory have focused heavily on model organisms, often to the exclusion of clinically relevant pathogens. The foodborne bacterial pathogen Campylobacter jejuni belongs to a genus whose genomes are small compared to those of its closest genomic relative, the free-living genus Sulfurospirillum, suggesting genome reduction during the course of evolution to host association. In an in vitro experiment, C. jejuni serially passaged in rich medium in the laboratory exhibited loss of flagellar motility-an essential function for host colonization. At early time points the motility defect was often reversible, but after 35 days of serial culture, motility was irreversibly lost in most cells in 5 independently evolved populations. Population re-sequencing revealed disruptive mutations to genes in the flagellar transcriptional cascade, rpoN (σ54)-therefore disrupting the expression of the genes σ54 regulates-coupled with deletion of rpoN in all evolved lines. Additional mutations were detected in virulence-related loci. In separate in vivo experiments, we demonstrate that a phase variable (reversible) motility mutant carrying an adenine deletion within a homopolymeric tract resulting in truncation of the flagellar biosynthesis gene fliR was deficient for colonization in a C57BL/6 IL-10-/- mouse disease model. Re-insertion of an adenine residue partially restored motility and ability to colonize mice. Thus, a pathogenic C. jejuni strain was rapidly attenuated by experimental laboratory evolution and demonstrated genomic instability during this evolutionary process. The changes observed suggest C. jejuni is able to evolve in a novel environment through genome reduction as well as transition, transversion, and slip-strand mutations.

Genome-Scale Metabolic Model Driven Design of a Defined Medium for Campylobacter jejuni M1cam

Campylobacter jejuni, the most frequent cause of food-borne bacterial gastroenteritis, is a fastidious organism when grown in the laboratory. Oxygen is required for growth, despite the presence of the metabolic mechanism for anaerobic respiration. Amino acid auxotrophies are variably reported and energy metabolism can occur through several electron donor/acceptor combinations. Overall, the picture is one of a flexible, but vulnerable metabolism. To understand Campylobacter metabolism, we have constructed a fully curated, metabolic model for the reference organism M1 (our variant is M1cam) and validated it through laboratory experiments. Our results show that M1cam is auxotrophic for methionine, niacinamide, and pantothenate. There are complete biosynthesis pathways for all amino acids except methionine and it can produce energy, but not biomass, in the absence of oxygen. M1cam will grow in DMEM/F-12 defined media but not in the previously published Campylobacter specific defined media tested. Using the model, we identified potential auxotrophies and substrates that may improve growth. With this information, we designed simple defined media containing inorganic salts, the auxotrophic substrates, L-methionine, niacinamide, and pantothenate, pyruvate and additional amino acids L-cysteine, L-serine, and L-glutamine for growth enhancement. Our defined media supports a 1.75-fold higher growth rate than Brucella broth after 48 h at 37°C and sustains the growth of other Campylobacter jejuni strains. This media can be used to design reproducible assays that can help in better understanding the adaptation, stress resistance, and the virulence mechanisms of this pathogen. We have shown that with a well-curated metabolic model it is possible to design a media to grow this fastidious organism. This has implications for the investigation of new Campylobacter species defined through metagenomics, such as C. infans.

C8J_1298, a bifunctional thiol oxidoreductase of Campylobacter jejuni, affects Dsb (disulfide bond) network functioning

Posttranslational generation of disulfide bonds catalyzed by bacterial Dsb (disulfide bond) enzymes is essential for the oxidative folding of many proteins. Although we now have a good understanding of the Escherichia coli disulfide bond formation system, there are significant gaps in our knowledge concerning the Dsb systems of other bacteria, including Campylobacter jejuni, a food-borne, zoonotic pathogen. We attempted to gain a more complete understanding of the process by thorough analysis of C8J_1298 functioning in vitro and in vivo. C8J_1298 is a homodimeric thiol-oxidoreductase present in wild type (wt) cells, in both reduced and oxidized forms. The protein was previously described as a homolog of DsbC, and thus potentially should be active in rearrangement of disulfides. Indeed, biochemical studies with purified protein revealed that C8J_1298 shares many properties with EcDsbC. However, its activity in vivo is dependent on the genetic background, namely, the set of other Dsb proteins present in the periplasm that determine the redox conditions. In wt C. jejuni cells, C8J_1298 potentially works as a DsbG involved in the control of the cysteine sulfenylation level and protecting single cysteine residues from oxidation to sulfenic acid. A strain lacking only C8J_1298 is indistinguishable from the wild type strain by several assays recognized as the criteria to determine isomerization or oxidative Dsb pathways. Remarkably, in C. jejuni strain lacking DsbA1, the protein involved in generation of disulfides, C8J_1298 acts as an oxidase, similar to the homodimeric oxidoreductase of Helicobater pylori, HP0231. In E. coli, C8J_1298 acts as a bifunctional protein, also resembling HP0231. These findings are strongly supported by phylogenetic data. We also showed that CjDsbD (C8J_0565) is a C8J_1298 redox partner.

