PerR controls oxidative stress defence and aerotolerance but not motility-associated phenotypes of Campylobacter jejuni

Small RNA CjNC110 regulates the activated methyl cycle to enable optimal chicken colonization by Campylobacter jejuni

Post-transcriptional gene regulation by non-coding small RNAs (sRNAs) is critical for colonization and survival of enteric pathogens, including the zoonotic pathogen Campylobacter jejuni. In this study, we utilized C. jejuni IA3902 (a representative isolate of the sheep abortion clone) and C. jejuni W7 (a highly motile variant of NCTC 11168, a human gastroenteritis strain) to further investigate regulation by sRNA CjNC110. Both motility and autoagglutination ability were confirmed to be phenotypes of conserved regulation by CjNC110. However, we demonstrated that W7∆CjNC110 does not change chicken colonization levels compared to W7 wild type, directly contrasting IA3902∆CjNC110, which had decreased colonization ability. Subsequently, we determined strain-specific phenotype variation between W7∆CjNC110 and IA3902∆CjNC110 when examining intracellular L-methionine (L-met) levels controlled by the activated methyl cycle (AMC). We hypothesized that the presence of a secondary system for L-met production conferred by MetAB in W7 but not IA3902 might explain the difference in both chicken colonization and L-met availability. Insertion of metAB within IA3902∆CjNC110 (naturally absent) restored intracellular L-met levels in IA3902∆CjNC110::metAB and overcame the colonization defect that resulted from mutagenesis of CjNC110 in IA3902. Deletion of metAB in W7∆CjNC110 (naturally present) led to a decrease in L-met in W7∆CjNC110∆metAB and a colonization defect which was otherwise masked in W7∆CjNC110. Our results indicate that regulation of the AMC leading to altered L-met availability is a conserved regulatory function of CjNC110 in C. jejuni and confirm that L-met generation via the AMC as activated by CjNC110 is critical for optimal host colonization.IMPORTANCEDuring this study, the regulatory action and conservation of function of CjNC110 between two different zoonotically important Campylobacter jejuni strains were examined. Critically, this work for the first time reveals regulation of L-methionine (L-met) production within the activated methyl cycle (AMC) by small RNA (sRNA) CjNC110 as a key factor driving C. jejuni optimal chicken colonization. As a growing body of evidence suggests that maintenance of L-met homeostasis appears to be critical for C. jejuni colonization, interventions targeting the AMC could provide a critical control point for therapeutic drug options to combat this zoonotic pathogen. Our results also indicate that even for conserved sRNAs such as CjNC110, strain-specific differences in phenotypes regulated by sRNAs may exist, independent of conserved regulatory action. Depending on the strain examined and accessory genomic content present, conserved regulatory actions might be masked, thus investigation in multiple strains may be warranted.

Mechanistic concepts involved in biofilm associated processes of Campylobacter jejuni: persistence and inhibition in poultry environments

Campylobacter species, predominantly Campylobacter jejuni, remains a significant zoonotic pathogen worldwide, with the poultry sector being the primary vector for human transmission. In recent years. there has been a notable rise in the incidence of human campylobacteriosis, necessitating a deeper understanding of the pathogen's survival mechanisms and transmission dynamics. Biofilm presence significantly contributes to C. jejuni persistence in poultry and subsequent food product contamination, and this review describes the intricate processes involved in biofilm formation. The ability of Campylobacter to form biofilms on various surfaces, including stainless steel, plastic, and glass, is a critical survival strategy. Campylobacter biofilms, with their remarkable resilience, protect the pathogen from environmental stresses such as desiccation, pH extremes, biocides and sanitizing agents. This review explores the molecular and genetic mechanisms of C. jejuni biofilm formation, highlighting regulatory genes involved in motility, chemotaxis, and stress responses. Flagellar proteins, particularly flaA, flaB, flaG, and adhesins like cadF and flpA, are identified as the main molecular components in biofilm development. The role of mixed-species biofilms, where C. jejuni integrates into existing biofilms of other bacteria to enhance pathogen resilience, is also discussed. This review also considers alternative interventions to control C. jejuni in poultry production, in the context of increasing antibiotic resistance. It explores the effectiveness of prebiotics, probiotics, synbiotics, bacteriocins, bacteriophages, vaccines, and organic acids, with a focus on their mechanisms of action in reducing bacterial colonization and biofilm formation. Studies show that mixtures of organic acids and compounds like Carvacrol and Eugenol significantly downregulate genes linked with motility and adhesion, thereby disrupting biofilm integrity. It discusses the impact of environmental factors, such as temperature and oxygen levels on biofilm formation, providing insights into how industrial conditions can be manipulated to reduce contamination. This paper stresses the need for a multifaceted approach to control Campylobacter in poultry, integrating molecular and genetic insights with practical interventions. By advancing our understanding of biofilm dynamics and gene regulation, we aim to inform the development of more effective strategies to enhance food safety and protect public health.

