Scientists now know that the tiny organisms living in our gut can affect many parts of our body, even the brain. One of these microbes, called Morganella morganii, has been linked to depression in several studies.
A team at Harvard Medical School discovered how this bacterium might cause changes in the brain. Their research, published in the Journal of the American Chemical Society, shows that a chemical from the environment can turn a harmless bacterial molecule into a trigger for inflammation.
How a Chemical Turns Trouble Into Inflammation
The chemical is diethanolamine (DEA), a compound found in many industrial and household products. When DEA enters the gut, it can replace a sugar piece in a molecule made by M. morganii. The new molecule behaves like a warning signal for the immune system.
Instead of staying quiet, this altered molecule tells the immune system to release proteins called cytokines, especially interleukin‑6 (IL‑6). High levels of IL‑6 are known to cause chronic inflammation, and long‑term inflammation has been connected to depression.
Earlier studies have already linked both IL‑6 and M. morganii to other inflammatory conditions such as type 2 diabetes and inflammatory bowel disease.
New Ways to Spot and Treat Depression
Because DEA is common in many products, it could be measured in the body to help identify a specific type of depression. If a patient shows high levels of this altered molecule, doctors might consider treatments that calm the immune system.
The findings also support the idea that some forms of depression involve the immune system. Medicines that modify immune responses could become useful options for those patients.
Teamwork Drives Discovery
The study was a collaboration between two labs. One lab studies tiny chemicals made by bacteria, while the other looks at how the gut microbiome influences health at a molecular level. Together they have also shown how other gut bacteria can affect inflammation and even cancer‑related treatments.
- A single bacterium, Akkermansia muciniphila, can protect against inflammation and improve cancer immunotherapy.
- The gut microbe Ruminococcus gnavus makes a sugar chain that may trigger Crohn’s disease.
- A fatty molecule on the surface of Streptococcus pyogenes can cause strong immune reactions, which might explain some autoimmune problems.
In the new study, the researchers found that when DEA joins the molecule from M. morganii, it acts like a type of fat called cardiolipin, which is known to start inflammation.