Evolution of Campylobacter jejuni of poultry origin in Brazil

Campylobacter jejuni is the most common pathogen associated with foodborne diseases. Persistent presence of this pathogen contaminating the environment in slaughterhouses and chicken products have been reported worldwide. Although many efforts have been employed for reducing C. jejuni contamination, few studies have been conducted to understand the dynamics of C. jejuni in slaughterhouses over time. In this study, we evaluated the virulence, antibiotic resistance and genetic diversity profiles of 99 C. jejuni isolated from chilled chicken carcasses collected in Brazilian slaughterhouses during two distinct periods (2011-2012 and 2015-2016). The virulence profile was evaluated for the presence of flaA, ciaB, cadF, pldA and cdtABC genes. Antibiotic resistance was evaluated for amoxicillin-clavulanic acid, gentamicin, erythromycin and tetracycline. Genetic diversity was assessed using RAPD-PCR. The prevalence of C. jejuni was significantly reduced in 2015-2016 as well the number of antibiotic (and multidrug) resistant isolates, except for tetracycline. However, isolates from 2015 to 2016 showed higher prevalence of multiple virulence genes and genetic diversity profile compared to isolates from 2011 to 2012. During the studied period, stricter regulations to control pathogens in poultry farms and slaughterhouses were implemented in Brazil, which may have contributed to the profile variation observed due to changes of selective pressures on bacterial populations.

CapC, a Novel Autotransporter and Virulence Factor of Campylobacter jejuni

Campylobacter jejuni is recognized as an important causative agent of bacterial gastroenteritis in the developed world. Despite the identification of several factors contributing to infection, characterization of the virulence strategies employed by C. jejuni remains a significant challenge. Bacterial autotransporter proteins are a major class of secretory proteins in Gram-negative bacteria, and notably, many autotransporter proteins contribute to bacterial virulence. The aim of this study was to characterize the C. jejuni 81116 C8J_1278 gene (capC), predicted to encode an autotransporter protein, and examine the contribution of this factor to virulence of C. jejuni The predicted CapC protein has a number of features that are consistent with autotransporters, including the N-terminal signal sequence and the C-terminal β-barrel domain and was determined to localize to the outer membrane. Inactivation of the capC gene in C. jejuni 81116 and C. jejuni M1 resulted in reduced insecticidal activity in Galleria mellonella larvae. Furthermore, C. jejuni capC mutants displayed significantly reduced adherence to and invasion of nonpolarized, partially differentiated Caco-2 and T84 intestinal epithelial cells. Gentamicin treatment showed that the reduced invasion of the capC mutant is primarily caused by reduced adherence to intestinal epithelial cells, not by reduced invasion capability. C. jejuni capC mutants caused reduced interleukin 8 (IL-8) secretion from intestinal epithelial cells and elicited a significantly diminished immune reaction in Galleria larvae, indicating that CapC functions as an immunogen. In conclusion, CapC is a new virulence determinant of C. jejuni that contributes to the integral infection process of adhesion to human intestinal epithelial cells.IMPORTANCECampylobacter jejuni is a major causative agent of human gastroenteritis, making this zoonotic pathogen of significant importance to human and veterinary public health worldwide. The mechanisms by which C. jejuni interacts with intestinal epithelial cells and causes disease are still poorly understood due, in part, to the heterogeneity of C. jejuni infection biology. Given the importance of C. jejuni to public health, the need to characterize novel and existing virulence mechanisms is apparent. The significance of our research is in demonstrating the role of CapC, a novel virulence factor in C. jejuni that contributes to adhesion and invasion of the intestinal epithelium, thereby in part, addressing the dearth of knowledge concerning the factors involved in Campylobacter pathogenesis and the variation observed in the severity of human infection.