Aerotolerancy of Campylobacter spp.: A Comprehensive Review

Campylobacter spp. constitute a group of microaerophilic bacteria that includes strains that are aerotolerant and capable of surviving in aerobic conditions. Recent studies have shown that aerotolerant strains are highly prevalent in meats, animals, and clinical settings. Changes in growth media and other environmental conditions can affect the aerotolerance of Campylobacter strains and must be considered when studying their aerotolerance in vitro. Polymicrobial interactions and biofilms also play a significant role in the ability of Campylobacter to survive oxygen exposure. Continuous subculturing may foster aerotolerance, and studies have demonstrated a positive correlation between aerotolerance and virulence and between aerotolerance and the ability to survive stressful environmental conditions. Various mechanisms and genetic origins for aerotolerance have been proposed; however, most of the potential genes involved in aerotolerance require further investigation, and many candidate genes remain unidentified. Research is also needed to investigate if there are any clinical implications for Campylobacter aerotolerance. Understanding the aerotolerance of Campylobacter remains an important target for further research, and it will be an important step towards identifying potential targets for intervention against this clinically important food-borne pathogen.

Development of Fluoroquinolone Resistance through Antibiotic Tolerance in Campylobacter jejuni

Antibiotic tolerance not only enables bacteria to survive acute antibiotic exposures but also provides bacteria with a window of time in which to develop antibiotic resistance. The increasing prevalence of Campylobacter jejuni isolates resistant to clinically important antibiotics, particularly fluoroquinolones (FQs), is a global public health concern. Currently, little is known about antibiotic tolerance and its effects on resistance development in C. jejuni. Here, we show that exposure to ciprofloxacin or tetracycline at concentrations 10 and 100 times higher than the MIC induces antibiotic tolerance in C. jejuni, whereas gentamicin or erythromycin treatment causes cell death. Interestingly, FQ resistance rapidly develops in C. jejuni after tolerance induction by ciprofloxacin and tetracycline. Furthermore, after tolerance is induced, alkyl hydroperoxide reductase (AhpC) plays a critical role in reducing FQ resistance development by alleviating oxidative stress. Together, these results demonstrate that exposure of C. jejuni to antibiotics can induce antibiotic tolerance and that FQ-resistant (FQR) C. jejuni clones rapidly emerge after tolerance induction. This study elucidates the mechanisms underlying the high prevalence of FQR C. jejuni and provides insights into the effects of antibiotic tolerance on resistance development. IMPORTANCE Antibiotic tolerance compromises the efficacy of antibiotic treatment by extending bacterial survival and facilitating the development of mutations associated with antibiotic resistance. Despite growing public health concerns about antibiotic resistance in C. jejuni, antibiotic tolerance has not yet been investigated in this important zoonotic pathogen. Here, our results show that exposure of C. jejuni to ciprofloxacin or tetracycline leads to antibiotic tolerance development, which subsequently facilitates the emergence of FQR C. jejuni. Importantly, these antibiotics are commonly used in animal agriculture. Moreover, our study suggests that the use of non-FQ drugs in animal agriculture promotes FQ resistance development, which is crucial because antibiotic-resistant C. jejuni is primarily transmitted from animals to humans. Overall, these findings increase our understanding of the mechanisms of resistance development through the induction of antibiotic tolerance.

Metaphenotypes associated with recurrent genomic lineages of Campylobacter jejuni responsible for human infections in Luxembourg

