Cells from all domains of life express glycan structures attached to lipids and proteins on their surface, called glycoconjugates. Cell-to-cell contact mediated by glycan:glycan interactions have been considered to be low-affinity interactions that precede high-affinity protein–glycan or protein–protein interactions. In several pathogenic bacteria, truncation of surface glycans, lipooligosaccharide (LOS), or lipopolysaccharide (LPS) have been reported to significantly reduce bacterial adherence to host cells. Here, we show that the saccharide component of LOS/LPS have direct, high-affinity interactions with host glycans. Glycan microarrays reveal that LOS/LPS of four distinct bacterial pathogens bind to numerous host glycan structures. Surface plasmon resonance was used to determine the affinity of these interactions and revealed 66 high-affinity host–glycan:bacterial–glycan pairs with equilibrium dissociation constants (K_D) ranging between 100 nM and 50 µM. These glycan:glycan affinity values are similar to those reported for lectins or antibodies with glycans. Cell assays demonstrated that glycan:glycan interaction-mediated bacterial adherence could be competitively inhibited by either host cell or bacterial glycans. This is the first report to our knowledge of high affinity glycan:glycan interactions between bacterial pathogens and the host. The discovery of large numbers of glycan:glycan interactions between a diverse range of structures suggests that these interactions may be important in all biological systems. Significance Pathogens use cell surface carbohydrates as a means of attachment to host tissues. In several pathogenic bacteria, truncation of surface carbohydrates, lipooligosaccharide, or lipopolysaccharide have been reported to significantly reduce bacterial adherence to host cells. Here, we show that the lipooligosaccharide/lipopolysaccharide of four distinct bacterial pathogens bind directly to a range of host glycans. Surface plasmon resonance data confirmed binding among 66 different host–glycan:bacterial–glycan pairs. We also demonstrated that bacterial adherence can be competitively inhibited by either host cell or bacterial glycans. Our discovery of high-affinity glycan:glycan interactions in infectious disease may provide new approaches for therapy and prevention. The discovery of the existence of extensive, high-affinity interactions between glycans will alter the perception of the importance of these macromolecular interactions in all biological systems.

Phase-variation of genes is defined as the rapid and reversible switching of expression — either ON-OFF switching or the expression of multiple allelic variants. Switching of expression can be achieved by a number of different mechanisms. Phase-variable genes typically encode bacterial surface structures, such as adhesins, pili, and lipooligosaccharide, and provide an extra contingency strategy in small-genome pathogens that may lack the plethora of ‘sense-and-respond’ gene regulation systems found in other organisms. Many bacterial pathogens also encode phase-variable DNA methyltransferases that control the expression of multiple genes in systems called phasevarions (phase-variable regulons). The presence of phase-variable genes allows a population of bacteria to generate a number of phenotypic variants, some of which may be better suited to either colonising certain host niches, surviving a particular environmental condition and/or evading an immune response. The presence of phase-variable genes complicates the determination of an organism's stably expressed antigenic repertoire; many phase-variable genes are highly immunogenic, and so would be ideal vaccine candidates, but unstable expression due to phase-variation may allow vaccine escape. This review will summarise our current understanding of phase-variable genes that switch expression by a variety of mechanisms, and describe their role in disease and pathobiology.

A rare chemotaxis receptor, Tlp11, has been previously identified in invasive strains of Campylobacter jejuni, the most prevalent cause of bacterial gastroenteritis worldwide. Here we use glycan and small-molecule arrays, as well as surface plasmon resonance, to show that Tlp11 specifically interacts with galactose. Tlp11 is required for the chemotactic response of C. jejuni to galactose, as shown using wild type, allelic inactivation and addition mutants. The inactivated mutant displays reduced virulence in vivo, in a model of chicken colonization. The Tlp11 sensory domain represents the first known sugar-binding dCache_1 domain, which is the most abundant family of extracellular sensors in bacteria. The Tlp11 signalling domain interacts with the chemotaxis scaffolding proteins CheV and CheW, and comparative genomic analysis indicates a likely recent evolutionary origin for Tlp11. We propose to rename Tlp11 as CcrG, Campylobacter ChemoReceptor for Galactose.

Campylobacter jejuni is the leading cause of bacterial gastroenteritis in the developed world. Cases of Campylobacteriosis are common, as the organism is an avian commensal and is passed on to humans through contaminated poultry meat, water, and food preparation areas. Although typically a fastidious organism, C. jejuni can survive outside the avian intestinal tract until it is able to reach a human host. It has long been considered that biofilms play a key role in transmission of this pathogen. The aim of this review is to examine factors that trigger biofilm formation in C. jejuni. A range of environmental elements have been shown to initiate biofilm formation, which are then affected by a suite of intrinsic factors. We also aim to further investigate the role that biofilms may play in the life cycle of this organism.

Background: Chemotaxis is crucial for the colonisation/infection of hosts with Campylobacter jejuni. Central to chemotaxis are the group A chemotaxis genes that are responsible for sensing the external environment. The distribution of group A chemoreceptor genes, as found in the C. jejuni sequenced strains, tlp1-4, 7, 10 and 11 were determined in 33 clinical human and avian isolates. Results: Group A tlp gene content varied among the strains with genes encoding tlp1 (aspartate receptor, ccaA) and tlp7 present in all strains tested, where as tlp11 was present in only one of our international collection clinical isolates, C. jejuni 520, but was more prevalent (9/13) in the freshly isolated clinical stains from patients who required hospitalisation due to C. jejuni infection (GCH1-17). Relative expression levels of the group A tlp genes were also determined in C. jejuni reference strains NCTC 11168-GS, 11168-O and 81116 using cells grown in vitro at 37°C, 42°C and maintained at room temperature and with cells isolated directly from murine and avian hosts by immune magnetic separation without subsequent culture. Gene expression of tlp genes was varied based on strain, growth conditions and in vivo isolation source. Tlp1, although the most conserved, showed the lowest and most varied mRNA expression and protein production under laboratory conditions. Tlp7 was highly expressed at most conditions tested, and gene expression was not influenced by the tlp7 gene encoding a full length protein or one expressed as separate periplasmic and cytoplasmic domains. Conclusion: We have shown that chemosensory receptor set variation exists among C. jejuni strains, but is not dependent on the isolation source.

Biofilms of the gastroenteric pathogen C. jejuni may serve an important role in the transmission of infection from reservoirs of infection to humans. Herein, we undertook a combinatorial approach examining differential gene expression and protein abundance during biofilm formation in C. jejuni. Biofilms induced a substantial rearrangement of the C. jejuni transcriptome and proteome, with ~600 genes differentially expressed when compared to planktonic cells. Genes and proteins induced in biofilms were involved in iron metabolism and acquisition, cell division, glycan production and attachment, while those repressed were associated with metabolism, amino acid usage, and large tracts of the chemotaxis pathway. We further examined the role of chemotaxis in C. jejuni biofilm formation by examining isogenic strains with deletions of the cheV and cheW signal transduction genes. Both ∆cheV and ∆cheW exhibited a significant decrease in directed motility when compared to wild-type C. jejuni as well as demonstrating an increase in autoagglutination ability and biofilm formation. A subtle difference was also observed between the phenotypes of ∆cheV and ∆cheW mutants, both in motility and biofilm formation. This suggests roles for CheV and CheW and may present signal transduction as a potential method for modulating C. jejuni biofilm formation.