Fig. 3: Tryptophan and fibre supplementation alters production of tryptophan metabolites in a defined community of gut microorganisms in vitro.
Tryptophan metabolites produced by the defined community in vitro. E. coli was selected as the major indole producer, B. thetaiotaomicron was selected as the fibre degrader and C. sporogenes was selected because of its ability to generate Stickland fermentation products. a–d, Concentrations of ILA (a), IPA (b), indole (c) and Trp (d) in the supernatants of the defined community cultured in mGAM supplemented with either 0.02% or 0.05% free tryptophan and with or without 0.5% apple pectin. Bars and error lines indicate the mean ± s.d. of three independent biological replicates. Statistical analysis was done using the Brown–Forsythe ANOVA test using an unpaired two-tailed t-test with Welch’s correction. Only two replicates are shown in the group of 0.02% Trp without pectin for ILA, IPA and Trp owing to technical issues during analysis. e, Relative expression from RT-qPCR targeting tnaA mRNA in E. coli in response to tryptophan and pectin supplementation. f, Relative expression from RT-qPCR targeting mRNAs of arabinose-utilizing genes (araA and araF), rhamnose-utilizing genes (rhaA and rhaT) and xylose-utilizing genes (xylA and xylG) in E. coli in response to tryptophan and pectin supplementation. Total RNA was extracted from early stationary phase cultures (∼1 OD), and mRNA levels were measured as described in Methods and reported as relative difference (fold change) to the 0.02% Trp condition. Results are the mean ± s.e.m. of three independent experiments. Unpaired two-tailed t-tests were performed on the expression ratios to determine the statistical significance of the relative expression differences. P values are shown in the figure panels.
