Harnessing the superpowers of the most resilient life form on Earth

Bake them, freeze them, fire them from a gun, or blast them into space: tardigrades can survive almost anything. Some experts even think this eight-legged micro-animal could outlive every other species on Earth – including humans – and survive right up until the Sun dies.

If you went into outer space without protection, you’d die. Yet a tiny animal no larger than 1mm long – about the size of a pinhead – has survived this and more. Under the microscope, tardigrades, also known as water bears or moss piglets, are fearsome looking creatures. Their podgy misshapen faces, ferocious claws and dagger-like teeth make them look more like a monster from Doctor Who than an animal.

Now scientists are trying to harness their superpowers for our own use – from protecting cancer patients from harmful radiation therapy, to preserving food and medicines during long-duration, deep-space exploration.

So far, scientists have identified around 1,500 species of tardigrade. Closely related to arthropods – which include insects and crustaceans – scientists have not yet determined where exactly where in the animal kingdom these creatures deserve to be classified.

Tardigrades love to hide out in damp environments where there is plenty of moss, lichen and leaves. You may even find them in your back garden. But they are also famous for being able to survive in extremely inhospitable places. They have been discovered up mountains in the Himalayas, at the bottom of the ocean, in Antarctica, and even in highly acidic Japanese hot springs – although this finding hasn’t been replicated.

It’s not just the harsh environs of Earth that tardigrades can live in. In 2007, tardigrades became the first-known animals to survive being blasted into space. When the satellite they were travelling on returned to Earth, scientists found that many – but not all – survived. Some of the females had even laid eggs in space, and the newly hatched young were healthy.

Tardigrades were also aboard a 2019 Israeli mission called Beresheet, which attempted to land on the Moon, although the probe crashed with its microscopic passengers in tow and it is unclear if they survived.

Scientists keen to test the survival limits of the tiny creatures have put them through a battery of tests. As a result, we know that tardigrades can withstand a huge amount of radiation – up to 1,000 times the lethal dose for humans. They can also cope with being heated to 150C (302F), and being frozen to just 0.01C (0.018F) above absolute zero. In 2021, scientists even fired bullets with tardigrades inside to see if they could survive the impact. The study showed that tardigrades could survive being fired at speeds of up to 900m per second (3,000km per hour), which is faster than a bullet fired from a typical handgun.

So how do these seemingly insignificant creatures survive in such extreme conditions, and why have they evolved these superpowers? It turns out that tardigrades have a host of tricks up their sleeves.

State of suspended animation

One environmental extreme that tardigrades have evolved to cope with is desiccation (essentially being dryed out). For most animals, life without water is completely impossible. As cells dry out, the membranes that hold them together shrink and lose volume.

“All the stuff that’s normally inside the cell gets smooshed together,” says Thomas Boothby, an assistant professor studying the biochemistry and mechanisms of extremotolerant organisms at the University of North Carolina at Chapel Hill, US. “Then the proteins start to clump and stick together. They become non-functional; they don’t work anymore.”

Somehow tardigrades can avoid all this, but how? One of the clues to this question came in 1922, after a German scientist found that when a tardigrade dries out it retracts its head and eight legs, before entering a deep state of suspended animation that closely resembles death.

“They literally pack their organs away, concentrating them within an extremely small, confined space,” says Nadja Møbjerg, associate professor of cellular biology and physiology at the University of Copenhagen.

In this “tun” state, the tardigrade’s metabolism slows to 0.01% of its normal rate. It can stay in this shrivelled state for decades, only reanimating when it comes into contact with water.

For example, in 1948 Italian zoologist Tina Franceschi took tardigrades that had been gathering dust in a museum for over 120 years and added water, after which one of the creature’s front legs started moving. Although the creature never fully revived, in 1995, desiccated tardigrades were brought back to life after eight years.

The tun state helps preserve the animal’s three-dimensional (3D) structure. Yet this by itself is not enough to explain tardigrade’s extreme survival skills. As ever, there is more to the story. In 2017, Boothby and his colleagues were monitoring the gene activity of tardigrades as they dried out and formed a tun when they noticed a spike in genes coding for mysterious proteins, later named “tardigrade-specific intrinsically disordered proteins”, or TDPs for short. When the team blocked the activity of these genes, the tardigrades were no longer able to survive desiccation. When they gave the genes to yeast and bacteria, the ability of these organisms to survive drying out increased by a factor of 100.