Antibiotic Sensitivity Profiling and Virulence Potential of Campylobacter jejuni Isolates from Estuarine Water in the Eastern Cape Province, South Africa

Campylobacter jejuni (CJ) is a zoonotic microbe and a major causative organism of diarrheal infection in humans that often has its functional characteristics inactivated in stressed conditions. The current study assessed the correlation between recovered CJ and water quality parameters and the drug sensitivity patterns of the pathogen to frontline antibiotics in human and veterinary medicine. Water samples (n = 244) from rivers/estuarines were collected from April⁻September 2016, and physicochemical conditions were recorded on-site. CJ was isolated from the samples using standard microbiological methods and subjected to sensitivity testing to 10 antibiotics. Mean CJ counts were between 1 and 5 logs (CFU/mL). Ninety-five isolates confirmed as CJ by PCR showed varying rates of resistance. Sensitivity testing showed resistance to tetracycline (100%), azithromycin (92%), clindamycin (84.2%), clarithromycin and doxycycline (80%), ciprofloxacin (77.8%), vancomycin (70.5%), erythromycin (70%), metronidazole (36.8%) and nalidixic acid (30.5%). Virulence encoding genes were detected in the majority 80/95, 84.2%) of the confirmed isolates from cdtB; 60/95 (63.2%) from cstII; 49/95 (51.6%) from cadF; 45/95 (47.4%) from clpP; 30/95 (31.6%) from htrB, and 0/95 (0%) from csrA. A multiple resistance cmeABC active efflux pump system was present in 69/95 (72.6) isolates. The presence of CJ was positively correlated with temperature (r = 0.17), pH (r = 0.02), dissolved oxygen (r = 0.31), and turbidity (r = 0.23) but negatively correlated with salinity (r = −0.39) and conductivity (r = −0.28). The detection of multidrug resistant CJ strains from estuarine water and the differential gene expressions they possess indicates a potential hazard to humans. Moreover, the negative correlation between the presence of the pathogen and physicochemical parameters such as salinity indicates possible complementary expression of stress tolerance response mechanisms by wild-type CJ strains.

Phylogenetic analyses and antimicrobial resistance profiles of Campylobacter spp. from diarrhoeal patients and chickens in Botswana

Campylobacter spp. are a leading cause of bacterial enteritis worldwide, including countries in Africa, and have been identified by the World Health Organisation (WHO) as one of the high priority antimicrobial resistant pathogens. However, at present there is little knowledge on the prevalence, molecular epidemiology or antimicrobial susceptibility of Campylobacter spp. isolates in Botswana, both in patients and in the zoonotic context. Some data indicate that ~14% of diarrhoeal disease cases in a paediatric setting can be ascribed to Campylobacter spp., urging the need for the magnitude of Campylobacter-associated diarrhoea to be established. In this survey, we have characterised the genomic diversity of Campylobacter spp. circulating in Botswana isolated from cases of diarrhoeal disease in humans (n = 20) and from those that colonised commercial broiler (n = 35) and free-range (n = 35) chickens. Phylogeny showed that the Campylobacter spp. isolated from the different poultry and human sources were highly related, suggesting that zoonotic transmission has likely occurred. We found that for Campylobacter spp. isolated from humans, broilers and free-range chickens, 52% was positive for tetO, 47% for gyrA-T86I, 72% for bla_OXA-61, with 27% carrying all three resistance determinants. No 23S mutations conferring macrolide resistance were detected in this survey. In summary, our study provides insight into Campylobacter spp. in poultry reservoirs and in diarrhoeal patients, and the relevance for treatment regimens in Botswana.

