Pyruvate metabolism in Campylobacter spp

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.

Bacteria and Methanogens in the Human Microbiome: a Review of Syntrophic Interactions

Methanogens are microorganisms belonging to the Archaea domain and represent the primary source of biotic methane. Methanogens encode a series of enzymes which can convert secondary substrates into methane following three major methanogenesis pathways. Initially recognized as environmental microorganisms, methanogens have more recently been acknowledged as host-associated microorganisms after their detection and initial isolation in ruminants in the 1950s. Methanogens have also been co-detected with bacteria in various pathological situations, bringing their role as pathogens into question. Here, we review reported associations between methanogens and bacteria in physiological and pathological situations in order to understand the metabolic interactions explaining these associations. To do so, we describe the origin of the metabolites used for methanogenesis and highlight the central role of methanogens in the syntrophic process during carbon cycling. We then focus on the metabolic abilities of co-detected bacterial species described in the literature and infer from their genomes the probable mechanisms of their association with methanogens. The syntrophic interactions between bacteria and methanogens are paramount to gut homeostasis. Therefore, any dysbiosis affecting methanogens might impact human health. Thus, the monitoring of methanogens may be used as a bio-indicator of dysbiosis. Moreover, new therapeutic approaches can be developed based on their administration as probiotics. We thus insist on the importance of investigating methanogens in clinical microbiology.

Enhancement of Campylobacter hepaticus culturing to facilitate downstream applications

Campylobacter hepaticus causes Spotty Liver Disease (SLD) in chickens. C. hepaticus is fastidious and slow-growing, presenting difficulties when growing this bacterium for the preparation of bacterin vaccines and experimental disease challenge trials. This study applied genomic analysis and in vitro experiments to develop an enhanced C. hepaticus liquid culture method. In silico analysis of the anabolic pathways encoded by C. hepaticus revealed that the bacterium is unable to biosynthesise L-cysteine, L-lysine and L-arginine. It was found that L-cysteine added to Brucella broth, significantly enhanced the growth of C. hepaticus, but L-lysine or L-arginine addition did not enhance growth. Brucella broth supplemented with L-cysteine (0.4 mM), L-glutamine (4 mM), and sodium pyruvate (10 mM) gave high-density growth of C. hepaticus and resulted in an almost tenfold increase in culture density compared to the growth in Brucella broth alone (log10 = 9.3 vs 8.4 CFU/mL). The type of culture flask used also significantly affected C. hepaticus culture density. An SLD challenge trial demonstrated that C. hepaticus grown in the enhanced culture conditions retained full virulence. The enhanced liquid culture method developed in this study enables the efficient production of bacterial biomass and therefore facilitates further studies of SLD biology and vaccine development.

Next-Generation Antimicrobial Resistance Surveillance System Based on the Internet-of-Things and Microfluidic Technique

Antimicrobial resistance (AMR) of foodborne pathogens is a global crisis in public health and economic growth. A real-time surveillance system is key to track the emergence of AMR bacteria and provides a comprehensive AMR trend from farm to fork. However, current AMR surveillance systems, which integrate results from multiple laboratories using the conventional broth microdilution method, are labor-intensive and time-consuming. To address these challenges, we present the internet of things (IoT), including colorimetric-based microfluidic sensors, a custom-built portable incubator, and machine learning algorithms, to monitor AMR trends in real time. As a top priority microbe that poses risks to human health, Campylobacter was selected as a bacterial model to demonstrate and validate the IoT-assisted AMR surveillance. Image classification with convolution neural network ResNet50 on the colorimetric sensors achieved an accuracy of 99.5% in classifying bacterial growth/inhibition patterns. The IoT was used to carry out a small-scale survey study, identifying eight Campylobacter isolates out of 35 chicken samples. A 96% agreement on Campylobacter AMR profiles was achieved between the results from the IoT and the conventional broth microdilution method. The data collected from the intelligent sensors were transmitted from local computers to a cloud server, facilitating real-time data collection and integration. A web browser was developed to demonstrate the spatial and temporal AMR trends to end-users. This rapid, cost-effective, and portable approach is able to monitor, assess, and mitigate the burden of bacterial AMR in the agri-food chain.

