Specific gut bacteria were associated with depression across two different human sample groups, each consisting of more than 1,000 individuals, a paper published online this week in Nature Microbiology reports. These findings resulted from bioinformatics analyses and will need to be confirmed experimentally, however, they may help direct and streamline future microbiome-brain research.

The relationship between gut microbial metabolism and mental health is a complex topic in microbiome research. Gut microbiome-brain communication has mostly been explored in animal models, with human research lagging behind.

Jeroen Raes and colleagues studied how microbiome features correlate with quality of life and depression. The authors combined microbiome data together with self-reported and general practitioner-diagnosed depression data from 1,054 human individuals enrolled in the Flemish Gut Flora Project (FGFP). They identified specific groups of gut bacteria that positively or negatively correlated with mental health. The authors found that two groups of bacteria, Coprococcus and Dialister, were consistently depleted in individuals with depression. This was validated in an independent group of 1,063 individuals from the Dutch LifeLinesDEEP cohort.

The authors also created a catalogue of gut microbiome functions based on the ability to produce or degrade molecules that can potentially interact with the human nervous system. They applied this catalogue to faecal metagenome data from a subset of the sample group, including treatment-resistant major depression patients and healthy controls. The results revealed a positive association between the potential ability of the gut microbiome to synthesize a dopamine metabolite and mental quality of life.