Structural heterogeneity of carbohydrate modifications affects serospecificity of Campylobacter flagellins

Evolution of paralogous multicomponent systems for site-specific O-sialylation of flagellin in Gram-negative and Gram-positive bacteria

Many bacteria glycosylate flagellin on serine or threonine residues using pseudaminic acid (Pse) or other sialic acid-like donor sugars. Successful reconstitution of Pse-dependent sialylation by the conserved Maf-type flagellin glycosyltransferase (fGT) may require (a) missing component(s). Here, we characterize both Maf paralogs in the Gram-negative bacterium Shewanella oneidensis MR-1 and reconstitute Pse-dependent glycosylation in heterologous hosts. Remarkably, we uncovered distinct acceptor determinants and target specificities for each Maf. Whereas Maf-1 uses its C-terminal tetratricopeptide repeat (TPR) domain to confer flagellin acceptor and O-glycosylation specificity, Maf-2 requires the newly identified conserved specificity factor, glycosylation factor for Maf (GlfM), to form a ternary complex with flagellin. GlfM orthologs are co-encoded with Maf-2 in Gram-negative and Gram-positive bacteria and require an invariant aspartate in their four-helix bundle to function with Maf-2. Thus, convergent fGT evolution underlies distinct flagellin-binding modes in tripartite versus bipartite systems and, consequently, distinct O-glycosylation preferences of acceptor serine residues with Pse.

Investigation on the substrate specificity and N-substitution tolerance of PseF in catalytic transformation of pseudaminic acids to CMP-Pse derivatives

Pseudaminic acid (Pse) belongs to a class of bacterial non-2-ulosonic acids, and has been implicated in bacterial infection and immune evasion. Various Pse structures with diverse N-substitutions have been identified in pathogenic bacterial strains like Pseudomonas aeruginosa, Campylobacter jejuni, and Acinetobacter baumannii. In this study, we successfully synthesized three new Pse species, including Pse5Ac7Fo, Pse5Ac7(3RHb) and Pse7Fo5(3RHb) using chemical methods. Furthermore, we investigated the substrate specificity of cytidine 5'-monophosphate (CMP)-Pse synthetase (PseF), resulting in the production of N-modified CMP-Pse derivatives (CMP-Pses). It was found that PseF was promiscuous with the Pse substrate and could tolerate different modifications at the two nitrogen atoms. This study provides valuable insights into the incorporation of variable N-substitutions in the Pse biosynthetic pathway.

The Retaining Pse5Ac7Ac Pseudaminyltransferase KpsS1 Defines a Previously Unreported glycosyltransferase family (GT118)

Cell surface sugar 5,7-diacetyl pseudaminic acid (Pse5Ac7Ac) is a bacterial analogue of the ubiquitous sialic acid, Neu5Ac, and contributes to the virulence of a number of multidrug resistant bacteria, including ESKAPE pathogens Pseudomonas aeruginosa, and Acinetobacter baumannii. Despite its discovery in the surface glycans of bacteria over thirty years ago, to date no glycosyltransferase enzymes (GTs) dedicated to the synthesis of a pseudaminic acid glycosidic linkage have been unequivocally characterised in vitro. Herein we demonstrate that A. baumannii KpsS1 is a dedicated pseudaminyltransferase enzyme (PseT) which constructs a Pse5Ac7Ac-α(2,6)-Glcp linkage, and proceeds with retention of anomeric configuration. We utilise this PseT activity in tandem with the biosynthetic enzymes required for CMP-Pse5Ac7Ac assembly, in a two-pot, seven enzyme synthesis of an α-linked Pse5Ac7Ac glycoside. Due to its unique activity and protein sequence, we also assign KpsS1 as the prototypical member of a previously unreported GT family (GT118).

Impairment of a cyanobacterial glycosyltransferase that modifies a pilin results in biofilm development

A biofilm inhibiting mechanism operates in the cyanobacterium Synechococcus elongatus. Here, we demonstrate that the glycosyltransferase homologue, Ogt, participates in the inhibitory process - inactivation of ogt results in robust biofilm formation. Furthermore, a mutational approach shows requirement of the glycosyltransferase activity for biofilm inhibition. This enzyme is necessary for glycosylation of the pilus subunit and for adequate pilus formation. In contrast to wild-type culture in which most cells exhibit several pili, only 25% of the mutant cells are piliated, half of which possess a single pilus. In spite of this poor piliation, natural DNA competence was similar to that of wild-type; therefore, we propose that the unglycosylated pili facilitate DNA transformation. Additionally, conditioned medium from wild-type culture, which contains a biofilm inhibiting substance(s), only partially blocks biofilm development by the ogt-mutant. Thus, we suggest that inactivation of ogt affects multiple processes including production or secretion of the inhibitor as well as the ability to sense or respond to it.

Bacterial Flagellar Filament: A Supramolecular Multifunctional Nanostructure

The bacterial flagellum is a complex and dynamic nanomachine that propels bacteria through liquids. It consists of a basal body, a hook, and a long filament. The flagellar filament is composed of thousands of copies of the protein flagellin (FliC) arranged helically and ending with a filament cap composed of an oligomer of the protein FliD. The overall structure of the filament core is preserved across bacterial species, while the outer domains exhibit high variability, and in some cases are even completely absent. Flagellar assembly is a complex and energetically costly process triggered by environmental stimuli and, accordingly, highly regulated on transcriptional, translational and post-translational levels. Apart from its role in locomotion, the filament is critically important in several other aspects of bacterial survival, reproduction and pathogenicity, such as adhesion to surfaces, secretion of virulence factors and formation of biofilms. Additionally, due to its ability to provoke potent immune responses, flagellins have a role as adjuvants in vaccine development. In this review, we summarize the latest knowledge on the structure of flagellins, capping proteins and filaments, as well as their regulation and role during the colonization and infection of the host.

