• Microbes capable of feeding and reproducing appeared on Earth a very, very long time ago, according to our partner The Conversation.

  • Germs can make us sick – and even kill us – but we also know they can help us in different ways.

  • This analysis was conducted by Juan Fontecilla, researcher in structural biology at the University of Grenoble Alpes.

A very, very long time ago on our planet, Earth, there was no life yet.

But little by little, microbes capable of feeding and reproducing appeared.

They were really tiny, like droplets much less than a millimeter in length.

At that time, he didn't have much to eat.

But there was already an inexhaustible source of energy, our Sun.

It was then that an extraordinary invention took place in certain marine microbes called cyanobacteria: they became able to use sunlight to make energy-rich foods such as sugars and fats;

this invention is called photosynthesis.

The production of large amounts of nutrients by cyanobacteria encouraged the appearance of other microbes, which took advantage of this boon, and life became increasingly varied.

Photosynthesis also had a huge impact on the composition of the atmosphere since it produced a lot of oxygen from water.

The oxygen released later played a fundamental role in the evolution of animals.

This gas allows, thanks to breathing, to recover, from digested food, the large amount of energy necessary to exist and reproduce.

Bacteria, and other microbes such as amoebas and viruses are always present on our Earth.

The invention of the microscope changed everything

We can still ask ourselves the following question: how do we know that microbes exist, given that they are too small to see with the naked eye?

Scientists long ago suspected that diseases were transmitted by invisible germs, but it took until the invention of the microscope four hundred years ago to confirm their existence.

Now we know that germs can make us sick and even kill us (hence the importance of getting vaccinated and having good hygiene).

But recently we also know that they can help us in different ways.

Indeed, each type of animal lives with a collection of different bacteria (there are even more bacteria in an animal's body than its own cells);

they are mostly found in the digestive system (mouth, stomach, intestine) where they can provide vitamins and help digest food.

The importance of diet

We are different from other animals because what we eat largely depends on our culture.

For example, because of fast food, there are generally far fewer different bacteria - and good for health - in the stool of a person in North America than in black Africa, where we eat much more products. untreated natural materials (Europe, including France, is between these two extremes).

The effect of what we eat on our bacteria was clearly demonstrated by Tim Spector, a professor in London, who in 2015 asked his son Tom to eat in a fast food restaurant for ten days.

Daily stool analysis revealed that during this period he had lost almost half of his bacteria and that they were much less varied.

This result proves that the bacterial population can vary rapidly depending on our diet.

It has also been shown, using laboratory mice, that if you eat too much fat, you increase the amount of a type of bacteria that promotes the absorption of fat in the intestine.

In reality the situation is more complex since, on the one hand, the bacteria can force us to eat what they prefer to consume and, on the other hand, our intestine can select the bacteria that suit us.

Our "BIOLOGY" file

Fortunately, it is possible to correct the bacterial composition, if it is not good, thanks to the transfer of stools from a healthy person to the patient.

This type of transplant has also been used to cure antibiotic-resistant bacterial infections and to improve the condition of autistic children.

In summary, microbes can be our enemies but also our friends.

This analysis was written by Juan Fontecilla, researcher in structural biology at the University of Grenoble Alpes.

The original article was published on The Conversation website.

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