Scientists find ancient living creatures after 24,000 years in permafrost


Rotifers are microscopic multicellular freshwater organisms. They are already known to withstand freezing (even in liquid nitrogen), boiling, desiccation and radiation, and the group persisted for millions of years without having sex. The humble but remarkably robust bdelloid rotifer once again surprised researchers – a recent study unearthed 24,000-year-old Siberian permafrost and found living (or at least revivable) rotifers. Surviving 24,000 years in deep frost is a new record for the species.

Rotifers aren’t the only living organisms that emerge from permafrost or ice. The same researchers behind this latest discovery had already found around 40,000 years ago viable roundworms in the region’s permafrost. Old moss, seeds, viruses and bacteria have all shown impressive longevity on ice, prompting legitimate concern find out if potentially harmful pathogens can also be released melting glaciers and permafrost.

Since bdelloids are generally only a threat to bacteria, algae, and detritus, there is no need to be concerned about this particular finding, however. But as key players at the bottom of the food chain, the newly reappeared rotifers indicate that perhaps we should be thinking about how species that have not been seen for millennia could reenter modern ecosystems.

The Soil Cryology Laboratory in Pushchino, Russia, has been digging through Siberian permafrost for ancient organisms for about a decade. The group estimates the age of organisms they find by radiocarbon dating surrounding soil samples (evidence has shown that there is no vertical movement through the permafrost layers). For example, last year, researchers reported a “frozen zooOf 35 viable protists (organisms containing a nucleus that are not animal, plant or fungus) that they calculated ranged from hundreds to tens of thousands of years.

In their most recent discovery, cryology researchers found the bdelloids alive after cultivating the soil samples for about a month. Among the classes of rotifers, bdelloids have the rather unusual ability to reproduce by parthenogenetics, that is, by cloning, and so the original specimens had already begun to do so. Although the clones made it difficult to identify the former parent, it greatly facilitated further investigation into the characteristics and behavior of the unfrozen strain.

In all of the above permafrost studies, there is always the concern of sample contamination by modern organisms. In addition to using techniques designed to prevent this, the team also addressed this problem by examining DNA present in soil samples, confirming that contamination was highly unlikely. Phylogenetic analysis further showed that the species did not correspond to any known modern rotifers, although there is a closely related species in Belgium.

The team was naturally interested in better understanding the freezing process and understanding how these rotifers survived for so long. First, the researchers then froze a selection of cloned rotifers at -15 ° C for a week and captured videos of the reviving rotifers.

The researchers found that not all of the clones survived. Surprisingly, the clones were generally not much more frost hardy than contemporary rotifers from Iceland, Alaska, Europe, North America, and even the Asian and African tropics. They were a bit more tolerant of frost than their genetic closest relative, but the difference was marginal.

The researchers found that rotifers could survive a relatively slow freezing process (around 45 minutes). This is remarkable because it was gradual enough that ice crystals formed inside the cells of the animals, a development that is usually catastrophic for living organisms. In fact, the protective mechanisms against this are highly sought after by all cryopreservation professionals, which makes this latest discovery particularly appealing from this point of view.

While the authors are not quite in this area, they are planning additional experiments to better understand cryptobiosis, the almost completely arrested state of metabolism that made the survival of rotifers possible. As for research on cryopreservation of larger organisms, the authors suggest that it becomes more delicate as the organism in question becomes more complex. That said, rotifers are among the most complex cryopreserved species to date, with organs such as a brain and gut.

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