Co-author: Sarah Wettstadt
Illustrations: Darcy Flynn

Viruses, bacteria and fungi (microbes) are all around us! They’re an intimate part of our bodies, our minds, and our environment at large. Our species has always evolved in the presence of microbes, and our immune system has arisen to control their influence. Despite the way microbes are portrayed in relation to disease, not all microbes are villains in the story of life. Inside every one of us exists an entire ecosystem of countless microbial constituents. Or as Ed Yong put it – “I Contain Multitudes”.

The Immune System in a Nutshell

Our immune system protects us from invading microbes every day. Because of its importance, the immune system now receives its own day of celebration – so a happy belated Day of Immunology 2020 to you and your white blood cells!

The history of immunity is as old as life itself. From the very beginning, organisms developed a memory log of the vast microbial world around them. In humans, this culminated in a well-oiled immune system, protecting the body from potential microbial hazards. However, the immune system is not perfect, sometimes leading to underwhelming immune responses (particularly as you age), or – even more dangerously – a hyperactive immune system that overreacts to potential threats (or just the perception of threat) – i.e. the evolution or allergies or sepsis. 

True Stories About the Microbial World

Our immune system learned to continuously recognize friend from foe and activate a response when necessary. Now, it is challenged with a new “invisible enemy”: a villainous virus, which forces our immune system into overdrive – all in an attempt to protect us. 

However, this is a stand-out case in the totality of the microbial world. Things are not always as simple as friends and enemies, or heroes and villains. The microbial world is instead a complex, interdependent mesh of narratives that play out differently across different environments; narratives about tribes tussling together for microbial dominance.

This is the perspective that Ed Yong presents to us in his 2016 book “I Contain Multitudes”. He reminds us that microbes are not only all around us, but also that they’re:

♦  Congregating to form the microbiome of our gut, mouths, skin etc.

♦  Influencing the way we think through the gut-brain axis

♦  Engaging in relationships with plants and animals everywhere. Either friendly and symbiotic, and selfish and parasitic, or just neutral.

Ed Yong encourages us to accept and appreciate this vast microbial world around us – we couldn’t have it any other way!

A Microbial Analogy

Although, it can be challenging to appreciate the vast microbial world around us when it is smaller than the eye can see! To help us appreciate this reality, Ed Yong magnified the dynamics of the microbial world through an analogy to our large scale ecosystems.

All of the concepts that ecologists use to describe the continental-scale ecosystems that we see through satellites also apply to ecosystems in our bodies that we peer at with microscopes. We can talk about the (bio)diversity of microbial species. We can draw food webs, where different organisms eat and feed each other. We can single out keystone microbes that exert a disproportionate influence of their environment – the equivalent of sea otters and wolves. We can treat disease causing microbes – pathogens – as invasive creatures, like cane toads or fire ants. We can compare the gut of a person with inflammatory bowel disease to a dying coral reef or a fallow field.” – Ed Yong , 2016

By drawing parallels between microbes and the organisms that we can see, we begin to understand the influence that microbes have on the ecosystem of our body, and the environment at large.

Could we live without them?

Towards the end of his book, Yong presents a thought experiment to drive home the importance of microbes. He asked what a world without microbes would look like. Yes, it would remove the possibility of infectious diseases, but it would also halt all microbial activity in or on our body or in the environment.

On a larger scale, the lack of soil microbes responsible for nutrient recycling would be devastating for food crops worldwide and the food web of the global ecosystem would quickly crumble. And what would be a world without fermented microbial products like beer, wine or spirits! In the fermentation process, bacteria break down the sugars of milk, grapes and flour and produce all sorts of different tastes. The delicious taste of chocolate would not exist without the work of all those microbes living on the cocoa bean. I surely would not want to live in such a dystopian vision of our world.

Yes, we had to develop an immune system because of all the microbial impact on our body, but it learned quite well to distinguish between helpful and harmful bacteria. And the helpful bacteria of our human microbiota even help us fight off the bad guys. Plus, the human microbiota is great at digesting those foods that our body is not able to. So, bacteria actually provide us with energy and produce building blocks for our cells. 

Because our microbiota is so considerate, we should do the same and support it. We can do this for example by eating probiotics that we find in many fermented foods. These probiotic strains then become part of our microbiota. Or we actually feed our microbiota with prebiotics which are those foods that our body is not able to digest, but the microbiota is happy to break down for us.

These examples really reiterate the attitude that Ed Yong shared with us in “I Contain Multitudes” – that microbes come in all different shapes, sizes and levels of helpfulness. While one harmful microbe is currently keeping the world at home, many people are busy appreciating the good microbial buddies by baking their own bread, brewing beer and making cheese! So alongside practising appropriate social distancing and hygiene behaviours, let’s also think twice before stigmatising all of our microbial allies! Because the truth is, I Contain Multiples!