INTRODUCTION TO THE GUT MICROBIOME
This is the first of a series of posts on the on the gut microbiome.
The posts will cover:
1. INTRODUCTION TO THE GUT MICROBIOME
2. GUT MICROBIOME MEMBERS
3. THE INTERACTIONS BETWEEN THE GUT AND THE IMMUNE SYSTEM
4. AN INTRODUCTION TO THE IMMUNE SYSTEM
5. THE GUT BARRIER
6. LEAKY GUT
9. MICROBIOME AND HEALTH
Our gut is home for a very large number of microbes collectively known as the gut microbiome (sometimes called the gut microbiota or biome). There are about 40,000,000,000,000 (40 trillion!) microbes in the gut, most in the lower intestine. This is in the same order of magnitude as the number of cells than we have in our body (Sender et. al., 2016).
According to Qin et. al. (2010) the gut microbes are predominantly bacteria, with at least 160 species in each individual and with most of those species common in all people. There are also archaea (functionally similar to bacteria but a different lineage), fungi, viruses and phage (the viruses of bacteria).
The collective genome, i.e. the total number of genes of all the microbes in the gut (confusingly also occasionally referred to as gut microbiome), has around 150 times as many genes as the human genome (Qin et. al., 2010).
Our bodies are well adapted to hosting so many guests. Rather than just tolerating their presence, our bodies have a mutually beneficial relationship with most of our gut microbes. The biological terms for this relationship are symbiosis, and in more intimate individualised relationships, mutualism.
We are only just beginning to understand the depth and breadth of these mutually beneficial interactions. It is, however, clear that these functions have a huge impact on our health and wellbeing, strongly affecting the body’s equilibrium (called homeostasis) that is fundamentally important for our survival.
The composition of the gut microbiome influences many aspects of human physiology, e.g., metabolic rate, cardiovascular function, nervous system function.
There are around the same number of microbial cells in our gut as there are cells in our body. The gut microbiome exists as an integral part of the host organism, us.
Sender R, Fuchs S, Milo R (2016) Revised Estimates for the Number of Human and Bacteria Cells in the Body. PLOS Biology 14(8): e1002533.
Qin, J., Li, R., Raes, J. et al. (2010) A human gut microbial gene catalogue established by metagenomic sequencing. Nature 464, 59–65. https://doi.org/10.1038/nature08821