Research from the University of Gothenburg, Sweden, clarifies the complex interaction between gut bacteria and irritable bowel syndrome. Experiments demonstrate that gut bacteria can produce the important substance serotonin. The finding may lead to new future treatments.
Irritable bowel syndrome (IBS), is a common gastrointestinal disorder, more common, in women, with symptoms such as abdominal pain, constipation or diarrhoea. The cause of the disease is not clear, but the intestinal environment including the gut microbiota and serotonin appear to be important factors.
Serotonin is best known as a neurotransmitter in the brain, but over 90% of the body's serotonin is produced in the gut, where it controls bowel movements via the enteric nervous system, sometimes called the ‘gut-brain’. Previous research has shown that the bacteria in the gut, the gut microbiota, affects how much serotonin is produced by the host, but until now it has been unclear whether gut bacteria themselves can form biologically active serotonin.
In the current study, published in the journal Cell Reports, the researchers have identified two bacteria that together can produce serotonin: Limosilactobacillus mucosae and Ligilactobacillus ruminis. When the bacteria were introduced into germ-free mice with serotonin deficiency, the levels of serotonin in the gut increased, as did the density of nerve cells in the colon. The bacteria also normalized the intestinal transit time.
“It is incredibly fascinating how the gut bacteria can produce bioactive signalling molecules that affect health,” says Fredrik Bäckhed, Professor of molecular medicine at Sahlgrenska Academy at the University of Gothenburg, and one of the leading authors of the study.
The researchers were also able to see that people with IBS had lower levels of one of the bacteria (L. mucosae) in their stool compared to healthy individuals, and that this bacterium also has the enzyme required for serotonin production.
Magnus Simrén is a Professor of Medical Gastroenterology at Sahlgrenska Academy at the University of Gothenburg: “Our results indicate that certain intestinal bacteria can produce bioactive serotonin and thus play an important role in intestinal health and open new avenues for the treatment of functional gastrointestinal disorders such as IBS,” he says.
“Our findings indicate that intestinal bacteria can form signalling substances such as serotonin, which may be the key to understanding how the intestine and its inhabitants can affect our brain and the behaviour,” concludes Fredrik Bäckhed.
Pictured above are study authors Fredrik Bäckhed and Magnus Simrén, Sahlgrenska Academy at the University of Gothenburg.
- Moretti CH, Grasset E, Zhu J, et al. Identification of human gut bacteria that produce bioactive serotonin and promote colonic innervation. Cell Reports. 2025 Oct 20. doi:10.1016/j.celrep.2025.116434. Online ahead of print.