Putative mechanisms and biological role of coccoid form formation in Campylobacter jejuni

Chicken Juice Enhances C. jejuni NCTC 11168 Biofilm Formation with Distinct Morphological Features and Altered Protein Expression

Campylobacter jejuni is the foodborne pathogen causing most gastrointestinal infections. Understanding its ability to form biofilms is crucial for devising effective control strategies in food processing environments. In this study, we investigated the growth dynamics and biofilm formation of C. jejuni NCTC 11168 in various culture media, including chicken juice (CJ), brain heart infusion (BHI), and Mueller Hinton (MH) broth. Our results demonstrated that C. jejuni exhibited a higher growth rate and enhanced biofilm formation in CJ and in 1:1 mixtures of CJ with BHI or MH broth compared to these measures in BHI or MH broth alone. Electron microscopy unveiled distinct morphological attributes of late-stage biofilm cells in CJ, including the presence of elongated spiral-shaped cells, thinner stretched structures compared to regular cells, and extended thread-like structures within the biofilms. Proteomic analysis identified significant alterations in protein expression profiles in C. jejuni biofilms, with a predominance of downregulated proteins associated with vital functions like metabolism, energy production, and amino acid and protein biosynthesis. Additionally, a significant proportion of proteins linked to biofilm formation, virulence, and iron uptake were suppressed. This shift toward a predominantly coccoid morphology echoed the reduced energy demands of these biofilm communities. Our study unlocks valuable insights into C. jejuni's biofilm in CJ, demonstrating its adaptation and survival.

Effect of biofilm formation in a hostile oxidative stress environment on the survival of Campylobacter jejuni recovered from poultry in Iraqi markets

Background and Aim

Campylobacter jejuni is a major contributor to bacterial enteritis, a common health problem. The resistance of this microaerophilic bacterium to oxidative stress allows it to thrive under aerobic conditions. This study aimed to investigate whether the capacity of C. jejuni to form biofilms in the presence of oxidative stress contributes to the pathogen's ability to thrive in agricultural settings as well as in chicken slaughter lines.

Materials and Methods

Twenty identified strains originating from chicken samples (eight from caeca contents and 12 from frozen chicken carcasses) were previously isolated and identified according to standard bacteriological protocols, followed by confirmation at the species level using multiplex polymerase chain reaction assay. Crystal violet staining was used to evaluate biofilm formation by these bacteria. Two exposure periods to gaseous ozone (1 and 2 min) were used to assess resistance to oxidative damage.

Results

Most of the strong biofilm-forming Campylobacter strains came from imported frozen chicken meat (25%), whereas only 10% came from caeca content. After exposure to gaseous ozone at 600 mg/h for 2 min, strong biofilm-producing strains exhibited a higher survival rate with a limited reduction of up to 3 logs, whereas negative biofilm-producing strains exhibited a limited survival rate with a reduction of 6 logs.

Conclusion

Based on our findings, we hypothesized that the presence of C. jejuni strains capable of forming biofilms in poultry farms and/or chicken production facilities triggers a public health alarm as this bacterium seems to be able to adapt more easily to live and thrive in hostile environmental conditions.

Multiple Campylobacter jejuni proteins affecting the peptidoglycan structure and the degree of helical cell curvature