Campylobacter jejuni is a leading cause of foodborne illnesses worldwide. Although considered fragile, this microaerophilic bacterium is able to survive in various challenging environments, which subsequently constitutes multiple sources of transmission for human infection. To test the assumption of acquiring specific features for adaptation and survival, we established a workflow of phenotypic tests related to the survival and the persistence of recurrent and sporadic strains. A representative collection of 83 strains isolated over 13 years from human, mammal, poultry, and environmental sources in Luxembourg, representing different spreading patterns (endemic, epidemic, and sporadic), was screened for survival to oxidative stresses, for acclimating to aerobic conditions (AC), and for persistence on abiotic surfaces. Using the cgMLST Oxford typing scheme for WGS data, the collection was classified into genomic lineages corresponding to host-generalist strains (lineages A and D, CC ST-21), host-specific strains (lineage B, CC ST-257 and lineage C, CC ST-464) and sporadic strains. We established that when a strain survives concentrations beyond 0.25 mM superoxide stress, it is six times more likely to survive hyperoxide stress and that a highly adherent strain is 14 times more likely to develop a biofilm. Surprisingly, more than half of the strains could acclimate to AC but this capacity does not explain the difference between recurrent genomic lineages and sporadic strains and the survival to oxidative stresses, while recurrent strains have a significantly higher adhesion/biofilm formation capacity than sporadic ones. From this work, the genomic lineages with more stable genomes could be characterized by a specific combination of phenotypes, called metaphenotypes. From the functional genomic analyses, the presence of a potentially functional T6SS in the strains of lineage D might explain the propensity of these strains to be strong biofilm producers. Our findings support the hypothesis that phenotypical abilities contribute to the spatio-temporal adaptation and survival of stable genomic lineages. It suggests a selection of better-adapted and persistent strains in challenging stress environments, which could explain the prevalence of these lineages in human infections.

Posttranscriptional Regulation in Response to Different Environmental Stresses in Campylobacter jejuni

The survival strategies that Campylobacter jejuni (C. jejuni) employ throughout its transmission and infection life cycles remain largely elusive. Specifically, there is a lack of understanding about the posttranscriptional regulation of stress adaptations resulting from small noncoding RNAs (sRNAs). Published C. jejuni sRNAs have been discovered in specific conditions but with limited insights into their biological activities. Many more sRNAs are yet to be discovered as they may be condition-dependent. Here, we have generated transcriptomic data from 21 host- and transmission-relevant conditions. The data uncovered transcription start sites, expression patterns and posttranscriptional regulation during various stress conditions. This data set helped predict a list of putative sRNAs. We further explored the sRNAs' biological functions by integrating differential gene expression analysis, coexpression analysis, and genome-wide sRNA target prediction. The results showed that the C. jejuni gene expression was influenced primarily by nutrient deprivation and food storage conditions. Further exploration revealed a putative sRNA (CjSA21) that targeted tlp1 to 4 under food processing conditions. tlp1 to 4 are transcripts that encode methyl-accepting chemotaxis proteins (MCPs), which are responsible for chemosensing. These results suggested CjSA21 inhibits chemotaxis and promotes survival under food processing conditions. This study presents the broader research community with a comprehensive data set and highlights a novel sRNA as a potential chemotaxis inhibitor. IMPORTANCE The foodborne pathogen C. jejuni is a significant challenge for the global health care system. It is crucial to investigate C. jejuni posttranscriptional regulation by small RNAs (sRNAs) in order to understand how it adapts to different stress conditions. However, limited data are available for investigating sRNA activity under stress. In this study, we generate gene expression data of C. jejuni under 21 stress conditions. Our data analysis indicates that one of the novel sRNAs mediates the adaptation to food processing conditions. Results from our work shed light on the posttranscriptional regulation of C. jejuni and identify an sRNA associated with food safety.

Phenotypic and genetic analyses of two Campylobacter fetus isolates from a patient with relapsed prosthetic valve endocarditis

Campylobacter fetus can cause intestinal and systemic disease in humans and are well established veterinary and economic pathogens. We report the complete genomic sequences of two C. fetus subsp. fetus (Cff) isolates recovered in 2017 (CITCf01) and 2018 (CITCf02) from a case of recurrent prosthetic valve endocarditis. Both were capable of growth aerobically. Their genomes were found to be highly conserved and syntenic with 99.97% average nucleotide identity (ANI) while differences in their respective sap loci defined the temporal separation of their genomes. Based on core genome phylogeny and ANI of 83 Cff genomes belonging to the previously described human-associated Cff lineage, CITCf01 and CITCf02 grouped in a clade of eleven sequence type (ST)3 Cff (including the Cff type strain NCTC 10842T). CITCf01 and CITCf02 were marked for their lack of unique genomic features when compared to isolates within the subspecies and the type strain in particular. We identified point mutations in oxidative stress response genes, among others, that may contribute to aerobiosis. We report a case of Cff causing relapsed prosthetic valve endocarditis and we highlight the sap island as a polymorphic site within the genetically stable ST3 lineage, central to pathogenicity.

