We are a home for trillions of microbes — bacteria, fungi and viruses — our microbiota, whom we are tightly connected with.
David Relman writes in his 2012 Nature article “the dawn of the twenty-first century has seen the emergence of a major theme in biomedical research: the molecular and genetic basis of what it is to be human. Surprisingly, it turns out that we owe much of our biology and our individuality to the microbes that live on and in our bodies — a realization that promises to radically alter the principles and practice of medicine, public health and basic science.”
Relman makes the case that microbes so affect our individuality that we cannot easily separate ourselves from their effects. Our biological identity and health are intertwined with that of our microbial partners.
About 99% of the microorganisms living inside the human body are bacteria.
Not long ago humans used to think that a good bacteria is a dead bacteria. But by today scientists have concluded that only about 0,1% of microorganisms living inside the human body are possible pathogens. The rest are either necessary for us, or their function is unknown.
The overwhelming majority of microbes are essential for ecosystem functioning and known for beneficial interactions with other microbes as well as macro-organisms.
Most of our body parts are inhabited — our skin, mouth, respiratory tract, genital tract. Even the brain, which we used to think of as a sterile organ. And all these microbes make up microbiota — the community of microbes living in and on our body.
However, the most diversely and densely inhabited place is our gastrointestinal tract. About 99% of bacteria live in the gut. And about 99% of these in the end part of the large intestine.
In the last decade we’ve made rapid progress in our understanding of the gut.
Our microbiota consists of about the same amount of cells that we have our own human cells. But these cells are smaller and lighter, so the microbiota together weighs about 2–3 kg.
However, genetic diversity of the microbiota is much more important. We humans have about 23 000 different genes in our genome (our total DNA). At the same time, microbes living inside a human body have a total of 2–20 million genes.
Therefore we are carrying around a world of bacteria that has a genome 100 times the size of our own. These genes have many different functions and help to adapt in different conditions. Our microbes compensate for what is beyond our genetic capacity.
Here is our understanding of gut importance, on a timeline:
For centuries we have looked at a human body as one organism consisting of our own cells. However as technology has evolved we’ve begun to see our bodies differently. In the last decade we have discovered the world in and on our body.
We have started to see the human body more from a holistic point of view, as the host and its associated microbiota are one unit that has co-evolved as one entity.
But, the truth is, the science of microbiota is still in its baby shoes and most probably we’re still scraping the tip of the iceberg.
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References and interesting reading:
- Microbiome definition re-visited: old concepts and new challenges
- The human microbiome: why our microbes could be key to our health
- The Human Superorganism: How the Microbiome Is Revolutionizing the Pursuit of a Healthy Life (by Rodney Dietert)
- Gut: the inside story of our body’s most under-rated organ (Giulia Enders)