Campylobacter jejuni is a Gram-negative helical bacterium. Its helical morphology, maintained by the peptidoglycan (PG) layer, plays a key role in its transmission in the environment, colonization, and pathogenic properties. The previously characterized PG hydrolases Pgp1 and Pgp2 are important for generating C. jejuni helical morphology, with deletion mutants being rod-shaped and showing alterations in their PG muropeptide profiles in comparison to the wild type. Homology searches and bioinformatics were used to identify additional gene products involved in C. jejuni morphogenesis: the putative bactofilin 1104 and the M23 peptidase domain-containing proteins 0166, 1105, and 1228. Deletions in the corresponding genes resulted in varying curved rod morphologies with changes in their PG muropeptide profiles. All changes in the mutants complemented except 1104. Overexpression of 1104 and 1105 also resulted in changes in the morphology and in the muropeptide profiles, suggesting that the dose of these two gene products influences these characteristics. The related helical ε-Proteobacterium Helicobacter pylori has characterized homologs of C. jejuni 1104, 1105, and 1228 proteins, yet deletion of the homologous genes in H. pylori had differing effects on H. pylori PG muropeptide profiles and/or morphology compared to the C. jejuni deletion mutants. It is therefore apparent that even related organisms with similar morphologies and homologous proteins can have diverse PG biosynthetic pathways, highlighting the importance of studying PG biosynthesis in related organisms.

Seasonal Prevalence and Molecular Identification of Thermophilic Campylobacter from Chicken, Cattle, and Respective Drinking Water in Kajiado County, Kenya

Thermophilic Campylobacter species are a leading cause of human gastroenteritis throughout the world and have been implicated in reproductive disorders (abortion), mastitis, enteritis, and/or diarrhoea in livestock. A cross-sectional survey was conducted in Kajiado County to determine prevalence, seasonality, and molecular detection of thermophilic Campylobacter species (with emphasis on C. jejuni, C. coli, and other thermophilic Campylobacter species) in chicken, cattle, and respective pooled drinking water. A total of 457 samples comprising 265 cattle rectal swabs, 142 chicken cloacal swabs, and 50 trough water samples were collected from 55 randomly selected smallholder farms. Individual samples were subjected to standard techniques for isolation and biochemical tests, followed by singleplex polymerase chain reaction (sPCR) assays for identification and confirmation of genus and species. Overall, thermophilic Campylobacter prevalence was 35.4% (95% confidence interval (95% CI) = 31.0–39.8), with C. jejuni dominating at 55.6% (95% CI = 47.9–63.3%) over C. coli in all sample types. The highest thermophilic Campylobacter prevalence was observed in cloacal swabs of live chicken at 44.4% (95% CI = 36.2–52.6%), followed by rectal swabs from live cattle at 30.9% (95% CI = 25.3–36.5%). Water samples from cattle drinkers/trough were found to be contaminated at 34% (95% CI = 20.9–47.1%). The isolation rate was higher in cattle under the confinement system (44.3%) (95% CI = 36.1–52.5%) than in those under the free-roaming grazing system. Thermophilic Campylobacter species were isolated in both seasons, with higher prevalence (39.8% (95% CI = 33.6–45.9)) recorded during rainy and cold season in all sample types except for water. There was significant (P < 0.05) association between season and thermophilic Campylobacter occurrence, even though there were no statistical differences in the prevalence values across the two seasons. Results of this study demonstrate that cattle, chicken, and respective drinking water harbour potentially pathogenic thermophilic campylobacters, with C. jejuni being widely distributed among farms. It is possible that seasonal variations and cattle confinement result in differences in thermophilic Campylobacter carriage. Further epidemiological and phylogenetic studies comparing distribution of thermophilic Campylobacter spp. isolates in livestock, environmental, and human samples are recommended to establish source attribution to reduce the impact of resultant diseases for the wellbeing of public and livestock.

Survival of Campylobacter jejuni 11168H in Acanthamoebae castellanii Provides Mechanistic Insight into Host Pathogen Interactions

