5 The Zoo inside You


One human body carries more microbes than there are stars in the Milky Way. Museums across North America and Canada are hosting exhibits to teach people about the importance of these for life. The human microbiome, first coined in 2001, remains an enigma – with science only recently making advancement in this field of study despite its initial inception in the late 1600s (Ursell et al., 2012). Currently, the International Microbiome Centre at the University of Calgary is spearheading research into the human microbiome. So, what is the human microbiome, and what does it do to suddenly warrant so much attention?

To better understand a human microbiome, we first need to define microbes. Microbes are the microscopic organisms that live inside or on a human being. These include, but are not limited to, bacteria, viruses, protozoa, and fungi (Yang, 2012). Humans house over 100 trillion of these microbes, most of which are beneficial to the body and found in the intestines (Centre for Ecogenetics and Environmental Health, 2014). The collective genetic material of these microbes, weighing around five pounds, makes up the human microbiome – which actually varies from individual to individual (Rinninella et al., 2019). Interestingly, the genes in the microbes of a human far outnumber the genes found in the human genome, by around 200 times (Centre for Ecogenetics and Environmental Health, 2014). This means we have more microbial cells than we do human cells in our body – most of which play a critical role in human health and disease.

The microbes found in humans perform a variety of tasks. For one, they help the body with digestion. Surprisingly, up to a thousand different species of bacteria colonize a baby’s intestines soon after birth (Rinninella et al., 2019). The two most common bacteria that aid in human digestion, according to Zhang et al. (2015), are bacteroidsand firmicutes. But these do more than simply metabolize food; they also protect the body from pathogenic bacteria (Pickard et al., 2017). This ‘pathogenic resistance’, as it is called, occurs in two ways. One is by the bacteria competing for nutrients with the pathogens. The other is by eradicating or diminishing the growth of pathogens through the release of bacterial toxins (Zhang et al., 2015). Microbes also supply much-needed vitamins to our bodies. Since humans lack the ability to synthesize most vitamins, microbes step in and produce them for us (LeBlanc et al., 2012). These include the production of vitamin B12, thiamine, riboflavin, and vitamin K. Moreover, the microbiota found in the gut has recently been found to influence mood as well (Pennisini, 2019). Studies indicate that people with depression lack a number of different bacteria in their intestines. More studies are currently being conducted to shed more light on this growing health issue.

To conclude, the human microbiome, comprised of nearly a thousand species of microorganisms, is responsible for much of human health. Without it, the human body would fall ill either due to a lack of vitamins or an infestation of cancer. The human mind would also fare no better since mental health has been shown to be linked to the presence of microbes in our bodies as well. It is fascinating that although we do not host a single microbe while in the womb, upon birth we are blessed with a myriad of colonies whose main mission is to keep us alive. In the wise words of Professor Pollan from the University of California, Berkeley: it turns out,some of our best friends are germs.



Center for Ecogenetics and Environmental Health. (2014). Fast facts about the human microbiome. Retrieved January 13, 2020 from https://depts.washington.edu/ceeh/downloads/FF_Microbiome.pdf

LeBlanc, J., Savoy de Giori, G. Milani, C. Sesma, F., van Sinderen, D., & Ventura, M. (2012). Bacteria as vitamin suppliers to their host: A gut microbiota perspective. Current Opinion in Biotechnology, 24(2), 1-9.

Pennisi, E. (2019). Evidence mounts that gut bacteria can influence mood, prevent depression. Retrieved January 17, 2020 from https://www.sciencemag.org/news/2019/02/evidence-mounts-gut-bacteria-can-influence-mood-prevent-depression

Pickard, J. Zeng, M. Caruso, R., Nunez, G. (2017). Gut microbiota: role in pathogen colonization, immune responses, and inflammatory disease. Immunological Reviews, 279(1), 70-89.

Rinninella, E., Raoul, P., & Mele, M. (2019). What is the healthy gut microbiota composition? A changing ecosystem across age, environment, diet, and diseases. Microorganisms, 7(1), 14-48.

Ursell, L., Metcalf, J. Parfrey, L., & Knight, R. (2012). Defining the human microbiome. Nutrition Reviews, 70(1), 38-44. doi:10.1111/j.1753-4887.2012.00493.x

Yang, J. (2012). The human microbiome project: Extending the definition of what constitutes a human. Retrieved January 13, 2020 from https://www.genome.gov/27549400/the-human-microbiome-project-extending-the-definition-of-what-constitutes-a-human

Zhang, Y., Li, S., Gan, R., Zhou, T., Xu, D., & Li, H. (2015). Impacts of gut bacteria on human health and diseases. International Journal of Molecular Science, 16(4), 7493-7519.


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