The gut microbiome has gained increasing popularity recently, but what exactly is it and how can it influence our health? The human microbiome refers to the diverse ecosystem of microorganisms located in our bodies, with the highest concentration being found in the lower part of the large intestine.
The broad range of microorganisms throughout the human body (including bacteria, protists, viruses, fungi and archaea) can vary widely in diversity and functionality. Different areas of the body develop their own specific combination of microorganisms as part of its normal function, and this collection of microorganisms that live in the same community is called the microbiota.
The human microbiota is overwhelmingly dominated by bacteria, with approximately 99%1 of these bacteria found in the lower part of the large intestine – often referred to as the gut microbiome. A recent study estimated there are about 40 trillion bacteria living in the human gut2 – just slightly more than all of our own human cells. There is a growing body of global research indicating that these 40 trillion bacterial cells making up our gut microbiome play a central role in health and disease. What is not understood though, is how the gut microbiome is influencing our health and this is what scientists are seeking to discover.
So what exactly is the microbiome?
The term microbiome refers to the full collection of all the genes contained by the microorganisms in a community. Gut bacteria have the ability to produce a large and diverse number of metabolites that can perform a variety of functions, but our microbiome is more than just bacteria, it also includes bacteriophage viruses, fungi and protists. Bacteriophage viruses are viruses that only infect bacteria and they potentially outnumber bacteria in the gut3. The genome (the DNA instructions for an organism’s construction and maintenance) of each individual gut microorganism is much smaller than our own human genome. However, their collective genetic and metabolic capacity (the combination of what they can all do) is much greater – with some scientists describing our gut microbiome as a hidden organ4.
Why is the microbiome important?
The complex interactions of our resident microbes play vital roles in nearly every aspect of our lives – including synthesising many of our vitamins5, protecting us from a range of toxins and diseases6, and shaping and regulating our immune systems7. And, perhaps most amazingly, recent research also suggests gut bacteria produce neurotransmitters8 such as serotonin, dopamine and GABA, affecting how we think and feel.
- Qin, J., Li, R., Raes, J., Arumugam, M., Burgdorf, K.S., Manichanh, C., … & Mende, D.R. (2010). A human gut microbial gene catalogue established by metagenomic sequencing. nature, 464(7285), 59-67. doi: Retrieved from http://dx.doi.org/10.1038/nature08821
- 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. https://doi.org/10.1371/journal.pbio.1002533
- Barr, J. J., Auro, R., Furlan, M., Whiteson, K. L., Erb, M. L., Pogliano, J., … & Salamon, P. (2013). Bacteriophage adhering to mucus provide a non–host-derived immunity. Proceedings of the National Academy of Sciences, 110(26), 10771-10776. https://doi.org/10.1073/pnas.1305923110
- O’Hara, A. M., & Shanahan, F. (2006). The gut flora as a forgotten organ. EMBO reports, 7(7), 688-693. https://doi.org/10.1038/sj.embor.7400731
- LeBlanc, J. G., Milani, C., de Giori, G. S., Sesma, F., Van Sinderen, D., & Ventura, M. (2013). Bacteria as vitamin suppliers to their host: a gut microbiota perspective. Current opinion in biotechnology, 24(2), 160-168. https://doi.org/10.1016/j.copbio.2012.08.005
- Bäumler, A. J., & Sperandio, V. (2016). Interactions between the microbiota and pathogenic bacteria in the gut. Nature, 535(7610), 85. https://doi.org/10.1038/nature18849
- Postler, T. S., & Ghosh, S. (2017). Understanding the holobiont: how microbial metabolites affect human health and shape the immune system. Cell metabolism, 26(1), 110-130. Retrieved from https://www.cell.com/cell-metabolism/fulltext/S1550-4131(17)30296-6. https://doi.org/10.1016/j.cmet.2017.05.008
- Lyte, M. (2013). Microbial endocrinology in the microbiome-gut-brain axis: how bacterial production and utilization of neurochemicals influence behavior. PLoS pathogens, 9(11), e1003726. https://doi.org/10.1371/journal.ppat.1003726