Campylobacter jejuni is the leading cause of bacterial foodborne gastroenteritis worldwide but is rarely transferred between human hosts. Although a recognized microaerophile, the majority of C. jejuni are incapable of growing in an aerobic environment. The persistence and transmission of this pathogen outside its warm-blooded avian and mammalian hosts is poorly understood. Acanthamoebae species are predatory protists and form an important ecological niche with several bacterial species. Here, we investigate the interaction of C. jejuni 11168H and Acanthamoebae castellanii at the single-cell level. We observe that a subpopulation of C. jejuni cells can resist killing by A. castellanii, and non-digested bacteria are exocytosed into the environment where they can persist. In addition, we observe that A. castellanii can harbor C. jejuni 11168H even upon encystment. Transcriptome analyses of C. jejuni interactions revealed similar survival mechanisms when infecting both A. castellanii and warm-blooded hosts. In particular, nitrosative stress defense mechanisms and flagellum function are important as confirmed by mutational analyses of C. jejuni 11168H. This study describes a new host–pathogen interaction for C. jejuni and confirms that amoebae are transient hosts for the persistence, adaptability, and potential transmission of C. jejuni.

Comparative Analysis of L-Fucose Utilization and Its Impact on Growth and Survival of Campylobacter Isolates

Campylobacter jejuni and Campylobacter coli were previously considered asaccharolytic, but are now known to possess specific saccharide metabolization pathways, including L-fucose. To investigate the influence of the L-fucose utilization cluster on Campylobacter growth, survival and metabolism, we performed comparative genotyping and phenotyping of the C. jejuni reference isolate NCTC11168 (human isolate), C. jejuni Ca1352 (chicken meat isolate), C. jejuni Ca2426 (sheep manure isolate), and C. coli Ca0121 (pig manure isolate), that all possess the L-fucose utilization cluster. All isolates showed enhanced survival and prolonged spiral cell morphology in aging cultures up to day seven in L-fucose-enriched MEMα medium (MEMαF) compared to MEMα. HPLC analysis indicated L-fucose utilization linked to acetate, lactate, pyruvate and succinate production, confirming the activation of the L-fucose pathway in these isolates and its impact on general metabolism. Highest consumption of L-fucose by C. coli Ca0121 is conceivably linked to its enhanced growth performance up to day 7, reaching 9.3 log CFU/ml compared to approximately 8.3 log CFU/ml for the C. jejuni isolates. Genetic analysis of the respective L-fucose clusters revealed several differences, including a 1 bp deletion in the Cj0489 gene of C. jejuni NCTC11168, causing a frameshift in this isolate resulting in two separate genes, Cj0489 and Cj0490, while no apparent phenotype could be linked to the presumed frameshift in this isolate. Additionally, we found that the L-fucose cluster of C. coli Ca0121 was most distant from C. jejuni NCTC11168, but confirmation of links to L-fucose metabolism associated phenotypic traits in C. coli versus C. jejuni isolates requires further studies.

Generation of Distinct Differentially Culturable Forms of Burkholderia following Starvation at Low Temperature

Bacteria have developed unique mechanisms to adapt to environmental stresses and challenges of the immune system. Here, we report that Burkholderia pseudomallei, the causative agent of melioidosis, and its laboratory surrogate, Burkholderia thailandensis, utilize distinct mechanisms for surviving starvation at different incubation temperatures. At 21°C, Burkholderia are present as short rods which can rapidly reactivate and form colonies on solid media. At 4°C, Burkholderia convert into coccoid forms that cannot be cultured on solid agar but can be resuscitated in liquid media supplemented with supernatant obtained from logarithmic phase cultures of B. thailandensis, or catalase and Tween 80, thus displaying characteristics of differentially culturable bacteria (DCB). These DCB have low intensity fluorescence when stained with SYTO 9, have an intact cell membrane (propidium iodide negative), and contain 16S rRNA at levels comparable with growing cells. We also present evidence that lytic transglycosylases, a family of peptidoglycan-remodeling enzymes, are involved in the generation of coccoid forms and their resuscitation to actively growing cells. A B. pseudomallei ΔltgGCFD mutant with four ltg genes deleted did not produce coccoid forms at 4°C and could not be resuscitated in the liquid media evaluated. Our findings provide insights into the adaptation of Burkholderia to nutrient limitation and the generation of differentially culturable bacteria. IMPORTANCE Bacterial pathogens exhibit physiologically distinct forms that enable their survival in an infected host, the environment and following exposure to antimicrobial agents. B. pseudomallei causes the disease melioidosis, which has a high mortality rate and is difficult to treat with antibiotics. The bacterium is endemic to several countries and detected in high abundance in the environment. Here, we report that during starvation at low temperature, B. pseudomallei produces coccoid forms that cannot grow in standard media and which, therefore, can be challenging to detect using common tools. We provide evidence that the formation of these cocci is mediated by cell wall-specialized enzymes and lytic transglycosylases, and that resuscitation of these forms occurs following the addition of catalase and Tween 80. Our findings have important implications for the disease control and detection of B. pseudomallei, an agent of both public health and defense interest.

