Single-celled microbes are rarely loners. They thrive in complex environments like the ocean, soil, and our own guts. Here, they engage in all kinds of interactions, from competition for nutrients to DNA swapping, and even eating each other. Sometimes, one cell will enter another and create a long-lasting bond. This process is called endosymbiosis, and it plays a crucial role in the evolution of complex life.
We can find examples of endosymbiosis everywhere. For instance, mitochondria in our cells, which generate energy, were once independent bacteria. Similarly, chloroplasts in plants, responsible for photosynthesis, started out as free-living organisms. Certain insects also rely on bacteria living inside them for vital nutrients. Recently, scientists found a new player called the “nitroplast,” which helps some algae process nitrogen.
Even though endosymbiotic relationships are vital for life, much about how they start is still a mystery. How does one cell avoid being digested by another? How does it reproduce inside a host? What makes two cells form a lasting partnership instead of just a temporary merge?
Recently, researchers tackled this issue head-on. They managed to create endosymbiosis in the lab by injecting bacteria into fungi. This innovative approach allowed them to see how these cells cooperated without harming each other. Their findings provide valuable insights into how such relationships may develop in nature.
To the researchers’ surprise, the cells adapted to each other faster than expected. Vasilis Kokkoris, a mycologist from Amsterdam, highlighted the importance of this discovery, suggesting that cooperation might be the norm rather than the exception.
Earlier studies showed that many attempts at forming these partnerships fail. However, understanding when and why cells accept endosymbionts can help us learn about crucial moments in evolution. This knowledge might even lead to creating synthetic cells with enhanced capabilities.
Julia Vorholt, a microbiologist from Switzerland, has investigated endosymbiosis for some time. The existing theories suggested that once a bacterium enters a host, the situation can quickly become tricky. If the bacterium reproduces too quickly, it can drain the host’s resources and provoke an immune response. Conversely, if it reproduces too slowly, it may not establish itself at all. Achieving a balance in reproduction is rare and is just the first step. To truly integrate, the bacterium must align with the host’s reproduction and even influence its genetic makeup over generations.
Ultimately, Vorholt notes, these cells may become so intertwined that they are “addicted to each other,” forming a deep and lasting connection that can shape their evolution.
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