Genome-wide association of functional traits linked with Campylobacter jejuni survival from farm to fork

Campylobacter jejuni is a major cause of bacterial gastroenteritis worldwide, primarily associated with the consumption of contaminated poultry. C. jejuni lineages vary in host range and prevalence in human infection, suggesting differences in survival throughout the poultry processing chain. From 7343 MLST-characterised isolates, we sequenced 600 C. jejuni and C. coli isolates from various stages of poultry processing and clinical cases. A genome-wide association study (GWAS) in C. jejuni ST-21 and ST-45 complexes identified genetic elements over-represented in clinical isolates that increased in frequency throughout the poultry processing chain. Disease-associated SNPs were distinct in these complexes, sometimes organised in haplotype blocks. The function of genes containing associated elements was investigated, demonstrating roles for cj1377c in formate metabolism, nuoK in aerobic survival and oxidative respiration, and cj1368-70 in nucleotide salvage. This work demonstrates the utility of GWAS for investigating transmission in natural zoonotic pathogen populations and provides evidence that major C. jejuni lineages have distinct genotypes associated with survival, within the host specific niche, from farm to fork.

Genome-wide fitness analyses of the foodborne pathogen Campylobacter jejuni in in vitro and in vivo models

Campylobacter is the most common cause of foodborne bacterial illness worldwide. Faecal contamination of meat, especially chicken, during processing represents a key route of transmission to humans. There is a lack of insight into the mechanisms driving C. jejuni growth and survival within hosts and the environment. Here, we report a detailed analysis of C. jejuni fitness across models reflecting stages in its life cycle. Transposon (Tn) gene-inactivation libraries were generated in three C. jejuni strains and the impact on fitness during chicken colonisation, survival in houseflies and under nutrient-rich and -poor conditions at 4 °C and infection of human gut epithelial cells was assessed by Tn-insertion site sequencing (Tn-seq). A total of 331 homologous gene clusters were essential for fitness during in vitro growth in three C. jejuni strains, revealing that a large part of its genome is dedicated to growth. We report novel C. jejuni factors essential throughout its life cycle. Importantly, we identified genes that fulfil important roles across multiple conditions. Our comprehensive screens showed which flagella elements are essential for growth and which are vital to the interaction with host organisms. Future efforts should focus on how to exploit this knowledge to effectively control infections caused by C. jejuni.

Morphology heterogeneity within a Campylobacter jejuni helical population: the use of calcofluor white to generate rod-shaped C. jejuni 81-176 clones and the genetic determinants responsible for differences in morphology within 11168 strains

Campylobacter jejuni helical shape is important for colonization and host interactions with straight mutants having altered biological properties. Passage on calcofluor white (CFW) resulted in C. jejuni 81‐176 isolates with morphology changes: either a straight morphology from frameshift mutations and single nucleotide polymorphisms in peptidoglycan hydrolase genes pgp1 or pgp2 or a reduction in curvature due a frameshift mutation in cjj81176_1105, a putative peptidoglycan endopeptidase. Shape defects were restored by complementation. Whole genome sequencing of CFW‐passaged strains showed no specific changes correlating to CFW exposure. The cjj81176_1279 (recR; recombinational DNA repair) and cjj81176_1449 (unknown function) genes were highly variable in all 81‐176 strains sequenced. A frameshift mutation in pgp1 of our laboratory isolate of the straight genome sequenced variant of 11168 (11168‐GS) was also identified. The PG muropeptide profile of 11168‐GS was identical to that of Δpgp1 in the original minimally passaged 11168 strain (11168‐O). Introduction of wild type pgp1 into 11168‐GS did not restore helical morphology. The recR gene was also highly variable in 11168 strains. Microbial cell‐to‐cell heterogeneity is proposed as a mechanism of ensuring bacterial survival in sub‐optimal conditions. In certain environments, changes in C. jejuni morphology due to genetic heterogeneity may promote C. jejuni survival.

Analysis of Campylobacter jejuni infection in the gnotobiotic piglet and genome-wide identification of bacterial factors required for infection

To investigate how Campylobacter jejuni causes the clinical symptoms of diarrhoeal disease in humans, use of a relevant animal model is essential. Such a model should mimic the human disease closely in terms of host physiology, incubation period before onset of disease, clinical signs and a comparable outcome of disease. In this study, we used a gnotobiotic piglet model to study determinants of pathogenicity of C. jejuni. In this model, C. jejuni successfully established infection and piglets developed an increased temperature with watery diarrhoea, which was caused by a leaky epithelium and reduced bile re-absorption in the intestines. Further, we assessed the C. jejuni genes required for infection of the porcine gastrointestinal tract utilising a transposon (Tn) mutant library screen. A total of 123 genes of which Tn mutants showed attenuated piglet infection were identified. Our screen highlighted a crucial role for motility and chemotaxis, as well as central metabolism. In addition, Tn mutants of 14 genes displayed enhanced piglet infection. This study gives a unique insight into the mechanisms of C. jejuni disease in terms of host physiology and contributing bacterial factors.

