Some microorganisms can survive incredibly long, up to a quarter of a billion years. The BBC Earth columnist shares how they manage to avoid the destruction that usually accompanies aging.
Certain types of coral live for thousands of years. American lobsters are at least 140 years old. One turtle managed to live to be 250 years old. And the oldest animal on Earth - a clam named Ming - was 507 years old when scientists accidentally killed it in the course of research.
However, compared to some creatures living on Earth, these creatures are mere babies. The oldest terrestrial organisms can easily break these longevity records, which is not bad for life forms that can only be seen under a microscope.
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In the coldest regions of Siberia, Antarctica and Canada, you can find soil that has been permanently frozen for thousands and even millions of years. This permafrost is home to bacteria of the same age as the ice itself.
Scientists have not yet been able to figure out how they manage to maintain the ability to live. However, some believe that by revealing their secrets, we can find the key to immortality.
In 1979, while working at the Vostok research station in Antarctica, the Russian scientist Sabit Abyzov discovered bacteria, fungi and other microorganisms living at a depth of 3, 600 meters in the ice layer above the subglacial Lake Vostok.
Surprisingly, the bacteria felt great in the ice, which has not melted for hundreds of thousands of years.
It is unlikely that bacteria could end up in the ice after its formation, so Abyzov concluded that the bacteria themselves should also be hundreds of thousands of years old. At that time, they were the oldest organisms ever discovered.
In 2007, the longevity record was broken again. Eske Villerslev and a group of scientists from the University of Copenhagen made a historic discovery.
Deep under the permafrost layer of Antarctica, Siberia and Canada, they found living bacteria that were half a million years old. Then scientists for the first time managed to isolate DNA from such ancient, but still active bacteria.
Just two years later, an even older microorganism was discovered. This time its age was 3.5 million years.
Russian scientist Anatoly Brushkov removed it from the ice in the region of Mammoth Mountain in Yakutia.
Later, he even injected himself with cells from this "immortal" bacteria known as Bacillus F, in the hope that it could prolong his life. Before that, he tested inactivated bacterial cells in mice, fruit flies and human blood cells. He states that he has not had the flu in two years since this injection.
What makes scientists think that bacteria living in permafrost are so ancient?
After all, we can assume that they are simply descendants of bacteria that got into the ice thousands or millions of years ago.
The answer is that bacteria don't have enough space in the ice to grow. Even if division took place, the new cells would have nowhere to go.
If reproduction is not possible, then the cells of microorganisms found in permafrost in our time must be cells frozen into the ice at the onset of the ice age.
This is how scientists substantiate the controversial statement that individual bacteria have managed to live for at least 250 million years. These microorganisms were found inside salt crystals at a depth of 600 meters during the construction of a radioactive waste storage facility in New Mexico, USA.
If they are really 250 million years old, they should have caught the period when the first dinosaurs appeared on Earth.
This discovery belongs to scientist Russell Vreeland of West Chester University, Pennsylvania. He says the bacterium, dubbed "Virgibacillus strain 2-9-3", is very similar to the modern-day Dead Sea Virgibacillus.
The microbes extracted from the crystals, placed in a test tube with nutrients, revived and began to develop.
Some researchers insist that the 2-9-3 strain is much younger than 250 million years old, explaining this by a violation of sterile conditions in the laboratory. However, Vreeland is firmly convinced that he is right. He considers it obvious that these bacteria were trapped inside the crystal.
"They were in crystals and were alive, " Vreeland says. "The chances of being trapped in a solid crystal from the outside are roughly zero, and the chance of infection is one in a billion."
Moreover, many similar bacteria have been found in salt crystals since then.
The most recent discovery is bacteria between 33 and 48 million years old, found in a salt lake in Central China. However, none of the latest finds have come close to 250 million years old.
Ancient microorganisms found in permafrost and salt crystals are on the brink of survival.
Deprived of the ability to reproduce due to lack of space, they channel the crumbs of energy that they manage to receive to support the life of a single cell.
"The bacteria could not divide inside the salt crystal due to lack of nutrients. In addition, they would not be able to get rid of toxic waste products, " says Vreeland.
It should be noted that the preservation of life for millions of years is an incredible ability. As a rule, DNA and proteins responsible for reactions inside living cells under the influence of radiation are destroyed in a fairly short period of time. What is the secret of bacteria that have managed to cope with this problem?
Some scientists believe that ancient bacteria could only live such a long life if they had mechanisms for repairing DNA and cellular structure.
But what exactly these mechanisms are and how they function in such unfavorable conditions remains unknown. So, for example, bacteria in permafrost or salt do not have access to water necessary for the synthesis of proteins involved in the process of cell repair.
