A lone rotifer has awakened after spending the past 24,000 years in frozen hibernation. Scientists hope that further studies of this multicellular animal may lead to better ways of cryopreserving human cells, tissues, and organs.
Rotifers are worm-like aquatic animals that prefer freshwater environments and moist soil. These complex organisms aren’t as charismatic as tardigrades, another microscopic animal, but they’re likewise known for their extreme survival skills, as they’re capable of withstanding dehydration, freezing temperatures, starvation, and low oxygen levels. By reviving a 24,000-year-old rotifer found in Siberian permafrost, scientists have demonstrated that these creatures are even tougher than previously thought. The new findings were published today in Current Biology.
“Our report is the hardest proof as of today that multicellular animals could withstand tens of thousands of years in cryptobiosis, the state of almost completely arrested metabolism,” said Stas Malavin, a co-author of the study, in a press release. Malavin is a biologist at the Soil Cryology Laboratory at the Institute of Physicochemical and Biological Problems in Soil Science in Pushchino, Russia.
An impressive feat for a microbe, but a record it is probably not. Back in 2018, Russian scientists claimed to have resurrected nematode worms pulled from permafrost deposits dated to at least 32,000 years ago. Previous rotifer recovery records range from between six and 10 years, involving specimens found in Antarctic soil and on a glacier. The tardigrade record is 30 years, but given their track record, I have a sneaking suspicion they can withstand even longer durations of frozen hibernation.
Credit for the new discovery goes to Russia’s Soil Cryobiology Lab, which uses drills to dig samples from Siberian permafrost. The resurrected rotifer was found near the Alazeya River in northeastern Siberia at a depth of 3.5 metres. The team used special extraction methods to prevent contamination with neighbouring layers, while also ruling out natural seepage from the layers above. The Late Pleistocene layer holding the rotifer specimen was radiocarbon-dated to approximately 24,000 years ago, which is roughly 12,500 years prior to the end of the most recent ice age.
Back in the lab, the scientists managed to revive the rotifer and even produce several secondary rotifer cultures from the same individual (rotifers reproduce asexually in a process known as parthenogenesis). The reported revival “constitutes the longest reported case of rotifer survival in a frozen state,” according to the paper. Genetic analysis of the specimen identified it as belonging to the genus Adineta, and it compared rather nicely to living samples sourced from Belgium.
To learn more about rotifers and how they’re able to pull off this trick, the team randomly selected 144 unrelated rotifer specimens and kept them frozen at -15 degrees C for one week. This experiment, though limited in scope, showed that the ancient Adineta specimen “was not significantly more freeze tolerant than contemporary species,” as the scientists wrote in their paper.
“The takeaway is that a multicellular organism can be frozen and stored as such for thousands of years and then return back to life — a dream of many fiction writers,” said Malavin. “Of course, the more complex the organism, the trickier it is to preserve it alive frozen and, for mammals, it’s not currently possible. Yet, moving from a single-celled organism to an organism with a gut and brain, though microscopic, is a big step forward.”
Somehow, Adineta rotifers are able to fight the formation of ice crystals — the mortal enemy of the freezing process. Ice crystals are like tiny knives, and they destroy the integrity of cells and organs. Rotifers likely have some sort of “biochemical mechanisms of organ and cell shielding necessary to survive low temperatures,” according to the paper. A better understanding of this rotifer defence mechanism could go a long way in improving cryopreservation techniques to store cells, organs, and tissues at cold temperatures.
More speculatively, these insights could even advance the nascent field of cryonics, in which deceased humans are stored at liquid nitrogen temperatures. The revival of these frozen people may never happen, but the resilient rotifers are, at the very least, giving us hope.