0.1mm "bear" is expected to help humans realize space travel

Author: Duan Yuechu and Huang Xianghong

A tardigrade seen through an electron microscope. It is less than 0.1 mm in diameter. STEVE GESCHMEISSNER/SCIENCE PHOTO LIBRARY

In May 2024, a research report on tardigrades written by Megan Bartels in the well-known publication Scientific American attracted widespread attention in the scientific community.

Tardigrades, tiny creatures less than 0.1 millimeters in diameter, have cute nicknames such as water bears and moss piglets. They are known for their charming chubby appearance, unique nicknames, and amazing adaptability to extreme conditions. "They are masters of protecting themselves," said Derrick Kolling, a chemist at Marshall University.

Kolin and his colleagues, including chemist Leslie Hicks of the University of North Carolina at Chapel Hill, have embarked on a landmark study aimed at uncovering a key mechanism that makes tardigrades so indestructible.

The research began when Colin accidentally put an instrument that detects "free radicals" into the machine used for detection. Free radicals are produced in cells during the normal metabolic process of animals and when faced with environmental stress, such as the influence of pollutants such as smoke, and he speculated that retarder may also produce such molecules.

When free radicals accumulate, they steal electrons from their surroundings to stabilize, a process called oxidation that can damage cells and compounds in the body. However, Hicks' research has shown that small amounts of free radicals can also act as signaling molecules, which can affect cell behavior by either engaging with or detaching from various proteins.

When Colin shared his observations of free radicals in tardigrades with Hicks, they designed a series of experiments together. The water bears were temporarily exposed to stress-inducing, free radical-producing conditions, such as high levels of salt, sugar, and hydrogen peroxide. Under these stresses, the water bears curled up into a temporary, protective dormant state called a "tun." The researchers monitored the conditions in which the water bears curled up and found that free radicals did seem to induce this "tun" state, but the specific mechanism was not clear.

Based on her research on the signaling interaction between free radicals and the amino acid cysteine, Hicks decided to test whether the cysteine ​​molecule plays a role in the formation of "tun". So she and her colleagues introduced different types of molecules known to block cysteine ​​oxidation as catalysts. The results showed that under stress conditions, because cysteine ​​cannot be oxidized by free radicals, the catalyst cannot form a regulator directed to cysteine ​​oxidation, indicating that cysteine ​​oxidation is a necessary mechanism for the formation of the "tun" state.

Kazuharu Arakawa, a biologist at Keio University in Japan, notes that the new study is consistent with previous research on the role of oxidation in a species of bee known for its tolerance to complete desiccation. The similarities suggest that the mechanism could be a common trigger for tun and other forms of cold-tolerant dormancy, a phenomenon scientists call cryptozoology.

Despite these important discoveries, there are still many unsolved mysteries about water bears. Hans Ram, a comparative animal physiologist at Roskilde University in Denmark, pointed out that when water bears enter the "tun" state, they temporarily shut down their metabolism, a phenomenon that cannot even fully explain cysteine ​​oxidation. "So far, no study has been able to explain this phenomenon," he said. "In my opinion, we are still far from understanding this."

Both Colin and Hicks agree that there is still a lot of research to be done to understand the mechanism of action of free radicals in tardigrades. The elastic "tun" state is not the only strategy for water bears to survive environmental pressures, and the team plans to further study other strategies. They also plan to study different types of water bears (currently only the typical jade snails have been studied), hoping to find that cysteine ​​oxidation is widely used in more animals.

In the long term, Hicks hopes the research will inform studies of aging and space travel, both of which involve free radical damage to key cellular machinery such as DNA and proteins.