Tryptophan regulates bile and nitrogen metabolism in two pig gut lactobacilli species in vitro based on metabolomics study.

Research has demonstrated that tryptophan (Trp) regulated the composition and metabolism of the gut microbiota. However, the detailed mode of action of Trp on the metabolism of intestinal commensal lactobacilli has not been well characterized. This study aimed to compare the effects of Trp concentration (0.2, 0.4, 0.6 mmol/L) in the media on the metabolism of Lactobacillus amylovorus and Limosilactobacillus mucosae isolated from the small intestine of piglets in vitro by high-performance liquid chromatography and metabolomics study. Results showed that increased Trp concentration increased (P < 0.05) net utilization of lysine, methionine, tryptophan, asparagine/aspartate, glutamine/glutamate, however, increased net production of glycine and taurine in Lac. amylovorus. In contrast, increased Trp concentration decreased (P < 0.05) net utilization of leucine, phenylalanine, and serine and increased (P < 0.05) net utilization of arginine and net production of ornithine and glycine in Lim. mucosae. Targeted metabolomics analysis showed that increased Trp concentration promoted (P < 0.05) the production of indole-3-lactic acid and 3-indoleacetic acid in the two lactobacilli strains. Increased concentration of Trp increased (P < 0.01) glycochenodeoxycholic acid metabolism in Lim. mucosae and glycocholic acid and taurocholic acid metabolism in Lac. amylovorus. Untargeted metabolomics analysis showed that metabolic pathways related to phenylalanine and tryptophan metabolism, and nicotinate and nicotinamide metabolism were regulated by Trp in Lim. mucosae. These findings will help develop new biomarkers and dietary strategies to maintain the functionality of the gut microbiota aiming at improving the nutrition and health of both humans and animals.