Development of a Selective Agar for Improving Campylobacter jejuni Detection in Food

BACKGROUND

Campylobacter jejuni is a major gastroenteritis-causing foodborne pathogen. However, it is difficult to isolate when competing bacteria or cold-damaged cells are present.

OBJECTIVE

Herein, a medium (Campylobacter selective agar, CSA) was developed and supplemented with catalase, L-serine, L-cysteine, and quercetin for the selective detection of C. jejuni in food.

METHODS

The C. jejuni-detection efficiency in broth media and chicken tenders was evaluated. The pathogen was enumerated on modified charcoal-cefoperazone-deoxycholate agar (mCCDA), CSA supplemented with 4 µM catalase (CSA-C4), 8 µM catalase (CSA-C8), 20 mM L-serine (CSA-S20) or 50 mM L-serine (CSA-S50), and mCCDA supplemented with 0.5 mM L-cysteine (mCCDA-LC0.5), 1 mM L-cysteine (mCCDA-LC1), 40 µM quercetin (mCCDA-Q40) or 320 µM quercetin (mCCDA-Q320). The detection efficiency was then evaluated by counting colonies on the selective agar media. Quantitative assessment was also performed using chicken and duck carcasses.

RESULTS

The C. jejuni detection efficiencies were higher (p < 0.05) in the groups CSA-C4 or CSA-C8 and CSA-S20 or CSA-S50 than mCCDA, and the detection efficiencies were maintained even in the presence of Acinetobacter baumannii, a competing bacterium. In the quantitative test, CSA-C8 and CSA-S50 demonstrated higher C. jejuni-detection efficiencies than mCCDA (control).

CONCLUSION

Therefore, CSA-C8 and CSA-S50 improved the detection efficiency of C. jejuni in poultry products by promoting the recovery of cold-damaged cells.

HIGHLIGHTS

When using CSA-C8 or CSA-S50 developed in this study for detection of C. jejuni in food, detection efficiency was higher than mCCDA.

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.

Analyses of energy metabolism and stress defence provide insights into Campylobacter concisus growth and pathogenicity

Campylobacter concisus is an emerging enteric pathogen that is associated with inflammatory bowel disease. Previous studies demonstrated that C. concisus is non-saccharolytic and hydrogen gas (H2) is a critical factor for C. concisus growth. In order to understand the molecular basis of the non-saccharolytic and H2-dependent nature of C. concisus growth, in this study we examined the pathways involving energy metabolism and oxidative stress defence in C. concisus. Bioinformatic analysis of C. concisus genomes in comparison with the well-studied enteric pathogen Campylobacter jejuni was performed. This study found that C. concisus lacks a number of key enzymes in glycolysis, including glucokinase and phosphofructokinase, and the oxidative pentose phosphate pathway. C. concisus has an incomplete tricarboxylic acid cycle, with no identifiable succinyl-CoA synthase or fumarate hydratase. C. concisus was inferred to use fewer amino acids and have fewer candidate substrates as electron donors and acceptors compared to C. jejuni. The addition of DMSO or fumarate to media resulted in significantly increased growth of C. concisus in the presence of H2 as an electron donor, demonstrating that both can be used as electron acceptors. Catalase, an essential enzyme for oxidative stress defence in C. jejuni, and various nitrosative stress enzymes, were not found in the C. concisus genome. Overall, C. concisus is inferred to have a non-saccharolytic metabolism in which H2 is central to energy conservation, and a narrow selection of carboxylic acids and amino acids can be utilised as organic substrates. In conclusion, this study provides a molecular basis for the non-saccharolytic and hydrogen-dependent nature of C. concisus energy metabolism pathways, which provides insights into the growth requirements and pathogenicity of this species.

The regulatory mechanism of Chryseobacterium sp. resistance mediated by montmorillonite upon cadmium stress