Reconstitution and optimisation of the biosynthesis of bacterial sugar pseudaminic acid (Pse5Ac7Ac) enables preparative enzymatic synthesis of CMP-Pse5Ac7Ac

Pseudaminic acids present on the surface of pathogenic bacteria, including gut pathogens Campylobacter jejuni and Helicobacter pylori, are postulated to play influential roles in the etiology of associated infectious diseases through modulating flagella assembly and recognition of bacteria by the human immune system. Yet they are underexplored compared to other areas of glycoscience, in particular enzymes responsible for the glycosyltransfer of these sugars in bacteria are still to be unambiguously characterised. This can be largely attributed to a lack of access to nucleotide-activated pseudaminic acid glycosyl donors, such as CMP-Pse5Ac7Ac. Herein we reconstitute the biosynthesis of Pse5Ac7Ac in vitro using enzymes from C. jejuni (PseBCHGI) in the process optimising coupled turnover with PseBC using deuterium wash in experiments, and establishing a method for co-factor regeneration in PseH tunover. Furthermore we establish conditions for purification of a soluble CMP-Pse5Ac7Ac synthetase enzyme PseF from Aeromonas caviae and utilise it in combination with the C. jejuni enzymes to achieve practical preparative synthesis of CMP-Pse5Ac7Ac in vitro, facilitating future biological studies.

Structural and Biosynthetic Diversity of Nonulosonic Acids (NulOs) That Decorate Surface Structures in Bacteria

Nonulosonic acids (NulOs) are a diverse family of 9-carbon α-keto acid sugars that are involved in a wide range of functions across all branches of life. The family of NulOs includes the sialic acids as well as the prokaryote-specific NulOs. Select bacteria biosynthesize the sialic acid N-acetylneuraminic acid (Neu5Ac), and the ability to produce this sugar and its subsequent incorporation into cell-surface structures is implicated in a variety of bacteria-host interactions. Furthermore, scavenging of sialic acid from the environment for energy has been characterized across a diverse group of bacteria, mainly human commensals and pathogens. In addition to sialic acid, bacteria have the ability to biosynthesize prokaryote-specific NulOs, of which there are several known isomers characterized. These prokaryotic NulOs are similar in structure to Neu5Ac but little is known regarding their role in bacterial physiology. Here, we discuss the diversity in structure, the biosynthesis pathways, and the functions of bacteria-specific NulOs. These carbohydrates are phylogenetically widespread among bacteria, with numerous structurally unique modifications recognized. Despite the diversity in structure, the NulOs are involved in similar functions such as motility, biofilm formation, host colonization, and immune evasion.

Specificity in glycosylation of multiple flagellins by the modular and cell cycle regulated glycosyltransferase FlmG

How specificity is programmed into post-translational modification of proteins by glycosylation is poorly understood, especially for O-linked glycosylation systems. Here we reconstitute and dissect the substrate specificity underpinning the cytoplasmic O-glycosylation pathway that modifies all six flagellins, five structural and one regulatory paralog, in Caulobacter crescentus, a monopolarly flagellated alpha-proteobacterium. We characterize the biosynthetic pathway for the sialic acid-like sugar pseudaminic acid and show its requirement for flagellation, flagellin modification and efficient export. The cognate NeuB enzyme that condenses phosphoenolpyruvate with a hexose into pseudaminic acid is functionally interchangeable with other pseudaminic acid synthases. The previously unknown and cell cycle-regulated FlmG protein, a defining member of a new class of cytoplasmic O-glycosyltransferases, is required and sufficient for flagellin modification. The substrate specificity of FlmG is conferred by its N-terminal flagellin-binding domain. FlmG accumulates before the FlaF secretion chaperone, potentially timing flagellin modification, export, and assembly during the cell division cycle.

The sps Genes Encode an Original Legionaminic Acid Pathway Required for Crust Assembly in Bacillus subtilis

The crust is the outermost spore layer of most Bacillus strains devoid of an exosporium. This outermost layer, composed of both proteins and carbohydrates, plays a major role in the adhesion and spreading of spores into the environment. Recent studies have identified several crust proteins and have provided insights about their organization at the spore surface. However, although carbohydrates are known to participate in adhesion, little is known about their composition, structure, and localization. In this study, we showed that the spore surface of Bacillus subtilis is covered with legionaminic acid (Leg), a nine-carbon backbone nonulosonic acid known to decorate the flagellin of the human pathogens Helicobacter pylori and Campylobacter jejuni We demonstrated that the spsC, spsD, spsE, spsG, and spsM genes of Bacillus subtilis are required for Leg biosynthesis during sporulation, while the spsF gene is required for Leg transfer from the mother cell to the surface of the forespore. We also characterized the activity of SpsM and highlighted an original Leg biosynthesis pathway in B. subtilis Finally, we demonstrated that Leg is required for the assembly of the crust around the spores, and we showed that in the absence of Leg, spores were more adherent to stainless steel probably because of their reduced hydrophilicity and charge.IMPORTANCE Bacillus species are a major economic and food safety concern of the food industry because of their food spoilage-causing capability and persistence. Their persistence is mainly due to their ability to form highly resistant spores adhering to the surfaces of industrial equipment. Spores of the Bacillus subtilis group are surrounded by the crust, a superficial layer which plays a key role in their adhesion properties. However, knowledge of the composition and structure of this layer remains incomplete. Here, for the first time, we identified a nonulosonic acid (Leg) at the surfaces of bacterial spores (B. subtilis). We uncovered a novel Leg biosynthesis pathway, and we demonstrated that Leg is required for proper crust assembly. This work contributes to the description of the structure and composition of Bacillus spores which has been under way for decades, and it provides keys to understanding the importance of carbohydrates in Bacillus adhesion and persistence in the food industry.

Sequence analysis of nonulosonic acid biosynthetic gene clusters in Vibrionaceae and Moritella viscosa

Nonulosonic acid (NulO) biosynthesis in bacteria is directed by nab gene clusters that can lead to neuraminic, legionaminic or pseudaminic acids. Analysis of the gene content from a set mainly composed of Aliivibrio salmonicida and Moritella viscosa strains reveals the existence of several unique nab clusters, for which the NulO products were predicted. This prediction method can be used to guide tandem mass spectrometry studies in order to verify the products of previously undescribed nab clusters and identify new members of the NulOs family.

