This has not happened in a billion years: two life forms merged into a single organism

Researchers have documented a phenomenon not seen for about a billion years: two different life forms have merged into a single organism. This remarkable example of primordial endosymbiosis between a seaweed and a bacterium is significant because it reminds us of the critical evolutionary leaps that define life on Earth today, Popular Mechanics reports.

The current discovery, published in the glossy Cell and Science, reflects the evolutionary milestones that led to the appearance of plants on Earth through similar symbiotic phenomena.

Primary endosymbiosis occurs when one microorganism completely engulfs another, but does not “digest” the latter, but transforms it into a functional part of the cell, an organelle (cell organelle), which then provides basic functions such as nutrient processing or energy production. This integration is so complete that the endosymbiont would no longer be able to survive on its own and would become a vital component of the host’s biology. As Tyler Coale, a researcher involved in the study, explains:

“It is very rare that these types of things form organelles. When something like this happened for the first time, it resulted in the complex living world we know today.”

Such a process probably took place for the first time more than two billion years ago, when an archaea (they used to be known as protobacteria, but science no longer calls them that) ingested a bacterium, which led to the formation of mitochondria, known as the powerhouse of the cell. Let’s take a big jump in time, and a billion years later, a similar event allowed the chloroplast to form from cyanobacteria – and essentially this is how plants’ photosynthesizing ability developed.

In the current discovery, the scientists studied the algae Braarudosphaera bigelowii, which has formed a unique relationship with a cyanobacterium, allowing it to fix atmospheric nitrogen – a feature not normally seen in plants. However, this ability is not only important because of its extraordinary scientific value (although, as you can see, its importance cannot be overemphasized), but it may even enable more efficient agricultural production over time by reducing the dependence on external nitrogen sources.

During the research, advanced X-ray imaging was used to observe the inner workings of the algae – thus they were convinced that this symbiotic relationship is transformed into a true organelle state, a process similar to the formation of mitochondria and chloroplasts. The team named this new organelle a nitroplast, referring to the organelle’s role in nitrogen fixation.

According to Jonathan Zehr, another co-author of the study, and Carolyn Larabell, who also significantly contributed to the research, the integration of the functions of the bacteria into the algal cell represents a profound evolutionary step. The bacterium relies on the alga for protein synthesis and other cellular functions, which therefore indicates a permanent union, i.e. the bacterium has changed from a mere endosymbiont to an organelle, a cell organelle.

This discovery is therefore not only important for understanding the evolution of cells, but also opens the door to biotechnological applications that can mimic these natural processes in order to increase crop resilience and productivity.

(Image: black arrow points to nitroplast inside alga, credit: Tyler Coale)