Published May 2026 | Source: University of Gothenburg — Cell Reports
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Key Finding: Two gut bacteria — Limosilactobacillus mucosae and Ligilactobacillus ruminis — can independently produce bioactive serotonin. People with IBS had measurably lower levels of one of these bacteria, directly linking gut microbiome composition to serotonin signaling and mood.
We’ve known for years that roughly 90% of the body’s serotonin is produced in the gut. But a new study from the University of Gothenburg has gone further — identifying two specific gut bacteria that manufacture bioactive serotonin entirely on their own, reshaping our understanding of the gut-anxiety connection.
The discovery
Published in Cell Reports, the study identified Limosilactobacillus mucosae and Ligilactobacillus ruminis as serotonin producers. When introduced into mice with serotonin deficiency, these bacteria raised gut serotonin levels, increased colon nerve cell density, and normalized intestinal function. The human finding was equally striking: people with IBS had significantly lower levels of L. mucosae — the species carrying the serotonin-producing enzyme — compared to healthy individuals.
Why this matters for anxiety
Gut serotonin regulates intestinal movement, inflammation, and vagus nerve signaling. When it is disrupted, the effects travel upstream through the gut-brain axis, influencing mood, stress reactivity, and anxiety. Co-author Fredrik Bäckhed stated that “intestinal bacteria can form signaling substances such as serotonin, which may be the key to understanding how the intestine and its inhabitants can affect our brain and behavior.”
What supports these bacteria
L. mucosae is a Lactobacillus strain — the same family found in fermented foods and many probiotic supplements. Yogurt, kefir, sauerkraut, and kimchi support these populations. Tryptophan — serotonin’s precursor — comes from eggs, turkey, salmon, and pumpkin seeds. Fermented foods and tryptophan-rich nutrition create the conditions these bacteria need to thrive.
What this means for you
This research is still developing, but it adds compelling new evidence to the case for gut-focused natural anxiety support — and reinforces why diet and microbiome diversity matter for mental health, not just digestion.
Source: University of Gothenburg. Cell Reports, 2025. DOI: 10.1016/j.celrep.2025.02.xxx
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