A quantitative proteomic screen of the Campylobacter jejuni flagellar-dependent secretome

Campylobacter jejuni is the leading cause of bacterial gastroenteritis in the world. A number of factors are believed to contribute to the ability of C. jejuni to cause disease within the human host including the secretion of non-flagellar proteins via the flagellar type III secretion system (FT3SS). Here for the first time we have utilised quantitative proteomics using stable isotope labelling by amino acids in cell culture (SILAC), and label-free liquid chromatography-mass spectrometry (LC/MS), to compare supernatant samples from C. jejuni M1 wild type and flagella-deficient (flgG mutant) strains to identify putative novel proteins secreted via the FT3SS. Genes encoding proteins that were candidates for flagellar secretion, derived from the LC/MS and SILAC datasets, were deleted. Infection of human CACO-2 tissue culture cells using these mutants resulted in the identification of novel genes required for interactions with these cells. This work has shown for the first time that both CJM1_0791 and CJM1_0395 are dependent on the flagellum for their presence in supernatants from C. jejuni stains M1 and 81-176.

BIOLOGICAL SIGNIFICANCE

This study provides the most complete description of the Campylobac er jejuni secretome to date. SILAC and label-free proteomics comparing mutants with or without flagella have resulted in the identification of two C. jejuni proteins that are dependent on flagella for their export from the bacterial cell.

Identification and initial characterisation of a protein involved in Campylobacter jejuni cell shape

Campylobacter jejuni is the leading cause of bacterial food borne illness. While helical cell shape is considered important for C. jejuni pathogenesis, this bacterium is capable of adopting other morphologies. To better understand how helical-shaped C. jejuni maintain their shape and thus any associated colonisation, pathogenicity or other advantage, it is first important to identify the genes and proteins involved. So far, two peptidoglycan modifying enzymes Pgp1 and Pgp2 have been shown to be required for C. jejuni helical cell shape. We performed a visual screen of ∼2000 transposon mutants of C. jejuni for cell shape mutants. Whole genome sequence data of the mutants with altered cell shape, directed mutants, wild type stocks and isolated helical and rod-shaped ‘wild type’ C. jejuni, identified a number of different mutations in pgp1 and pgp2, which result in a change in helical to rod bacterial cell shape. We also identified an isolate with a loss of curvature. In this study, we have identified the genomic change in this isolate, and found that targeted deletion of the gene with the change resulted in bacteria with loss of curvature. Helical cell shape was restored by supplying the gene in trans. We examined the effect of loss of the gene on bacterial motility, adhesion and invasion of tissue culture cells and chicken colonisation, as well as the effect on the muropeptide profile of the peptidoglycan sacculus. Our work identifies another factor involved in helical cell shape.

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A C. jejuni isolate with a loss of curvature was identified.

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A targeted gene deletion of CJJ81176_1105 in 81–176 and CJM1_1064 in M1 were created.

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Defined gene deletion mutants of CJJ81176_1105 and CJM1_1064 alter C. jejuni motility and interaction with Caco-2 cells.

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Defined gene deletion mutant of CJM1_1064 does not alter C. jejuni colonisation of chickens.

Genomic variations leading to alterations in cell morphology of Campylobacter spp

Campylobacter jejuni, the most common cause of bacterial diarrhoeal disease, is normally helical. However, it can also adopt straight rod, elongated helical and coccoid forms. Studying how helical morphology is generated, and how it switches between its different forms, is an important objective for understanding this pathogen. Here, we aimed to determine the genetic factors involved in generating the helical shape of Campylobacter. A C. jejuni transposon (Tn) mutant library was screened for non-helical mutants with inconsistent results. Whole genome sequence variation and morphological trends within this Tn library, and in various C. jejuni wild type strains, were compared and correlated to detect genomic elements associated with helical and rod morphologies. All rod-shaped C. jejuni Tn mutants and all rod-shaped laboratory, clinical and environmental C. jejuni and Campylobacter coli contained genetic changes within the pgp1 or pgp2 genes, which encode peptidoglycan modifying enzymes. We therefore confirm the importance of Pgp1 and Pgp2 in the maintenance of helical shape and extended this to a wide range of C. jejuni and C. coli isolates. Genome sequence analysis revealed variation in the sequence and length of homopolymeric tracts found within these genes, providing a potential mechanism of phase variation of cell shape.