In 2022, Takekazu Kunieda, professor of biology at the University of Tokyo, and colleagues honed in further on the mechanism of how tardigrades survive losing all the water in their bodies. They discovered that a class of TDPs known as cytoplasmic-abundant heat soluble (CAHS) proteins are responsible. When surrounded by water, TDPs have a jelly-like consistency, and don’t fold into 3D structures like normal proteins do. But when dried out, the proteins transform into a semi-solid gel, which cushions the contents of the cell, holding them in place.

“When tardigrades begin to dry out, they start making these proteins at very, very high levels, essentially filling the inside of their cells with these weird, disordered, floppy proteins,” says Boothby.

“The proteins start by floating in the liquid, but as the cell dries out they actually come together and form this spider web-like network within the cell. We think these spider web fibres can wrap around sensitive proteins and help keep them folded or prevent them from aggregating.”

A similar trick is used by animals like tree frogs, nematodes and brine shrimps, which produce a sugar called trehalose that forms a glass-like sanctuary, protecting cells from destruction.

Life at the extremes

Forming a tun state or producing TDPs may also be key to tardigrades’ ability to withstand extreme heat.

This ability has fascinated scientists for centuries. In 1842 French scientist Louis Michel François Doyère showed that a tardigrade in its tun state could survive being heated to temperatures of 125C (257F) for several minutes. In the 1920s, Benedictine monk Gilbert Franz Rahm brought tardigrades back to life after heating them to 151C (304F) for 15 minutes. Yet tardigrades can only do this when in their tun state.

“Many species of tardigrades are able to survive temperatures well above 100C (212F) , but they only do so when they’re dry,” says Boothby. “If you have a tardigrade in a droplet of water, and you heat that water up to really high levels, the tardigrade will die pretty much just as readily as any other organism.”

In fact, even though they are known for their resilience in specific situations, tardigrades are generally vulnerable to high temperatures, suggesting even they may suffer from the effects of climate change. A study by Møbjerg found that if they do not have time to enter their tun state, some species of tardigrades die at temperatures above just 37C (99F).

While it’s difficult to know whether tardigrade populations are declining, such a decline could have knock-on effects on soil ecosystems. For example, some studies have suggested that carnivorous tardigrades can boost the health of soils by eating parasitic nematodes.

When it comes to the question of how tardigrades survive other extremes, less is known. It turns out that tardigrades can survive freezing, radiation, and low-oxygen conditions without forming a tun or making TDPs. So they must have other protection mechanisms too.

In 2016, a team of scientists from Japan brought tardigrades back to life that had been in a frozen state in Antarctica for 30 years. The two tardigrades in the sample were named SB-1 and SB-2 (SB stands for sleeping beauty), respectively.

Freezing is particularly dangerous for living creatures, as at low temperatures cell membranes lose their fluidity and become more brittle. The biggest danger, though, is ice crystals.

“Crystals are really bad things to have inside of cells because they’re sharp and pointy,” says Boothby. “They can puncture membranes, crush proteins, or disrupt nucleic acids like DNA – the blueprint of the cell.”

Despite this, some tardigrades can tolerate being frozen to just above absolute zero. Why they need to do this is somewhat a mystery, as the lowest temperature ever recorded on Earth was a balmy -89.2C (-128.6F) in central Antarctica in 1983.

“The intriguing part of these organisms is that the adaptations that they have evolved go far beyond what they actually need. I mean, you would never be cooled to do absolute zero – you wouldn’t find those conditions on Earth,” says Møbjerg.

How exactly they survive freezing is not known, although it is has been discovered that they can go into a state of suspended animation called cryobiosis, where they slow or shut down their metabolic processes.

The question of how tardigrades survive being irradiated, on the other hand, is better understood. In 2016, Kunieda and his team discovered a protein, known as Dsup (damage-suppressor protein), which appears to wrap around DNA like a blanket, protecting it from the harmful effects of ionising radiation. What’s more, the researchers engineered human cells so that they too could produce Dsup. They then exposed those cells to X-rays, and found that Dsup prevented the human DNA from breaking apart.

“Radiation can damage DNA directly, but most biological damage occurs indirectly,” says Kunieda. For example, radiation energy is absorbed by water molecules, which break down and produce very toxic molecules known as reactive oxygen species (ROS). The ROS then attacks the DNA and breaks it.

