Environmental tolerance in tardigrades

This means that their chances of dying increase the longer they are exposed to the extreme environments,[4] whereas true extremophiles thrive there.

[1] Terrestrial and freshwater tardigrades are able to tolerate long periods when water is not available, such as when the moss or pond they are living in dries out, by drawing their legs in and forming a desiccated cyst, the cryptobiotic 'tun' state, where no metabolic activity takes place.

[18] Earlier experiments attributed this to their lowered water content, providing fewer reactants for ionizing radiation.

[18] However, tardigrades, when hydrated, remain much more resistant to shortwave UV radiation than other animals; one reason is their ability to repair damage to their DNA.

[21] In 2011, tardigrades went on the International Space Station STS-134,[22] showing that they could survive microgravity and cosmic radiation,[23][24] and should be suitable model organisms.

[25][26] In 2019, a capsule containing tardigrades in a cryptobiotic state was on board the Israeli lunar lander Beresheet which crashed on the Moon.

[30] Anhydrobiosis in response to desiccation has a complex molecular basis; in Hypsibius exemplaris, 1,422 genes are upregulated during the process.

[32] The Dsup proteins of Ramazzottius varieornatus and H. exemplaris promote survival by binding to nucleosomes and protecting chromosomal DNA from hydroxyl radicals.