World Microbiome Day 2021

by Katrina Bhowruth, on 23/06/21 08:40

World Microbiome Day takes place on 27th June 2021. It was developed by the APC Microbiome Institute at UCC, Ireland, with the aim to showcase the vibrant and diverse worlds of microbiomes.

In this article, we are going to look at what a microbiome is, the role of the human microbiome and the relationship between the gut microbiome and the brain.

What is a microbiome?

Each of us has more microbes in our body than there are stars in the Milky Way – this community of bacteria is called our microbiota and 95% of them live in our gut. And the microbiome is the word used to describe all the genes that these bacteria have. In fact, there are so many genes in the microbiome that the genes in your microbiome outnumber the genes in your own genome by about 150:1. It is thought that 90% of disease can be linked in some way back to the gut and health of the microbiome.

Pic 1 microbiome blog

The role of the human microbiome:

Humans have microbiomes in many parts of our body that are in contact with the outside world. For example, the skin, mouth, vagina, lung and the gut which is the most diverse and best studied human microbiome. This gut microbiome carries out many essential functions for us such as:

  1. Helping digestion by breaking down foods.
  2. Developing the immune system.
  3. Preventing infections by competing with disease causing microorganisms.
  4. Synthesis of essential nutrients such as vitamins K & B12 and short chain fatty acids.

Many people take a probiotic supplement to support the bacteria in their microbiome. One of the important things to realise about probiotics is that each bacterial culture is unique and will have different activities in the microbiome. Each probiotic is different and it’s important to choose one for the specific action you want.

Pic 2 microbiome blog

Relationship between the brain-gut microbiome:

The connection between our brain and our gut is already part of how we describe experiences, having a "gut-feeling" a "gut-wrenching" moment or feeling nervous with "butterflies" in the stomach. These expressions have become commonplace for a reason. We now know there is a connection between our brain and our gut. Scientists call this connection the gut-brain axis - the two-way dialogue between the brain and the gut where information flows between the two organs.1

There are three main communication channels between the brain and the gut:2

  • the nervous system
  • the immune system
  • the endocrine system (hormones)

 A key physical link that relays the information between the gut and the brain is the vagus nerve.3 This nerve relays information using molecules called neurotransmitters (chemical messengers). 80-90% of nerve fibres in the vagus nerve are going from the gut to the brain.4

pic 3 microbiome blog

For more information regarding microbiomes or World Microbiome Day itself, please click the link below:


  1. Psychobiotics and the gut–brain axis: in the pursuit of happiness. Zhou et al., Neuropsychiatric Disease and Treatment 2015.
  2. The impact of gut microbiota on brain and behaviour: implications for psychiatry Dinan et al., Clinical Nutrition & Metabolic Care 2015.
  3. Vagus Nerve as Modulator of the Brain–Gut Axis in Psychiatric and Inflammatory Disorders. Breit et al., Front Psychiatry 2018.
  4. Tubbs RS, Rizk E, Shoja MM, Loukas M, Barbaro N, Spinner RJ. Nerves & Nerve Injuries: Vol 1: History, Embryology, Anatomy, Imaging, and Diagnostics. Cambridge, Massachusetts: Academic Press 2015.