Depression is a mental health issue that is now being understood to have roots reaching into the gut. Researchers in Belgium used a population-level study to identify specific gut bacteria linked to depression and also compiled more evidence that gut bacteria can produce neuroactive compounds.
Professor Jeroen Raes and his team from the Flanders Institute for Biotechnology published their findings in the journal Nature Microbiology. They were able to identify a specific group of microorganisms that positively or negatively correlated with mental health. Two bacteria in particular, Coprococcus and Dialister, were low across the board in individuals with depression regardless of antidepressant treatment.
"The relationship between gut microbial metabolism and mental health is a controversial topic in microbiome research,” Raes said. “The notion that microbial metabolites can interact with our brain—and thus behaviour and feelings—is intriguing, but gut microbiome-brain communication has mostly been explored in animal models, with human research lagging behind. In our population-level study we identified several groups of bacteria that co-varied with human depression and quality of life across populations."
Raes and his team previously found a microbial community with low microbial count and biodiversity that is prevalent in Crohn’s disease patients. They found a similar community type in this study linked to depression and a generally reduced quality of life.
"This finding adds more evidence pointing to the potentially dysbiotic nature of the Bacteroides2 enterotype we identified earlier,” Raes said. “Apparently, microbial communities that can be linked to intestinal inflammation and reduced wellbeing share a set of common features."
The work Raes and his team did will pay dividends in the future regarding additional research. They began the process of cataloging gut bacteria able to produce neuroactive compounds. They studied genomes of more than 500 bacteria looking for those that could potentially interact with the human nervous system and found some able to carry out a broad range of functions.
"Many neuroactive compounds are produced in the human gut,” said researcher Mireia Valles-Colomer. “We wanted to see which gut microbes could participate in producing, degrading, or modifying these molecules. Our toolbox not only allows us to identify the different bacteria that could play a role in mental health conditions, but also the mechanisms potentially involved in this interaction with the host. For example, we found that the ability of microorganisms to produce DOPAC, a metabolite of the human neurotransmitter dopamine, was associated with better mental quality of life."