Cadmium (Cd) is a toxic heavy metal and its uptake by living organisms causes adverse effect, further resulting in cycle pollution of the biosphere. The specific regulatory mechanism between clays and microbes under Cd stress remains unclear. In this study, interface interactions among clays, microbes and Cd were confirmed. Comparative transcriptome was conducted to investigate how it regulated gene expression patterns of microbes (Chryseobacterium sp. WAL2), which exposed to a series of gradient concentrations of Cd (16, 32, 64 and 128 μg mL^-1) for 12 d in the presence and absence of clay montmorillonite (Mt) (16 g L^-1). Cd was highly enriched by the unique interface interactions between Mt and bacteria (67.6-82.1%), leading to a more hostile environment for bacterial cells. However, Mt ultimately enhanced bacterial resistance to Cd stress by stimulating the mechanism of bacterial resistance; namely: (i) Mt increased genes expression connected with ion transport, enhancing the uptake of Cd; (ii) Mt stimulated genes expression related to efflux pump and positively regulated cellular oxidative stress (e.g., glutathione) and Cd accumulation (e.g., cysteine) processes. Further, genes expression related to intracellular metabolic processes was enforced, which supplied a driving force and accelerated electron transfer; (iii) Mt improved genes expression involved in DNA replication and other biological processes (e.g., terpenoid backbone biosynthesis) to maintain bacterial vitality. Therefore, the study not only optimized a unique Cd resistance mechanism of Mt on Chryseobacterium sp., but also provided a novel insight for environmental mitigation of heavy metals from the perspective of molecular biology.

Campylobacter jejuni: collective components promoting a successful enteric lifestyle

Campylobacter jejuni is the leading cause of bacterial diarrhoeal disease in many areas of the world. The high incidence of sporadic cases of disease in humans is largely due to its prevalence as a zoonotic agent in animals, both in agriculture and in the wild. Compared with many other enteric bacterial pathogens, C. jejuni has strict growth and nutritional requirements and lacks many virulence and colonization determinants that are typically used by bacterial pathogens to infect hosts. Instead, C. jejuni has a different collection of factors and pathways not typically associated together in enteric pathogens to establish commensalism in many animal hosts and to promote diarrhoeal disease in the human population. In this Review, we discuss the cellular architecture and structure of C. jejuni, intraspecies genotypic variation, the multiple roles of the flagellum, specific nutritional and environmental growth requirements and how these factors contribute to in vivo growth in human and avian hosts, persistent colonization and pathogenesis of diarrhoeal disease.

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

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

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

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

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

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

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

An Alternative Approach for the Rising Challenge of Hypertensive Illness via Helicobacter pylori Eradication

Background

The aim of the study was to demonstrate the effect of natural Helicobacter pylori eradication on blood pressure values. The prevalence of hypertension in developing countries has been considered by some reports a consequence of progress and life style changes. In spite of that, traditional risk factors do not appear fully sufficient to explain the rising figures of hypertensive illness which further indicates that attempts to control the problem depending upon traditional measures can never be adequate or decisive. H. pylori could migrate or get forced to migrate to the colon; it will continue producing ammonia for a reason or no reason leading to accumulation of profuse toxic amounts of ammonia, unopposed or buffered by any acidity, which could lead to multiple colonic and a high rectal spasm. A colonic re-absorptive error is established with excessive fluid and salt retention in the body that would definitely lead to hypertension which is supposed to remain inadequately controlled without correction of the underlying etiologic pathological error. It is a prospective study, conducted at Balghsoon Polyclinic, Jeddah, Saudi Arabia.

Methods

Ninety-nine middle-aged male patients with essential hypertension under medications and positive for H. pylori dyspepsia were included in the study. They were given natural therapy for H. pylori eradication.

Results

Ninety patients were able to resume normal blood pressure (BP) values and quit their medications.

Conclusion

The concept of the colonic re-absorptive error considered in this study is not just hypothetical as upon its basis, most patients of the study (90.9%) were able to quit medications and maintain normal BP values.

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

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

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

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

Aerobic growth of campylobacter in media supplemented with C3-monocarboxylates and C4-dicarboxylates

