Tardigrades: The toughest animals in the world - BIOCLIFF

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Sunday, July 1, 2018

Tardigrades: The toughest animals in the world

As a part of the 24th Japanese Antarctic Research Expedition (JARE), Japanese scientists had collected moss samples from Antarctica in 1983 which were stored in -20OC. In 2016, almost 30 years later, these samples were thawed. From, the moss crawled forth two microscopic creatures that have captured the attention of not only the scientific community but the public as well. These minute beings are called Tardigrades aka “water bears”. Tardigrades are water-dwelling microscopic animals having four pairs of legs with a size range 0.3-1mm. There are more than a thousand species identified worldwide from freshwater, marine, and other limno-terrestrial habitats. For tardigrades, size does not matter when we gaze upon their extraordinary abilities of stress tolerance. It is speculated that tardigrades have survived all five mass extinctions. Mathematical predictions indicate that they can even survive various life-threatening events in the future. So, even if we are wiped out these animals will probably be hanging around in this planet.


Tardigrades are known to tolerate extreme environmental conditions which are lethal for human survival. They can survive prolonged periods of desiccation (complete absence of water), tolerate ionizing radiations like UV, X-rays and gamma radiations. They also exhibit tolerance to extreme temperatures and pressure. Tardigrades had once again captured the world’s attention they were taken to low earth orbit conditions exposing them to space vacuum and various galactic radiations. Surprisingly, their post-exposure survival to these harsh conditions made them the first animal that could survive in extraterrestrial environments.
The story of their stress tolerance doesn’t end here but the mechanisms that are evolved combat such extreme conditions are fascinating and unique. Presence of trehalose (a disaccharide) acts as a bioprotectant in certain tardigrades during desiccation. They have also developed mechanisms to tolerate oxidative stress by having multiple copies of genes like catalase and superoxide dismutase. Presence of pigments like carotenoids also helps them to reduce oxidative stress. Researchers have identified different tardigrade specific proteins like CAHS (Cytoplasmic Abundant Heat Soluble) and SAHS (Secretory Abundant Heat Soluble) proteins which are intrinsically disordered and protects the cellular components of tardigrades through a process called vitrification. Recently, a tardigrade unique DNA binding protein, Dsup (Damage suppressor protein) isolated from the tardigrade, Ramazzottius varieornatus was expressed in human embryonic kidney cells making them less vulnerable to radiation-induced DNA damage. This indeed showed that stress tolerance mechanisms of tardigrades can be harnessed for human benefit. If we take a look into the genome of these animals, they have selectively lost pathways like β-oxidation, peroxisomal oxidative pathway. Apart from this, genes linking hypoxia, oxidative stress and DNA damage to the mTORC1 pathway (a nutrient/metabolic pathway) are also absent. It is like the tardigrades have “re-engineered” their genome through evolution to tolerate stress conditions. Hence, these extraordinary animals have been named the “toughest animals” in the world.


Despite having such astounding abilities, “tardigradology” is still in its infancy. But the recent advances in genome and transcriptome are slowly bringing tardigrades into the forefront of research. Like our laboratory in Indian Institute of Science, there are only a few places in India that do full-time research on tardigrades. India being a country with different biodiversity hotspots, there are more chances to identify new varieties of tardigrades with extraordinary abilities than anywhere else in the world. Understanding their stress tolerance mechanisms can give us insights into different technological breakthroughs for human betterment, which only time will tell. The coming years will be an exciting period for all the tardigradologists out there.

Tardigrade laboratory in IISc, Bengaluru: Tardigrade lab







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