A hydrothermal vent in Loki's Forest, deep beneath the North Atlantic - (Photo by R.B. Pedersen, Centre for Geobiology, University of Bergen)

Researchers sifting the depths of the Atlantic Ocean may have found a missing link between unicellular organisms and modern life.

The microorganism they discovered—found in a field of hydrothermal vents known as “Loki’s Castle”—has been named Lokiarchaeota (“Loki” for short). Loki’s Castle is a deep complex located between Greenland and Norway on the Mid-Atlantic Ridge, some 7,000 feet (2,133 meters) below the surface.

Loki represents an intermediate stage of life—somewhere between simple cellular life and the more complex cells, which form the building blocks of more advanced organisms (like people).

When people think of the missing link they tend to picture hairy proto-humans roaming around the savannah on this side of the dawn of time. But evolution is long process and there are a lot of links in the chain between the basic building blocks of life and the modern human being.

Image by Joe McNally. Reconstruction by Kennis and Kennis

One of the most mysterious missing links in that chain has been the evolutionary gap between simple and complex cells. Basic, small unicellular organisms called prokaryotes are abundant. Bacteria constitute one domain of prokaryotes; the other domain is called Archaea, and is believed to represent the ancestral origin of modern eukaryotic life, including all multicellular organisms found on Earth today.

Cellular life emerged on Earth as long as 3.5 billion years ago. Eukaryotes emerged around 1.6 billion to 2 billion years ago. They are more closely related to Archaea than bacteria on the genetic scale, but internally, their structure are more similar to bacterial cell structures. Eukaryotes possess a nucleus and other organelles absent from Archaea prokaryotes. There had been no clear mechanism for the evolution of those structures between the two life forms.

Loki is a prokaryote, but when Uppsala University scientists sequenced its genome, they found a high degree of genetic correlation with eukaryotic organisms. Loki’s genome includes “an expanded repertoire of eukaryotic signature proteins that are suggestive of sophisticated membrane remodeling capabilities," according to the article published this month in Nature.

In other words, Loki demonstrates most of the precursor elements required for a prokaryotic organism to make the evolutionary jump to the more complex form of a membrane-bound eukaryotic structure.

The Swedish scientists from Uppsala, along with collaborators from Norway and Austria who assisted with the study, believe they have only scratched the surface of possible discoveries surrounding the organisms populating the seafloor near hydrothermal vents. The genomic sequencing performed to analyze Loki is an important tool for unlocking the history of those organisms, and further discoveries are expected to follow.

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