Biologists appear to be getting closer to understanding how life and complex life on Earth began. Last week a study showed that, due to the complex interactions of organic chemicals and minerals, the first simple life forms could have emerged from hydrothermal vents.

This week a study published in Nature appears to have found the ‘missing link’ between basic, single celled organisms and more complex life forms. Once again, hydrothermal vents, seem to play a role.

All life on Earth is made up of cells however, the cells that make up microbes such as bacteria are small and simple. More complex life forms are made up of larger and more complex cell types. Biologists refer to the life forms made of complex cells, including plants, animals and humans as ‘eukaryotes.’

However the evolution of cells from the simple to the complex type has remained a mystery. Now researchers from Sweden’s Uppsala University have discovered a new group of microorganisms which seem to be made of cells which are in between the two types.

The first “missing link” in this area were the Archaea, discovered by Carl Woese in the 1970s. The Archaea, were found to be a new branch in the “tree of the “Tree of Life”. Although they were made of small, simple cells, those cells were found to be more closely related to complex eukaryote cells than those found in other microscopic organisms. How these unusual cells came to be has remained a mystery.

Now, the Swedish researchers, along with colleagues from Bergen, Norway and Vienna, Austria report the discovery of a new group of Archaea. The new type is called the Lokiarchaeota, or ‘Loki’ for short, and they fill in another link in the story of evolution according to the team.

“The puzzle of the origin of the eukaryotic cell is extremely complicated, as many pieces are still missing. We hoped that Loki would reveal a few more pieces of the puzzle, but when we obtained the first results, we couldn’t believe our eyes. The data simply looked spectacular”, said Thijs Ettema of Uppsala University who lead the study in a statement.

“By studying its genome, we found that Loki represents an intermediate form in-between the simple cells of microbes, and the complex cell types of eukaryotes”, added Ettema.

The researchers report that the idea was confirmed by plugging the cells into one of the gaps in the Tree of Life.

“In addition, we found that Loki shares many genes uniquely with eukaryotes, suggesting that cellular complexity emerged in an early stage in the evolution of eukaryotes”, said Anja Spang, researcher at Department of Cell and Molecular Biology at Uppsala University.

This is interesting in light of the previous study showing that the first simple life forms may have emerged from such vents.

“There is a lot of speculation that hydrothermal vents could be the location where life on Earth began. There is a lot of CO2 dissolved in the water, which could provide the carbon that the chemistry of living organisms is based on, and there is plenty of energy, because the water is hot and turbulent. What our research proves is that these vents also have the chemical properties that encourage these molecules to recombine into molecules usually associated with living organisms,” said Nora de Leeuw, leader of the team that conducted the previous study.

“Extreme environments generally contain a lot of unknown microorganisms, which we refer to as microbial dark matter”, said Jimmy Saw, researcher at Department of Cell and Molecular Biology, Uppsala University, and co-lead author of the study released this week.

The researchers admit that there is considerable research yet to be done and that there could be other organisms waiting to be discovered.

“In a way, we are just getting started. There is still a lot out there to discover, and I am convinced that we will be forced to revise our biology textbooks more often in the near future”, said Thijs Ettema.