Human gut-associated Bifidobacterium species salvage exogenous indole, a uremic toxin precursor, to synthesize indole-3-lactic acid via tryptophan

Figures & data

Figure 1. Consumption of exogenously added indole by selected bifidobacterial strains.

A. A possible route of TrpB- and ALDH-positive bifidobacteria to consume exogenous indole. B. The concentration of indole in the culture supernatants of selected Bifidobacterium strains grown in MRS medium supplemented with the spent medium of a TIL-positive E. coli. Non-inoculated medium was used as a control. Values of three biological replicates were plotted, while bars represent the mean. See Supplementary Table S5 and Source Data for plot data and statistical values.

Figure 2. Bifidobacterial bioconversion of indole to ILA occurs with Trp as an intermediate.

a and b, Concentrations of ILA (green bars) and Trp (blue bars) with m/z of [M + 1 + H]⁺ values in the supernatants of cell suspensions after incubation for 3 h with and without 4 μM of (2-¹³C)-indole plus l-serine. Values of three biological replicates were plotted, with bars representing the mean. See Supplementary Tables S6 (for a), S7 and S8 (for b), and Source Data (for a and b) for plot data and statistical values. a, Overnight cultures of the selected bifidobacterial strains grown in MRS medium were centrifuged, and the harvested cells suspended in PBS were used for the reactions. b, Cell suspensions of WT, trpB, and aldh strains were similarly prepared and used for the reactions.