Are We Human?

This topic is a little harder to see, but it’s as obvious as the nose on your face. In fact, it’s in your nose, on your skin and in every nook and cranny over your body. It’s time to get back to my nerdy microbiology roots and talk about the trillions of microorganisms moved in for long-term rent in the prime real estate of the human body.

I would say it’s common knowledge that we have a variety of bacteria, viruses and even worms living harmoniously with us every day. But what if I told you that they outnumbered us 10-1! That’s right, for every one human cell, there are thought to be ten ‘intruders’ living with us. Collectively they are known as the microbiome - a term first described by Joshua Lederberg who defined it as “the ecological community of commensal, symbiotic, and pathogenic microorganisms that literally share our body space”. Does this make us less human? Let’s investigate.

The human genome is the total of all the human genes in our bodies. In 2003, a colossal research program known as the Human Genome Project was completed that mapped out - and gave us a greater understanding - of our genome. The results, however, posed further questions. How could we stop there when we know there are many more living organisms in our body? Do their genes interact with ours? How many genes belonging to microorganisms are there inside us? These questions, with so many more, initiated the Human Microbiome Project (HMP).

The goals weren’t just inquisitive by nature. How microorganisms interact with our cells could have a significant impact on our health and well-being. The microflora of the gut is a key example. Here is found is the most extensive collection of microorganisms in our body, with an estimated 100 trillion bacteria that potentially:

• Harvest nutrients from food.
• Synthesise vitamins.
• Regulate drug metabolism.
• Renew gut cells.
• Help the response of our immune system to disorders like Crohn’s disease or inflammatory bowel diseases.
• Affect Cardiac size.
• Change behavioural patterns.

Understanding the interaction of microorganisms in our gut has the potential to transform modern medicine. The harvesting of nutrients, for example, could have considerable implications in the treatment and care of people at risk of malnourishment or obesity – two battles that we are currently losing. According to the 2018 Global Nutrition Report, malnutrition has the most significant negative impact on human health than any other cause, whilst overweight and obesity affect an astonishing 38.9% of individuals. Of course, the front line in this fight should focus on an improved diet, education and funding to developing countries. But understanding those little bacteria in there could provide an additional weapon in this fight.

When we hear the word ‘virus’, a general shudder usually follows. Viruses infect humans or other host types to replicate and spread, normally resulting in a disease. Not a happy scenario. Though now there is growing evidence that some viruses not only live amicably inside our bodies, but may be beneficial to our survival. Different viral species have recently been identified that help fend off infections, help slow down disease progression in people with HIV, or help form the placenta. Certainly surprising and astonishing results, with further research promising to uncover more viral friends.

So, are we human? Of course we are. Although we are mostly made up of non-human cells, collectively all those invaders only weigh a little over two kilograms. Hardly tipping the scales in their favour. The HMP showed us the variety of our microbiome, but many questions remain. Most notably, the reasons behind the vast diversity in the microflora between individuals. The role of diet, the environment, genetics, host immunity and early exposure to microbes are potentially all key players to provide further answers that hopefully lead to a better understanding of the causes of disease, and how to treat them effectively.

References

Angelakis E, Armougom F, Million M, Raoul D. The relationship between gut microbiota and weight gain in humans. Future Microbiol. (2012) 7(1), 91–109

Center for Virus Research. Review article: Virus-host symbiosis mediated by persistence. Symbiosis 2007; 44 (1): 1-9

Global Nutrition Report. 2018. Executive Summary. [https://globalnutritionreport.org/reports/global-nutrition-report-2018/executive-summary/] Accessed 25 February 2020.

Lederberg J, McCray AT. ‘Ome sweet ‘ Omics – A Genealogical Treasury of Words. Science 2001; 15(7).

National Human Genome Research Institute. What is the Human Genome Project? [https://www.genome.gov/human-genome-project/What] Accessed 24 February 2020

Roossinck MJ, Bazán ER. Symbiosis: Viruses as Intimate Partners. Annual Review of Virology 2017; Vol. 4:123-139.

Tetro J. Not All Viruses Are Enemies. 2015. [https://www.popsci.com/our-viral-friends/]

The Human Microbiome Project Consortium. Structure, Function and Diversity of the Healthy Human Microbiome. Nature 2012; 486: 207-214.

The NIH HMP Working Group. The NIH Human Microbiome Project. Genome Research 2009 19: 2317-2323.

Turnbaugh PJ, Ley RE et al. The Human Microbiome Project. Nature 2007; 449: 804-810.