Written by Brian S. (KIS '19)
Edited by Angela Y. (VHS '21)
━━ August 12th, 2018 ━━
The King of Survival: Tardigrades
What is the first thing that pops into your mind when you hear the words “water bear”? A brown grizzly bear by a river hunting for salmon? A black bear scratching its back on a tree? The water bear is neither of these things. Instead, it is a microscopic creature, with a maximum size of about 1 mm. Allow me to introduce to you the water bear, or more scientifically known as the tardigrade.
At first glance, these creatures seem quite normal, maybe a little creepy. They can be found in most places on the planet, usually in moss, ferns, lichens, and other damp places. Their lifespan, when continuously hydrated, is usually no more than a few months. Most tardigrades’ main diet comes from sucking the fluid out of moss, lichen, or algae. There are some species of tardigrades that are carnivorous and will sometimes prey on their own species. Once you look past the basic information, however, is when the tardigrades true uniqueness begins to be realized.
The superpower that tardigrades have is that they are seemingly able to come back from the dead. Even though their life span is quite short when they live normally, but the tardigrades are able to withstand some of the harshest conditions known to man. Tardigrades have been found to be able to survive in space, temperatures nearing absolute zero, where all molecules come to a near standstill, and 150 degrees Celsius, and even large amounts of radiation. This all comes from their ability to change their body so that they can enter a state called the “tun” state.
In the “tun” state, the tardigrades seem dead. Their metabolism slows down to nearly 0.01% of their normal metabolism; their head and eight legs tuck in; And they shed almost all of the water present in their body. In this form, the tardigrades can survive almost anything, not needing food or water. Once they come into contact with water is when they come back to life. This state is very sustainable for them, allowing them to live on for decades.
If humans were to go to space without any protection, they would die. That’s not only for humans either. Most animals cannot survive in the vacuum of space, especially with the constant radiation from the sun. The tardigrade, on the other hand, can survive both the vacuum and radiation in space. In 1964, scientists exposed tardigrades to lethal doses of x rays and gamma, alpha, and ultraviolet radiation. Radiation wreak havoc on your body by destroying your DNA; when exposed to high enough doses of radiation, your DNA could end up ripping apart. In all of these experiments, the tardigrades were found to have survived, even though they didn’t enter the “tun” state.
Another amazing feature of the tardigrade is that they are able to survive at nearly absolute zero temperatures. In the 1920s, a Benedictine friar named Gilbert Franz Rahm placed tardigrades in liquid helium (-272 degrees celsius) for eight hours. After taking them out and warming them up, Rahm observed them to be alive and well again. The biggest challenge that animals face when entering extremely cold areas is ice forming within their cells. Fish that live in the antarctic have created solutions for this problem by evolving to create anti freezing proteins, which lowers the freezing point of their cells to ensure that ice doesn’t form. However, tardigrades don’t seem to have this protein. Instead, scientists have two different hypotheses for this. One is that tardigrades don’t mind that ice forms in their cells, as they are able to either repair their DNA or protect their DNA from the damage caused by ice formation. The other theory is that tardigrades are able to create chemicals that encourage freezing outside of their cells, so that their insides will stay unfrozen.
Tardigrades are also able to withstand extreme pressures. Scientists have been able to find that tardigrades are able to withstand pressures up to 600 megapascals. To put that into perspective, the deepest part of the ocean is in the Mariana Trench, where only 100 megapascals of force is applied. Similar with radiation and extreme cold, pressure also breaks apart protein and DNA in the cells. Somehow, Tardigrades are survive to do this.
The vacuum, radiation, extremely cold temperatures, and extremely high pressures essentially all do the same thing: they denature and destroy protein. So, if tardigrades were to be able to protect against this, then they would be able to survive through all of these conditions. It turns out that tardigrades have a special protein called the damage suppressor protein, or the Dsup protein. This protein is unique to the tardigrade, and as the name suggests, reduces the damage done to the DNA. Although scientists have been only able to prove that this protein is effective against radiation, perhaps something similar to these proteins are what is used to protect tardigrades against the other forms of DNA destruction.
Tardigrades are truly one unique organism. They have somehow managed to evolve to outlast any other creature on the planet. Move aside cockroaches, as the tardigrades take your place as the sole survivors of a nuclear war.
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