This study investigated the effect of high-fiber-low-protein
(HF)
and high-protein-low-fiber (HP) diets on microbial catabolism of tryptophan
in the proximal colon (PC) and distal colon(DC) compartments of the
Simulator of the Human Intestinal Microbial Ecosystem. The microbiota
in PC and DC was dominated by Bacteroidetes and Firmicutes, in which
Bacteroidetes were more abundant in DC (∼60% versus 50%) and
Firmicutes were more abundant in PC (∼40% versus 25%). Most
of the tryptophan catabolites were determined at a higher concentration
in PC samples than in DC samples, but the overall concentration of
tryptophan catabolites was over 10-fold higher in DC samples than
that in PC samples. Interestingly, indole-3-propionic acid and oxindole
were only identified in DC samples. A two-week dietary intervention
by the HF diet enriched the abundance of Firmicutes in PC, whereas
the HP diet enriched the abundance of Proteobacteria. Compared to
the HP diet, the HF diet favored the microbial production of indole-3-acetic
acid, indole-3-lactic acid, indole-3-aldehyde, and indole-3-propionic
acid in both PC and DC compartments. To conclude, these findings increase
the understanding of the effect of diets on the microbial production
of tryptophan catabolites in the colon.