Fig. 2: Carbohydrate supplementation inhibits indole production in faecal cultures.
a, Schematic representation of tryptophanase-mediated catabolism of tryptophan to produce indole, pyruvate and ammonia. b–d, Concentrations of indole (b), Trp (c) and ILA (d) in the faecal culture supernatants after cultivation in YCFA medium supplemented with 0.05%, 0.1% or 0.2% glucose, maltose and cellobiose, collectively referred to as GMC. One infant faecal sample (23.11) was selected for cultivation in three replicates as it contained both ILA and IPA producers (for example, P. anaerobius and Bifidobacterium longum) and indole producers (Escherichia). Metabolites were normalized to the final OD600 of the culture in the individual culture supernatants. Results are the mean ± s.d. of three independent experiments. Statistical analysis was done using a two-tailed unpaired t-test comparing lowest and highest GMC concentrations, with *P < 0.05; **P < 0.01 (indole, P = 0.0061; Trp, P = 0.0126; ILA, P = 0.0456). Individual replicates and their 16S rRNA profiles are shown in Extended Data Fig. 3.
