Rotifers are microscopic Multicellular organisms that live in fresh water. It is already known to withstand freezing (even in liquid nitrogen), boiling, dehydration and radiationThe group continued for millions of years without having sex. The humble but hardy rotifer has now surprised researchers once again – a recent study He explored the 24,000-year-old Siberian permafrost and found living (or at least revivable) rotifers there. Surviving 24,000 years in a deep freeze is a new record for this species.
Rotifers are not the only organisms that emerged from permafrost or ice. The same researchers behind this latest discovery have already found it nearly 40,000 years ago live worms In the permafrost in the area. Ancient algae, seeds, viruses and bacteria have shown amazing longevity on ice, prompting legitimate concern About whether any potentially harmful pathogens can also be released as Melting glaciers and permafrost.
Since bdelloids generally only pose a threat to bacteria, algae, and detritus, you don’t have to worry about this particular finding. But as major players at the bottom of the food chain, the newly emerging rotifers suggest that perhaps we should think about how species not seen for millennia are integrated into modern ecosystems.
The Soil Remnants Laboratory in Bushino, Russia, has been digging up Siberian permafrost in search of ancient organisms for nearly a decade. The group estimates the age of the organisms it found by radiocarbon dating of the surrounding soil samples (evidence showed no vertical movement through the permafrost layers). For example, last year researchers reported “frozen zoo“Of the 35 viable protists (organisms containing a nucleus that are not animal, plant, or fungal) that they counted ranged from hundreds to tens of thousands of years ago.
In their latest discovery, cryobiologists found the organisms after cultivating soil samples for about a month. Among the rotifer classes, bdelloids have a somewhat unusual ability to reproduce by parthenogenesis – that is, by cloning – and so the original specimens have already begun to do so. Although the clones made identification of the ancient parent difficult, this greatly facilitated further investigation of the characteristics and behavior of the unfrozen strain.
In all the above-mentioned studies on permafrost, there is always the concern of samples being contaminated by organisms in modern times. Besides using techniques designed to prevent this, the team also addressed this issue by looking at the DNA found in soil samples, confirming that contamination is highly unlikely. Furthermore, genetic analysis showed that the species does not match any known modern rotifers, although there are closely related species found in Belgium.
The team was naturally interested in better understanding the freezing process and gaining insight into how these rotifers survive for so long. As a first step, the researchers then frozen a selection of cloned rotifers at -15°C for one week and captured videos of rotifers resurrecting.
The researchers found that not all clones survived. Surprisingly, clones were generally no more tolerant of freezing than contemporary rotifers from Iceland, Alaska, Europe, North America, and even the Asian and African tropics. They were more tolerant of freezing than their closest genetic relatives, but the difference was marginal.
The researchers found that rotifers can survive a relatively slow freezing process (about 45 minutes). This is noteworthy because it was gradual enough for ice crystals to form inside the animal cells – a development that would normally be catastrophic for organisms. In fact, the mechanisms of protection against this are in high demand by anyone working in the field of cryopreservation, which makes this latest discovery particularly attractive from this perspective.
Although the authors aren’t quite in this area, they plan additional experiments to better understand cryptobiosis – the almost completely halted metabolic state that made rotifer survival possible. For research into cryopreservation of larger organisms, the authors suggest that this becomes more complex as the organism in question becomes more complex. However, rotifers are among the most complex cryopreserved species to date – complete with organs such as the brain and intestines.