With Mathilde Fontez, editor-in-chief of the scientific magazine Epsiloon, we are talking about dust mites today. But not to mention the allergies that are caused by these little beasts…
franceinfo: A comprehensive genetic study has just been published on a particular species of mite that lives on our skin, and it shows that they are merging with us ?
Mathilde Fontez: Yes. This is the first comprehensive DNA study of this species of mites called demodex folliculorum, and which indeed lives on our skin. They take refuge in our pores. It’s always a bit chilling when we say that, but we each have a few thousand of these mites on our skin. Each measuring 0.3 millimeters. They look like tiny worms. And this study shows that they are changing status: they were parasites. They become symbionts: they live in symbiosis with us.
What is the difference ?
The difference is that they have become totally dependent on us to live. They can no longer change medium. The researchers first discovered that their DNA has become simpler: they have fewer genes than other species of mites. They operate on less protein – their protein repertoire is the lowest ever seen in this type of species.
And as a result, their body has become simpler: they have fewer cells. For example, their legs only move with three muscles, each made up of a single cell. Another example, they do not produce melatonin, unlike other mites, because they have become accustomed to finding it on our skin. The production function of this molecule which protects against UV rays, among other things, has gradually disappeared from their genome.
How did this happen?
This is because we are very comfortable. They found everything they needed at home: food, the sebum produced by our skin cells. And a shelter: our pores. We are talking about an extreme adaptation to the host. Except that when a living being is no longer exposed to external threats, there is no more competition, no more genetic mixing. These mites reproduce only among themselves, no new gene is added to their heritage.
They even stopped spreading from human to human. They are passed only from mother to child. All of this has made them extremely dependent on us. So much so that they are part of our body. And so much so that researchers also fear that they have reached an evolutionary impasse: they might not survive our own evolutions…
Perhaps we will soon be rid of it?
It’s possible. And that’s not necessarily such good news. Because at the same time that we discover their vulnerability, we also discover that they are not so harmful. These mites were thought to be associated with skin diseases. However, researchers have shown that this is not really the case. They are even rather useful to us, because they permanently clean our pores…