Experiments were conducted to examine aerobic growth of Campylobacter spp. in basal media supplemented with C4-dicarboxylates (fumarate, succinate, or malate) and C3-monocarboxylates (pyruvate or lactate). Basal medium was supplemented with 30 mM fumarate, succinate, or malate and 0 to 100 mM lactate or pyruvate; inoculated with 10(6) CFU/ml of Campylobacter coli, Campylobacter fetus, or Campylobacter jejuni; then incubated aerobically at 37 °C for 72 h. Optical density (OD) of cultures was measured at 600 nm during incubation. The effect of adding 0 to 0.20% agar and 0 to 0.10% sodium bicarbonate (NaHCO3) to media supplemented with 30 mM fumarate and 100 mM pyruvate on Campylobacter growth was also determined. Finally, CFU per milliliter of Campylobacter spp. recovered from media containing 30 mM fumarate, 100 mM pyruvate, 0.15% agar, and 0.05% NaHCO3 was determined after inoculated media were incubated aerobically or microaerophilically. Results indicated that the OD600 of Campylobacter cultures incubated in media supplemented with C4-dicarboxylates and C3-monocarboxylates was generally significantly (P ≤ 0.05) greater than growth of cultures incubated in media supplemented with a C4-dicarboxylate only. The OD600 of cultures of Campylobacter spp. grown in media supplemented with fumarate and pyruvate was higher (P ≤ 0.05) when agar was added, and the addition of NaHCO3 produced an additional increase (P ≤ 0.05) in the OD600 of most of the isolates. There was also a 5- to 6-log increase in Campylobacter spp. recovered from media supplemented with 30 mM fumarate, 100 mM pyruvate, 0.15% agar, and 0.05% NaHCO3 that was inoculated 10(3) CFU/ml and incubated aerobically or microaerophilically. Findings indicate that this medium might provide an alternative to incubating Campylobacter spp. microaerophilically, thus eliminating costs and training required for producing special atmospheres for culturing the pathogen.

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

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

Nutrient acquisition and metabolism by Campylobacter jejuni

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

Dynamic proteome changes in Campylobacter jejuni 81-176 after high pressure shock and subsequent recovery

Campylobacter jejuni is one of the most intriguing human foodborne bacterial pathogen. Its survival throughout the food processing chain and its pathogenesis mechanisms in humans remain enigmatic. Living in the animal guts and particularly in avian intestine as a commensal bacterium, this microorganism is frequently isolated from meat products. Ultra high pressure (HP) is a promising alternative to thermal technology for microbial safety of foodstuffs with less organoleptic and nutritional alterations. Its application could be extended to meat products potentially contaminated by C. jejuni. To evaluate the response of Campylobacter to this technological stress and subsequent recovery at a molecular level, a dynamic 2-DE-based proteomic approach has been implemented. After cultivation, C. jejuni cells were conditioned in a high-pressure chamber and transferred to fresh medium for recovery. The protein abundance dynamics at the proteome scale were analyzed by 2-DE during the cellular process of cell injury and recovery. Monitoring protein abundance through time unraveled the basic metabolisms involved in this cellular process. The significance of the proteome evolution modulated by HP and subsequent recovery is discussed in the context of a specific cellular response to stress and recovery of C. jejuni with 69 spots showing significant changes through time.

Temperature affects sole carbon utilization patterns of Campylobacter coli 49941

Campylobacter spp. are small, asaccharolytic bacteria exhibiting unique nutritional and environmental requirements. Campylobacter spp. exist as commensal organisms in some animal species, yet are estimated to be the most common causative agents of foodborne illness in humans. C. jejuni is most often associated with poultry, while C. coli are more frequently associated with swine. Temperature has been suggested to trigger potential colonization or virulence factors in C. jejuni, and recent studies have demonstrated temperature-dependent genes are important to colonization. It is possible that temperature-dependent colonization factors are in part responsible for the species-specific colonization characteristics of C. coli also. We determined utilization of 190 different sole carbon substrates by C. coli ATCC 49941 at 37 and 42°C using phenotype microarray (PM) technology. Temperature did affect amino acid utilization. L-asparagine and L-serine allowed significantly (P = 0.004) more respiration by C. coli ATCC 49941 at the lower temperature of 37°C as compared to 42°C. Conversely, L-glutamine was utilized to a significantly greater extent (P = 0.015) at the higher temperature of 42°C. Other organic substrates exhibited temperature-dependent utilization including succinate, D,L-malate, and propionate which all supported active respiration by C. coli to a significantly greater extent at 42°C. Further investigation is needed to determine the basis for the temperature-dependent utilization of substrates by Campylobacter spp. and their possible role in species-specific colonization.

