How Tardigrades Survive Freezing Temperatures

Tardigrades are excellent at adjusting to severe environmental problems. Back in 2019, Ralph Schill, one professor at the Institute of Biomaterials and Biomolecular Systems at the College of Stuttgart, proved that anhydrobiotic (dried) tardigrades can survive undamaged for many years without absorbing water. Whether they mature faster or slower in a frozen state, or whether aging even comes to a halt, was previously unclear. But the mystery has currently been resolved: Frozen tardigrades do not age.

Tardigrades, additionally called water bears, belong to the family of nematodes. Their gait is reminiscent of that of one bear; therefore, that is the only similarity. The tardigrades, that are barely one millimeter in dimension, have managed to adapt perfectly to quickly changing ecological problems throughout evolution and can dry out in severe heat and freeze in cold conditions. “They don’t die; they fall into one deep sleep,” explains Schill.

The Sleeping Beauty Theory

For a cell organism, freezing or drying out causes different types of stress. But tardigrades can survive both warm and cold equally unscathed. They no longer reveal any obvious signs of life. And this raises the question of what occurs to the animals’ internal clock and whether they age in this resting state.

For dried tardigrades, which wait several years in their habitat for the next rain, Ralph Schill and his group answered the question of aging several years back. In a fairytale by the Grimm siblings, the princess comes under a deep sleep. When a royal prince kisses her 100 years later on, she awakens and also still looks as young and beautiful as before. It is the same with tardigrades in one dried state, and therefore this is also called the “Sleeping Beauty” hypothesis (” Sleeping Beauty” model).

“Throughout inactive periods, the internal clock stops and just resumes running once the organism is reactivated,” explains Schill. “So, tardigrades, that usually only live for a few months without rest periods can live for many years or even decades.”

Until now, it was still not clear whether this also applies to frozen animals. Do they mature faster or slower than the dried animals, or does aging also come to a halt?

The aging process also stops when frozen

To explore this, Schill and his group conducted several experiments in which they iced up one total of more than 500 tardigrades at -30 ° C, thawed them out again, counted them, fed them, and froze them again. This was repeated until all the animals died. At the same time, control teams were kept at constant room temperature. Excluding the time in frozen conditions, the comparison with the control groups revealed an almost identical lifetime. “So also in ice, tardigrades stop their internal clocks like Sleeping Beauty,” concludes Schill.

Read the original article on PHYS.