CosR Regulation of perR Transcription for the Control of Oxidative Stress Defense in Campylobacter jejuni

Oxidative stress resistance is an important mechanism to sustain the viability of oxygen-sensitive microaerophilic Campylobacter jejuni. In C. jejuni, gene expression associated with oxidative stress defense is modulated by PerR (peroxide response regulator) and CosR (Campylobacter oxidative stress regulator). Iron also plays an important role in the regulation of oxidative stress, as high iron concentrations reduce the transcription of perR. However, little is known about how iron affects the transcription of cosR. The level of cosR transcription was increased when the defined media MEMα (Minimum Essential Medium) was supplemented with ferrous (Fe²⁺) and ferric (Fe³⁺) iron and the Mueller-Hinton (MH) media was treated with an iron chelator, indicating that iron upregulates cosR transcription. However, other divalent cationic ions, such as Zn²⁺, Cu²⁺, Co²⁺, and Mn²⁺, did not affect cosR transcription, suggesting that cosR transcription is regulated specifically by iron. Interestingly, the level of perR transcription was increased when CosR was overexpressed. The positive regulation of perR transcription by CosR was observed both in the presence or in the absence of iron. The results of the electrophoretic mobility shift assay showed that CosR directly binds to the perR promoter. DNase I footprinting assays revealed that the CosR binding site in the perR promoter overlaps with the PerR box. In the study, we demonstrated that cosR transcription is increased in iron-rich conditions, and CosR positively regulates the transcription of PerR, another important regulator of oxidative stress defense in C. jejuni. These results provide new insight into how C. jejuni regulates oxidative stress defense by coordinating the transcription of perR and cosR in response to iron.

Metal homeostasis in pathogenic Epsilonproteobacteria: mechanisms of acquisition, efflux, and regulation

Epsilonproteobacteria are a diverse class of eubacteria within the Proteobacteria phylum that includes environmental sulfur-reducing bacteria and the human pathogens, Campylobacter jejuni and Helicobacter pylori. These pathogens infect and proliferate within the gastrointestinal tracts of multiple animal hosts, including humans, and cause a variety of disease outcomes. While infection of these hosts provides nutrients for the pathogenic Epsilonproteobacteria, many hosts have evolved a variety of strategies to either sequester metals from the invading pathogen or exploit the toxicity of metals and drive their accumulation as an antimicrobial strategy. As a result, C. jejuni and H. pylori have developed mechanisms to sense changes in metal availability and regulate their physiology in order to respond to either metal limitation or accumulation. In this review, we will discuss the challenges of metal availability at the host-pathogen interface during infection with C. jejuni and H. pylori and describe what is currently known about how these organisms alter their gene expression and/or deploy bacterial virulence factors in response to these environments.

A novel high-content screening approach for the elucidation of C. jejuni biofilm composition and integrity

BACKGROUND

Campylobacter jejuni is the leading cause of bacterial gastroenteritis worldwide and the main source of infection is contaminated chicken meat. Although this important human pathogen is an obligate microaerophile, it must survive atmospheric oxygen conditions to allow transmission from contaminated chicken meat to humans. It is becoming increasingly evident that formation of biofilm plays a key role in the survival of this organism for extended periods on poultry products. We have recently demonstrated a novel inducible model for the study of adherent C. jejuni biofilm formation under aerobic conditions. By taking advantage of supercoiling mediated gene regulation, incubation of C. jejuni with subinhibitory concentrations of the Gyrase B inhibitor novobiocin was shown to promote the consistent formation of metabolically active adherent biofilm.

RESULTS

In this study, we implement this model in conjunction with the fluorescent markers: TAMRA (live cells) and SytoX (dead cells, eDNA) to develop a novel systematic high-content imaging approach and describe how it can be implemented to gain quantifiable information about the integrity and extracellular polymeric substance (EPS) composition of adherent C. jejuni biofilm in aerobic conditions. We show that this produces a model with a consistent, homogenous biofilm that can be induced and used to screen a range of inhibitors of biofilm adherence and matrix formation.

CONCLUSIONS

This model allows for the first time a high throughput analysis of C. jejuni biofilms which will be invaluable in enabling researchers to develop mechanisms to disrupt these biofilms and reduce the viability of these bacteria under aerobic conditions.

