The World’s Oldest Bacteria

Eske Willerslev collects soil samples in the permafrost of Canada’s Yukon Territory. Samples for the study were also collected from Northeastern Siberia and Antarctica.
Credit: Duane Froese

A research team has for the first time discovered DNA from living bacteria that are more than half a million years old. Never before have traces of still living organisms that old been found. The exceptional discovery can lead to a better understanding of the aging of cells and might even cast light on the question of life on Mars.

The discovery is published in the current issue of PNAS (Proceedings of The National Academy of Sciences of The United States of America). The discovery was made by Professor Eske Willerslev from the University of Copenhagen and his international rearch team.

All cells decompose with time. But some cells are better than others to postpone the decomposing and thus delay ageing and eventually death. And there are even organisms that are capable of regenerating and thereby repairing damaged cells. These cells – and their DNA – are very interesting to the understanding of the process of how cells break down and age.

The research team, which consists of experts in, among other things, DNA-traces in sediments and organisms, have found ancient bacteria that still contains active and living DNA. So far, it is the oldest finding of organisms containing active DNA and thus life on Earth. The discovery was made after excavations of layers of permafrost in Northwestern Canada, Northeastern Siberia and Antarctica.

All cells degrade over time, but some cells are better at others in repairing damage to their DNA and thereby extending their lifetimes.
Credit: PBS

"Our project is about examining how bacteria can live after having been frozen for millions of years," says Eske Wilerslev. "Other researchers have tried to uncover the life of the past and the following evolutionary development by focusing on cells that are in a state of death-like lethargy. We, on the other hand, have found a method that makes is possible to extract and isolate DNA-traces from cells that are still active. It gives a more precise picture of the past life and the evolution towards the present because we are dealing with cells that still have a metabolistic function – unlike “dead” cells where that function has ceased."

After the fieldwork and the isolation of the DNA, the researchers compared the DNA to DNA from a worldwide gene bank in the US to identify the ancient material. Much in the same way the police compare fingerprints from a crime, the researchers were able to identify the DNA more precisely and to place it in a context.

All forms of life as we know it on Earth have similar DNA-based chemistry. Understanding how DNA degrades and the likelihood of cells surviving over time can help scientists determine the best ways of searching for signs of past life on distant planets such as Mars.
Credit: NASA

"There is a very long way, of course, from our basic research towards understanding why some cells can become that old," says Eske Willerslev. "But it is interesting in this context to look at how cells break down and are restored and thus are kept over a very long period. Our methods and results can be used to determine if there was ever life on Mars the way we perceive life on Earth. And then there is the grand perspective in relation to Darwin’s evolution theory. It predicts that life never returns to the same genetic level. But our findings allow us to pose the question: are we dealing with a circular evolution where development, so to speak, bites its own tail if and when ancient DNA are mixed with new?"


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