Have 46,000-year-old Nematodes in Suspended Animation Really Been Resuscitated?

For more than two decades scientists have been collecting frozen microbes from deep layers of the Siberian permafrost, to see if they can be thawed and brought back to life. In the most recent revival experiments, a team of genetic researchers from Russia and Germany first reawakened and then identified a previously undiscovered nematode species, which they claim is 46,000 years old. Assuming this is true, this is the most ancient type of microscopic lifeform to have even been recovered from the freeze-dried Siberian soil.

In an article about their research just published in PLOS Genetics, the genetic researchers describe how they confirmed the existence of this new species of roundworm, which was unearthed near Siberia’s Kolyma River and has now been named  Panagrolaimus kolymaensis (or P. kolymaensis). There are many nematode species that belong to the  Panagrolaimus line, so this ancient species has living relatives.

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Location of the Duvanny Yar outcrop on the Kolyma River, northeastern Siberia. (Shatilovich et al, 2023, PLOS Genetics/CC-BY 4.0)

Interestingly, P. kolymaensis was not recognized as a new type of nematode when it was first revived in 2018. It was incorrectly identified as belonging to another previously identified species, which lived 42,000 years ago.

But in the latest study, anomalies were detected that threw the initial identification of this variety of microscopic roundworm into doubt. Further analysis revealed it was a different species altogether, and one that had lived in an earlier time period.

 “The radiocarbon dating is absolutely precise, and we now know that they really survived 46,000 years,” study co-author Teymuras Kurzchalia, a cell biologist affiliated with the the Max Planck Institute of Molecular Cell Biology and Genetics in Dresden, Germany, told Scientific American.

The scientist explained that radiocarbon dating tests performed on the freeze-dried plant matter that surrounded the newly identified nematode led to the change in timeframe. No such testing had been done before, as it was simply assumed that  P. kolymaensis was a familiar species.

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Meet the Incredible, Indestructible Nematode

The discovery of this new and astoundingly ancient species of nematode highlights the impressive ability of this tiny animal to wake from a state of suspended animation unharmed, despite an immense passage of time.

Nematodes are truly one of the most ubiquitous lifeforms found on the planet. They can live in the soil or in the water, and have been found in abundance in soil or sediment samples collected from deserts, tropical forests, swamps, ocean floors and frozen wastelands (including Antarctica as well as Siberia). Most feed on bacteria, fungi and other microbes, although a few do have the capacity to act as parasites that infect human beings or animals.

General morphology of P. kalamansis, female. Scanning electron pictures. (Halilovic et al, 2023, PLOS Genetics/CC-BY 4.0)

When stressed by extreme cold that freezes them or excessively dry conditions where there is no water to sustain them, nematodes will enter a state of extreme inactivity known as cryptobiosis. All nematode biological activity will seemingly cease, giving them the appearance of being dead. But when thawed or re-hydrated, either by climate change or through the intervention of scientists in laboratories, nematodes will spring back to life—and the length of time that has passed since they entered cryptobiosis seems to have no relevance with respect to their resiliency.

In the case of the newly revived  P. kolymaensis, being frozen for 46 hours, 46 days or 46,000 years would have made no difference.

“We can say that they are alive, because they move, they eat bacteria on the culture plates, and they reproduce,” said study co-author and University of Cologne (Germany) evolutionary biologist Philipp Schiffer, in an interview with the Washington Post. 

If it were released into the environment, the newly discovered species would have no trouble adapting and surviving.

The Skeptical View

Because microscopic creatures like nematodes are so incredibly small and so incredibly common, studying their genetics is a complicated affair. For this reason, the announcement by the Russian-German research team that they’ve discovered a new species of nematode is being greeted with skepticism by some experts.

Bryon Adams, a biologist from Brigham Young University, told Scientific American there were reasons to be cautious about the legitimacy of this apparent discovery.

“I don’t doubt the age of the organic material in the permafrost,” he said, referring to the plant matter dated as being 46,000 years old. “Those values are likely legit.”

However, he stated, “the authors haven’t done the work to show that the animals they have recovered are not simply surface contaminants.”

With invisible microbes whose movements can’t be traced, this kind of contamination is always possible. Another issue is that while there are millions of nematode species currently living only a few thousand have ever been identified. So, the fact that  P. kolymaensis hasn’t been identified before doesn’t mean it isn’t living on the earth right now.

But study co-author Teymuras Kurzchalia finds the skeptical arguments unconvincing. While he was not involved in the actual recovery process of the nematodes out in the field, he studied the methodology of the collectors and is certain contamination of the soil samples by surface-dwelling nematodes would not have been a problem. Even though the possibility can’t be ruled out with 100-percent certainty, he considers that explanation extremely unlikely.

A Survival Kit for the Ages

As a part of their analysis, the Russian and German researchers compared the newly discovered  P. kolymaensis with a modern species known as  Caenorhabditis elegans (C. elegans). The latter type of nematode is a soil-eating bacteria that has been “domesticated” for use in laboratory experiments. Consequently, it has become the most studied and most well-known species of nematode on the planet.

Despite the separation in time between  P. kolymaensis and C. elegans, the researchers found significant genetic overlaps between the two. One of the commonalities was in the pathways each used to enter a state of cryptobiosis.

One particular form of  C. elegans, known as the dauer larva, has shown it must process a sugar known as trehalose in order to successfully transition to cryptobiosis when exposed to freezing temperatures. Trehalose is found in the bacteria and fungi nematodes eat while living in the soil, and research has shown that this type of sugar helps protect living cells exposed to high heat, drought, salt water or intense UV rays.

In the new study that revealed the existence of  P. kolymaensis, genetic researchers discovered that this ancient species needed to have plentiful supplies of trehalose to enter cryptobiosis as well. It is clear that evolutionary processes have preserved the nematode’s capacity to achieve a state of suspended animation for tens of thousands of years, despite all the genetic mutations that have created the millions of separate nematode species living today.

“This survival kit is the same as it was 46,000 years ago,” Kurzchalia noted, expressing marvel at nature’s remarkable ingenuity and staying power.  

Top image: A species of nematode similar to the 46,000 year old worms that have been resuscitated.       Source: Hussmann/Adobe Stock

By Nathan Falde