Advances in Campylobacter biology and implications for biotechnological applications

Campylobacter jejuni is a major foodborne pathogen of animal origin and a leading cause of bacterial gastroenteritis in humans. During the past decade, especially since the publication of the first C. jejuni genome sequence, major advances have been made in understanding the pathobiology and physiology of this organism. It is apparent that C. jejuni utilizes sophisticated mechanisms for effective colonization of the intestinal tracts in various animal species. Although Campylobacter is fragile in the environment and requires fastidious growth conditions, it exhibits great flexibility in the adaptation to various habitats including the gastrointestinal tract. This high adaptability is attributable to its genetically, metabolically and phenotypically diverse population structure and its ability to change in response to various challenges. Unlike other enteric pathogens, such as Escherichia coli and Salmonella, Campylobacter is unable to utilize exogenous glucose and mainly depends on the catabolism of amino acids as a carbon source. Campylobacter proves highly mutable in response to antibiotic treatments and possesses eukaryote‐like dual protein glycosylation systems, which modify flagella and other surface proteins with specific sugar structures. In this review we will summarize the distinct biological traits of Campylobacter and discuss the potential biotechnological approaches that can be developed to control this enteric pathogen.

The role of respiratory donor enzymes in Campylobacter jejuni host colonization and physiology

The human pathogen Campylobacter jejuni utilizes oxidative phosphorylation to meet all of its energy demands. The genome sequence of this bacterium encodes a number of respiratory enzymes in a branched electron transport chain that predicts the utilization of a number of electron transport chain donor and acceptor molecules. Three of these electron donor enzymes: hydrogenase, formate dehydrogenase, and 2-oxoglutarate:acceptor oxidoreductase (OOR), oxidize hydrogen, formate and alpha-ketoglutarate as electron donors, respectively. Mutations were created in these donor enzymes to isolate mutants in hydrogenase (HydB::CM), formate dehydrogenase (Fdh::CM), and OOR (OorB::CM), as well as a strain with insertions in both hydrogenase and formate dehydrogenase (Hyd::Fdh). These mutants are deficient in their respective enzyme activities and do not reduce the components of the electron transport chain when provided with their respective substrates. The presence of either hydrogen or formate in the media stimulated the growth of wild type (WT) C. jejuni (but not the associated mutant strains) and at least one of these alternative substrates is required for growth of the OOR mutant strain OorB::CM. Finally, the importance of hydrogenase, formate dehydrogenase and OOR as well as the complex I of C. jejuni are elucidated by chicken colonization assays, where the double mutant Hyd::Fdh, OorB::CM and nuo mutants are severely impaired in host colonization.

Metabolite and transcriptome analysis of Campylobacter jejuni in vitro growth reveals a stationary-phase physiological switch

Campylobacter jejuni is a prevalent cause of food-borne diarrhoeal illness in humans. Understanding of the physiological and metabolic capabilities of the organism is limited. We report a detailed analysis of the C. jejuni growth cycle in batch culture. Combined transcriptomic, phenotypic and metabolic analysis demonstrates a highly dynamic ‘stationary phase’, characterized by a peak in motility, numerous gene expression changes and substrate switching, despite transcript changes that indicate a metabolic downshift upon the onset of stationary phase. Video tracking of bacterial motility identifies peak activity during stationary phase. Amino acid analysis of culture supernatants shows a preferential order of amino acid utilization. Proton NMR (1H-NMR) highlights an acetate switch mechanism whereby bacteria change from acetate excretion to acetate uptake, most probably in response to depletion of other substrates. Acetate production requires pta (Cj0688) and ackA (Cj0689), although the acs homologue (Cj1537c) is not required. Insertion mutants in Cj0688 and Cj0689 maintain viability less well during the stationary and decline phases of the growth cycle than wild-type C. jejuni, suggesting that these genes, and the acetate pathway, are important for survival.

Amino acid-dependent growth of Campylobacter jejuni: key roles for aspartase (AspA) under microaerobic and oxygen-limited conditions and identification of AspB (Cj0762), essential for growth on glutamate

