What’s The Link Between Gut Bacteria and Depression?

  • Researchers detected specific types of microbes in the human gut that were associated with mental health conditions. 
  • They developed a framework that can easily identify such bacteria and reveal the mechanism involved in this connection with the nervous system. 

Neural and immune communication lines connect the human gut microbiota (viruses, fungi, protists, bacteria, and archaea) to the host central nervous system. The communication along these lines is believed to be bidirectional, where the gut microbiota plays a crucial role in processes associated with physiology and brain development.

Such bidirectional communication has been extensively studied in animal models, but human research lags far behind. Despite recent advances in sequencing technology, functional interpretation of metagenomes — in context of the link between gut bacteria and depression — remains challenging. The lack of dedicated reference data of microbiota-induced neuroactive compounds makes the interpretation even harder.

Now, a team of researchers at Flanders Institute for Biotechnology, Belgium, have conducted a population-level study on the relationship between gut bacteria and mental health. The aim is to detect particular gut bacteria associated (directly or indirectly) with depression and provide evidence of different bacteria producing neuroactive compounds.

Population-Level Study

The team first assessed gut microbiota compositional covariation with quality life indicators and merged this data with general practitioner-reported depression in 1,054 people registered in the Flemish Gut Flora Project (FGFP).

They detected certain classes of microorganisms that were associated (either negatively or positively) with mental health. They discovered that two groups of bacterial —  Dialister and Coprococcus — were consistently reduced in depressed people, regardless of their treatment procedures.

Reference: Nature Microbiology | doi:10.1038/s41564-018-0337-x | VIB

These outcomes were validated both in the Dutch LifeLines DEEP cohort with self-reported depression metadata collected from 1,063 individuals, and in previously published researches on depression.

According to the researchers, microbial communities associated with intestinal inflammation and decreased wellbeing share some common features. The new study provides more evidence of dysbiotic nature of Bacteroides enterotype detected earlier.

A Module-based Analytical Framework

The team has also developed an analytical framework that will make it easier to identify gut bacteria linked with the nervous system. They used reference genome mining to catalogue the neuroactive potential of gut isolates.

More specifically, they examined over 500 bacterial genomes that can potentially create a group of neuroactive compounds. As expected, a few bacteria were carrying a wide range of these features.

Several neuroactive compounds are generated within the human gut. Researchers wanted to detect exactly which microorganisms in the gut are responsible for creating, altering and degrading these molecules.

Along with identifying different groups of bacteria that affect mental quality, their new framework also reveals the mechanisms involved in this process. For instance, researchers discovered that the microbes’ ability to generate 3,4-dihydroxyphenylacetic acid (a metabolite of the neurotransmitter dopamine) was linked with good mental health conditions.

Read: New Microfluidic Method Can Detect Electricity-Producing Bacteria

The results obtained from bioinformatics examinations haven’t been verified experimentally, but they are expected to speed up the future research on human microbiome-brain. Moreover, the team plans to conduct another sampling round of the FGFP.

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