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Tardigrade: the incredible and tiny Terminator of the living

Tardigrades are everywhere! From high snow-capped mountains to the darkest seabed, from the most banal of house roofs to the emptiness of space, the tardigrade is able to withstand the most extreme conditions. A dream source of inspiration for researchers!

Microscopic view of two tardigrades. © Eye of Science

Tardigrades, many ever more incredible species!

The so-called tardigrade (or “water bear”) is not a species, but a phylum animal: vertebrates being for example a sub-branch of the animal kingdom. So there are more 1300 listed species of tardigrades! While most of them are terrestrial, others are marine species found both near the coast and in the abyss. Tardigrades feed mainly on diatoms, single-celled algae that we told you about in our Incredible Nature podcast. As you know now that you've listened to this fabulous podcast, diatoms have an external skeleton: a protective silica capsule called a frustule. So, to feed, the tardigrades manage to pierce the frustule, which allows them to suck up the algae cell.

Usually measuring less than a millimeter (although the largest still reach 1.5 mm), tardigrades are best known for their toughness. They survive temperatures of -272°C, which is almost absolute zero! They also withstand high pressures (more than 6000 bars!) or, conversely, vacuum. They are also 1000 times more resistant than us to UV radiation and X-rays, and also tolerate certain toxic substances. And as if that wasn't enough, tardigrades can also survive several days without oxygen.

Warning all the same, even if the listing that we have drawn up is impressive, it is however necessary to qualify our comments. If you go back a few lines above, we told you that tardigrades represent several species, so they are not all equally resistant. If we are interested in UV resistance, demonstrated in 2020 by a group of Indian researchers in a paper published by the Royal Society, we can see that it is not present in all species of tardigrades. For example, those of the genus Paramacrobiotus survived without problems to a 15 minute UV exposure while tardigrades of the species Hypsibius exemplaris died within a day of exposure.

Nevertheless, the tardigrades' secret weapon, their ultimate superpower, which allows them to survive many extreme conditions, is present in all species, namely: cryptobiosis!

Cryptobiosis, the tardigrade's secret weapon that inspires research

Cryptobiosis is the ability of a living being to slow down its metabolism to such an extent that it practically stops. All biological functions are suspended and the organism no longer even meets the usual definition of a living being! Organisms capable of entering into cryptobiosis can then return to a state of active life: this is called reviviscence.

As you understood, the tardigrade is one of those animals capable of putting their lives on hold. But how does he do it? The tardigrade evacuates water from its body and produces a sugar, trehalose, which helps preserve the integrity of its cells. Then these cells contract and the different elements (called organelles) they contain pile up on top of each other. In most animals, this state is irreversible, even after rehydration. Tardigrade, on the other hand, has specific proteins called Tardigrade-Specific Intrinsically Disordered Proteins. These famous proteins are inserted between the organelles of the cell like bubble wrap, and protect them from each other. The tardigrade can thus remain in a state of stasis, that is to say totally inactive, practically indefinitely. A Japanese laboratory has kept specimens for over 30 years! Even crazier: tardigrades have been found in ice caps over 2000 years old, and they resumed their activity, as if nothing had happened, when it melted! Currently, the maximum survival time of the tardigrade in a state of cryptobiosis is therefore still unknown.

Principle of cryptobiosis in the tardigrade. © Emily Harrington

Tardigrade cryptobiosis is of great interest to research (and to curious people) in particular to improve the conservation of biological material in the medical field. In particular, the process may prove useful in facilitating the storage of vaccines at room temperature. It is precisely for this purpose that the company Biomatrica has developed DNA and RNA storage techniques at room temperature inspired by tardigrade cryptobiosis. An excellent example of biomimicry applied to health sector!

© Maryam Clark, UCL

Tardigrades and Space Missions: To Infinity and Beyond?

As we have seen, tardigrades resist both vacuum, cold, lack of oxygen and radiation. They are therefore ideal candidates for space travel. So in 2007, researchers sent a capsule of tardigrades into orbit for 10 days. Tardigrades not only survived but even reproduced when they returned! In contrast, tardigrades that were not protected from the sun did not survive long. It should be noted, however, that the tardigrades sent into space do not belong to the species renowned for its UV resistance.

The capsule of the FOTON-M3 mission that took tardigrades into orbit. © ESA

Precisely speaking of UV resistance, the origin of this resistance could inspire UV protection for astronauts on future long-duration missions. Indeed, we know that these tardigrades protect themselves from the effects of UV rays thanks to fluorescent pigments. The light emitted by the pigments of the tardigrades makes it possible to reflect the radiation, this therefore prevents the radiation from reaching their organism. The fluorescence of the tardigrade ultimately serves as a shield! And again, the tardigrade has not said its last word. If this fluorescence is applied to tardigrades that are not UV-resistant, they survive radiation much better! The researchers behind this discovery even tested it on nematode worms, an animal species completely different from the tardigrade. They were able to observe, here again, a marked improvement in the survival of nematodes under UV light. When will there be a transposition to use this fluorescence in the field spatial ?

Finally, the resistance of the tardigrades could also inspire new materials. In particular dry adhesives inspired by the spatulae (fine hairs) of the gecko, which resemble those used in the field of robotics. Indeed, researchers at the Berlin Institute of Technology are interested in tardigrade to improve the spatial stability of this type of adhesive. Existing applications, based on polymers, degrade and lose their elasticity in such a harsh environment, which affects the adhesive power of the assembly. Tardigrade-inspired materials could be a game-changer, although current research is still very exploratory.

The tardigrade therefore has more than one string to its bow to amaze us! In addition to being a biological curiosity for its multiple exploits, it could also inspire researchers and engineers for various applications. Who knows what this little tough guy still has in store for us?


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