Small Noncoding RNA CjNC110 Influences Motility, Autoagglutination, AI-2 Localization, Hydrogen Peroxide Sensitivity, and Chicken Colonization in Campylobacter jejuni

Small noncoding RNAs (ncRNAs) are involved in many important physiological functions in pathogenic microorganisms. Previous studies have identified the presence of noncoding RNAs in the major zoonotic pathogen Campylobacter jejuni; however, few have been functionally characterized to date. CjNC110 is a conserved ncRNA in C. jejuni, located downstream of the luxS gene, which is responsible for the production of the quorum sensing molecule autoinducer-2 (AI-2). In this study, we utilized strand specific high-throughput RNAseq to identify potential targets or interactive partners of CjNC110 in a sheep abortion clone of C. jejuni These data were then utilized to focus further phenotypic evaluation of the role of CjNC110 in motility, autoagglutination, quorum sensing, hydrogen peroxide sensitivity, and chicken colonization in C. jejuni Inactivation of the CjNC110 ncRNA led to a statistically significant decrease in autoagglutination ability as well as increased motility and hydrogen peroxide sensitivity compared to the wild-type. Extracellular AI-2 detection was decreased in ΔCjNC110; however, intracellular AI-2 accumulation was significantly increased, suggesting a key role of CjNC110 in modulating the transport of AI-2. Notably, ΔCjNC110 also showed a decreased ability to colonize chickens. Complementation of CjNC110 restored all phenotypic changes back to wild-type levels. The collective results of the phenotypic and transcriptomic changes observed in our data provide valuable insights into the pathobiology of C. jejuni sheep abortion clone and strongly suggest that CjNC110 plays an important role in the regulation of energy taxis, flagellar glycosylation, cellular communication via quorum sensing, oxidative stress tolerance, and chicken colonization in this important zoonotic pathogen.

Agricultural intensification and the evolution of host specialism in the enteric pathogen Campylobacter jejuni

Modern agriculture has dramatically changed the distribution of animal species on Earth. Changes to host ecology have a major impact on the microbiota, potentially increasing the risk of zoonotic pathogens being transmitted to humans, but the impact of intensive livestock production on host-associated bacteria has rarely been studied. Here, we use large isolate collections and comparative genomics techniques, linked to phenotype studies, to understand the timescale and genomic adaptations associated with the proliferation of the most common food-born bacterial pathogen (Campylobacter jejuni) in the most prolific agricultural mammal (cattle). Our findings reveal the emergence of cattle specialist C. jejuni lineages from a background of host generalist strains that coincided with the dramatic rise in cattle numbers in the 20th century. Cattle adaptation was associated with horizontal gene transfer and significant gene gain and loss. This may be related to differences in host diet, anatomy, and physiology, leading to the proliferation of globally disseminated cattle specialists of major public health importance. This work highlights how genomic plasticity can allow important zoonotic pathogens to exploit altered niches in the face of anthropogenic change and provides information for mitigating some of the risks posed by modern agricultural systems.

Binding of Phage-Encoded FlaGrab to Motile Campylobacter jejuni Flagella Inhibits Growth, Downregulates Energy Metabolism, and Requires Specific Flagellar Glycans

Many bacterial pathogens display glycosylated surface structures that contribute to virulence, and targeting these structures is a viable strategy for pathogen control. The foodborne pathogen Campylobacter jejuni expresses a vast diversity of flagellar glycans, and flagellar glycosylation is essential for its virulence. Little is known about why C. jejuni encodes such a diverse set of flagellar glycans, but it has been hypothesized that evolutionary pressure from bacteriophages (phages) may have contributed to this diversity. However, interactions between Campylobacter phages and host flagellar glycans have not been characterized in detail. Previously, we observed that Gp047 (now renamed FlaGrab), a conserved Campylobacter phage protein, binds to C. jejuni flagella displaying the nine-carbon monosaccharide 7-acetamidino-pseudaminic acid, and that this binding partially inhibits cell growth. However, the mechanism of this growth inhibition, as well as how C. jejuni might resist this activity, are not well-understood. Here we use RNA-Seq to show that FlaGrab exposure leads C. jejuni 11168 cells to downregulate expression of energy metabolism genes, and that FlaGrab-induced growth inhibition is dependent on motile flagella. Our results are consistent with a model whereby FlaGrab binding transmits a signal through flagella that leads to retarded cell growth. To evaluate mechanisms of FlaGrab resistance in C. jejuni, we characterized the flagellar glycans and flagellar glycosylation loci of two C. jejuni strains naturally resistant to FlaGrab binding. Our results point toward flagellar glycan diversity as the mechanism of resistance to FlaGrab. Overall, we have further characterized the interaction between this phage-encoded flagellar glycan-binding protein and C. jejuni, both in terms of mechanism of action and mechanism of resistance. Our results suggest that C. jejuni encodes as-yet unidentified mechanisms for generating flagellar glycan diversity, and point to phage proteins as exciting lenses through which to study bacterial surface glycans.

Synthesis of Butenolides via a Horner-Wadsworth-Emmons Cascading Dimerization Reaction

The efficient synthesis of a range of structurally related butenolides has been observed while we were exploring the substrate-scope of a Horner-Wadsworth-Emmons (HWE) reaction. While aliphatic aldehydes gave the expected HWE product, aromatic aldehydes furnished butenolides, resulting from the dimerization of the HWE product during desilylation of the initially formed HWE adduct. In addition to isolating butenolides in a high yield, we have also determined precisely when dimerization occurs.

Cj1388 Is a RidA Homolog and Is Required for Flagella Biosynthesis and/or Function in Campylobacter jejuni

Campylobacter jejuni is the leading bacterial cause of acute gastroenteritis worldwide and thus significant to public health. C. jejuni primarily lives in the gastrointestinal tracts of poultry and can contaminate meat during processing. Despite a small genome, the metabolic plasticity of C. jejuni allows proliferation in chicken ceca and mammalian host intestines, and survival in environments with a variety of temperatures, pH, osmotic conditions, and nutrient availabilities. The exact mechanism of C. jejuni infection is unknown, however, virulence requires motility. Our data suggest the C. jejuni RidA homolog, Cj1388, plays a role in flagellar biosynthesis, regulation, structure, and/or function and, as such is expected to influence virulence of the organism. Mutants lacking cj1388 have defects in motility, autoagglutination, and phage infectivity under the conditions tested. Comparison to the RidA paradigm from Salmonella enterica indicates the phenotypes of the C. jejuni cj1388 mutant are likely due to the inhibition of one or more pyridoxal 5'-phosphate-dependent enzymes by the reactive enamine 2-aminoacrylate.