The effect of natural antimicrobials on the Campylobacter coli T6SS+/- during in vitro infection assays and on their ability to adhere to chicken skin and carcasses

Reducing the Campylobacter load on poultry carcasses represents a major tasks for the industry as its ability to reduce their presence is of major interest aiming to increase consumer safety. This study investigated the ability of a mixture of natural antimicrobials (A3001) to reduce the adherence of the T6SS^+/-C. coli isolates (NC1^hcp-, NC2 ^hcp- and NC3 ^hcp+) to chicken neck skin and whole carcasses. Overall, the antimicrobial mixture induced a significant reduction in the capability of our C. coli isolates to colonise the chicken skin (p < 0.05) and carcasses (p < 0.0001) but with a greater effect (≈3 log reduction) on the NC3 isolate. Using the HCT-8 in vitro infection model we also show that at a concentration of 0.5% A3001, the impact on the NC3 isolate is accompanied by the downregulation of the hcp gene (p = 0.0001), and indicator of the T6SS presence. The results described herein also indicated that these isolates are highly resistant to H₂O₂, up to 20 mM, suggesting a high resilience to environmental stresses. In summary our study shows that natural antimicrobials can reduce the ability of T6SS positive chicken C. coli isolates to adhere to chicken skin or to the whole carcass and to infect epithelial cells in vitro and could be considered a potential intervention at processor level.

Small-scaled association between ambient temperature and campylobacteriosis incidence in Germany

Campylobacteriosis is the leading bacterial cause of human diarrheal illness worldwide. Campylobacteriosis incidence exhibits seasonality and has been attributed to ambient temperature. However, the role of ambient temperature on campylobacteriosis remains poorly understood. To examine the impact of ambient temperature on local campylobacteriosis in Germany, weekly incidences on NUTS-3 level were analysed using a novel small-scaled approach, regression and time lags. Campylobacteriosis incidence correlated positively with temperatures between - 5 and 28 °C. The sigmoid regression model estimated an incidence increase of 0.52 per 5 °C temperature rise in the observation period. The weekly average of daily minimum temperature was most significant at a time lag of two weeks and showed the steepest incidence increase of 0.13 per 1 °C temperature increase in a temperature corridor of 5.1 to 12.2 °C. The impact of average minimum temperatures on campylobacteriosis incidence is crucial, likely to be indirect and especially relevant in the recent part of the infection chain. Vectors or human behaviour are presumably more directly linked with temperature than the pathogen's microbiology and should be examined. These variables outweigh the direct temperature-pathogen relationship when the whole chain of infection is considered. In the context of climate change, campylobacteriosis is likely to increase in Germany due to an increased temperature effect.

Electrochemical and Optical Biosensors for the Detection of Campylobacter and Listeria: An Update Look

Foodborne safety has aroused tremendous research interest in recent years because of a global public health problem. The rapid and precise detection of foodborne pathogens can reduce significantly infection diseases and save lives by the early initiation of an effective treatment. This review highlights current advances in the development of biosensors for detection of Campylobacter spp. and Listeria monocytogenes that are the most common causes of zoonosis. The consumption of pathogen contaminated food is responsible for humans hospitalization and death. The attention focused on the recognition elements such as antibodies (Ab), DNA probes and aptamers able to recognize cells, amplicons, and specific genes from different samples like bacteria, food, environment and clinical samples. Moreover, the review focused on two main signal-transducing mechanisms, i.e., electrochemical, measuring an amperometric, potentiometric and impedimetric signal; and optical, measuring a light signal by OLED (Organic Light Emitting Diode), SPR (Surface Plasmon Resonance), and Optical fiber. We expect that high-performance of devices being developed through basic research will find extensive applications in environmental monitoring, biomedical diagnostics, and food safety.

