46,000-year-old frozen roundworms revived in Siberia

Russia An ancient roundworm species awakens after tens of thousands of years of hibernation in a fossilized squirrel burrow from the late Pleistocene.

Ancient roundworms revived from permafrost in Siberia. Photo: Times

A tiny worm has survived 46,000 years in the Siberian permafrost, tens of thousands of years longer than any other previously revived worm. The newly described species, Panagrolaimus kolymaensis , was discovered curled up in a fossilized squirrel burrow taken from permafrost near the Kolyma River in the northeastern Arctic in 2002. Scientists previously revived a frozen nematode in 2018, but its age and species are unknown.

A study published on July 27 in the journal PLOS Genetics seeks to answer these questions. "Survival in extreme environments for long periods of time is a challenge that only a few organisms can overcome," said a team of researchers from Russia and Germany. "Here, we demonstrate that the soil-dwelling nematode Panagrolaimus kolymaensis has been dormant for 46,000 years in Siberian permafrost."

Organisms such as nematodes and tardigrades can enter a state of dormancy, a metabolic process called "cryptobiosis," in response to freezing or complete dehydration. In both cases, they reduce their oxygen consumption and metabolic heat output to undetectable levels.

The new nematode hibernated during the late Pleistocene (2.6 million to 11,700 years ago), a period that included the last ice age. Permafrost kept the creatures frozen and unthawed ever since. This is the longest recorded hibernation period for a nematode. Previously, an Antarctic nematode named Plectus murrayi frozen in moss and a desiccated specimen of Tylenchus polyhypnus in a herbarium lasted 25.5 and 39 years, respectively.

The researchers analyzed the genes of P. kolymaensis and compared them to the roundworm Caenorhabditis elegans, the first multicellular organism to have its entire genome sequenced. C. elegans provided a perfect model for comparison. The analysis revealed several common genes involved in hibernation.

To find out exactly how the nematodes survived for such a long time, the team took a fresh group of P. kolymaensis and C. elegans and dried them in the lab. As the worms entered a dehydrated state, they observed a spike in a sugar called trehalose, which may help protect the nematodes’ cell membranes from dehydration. They then froze the worms at -80 degrees Celsius and found that the drying improved the survival of both species. Worms frozen at this temperature without first being dehydrated would have died instantly.

Equipped with molecular machinery to withstand Arctic conditions, nematodes have evolved to survive in a dormant state for thousands of years. Ancient nematodes may be able to revive if they escape permafrost. Significant changes in the environment, including temperature fluctuations and natural radioactivity, can awaken nematodes from deep dormancy.

An Khang (According to Live Science )

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