Genetics behind the Biosynthesis of Nonulosonic Acid-Containing Lipooligosaccharides in Campylobacter coli

Campylobacter jejuni and Campylobacter coli are the most common causes of bacterial gastroenteritis in the world. Ganglioside mimicry by C. jejuni lipooligosaccharide (LOS) is the triggering factor of Guillain-Barré syndrome (GBS), an acute polyneuropathy. Sialyltransferases from glycosyltransferase family 42 (GT-42) are essential for the expression of ganglioside mimics in C. jejuni Recently, two novel GT-42 genes, cstIV and cstV, have been identified in C. coli Despite being present in ∼11% of currently available C. coli genomes, the biological role of cstIV and cstV is unknown. In the present investigation, mutation studies with two strains expressing either cstIV or cstV were performed and mass spectrometry was used to investigate differences in the chemical composition of LOS. Attempts were made to identify donor and acceptor molecules using in vitro activity tests with recombinant GT-42 enzymes. Here we show that CstIV and CstV are involved in C. coli LOS biosynthesis. In particular, cstV is associated with LOS sialylation, while cstIV is linked to the addition of a diacetylated nonulosonic acid residue.IMPORTANCE Despite the fact that Campylobacter coli a major foodborne pathogen, its glycobiology has been largely neglected. The genetic makeup of the C. coli lipooligosaccharide biosynthesis locus was largely unknown until recently. C. coli harbors a large set of genes associated with lipooligosaccharide biosynthesis, including genes for several putative glycosyltransferases involved in the synthesis of sialylated lipooligosaccharide in Campylobacter jejuni In the present study, C. coli was found to express lipooligosaccharide structures containing sialic acid and other nonulosonate acids. These findings have a strong impact on our understanding of C. coli ecology, host-pathogen interaction, and pathogenesis.

Immunoproteomics Methods and Techniques

The varied landscape of the adaptive immune response is determined by the peptides presented by immune cells, derived from viral or microbial pathogens or cancerous cells. The study of immune biomarkers or antigens is not new, and classical methods such as agglutination, enzyme-linked immunosorbent assay, or Western blotting have been used for many years to study the immune response to vaccination or disease. However, in many of these traditional techniques, protein or peptide identification has often been the bottleneck. Recent progress in genomics and mass spectrometry have led to many of the rapid advances in proteomics approaches. Immunoproteomics describes a rapidly growing collection of approaches that have the common goal of identifying and measuring antigenic peptides or proteins. This includes gel-based, array-based, mass spectrometry-based, DNA-based, or in silico approaches. Immunoproteomics is yielding an understanding of disease and disease progression, vaccine candidates, and biomarkers. This review gives an overview of immunoproteomics and closely related technologies that are used to define the full set of protein antigens targeted by the immune system during 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.

A DNA prime/protein boost vaccine protocol developed against Campylobacter jejuni for poultry

Vaccination of broilers is one of the potential ways to decrease Campylobacter intestinal loads and therefore may reduce human disease incidence. Despite many studies, no efficient vaccine is available yet. Using the reverse vaccinology strategy, we recently identified new vaccine candidates whose immune and protective capacities need to be evaluated in vivo. Therefore, the goal of the present study was to develop and evaluate an avian subunit vaccine protocol for poultry against Campylobacter jejuni. For this, flagellin was used as vaccine antigen candidate. A DNA prime/protein boost regimen was effective in inducing a massive protective immune response against C. jejuni in specific pathogen free Leghorn chickens. Contrastingly, the same vaccine regimen stimulated the production of antibodies against Campylobacter in conventional Ross broiler chickens harbouring maternally derived antibodies against Campylobacter, but not the control of C. jejuni colonization. These results highlight the strength of the vaccine protocol in inducing protective immunity and the significance of the avian strain and/or immune status in the induction of this response. Nevertheless, as such the vaccine protocol is not efficient in broilers to induce protection and has to be adapted; this has been done in one of our recent published work.

A new approach to the synthesis of legionaminic acid analogues

Legionaminic acid is a member of the nonulosonic acids, which are a class of sugars considered to be a virulence factor within a wide variety of pathogenic bacteria. We have developed a synthetic pathway towards C-7 analogues of legionaminic acid starting from Neu5Ac, resulting in the complete synthesis of both legionaminic acid, and its C-7 epimer, from a common precurser. Our approach involves the late-stage introduction of the requisite C-7 nitrogen functionality, thus making our strategy amenable to the introduction of a range of different amide groups at C-7 of legionaminic acid.

We report the synthesis of the bacterial nonulosonic acid legionaminic acid, together with its C-7 epimer, from a common precursor derived from N-acetylneuraminic acid.

A novel glycan modifies the flagellar filament proteins of the oral bacterium Treponema denticola

While protein glycosylation has been reported in several spirochetes including the syphilis bacterium Treponema pallidum and Lyme disease pathogen Borrelia burgdorferi, the pertinent glycan structures and their roles remain uncharacterized. Herein, a novel glycan with an unusual chemical composition and structure in the oral spirochete Treponema denticola, a keystone pathogen of periodontitis was reported. The identified glycan of mass 450.2 Da is composed of a monoacetylated nonulosonic acid (Non) with a novel extended N7 acyl modification, a 2-methoxy-4,5,6-trihydroxy-hexanoyl residue in which the Non has a pseudaminic acid configuration (L-glycero-L-manno) and is β-linked to serine or threonine residues. This novel glycan modifies the flagellin proteins (FlaBs) of T. denticola by O-linkage at multiple sites near the D1 domain, a highly conserved region of bacterial flagellins that interact with Toll-like receptor 5. Furthermore, mutagenesis studies demonstrate that the glycosylation plays an essential role in the flagellar assembly and motility of T. denticola. To our knowledge, this novel glycan and its unique modification sites have not been reported previously in any bacteria.

Characterizing Glycoproteins by Mass Spectrometry in Campylobacter jejuni

The glycosylation systems of Campylobacter jejuni (C. jejuni) are considered archetypal examples of both N- and O-linked glycosylations in the field of bacterial glycosylation. The discovery and characterization of these systems both have revealed important biological insight into C. jejuni and have led to the refinement and enhancement of methodologies to characterize bacterial glycosylation. In general, mass spectrometry-based characterization has become the preferred methodology for the study of C. jejuni glycosylation because of its speed, sensitivity, and ability to enable both qualitative and quantitative assessments of glycosylation events. In these experiments the generation of insightful data requires the careful selection of experimental approaches and mass spectrometry (MS) instrumentation. As such, it is essential to have a deep understanding of the technologies and approaches used for characterization of glycosylation events. Here we describe protocols for the initial characterization of C. jejuni glycoproteins using protein-/peptide-centric approaches and discuss considerations that can enhance the generation of insightful data.