Comparison of the Pathogenic Potential of Campylobacter jejuni, C. upsaliensis and C. helveticus and Limitations of Using Larvae of Galleria mellonella as an Infection Model

Campylobacter enteritis in humans is primarily associated with C. jejuni/coli infection. Other species cause campylobacteriosis relatively infrequently; while this could be attributed to bias in diagnostic methods, the pathogenicity of non-jejuni/coli Campylobacter spp. such as C. upsaliensis and C. helveticus (isolated from dogs and cats) is uncertain. Galleria mellonella larvae are suitable models of the mammalian innate immune system and have been applied to C. jejuni studies. This study compared the pathogenicity of C. jejuni, C. upsaliensis, and C. helveticus isolates. Larvae inoculated with either C. upsaliensis or C. helveticus showed significantly higher survival than those inoculated with C. jejuni. All three Campylobacter species induced indistinguishable histopathological changes in the larvae. C. jejuni could be isolated from inoculated larvae up to eight days post-inoculation whereas C. upsaliensis and C. helveticus could only be isolated in the first two days. There was a significant variation in the hazard rate between batches of larvae, in Campylobacter strains, and in biological replicates as random effects, and in species and bacterial dose as fixed effects. The Galleria model is applicable to other Campylobacter spp. as well as C. jejuni, but may be subject to significant variation with all Campylobacter species. While C. upsaliensis and C. helveticus cannot be considered non-pathogenic, they are significantly less pathogenic than C. jejuni.

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.

Retail liver juices enhance the survivability of Campylobacter jejuni and Campylobacter coli at low temperatures

The high prevalence of Campylobacter spp. in retail liver products was previously reported and has been linked to several outbreaks of campylobacteriosis. The main objective of this study was to investigate the influence of retail liver juices on the survivability of several strains of C. jejuni and C. coli, which were previously isolated from various retail meats at 4 °C. All tested Campylobacter strains showed higher survival in beef liver juice (BLJ) and chicken liver juice (CLJ) as compared to beef and chicken juices (BJ and CJ) or Mueller Hinton broth (MHB) at 4 °C. Overall, C. jejuni strains showed greater survival in retail liver and meat juices as compared to C. coli. CLJ enhanced biofilm formation of most C. coli strains and supported growth in favorable conditions. When diluted, retail liver and meat juices enhanced survival of Campylobacter strains at low temperatures and increased aerotolerance. In conclusion, beef and chicken liver juices enhanced the survival of C. jejuni and C. coli strains at low temperatures, which helps explain the high prevalence of Campylobacter spp. in retail liver products.

Redox Sensing by Fe2+ in Bacterial Fur Family Metalloregulators

SIGNIFICANCE

Iron is required for growth and is often redox active under cytosolic conditions. As a result of its facile redox chemistry, iron homeostasis is intricately involved with oxidative stress. Bacterial adaptation to iron limitation and oxidative stress often involves ferric uptake regulator (Fur) proteins: a diverse set of divalent cation-dependent, DNA-binding proteins that vary widely in both metal selectivity and sensitivity to metal-catalyzed oxidation. Recent Advances: Bacteria contain two Fur family metalloregulators that use ferrous iron (Fe²⁺) as their cofactor, Fur and PerR. Fur functions to regulate iron homeostasis in response to changes in intracellular levels of Fe²⁺. PerR also binds Fe²⁺, which enables metal-catalyzed protein oxidation as a mechanism for sensing hydrogen peroxide (H₂O₂).

CRITICAL ISSUES

To effectively regulate iron homeostasis, Fur has an Fe²⁺ affinity tuned to monitor the labile iron pool of the cell and may be under selective pressure to minimize iron oxidation, which would otherwise lead to an inappropriate increase in iron uptake under oxidative stress conditions. Conversely, Fe²⁺ is bound more tightly to PerR but exhibits high H₂O₂ reactivity, which enables a rapid induction of peroxide stress genes.

FUTURE DIRECTIONS

The features that determine the disparate reactivity of these proteins with oxidants are still poorly understood. A controlled, comparative analysis of the affinities of Fur/PerR proteins for their metal cofactors and their rate of reactivity with H₂O₂, combined with structure/function analyses, will be needed to define the molecular mechanisms that have facilitated this divergence of function between these two paralogous regulators.

Campylobacter coli From Retail Liver and Meat Products Is More Aerotolerant Than Campylobacter jejuni