Expression of Escherichia coli araE and modified lacY genes in Campylobacter jejuni is not sufficient for arabinose transport

Introduction

Unlike Escherichia coli, Campylobacter jejuni is unable to import a range of sugars, including arabinose, which makes common expression vectors, such as pBAD33, non-functional in these bacteria.

Aim

The aim of this study was to investigate whether the E. coli transporters AraE and modified LacY (LacYA177C) would enable C. jejuni to uptake arabinose.

Methodology and Results

The respective genes of E. coli were constitutively expressed in C. jejuni strain 11168H after integration into the chromosome via homologous recombination. Vectors carrying these genes also contained a reporter gene, gfp, under the control of the arabinose-inducible promoter, pBAD. These constructs were verified in E. coli by demonstrating the induction of gfp in the presence of arabinose. Integration of the genes into one of the rRNA gene clusters was verified by PCR and genome sequencing. The latter also confirmed that the inserted gene clusters contained no mutations. Expression of the gfp gene in the presence of arabinose inducer was monitored using fluorescence microscopy of colonies and fluorimetry using both whole cells and lysates.

Conclusion

The results demonstrated the inability of C. jejuni to use arabinose transporters, which are fully functional in E. coli, suggesting a remarkable difference in the physiology of these bacteria.

The Campylobacter jejuni helical to coccoid transition involves changes to peptidoglycan and the ability to elicit an immune response

Campylobacter jejuni is a prevalent enteric pathogen that changes morphology from helical to coccoid under unfavorable conditions. Bacterial peptidoglycan maintains cell shape. As C. jejuni transformed from helical to coccoid, peptidoglycan dipeptides increased and tri- and tetrapeptides decreased. The DL-carboxypeptidase Pgp1 important for C. jejuni helical morphology and putative N-acetylmuramoyl-L-alanyl amidase AmiA were both involved in the coccoid transition. Mutants in pgp1 and amiA showed reduced coccoid formation, with ∆pgp1∆amiA producing minimal coccoids. Both ∆amiA and ∆amiA∆pgp1 lacked flagella and formed unseparated chains of cells consistent with a role for AmiA in cell separation. All strains accumulated peptidoglycan dipeptides over time, but only strains capable of becoming coccoid displayed tripeptide changes. C. jejuni helical shape and corresponding peptidoglycan structure are important for pathogenesis-related attributes. Concomitantly, changing to a coccoid morphology resulted in differences in pathogenic properties; coccoid C. jejuni were non-motile and non-infectious, with minimal adherence and invasion of epithelial cells and an inability to stimulate IL-8. Coccoid peptidoglycan exhibited reduced activation of innate immune receptors Nod1 and Nod2 versus helical peptidoglycan. C. jejuni also transitioned to coccoid within epithelial cells, so the inability of the immune system to detect coccoid C. jejuni may be significant in its pathogenesis.

