How the Remarkable Tardigrade Springs Back to Life after Drying Out
A particular protein helps these these tiny critters survive dehydration for over a decade at a time
In the last few years, tardigrades, also known as water bears or moss piglets, have gotten a lot of attention for being tough. The can survive temperatures up to 212 degrees Fahrenheit and 459 degrees below zero. They can resist up to ten days of cosmic radiation while floating in space. And, most impressively, in dry conditions they can pull their eight legs and head into their body, create a ball and shrivel up for over a decade. During this time they can reduce their metabolism to almost nothing—but with a little water, they pop back to life. Now, researchers think have finally figured out how tardigrades perform that impressive trick. They published research last week in the journal Molecular Cell.
Scientists previously believed that tardigrades survive desiccation by using a sugar called trehalose found in other creatures that can complete such a feat, including brine shrimp, yeast and tree frogs. But the creatures don't contain detectable traces of the compound. So Thomas Boothby, a postdoctoral fellow at the University of North Carolina, Chapel Hill, and his colleagues decided to dig deeper into the tardigrade mystery.
As Nicholas St. Fleur at The New York Times reports, the team examined the genes that are active when tardigrades dry up, a state called anhidrosis. They placed the moss piglets in a humidity chamber and slowly reduced the moisture until the tardigrades went into their dehydrated state, mimicking a pond or puddle drying up.
What they found is that drying activates genes that produce a series of proteins they call tardigrade-specific intrinsically disordered proteins or TDPs. Those proteins encapsulate molecules inside tardigrade cells with a glass-like solid structure that allows them to survive drying out.
“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,” Boothby tells Andy Coughlan at New Scientist.
Intrinsically disordered proteins, however, are a bit unusual, explains Madeline K. Sofia at NPR. Unlike other proteins, they do not have a set three-dimensional structure. Boothby describes them to Sofia as “wiggly spaghetti springs where they are constantly changing shape." When the proteins come in contact with liquid, they melt away, allowing the tardigrade to go on its merry way.
When they removed the gene from the tardigrades that coded for these proteins, the creatures did not fare as well during the drying process. When they added the gene to yeasts and bacteria, however, those organisms were then able to survive drying similar to the water bears.
There are practical applications to be had from the study, Boothby tells Sofia. For instance, he points out that many protein-based pharmaceuticals and vaccines are unstable and require refrigeration. Stabilizing them with TDPs could allow them to be stored and shipped around the world at room temperature. “This could help us break dependence on the cold-chain, a huge economic and logistical hurdle for getting medicine to people in remote or developing parts of the world,” he tells Coughlan.
There might be other uses as well, reports George Dvorsky at Gizmodo, such as developing food crops that could use TDPs to survive droughts. He also speculates that it could (maybe) eventually be used in humans. Such a feat could, for example, help colonists on Mars survive long stretches without water.