Aerotolerance in the microaerophilic species Campylobacter was previously reported and could increase bacterial survival and transmission in foods during stressful processing and storage conditions. In this study, 167 Campylobacter isolates (76 C. jejuni and 91 C. coli) were screened for aerotolerance; these strains were previously isolated from retail chicken meat, chicken livers, chicken gizzards, turkey, pork, and beef liver samples. Bacterial cultures were incubated aerobically in Mueller Hinton broth with agitation and viable cell counts were taken at 0, 6, 12, and 24 h. Approximately 47% of the screened Campylobacter isolates were aerotolerant (viable after a 12-h aerobic incubation period), whereas 24% were hyper-aerotolerant (viable after a 24-h aerobic incubation). A greater prevalence of aerotolerant strains (80%) was found among C. coli isolates as compared to C. jejuni isolates (6%). Differences in the oxidative stress response related genes were detected among C. jejuni and C. coli isolates when comparative genomics was used to analyze 17 Whole Genome Sequenced (WGS) strains from our laboratory. Genes encoding putative transcriptional regulator proteins and a catalase-like heme binding protein were found in C. coli genomes, but were absent in the genomes of C. jejuni. PCR screening showed the presence of a catalase-like protein gene in 75% (68/91) of C. coli strains, which was absent in all tested C. jejuni strains. While about 79% (30/38) of the hyper-aerotolerant C. coli strains harbored the catalase-like protein gene, the gene was also present in a number of the aerosensitive strains. The Catalase like protein gene was found to be expressed in both aerobic and microaerobic conditions with a 2-fold higher gene expression detected in aerobic conditions for an aerosensitive strain. However, the exact function of the gene remains unclear and awaits further investigation. In conclusion, aerotolerant Campylobacter strains (especially C. coli) are prevalent in various retail meats. Further studies are needed to investigate whether the genes encoding catalase-like heme binding protein and putative transcriptional regulators in C. coli strains are involved in stress response.

FliW controls growth-phase expression of Campylobacter jejuni flagellar and non-flagellar proteins via the post-transcriptional regulator CsrA

Campylobacter jejuni is an important human pathogen that causes 96 million cases of acute diarrheal disease worldwide each year. We have shown that C. jejuni CsrA is involved in the post-transcriptional regulation of more than 100 proteins, and altered expression of these proteins is presumably involved in the altered virulence-related phenotypes of a csrA mutant. Mutation of fliW results in C. jejuni cells that have greatly truncated flagella, are less motile, less able to form biofilms, and exhibit a reduced ability to colonize chicks. The loss of FliW results in the altered expression of 153 flagellar and non-flagellar proteins, the majority of which are members of the CsrA regulon. The number of proteins dysregulated in the fliW mutant was greater at mid-log phase (120 proteins) than at stationary phase (85 proteins); 52 proteins showed altered expression at both growth phases. Loss of FliW altered the growth-phase- and CsrA-mediated regulation of FlaA flagellin. FliW exerts these effects by binding to both FlaA and to CsrA, as evidenced by pull-down assays, protein-protein cross-linking, and size-exclusion chromatography. Taken together, these results show that CsrA-mediated regulation of both flagellar and non-flagellar proteins is modulated by direct binding of CsrA to the flagellar chaperone FliW. Changing FliW:CsrA stoichiometries at different growth phases allow C. jejuni to couple the expression of flagellar motility to metabolic and virulence characteristics.

Crystal structure of Campylobacter jejuni peroxide regulator

In Campylobacter jejuni (Cj), the metal-cofactored peroxide response regulator (PerR) transcription factor allows C. jejuni to respond to oxidative stresses. The crystal structure of the metalated form of CjPerR shows that the protein folds as an asymmetric dimer displaying structural differences in the orientation of its DNA-binding domain. Comparative analysis shows that such asymmetry is a conserved feature among crystallized PerR proteins, and mutational analysis reveals that residues found in the first α-helix of CjPerR contribute to DNA binding. These studies present the structure of CjPerR protein and highlight structural heterogeneity in the orientation of the metalated PerR DNA-binding domain which may underlie the ability of PerR to recognize DNA, control gene expression, and contribute to bacterial pathogenesis.

A Mutator Phenotype Promoting the Emergence of Spontaneous Oxidative Stress-Resistant Mutants in Campylobacter jejuni

Campylobacter jejuni is a leading cause of foodborne illnesses worldwide. As a microaerophilic organism, C. jejuni must be able to defend against oxidative stress encountered both in the host and in the environment. How Campylobacter utilizes a mutation-based mechanism for adaptation to oxidative stress is still unknown. Here we present a previously undescribed phenotypic and genetic mechanism that promotes the emergence of oxidative stress-resistant mutants. Specifically, we showed that a naturally occurring mutator phenotype, resulting from a loss of function mutation in the DNA repair enzyme MutY, increased oxidative stress resistance (OXR) in C. jejuni We further demonstrated that MutY malfunction did not directly contribute to the OXR phenotype but increased the spontaneous mutation rate in the peroxide regulator gene perR, which functions as a repressor for multiple genes involved in oxidative stress resistance. Mutations in PerR resulted in loss of its DNA binding function and derepression of PerR-controlled oxidative stress defense genes, thereby conferring an OXR phenotype and facilitating Campylobacter survival under oxidative stress. These findings reveal a new mechanism that promotes the emergence of spontaneous OXR mutants in bacterial organisms.IMPORTANCE Although a mutator phenotype has been shown to promote antibiotic resistance in many bacterial species, little is known about its contribution to the emergence of OXR mutants. This work describes the link between a mutator phenotype and the enhanced emergence of OXR mutants as well as its underlying mechanism involving DNA repair and mutations in PerR. Since DNA repair systems and PerR are well conserved in many bacterial species, especially in Gram positives, the same mechanism may operate in multiple bacterial species. Additionally, we developed a novel method that allows for rapid quantification of spontaneous OXR mutants in a bacterial population. This method represents a technical innovation and may also be applied to other bacterial species. These findings significantly advance our understanding of bacterial mechanisms for survival under oxidative stress.

