The tardigrade, the microscopic animal with a thousand powers


Invisible to the naked eye, the tardigrade fascinates the scientific community with its faculties of resistance. Extreme temperatures, dehydration, radiation, space vacuum, pressure, organic solvent … the animal survives the worst treatments. Zoom into a microscopic being but overpowered.

The tardigrade, older than the dinosaur

The tardigrade (Tardigrada) was present on Earth more than 540 million years, before the dinosaurs. Today there are nearly 1300 species terrestrial and aquatic (freshwater and ocean) but, according to the researchers, it remains the double to discover. In the current classification, these tiny invertebrates belong to the group of panarthropods, alongside arthropods and onychophores. First described by Johann August Ephraim Goeze in 1773, its name comes from the Latin tardus (slow) and gradi (walking). Sometimes nicknamed water bear, the tardigrade is an animal extremophile, being able to survive the most hostile environments, but not all species display the same resistance to attacks.

Tardigrade: the animal of extremes

The tiny cub-like animal measures 50 micrometers to 1.2 mm. Protected by a cuticle, its body is extended by four segments, each of which has two short legs clawed but not articulated. The tardigrade lives everywhere on the planet and under all climates : from the peaks ofHimalayas at more than 6000 m of altitude to the abyss of the oceans, by 4000 m of depth. The animal is most often found in areas rich in mousse and in lichens (tree trunks, roofs, walls)… which it feeds on. Maritime species prefer algae when others capture young toward (nematodes) and animals with infinitesimal dimensions.

The near death of the tardigrade

After decades of research, scientists have discovered the secret behind tardigrade’s resistance: TDP protein (Tardigrade specific intrinsically Disordered Protein) forms a kind of glass which vitrifies the cellular constituents and protects them from degradation. Concretely, the small animal curls up and empties all its water which it replaces with a sugar, reducing its vital activity to 0.01% of normal. In short, it turns into a dehydrated crystal which plunges it into a state of near death, phenomenon called cryptobiosis. Only rehydration can repair damaged DNA and extract the animal from its lethargy.

The extraordinary powers of the tardigrade

When it enters into a state of cryptobiosis, the tardigrade is able to withstand assaults the most diverse such as:

  • Extreme temperatures. The animal can survive for several days at −272.8 ° C. This temperature is approaching absolute zero (established at 0 kelvin or -273.15 ° C) from which all movement of molecules and atoms is stopped, and nothing moves. Tardigrades harvested in ice cores where they had been for 2,000 years have thus come back to life. Their tolerance is also impressive in the event of exposure to hot weather : about thirty minutes at 150 ° C;
  • The dehydration. During extreme drought, the animal is able to almost completely dry out and survive on only 1% of the water it contains in the normal state. This ability allows him to colonize the most arid deserts in the world;
  • Radiation. Even more surprisingly, tardigrade demonstrates resistance to X-rays or ultraviolet rays that exceed 570,000 rads, a level 1,100 times higher than the dose deadly for the man. This tolerance is due to the expression of Dsup protein, for Damage Suppressor which forms a shield protecting the DNA of the animal;
  • Space vacuum and pressure. In 2007, thousands of water bears were taken aboard a Russian rocket at an altitude of 270 kilometers around Earth for 12 days. On their return, most of them presented no alteration biological that could have been caused by the vacuum of space and the lack ofoxygen. The tiny invertebrates woke up and began to lay eggs. At the same time, these organizations support pressures 600 megapascals, that is to say four times greater than those measured in the depths of the ocean;
  • Intoxication. An experiment has shown that, immersed in a 99.8% solution of cyanide methyl (acetonitrile), a solvent which dissolves virtually all substances used in chemistry, tardigrade survives. Its resistance to many products toxic is believed to be due to chemobiosis, an immune response to high levels of environmental toxins;
  • Salinity. Tardigrade tolerates environments with very high salinity by osmobiosis: it swells and becomes raincoat to the internal diffusion of salts.

The tardigrade: a hope for man

The tardigrades aquatic have a lifespan of between 1 and 2 years and the species terrestrial between 15 and 30 months. In the cryptobiosis phase, the microscopic being can survive much longer: the laboratory record is established at 9 years after which the water bear came back to life. The original properties of tardigrade open up outlook promising to scientists. The animal’s TDP and Dsup proteins begin to be produced in vitro with the aim of advancing research aimed at protecting human cells desiccation or radiation.

Photo credit: Goldstein lab