“The vast majority of nematode species have not been described,” William Crow, a nematologist at the University of Florida who was not involved in the study, wrote in an email. The ancient Siberian worm could be a species that has since gone extinct, he said. “However, it very well could be a commonly occurring nematode that no one got around to describing yet.”

Beyond the “wow” factor of a time-traveling nematode, there’s a practical reason to study how these tiny, spindle-shaped creatures go dormant to survive extreme environments, said Philipp Schiffer, group leader at the Institute for Zoology at the University of Cologne and one of the authors of the study. Such work may reveal more about how, at a molecular level, animals can adapt as habitats shift because of soaring global temperatures and changing weather patterns.

“We need to know how species adapted to the extreme through evolution to maybe help species alive today and humans as well,” Schiffer wrote in an email.

A prehistoric nematode, resurrected

Scientists have long known that some microscopic critters are able to hit pause on life to survive harsh environments, slipping into the deepest of sleeps by slowing their metabolism to undetectable levels in a process called cryptobiosis.

As far back as 1936, a viable several-thousand-year-old crustacean was discovered buried in the permafrost east of Russia’s Lake Baikal. In 2021, researchers announced they had resurrected ancient bdelloid rotifers, microscopic multicellular animals, after 24,000 years in the Siberian permafrost.

The previous resuscitation record for a nematode was set by an Antarctic species that started wriggling around again after just a few dozen years.

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This new species of nematode, dubbed Panagrolaimus kolymaensis, breaks that dormancy record by tens of thousands of years. The frozen soil the nematode was embedded in came from an ancient gopher hole, excavated from about 130 feet below the surface. Scientists used radiocarbon dating to determine that the soil was 46,000 years old, give or take a thousand years.

“The age over which it survived is one of the shocking things,” said Gregory Copenhaver, a co-editor of PLOS Genetics and director of the Institute for Convergent Science at the University of North Carolina at Chapel Hill. The past 46,000 years reach into the previous geologic epoch, called the Pleistocene, he noted, and “this single organism, the actual individual they found, has been alive over that period of time.”

The molecular underpinnings of suspended animation

The recipe for reviving these creatures is fairly simple, Schiffer said. Researchers thaw the soil, taking care to not warm it too quickly to avoid cooking the nematodes. The worms then start wriggling around, eating bacteria in a lab dish and reproducing.

Scientists have continued to raise more than 100 generations from this single nematode, which reproduces without a mate through a process called parthenogenesis.

What intrigues the researchers is not just the age of the specimen, but how it enters a state of limbo.

Through experiments, they found that, like another microscopic roundworm, C. elegans, the new nematode species survives freezing and drying out better if it is exposed to mildly desiccating conditions before the deep freeze. During this preconditioning, the nematodes begin pumping out a sugar called trehalose, which may be involved in helping protect their DNA, cells and proteins from degrading.

Study co-leader Teymuras Kurzchalia, a professor emeritus at the Max Planck Institute for Molecular Cell Biology and Genetics, said that efforts to unravel which proteins are necessary for the process are ongoing, using tools that can silence or knock out genes.

“We have still much to learn about the mechanisms of the desiccation tolerance,” Kurzchalia said.

Researchers are also curious whether there is any limit on how long an organism can survive and be resurrected, and what it means for evolution and even the notion of extinction if animals that typically live, reproduce and die over weeks can stretch out their existence by centuries or millennia.

The normal life span of the 46,000-year-old nematode species is just one to two months.

“We can say that they are alive, because they move, they eat bacteria on the culture plates, and they reproduce,” Schiffer said.