Spotty Liver Disease: A review of an ongoing challenge in commercial free-range egg production

Spotty Liver Disease is an acute infectious disease of layer chickens that was likely first described in the USA and Canada in the 1950s and 1960's. The disease occurs almost exclusively in barn and free-range production systems. Outbreaks usually, but not exclusively occur in young layers (≅25 weeks) at peak of lay. Indicators of SLD include an acute drop in egg production of up to 35%, together with increased mortality of up to 15%. A presumptive diagnosis at post mortem is made with the detection of characteristic small yellow-white necrotic hepatic lesions, together with a fibrinous peri-hepatitis, excess pericardial and peritoneal fluid, and usually enteritis with diarrhoea. Histopathology reveals a multifocal acute hepatocellular necrosis with fibrin and occasional haemorrhage. Control measures trialled include use of antibiotics, improved biosecurity and hygiene, as well as management practices directed at reducing stress in flocks. However, none other than treatment with antibiotics has been consistently effective which suggested a bacterial aetiology. In 2015, a novel fastidious thermophilic, microaerobic campylobacter was isolated from symptomatic SLD flocks in the UK. Subsequently, an Australian group isolated and further characterised a genetically similar bacterium and named it Campylobacter hepaticus. The bacterium can be cultured from the liver and bile of infected birds, although recovery from non-sterile organs such as the caecum and duodenum remains elusive. Consequently, the route of transmission remains unconfirmed, although molecular detection by PCR of C. hepaticus DNA in the gastrointestinal tract and faeces of SLD infected birds is highly suggestive of a faecal-oral route.

Overexpression of spoT gene in coccoid forms of clinical Helicobacter pylori isolates

Helicobacter pylori (H. pylori) can convert to coccoid form in unfavorable conditions or as a result of antibiotic treatment. In order to adapt to harsh environments, H. pylori requires a stringent response which, encoded by the spoT gene, has a bifunctional enzyme possessing both (p)ppGpp synthetic and degrading activity. Our goal in this study was to compare spoT gene expression in spiral and induced coccoid forms of H. pylori with use of amoxicillin. First, clinical isolate coccoid forms were induced with amoxicillin; then, the viability test was analyzed by flow cytometer. After RNA extraction, cDNA synthesis and designing a specific primer for spoT gene, evaluation of the desired gene expression in both forms were studied. Bacterial isolates exposed to amoxicillin at MIC and 1/2 MIC induced morphological conversion better and faster than other MIC concentration. The expression of spoT gene was significantly downregulated in spiral forms of H. pylori, while the gene expression was upregulated and + 30.3-fold changes was seen in coccoid forms of bacterium. To summarize, spoT gene is one of the key factors for antibiotic resistance and its enhanced expression in coccoid form can be a valuable diagnostic marker for recognition of H. pylori during morphological conversion.

A proposed role for diffusible signal factors in the biofilm formation and morphological transformation of Helicobacter pylori

Due to the increasing resistance of Helicobacter pylori to antibiotics, there is a growing need for new strategies for the effective eradication of this pathogen. The inhibition of quorum-sensing activity in most microorganisms leads to a decrease in virulence. A different reaction is observed in H. pylori, as interfering with the production of autoinducer-2 initiates biofilm formation and increases the survival of these bacteria. Therefore, it is believed that there is an alternative way to control the physiological changes of H. pylori exposed to environmental stress. In this article, we present the compounds probably involved in the modulation of H. pylori virulence. Diffusible signal factors (DSFs) are fatty acid signal molecules involved in communication between microbes. DSFs are likely to stimulate H. Pylori transition into a sedentary state that correlates with bacterial transformation into a more resistant coccoid form and initiates biofilm formation. Biofilm is a structure that plays a crucial role in protecting against adverse environmental factors (low pH, oxidative stress, action of immune system) and limiting the effective concentration of antimicrobial substances. This article has suggested and characterized the existence of an alternative DSF-mediated cell-cell signaling of H. pylori, which controls autoaggregative behaviors, biofilm formation, and the transition of microorganisms into the coccoid form.

