Distant relatives have been discovered at the bottom of the ocean (Image: R.B. Pedersen, Centre for Geobiology, University of Bergen)

SO THAT’S where they’ve been hiding. An entirely new group of organisms discovered at the bottom of the Arctic Ocean are our closest simple-celled relatives ever found.

Approximately 2 billion years ago, complex eukaryotic cells, which make up animals, plants and fungi, split from smaller, simpler cells called prokaryotes. Researchers have now identified our closest relatives from before this split.

Thijs Ettema at Uppsala University, Sweden, and his team discovered the new organisms when they analysed DNA extracted from underwater sediment near Loki’s Castle, a region of hydrothermal vents along the Arctic mid-ocean ridge (Nature, DOI: 10.1038/nature14447).


Named Lokiarchaea, the organisms are a new type of archaea. Like fellow prokaryotic bacteria, archaea lack a true cell nucleus and other complex cell machinery. But intriguingly, the Lokiarchaea appear to have more than 100 genes coding for sophisticated cellular functions such as deforming cell membranes and forming and transporting bubble-like vesicles around the cell – functions that are usually only seen in eukaryotes like us.

The Lokiarchaea are an entirely new group with sophisticated cellular functions

“It is a truly remarkable, landmark discovery,” says Eugene Koonin at the National Center for Biotechnology Information in Bethesda, Maryland. It suggests that our sophisticated cells could have evolved from special, more elaborate forms of ancient prokaryote.

“We were really blown away when we got the first genome data,” says Ettema. “We can now say that the archaeal ancestor of eukaryotes was perhaps already quite complex.”

“Ettema’s team have certainly thrown the cat among the pigeons,” says Anthony Poole at the University of Canterbury in New Zealand. He says that the discovery of Lokiarchaea blurs the lines between archaea and eukaryotes. “It’s still 100 per cent archaeon, but the presence of genes we usually associate with eukaryote cell biology is absolutely fascinating.”

Ettema’s team argue that their finding helps bridge the gap between our cells and those of the typical prokaryotic organisms from which we are believed to have evolved.

Others are more sceptical. “We’re getting closer to an archaeal ancestor of the eukaryotes,” says Nick Lane of University College London. However, even though the Lokiarchaea are relatively complex compared with other known archaea, they lack the large genome and energy-producing mitochondria of true eukaryotic cells. “It’s a thousandth of the way towards the complexity of a eukaryote,” says Lane. So we can’t really call them an intermediate step or a missing link.

Lane believes the crucial step in the evolution of the eukaryotes was acquiring mitochondria, which would have provided the energy to develop more complicated cellular processes and acquire a larger genome. Ettema does not think the Lokiarchaea have mitochondria, but he says some form of intracellular transport may have evolved before our ancestors acquired their powerhouses.

And while DNA data shows that the Lokiarchaea are our closest known prokaryotic relatives, they may still be very different from the common ancestor that we shared 2 billion years ago.

Unfortunately, we cannot know exactly how the Lokiarchaea use their genes until we can observe one of their cells directly. Ettema’s team did not actually see the cells: they used computational methods to piece together the genomes from the DNA found in the seafloor sediment.

Archaea can be particularly difficult to collect and culture in a laboratory, so we may never get a good look at our long-lost prokaryotic cousins.

This article appeared in print under the headline “Long-lost relatives found at bottom of Arctic Ocean”