Tardigrades are very small creatures ranging in size from 0.2 to 1.2 mm. They live almost everywhere, but prefer to inhabit aquatic or humid environments. They are also called water bears. But they are best known for their ability to survive in almost any conditions. They can survive extremely low temperatures close to absolute zero, but also scorching heat reaching up to 150 degrees C. They can withstand a pressure of over 6,000 atmospheres. They will survive without water for decades. And they are the only life form known to us that has survived in space.
Scientists from Marshall University in West Virginia and the University of North Carolina at Chapel Hill say they have determined in a recent study how tardigrades can survive extreme conditions. They say tiny molecular sensors in their cells can detect when too many harmful molecules called free radicals are being produced. When this situation occurs, these animals enter a state of dormancy which allows them to survive.
The results and description of the research were published in the journal “PLOS ONE” (DOI: 10.1371/journal.pone.0295062).
The paper’s co-author, Derrick Kolling of Marshall University, exposed tardigrades to high levels of hydrogen peroxide, sugar, salt and cold temperatures of minus 80 degrees Celsius to put the invertebrates into a dormant state. He then placed the tardigrades in a machine that detects harmful, highly reactive free radicals, which are atoms or molecules containing unpaired electrons. And he actually saw the creation of such atoms in tardigrades. This isn’t all that surprising, since an animal’s normal metabolic processes, as well as environmental stressors like smoke and other pollutants, create free radicals in cells.
Free radicals snatch electrons from their surroundings to achieve stability. In this process they damage cells and other compounds such as DNA or proteins. When Leslie Hicks, a chemist at the University of North Carolina at Chapel Hill, learned of Kolling’s experiments, she began to wonder whether free radicals might play a role in these animals’ incredible survival skills.
Under the influence of poor environmental conditions or other stressors, tardigrades shrink, shrivel and enter a dormant state, which helps them survive unfavorable conditions. The researchers monitored the tardigrades as they entered this protective state, and then tested whether and how they could wake up and resume normal activity when environmental conditions improved.
Hicks studies signaling interactions between free radicals and cysteine, a key component of proteins. The researchers exposed the tardigrades to several types of molecules known to block cysteine oxidation.
Scientists have determined that cysteine oxidation leads to changes in protein structure and function, signaling entry into a dormant state. This process also acts as a kind of regulatory sensor in response to stress. When there was no cysteine, the tardigrades were helpless and unable to enter the protective state of dormancy.
Kazuharu Arakawa of Keio University in Japan, who studies tardigrades, says the new work is in line with previous research showing a role for cysteine oxidation in a certain fly known for its resistance to complete desiccation. The similarities suggest that this mechanism may be a common trigger of dormancy.
However, scientists say there is still much work to be done to understand how free radicals affect tardigrades. The resilient state of cryptobiosis is not the only tactic used by tardigrades to survive environmental stress. The researchers plan to examine the remaining strategies in detail. Hicks hopes that, in the long term, this discovery could help research into aging and space travel, which involve free radicals that damage important cellular mechanisms such as DNA and proteins.
2024-01-24 11:00:28
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