Amino acids are key carbon and energy sources for the asaccharolytic food-borne human pathogen Campylobacter jejuni. During microaerobic growth in amino acid rich complex media, aspartate, glutamate, proline and serine are the only amino acids significantly utilized by strain NCTC 11168. The catabolism of aspartate and glutamate was investigated. An aspartase (aspA) mutant (unable to utilize any amino acid except serine) and a Cj0762c (aspB) mutant lacking aspartate:glutamate aminotransferase (unable to utilize glutamate), were severely growth impaired in complex media, and an aspA sdaA mutant (also lacking serine dehydratase) failed to grow in complex media unless supplemented with pyruvate and fumarate. Aspartase was shown by activity and proteomic analyses to be upregulated by oxygen limitation, and aspartate enhanced oxygen-limited growth of C. jejuni in an aspA-dependent manner. Stoichiometric aspartate uptake and succinate excretion involving the redundant DcuA and DcuB transporters indicated that in addition to a catabolic role, AspA can provide fumarate for respiration. Significantly, an aspA mutant of C. jejuni 81-176 was impaired in its ability to persist in the intestines of outbred chickens relative to the parent strain. Together, our data highlight the dual function of aspartase in C. jejuni and suggest a role during growth in the avian gut.

Pyruvate relieves the necessity of high induction levels of catalase and enables Campylobacter jejuni to grow under fully aerobic conditions

AIMS

Several cases of campylobacteriosis reported worldwide seemingly conflict with the strict growth requirements and sensitivity to environmental stress of Campylobacter jejuni. In this study, the need for a micro-aerobic environment [dissolved oxygen tension (DOT): 0.1-90%; 100% air saturation)] and the adaptive responses to oxygen stress were studied.

METHODS AND RESULTS

The growth of C. jejuni in continuous culture was assessed under different DOT in the presence or absence of pyruvate. In a medium without pyruvate, continuous cultures of C. jejuni showed typically micro-aerobic behaviour and cells were unable to grow under fully aerobic conditions. However in the presence of pyruvate (25 mmol l(-1)), continuous cultures of C. jejuni were able to grow in a broad DOT range, varying from 0.1% to at least 90%, and the catalase activity was decreased.

CONCLUSIONS

Addition of pyruvate results in the decrease in the concentration of hydrogen peroxide, which enables C. jejuni to grow aerobically.

SIGNIFICANCE AND IMPACT OF THE STUDY

New information on the oxidative physiology of C. jejuni and its ability to grow aerobically in media supplemented with pyruvate is presented.

The Campylobacter jejuni NADH:ubiquinone oxidoreductase (complex I) utilizes flavodoxin rather than NADH

Campylobacter jejuni encodes 12 of the 14 subunits that make up the respiratory enzyme NADH:ubiquinone oxidoreductase (also called complex I). The two nuo genes not present in C. jejuni encode the NADH dehydrogenase, and in their place in the operon are the novel genes designated Cj1575c and Cj1574c. A series of mutants was generated in which each of the 12 nuo genes (homologues to known complex I subunits) was disrupted or deleted. Each of the nuo mutants will not grow in amino acid-based medium unless supplemented with an alternative respiratory substrate such as formate. Unlike the nuo genes, Cj1574c is an essential gene and could not be disrupted unless an intact copy of the gene was provided at an unrelated site on the chromosome. A nuo deletion mutant can efficiently respire formate but is deficient in alpha-ketoglutarate respiratory activity compared to the wild type. In C. jejuni, alpha-ketoglutarate respiration is mediated by the enzyme 2-oxoglutarate:acceptor oxidoreductase; mutagenesis of this enzyme abolishes alpha-ketoglutarate-dependent O2 uptake and fails to reduce the electron transport chain. The electron acceptor for 2-oxoglutarate:acceptor oxidoreductase was determined to be flavodoxin, which was also determined to be an essential protein in C. jejuni. A model is presented in which CJ1574 mediates electron flow into the respiratory transport chain from reduced flavodoxin and through complex I.

Novel Campylobacter isolation method using hydrophobic grid membrane filter and semisolid medium