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.

The Campylobacter jejuni Oxidative Stress Regulator RrpB Is Associated with a Genomic Hypervariable Region and Altered Oxidative Stress Resistance

Campylobacter jejuni is the leading cause of bacterial foodborne diarrhoeal disease worldwide. Despite the microaerophilic nature of the bacterium, C. jejuni can survive the atmospheric oxygen conditions in the environment. Bacteria that can survive either within a host or in the environment like C. jejuni require variable responses to survive the stresses associated with exposure to different levels of reactive oxygen species. The MarR-type transcriptional regulators RrpA and RrpB have recently been shown to play a role in controlling both the C. jejuni oxidative and aerobic stress responses. Analysis of 3,746 C. jejuni and 486 C. coli genome sequences showed that whilst rrpA is present in over 99% of C. jejuni strains, the presence of rrpB is restricted and appears to correlate with specific MLST clonal complexes (predominantly ST-21 and ST-61). C. coli strains in contrast lack both rrpA and rrpB. In C. jejuni rrpB⁺ strains, the rrpB gene is located within a variable genomic region containing the IF subtype of the type I Restriction-Modification (hsd) system, whilst this variable genomic region in C. jejuni rrpB^- strains contains the IAB subtype hsd system and not the rrpB gene. C. jejuni rrpB^- strains exhibit greater resistance to peroxide and aerobic stress than C. jejuni rrpB⁺ strains. Inactivation of rrpA resulted in increased sensitivity to peroxide stress in rrpB⁺ strains, but not in rrpB^- strains. Mutation of rrpA resulted in reduced killing of Galleria mellonella larvae and enhanced biofilm formation independent of rrpB status. The oxidative and aerobic stress responses of rrpB^- and rrpB⁺ strains suggest adaptation of C. jejuni within different hosts and niches that can be linked to specific MLST clonal complexes.

The PAS Domain-Containing Protein HeuR Regulates Heme Uptake in Campylobacter jejuni

Campylobacter jejuni is a leading cause of bacterially derived gastroenteritis. A previous mutant screen demonstrated that the heme uptake system (Chu) is required for full colonization of the chicken gastrointestinal tract. Subsequent work identified a PAS domain-containing regulator, termed HeuR, as being required for chicken colonization. Here we confirm that both the heme uptake system and HeuR are required for full chicken gastrointestinal tract colonization, with the heuR mutant being particularly affected during competition with wild-type C. jejuni Transcriptomic analysis identified the chu genes-and those encoding other iron uptake systems-as regulatory targets of HeuR. Purified HeuR bound the chuZA promoter region in electrophoretic mobility shift assays. Consistent with a role for HeuR in chu expression, heuR mutants were unable to efficiently use heme as a source of iron under iron-limiting conditions, and mutants exhibited decreased levels of cell-associated iron by mass spectrometry. Finally, we demonstrate that an heuR mutant of C. jejuni is resistant to hydrogen peroxide and that this resistance correlates to elevated levels of catalase activity. These results indicate that HeuR directly and positively regulates iron acquisition from heme and negatively impacts catalase activity by an as yet unidentified mechanism in C. jejuni IMPORTANCE: Annually, Campylobacter jejuni causes millions of gastrointestinal infections in the United States, due primarily to its ability to reside within the gastrointestinal tracts of poultry, where it can be released during processing and contaminate meat. In the developing world, humans are often infected by consuming contaminated water or by direct contact with livestock. Following consumption of contaminated food or water, humans develop disease that is characterized by mild to severe diarrhea. There is a need to understand both colonization of chickens, to make food safer, and colonization of humans, to better understand disease. Here we demonstrate that to efficiently colonize a host, C. jejuni requires iron from heme, which is regulated by the protein HeuR. Understanding how HeuR functions, we can develop ways to inhibit its function and reduce iron acquisition during colonization, potentially reducing C. jejuni in the avian host, which would make food safer, or limiting human colonization.

