Bdelloid rotifers are multicellular animals, so small that you need a microscope to see them. Despite their large size, they are known for their toughness and ability to survive in dry, frozen, hungry and low-oxygen environments. A paper published June 7, 2021 in the journal Contemporary Biology shows that they can not only withstand freezing, but also survive at least 24,000 years in the permafrost of Siberia.
The researchers say the paper is the hardest evidence to date that multicellular animals can withstand tens of thousands of years of freezing, a state in which metabolism almost completely stops. The researchers specialized in isolating microscopic organisms from the ancient permafrost of Siberia. To collect samples, they used rigs in some of the most remote Parts of the Arctic.
They have previously identified many single-celled microbes. There is also a report on 30,000-year-old frontline worms. Mosses and some plants have also been reborn after being trapped in ice for thousands of years. Now, the team has added rotifers to the list of creatures with extraordinary abilities that appear to be able to survive indefinitely in suspension below the frozen surface.
According to early evidence, rotifers can survive up to 10 years in a frozen state. In the new study, the researchers used radiocarbon assays to determine that the rotifers they found in permafrost are about 24,000 years old. Once thawed, the rotifers are able to reproduce in a cloning process known as parthenogenesis. To track the freezing and recovery process of ancient rotifers, the researchers froze dozens of rotifers in the lab and then thawed them.
Studies have shown that Rotifers can resist the formation of crystals during slow freezing. This suggests that they have mechanisms in place to protect their cells and organs from harm at ultra-low temperatures. The researchers say their harvest is that a multicellular organism can be frozen and stored in this way for thousands of years before being brought back to life. Of course, the more complex the organism, the trickier it is to cryopreserve, which is currently impossible for mammals. However, going from a single-celled organism to an organism with an intestine and brain that can withstand freezing and survive is a big step forward, albeit microscopic.
The researchers say they will continue to explore samples from the Arctic to find other organisms that can tolerate this long-term freezing and survive. Eventually, they hope to learn more about the biological mechanisms that make rotifers live. The hope that the revelations from these tiny animals will provide clues on how to better cryopreserve the cells, tissues and organs of other animals, including humans.