Research from the University of Gothenburg has revealed a complex interaction between gut bacteria and Irritable Bowel Syndrome (IBS), which could lead to new future treatments for the disease.
The study, published in Cell Reports, demonstrated that gut bacteria can produce the important substance serotonin and are found at lower levels in individuals with IBS than in healthy individuals.
IBS is a common gastrointestinal disorder that presents with symptoms such as abdominal pain, constipation or diarrhoea. It is more common in women than in men.
The cause of the disease is not clear, but the intestinal environment, including the gut microbiota and serotonin levels, appears to be an important factor.
Serotonin is best known as a neurotransmitter in the brain, but more than 90% of the body's serotonin is actually produced in the gut.
Here, 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) affect how much serotonin is produced by the host. However, until now, it has been unclear whether gut bacteria themselves can form biologically active serotonin.
Better bowel function
In the current study, 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 normalised 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.
New treatment options
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, Professor of Medical Gastroenterology at Sahlgrenska Academy at the University of Gothenburg, added: “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."
“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 behaviour."