Fig. 6

ILA promotes the microbial synthesis of IPA and IAA. A Experimental scheme to examine the role of cross-feeding (n = 4). The intestinal microbiota was depleted by 2 weeks of antibiotic administration in the drinking water, followed by oral gavage of ArAT-deficient mutant (△L.R) or heat-killed L. reuteri for another 2 weeks with or without oral administration of 40 mg/kg ILA in the second week. Colitis was induced by adding 3% DSS in drinking water in the fifth week. Colitis severity was assessed by determining the changes in body weight (B) and colon length (C). The concentrations of IAA (D) and IPA (E) were measured in the colon contents. F Experimental scheme to evaluate the role of the intestinal microbiota on ILA-mediated synthesis of IPA and IAA. Mice were administered with or without a cocktail of antibiotics for 2 days, followed by induction of dysbiosis for a week (n = 7 or 8). Three different dysbiosis models were employed including 3% DSS in drinking water, antibiotic cocktail in drinking water, and oral daily challenged with 10⁸ CFU/ml C. rodentium. G Richness and Shannon Index of the colonic microbiota among different groups of mice on day 9. H PCoA plot of the Bray–Curtis distance. Comparisons of the concentrations of IAA (I) and IPA (J) in the colon contents among groups are shown (n = 5). *p < 0.05, **p < 0.01, ***p < 0.001, ****p < 0.0001; ns, not significant