Discover How Frozen Microorganisms Survive for 100,000 Years

Microorganisms found in Siberian permafrost seem to have existed for more than 100,000 years as indicated by DNA analysis. The genetic similarities with other species imply that such long life spans might be common among the closest living relatives of complex cell organisms.

Additionally, microorganisms gathered from ancient marine sediments, some over 100 million years old, raise questions about the survival of individual organisms over such spans. “You can’t conduct experiments over that duration,” states Karen Lloyd from the University of Southern California. “[Time] Coexistence is an unpredictable variable.”

Lloyd and her team aimed to find microorganisms in areas that had been stable for extensive periods. Their exploration led them to the Chukchi Peninsula, the easternmost point of Siberia, where they extracted a 22-meter core of permafrost.

This core allowed them to extract DNA from layers of marine sediment that dates back between 100,000 and 120,000 years. These sediments contained pores filled with liquid water that might have trapped microorganisms, preventing any exchange of nutrients or organisms. “Being frozen means that ice structures encapsulate them,” Lloyd explains.

The subsequent question was how to differentiate between living and non-living cells. Researchers sequenced millions of DNA fragments from the permafrost, utilizing them to reconstruct the genomes of various microbial species present. The degraded DNA was repaired, and enzymes that facilitated genome reconstitution were introduced into the mix.

After incorporating DNA repair enzymes, most reconstructed genomes showed significant completeness, indicating they originated from dead cells that do not actively preserve DNA integrity, according to Lloyd. Conversely, the genomes of six species showed minimal alteration, suggesting that these DNA samples came from living cells actively maintaining their genome since being frozen at least 100,000 years ago.

All six species with intact DNA were from the gate forest, also known as Asgard Archaea. These organisms are recognized as the closest modern relatives to all eukaryotes, encompassing animals, plants, fungi, and other native forms of life.

“Discovering Asgard archaea thriving in ancient permafrost offers insight into their evolutionary path… and their role in the emergence of complex life,” remarks team member Rend Liang at the University of Earth Sciences in China, especially during an era when the Earth was fully frozen.

Even more remarkably, the long-lived species were similar to Asgard Archaea found in less extreme environments, sharing genes associated with protein and DNA repair. This may have facilitated gradual exchanges of cellular components in low-energy conditions without cell division. “They’re like the most uneventful Asgards ever,” Lloyd comments. “Their lack of excitement suggests they possess capabilities.”

Stephen de Hon from the University of Rhode Island considers the study a “significant advancement” in understanding exceptionally long life spans.

Nevertheless, he warns that these findings should not be generalized to environments beyond freezing conditions like permafrost. “Long periods of inactivity in frozen states are different from living extensively at minimal activity levels.”