An international effort to revive an ancient roundworm, frozen in the Siberian permafrost for millennia, has uncovered a form of life even older than scientists thought.
In 2018, several resurrected nematodes, from the genus Panagrolaimus, were dated to be around 32,000 years old. But now, more precise radiocarbon dating suggests that these soil worms have lain “dead awake” in parts of Siberia since at least the Late Pleistocene, about 46,000 years ago.
If true, the record absolutely breaks the longest known state of extreme inactivity among animal life, a phenomenon known as cryptobiosis.
After reviving the frozen worm in the laboratory and culturing it for more than 100 generations, the researchers, led by experts from the Max Planck Institute in Germany, carried out an analysis of the genome. They claim that this creature is a newly recorded species, which they call Panagrolaimus kolymaensis.
To date, scientists know of very few animals capable of suspending themselves in a limbo state in response to harsh environmental conditions.
Tardigrades, nematodes, and microscopic aquatic organisms, called rotifers, are just a few of the animals known to enter cryptobiosis. For all we know about this unique state of life, these animals could very well remain in this desiccated state “indefinitely,” or at least until conditions become better for their survival.
The longest recorded time of cryptobiosis among living worms is only 39 years. Even tardigrades have only returned to their normal metabolic state after 30 years of freezing. The new king of cryptobiosis is tens of thousands of years older.
The ancient worm was found in the Siberian permafrost, about 40 meters deep. When the researchers dated plant material found near the creature, they established an initial freezing period between 45,839 and 47,769 years ago.
This beats another ancient nematode, of the genus Plectus, which was also found frozen in Siberia and was dated to around 42,000 years ago in 2018.
Both nematodes are almost twice as old as an ancient Siberian rotifer, which was recently revived after 24,000 years of cryptobiosis.
When the researchers compared the genomes of P. kolymaensis with that of one of its living relatives, Caenorhabditis elegans, they found a large number of genes that overlapped among the soil worms. Many of the shared genes are related to survival mechanisms in harsh environmental conditions.
This is interesting, as C. elegans is often found in temperate regions, hiding in decaying fruits or plants.
The study authors state that their findings “indicate that by adapting to survive in a cryptobiotic state for short periods of time in environments such as permafrost, some nematode species acquired the potential for individual worms to remain in that state for geologic periods of time.” .
The team now wants to find out what role these shared genes play in cryptobiosis, and whether there is an upper limit to how long nematodes can remain in this mysterious state.
There is even the possibility that unlocking the secrets of cryptobiosis in the long term will provide scientists with a better way to store cells and tissues for long periods of time.