Why tiny tardigrades are nearly indestructible

Tardigrades are microscopic animals blessed with two very cool nicknames — the water bear and the moss piglet. They are segmented and reach a maximum length of a millimeter, maybe a millimeter and a half.

Water bears are as indestructible as they are tiny. They've been known to survive in temperatures as cold as minus 459 degrees Fahrenheit and as hot as 304 degrees F. They shrug off extreme doses of radiation and laugh in the face of the silent vacuum of space itself. In an experiment in 2007, water bears were exposed to outer space for 10 days. After returning to Earth it was discovered that a lot of the bears survived and some even had babies.

More recently, scientists tried to rid the planet of tardigrades (only in theory) by putting the creatures through a series of tests that mimicked what they would experience if a deadly asteroid or radiation burst hit the Earth. But the tardigrades outlasted billions of years worth of theoretic disaster events, according to the study published in the journal Scientific Reports. For example, researchers found some water bears can survive radiation doses of 5,000 to 6,000 grays (humans would barely survive a dose of 5).

Called "Earth's hardiest animals," these resilient creatures have long been the subject of scientific curiosity.

Despite their nickname, water bears (watch one wiggle in this video on youtube) also can go without water for about 10 years, living as a dried-out shell. For 250 years, we had no idea how these tiny creatures survived this extreme drying out, but a group of researchers from University of North Carolina at Chapel Hill may have found an answer.

Published in Molecular Cell, the study follows how researchers dried out tardigrades to see which genes turned on as a response to the stress. Researchers found that intrinsically disordered proteins (IDPs) kicked into gear, filling up the tardigrades' cells with an "amorphous matrix" that prevents them from going completely dry and dying.

IDPs are a little odd. Most proteins are stable and structured, but IDPs are, as their name might suggest, a little looser. They do not have a set shape. Thomas Boothby, the lead author on the study, described them to NPR as "wiggly spaghetti springs where they are constantly changing shape." This shape-shifting allows them wiggle into and keep cells together, creating that previously-mentioned matrix of prorection.

Boothby and the other researchers then took the tardigrade IDPs and to see if yeast and bacteria would get the same desiccation protection. Some bacteria and yeast survived desiccation by 100-fold. Given that, things like drugs that need to remain cold during shipments or crops in drought-prone areas, may similarly benefit from the tardigrade IDPs.
Radiation resistance

In 2016, a team of Japanese researchers figured out the secret behind the hardy critter's amazing survival capabilities against radiation. They discovered that among the animal's many coping strategies is a protein that protects its DNA from radiation damage. The researchers named it "Dsup" (short for "damage suppressor"). When the scientists transplanted the Dsup protein into human cells in the lab, they found it protected those cells too.

The scientists suggest that the finding means that genes from these "extremeophiles" could one day be used to protect humans from radiation, perhaps from X-rays, for example.

The study was published in the journal Nature Communications.

Interestingly, the tardigrades were more resistant to radiation than the human cells that the researchers manipulated by adding Dsup protein.

"[So] tardigrades have other tricks up their sleeves, which we have yet to identify," Professor Matthew Cobb from the University of Manchester, who was not involved with the study, told the BBC.

Cobb said that in principle, "these genes could even help us bioengineer organisms to survive in extremely hostile environments, such as on the surface of Mars - [perhaps] as part of a terra-forming project to make the planet hospitable for humans."