cj0371: A Novel Virulence-Associated Gene of Campylobacter jejuni

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

Reaction of PerR with Molecular Oxygen May Assist H2O2 Sensing in Anaerobes

PerR is the peroxide resistance regulator found in several pathogenic bacteria and governs their resistance to peroxide stress by inducing enzymes that destroy peroxides. However, it has recently been implicated as a key component of the aerotolerance in several facultative or strict anaerobes, including the highly pathogenic Staphylococcus aureus. By combining (18)O labeling studies to ESI- and MALDI-TOF MS detection and EMSA experiments, we demonstrate that the active form of PerR reacts with dioxygen, which leads ultimately to disruption of the PerR/DNA complex and is thus physiologically meaningful. Moreover, we show that the presence of O2 assists PerR sensing of H2O2, another feature likely to be important for anaerobic organisms. These results allow one to envisage different scenarios for the response of anaerobes to air exposure.

Conservation of σ28-Dependent Non-Coding RNA Paralogs and Predicted σ54-Dependent Targets in Thermophilic Campylobacter Species

Assembly of flagella requires strict hierarchical and temporal control via flagellar sigma and anti-sigma factors, regulatory proteins and the assembly complex itself, but to date non-coding RNAs (ncRNAs) have not been described to regulate genes directly involved in flagellar assembly. In this study we have investigated the possible role of two ncRNA paralogs (CjNC1, CjNC4) in flagellar assembly and gene regulation of the diarrhoeal pathogen Campylobacter jejuni. CjNC1 and CjNC4 are 37/44 nt identical and predicted to target the 5' untranslated region (5' UTR) of genes transcribed from the flagellar sigma factor σ⁵⁴. Orthologs of the σ⁵⁴-dependent 5' UTRs and ncRNAs are present in the genomes of other thermophilic Campylobacter species, and transcription of CjNC1 and CNC4 is dependent on the flagellar sigma factor σ²⁸. Surprisingly, inactivation and overexpression of CjNC1 and CjNC4 did not affect growth, motility or flagella-associated phenotypes such as autoagglutination. However, CjNC1 and CjNC4 were able to mediate sequence-dependent, but Hfq-independent, partial repression of fluorescence of predicted target 5' UTRs in an Escherichia coli-based GFP reporter gene system. This hints towards a subtle role for the CjNC1 and CjNC4 ncRNAs in post-transcriptional gene regulation in thermophilic Campylobacter species, and suggests that the currently used phenotypic methodologies are insufficiently sensitive to detect such subtle phenotypes. The lack of a role of Hfq in the E. coli GFP-based system indicates that the CjNC1 and CjNC4 ncRNAs may mediate post-transcriptional gene regulation in ways that do not conform to the paradigms obtained from the Enterobacteriaceae.

A PAS domain-containing regulator controls flagella-flagella interactions in Campylobacter jejuni

The bipolar flagella of the foodborne bacterial pathogen Campylobacter jejuni confer motility, which is essential for virulence. The flagella of C. jejuni are post-translationally modified, but how this process is controlled is not well understood. In this work, we have identified a novel PAS-domain containing regulatory system, which modulates flagella-flagella interactions in C. jejuni. Inactivation of the cj1387c gene, encoding a YheO-like PAS6 domain linked to a helix-turn-helix domain, resulted in the generation of a tightly associated “cell-train” morphotype, where up to four cells were connected by their flagella. The morphotype was fully motile, resistant to vortexing, accompanied by increased autoagglutination, and was not observed in aflagellated cells. The Δcj1387c mutant displayed increased expression of the adjacent Cj1388 protein, which comprises of a single endoribonuclease L-PSP domain. Comparative genomics showed that cj1387c (yheO) orthologs in bacterial genomes are commonly linked to an adjacent cj1388 ortholog, with some bacteria, including C. jejuni, containing another cj1388-like gene (cj0327). Inactivation of the cj1388 and cj0327 genes resulted in decreased autoagglutination in Tween-20-supplemented media. The Δcj1388 and Δcj0327 mutants were also attenuated in a Galleria larvae-based infection model. Finally, substituting the sole cysteine in Cj1388 for serine prevented Cj1388 dimerization in non-reducing conditions, and resulted in decreased autoagglutination in the presence of Tween-20. We hypothesize that Cj1388 and Cj0327 modulate post-translational modification of the flagella through yet unidentified mechanisms, and propose naming Cj1387 the Campylobacter Flagella Interaction Regulator CfiR, and the Cj1388 and Cj0327 protein as CfiP and CfiQ, respectively.