Helicobacter pylori lipopolysaccharide is synthesized via a novel pathway with an evolutionary connection to protein N-glycosylation.

Lipopolysaccharide (LPS) is a major component on the surface of Gram negative bacteria and is composed of lipid A-core and the O antigen polysaccharide. O polysaccharides of the gastric pathogen Helicobacter pylori contain Lewis antigens, mimicking glycan structures produced by human cells. The interaction of Lewis antigens with human dendritic cells induces a modulation of the immune response, contributing to the H. pylori virulence. The amount and position of Lewis antigens in the LPS varies among H. pylori isolates, indicating an adaptation to the host. In contrast to most bacteria, the genes for H. pylori O antigen biosynthesis are spread throughout the chromosome, which likely contributed to the fact that the LPS assembly pathway remained uncharacterized. In this study, two enzymes typically involved in LPS biosynthesis were found encoded in the H. pylori genome; the initiating glycosyltransferase WecA, and the O antigen ligase WaaL. Fluorescence microscopy and analysis of LPS from H. pylori mutants revealed that WecA and WaaL are involved in LPS production. Activity of WecA was additionally demonstrated with complementation experiments in Escherichia coli. WaaL ligase activity was shown in vitro. Analysis of the H. pylori genome failed to detect a flippase typically involved in O antigen synthesis. Instead, we identified a homolog of a flippase involved in protein N-glycosylation in other bacteria, although this pathway is not present in H. pylori. This flippase named Wzk was essential for O antigen display in H. pylori and was able to transport various glycans in E. coli. Whereas the O antigen mutants showed normal swimming motility and injection of the toxin CagA into host cells, the uptake of DNA seemed to be affected. We conclude that H. pylori uses a novel LPS biosynthetic pathway, evolutionarily connected to bacterial protein N-glycosylation.

Entry exclusion in the IncHI1 plasmid R27 is mediated by EexA and EexB.

Conjugative plasmids have evolved entry exclusion mechanisms to inhibit redundant DNA transfer from donor cells into recipients harboring isogenic or closely related plasmids. This exclusion phenomenon has been documented in the incompatibility H group (IncH) plasmid R27. A cosmid library representing the majority of the large (180kb) R27 plasmid was transformed into recipient cells and a conjugation assay identified that an operon located in the conjugative transfer region 2 (Tra2) of R27, the Z operon, mediated entry exclusion in the IncH plasmid. Reverse-transcriptase analysis revealed that the Z operon is comprised of four genes, 015, eexB, 017, and eexA. Sub-cloning of the individual genes located within the Z operon and subsequent screening for the entry exclusion phenotype determined that two genes, eexA and eexB, independently inhibit the entry of IncH-related plasmids. Bacterial fractionation studies predominantly localized the EexA protein to the cytoplasmic membrane, and the EexB protein to the outer membrane. Recipient cells expressing EexA and EexB were unable to exclude the entry of R27 plasmids harboring mutations within the IncH entry exclusion genes eexA and eexB. The IncH entry exclusion proteins EexA and EexB likely prevent redundant plasmid transfer by interaction with one another.