Preharvest Food Safety in Broiler Chicken Production

Preharvest food safety in broiler production is a systematic approach to control the introduction, propagation, and dissemination of Salmonella and Campylobacter from breeder flocks to the end of their progeny (broilers) life cycle. New and revised more stringent performance standards for these pathogens at the processing plant level require continuous evaluation of the preharvest management practices and intervention strategies used by the poultry industry. The implementation of stricter biosecurity plans, vaccination of breeder flocks for Salmonella , and usage of feed that is free of animal by-products are some of the measures recommended to control the pathogens. Interventions shown to be effective in experimental settings need to be assessed for their cost-effectiveness and efficiency when applied at the farm level.

In Azospirillum brasilense, mutations in flmA or flmB genes affect polar flagellum assembly, surface polysaccharides, and attachment to maize roots

Azospirillum brasilense is a soil bacterium capable of promoting plant growth. Several surface components were previously reported to be involved in the attachment of A. brasilense to root plants. Among these components are the exopolysaccharide (EPS), lipopolysaccharide (LPS) and the polar flagellum. Flagellin from polar flagellum is glycosylated and it was suggested that genes involved in such a posttranslational modification are the same ones involved in the biosynthesis of sugars present in the O-antigen of the LPS. In this work, we report on the characterization of two homologs present in A. brasilense Cd, to the well characterized flagellin modification genes, flmA and flmB, from Aeromonas caviae. We show that mutations in either flmA or flmB genes of A. brasilense resulted in non-motile cells due to alterations in the polar flagellum assembly. Moreover, these mutations also affected the capability of A. brasilense cells to adsorb to maize roots and to produce LPS and EPS. By generating a mutant containing the polar flagellum affected in their rotation, we show the importance of the bacterial motility for the early colonization of maize roots.

Clinical applications of bacterial glycoproteins

There is an ongoing race between bacterial evolution and medical advances. Pathogens have the advantages of short generation times and horizontal gene transfer that enable rapid adaptation to new host environments and therapeutics that currently outpaces clinical research. Antibiotic resistance, the growing impact of nosocomial infections, cancer-causing bacteria, the risk of zoonosis, and the possibility of biowarfare all emphasize the increasingly urgent need for medical research focussed on bacterial pathogens. Bacterial glycoproteins are promising targets for alternative therapeutic intervention since they are often surface exposed, involved in host-pathogen interactions, required for virulence, and contain distinctive glycan structures. The potential exists to exploit these unique structures to improve clinical prevention, diagnosis, and treatment strategies. Translation of the potential in this field to actual clinical impact is an exciting prospect for fighting infectious diseases.

Total Synthesis of Native 5,7-Diacetylpseudaminic Acid from N-Acetylneuraminic Acid

The pseudaminic acids are a family of 5,7-diamino-3,5,7,9-tetradeoxynonulosonic acids that are functional components of flagellin and pili proteins within clinically relevant Gram-negative bacteria. Herein, we describe the total synthesis of the most common pseudaminic acid, 5,7-diacetylpseudaminic acid, from N-acetylneuraminic acid. The divergent nature of the route reported here provides a robust and versatile means to access other members of the family, together with analogues, for probing the functional role of the pseudaminic acids and pseudaminic acid derived proteins in the future.

Bacterial Surfaces: Front Lines in Host-Pathogen Interaction

All bacteria are bound by at least one membrane that acts as a barrier between the cell's interior and the outside environment. Surface components within and attached to the cell membrane are essential for ensuring that the overall homeostasis of the cell is maintained. However, many surface components of the bacterial cell also have an indispensable role mediating interactions of the bacteria with their immediate environment and as such are essential to the pathogenesis of infectious disease. During the course of an infection, bacterial pathogens will encounter many different ecological niches where environmental conditions such as salinity, temperature, pH, and the availability of nutrients fluctuate. It is the bacterial cell surface that is at the front-line of these host-pathogen interactions often protecting the bacterium from hostile surroundings but at the same time playing a critical role in the adherence to host tissues promoting colonization and subsequent infection. To deal effectively with the changing environments that pathogens may encounter in different ecological niches within the host many of the surface components of the bacterial cell are subject to phenotypic variation resulting in heterogeneous subpopulations of bacteria within the clonal population. This dynamic phenotypic heterogeneity ensures that at least a small fraction of the population will be adapted for a particular circumstance should it arise. Diversity within the clonal population has often been masked by studies on entire bacterial populations where it was often assumed genes were expressed in a uniform manner. This chapter, therefore, aims to highlight the non-uniformity in certain cell surface structures and will discuss the implication of this heterogeneity in bacterial-host interaction. Some of the recent advances in studying bacterial surface structures at the single cell level will also be reviewed.

Comprehensive analysis of flagellin glycosylation in Campylobacter jejuni NCTC 11168 reveals incorporation of legionaminic acid and its importance for host colonization

Campylobacter jejuni is the leading cause of bacterial gastroenteritis. It relies on several virulence factors for host colonization, including glycosylated flagella. C. jejuni NCTC 11168 modifies its flagellins with pseudaminic acid derivatives. It is also presumed to modify these proteins with legionaminic acid, although no glycopeptide evidence was available at the onset of this study. The enzyme encoded by cj1319 can be used to make legionaminic acid in vitro, but the pathway for legionaminic acid synthesis partially inferred by knockout mutagenesis in Campylobacter coli VC167 excludes Cj1319. To address this contradiction, we examined the presence of legionaminic acid in flagellin glycopeptides of wild-type (WT) C. jejuni NCTC 11168 and of a cj1319 knockout mutant. We used high-energy collision-induced dissociation to obtain amino acid sequences while also visualizing signature sugar oxonium ions. Data analysis was performed with PEAKS software, and spectra were manually inspected for glycopeptide determination and verification. We showed that legionaminic acid is present on the flagellins of C. jejuni NCTC 11168 and that flagellin glycosylation is highly heterogeneous, with up to six different sugars singly present at a given site. We found that the cj1319 mutant produces more legionaminic acid than WT, thus excluding the requirement for Cj1319 for legionaminic acid synthesis. We also showed that this mutant has enhanced chicken colonization compared with WT, which may in part be attributed to the high content of legionaminic acid on its flagella.

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.

