How to Kill a Tardigrade
How do you destroy nature’s most indestructible organism?
Ever heard of a “water bear” or a “moss piglet?” Tardigrades are animals of many names, most of which are derived from their unique physique. Measuring just under 1.5 millimeters in length, the tardigrade has a chubby build with four pairs of clawed, stumpy legs. Its strange yet adorable anatomy has continually captured the attention of biologists everywhere.
But the fascination of tardigrades isn’t only due to their appearance. Even more intriguing is the tardigrades’ title of nature’s “most indestructible” organism.
In 2007, to test the tardigrades’ survival limits, scientists sent thousands of tardigrades into outer space on the surface of a satellite. When the tardigrade-infested satellite returned to Earth, a large number of the tardigrades had survived. Furthermore, several of the female tardigrades had even laid eggs in space. After the eggs hatched, the space-born tardigrades were deemed healthy.
However, in comparison to the tardigrade, an unprotected human sent to outer space would die in a matter of seconds. Their lungs would collapse, their skin would swell, their eardrums would rupture, and their blood would boil. If that’s not enough, ionizing radiation would break down the individual’s cellular DNA, finally rendering them unconscious.
Additionally, unlike virtually any other species, tardigrades can survive for decades without water. This is particularly interesting because tardigrades are specifically designed to live in water (both fresh and salt water are suitable).
Typically, most water-deprived cells should become useless when they dry out. The cellular membranes should split and leak and the cell’s proteins should unfold and cluster together. Furthermore, like outer space’s effect on a human body, a typical cell’s DNA should also start to break down.
So, how does a tardigrade avoid this? If a tardigrade no longer has access to water and effectively “dries out,” the tardigrade retracts its head and legs to enter a state called “Tönnchenform” or tun. While in the tun state, the tardigrade appears to be dead, halting all unnecessary bodily functions and slowing its metabolism to 0.01% of its normal rate. This is what allows the tardigrade to remain in suspended animation for so long. Once the tardigrade comes into contact with water again, it will return to normal.
If a tardigrade remains in the tun state for too long, their DNA will eventually become scrambled. Fortunately, the tardigrade is able to immediately repair any DNA problems that may occur upon reawakening from tun.
Yet, contrary to what you might think, this doesn’t quite make tardigrades immortal. Like any other organism, tardigrades will die of old age. Excluding time spent in a tun state, most tardigrades have short natural lifespans of about two years.
Other than natural causes though, it would seem almost impossible to “kill” a tardigrade. Almost.
In addition to a tardigrade’s unique abilities to withstand outer space and survive without water, tardigrades can take on some of the most extreme temperature conditions. From glaciers in the Arctic to active lava fields, tardigrades appear to be unbothered by how hot or cold their environment is.
But, it turns out that extended time spent in exceptionally high temperatures is the tardigrade’s fatal weakness. Previously, this limit was thought to have been sufficiently explored when an experiment found that tardigrades could survive being boiled up to 303.8° F for an hour. Unfortunately for the tardigrade, this isn’t the case for longer periods of time.
When a group of tardigrades was exposed to sudden 104° F temperatures for 48 hours, 100% of all non-tun tardigrades died. On the flip side, when the temperature was gradually increased to 104° F over the 48 hours, the survival rate had a drastic difference, with only 28% of the non-tun tardigrades dying.
Using a 50% kill rate, researchers explored what it would take to kill the remaining tun state tardigrades. It was concluded that an hour spent in a temperature of 180.9° F could reach this goal.
These newfound results were both shocking and unnerving to the science community. Researchers running these experiments expected the tardigrade to withstand much higher temperatures. These limits undermine previous claims that tardigrades will be able to survive “anything.”
Still, these current limitations may not hold true for long. Knowing that the survival rate was higher when the tardigrade populations were acclimated to higher temperatures, tardigrades will likely evolve to expand their tolerance for heat. Thanks to global warming, tardigrades (along with a vast number of other plant and animal species) have been forced to adapt to rising temperatures.
Scientists expect that the tardigrades will only go extinct on Earth if all of the oceans were boiled away. Unless that happens, tardigrades will continue to survive and thrive.
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