Water-Dwelling Tardigrades Survive Dry Spells by Turning Into Glass

via. Sebastian Kaulitzki/Shutterstock

The tough-as-nails creatures can survive desiccation for a decade, and revive in an hour after being exposed to water.

Behold the mighty tardigrade, quite likely the toughest creature on Earth. Also known as water bears or moss piglets (swoon), these Miyazaki-esque micro-animals can survive the vacuum of space, blasts of radiation, being frozen for decades and even desiccation.

How do they do it?

The mystery behind this remarkable perseverance has stumped scientists for more than 250 years, but now researchers have shed some light on at least one facet of their amazing endurance: How a water-dwelling creature can dry up into a shriveled little thing and survive for as long as a decade, only to pop back to life within an hour after being exposed to water.

What’s the secret to their success? “Tardigrade-specific intrinsically disordered proteins (TDPs),” say the researchers. These TDP genes form “non-crystalline amorphous solids (vitrify) upon desiccation, and this vitrified state mirrors their protective capabilities.”

“When the animal completely desiccates, the TDPs vitrify, turning the cytoplasmic fluid of cells into glass,” says lead author Thomas Boothby of the University of North Carolina at Chapel Hill.

“We think this glassy mixture is trapping [other] desiccation-sensitive proteins and other biological molecules and locking them in place, physically preventing them from unfolding, breaking apart or aggregating together,” says Boothby.

As Andy Coghlan describes it for New Scientist:

When there is water around, these anti-dehydration proteins are jelly-like and don’t form into well-defined three-dimensional structures like most known proteins. But when water bears start to dry out, these proteins turn into a kind of glassy sanctuary that cocoons all dehydration-sensitive materials in the animal from harm.

If the moss piglet’s trick brings to mind the magic of Sea Monkeys, you wouldn’t be too far off. For a long time, it had been thought that perhaps the tardigrade was able to survive dehydration because of a specialised sugar known as trehalose, which allows brine shrimp (AKA Sea Monkeys) and tree frogs to go dormant during dry spells.

The team found that the tardigrade’s mechanism didn’t rely on trehalose, but worked in the same way, providing yet another wonderful example of convergent evolution. “.... some animals have evolved to rely on trehalose, while tardigrades have also evolved the ability to vitrify, but using a completely different type of molecule – a protein,” says Boothby.

“It is amazing to see that evolution has found several biochemical ways to obtain the same kind of mechanism for solving the problem of desiccation. Trehalose in nematodes and brine shrimps, and apparently TDPs in tardigrades,” says Ingemar Jönsson from Sweden's Kristianstad University. “And what a wonderful adaptation to turn into a stable glassy state when the body dries out!”