Host-like carbohydrates promote bloodstream survival of Vibrio vulnificus in vivo

Sialic acids are found on all vertebrate cell surfaces and are part of a larger class of molecules known as nonulosonic acids. Many bacterial pathogens synthesize related nine-carbon backbone sugars; however, the role(s) of these non-sialic acid molecules in host-pathogen interactions is poorly understood. Vibrio vulnificus is the leading cause of seafood-related death in the United States due to its ability to quickly access the host bloodstream, which it can accomplish through gastrointestinal or wound infection. However, little is known about how this organism persists systemically. Here we demonstrate that sialic acid-like molecules are present on the lipopolysaccharide of V. vulnificus, are required for full motility and biofilm formation, and also contribute to the organism's natural resistance to polymyxin B. Further experiments in a murine model of intravenous V. vulnificus infection demonstrated that expression of nonulosonic acids had a striking benefit for bacterial survival during bloodstream infection and dissemination to other tissues in vivo. In fact, levels of bacterial persistence in the blood corresponded to the overall levels of these molecules expressed by V. vulnificus isolates. Taken together, these results suggest that molecules similar to sialic acids evolved to facilitate the aquatic lifestyle of V. vulnificus but that their emergence also resulted in a gain of function with life-threatening potential in the human host.

A new approach towards the synthesis of pseudaminic acid analogues

The pseudaminic acids are a family of 5,7-diamino-3,5,7,9-tetradeoxynonulosonic acids that are essential components of bacterial polysaccharides and glycoproteins. This paper describes our approach towards the synthesis of analogues of pseudaminic acid, and involves the efficient introduction of the requisite nitrogen functionalities from a readily available precursor.

The sweet tooth of bacteria: common themes in bacterial glycoconjugates

Humans have been increasingly recognized as being superorganisms, living in close contact with a microbiota on all their mucosal surfaces. However, most studies on the human microbiota have focused on gaining comprehensive insights into the composition of the microbiota under different health conditions (e.g., enterotypes), while there is also a need for detailed knowledge of the different molecules that mediate interactions with the host. Glycoconjugates are an interesting class of molecules for detailed studies, as they form a strain-specific barcode on the surface of bacteria, mediating specific interactions with the host. Strikingly, most glycoconjugates are synthesized by similar biosynthesis mechanisms. Bacteria can produce their major glycoconjugates by using a sequential or an en bloc mechanism, with both mechanistic options coexisting in many species for different macromolecules. In this review, these common themes are conceptualized and illustrated for all major classes of known bacterial glycoconjugates, with a special focus on the rather recently emergent field of glycosylated proteins. We describe the biosynthesis and importance of glycoconjugates in both pathogenic and beneficial bacteria and in both Gram-positive and -negative organisms. The focus lies on microorganisms important for human physiology. In addition, the potential for a better knowledge of bacterial glycoconjugates in the emerging field of glycoengineering and other perspectives is discussed.

Campylobacter jejuni motility is required for infection of the flagellotropic bacteriophage F341

Previous studies have identified a specific modification of the capsular polysaccharide as receptor for phages that infect Campylobacter jejuni. Using acapsular kpsM mutants of C. jejuni strains NCTC11168 and NCTC12658, we found that bacteriophage F341 infects C. jejuni independently of the capsule. In contrast, phage F341 does not infect C. jejuni NCTC11168 mutants that either lack the flagellar filaments (ΔflaAB) or that have paralyzed, i.e., nonrotating, flagella (ΔmotA and ΔflgP). Complementing flgP confirmed that phage F341 requires rotating flagella for successful infection. Furthermore, adsorption assays demonstrated that phage F341 does not adsorb to these nonmotile C. jejuni NCTC11168 mutants. Taken together, we propose that phage F341 uses the flagellum as a receptor. Phage-host interactions were investigated using fluorescence confocal and transmission electron microscopy. These data demonstrate that F341 binds to the flagellum by perpendicular attachment with visible phage tail fibers interacting directly with the flagellum. Our data are consistent with the movement of the C. jejuni flagellum being required for F341 to travel along the filament to reach the basal body of the bacterium. The initial binding to the flagellum may cause a conformational change of the phage tail that enables DNA injection after binding to a secondary receptor.

Bacterial cell-envelope glycoconjugates

Prokaryotic glycosylation fulfills an important role in maintaining and protecting the structural integrity and function of the bacterial cell wall, as well as serving as a flexible adaption mechanism to evade environmental and host-induced pressure. The scope of bacterial and archaeal protein glycosylation has considerably expanded over the past decade(s), with numerous examples covering the glycosylation of flagella, pili, glycosylated enzymes, as well as surface-layer proteins. This article addresses structure, analysis, function, genetic basis, biosynthesis, and biomedical and biotechnological applications of cell-envelope glycoconjugates, S-layer glycoprotein glycans, and "nonclassical" secondary-cell wall polysaccharides. The latter group of polymers mediates the important attachment and regular orientation of the S-layer to the cell wall. The structures of these glycopolymers reveal an enormous diversity, resembling the structural variability of bacterial lipopolysaccharides and capsular polysaccharides. While most examples are presented for Gram-positive bacteria, the S-layer glycan of the Gram-negative pathogen Tannerella forsythia is also discussed. In addition, archaeal S-layer glycoproteins are briefly summarized.

Gram-negative flagella glycosylation

Protein glycosylation had been considered as an eccentricity of a few bacteria. However, through advances in analytical methods and genome sequencing, it is now established that bacteria possess both N-linked and O-linked glycosylation pathways. Both glycosylation pathways can modify multiple proteins, flagellins from Archaea and Eubacteria being one of these. Flagella O-glycosylation has been demonstrated in many polar flagellins from Gram-negative bacteria and in only the Gram-positive genera Clostridium and Listeria. Furthermore, O-glycosylation has also been demonstrated in a limited number of lateral flagellins. In this work, we revised the current advances in flagellar glycosylation from Gram-negative bacteria, focusing on the structural diversity of glycans, the O-linked pathway and the biological function of flagella glycosylation.

Campylobacter jejuni strain discrimination and temperature-dependent glycome expression profiling by lectin microarray

Gram-negative Campylobacter jejuni is the leading cause of bacterial gastroenteritis in humans worldwide and the most frequently identified infectious trigger in patients developing Guillain-Barré syndrome (GBS). While C. jejuni is pathogenic in humans, it is a commensal in avian hosts. Bacterial cell surface carbohydrates are important virulence factors and play roles in adherence, colonisation and infection. The mechanisms leading to infection or persistent colonisation of C. jejuni are not well understood but host temperature may provide an important stimulus for specific adaptation. Thus, examination of the modulation of the total surface glycome of C. jejuni in response to temperature may help shed light on commensal and pathogenic mechanisms for this species. C. jejuni strains 81116 and 81-176 were cultured at 37 and 42°C to simulate human and avian host conditions, respectively, and whole cells were profiled on lectin microarrays constructed to include a wide range of binding specificities. C. jejuni 81116 profiles indicated that the previously characterised lipopolysaccharide (LPS)-like molecule and N-linked glycans were the predominantly recognised cell surface structures while capsular polysaccharide (CPS), lipooligosaccharides (LOS) and N-linked glycosylation were best recognised for strain 81-176 at 37°C. The profiles of both strains varied and were distinguishable at both temperatures. At the higher temperature, reduced dominance of the LPS-like structure was associated with strain 81116 and a change in the relative distribution of CPS and LOS structures was indicated for strain 81-176. This change in LOS molecular mass species distribution between temperatures was confirmed by SDS-PAGE analysis. Additionally, opposite behaviour of certain lectins was noted between the plate agglutination assay and the microarray platform. Insights into the important glycosylation involved in C. jejuni host cell tropism at different growth temperatures were gained using the lectin microarray platform.

