Fig. 4: Dietary fibre and tryptophan supplementation modulates production of tryptophan metabolites by a defined community in vivo.
a, Schematic representation of the experimental plan to evaluate the effect of dietary tryptophan and pectin on the production of tryptophan metabolites in vivo. GF mice were placed in four groups (n = 5 per group) and fed a diet containing 2 g kg−1 tryptophan and 50 g kg−1 pectin for 7 days for adaptation. They were then orally gavaged with a mixed culture of E. coli, B. thetaiotaomicron and C. sporogenes in equal amounts (OD600) and remained for another 7 days on the same diet for stabilization. The diets were then changed; the mice were fed a diet with either 2 g kg−1 or 16 g kg−1 tryptophan, with or without 50 g kg−1 pectin for two more weeks. Diet compositions are described in Supplementary Table 1. Samples were collected as shown in the scheme. b, The 16S rRNA gene sequencing profiles show the composition of the defined community in the caecum of each mouse in the four groups, overlaid with indole values measured in the individual caeca. c, Absolute concentrations of indole in caeca. d, Indole concentration in the caeca, normalized to the relative abundance of E. coli. e, Absolute concentrations of Trp, ILA, IAcrA and IPA in serum. f, Serum tryptophan metabolites (ILA, IAcrA and IPA) normalized to C. sporogenes relative abundance in caecum. For c, lines and error bars indicate means and standard deviations, respectively; for d–f, lines and error bars indicate medians and interquartile ranges (IQRs), respectively. Statistical analysis was done across groups within each metabolite measured using one-way ANOVA (c) or Kruskal–Wallis tests (d–f), using uncorrected Fisher’s LSD or Dunn’s post hoc tests (two tailed) to compare between individual groups. For c–f, n = 5 mice samples per group were used for statistical analysis. However, for e and f, one value for tryptophan and ILA was excluded as an extreme outlier (Grubbs test, alpha < 0.01). P values are shown in the figure panels. Panel a was created with BioRender.com.
