Scientists baffled as two lifeforms merge in ‘once-in-a-billion-year’ event

Last time the phenomena occurred, Earth got plants for the first time

The process, which is officially known as primary endosymbiosis, and it happens when one microbial organism swallows up another, and begins to use it like an internal organ.

The host cell provides the symbiote with everything it needs, such as energy and nutrients, so that soon enough it essentially becomes one with the host. In microbial cells, this is known as organelle.

Primary endosymbiosis has only taken place twice during the Earth's 4 billion year history, and both times have been pretty darn important to evolution.

The first time was when the mitochondria came about after a bacterium was engulfed by an archaea 2.2 billion years back. Those who remember their biology will know that the mitochondria is known as 'the powerhouse of the cell', and has been pretty essential to all complex life.

The second time round was 1.6 billion years back, when a cyanobacteria (a cell that uses energy from the sun) was absorbed by another cell. These organelles became a chloroplasts, which are some of the handiest cells around as they in turn gave us plants.

So, with the mitochondria and plants being a result of primary endosymbiosis, you can see why it's such a big deal that it's happening again.

This time round, it's algae called Braarudosphaera bigelowii that have gobbled up a cyanobacterium. This cyanobacterium will allow the algae to 'fix' nitrogen directly from the air and use it to create more useful compounds.

Normally, plants gain their nitrogen through symbiotic relationships with separate bacteria. Scientists assumed this is what the algae was up to, combined with a bacterium called UCYN-A. However, it seems the Braarudosphaera bigelowii and cyanobacterium got a lot closer than that.

New Atlas reports that the size ratio of the algae and UCYN-A is consistent among different related breeds of the algae in a recent study. This indicates linked metabolisms as the growth is controlled by the exchange of nutrients.

“That’s exactly what happens with organelles,” said Jonathan Zehr, one of the study's authors. “If you look at the mitochondria and the chloroplast, it’s the same thing: they scale with the cell.”

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