The renaissance of bacillosamine and its derivatives: pathway characterization and implications in pathogenicity

Prokaryote-specific sugars, including N,N′-diacetylbacillosamine (diNAcBac) and pseudaminic acid, have experienced a renaissance in the past decade because of their discovery in glycans related to microbial pathogenicity. DiNAcBac is found at the reducing end of oligosaccharides of N- and O-linked bacterial protein glycosylation pathways of Gram-negative pathogens, including Campylobacter jejuni and Neisseria gonorrhoeae. Further derivatization of diNAcBac results in the nonulosonic acid known as legionaminic acid, which was first characterized in the O-antigen of the lipopolysaccharide (LPS) in Legionella pneumophila. Pseudaminic acid, an isomer of legionaminic acid, is also important in pathogenic bacteria such as Helicobacter pylori because of its occurrence in O-linked glycosylation of flagellin proteins, which plays an important role in flagellar assembly and motility. Here, we present recent advances in the characterization of the biosynthetic pathways leading to these highly modified sugars and investigation of the roles that each plays in bacterial fitness and pathogenicity.

Posttranslational modification of flagellin FlaB in Shewanella oneidensis

Shewanella oneidensis is a highly motile organism by virtue of a polar, glycosylated flagellum composed of flagellins FlaA and FlaB. In this study, the functional flagellin FlaB was isolated and analyzed with nano-liquid chromatography-mass spectrometry (MS) and tandem MS. In combination with the mutational analysis, we propose that the FlaB flagellin protein from S. oneidensis is modified at five serine residues with a series of novel O-linked posttranslational modifications (PTMs) that differ from each other by 14 Da. These PTMs are composed in part of a 274-Da sugar residue that bears a resemblance to the nonulosonic acids. The remainder appears to be composed of a second residue whose mass varies by 14 Da depending on the PTM. Further investigation revealed that synthesis of the glycans initiates with PseB and PseC, the first two enzymes of the Pse pathway. In addition, a number of lysine residues are found to be methylated by SO4160, an analogue of the lysine methyltransferase of Salmonella enterica serovar Typhimurium.

Immunoproteomics: current technology and applications

The varied landscape of the adaptive immune response is determined by the peptides presented by immune cells, derived from viral or microbial pathogens or cancerous cells. The study of immune biomarkers or antigens is not new and classical methods such as agglutination, enzyme-linked immunosorbent assay, or Western blotting have been used for many years to study the immune response to vaccination or disease. However, in many of these traditional techniques, protein or peptide identification has often been the bottleneck. Recent advances in genomics and proteomics, has led to many of the rapid advances in proteomics approaches. Immunoproteomics describes a rapidly growing collection of approaches that have the common goal of identifying and measuring antigenic peptides or proteins. This includes gel based, array based, mass spectrometry, DNA based, or in silico approaches. Immunoproteomics is yielding an understanding of disease and disease progression, vaccine candidates, and biomarkers. This review gives an overview of immunoproteomics and closely related technologies that are used to define the full set of antigens targeted by the immune system during disease.

Identification of an O-linked repetitive glycan chain of the polar flagellum flagellin of Azospirillum brasilense Sp7

This is the first report to have identified an O-linked repetitive glycan in bacterial flagellin, a structural protein of the flagellum. Studies by sugar analysis, Smith degradation, (1)H and (13)C NMR spectroscopy, and mass spectrometry showed that the glycan chains of the polar flagellum flagellin of the plant-growth-promoting rhizobacterium Azospirillum brasilense Sp7 are represented by a polysaccharide with a molecular mass of 7.7 kDa, which has a branched tetrasaccharide repeating unit of the following structure:

The role of WlaRG, WlaTB and WlaTC in lipooligosaccharide synthesis by Campylobacter jejuni strain 81116

Campylobacter jejuni is a major bacterial cause of gastroenteritis world-wide. C. jejuni produces a range of glycans including lipooligosaccharide (LOS), an important virulence factor. The genetic content of the LOS synthesis locus varies between C. jejuni strains and 19 classes have been described. Three LOS synthesis genes of C. jejuni strain 81116 (NCTC 11828), wlaRG, wlaTB and wlaTC were the focus of this study. WlaRG and the remaining two proteins of interest share sequence similarity to aminotransferases and glycosyltransferases, respectively. These genes were insertionally inactivated and phenotypically characterised. Each mutant produced truncated LOS. Mutants lacking WlaRG, WlaTB and WlaTC produced LOS with reduced immunogenicity. Both the wlaRG and wlaTC mutants were non-motile and aflagellate. In vitro invasion and adhesion assays revealed that the wlaRG, wlaTB and wlaTC mutants displayed reduced adherence to chicken embryo fibroblasts. All mutants were less invasive of human cells than 81116 confirming the role of intact LOS during invasion of human cells in vitro. Here we propose the general composition for the 81116 LOS core backbone based on capillary electrophoresis-mass spectrometry.