Phenotypic and Transcriptomic Responses of Campylobacter jejuni Suspended in an Artificial Freshwater Medium

Campylobacter jejuni is the leading cause of campylobacteriosis in the developed world. Although most cases are caused by consumption of contaminated meat, a significant proportion is linked to ingestion of contaminated water. The differences between C. jejuni strains originating from food products and those isolated from water are poorly understood. Working under the hypothesis that water-borne C. jejuni strains are better equipped at surviving the nutrient-poor aquatic environment than food-borne strains, the present study aims to characterize these differences using outbreak strains 81116 and 81-176. Strain 81116 caused a campylobacteriosis outbreak linked to consumption of water, while strain 81-176 was linked to consumption of raw milk. CFU counts and viability assays showed that 81116 survives better than 81-176 at 4°C in a defined freshwater medium (Fraquil). Moreover, 81116 was significantly more resistant to oxidative stress and bile salt than strain 81-176 in Fraquil. To better understand the genetic response of 81116 to water, a transcriptomic profiling study was undertaken using microarrays. Compared to rich broth, strain 81116 represses genes involved in amino acid uptake and metabolism, as well as genes involved in costly biosynthetic processes such as replication, translation, flagellum synthesis and virulence in response to Fraquil. In accordance with the observed increase in stress resistance in Fraquil, 81116 induces genes involved in resistance to oxidative stress and bile salt. Interestingly, genes responsible for cell wall synthesis were also induced upon Fraquil exposure. Finally, twelve unique genes were expressed in Fraquil; however, analysis of their distribution in animal and water isolates showed that they are not uniquely and ubiquitously present in water isolates, and thus, unlikely to play a major role in adaptation to water. Our results show that some C. jejuni strains are more resilient than others, thereby challenging current water management practices. The response of 81116 to Fraquil serves as a starting point to understand the adaptation of C. jejuni to water and its subsequent transmission.

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.

Description of Campylobacter jejuni Bf, an atypical aero-tolerant strain

BACKGROUND

Campylobacter jejuni is a leading cause of bacterial enteritis worldwide. This microaerophilic bacterium can survive in aerobic environments, suggesting it has protective mechanisms against oxidative stress. The clinical C. jejuni Bf strain is characterized by an increased resistance to oxygen. This study aimed to characterize the behavior of the clinical C. jejuni Bf strain under an aerobic atmosphere and in response to ROS-promoter agents.

METHODS

Growth was studied in both aerobic and microaerobic conditions using classic cultivable methods. Electronic microscopy and mreB gene expression were used to evaluate the morphology of this strain under aerobic conditions. The survival under oxidative stress was tested in the presence of different concentrations of hydrogen peroxide (H2O2) and paraquat (PQ).

RESULTS

The results showed that C. jejuni Bf strain can grow aerobically, unlike other strains of C. jejuni tested. Cells of C. jejuni Bf exposed to oxidative stress presented changes in morphology and the gene mreB, responsible for maintaining the bacillary cell morphology, was down-expressed. In aerobically acclimated conditions, C. jejuni Bf exhibited a higher survival rate of 52 % in the presence of H2O2 (1 mM) compared to the reference strain NCTC 11168. Concentrations above 1 mM PQ were lethal for the reference strain but not for C. jejuni Bf.

CONCLUSIONS

Taken together, these data highlight the resistance to oxidative stress conditions of C. jejuni Bf, indicating that this microorganism seems more adapted to survival in hostile environmental conditions.

Mechanisms of bacterial morphogenesis: evolutionary cell biology approaches provide new insights

How Darwin's "endless forms most beautiful" have evolved remains one of the most exciting questions in biology. The significant variety of bacterial shapes is most likely due to the specific advantages they confer with respect to the diverse environments they occupy. While our understanding of the mechanisms generating relatively simple shapes has improved tremendously in the last few years, the molecular mechanisms underlying the generation of complex shapes and the evolution of shape diversity are largely unknown. The emerging field of bacterial evolutionary cell biology provides a novel strategy to answer this question in a comparative phylogenetic framework. This relatively novel approach provides hypotheses and insights into cell biological mechanisms, such as morphogenesis, and their evolution that would have been difficult to obtain by studying only model organisms. We discuss the necessary steps, challenges, and impact of integrating "evolutionary thinking" into bacterial cell biology in the genomic era.