A199 UTILIZATION OF MUCUS-DERIVED O-GLYCAN SUGARS BY THE PATHOGEN C. RODENTIUM FACILITATE ITS COLONIZATION OF THE MURINE GUT

Background

The ability of enteric pathogens to colonize and expand within the mammalian gastrointestinal (GI) tract is determined by several factors, including the ability to find and acquire nutrients. The thick mucus layer that lines the inner surface of the large intestine is rich in sugars that can serve as nutrient sources for several members of the microbiota. Whether these sugars can also be used by invading bacterial pathogens to colonize the GI tract is still unclear, in particular for the family of attaching and effacing (A/E) bacterial pathogens, including the human diarrheal pathogens EHEC and EPEC.

Aims

To investigate the ability of the murine A/E pathogen Citrobacter rodentium to use mucin-derived sugars as a nutrient source, and the importance of these sugars in the virulence of C. rodentium during in-vivo infection.

Methods

To identify which sugar(s) are required for C. rodentium to colonize and grow in the murine GI tract, we generated mutants lacking single or multiple genes involved in the uptake and catabolism of mucin-derived O-glycan sugars. This was followed by in-vitro growth assays in minimal media supplemented with mucin sugars to investigate the growth properties of C. rodentium and the generated mutants on mucin sugars.

Results

We determined that C. rodentium was able to use three mucin O-glycan sugars: sialic acid, galactose, and N-acetylglucosamine (GlcNAc) as both carbon and nitrogen sources for in-vitro growth. C. rodentium exhibited the maximal growth rate and density on GlcNAc, followed by sialic acid, and finally galactose. A mutant C. rodentium strain carrying a deletion in the nagA gene was unable to grow on both GlcNAc and sialic acid, confirming that the breakdown pathways for these two sugars merge and are processed by shared suite of enzymes. As for galactose, combined deletions in the genes mglB and galP were required to abolish growth on this sugar. Notably, a mutant strain carrying simultaneous deletions in nagA, mglB, and galP was unable to grow on all three mucin sugars, as well as on purified mucin.

Conclusions

Our results demonstrate that intestinal mucin sugars serve as potential nutrient sources for C. rodentium and that C. rodentium can catabolize three of these sugars. Future work will examine whether these sugar pathways contribute to C. rodentium colonization of the murine GI tract.

Funding Agencies

CCC, CIHRCH.I.L.D. Fdn

A51 UTILIZING MUCIN-DERIVED SUGARS CONFERS A FITNESS ADVANTAGE TO THE ENTERIC PATHOGEN CITROBACTER RODENTIUM THAT PROMOTES INTESTINAL COLONIZATION

Background

Citrobacter rodentium is an enteric murine pathogen used to model the human diarrheal pathogens. Following inoculation, C. rodentium colonizes the mouse cecum where it expands and ultimately spreads to the distal colon. During this process, C. rodentium has to compete with commensal microbes for available nutrients. Moreover, to spread throughout the gut, and infect the intestinal epithelium, C. rodentium has to cross through, and or dwell within the intestinal mucus layer which is composed of the heavily glycosylated protein Muc2. Muc-2 is glycosylated and coated by 5 distinct terminal sugar residues: galactose, N-acetylgalactosamine, N-acetylglucosamine, fucose, and sialic acid. Many commensal microbes have the ability to cleave and free these sugars from the Muc2 protein, releasing them for their own consumption, however pathogens appear to exploit this process. While studies have indicated that C. rodentium uses these terminal sugar residues as a nutritional source, their relative importance in the pathogenic strategy of C. rodentium (and other gut pathogens) remains unclear

Aims

Investigate the role played by mucin sugar residues in controlling C. rodentium pathogenesis

Methods

Deletions of agaW, nagE, mglB, galP, fucK, and nanT were generated on the chromosome of C. rodentium (Strepr) by overlap extension PCR. Growth assays were performed to examine the growth kinetics of mutants C. rodentium in minimal (M9) media supplemented with one of the 5 mucin sugars or M9 with whole mucin as control. Specific pathogen free (SPF) C57BL/6 mice, or germfree C57BL/6 mice were orally gavaged with wildtype C. rodentium (Strepr) or one of ΔagaW, ΔnagE, ΔmglB, ΔgalP, ΔfucK, or ΔnanT strains. Mice were euthanized at 6 days post-infection, and the cecum, colon, and spleen were collected and histologically scored for pathology and intestinal and systemic bacterial burden. Stool samples were collected throughout the 6 days to quantify C. rodentium burdens

Results

Growth assays confirmed that the specific sugar transporter/kinase mutant C. rodentium strains grew normally when placed in media supplemented with whole mucin, or with most sugars, only showing overt defects in growth when solely supplemented with the sugar for which they were impaired. Several of the C. rodentium mutants including ΔnanT showed overt defects in colonization/infection of SPF C57BL/6 mice, but their pathogenesis was normalized in germfree mice, or in mice treated with the antibiotic streptomycin at each day post-infection. These findings indicate that the impact of mucin sugar utilization on C. rodentium virulence is microbiota-dependent

Conclusions

C. rodentium uses mucin sugars as nutrient source in the mouse gut, and an inability to use these sugars impairs their ability to infect their hosts in a microbiota dependent manner

Funding Agencies

CAG, CCC, CIHR, NRC