What are tardigrades?
Tardigrades are a group of 900 species which can survive extremes not even seen on Earth. They are very tiny (ranging in size from 0.05-1.2 millimeters, or 0.002-0.06 inches), eight legged creatures that typically feed on the juices of moss, algae, and lichens. Some prefer to eat other tardigrades.
What makes them so amazing is not just that they can survive some extremes, but that they can survive all of them. Many of the environments they can thrive in are more extreme than what most extremophiles can endure, yet these “water bears,” as they are known, go along their merry way like nothing is wrong.
How do tardigrades survive?
One of the main methods they survive is by going into the “tun” state. The tun state is like hibernation; it is a dormant state the tardigrade can go into by retracting its head and legs into a small, dry husk. It removes nearly all of the water in its body and slows down its metabolism to 0.01% of its normal rate. This allows it to stay dormant for decades. Once it comes into contact with water, it’ll reanimate.
After staying in the tun state for an extended period of time, its DNA gets damaged. That’s no problem, because it can just fix it! As is usual with extremophiles, tardigrades can repair their own DNA. This also allows it to survive other extremes, including a dose of radiation roughly 2000 times stronger than the lethal dose for a human. They produce a unique protein, called Dsup, that binds itself to DNA and shields it against radiation.
Radiation isn’t the only danger. High pressures tear apart DNA and liquefy cell membranes, essentially melting the pieces that make us up biologically. Bacteria barely survive above 3,000 atmospheres. Meanwhile, the tardigrade can survive twice that, withstanding pressures of 6,000 atmospheres.
While pressure liquefies cells, cold temperatures tear them apart. Ice crystals can form in an organism’s body and cut through its cell membranes. Tardigrades lack the ability to make the antifreeze proteins that protect most extremophiles. They don’t need to: they can either repair the damage or protect themselves from it. To protect themselves, they may produce chemicals that help ice crystals form outside of their cells, rather than inside. This way, the cells stay unpenetrated. Tardigrades can survive cold even as low as -272.8°C (-459°F). Compare this to absolute zero (-273.15°C, or -459.67°F). When dehydrated, they survive even better. They can handle cold, but they can also take the heat. In the 1920s, Benedectine friar Gilbert Franz Rahm revitalized tardigrades after heating them to 151°C (304°F) for 15 minutes.
Handling the most extreme environment: space
Space is the most inhospitable environment for any living thing. Tardigrades, almost unsurprisingly at this point, can take it. Tardigrades were taken into low Earth orbit and survived. Granted, not all of them survived, but the fact that there were any survivors is remarkable. Even more so since some laid eggs and had healthy offspring in space. They were exposed to a complete vacuum, imposing not only a complete lack of pressure, but also an anhydrous and anaerobic environment. No pressure, no water, no oxygen, no life – unless you’re a tardigrade. They were also exposed to UV and cosmic (gamma and X-ray) radiation. So next time someone says nothing could survive in space, introduce the tardigrade!