Human milk oligosaccharides (HMOs) shape the gut microbiota in infants by selectively stimulating the growth of bifidobacteria. Here, we investigated the impact of HMOs on adult gut microbiota and gut barrier function using the Simulator of the Human Intestinal Microbial Ecosystem (SHIME^®), Caco2 cell lines, and human intestinal gut organoid-on-chips. We showed that fermentation of 2’-O-fucosyllactose (2’FL), lacto-N-neotetraose (LNnT), and combinations thereof (MIX) led to an increase of bifidobacteria, accompanied by an increase of short chain fatty acid (SCFA), in particular butyrate with 2’FL. A significant reduction in paracellular permeability of FITC-dextran probe was observed using Caco2 cell monolayers with fermented 2’FL and MIX, which was accompanied by an increase in claudin-8 gene expression as shown by qPCR, and a reduction in IL-6 as determined by multiplex ELISA. Using gut-on-chips generated from human organoids derived from proximal, transverse, and distal colon biopsies (Colon Intestine-Chips), we showed that claudin-5 was significantly upregulated across all three gut-on-chips following treatment with fermented 2’FL under microfluidic conditions. Taken together, these data show that, in addition to their bifidogenic activity, HMOs have the capacity to modulate immune function and the gut barrier, supporting the potential of HMOs to provide health benefits in adults.

Ruminococcus gnavus is a human gut symbiont wherein the ability to degrade mucins is mediated by an intramolecular trans-sialidase (RgNanH). RgNanH comprises a GH33 catalytic domain and a sialic acid-binding carbohydrate-binding module (CBM40). Here we used glycan arrays, STD NMR, X-ray crystallography, mutagenesis and binding assays to determine the structure and function of RgNanH_CBM40 (RgCBM40). RgCBM40 displays the canonical CBM40 β-sandwich fold and broad specificity towards sialoglycans with millimolar binding affinity towards α2,3- or α2,6-sialyllactose. RgCBM40 binds to mucus produced by goblet cells and to purified mucins, providing direct evidence for a CBM40 as a novel bacterial mucus adhesin. Bioinformatics data show that RgCBM40 canonical type domains are widespread among Firmicutes. Furthermore, binding of R. gnavus ATCC 29149 to intestinal mucus is sialic acid mediated. Together, this study reveals novel features of CBMs which may contribute to the biogeography of symbiotic bacteria in the gut.

Significance: Gut bacteria play a key role in health and disease, but the molecular mechanisms underpinning their interaction with the host remain elusive. The serine-rich repeat proteins (SRRPs) are a family of adhesins identified in many Gram-positive pathogenic bacteria. We previously showed that beneficial bacterial species found in the gut also express SRRPs and that SRRP was required for the ability of Lactobacillus reuteri strain to colonize mice. Here, our structural and biochemical data reveal that L. reuteri SRRP adopts a β-solenoid fold not observed in other structurally characterized SRRPs and functions as an adhesin via a pH-dependent mechanism, providing structural insights into the role of these adhesins in biofilm formation of gut symbionts.

Background: Human milk oligosaccharide supplementation safely modulates fecal bifidobacteria abundance and holds the potential to manage symptoms in irritable bowel syndrome (IBS). Here, we aimed to determine the role of a 4:1 mix of 2′-O-fucosyllactose and lacto-N-neotetraose (2′FL/LNnT) on the modulation of the gut microbiota composition and host mucosal response, as well as the link between the bifidobacteria abundance and metabolite modulation, in IBS patients. Methods: Biological samples were collected from IBS patients (n = 58) at baseline and week 4 post-supplementation with placebo, 5 g or 10 g doses of 2′FL/LNnT. The gut microbiota composition, metabolite profiles and expression of genes related to host mucosal response were determined. Results: Moderate changes in fecal, but not mucosal, microbial composition (β-diversity) was observed during the intervention with higher dissimilarity observed within individuals receiving 10g 2′FL/LNnT compared to placebo. Both fecal and mucosal Bifidobacterium spp. increased after 2′FL/LNnT intake, with increased proportions of Bifidobacterium adolescentis and Bifidobacterium longum. Moreover, the intervention modulated the fecal and plasma metabolite profiles, but not the urine metabolite profile or the host mucosal response. Changes in the metabolite profiles were associated to changes in bifidobacteria abundance. Conclusion: Supplementation with 2′FL/LNnT modulated the gut microbiota, fecal and plasma metabolite profiles, but not the host mucosal response in IBS. Furthermore, the bifidogenic effect was associated with metabolite modulation. Overall, these findings support the assertion that 2′FL/LNnT supplementation modulate the intestinal microenvironment of patients with IBS, potentially related to health.

Background: Celiac disease is an enteropathy triggered by dietary gluten found in wheat, barley, and rye. The current treatment is a strict gluten-free diet. Quinoa is a highly nutritive plant from the Andes, with low concentrations of prolamins, that has been recommended as part of a gluten-free diet; however, few experimental data support this recommendation.