Scientists have increasingly recognized that the gut microbiome plays an important role in overall health, including the brain. However, researchers are still working to identify which specific bacteria are involved in disease and exactly how they influence the body. One bacterium in particular, Morganella morganii , has been linked in several studies to major depressive disorder. Until recently, though, it was unclear whether this microbe contributes to depression, whether depression changes the microbiome, or whether another factor explains the connection. Researchers at Harvard Medical School have now identified a biological mechanism that strengthens the case that M. morganii can affect brain health. Their findings offer a clearer explanation of how this bacterium may influence depression. Published in the Journal of the American Chemical Society , the study points to an inflammation-triggering molecule and suggests a possible new target for diagnosing or treating certain cases of depression.…