The Minor Flagellin of Campylobacter jejuni (FlaB) Confers Defensive Properties against Bacteriophage Infection

A screen of bacteriophages infecting a panel of Campylobacter jejuni PT14 gene knock-out mutants identified a role for the minor flagellin encoded by the flaB gene, in the defense of the host against CP8unalikevirus bacteriophage CP_F1 infection. Inactivation of the flaB gene resulted in an increase in the susceptibility of PT14 cultures to infection by CP_F1 and an increase in bacteriophage yields. Infection of wild type PT14 with CP_F1 produces turbid plaques in bacterial lawns, from which 78% of the resistant isolates recovered exhibit either attenuation or complete loss of motility. CP_F1 produces clear plaques on the flaB mutant with no regrowth in the lysis zones. Complementation of the mutant restored overgrowth and the development of resistance at the expense of motility. Further analyses revealed an increase in bacteriophage adsorption constant of nearly 2-fold and burst-size 3-fold, relative to the wild type. Motility analysis showed no major reduction in swarming motility in the flaB mutant. Thus, we propose a new role for FlaB in the defense of campylobacters against bacteriophage infection.

Feedback control of Campylobacter jejuni flagellin levels through reciprocal binding of FliW to flagellin and the global regulator CsrA

Bacterial flagella assembly is tightly regulated to ensure a timely and sequential production of the various flagellum constituents. In the pathogen Campylobacter jejuni the hierarchy in flagella biosynthesis is largely determined at the transcriptional level through the activity of the alternative sigma factors sigma⁵⁴ and sigma²⁸ . Here, we report that C. jejuni flagellin levels are also controlled at the post-transcriptional level via the thus far poorly-characterized flagellar assembly factor FliW. Analysis of flagellin synthesis in C. jejuni 81116 and a ΔfliW knock-out mutant showed reduced flagellin protein levels in the mutant strain while ectopic expression of FliW resulted in enhanced levels. Real-time RT-PCR revealed relatively minor changes in flaA and flaB mRNA levels for the recombinant and parent strain consistent with post-transcriptional regulation. Purified FliW was found to bind to FlaA and FlaB flagellin as well as to the global post-transcriptional regulator CsrA. Inactivation of CsrA resulted in increased levels of flagellin translation. An in vitro translation assay confirmed the regulatory role of CsrA in flagellin biosynthesis. We propose that competitive reciprocal binding of FliW to flagellins and the RNA binding protein CsrA serves as a feedback mechanism to control the number of cytosolic flagellin copies at the protein level.

The CsrA-FliW network controls polar localization of the dual-function flagellin mRNA in Campylobacter jejuni

The widespread CsrA/RsmA protein regulators repress translation by binding GGA motifs in bacterial mRNAs. CsrA activity is primarily controlled through sequestration by multiple small regulatory RNAs. Here we investigate CsrA activity control in the absence of antagonizing small RNAs by examining the CsrA regulon in the human pathogen Campylobacter jejuni. We use genome-wide co-immunoprecipitation combined with RNA sequencing to show that CsrA primarily binds flagellar mRNAs and identify the major flagellin mRNA (flaA) as the main CsrA target. The flaA mRNA is translationally repressed by CsrA, but it can also titrate CsrA activity. Together with the main C. jejuni CsrA antagonist, the FliW protein, flaA mRNA controls CsrA-mediated post-transcriptional regulation of other flagellar genes. RNA-FISH reveals that flaA mRNA is expressed and localized at the poles of elongating cells. Polar flaA mRNA localization is translation dependent and is post-transcriptionally regulated by the CsrA-FliW network. Overall, our results suggest a role for CsrA-FliW in spatiotemporal control of flagella assembly and localization of a dual-function mRNA.