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Microbiota, the intestinal revolution. © INRA

Microbiota, the intestinal revolution

Symbiotic man (1)

No need to plumb the ocean’s depths or travel to far-flung planets to discover new worlds. If you seek the unknown, you have only to look inside yourself. Each one of us harbours extremely diverse colonies of microorganisms which were a near-total mystery to science just 15 years ago. Research on the microbiota of the intestines, mouth, vagina, lungs and skin has already been revolutionising the treatment of disorders such as Crohn’s disease, obesity and allergies. Little by little, scientists are finding that man and his microbiota live in true symbiosis, a sort of hybrid human-microbe creature. The interactions between our cells, organs and microbiota shape us from the moment of birth.

The intestinal microbiota is, without a doubt, an indispensable aid to good digestion. Among other things, it is what ensures the proper breakdown of dietary fibre that our cells would otherwise not know what to do with. The microbiota is also partly responsible for how the human immune system matures, as it learns not to overreact to commensal* bacteria or foreign substances, and to deal appropriately with aggressors. But the story doesn’t end there: our liver and adipose tissue also receive signals from the microbiota that allow them to achieve balance and work properly. Even our brain responds to stimuli from this impressive population of bacteria. Recent studies have shown to what extent anxiety and stress can be linked to an imbalance in the microbiota. Each day, science is learning just how central a role the microbiota plays in human health. 

Updated on 04/28/2017
Published on 02/16/2017

Scanning electron microscope image of a sample of human faeces, showing the abundance and diversity of the bacterial population.. © INRA, Thierry Meylheuc
Scanning electron microscope image of a sample of human faeces, showing the abundance and diversity of the bacterial population. © INRA, Thierry Meylheuc

100 thousand billion of your closest friends

It’s an idea we all need to get used to: inside our own bodies, the number of microorganisms exceeds the number of our cells. Each microbiota contains bacteria that belong to some 200 different species organised into a highly-structured trophic network*. Some 100 thousand billion microorganisms make up the intestinal microbiota, by far the biggest and most diverse of the microbiota that take up residence in our bodies. Weighing in at no less than two kilos, it outweighs the brain itself. That is why scientists think of the microbiota as an organ in its own right, but an organ that has not yet revealed all its secrets.


A microbiota to suit every taste

Robot from the high throughput cloning-phenotyping platform.. © INRA, NICOLAS Bertrand
Robot from the high throughput cloning-phenotyping platform. © INRA, NICOLAS Bertrand

While it is the intestinal microbiota that most interests researchers, science is no less fascinated by the microbes that dwell in the mouth, on the skin, in the vagina, or in the lungs of every human. And no two microbiota are alike. For example, unlike the bacteria that populate the gut, those that live in our mouths can better withstand oxygen. The oral microbiota is organised primarily in biofilms that line the teeth, tongue or the inside of the cheeks. As a result, the microbiota of those who have cavities is different from the microbiota of those who are cavity-free. This has piqued the curiosity of scientists, who are trying to learn more about the relationships between microbes and oral health, and overall general health.

A germ-free life is a life not worth living

Imagine a mouse that is so squeaky clean that it has never in its life come into contact with a single germ. They exist: they are called axenic* mice. These lab animals, raised “in bubbles” in sterile conditions, lack a microbiota, and life is no picnic for them. The absence of bacteria makes them particularly susceptible to disease, allergies and stress. Moreover, studies have shown that axenic mice have poor growth compared with other mice which do harbour bacteria. Axenic mice are nevertheless used in many experiments involving the study of the microbiota. For example, they are useful in studying the effects of microbiota transplants, or in characterising the effects of different strains of bacteria on health.

What’s your microbiota type?

No two microbiota are alike. Nevertheless, thanks to the programme MetaHIT*, researchers have classified all microbiota into three groups, called enterotypes. The enteroptype depends on the population of three types of the most prevalent bacteria: Bacteroides, Prevotella and Ruminococcus. Surprisingly, a person’s enterotype depends neither on geographic origin, nor gender, nor health. This classification allows scientists to carry out comparative studies in order to better describe changes in the microbiota linked to certain diseases.

The other genome

The figures are enough to make your head spin: each individual microbiota contains some 600 000 genes. The 23 000 genes that make up our DNA pale in comparison. Before the dawn of high throughput sequencing, exploring this unknown continent was but a dream. INRA is a world leader in this technology, spearheading the international consortium MetaHIT which led to the very first gene catalogue of the human microbiota. The latest edition, published in July 2014, identified some 10 million genes from 1 200 people from Asia, Europe and America. The catalogue is an indispensable tool for studying the different functions of the microbiota and for characterising the most important genes from a medical point of view.

. © INRA

Metagenopolis: a game-changer

Launched in 2012, the MetaGenoPolis project, overseen by INRA, is a centre of excellence for studying the human microbiota. Consisting of four platforms, it gives researchers access to state-of-the-art equipment in Europe, such as a biobank that can store over one million human intestinal samples, and functional and quantitative metagenomic platforms. Designed to boost innovation in nutrition, risk prevention and therapeutic treatments, this ambitious project gives scientists, clinical staff and industrial players a unique opportunity to work in close collaboration with one another. MetaGenoPolis is breaking new ground in the probiotics* of tomorrow, new molecules, and treatments based on shaping the microbiota.