At the moment, with the support of the Howard Hughes Medical Institute, Vreeland is working on the determination of the gene sequence of the 2-9-3 strain. This will allow them to learn more about how they were able to live for so long.
At the same time, some ancient bacteria have an alternative long-term survival plan. They can fall into a kind of "lethargic sleep".
We know that under especially unfavorable conditions bacteria are able to form dormant forms - spores. Spores are similar to plant seeds: a strong shell forms around the vulnerable cell.
However, unlike seeds, spores are incredibly viable. They can survive the effects of radiation and go for years without water and nutrients. Inside the shell, the microbe is in a completely inert state, but if conditions improve, it can return to life.
Back in 1995, scientist Raul Cano and his colleagues were able to revive the bacterial spores extracted from the stomach of an ancient bee, which were about 30 million years old.
A bee with bacteria inside was stuck in a drop of tree resin, which later turned into amber.
However, some scientists believe that the ability to form spores alone is not enough to survive for 250 million years. In their opinion, over such a long period, their DNA would inevitably have collapsed.
DNA is adversely affected by high-energy cosmic radiation, solar radiation in the form of gamma rays and ultraviolet rays, and radiation resulting from the spontaneous decay of atomic nuclei.
Paul Falkowski of Rutgers University in the United States conducted an experiment using five ice samples that were between 100, 000 and 8 million years old.
The ice was dredged in Antarctica, in the Beacon Valley and Mullins Valley. Together with a group of colleagues, he tried to cultivate microorganisms in the ice. He found that the older the ice was, the shorter the DNA sections inside it, and the fewer bacteria that could be revived. In other words, over time, DNA is steadily destroyed.
Falkowski managed to cultivate microorganisms from a piece of ice two million years old. He calculated that after 1.1 million years, half of the original DNA was destroyed.
"We can assume that, given the intensity of the radiation at the poles, bacteria will live no more than two to three million years, " says Falkowski.
“Just a couple of hits from cosmic rays and that's it. For a short period of time, the probability of hitting is very low. But when we talk about millions of years, it will definitely happen.
This phenomenon can be compared to lightning: for millions of years it has hit almost every point on Earth, despite the fact that the probability of it hitting a certain place in a short period of time is very low. "
Nevertheless, Vreeland does not lose faith in the fact that under the right conditions bacteria can live much longer than Falkowski's experiments suggest.
"Oxygen does not get into the salt crystal, so there is no oxidation, " he says. "In addition, bacteria are located at a depth where ultraviolet rays cannot penetrate."
Vreeland also notes that when spores form around the DNA molecule, a dense shell is formed, making it less accessible for radiation. In addition, the salt crystal itself protects bacteria from radioactive radiation, blocking access to heavy metals.
This means that the only potential source of radioactive radiation is potassium-40, a radioactive isotope of potassium with a half-life of 1.25 billion years. Therefore, the likelihood that potassium-40 will emit radiation is very low.
Finally, there is no water in salt crystals, and this helps to strengthen chemical bonds in DNA molecules. In other words, it becomes more difficult to destroy it.
“As a result of our research, we found that in a salt crystal it takes 1000 times more DNA hits to completely destroy DNA than under normal conditions, ” says Vreeland.
"Considering all these factors, one can conclude that the crystals provide very reliable protection."
What is the significance of the ability of individual bacteria to survive for many millions of years?
If dormant forms of bacteria can survive for millions of years, it cannot be ruled out that cells or DNA first appeared on another planet in another galaxy and were brought to Earth by a comet or asteroid.
After all, the closest galaxy to our Milky Way - the Andromeda galaxy - is only 2-3 million light years away. For a bacterium living for 250 million years, this distance is quite surmountable.
Vreeland's work also supports the idea that life could exist on Mars, with salt found in Martian meteorites.
At the same time, long-lived organisms can pose a threat to the world's population. It cannot be ruled out that pathogenic bacteria or viruses could remain in the ice. For example, a similar virus was discovered in 2014 in Siberian permafrost, which is at least 30, 000 years old, at a depth of 30 meters.
This ancient "giant" (up to 1.5 µm in length) virus called Pithovirus sibericum can be seen with an ordinary microscope. In laboratory conditions, scientists managed to revive it and restore its pathogenic properties. This virus is not dangerous to humans, as it only infects single-celled amoebas.
However, researchers believe that the Siberian permafrost may contain microorganisms that can cause disease in humans.
It is possible that they will be able to return to life when the ice melts.
For example, these can be ancient forms of smallpox.
Not all viruses dangerous to humans will be able to survive in ice. Influenza and HIV, which are lipid-coated, are more fragile than protein-coated viruses.
One way or another, these studies can serve as a warning to humanity.
Despite their small size, the main centenarians on our planet can have a huge impact on the modern world.