Culture procedures for isolation of thermophilic campylobacters from food matrices are complex, labor intensive, and time-consuming. Most available methods include the use of antibiotics as selective agents to prevent the growth of competing microflora. A simple procedure for isolation of thermophilic campylobacters after enrichment in Rosef's enrichment broth was developed using a hydrophobic grid membrane filter (HGMF) on semisolid medium (SSM). SSM contains no antibiotics, and the HGMF physically separates Campylobacter from the enrichment broth, allowing isolation based on differential motility. The HGMF-SSM method was compared to the Agriculture and Agri-Food Canada Food Safety Procedures Manual (FSPM-10) method (Isolation of Thermophilic Campylobacters from Fresh Pork, Beef Veal, Poultry and Ready-to-Eat Meat Products), which includes the use of selective antibiotics. During the initial study, after enrichment the HGMF-SSM method yielded pure cultures of campylobacters after 16 to 18 h (overnight) compared with 48 h for the FSPM-10 method. Ninety-four turkey samples collected at local retail stores and 38 frozen pig fecal samples were processed by both methods. Thirty-five samples (26.5%) were positive by the HGMF-SSM method; 24 (18.2%) of these positive samples contained Campylobacter jejuni and 11 (8.3%) contained Campylobacter coli. With the FSPM-10 method, 25 samples (18.9%) were positive: 21 (15.9%) with C. jejuni and 4 (3%) with C. coli. For a subsequent field study, only the HGMF-SSM method was used to isolate Campylobacter from 1,200 chicken samples and 454 turkey samples sold at retail. Analysis of five subisolates from various samples indicated that only one type of Campylobacter was recovered by the HGMF-SSM method, as ascertained by MICs for 10 antimicrobials, sequencing of the short variable region of the flaA gene, and fingerprinting based on amplified fragment length polymorphism. The absence of antibiotics in the SSM may explain the higher recovery of thermophilic campylobacters. The HGMF-SSM method resulted in improved isolation of campylobacters and is simpler, faster, cheaper, and less labor intensive than the FSPM-10 method. The recovery of one type of Campylobacter from the chicken samples may have important implications, particularly in epidemiological studies.

Redirection of carbon flux to lysine in a recombinant of Corynebacterium lactofermentum ATCC 21799 by limited supply of pantothenate

To increase carbon flux to lysine, minimized production of amino acids that are biosynthetically related to lysine, for example, isoleucine and valine, is required. By limiting the supply of pantothenate, the precursor of coenzyme A, the carbon flux was redirected from isoleucine and valine to lysine in the recombinant of Corynebacterium lactofermentum ATCC 21799 containing the plasmid pGC77. The pGC77 contains hom(dr), thrB, and ilvA encoding feedback-deregulated homoserine dehydrogenase, homoserine kinase, and threonine dehydratase, respectively. At 250 microM of isopropyl-beta-d-thiogalactopyranoside, the recombinant (pGC77) produced lysine, valine, and isoleucine. Limiting the supply of pantothenate from 300 microg/l to 30 microg/l resulted in an increase in lysine (from 4.5 to 6.4 g/l) and decreases in valine (from 3.1 to 1.6 g/l) and isoleucine (from 0.9 to 0.3 g/l) production. The concentration of pyruvate was higher and that of acetate lower in the pantothenate-limited culture than in the control, suggesting that the limited supply of pantothenate delayed the conversion of pyruvate to acetyl-CoA. Increased availability of pyruvate by limiting the supply of pantothenate might favor the integration of pyruvate into the lysine branch. The results of this study are useful for the production of lysine with decreased concentrations of byproducts.

The pattern and kinetics of substrate metabolism of Campylobacter jejuni and Campylobacter coli

AIMS

The main aim was to investigate the patterns and kinetics of substrate oxidation by Campylobacter jejuni and C. coli.

METHODS AND RESULTS

Substrate oxidation profiles by 100 strains were determined using oxygen electrode system. All the isolates tested oxidized formate, l-lactate, cysteine, glutamine and serine with high oxidation rates and high affinity but varied in their ability to oxidize citric acid cycle intermediates, aspartic acid and serine.

CONCLUSIONS

Based on the oxidation ability of alpha-ketoglutarate, succinate, fumarate and aspartic acid, Campylobacter strains tested were divided into three distinct metabolic categories. The first group was able to metabolize alpha-ketoglutarate, succinate, fumarate and aspartic acid; the second group was unable to oxidize alpha-ketoglutarate; and the third group was unable to oxidize, succinate, fumarate, and aspartic acid. Furthermore, serine oxidation rate enabled the differentiation of C. jejuni and C. coli.

SIGNIFICANCE AND IMPACT OF THE STUDY

Overall, the results highlights the extensive metabolic diversity between and within Campylobacter species. In addition, the kinetic data of oxidized substrates obtained may improve the isolation procedures of the organism.

