Rotifers are microscopic multicellular organisms that inhabit freshwater. They are already known to withstand freezing (even in liquid nitrogen), boiling, drying and radiation, and the group persisted for millions of years without sex. The modest but extremely durable bdeloid rotifer has now surprised researchers again a recent study excavated a 24,000-year-old Siberian permafrost and found living (or at least invigorating) wheels there. Surviving 24,000 years in deep freezing is a new record for this species.
Rotifers are not the only living organisms that emerge from permafrost or ice. The same researchers behind this latest discovery have previously found approximately 40,000 years viable roundworms in permafrost in the region. Ancient moss, seeds, viruses and bacteria have shown impressive longevity on ice, leading to this justified concern about whether potentially harmful pathogens can also be released as melting glaciers and permafrost.
Given that bdeloids are generally only a threat to bacteria, algae, and detritus, however, there is not much need to worry about this particular discovery. But as key players at the bottom of the food chain, emerging wheelers suggest that perhaps we should consider how species that have not been seen for millennia could be reintegrated into modern ecosystems.
The Pushchino Soil Cryology Laboratory in Russia has been digging up Siberian permafrost in search of ancient organisms for about ten years. The group estimates the age of the organisms it finds using radiocarbon by dating surrounding soil samples (evidence has shown that there is no vertical movement through the permafrost layers). For example, last year researchers reported “frozen zoo“Of the 35 viable protists (organisms that contain nuclei that are neither animals, plants, nor fungi) that have been calculated to range from hundreds to tens of thousands of years.
In their latest discovery, cryology researchers found live bdeloids after growing soil samples for about a month. Among the classes of rotifers, bdeloids have a rather unusual ability to reproduce parthenogenetically – ie. By cloning – so the original samples have already started. Although the clones caused the identification of the ancient parent, this greatly facilitated further investigation of the characteristics and behavior of the thawed strain.
Through all of the above permafrost studies, there is always concern about the contamination of samples with modern organisms. In addition to using techniques designed to prevent this, the team also addressed this problem by looking at the DNA present in soil samples, confirming that contamination is very unlikely. In addition, phylogenetic analysis showed that the species did not coincide with 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 gaining insight into how these wheels survived for so long. As a first step, the researchers then froze the selection of cloned rotators at -15 ° C for one week and recorded videos of rotator resuscitation.
The researchers found that not all clones survived. Surprisingly, clones were generally no more frost-tolerant than modern rotifers from Iceland, Alaska, Europe, North America, and even the Asian and African tropics. They were a little more tolerant of freezing than their closest genetic cousin, but the difference was marginal.
The researchers found that rotifers could survive a relatively slow freezing process (about 45 minutes). This is worth noting because it was gradual enough that ice crystals formed inside the animal cells – a development that is usually catastrophic for living organisms. In fact, safeguards against it are highly sought after by everyone in the cryopreservation business, making this latest discovery particularly tempting from that perspective.
Although the authors are not engaged in this work, they are planning additional experiments to better understand cryptobiosis – a condition of almost completely arrested metabolism that allowed the rotifer to survive. Regarding the research of cryopreservation of larger organisms, the authors suggest that this becomes more complex as the organism in question becomes more complex. Still, rotifers are among the most complex cryo-preserved species to date – along with organs such as the brain and intestines.