Identification of genes involved in the acetamidino group modification of the flagellin N-linked glycan of Methanococcus maripaludis

N-linked glycosylation of protein is a posttranslational modification found in all three domains of life. The flagellin proteins of the archaeon Methanococcus maripaludis are known to be modified with an N-linked tetrasaccharide consisting of N-acetylgalactosamine (GalNAc), a diacetylated glucuronic acid (GlcNAc3NAc), an acetylated and acetamidino-modified mannuronic acid with a substituted threonine group (ManNAc3NAmA6Thr), and a novel terminal sugar residue [(5S)-2-acetamido-2,4-dideoxy-5-O-methyl-α-L-erythro-hexos-5-ulo-1,5-pyranose]. To identify genes involved in biosynthesis of the component sugars of this glycan, three genes, mmp1081, mmp1082, and mmp1083, were targeted for in-frame deletion, based on their annotation and proximity to glycosyltransferase genes known to be involved in assembly of the glycan. Mutants carrying a deletion in any of these three genes remained flagellated and motile. A strain with a deletion of mmp1081 had lower-molecular-mass flagellins in Western blots. Mass spectrometry of purified flagella revealed a truncated glycan with the terminal sugar absent and the threonine residue and the acetamidino group missing from the third sugar. No glycan modification was seen in either the Δmmp1082 or Δmmp1083 mutant grown in complex Balch III medium. However, a glycan identical to the Δmmp1081 glycan was observed when the Δmmp1082 or Δmmp1083 mutant was grown under ammonia-limited conditions. We hypothesize that MMP1082 generates ammonia and tunnels it through MMP1083 to MMP1081, which acts as the amidotransferase, modifying the third sugar residue of the M. maripaludis glycan with the acetamidino group.

Motility and chemotaxis in Campylobacter and Helicobacter

Flagellar motility of Campylobacter jejuni and Helicobacter pylori influences host colonization by promoting migration through viscous milieus such as gastrointestinal mucus. This review explores mechanisms C. jejuni and H. pylori employ to control flagellar biosynthesis and chemotactic responses. These microbes tightly control the activities of σ(54) and σ(28) to mediate ordered flagellar gene expression. In addition to phase-variable and posttranslational mechanisms, flagellar biosynthesis is regulated spatially and numerically so that only a certain number of organelles are placed at polar sites. To mediate chemotaxis, C. jejuni and H. pylori combine basic chemotaxis signal transduction components with several accessory proteins. H. pylori is unusual in that it lacks a methylation-based adaptation system and produces multiple CheV coupling proteins. Chemoreceptors in these bacteria contain nonconserved ligand binding domains, with several chemoreceptors matched to environmental signals. Together, these mechanisms allow for swimming motility that is essential for colonization.

Protein glycosylation in Helicobacter pylori: beyond the flagellins?

Glycosylation of flagellins by pseudaminic acid is required for virulence in Helicobacter pylori. We demonstrate that, in H. pylori, glycosylation extends to proteins other than flagellins and to sugars other than pseudaminic acid. Several candidate glycoproteins distinct from the flagellins were detected via ProQ-emerald staining and DIG- or biotin- hydrazide labeling of the soluble and outer membrane fractions of wild-type H. pylori, suggesting that protein glycosylation is not limited to the flagellins. DIG-hydrazide labeling of proteins from pseudaminic acid biosynthesis pathway mutants showed that the glycosylation of some glycoproteins is not dependent on the pseudaminic acid glycosylation pathway, indicating the existence of a novel glycosylation pathway. Fractions enriched in glycoprotein candidates by ion exchange chromatography were used to extract the sugars by acid hydrolysis. High performance anion exchange chromatography with pulsed amperometric detection revealed characteristic monosaccharide peaks in these extracts. The monosaccharides were then identified by LC-ESI-MS/MS. The spectra are consistent with sugars such as 5,7-diacetamido-3,5,7,9-tetradeoxy-L-glycero-L-manno-nonulosonic acid (Pse5Ac7Ac) previously described on flagellins, 5-acetamidino-7-acetamido-3,5,7,9-tetradeoxy-L-glycero-L-manno-nonulosonic acid (Pse5Am7Ac), bacillosamine derivatives and a potential legionaminic acid derivative (Leg5AmNMe7Ac) which were not previously identified in H. pylori. These data open the way to the study of the mechanism and role of protein glycosylation on protein function and virulence in H. pylori.

Genomic and metabolic profiling of nonulosonic acids in Vibrionaceae reveal biochemical phenotypes of allelic divergence in Vibrio vulnificus

Nonulosonic acids (NulOs) encompass a large group of structurally diverse nine-carbon backbone α-keto sugars widely distributed among the three domains of life. Mammals express a specialized version of NulOs called sialic acids, which are displayed in prominent terminal positions of cell surface and secreted glycoconjugates. Within bacteria, the ability to synthesize NulOs has been demonstrated in a number of human pathogens and is phylogenetically widespread. Here we examine the distribution, diversity, evolution, and function of NulO biosynthesis pathways in members of the family Vibrionaceae. Among 27 species of Vibrionaceae examined at the genomic level, 12 species contained nab gene clusters. We document examples of duplication, divergence, horizontal transfer, and recombination of nab gene clusters in different Vibrionaceae lineages. Biochemical analyses, including mass spectrometry, confirmed that many species do, in fact, produce di-N-acetylated NulOs. A library of clinical and environmental isolates of Vibrio vulnificus served as a model for further investigation of nab allele genotypes and levels of NulO expression. The data show that lineage I isolates produce about 20-fold higher levels of NulOs than lineage II isolates. Moreover, nab gene alleles found in a subset of V. vulnificus clinical isolates express 40-fold higher levels of NulOs than nab alleles associated with environmental isolates. Taken together, the data implicate the family Vibrionaceae as a "hot spot" of NulO evolution and suggest that these molecules may have diverse roles in environmental persistence and/or animal virulence.

Flagellar glycosylation in Burkholderia pseudomallei and Burkholderia thailandensis

Glycosylation of proteins is known to impart novel physical properties and biological roles to proteins from both eukaryotes and prokaryotes. In this study, gel-based glycoproteomics were used to identify glycoproteins of the potential biothreat agent Burkholderia pseudomallei and the closely related but nonpathogenic B. thailandensis. Top-down and bottom-up mass spectrometry (MS) analyses identified that the flagellin proteins of both species were posttranslationally modified by novel glycans. Analysis of proteins from two strains of each species demonstrated that B. pseudomallei flagellin proteins were modified with a glycan with a mass of 291 Da, while B. thailandensis flagellin protein was modified with related glycans with a mass of 300 or 342 Da. Structural characterization of the B. thailandensis carbohydrate moiety suggests that it is an acetylated hexuronic acid. In addition, we have identified through mutagenesis a gene from the lipopolysaccharide (LPS) O-antigen biosynthetic cluster which is involved in flagellar glycosylation, and inactivation of this gene eliminates flagellar glycosylation and motility in B. pseudomallei. This is the first report to conclusively demonstrate the presence of a carbohydrate covalently linked to a protein in B. pseudomallei and B. thailandensis, and it suggests new avenues to explore in order to examine the marked differences in virulence between these two species.