Tardigrades, tiny, eight-legged creatures that look like alien bears, are tougher than any beast on Earth. These little guys can withstand massive amounts of radiation, nearly 1,000 times higher than the lethal level for humans, and survive in harsh environments that no other organism can withstand. A recently discovered species of tardigrades reveals new insights into how the microscopic animal pulls it off by repairing damage to its DNA when exposed to high doses of gamma rays.
There are roughly 1,500 known species of tardigrades, affectionately known as water bears, but there’s still much to be known about the mechanism through which the hardy invertebrates protect themselves against radiation. A new study specifically examines one species, named Hypsibius henanensis, to uncover clues behind the molecular mechanism that gives tardigrades their super powers. The results could inform new ways to help mitigate the effects of radiation on astronauts in space, and facilitate long-duration spaceflight for humans.
“Extreme environmental resistance of extremophiles such as tardigrades is a treasure trove of unexplored molecular mechanisms of stress resistance,” Lei Li, a researcher at the Chinese Academy of Science, and lead author of the paper, said in a statement. “Functional research on these radiotolerance mechanisms… will further broaden our understanding of cellular survival under extreme conditions.”
The scientists behind the study, published Thursday in Science, sequenced the genome of the tardigrade species, which they had discovered around six years ago in China’s Henan province. When exposed to radiation, the tardigrade species activated a sophisticated system of defense that not only protects their DNA from the damage but also repairs any breaks that happen to occur.
The most well-known defense mechanism for tardigrades is their ability to enter a death-like state of dormancy in which they suck in all eight of their limbs and curl up into a ball while depleting nearly all of their internal water supply (the water bears would be a great fit for Dune’s fictional planet, Arrakis). This dehydrated state, among other defensive measures, allows them to live through the most extreme conditions for decades or possibly longer, surviving freezing temperatures, intense radiation, or the vacuum of space.
The recently found species, Hypsibius henanensis, has a total of 14,701 genes, 30% of which are unique to tardigrades. Through a series of experiments, the scientists exposed their newly found water bears to doses of 200 and 2,000 grays of radiation, and, in response, found that 2,801 genes involved in DNA repair, cell division, and immune responses became active (“grays” are a standard unit of measurement for radiation doses). One of those genes, TRID1, summons a protein (called 53BP1) at sites of damage to help repair double-strand breaks in DNA.
The species of water bears also calls on other genes to help its surprising resilience, including DODA1, which produces antioxidant pigments typically found in bacteria, plants, and fungi to clean up the reactive chemicals caused by exposure to radiation. Another gene, BCS1, shields the tardigrades’ cells from mitochondrial damage.
“Tardigrade are found nearly everywhere on Earth from deep ocean environments to the tops of tall mountains,” Thomas Boothby, assistant professor for the Department of Molecular Biology at the University of Wyoming, who was not involved in the study, told Gizmodo. “Tardigrades have been found on every continent, including Antarctica. Their ability to tolerate extreme stresses has likely helped with their expansive colonization of different biomes.”
In 2021, Boothby sent water bears to space, exposing them to the harsh conditions on board the International Space Station to better understand how they tolerate extreme environments. “It is important to understand how tardigrades survive in space and under spaceflight conditions as this can help us develop therapies and countermeasures to the stresses and dysfunctions experienced by humans during prolonged spaceflight,” Boothby said. “This is essential for promoting a safe and productive human presence in space as well as expanding our space economy.”
Tardigrades have long fascinated scientists, particularly within the context of spaceflight. Identifying the ways in which the tiny creatures survive in the stressful environment, with microgravity and elevated levels of radiation, can help researchers identify ways through which to protect humans from the effects of long-duration spaceflight.
“Better understanding the unique strategies mounted by tardigrades to cope with extreme stresses, including those such as radiation that are experienced during spaceflight, will help us understand how we might safeguard humans against these stresses,” Boothby said. “This would be important for safe and productive deep space or long-term manned space missions.”