The genome-sequenced variant of Campylobacter jejuni NCTC 11168 and the original clonal clinical isolate differ markedly in colonization, gene expression, and virulence-associated phenotypes

The genome sequence of the enteric bacterial pathogen Campylobacter jejuni NCTC 11168 (11168-GS) was published in 2000, providing a valuable resource for the identification of C. jejuni-specific colonization and virulence factors. Surprisingly, the 11168-GS clone was subsequently found to colonize 1-day-old chicks following oral challenge very poorly compared to other strains. In contrast, we have found that the original clinical isolate from which 11168-GS was derived, 11168-O, is an excellent colonizer of chicks. Other marked phenotypic differences were also identified: 11168-O invaded and translocated through tissue culture cells far more efficiently and rapidly than 11168-GS, was significantly more motile, and displayed a different morphology. Serotyping, multiple high-resolution molecular genotyping procedures, and subtractive hybridization did not yield observable genetic differences between the variants, suggesting that they are clonal. However, microarray transcriptional profiling of these strains under microaerobic and severely oxygen-limited conditions revealed dramatic expression differences for several gene families. Many of the differences were in respiration and metabolism genes and operons, suggesting that adaptation to different oxygen tensions may influence colonization potential. This correlates biologically with our observation that anaerobically priming 11168-GS or aerobically passaging 11168-O caused an increase or decrease, respectively, in colonization compared to the parent strain. Expression differences were also observed for several flagellar genes and other less well-characterized genes that may participate in motility. Targeted sequencing of the sigma factors revealed specific DNA differences undetected by the other genomic methods [corrected].

Transposon mutagenesis of Campylobacter jejuni identifies a bipartite energy taxis system required for motility

Campylobacter jejuni constitutes the leading cause of bacterial gastroenteritis in the United States and a major cause of diarrhoea worldwide. Little is known about virulence mechanisms in this organism because of the scarcity of suitable genetic tools. We have developed an efficient system of in vitro transposon mutagenesis using a mariner-based transposon and purified mariner transposase. Through in vitro transposition of C. jejuni chromosomal DNA followed by natural transformation of the transposed DNA, large random transposon mutant libraries consisting of approximately 16 000 individual mutants were generated. The first genetic screen of C. jejuni using a transposon-generated mutant library identified 28 mutants defective for flagellar motility, one of the few known virulence determinants of this pathogen. We developed a second genetic system, which allows for the construction of defined chromosomal deletions in C. jejuni, and demonstrated the requirement of sigma28 and sigma54 for motility. In addition, we show that sigma28 is involved in the transcription of flaA and that sigma54 is required for transcription of three other flagellar genes, flaB and flgDE. We also identified two previously uncharacterized genes required for motility encoding proteins that we call CetA and CetB, which mediate energy taxis responses. Through our analysis of the Cet proteins, we propose a unique mechanism for sensing energy levels and mediating energy taxis in C. jejuni.

Fumarate metabolism and the microaerophily of Campylobacter species

(1) The role of fumarate metabolism in the microaerophily of the Campylobacter genus and the effects of therapeutic agents against it were investigated. (2) NMR spectroscopy was employed to determine the properties of Campylobacter fumarase (Fum) and fumarate reductase (Frd). Radiotracer analysis was used to determine the production of carbon dioxide by Campylobacter cells. Standard microbiological techniques were used to measure the effects of environmental conditions and inhibitors on bacterial growth. (3) All Campylobacter species tested showed both Fum and Frd activities. Frd activity was observed with or without the addition of an exogenous electron donor in the particulate fractions obtained from lysates. Fumarate was oxidized to carbon dioxide via the acetyl-CoA cleavage pathway. The genes encoding proteins involved in fumarate metabolism were identified in the Campylobacter jejuni genome. Cells grew better in atmospheres with 5 and 10% oxygen levels. Fum activity was the same in cultures grown under different oxygen tensions and did not vary with the age of cultures. Frd activity was higher in cultures which grew at faster rates and decreased with the age of cultures. Four Frd inhibitors showed bactericidal effects against Campylobacter spp. with different potencies. The relative strengths of inhibition of the compounds followed the same order as the bactericidal effects. (4) The results suggested that Frd and Fum are constitutive and play a fundamental role in these microaerophiles which show characteristics of anaerobic metabolism, and that the Frd inhibitors tested would not be of therapeutic use.