UDP-glucuronic acid decarboxylases of Bacteroides fragilis and their prevalence in bacteria.

Xylose is rarely described as a component of bacterial glycans. UDP-xylose is the nucleotide-activated form necessary for incorporation of xylose into glycans and is synthesized by the decarboxylation of UDP-glucuronic acid (UDP-GlcA). Enzymes with UDP-GlcA decarboxylase activity include those that lead to the formation of UDP-xylose as the end product (Uxs type) and those synthesizing UDP-xylose as an intermediate (ArnA and RsU4kpxs types). In this report, we identify and confirm the activities of two Uxs-type UDP-GlcA decarboxylases of Bacteroides fragilis, designated BfUxs1 and BfUxs2. Bfuxs1 is located in a conserved region of the B. fragilis genome, whereas Bfuxs2 is in the heterogeneous capsular polysaccharide F (PSF) biosynthesis locus. Deletion of either gene separately does not result in the loss of a detectable phenotype, but deletion of both genes abrogates PSF synthesis, strongly suggesting that they are functional paralogs and that the B. fragilis NCTC 9343 PSF repeat unit contains xylose. UDP-GlcA decarboxylases are often annotated incorrectly as NAD-dependent epimerases/dehydratases; therefore, their prevalence in bacteria is underappreciated. Using available structural and mutational data, we devised a sequence pattern to detect bacterial genes encoding UDP-GlcA decarboxylase activity. We identified 826 predicted UDP-GlcA decarboxylase enzymes in diverse bacterial species, with the ArnA and RsU4kpxs types confined largely to proteobacterial species. These data suggest that xylose, or a monosaccharide requiring a UDP-xylose intermediate, is more prevalent in bacterial glycans than previously appreciated. Genes encoding BfUxs1-like enzymes are highly conserved in Bacteroides species, indicating that these abundant intestinal microbes may synthesize a conserved xylose-containing glycan.

Immunochemical characterization of polysaccharide antigens from six clinical strains of Enterococci.

BACKGROUND: Enterococci have become major nosocomial pathogens due to their intrinsic and acquired resistance to a broad spectrum of antibiotics. Their increasing drug resistance prompts us to search for prominent antigens to develop vaccines against enterococci. Given the success of polysaccharide-based vaccines against various bacterial pathogens, we isolated and characterized the immunochemical properties of polysaccharide antigens from five strains of Enterococcus faecalis and one strain of vancomycin-resistant E. faecium. RESULTS: We cultured large batches of each strain, isolated sufficient quantities of polysaccharides, analyzed their chemical structures, and compared their antigenic specificity. Three classes of polysaccharides were isolated from each strain, including a polyglucan, a teichoic acid, and a heteroglycan composed of rhamnose, glucose, galactose, mannosamine, and glucosamine. The polyglucans from all six strains are identical and appear to be dextran. Yields of the teichoic acids were generally low. The most abundant polysaccharides are the heteroglycans. The six heteroglycans are structurally different as evidenced by NMR spectroscopy. They also differ in their antigenic specificities as revealed by competitive ELISA. The heteroglycans are not immunogenic by themselves but conjugation to protein carriers significantly enhanced their ability to induce antibodies. CONCLUSION: The six clinical strains of enterococci express abundant, strain-specific cell-surface heteroglycans. These polysaccharides may provide a molecular basis for serological typing of enterococcal strains and antigens for the development of vaccines against multi-drug resistant enterococci.

Cellular and humoral immunity are synergistic in protection against types A and B Francisella tularensis.

Herein we report studies with a novel combination vaccine that, when administered to mice, conferred protection against highly virulent strains of Francisella tularensis by stimulating both arms of the immune system. Our earlier studies with Ft.LVS::wbtA, an O-polysaccharide (OPS)-negative mutant derived from the available live vaccine strain of F. tularensis (Ft.LVS), elucidated the role of antibodies to the OPS - a key virulence determinant - in protection against virulent type A organisms. However, when expressed on the organism, the OPS enhances virulence. In contrast, in purified form, the OPS is completely benign. We hypothesized that a novel combination vaccine containing both a component that induces humoral immunity and a component that induces cellular immunity to this intracellular microbe would have an enhanced protective capacity over either component alone and would be much safer than the LVS vaccine. Thus we developed a combination vaccine containing both OPS (supplied in an OPS-tetanus toxoid glycoconjugate) to induce a humoral antibody response and strain Ft.LVS::wbtA (which is markedly attenuated by its lack of OPS) to induce a cell-mediated protective response. This vaccine protected mice against otherwise-lethal intranasal and intradermal challenge with wild-type F. tularensis strains Schu S4 (type A) and FSC 108 (type B). These results represent a significant advance in our understanding of immunity to F. tularensis and provide important insight into the development of a safer vaccine effective against infections caused by clinical type A and B strains of F. tularensis.

Human symbionts use a host-like pathway for surface fucosylation.

The mammalian intestine harbors a beneficial microbiota numbering approximately 10(12) organisms per gram of colonic content. The host tolerates this tremendous bacterial load while maintaining the ability to efficiently respond to pathogenic organisms. In this study, we show that the Bacteroides use a mammalian-like pathway to decorate numerous surface capsular polysaccharides and glycoproteins with l-fucose, an abundant surface molecule of intestinal epithelial cells, resulting in the coordinated expression of this surface molecule by host and symbiont. A Bacteroides mutant deficient in the ability to cover its surface with L-fucose is defective in colonizing the mammalian intestine under competitive conditions.