Des vers nématodes sibériens conservés pendant 42.000 ans dans le pergélisol reviennent à la vie (en anglais)
A. V. Shatilovich and a team of Russian researchers published the results of a surprising experiment in the journal Doklady Biological Sciences. They analysed more than 300 samples of Arctic permafrost and they found viable nematodes in two of them. Also called "roundworms", nematodes belong to the Animalia kingdom. They can live in salt of fresh water, or in the soils. Thanks to carbon dating analysis, the two samples appeared to date from Pleistocene: the first one was collected from a fossil squirrel burrow and was estimated to be about 32,000 years old. The second one came from the Kolyma River in northeastern Siberia, and the age of nearby deposits was around 42,000 years old.
The scientists wanted to obtain "data demonstrating the capability of multicellular organisms for long-term cryobiosis in permafrost deposits"1. Cryobiosis is a form of cryptobiosis, which is a suspension of vital functions to withstand a long period of absence of water or oxygen, usually in extreme environmental conditions such as desiccation or freezing. Cryobiosis occurs in reaction to decreased temperature, when the water surrounding the organism's cells has been frozen. Stopping molecule mobility allows the organism to endure the freezing temperatures until more hospitable conditions return2.
Until now, only bacteria and a giant virus3 were revived after such long periods of cryobiosis. In 2016, in an article about tardigrades4 (another type of micro animal), a first record of nematodes reviving was evoked. It was reported in 1946, and they were revived after...only 39 years ! The result of the experiment of the Russian study is all the more striking. Indeed, after removing the worms from the glacial samples, they were brought back to the Russian Academy of Science and placed in 20°C culture with agar and E. coli bacteria as food. After defrosting, the nematodes showed signs of life. Further study will now be needed to understand the mechanisms that enabled those organisms to survive such lengthy freezing.
Learning more about the biochemical mechanisms nematodes use to limit the damage of ice and hold off the ravages of oxidation on DNA over the millennia might point the way to better cryopreservation technologies. "It is obvious that this ability suggests that the Pleistocene nematodes have some adaptive mechanisms that may be of scientific and practical importance for the related fields of science, such as cryomedicine, cryobiology, and astrobiology," the researchers write in their report.
1 SHATILOVICH A. V., TCHESUNOV A. V., NERETINA T. V., et al. Viable Nematodes from Late Pleistocene Permafrost of the Kolyma River Lowland. Doklady Biological Sciences. 2018, vol. 480, issue 1, pp. 100-102. Available on: https://link.springer.com/article/10.1134/S0012496618030079 (accessed 09/12/2018).
2 WIKIPEDIA. Cryptobiosis. Available on: https://en.wikipedia.org/wiki/Cryptobiosis (accessed 09/12/2018).
3 GHOSE T. Giant virus resurrected from permafrost after 30,000 yers. In: LiveScience website. Available on: https://www.livescience.com/43800-giant-virus-found-permafrost.html (accessed 09/12/2018).
4 NATIONAL INSTITUTE OF POLAR RESEARCH. Animals revived after being in a frozen state for over 30 years. In: NIPR website. Available on: http://www.nipr.ac.jp/english/news/20160217.html (accessed 09/12/2018)