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Freshly Baked Science

Tardigrade: The Indestructible

'Water Bear'

by Sarah Atkinson

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22nd January 2019

Tardigrades are some of the toughest beings in the animal kingdom! They are nicknamed ‘water bears’ due to their apparent bear-like appearance and swimming-like motion. Though if you ask me, they look more like a cross between a floating hippo and a vacuum cleaner! They are between 0.05 mm and 1.2 mm in length and have eight legs, each ending in 4 – 8 small claws. One of the most amazing things about them is that they are found in almost every natural environment on earth, and there are over 900 different species!

 

These magnificent creatures can survive in some of the most extreme conditions! For example, they can survive in an incredibly wide range of temperatures, from -273 °C to 151 °C. To put this into perspective, the coldest surface temperature ever recorded in the Antarctic was -89.2 °C. Tardigrades can survive in conditions three times colder than this! If you think about this in terms of the human body, which maintains a healthy internal temperature of 37 °C, this is nearly 300 °C lower than what our bodies can withstand. A drop of our core body temperature to only 32 °C can cause memory loss, a drop to 27 °C results in loss of consciousness, and a drop to 21 °C can result in death!

 

At the other end of the spectrum, tardigrades can also survive at temperatures up to

151 °C! This is nearly 100 °C higher than the highest recorded surface temperature on earth (56.7 °C, Death Valley, California, 1913). To put this into context, the human body would begin to burn and blister within minutes when exposed to temperatures above

50 °C in moist air and we would rapidly start to dehydrate if exposed to dry air above

60 °C for more than ten minutes. So not only can these little water bears withstand huge changes in temperature, they can also survive high levels of dehydration! But how?!

 

Well, although tardigrades can survive in these extreme conditions, they do not actively live in these conditions. They survive by bringing their whole body to a complete standstill. It’s almost as if they freeze themselves in time! Looking from the outside, you would probably assume they were dead. But amazingly, they can bring themselves ‘back to life’.  In periods of extreme dehydration, tardigrades tuck themselves into small balls called ‘tuns’, and produce a protective sugar called trehalose (Fig.1) which can move into their cells to replace lost water. Whilst in a tun, a tardigrade’s bodily functions perform at a rate 1/10,000th of what is considered to be normal! Even more amazingly, they can return to a ‘normal’ living state in only a couple of hours! Of course, as with any living being, the risk of them actually dying does increase depending on just how long they are exposed to such an extreme environment!

Fig.1. Molecular structure of Trehalose

Tardigrades can also use their ‘tun state’ to survive at pressures of 600 MPa (megapascals). This is 6 times the water pressure in the deepest part of the sea (100 MPa, Mariana Trench, Pacific Ocean)! If we were exposed to pressures as high as this, our cells would tear apart. Even our DNA would be destroyed!

In addition to this, tardigrades can also survive exposure to high radiation, so they’re more than ready for a nuclear apocalypse! In fact, they are so tough that they can even survive the vacuum of space!

 

Tardigrades belong to the invertebrate class of the animal kingdom – meaning that they have no backbone. It seems almost unfitting because you certainly need to have ‘a lot of backbone’ to survive all these extreme conditions! Though there is still so much that is unknown about how these tiny beings survive, they certainly do seem to be indestructible! Maybe we could learn a thing or two from them, as they’re certainly on track to outlive the human race!

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