An international team of scientists has managed to bring a nematode back to life after spending some 46,000 years, from the Pleistocene, frozen under the Siberian permafrost. The worm, which was 40 meters below the surface, is a new species to science.
Some animals, such as the ultra-hardy tardigrades (they live without water for decades and withstand radiation), rotifers (multicellular beings that are only visible under a microscope), and nematodes, can survive harsh conditions by entering a state of dormancy known as cryptobiosis. . It is not the first time that researchers have recovered these creatures after thousands of years of freezing. In 2018, for example, the thawing of the Siberian permafrost allowed the resurrection of some 42,000-year-old nematodes.
In the new study, published Thursday in PLoS Genetics, Anastasia Shatilovich, from the RAS Institute of Physicochemical and Biological Problems in Soil Science in Russia, managed to revive two frozen nematodes in a fossilized burrow in silt deposits in the permafrost. After thawing the worms in the laboratory, a radiocarbon analysis of plant material from the burrow revealed that these intact deposits, 40 meters down, had not thawed since the late Pleistocene, between 45,839 and 47,769 years ago.
The researchers began working with the worms to try to understand what molecular and metabolic pathways these organisms use to remain dormant and for how long they can suspend life as ‘zombies’, something that is not fully understood.
Through genome sequencing, assembling, and phylogenetic analysis of the nematode’s relationship to modern species, the researchers determined that the worms belong to a previously undescribed species, which they named Panagrolaimus kolymaensis, in recognition of the Kolyma River region in which it originated. By comparing its genome with that of the model organism, Caenorhabditis elegansidentified common genes that are involved in cryptobiosis.
record freezing
When slightly desiccated in the lab, both species increased production of a sugar called trehalose, which can help them survive severe desiccation and freezing. They tested the survival capabilities of P. kolymaensis and found that exposure to mild desiccation before freezing helped prepare the worms for cryptobiosis and improved survival at extreme temperatures of -80°C. This treatment also benefited the larvae of C. eleganswhich then survived 480 days at -80°C with no reductions in viability or reproduction after thawing.
This study extends the longest discovered cryptobiosis in nematodes by thousands of years. By adapting to cope with extreme conditions, such as permafrost, for short periods of time, the nematodes could have gained the potential to remain dormant over geologic time scales.
“Our findings are essential for understanding evolutionary processes because generation times can range from days to millennia and because the long-term survival of individuals of a species can result in the revival of lineages that would otherwise have gone extinct.” concludes Philipp Schiffer, one of the authors who supervised the study. The researcher is convinced that “studying the adaptation of species to such extreme environments by analyzing their genomes will allow us to develop better conservation strategies against global warming.”
