Two life forms have merged into a single organism for the first time in at least a billion years.
Primary endosymbiosis, or two life forms merging into one, has occurred only twice in the history of Earth. The first time, it gave rise to all complex life as we know it through mitochondria. The second time, it caused the emergence of plants.
An international team of scientists have observed the evolutionary phenomenon between a species of algae commonly found in the ocean and a bacterium. Tyler Coale, a postdoctoral researcher at the University of California, Santa Cruz, said, "The first time we think it happened, it gave rise to all complex life."
Coale, the lead researcher on one of the two studies that uncovered the phenomenon, added, "Everything more complicated than a bacterial cell owes its existence to that event. A billion years ago or so, it happened again with the chloroplast, and that gave us plants."
According to the study published in Science and Cell, the algae engulfed the bacterium, providing it nutrients, energy and protection in return for functions. The algae could not perform some functions earlier, like the ability to "fix" nitrogen from the air.
Then, the algae incorporated the bacterium as an internal organ. This organelle became crucial to the host's ability to function.
"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."
Researchers from the United States and Japan who made the discovery said it will offer new insights into evolution. This rare phenomenon also has the potential to change agriculture fundamentally.
Dr Coale stated, "This system is a new perspective on nitrogen fixation, and it might provide clues into how such an organelle could be engineered into crop plants."
The scientists involved came from the Massachusetts Institute of Technology (MIT), the University of Rhode Island, the University of California, San Francisco, UC Santa Cruz, the Lawrence Berkeley National Laboratory, Institut de Ciències del Mar in Barcelona, National Taiwan Ocean University, and Kochi University in Japan.