Scientists have learned how tardigrades can survive dehydration

Tardigrades are micro-animals that can survive in the harshest conditions: extreme pressure, extreme temperature, radiation, dehydration, starvation, and even in the vacuum of outer space. The journal PLoS Biology published an article in which scientists at the University of Tokyo have identified a mechanism that explains how tardigrades can survive extreme dehydration, including finding a protein that forms a protective gel-like network to protect dehydrated cells, reports Ars Technica.

These creatures were first described by the German zoologist Johann Goeze in 1773, and four years later the Italian biologist Lazzaro Spallanzani called them tardigrada, that is, “slow walkers” or “slow steppers”. This has to do with how slow the animals move. Because they can survive almost anywhere, they can be found in many places: deep-sea trenches, saltwater and freshwater sediments, tropical rainforests, Antarctica, mud volcanoes, sand dunes, beaches, and lichens and mosses. Another name for them is “moss piglets”.

However, when their moist habitat dries up, the tardigrades go into a state known as “tun,” a kind of suspended animation that the animals can remain in for up to 10 years. When water begins to appear again, water bears absorb it, rehydrate and return to life. They’re not technically members of the extremophile class of organisms since they don’t so much thrive in extreme conditions as endure. Technically they belong to the class of extremotolerant organisms, but their hardiness makes tardigrades a favorite subject of research for scientists.

In 2019, an Israeli spacecraft carrying the tiny creatures in a “tun” state crash-landed on the moon, leading to speculation that the tardigrades may have survived the impact. However, it is unlikely that the tardigrades survived, according to a study published last year by British scientists. They put several tardigrades in a “tun” state and placed two to four at a time in a hollow nylon ball. Subsequently, the scientists fired tardigrades at a sand target at increasing speeds with the help of a two-stage light gas gun. As a result, it turned out that water bears can withstand a collision with a speed of about 3000 kilometers per hour and an instantaneous shock pressure of up to 1.14 gigapascals.

The lander may have crashed at several hundred meters per second, but the shock of its metal frame hitting the surface would have created pressures “well above” 1.14 GPa, reported Science researchers.

A new study by scientists at the University of Tokyo explains this stability of tardigrades by water retention in the proteins. “Our data suggest a novel desiccation resistance mechanism based on filament/gel formation,” write the authors of the new study.

“Although water is essential to all life we know of, some tardigrades can live without it potentially for decades. The trick is in how their cells deal with this stress during the process of dehydration,” said Takekazu Kunieda of the University of Tokyo. “It’s thought that as water leaves a cell, some kind of protein must help the cell maintain physical strength to avoid collapsing in on itself. After testing several different kinds, we have found that cytoplasmic-abundant heat soluble (CAHS) proteins, unique to tardigrades, are responsible for protecting their cells against dehydration.”

In this scenario, the CAHS proteins kick into action when they sense that their encapsulating cell has become dehydrated, forming gel-like filaments (as opposed to a glassy matrix) as they dry out. Those filaments, in turn, form networks that maintain the structural shape of the cell without its water. When the tardigrade rehydrates, the filaments gradually recede, ensuring that the cell isn’t stressed or damaged as it regains water.

Kunieda and his colleagues also inserted the protein’s genes into cultured insect and human cells. At first, this was a difficult task because the cells had to be stained so that they could be seen under the microscope. Most staining methods involve the use of water-based solutions, and water concentration was a key variable to be controlled in this study. Scientists solved this problem by including a dye in a solution based on methanol. Result: CAHS proteins showed the same behavior in insect cells and even showed limited functionality in human cells, suggesting that this feature may not be limited to tardigrade cells.

Among other potential applications, such a discovery could one day lead to new methods of preserving biological materials for long periods of time, which is useful for extending the shelf life of certain drugs or vaccines or even whole organs awaiting transplantation.