They survived the freezing and then about 24,000 years in cold sleep: Scientists have awakened ancient rotifers from the permafrost soil of Siberia. Unraveling the mechanisms of astounding long survivability could benefit the development of cryopreservation techniques, the researchers say.
Freezing is fatal for us and most animals and plants – ice crystals destroy the complex cell structures and thus make resuscitation impossible. But there are exceptions: some higher living beings can survive temperatures well below freezing due to certain antifreeze substances in their body fluids, earlier studies have already shown. The duration of the possible cold sleep is rather limited with the known frost-resistant insects and amphibians. However, some plant species and tiny nematode worms have already shown that they can survive in the ice for thousands of years. Now the researchers headed by Stas Malavin from the Soil Cryology Laboratory in Pushchino, Russia, are adding rotifers (Rotifera) to the list of higher organisms that can survive an astonishingly long in a state of frozen apparent death.
Soil samples from icy depths
It is a species-rich group of animals, usually less than a millimeter in size, with movable eyelashes on their heads with which they feed themselves food particles. Rotifers are found in many aquatic or humid habitats on earth. They live in moss or between soil particles as well as in bodies of water. The tiny creatures are already known for their toughness: Studies have already shown that they can survive a lack of food and oxygen, as well as drying out and freezing. Malavin and his colleagues have now uncovered the extremes that the latter ability can reach by examining drill cores from the permafrost of Siberia. They come from a depth of 3.5 meters and were obtained using techniques that prevent contamination with material from upper layers.
As the scientists report, they discovered under the microscope how some rotifers trapped in the ice came to life after thawing. They were then able to reproduce successfully through so-called parthenogenesis. The more detailed investigations then showed that the resurrected were representatives of the genus Adineta. To determine how long the animals lay in cold sleep, the researchers carried out radiocarbon dating of the organic material in the samples. This resulted in an age of around 24,000 years. “We were able to prove that these multicellular animals can survive tens of thousands of years in what is known as cryptobiosis,” says Malavin.
Amazingly sustainable frost residence
In order to investigate the process of freezing and resuscitation, the researchers then frozen some of the rotifers’ offspring from the samples, as well as today’s representatives of Adineta, at minus 15 degrees Celsius in the laboratory and thawed them again a week later. It was found that all of them have a similarly good ability to resist the formation of ice crystals in a slow freezing process.
Apparently, the Adineta rotifers have mechanisms to protect their cells and organs from damage caused by extremely low temperatures. The scientists now want to clarify which these are through further investigations. They also plan to examine more samples from the Arctic, possibly to uncover other organisms that are capable of long-term cryptobiosis. The hope is that knowledge about the biology of frost-resistant organisms can provide clues as to how cells, tissues and organs of animals and humans can be better cryopreserved.
“Methods of freezing and resuscitating people after a long time are science fiction so far,” says Malavin. “Cryopreservation is more difficult, the more complex an organism is – this is currently not possible for mammals”. The researchers are convinced that research results such as the current ones can be important on the way to the development of corresponding processes: “Our discovery is not only interesting for biology, but also for practical applications in cryopreservation and biotechnology,” write Malavin and his colleagues in conclusion.
Source: Cell Press, technical article: Current Biology, doi: 10.1016 / j.cub.2021.04.077