The original version of this story appeared in Quanta Magazine.

Far of solo operators, most unicellular microbes are in complex relationships. In the sea, the soil and your intestines they can fight and eat each other, exchange DNA, compete for nutrients, or feed on each other’s by -products. Sometimes they become even more intimate: one cell can slip into another and make itself comfortable. If the conditions are just right, it can remain and welcome, resulting in a relationship that can last for generations – or billions of years. This phenomenon of one cell that lives in another, called endosymbiosis, fueled the evolution of complex life.

Examples of endosymbiosis are everywhere. Mitochondria, the energy factories in your cells, were once free -living bacteria. Photosynthetic plants have their sun -pinned sugars thanks to the chloroplast, which was also originally an independent organism. Many insects receive essential nutrients of bacteria that live in them. And last year, researchers discovered the “nitroplast”, an endosymbiont that helps some algae process nitrogen.

So much of life relies on endosymbiotic relationships, but scientists have struggled to understand how it happens. How does an internalized cell digestion evade? How does it learn to reproduce in his host? What makes a random merger of two independent organisms to a stable, lasting partnership?

Now, for the first time, researchers have been watching the opening choreography of this microscopic dance by causing endosymbiosis in the laboratory. After bacteria were injected into a fungus – a process that required creative problem solving (and a bicycle pump) – the researchers managed to stimulate cooperation without killing the bacteria or the host. Their observations provide a look at the conditions that make the same thing happen in microbial nature.

The cells adapted even faster than expected. “For me, this means that organisms actually want to live together, and symbiosis is the norm,” says Vasilis Kokkoris, a mycologist who studies the cell biology of symbiosis at VU University in Amsterdam and was not involved in the new study. “So it’s great, big news for me and for this world.”

Early efforts that were too short revealed that most cellular love relationships are unsuccessful. But by understanding how, why and when organisms accept endosymbionte, researchers can better understand key moments in evolution, and also develop potentially synthetic cells designed with super -powered endosymbionte.

The cell wall breakthrough

Julia Vorholt, a microbiologist at the Swiss Federal Institute of Technology Zurich in Switzerland, has long been on the conditions of endosymbiosis. Researchers in the field theorized theorized that once a bacterium crept into a host cell, the relationship between infection and harmony faltered. If the bacterium reproduces too quickly, it runs the risk of extracting the host resources and unleashing an immune reaction, leading to the death of the gas, the host or both. If it reproduces too slowly, it will not settle in the cell. Only in rare cases, they thought, the bacterium reached a golden-fate planting rate. Then, to become a true endosymbiont, it must penetrate its host’s reproductive cycle to make a ride to the next generation. Finally, the host’s genome must eventually mutate to accommodate the bacterium – which allows the two to develop as a unit.

“They get addicted to each other,” Vorholt said.