Scientists ran a DNA analysis on a sediment core which was found on the floor of the Arctic Ocean in 2010. A previously unknown organism which belongs to the domain of microbes called Archaea appeared to have genomic characteristics of an entirely different domain known as Eukaryota. The discovery is named Lokiarchaeota, after the Loki’s Castle hydrothermal vent near Greenland where it was found. There were doubts about the contamination in the core but Japanese scientists have isolated Lokiarchaeota, and grown it in a lab. Researchers can now freely study and interact with Lokiarchaeota, which could help find our first ancestors on Earth. The work can be found here.
The tree of life has 3 major domains which start with bacteria – single-celled microbes without a nucleus and move around with flagella. Another domain is eukaryotes, which contain cells with a nucleus and a membrane which includes humans, plants, animals, etc. There is another domain Archaea which are like bacteria which lack nuclei and membrane-bound organs and move using flagella. The differences include their cells walls and RNA which are found to be different.
Later came the Lokiarchaeota followed by Thorarchaeota, Odinarchaeota and Heimdallarchaeota which show eukaryotic characteristics. They were collectively named Asgard archaea and is believed to be the origin of eukaryotic life. The sediment was retrieved from a seabed in Nankai Trough (2533 meters below sea level). On performing RNA analysis of their rich sample revealed the presence of a Lokiarchaeota-like organism. They cultivated their samples for 5 years in methane fed continuous flow bioreactor system which mimics deep-sea methane vents. Eventually, the microbes multiplied. The samples were placed in glass tubes in a bioreactor to keep it growing and finally, a very faint population of Lokiarchaeota grew after another year.
The team invested in isolation, cultivating and growing this slow dividing population. Lokiarchaeota took 20 days where a normal bacterium takes an hour and a half to double. The culture has 30-60 lag phase and 3 months to reach full-grown phase. Variation of growth parameters, combinations and concentrations did not significantly improve the lag phase and growth. The experiment took 12 years in total. The researchers named their cultivated microbe Prometheoarchaeum syntrophicum.
Various findings included Prometheoarchaeum which grows in the presence of one or two microbes (archaeon Methanogenium and bacterium Halodesulfovibrio). Prometheoarchaeum helps in breaking down amino acids into food, hydrogen is produced which is fed upon by other microbes. Prometheoarchaeum’s slow growth could be hampered by the presence of hydrogen. Examining the organisms in an electron microscope found the unusual shape for archaeon which has long tentacles sprouting from its body between which partner microbes are nested. With the increase of oxygen on Earth, it might have switched relationship to an oxygen-using bacteria, leading to eukaryotic life.
DNA sequencing revealed the eukaryotic characteristics that were observed in the rest of the Asgard archaea. More work has to be done as there is no definitive proof that eukaryotes evolved from archaea and Prometheoarchaeum might be quite different from the archaea of billions of years ago. The work is yet to be peer-reviewed but whatever be the results it is a monumental paper behind which a vast amount of perseverance.
Research Paper: Isolation of an archaeon at the prokaryote-eukaryote interface