Tiny zombies that were frozen in Arctic permafrost for 24,000 years were recently brought back to life and have produced clones in a lab in Russia.
These hardy creatures are bdelloid rotifers, or wheel animals, so-named for the wheel-like ring of tiny hairs that circle their mouths. Rotifers are multicellular microscopic animals that live in freshwater environments, and they’ve been around for about 50 million years.
The researchers previously found that modern Rotifers can be frozen at temperatures below 4 degrees Fahrenheit (-20 degrees Celsius), and then revived after 10 years.
Now, scientists have revived Rotifers that froze in ancient Siberian permafrost during the latter part of the Pleistocene (2.6 million to about 11,700 years ago). Once the ice melted, this ancient Pleistocene began to reproduce asexually through parthenogenesis, producing genetic duplicates.
Permafrost can maintain traces of life (and death) for thousands of years. For example, the carcass of a young bird was found in the permafrost of Siberia in 2020, and it was 46,000 years old, but it looks like it “died only a few days ago,” Live Science previously reported.
A frozen and mummified cave bear was also found in Siberia in 2020, and it dates back to about 39,000 years ago.
Retaining a lifelike appearance after spending thousands of years in ice is impressive. But some types of plants and animals locked in ancient permafrost have managed to do something even more astonishing; return to life from a frozen state.
In 2012, scientists described how they regenerated 30,000-year-old plants from immature fruit tissue frozen in Siberian permafrost, Live Science reported that year.
Two years later, scientists recreated Antarctic moss that had been surrounded by ice in Antarctica for 1,500 years. Tiny worms called nematodes were also recovered and revived from ancient permafrost at two Siberian sites: at one site the rocks were about 32,000 years old, and at the other site they were about 42,000 years old, Live Science reported in 2018.
Now, more animal “zombies” frozen in permafrost have been revived from a suspended metabolic state known as cryptobiosis.
“Rotifers have evolved to use cryptobiosis because most of them live in aquatic habitats that often freeze or dry up,” said Stas Malavin, a researcher at the Institute of Physical and Biological Problems in Soil Science in Bushino, Russia, and lead author of a new study describing: Resurrected Rotifers.
“They suspend their metabolism and accumulate certain compounds like chaperone proteins that help them to recover from cryptobiosis when the conditions improve,” Malavin told Live Science in an email. Rotifers also have mechanisms for repairing DNA damage and for protecting their cells against harmful molecules called reactive oxygen species, Malavin explained.
In the new study, scientists collected samples of permafrost by drilling 11.5 feet (3.5 meters) below the surface of the Alazeya River in Siberia, where radiocarbon dating showed the soil to be about 24,000 years old. And when they thawed the samples, they discovered Rotifers in the genus Adineta in a state of hidden vitality.
First, the scientists isolated and analyzed the permafrost samples to ensure they were not contaminated with modern microorganisms, according to the study.
To revive frozen items, “we put a piece of permafrost in a Petri dish filled with a suitable medium and wait until the organisms recover from their dormancy, begin to move, and reproduce,” 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 surviving from permafrost probably represent the best models for permafrost research,” Malavin said, and could provide valuable clues about the mechanisms that allow those organisms to survive. These mechanisms can then be tested in cryopreservation experiments with human cells, tissues and organs, he said.
However, it doesn’t mean that humans will be capable of duplicating 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.”