Earlier research had already shown that tardigrades make enzymes that detoxify ROS. But Kunieda’s study showed that Dsup offers further protection.

“Our data suggests that Dsup binds to DNA and creates a physical shield around it,” he says “It forms a protective shell that prevents the breakage of the DNA from ROS.”

As tardigrades also make ROS when faced with extremely dry or salty conditions, then Dsup could also protect the DNA from these stresses too.

In 2020, researchers at the Centre for Plant Biotechnology and Genomics in Madrid, Spain, modelled how Dsup interacts with DNA, and found that Dsup is an extremely flexible protein that is able to adjust its structure to precisely wrap around and fit the DNA’s shape. By holding the DNA in place, Dsup is able to stop it breaking apart in response to radiation.

Meanwhile in 2024, a separate team of researchers in France found a second protein, called TDR1, which also appears to bind to DNA and protect it from radiation damage. The study showed that tardigrades can also repair their own DNA, another handy tool in their belt that helps them cope with being irradiated.

Survival tricks for humans

As we have discovered more about tardigrades in recent years, some researchers have begun considering how we could use their unusual properties to help humans. Some scientists, for example, hope to use their knowledge of tardigrades to protect people living with cancer from the harmful effect of radiotherapy.

Radiotherapy is a treatment that uses high-energy radiation to kill cancer cells, but it unfortunately also damages nearby healthy tissues. In some cases the side effects are so severe they can lead to people delaying treatment or stopping it altogether.

Inspired by the resilience of the tardigrade, researchers at MIT, Brigham and Women’s Hospital in Boston, and the University of Iowa injected messenger RNA encoding the Dsup protein into the cheek and rectum of mice. As its name suggests, messenger RNA acts as a kind of courier or go-between, decoding DNA and using the information contained within it to produce proteins.

The study showed that once injected, the mice began producing Dsup themselves. When researchers gave the mice doses of radiation similar to that which cancer patients would receive, the cancer cells were destroyed, but the surrounding healthy tissues survived.

However more work needs to be done to understand how the mammalian immune system responds to such proteins before the treatment could be used in humans, as Dsup would be flagged as an intruder by the body’s immune system.

Scientists think there may be other ways to use tardigrades’ superpowers to help humans too. For instance, as well as shielding tardigrade cells, TDPs could help preserve vaccines or other sensitive biological materials that need to be kept in storage for long periods of time.

Take haemophilia, a rare blood clotting disorder. People with this condition may bleed to death if they are involved in a car accident or suffer trauma. To stop this, they are given human blood clotting protein Factor VIII, which has to be stored frozen, limiting its use in poorer countries, or during natural disasters. However Boothby recently found that if you mix Factor VIII with tardigrade TDPs, the medicine remains stable at room temperature, removing the need for refrigerators or freezers.

NASA is also interested in finding out how tardigrades survive the inhospitable environment of space. In the future it could use this information to protect food and medicine from drying out, or radiation exposure, which would be invaluable for long-duration space exploration missions.

The enduring mystery of tardigrades’ superpowers

But why have tardigrades evolved this suite of defence mechanisms in the first place?

“Tardigrades are aquatic organisms, so they need a film of water to surround them in order to be active,” says Møbjerg. “One of the reasons why they need to be so tolerant is because their skin or cuticle is really permeable. It’s not like an insect, which has a wax layer that can stop them losing water by evaporation.”

According to Boothby, one theory that could explain their resilience is that as tardigrades are so tiny, when they dry out they may be picked up by gusts of wind and carried around the planet.

“If dust in sand from the Sahara Desert can be blown to the Amazon, then tardigrades almost assuredly could undergo the same sort of circulation within the atmosphere,” says Boothby.

“They might get deposited in a place that’s quite austere. Maybe it’s cold, maybe it’s hot, maybe it doesn’t rain, or maybe it rains all the time. Maybe they’re on the top of a mountain where they’re exposed to more UV radiation. So perhaps tardigrades have evolved to survive all these stresses because they’ve been exposed to them.”

However, while water bears often have to cope with drying out, it’s less clear why they would need to survive baking hot temperatures, being cooled to just above absolute zero, or radiation only found in outer space.

Whatever the case, decoding the mystery behind these creatures’ amazing abilities may not just help humans – be it through improving storage of vaccines, reducing the harmful effects of radiotherapy, or preserving food for long distance spaceflight. It could also help to protect tardigrades themselves from the harmful effects of climate change.