Overview
- Limosilactobacillus mucosae and Ligilactobacillus ruminis were identified as human gut microbes that produce biologically active serotonin.
- Serotonin synthesis arose via decarboxylation of 5‑hydroxytryptophan and appeared to require cooperation between the two species, as monocultures did not produce serotonin in vitro.
- In germ‑free mice with serotonin deficiency, co‑colonization elevated gut serotonin, increased colonic nerve‑cell density, and normalized intestinal transit time, with effects confined locally rather than in serum.
- In a human cohort, individuals with IBS showed lower stool abundance of L. mucosae than controls, while overall fecal and serum serotonin levels did not differ between groups.
- The peer‑reviewed findings expand prior observations that microbiota influence host serotonin by demonstrating direct microbial production, though mechanisms, safety, and clinical efficacy in humans remain unproven.