24,000-year-old “Zombies” from the Arctic Revived and Cloned

Tiny zombies that were frozen in Arctic permafrost for 24,000 years were recently brought back to life. Now, they are being cloned in a lab in Russia. 

The creatures are called bdelloid rotifers, or wheel animals. They are named for the wheel-like ring of tiny hairs that circle their mouths. Rotifers are multicellular microscopic animals that live in freshwater environments. They have been around for about 50 million years. 

During that time, rotifers have learned how to survive pretty extreme conditions.

Researchers have found that modern rotifers could be frozen at negative 4 degrees Fahrenheit and then revived up to 10 years later.

Now, scientists have revived rotifers that froze in ancient Siberian permafrost during the latter part of the Pleistocene epoch (2.6 million to about 11,700 years ago). Once the creatures were thawed, they began reproducing asexually through parthenogenesis, creating genetically identical clones of themselves.

Permafrost is ground that has been frozen solid for two years or more. It can preserve snapshots of both life and death from thousands of years ago. For example, a small bird carcass found in Siberian permafrost in 2020 was 46,000 years old. However, it looked like it had only died days prior. A frozen and mummified bear that was also found in Siberia in 2020 dated back to 39,000 years ago, and it still had a fleshy black nose and much of its fur.

Being able to retain a lifelike appearance after being frozen in ice for thousands of years is impressive in and of itself. But rotifers being able to come back to life and reproduce after their thousands of years long frozen slumber is even more astonishing.

That “frozen sleep” is actually a metabolic state called cryptobiosis. Rotifers evolved to use cryptobiosis because most of them live in watery habitats that often freeze or dry up, according to Stas Malavin, a researcher at the Institute of Physicochemical and Biological Problems in Soil Science in Pushchino, Russia, and lead author of a new study describing the revived rotifers.

“They suspend their metabolism and accumulate certain compounds like chaperone proteins that help them to recover from cryptobiosis when the conditions improve,” Malavin said. Rotifers can also repair DNA damage and protect their cells against harmful molecules called reactive oxygen species, Malavin explained.

For the new study, scientists collected permafrost samples by drilling to depths of 11.5 feet (3.5 meters) below the surface in Siberia’s Alazeya River, where radiocarbon dating showed that the soil was around 24,000 years old. When they thawed the samples, the researchers discovered rotifers in the Adineta genus in a cryptobiotic state.

First, the scientists isolated and analyzed the permafrost samples to make sure that they weren’t contaminated by modern microorganisms, according to the study. To revive the frozen sleepers, “We put a piece of permafrost into a Petri dish filled with [a] suitable medium and wait until organisms that are alive recover from their dormancy, start moving, and multiply,” Malavin said. 

Of course, once the defrosted survivors began cloning themselves, the scientists couldn’t tell which ones were ancient and which were newborns, as the rotifers were genetically identical. Because rotifers typically only live for about two weeks, the scientists gathered their data from the clones of the 24,000-year-old rotifers, rather than from the Ice Age survivors themselves, Malavin said.

“Organisms isolated alive from permafrost potentially represent the best models for cryobiology research,” and could provide valuable clues about the mechanisms that allow those organisms to survive, Malavin said. Those mechanisms could then be tested in cryopreservation experiments with human cells, tissues and organs,” he said. 

Unfortunately, this doesn’t mean that humans will be able to copy the rotifers’ deep-freeze sleep and recovery anytime soon, Malavin added. 

“The more complex the organism, the trickier it is to preserve it alive frozen,” he said. “For mammals, it’s not currently possible.”

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