Food for thought! Host glycan availability influences the colonic microbiota

▸ Kashyap PC, Marcobal A, Ursell LK, et al. Genetically dictated change in host mucus carbohydrate landscape exerts a diet-dependent effect on the gut microbiota. PNAS 2013;110:17059–64.

The colonic environment is rich in nutrients including host-derived glycans and complex dietary polysaccharides that provide the gut microbiota with a relatively continuous nutrient supply. The consumption of glycans by intestinal bacteria is well documented; however, there is limited information detailing how changes in host glycan availability impact on the gut microbiota composition or function. Fucose residues are dominant in the mucin glycans of individuals who possess functional α1–2 fucosyltransferase (FUT2) gene. FUT2 gene is known as the secretor gene. Around 20% of humans lack functional copies of FUT2 and are therefore referred to as ‘non-secretors’. Secretor genotype has important implications in host–pathogen interactions with several pathogenic infections including Helicobacter pylori, Campylobacter jejuni, Vibrio cholerae and several viral infections affected by secretor status. Recent genome-wide association studies have implicated FUT2 in the pathogenesis of several conditions including Crohn's disease, primary sclerosing cholangitis, coeliac disease and type-1 diabetes. Non-secretors have increased susceptibility to these chronic inflammatory conditions and have also been associated with alterations in the gut microbiota. This recent study by Kashyap and colleagues employed germ-free Fut2^−/− mice to show that the gut microbiota is altered compositionally and functionally by changes in glycan availability. The study also demonstrated that switching dietary intake impacts on the microbiota composition. This indicates that diet can exert a dominant effect over host genetics. The findings reinforce the need to assess both host and dietary glycan function, as both have the ability to affect the gut microbiota. The findings also however emphasise the need to assess colonic nutrient reservoirs and host glycan expression profiles when considering potential dietary interventions which are intended to impact …