The oldest organisms alive were born while humans were busy learning how to fish and make instruments, nearly 42 000 years ago. What was the Earth like in those days? For thousands of years, these ancient organisms have been frozen in the soil in Siberia, but with the help of Russian scientists, they have been reanimated. They are the nematode.
What are Nematodes?
Nematodes are more commonly known as roundworms. The name nematode is based on ancient Greek words, and means ‘thread species’. While different species of nematodes vary in size, from 0.1 millimeters in length up to 1 meter, they tend to be thin (less than 100 micrometers thick) and all share the trait of a cylindrical digestive system that stretches the length of the worm and has openings at each end. Nematodes have noticeable head structures that can be distinguished from the rest of their tubular body.
There are many different species of roundworm, and most are parasitic. One non-parasitic species is C. elegans, a model organism; hookworms and pinworms are common nematode parasites that infect humans.
Nematodes are very resilient organisms that have adapted to be able to live in almost every type of environment, including in permafrost soil.
How Were the Frozen Nematodes Discovered?
Three hundred different permafrost soil samples were collected from different locations in Russia. Of these samples, two were found to contain well preserved frozen nematodes; one sample was from the burrow of a ground squirrel one hundred feet below the surface, and the other sample was dug up from eleven feet below the surface. The samples containing frozen nematodes were carbon-dated and found to be from 32 000 years ago and 41 700 years ago, respectively.
A concern that the nematodes found in the samples were not from the same time period as the dated samples has been considered. The researchers were careful to handle the samples as aseptically as possible to ensure that no modern nematodes were accidentally introduced into the soil samples. The consideration that modern nematodes may have naturally migrated down to the areas from which the samples were taken is also slim; the permafrost topsoil in the area from which the samples were removed typically thaws approximately two and a half feet down only. The ground hasn’t thawed deeper than approximately five feet in over 100 000 years. It is unlikely that any nematode could have wriggled down to the appropriate depths anytime in the last few millennia.
How Were the Nematodes Reanimated?
The permafrost soil samples were stored at -20 °C in the laboratory. Once the nematodes had been found in the permafrost samples, they were removed from the soil and placed onto nutrient media in Petri dishes. The dishes were stored at 20 °C for several weeks, at which point, the nematodes began to show signs that they were alive.
What Happened When the Nematodes Were Reanimated?
Once the nematodes had slowly revived, they began to show signs of life by moving around and even eating. Nematodes that live in the soil tend to eat bacteria at a rapid rate (up to five thousand per minute!). The digestive system has no stomach, but rather a large stretch of intestine. Food enters the nematode via the mouth, which has three or six sets of lips lined with teeth and passes into the pharynx where enzymes are produced by digestive glands to break down the food consumed. The nutrients generated are absorbed along the length of the rest of the intestine.
One of the nematodes was determined to be from the Panagrolaimus detritophagus species, while the other, the more shallowly buried nematode, was found to be of the Plectus parvus species. Both of these species are known today, but it is possible that the newly revived nematodes are quite different from their modern counterparts. It was also found that both of the nematodes are female.
What Is the Big Picture Meaning of This Discovery?
Early in 2017, researchers from the British Antarctic Survey (BAS) and from the University of Otago in New Zealand performed research on an Antarctic nematode to study its ability to survive freezing and to avoid freezing. The nematodes can avoid freezing by removing all of the water from inside of itself in a process called cryoprotective dehydration. While impressive, what is even more unique about the nematode is its ability to survive freezing. Ordinarily, when cells are frozen, ice crystals form within the cell and puncture the cell membrane. When the cells are defrosted, they are no longer alive as their membranes are full of holes. The nematode from the Antarctic is able to survive this process, and even to continue to reproduce after having been completely frozen and then thawed.
This year, Russian researchers found that nematodes can survive for incredibly long periods of time having been frozen in an extreme example of cryopreservation. Of course, other organisms have been discovered as preserved specimens and brought back to life. One example is a virus found also in the permafrost of Siberia from approximately 30 000 years ago. Another example is the Bacillus spores found in salt crystals from 250 million years ago which were found and revived. However, these examples are of single-cell organisms and are not as complex as multicellular nematodes. In terms of multicellular organisms, tardigrades frozen for thirty years and nematodes frozen for 39 years have been previously successfully revived. These were the longest times that any multicellular organisms had been frozen and returned to life. To find complex organisms that once lived over 40 000 years ago and bring them back to life is, quite simply, amazing.
Each new discovery allows scientists to better understand cold tolerance and the adaptations that have allowed the ability to survive while being completely frozen for so long to occur. There are many possible applications for this kind of development in technology, including the preservation of endangered animal species or even space travel for humans. Perhaps one day, science and technology will have used this knowledge to allow astronauts to take a chilly snooze while cruising through space towards some far-off star system.