Photograph: Nature

A new discovery by a Japanese team has identified a type of microorganism they’ve called an Asgard archaeon, which could shed light on how early eukaryotic cells evolved. The project took 12 years after finding the cells in deep-sea mud. Published in Nature, the findings of the closest Archaeal relative to eukaryotes so far will allow further detailed cellular and metabolic investigations to find out more about the origins of complex life.

Two microbial kingdoms were present during the first two billion years of life on Earth – bacteria and archaea. Scientists believe that eukaryotes arose when an archaeal cell engulfed a bacterial cell which evolved into energy-generating organelles, such as mitochondria who contain their own circular genome within our cells much like a bacterium.

The Japanese scientists have succeeded for the first time in culturing a species of archaea believed to be similar to the ancestor that gave rise to eukaryotes. Both bacteria and archaea continue to thrive on Earth today, but their research has been limited even though they’re thought to play such a pivotal role in the origins of complex life.

In 2006, the project began with the collection of deep-sea mud from the 2.5km deep Omine Ridge off the coast of Japan. The team’s original goal was to find organisms that could degrade methane, so the mud was placed in a bioreactor and continuously fed with methane for more than five years.

The organism they found had properties completely opposite to others cultured in the laboratory. They reproduce 1,000 times slower than E. coli – taking two to four weeks to replicate and divide, depend on symbiotic partners to grow, and only live in small numbers.

To help them grow, the team took a smaller sample from the reactor and placed them in a glass tube, helping them grow with a blend of nutrients such as powdered baby milk, and only showed obvious signs of life after one year.

Whilst this experiment was taking place, another team in the Netherlands were also researching an archaeon that they had collected from a hydrothermal vent off the coast of Greenland. The Dutch team sequenced the microbial DNA and found that there were segments scattered through its genome that were similar to DNA found in eukaryotic cells. The Japanese then sequenced the DNA in their samples and discovered that they had found the same archaea.

The scientists decided to call it the Asgard archaea and suggested that ancestors of the evolutionary branch could have played a role in the formation of complex life. Asgard archaea are small simple cells featuring long tentacle-like structures that reach out of the cell. The scientists theorise that one of these cells could have engulfed a bacterium, forming a symbiotic relationship and over time, the two together became a primitive eukaryote.

This discovery is likely to pique an interest back into under-explored microbes, and further investigate how the origins of complex life came to be.