Tardigrades, an Unlikely Sleeping Beauty

Tardigrades, an Unlikely Sleeping Beauty
Water bear. Coloured scanning electron microscope (SEM), of a water bear or tardigrade (phylum Tardigrada). Water bears are tiny, segmented micro-animals that live in water. They have eight legs and can survive in damp habitats like moss and lichen. They are classified as extremeophiles because they can survive dry conditions by becoming desiccated, which allows them to remain for many years. Whilst in this form (known as a tun) they can withstand the most extreme environments and can tolerate radiation levels as high as x1000 more than other animals, including humans. They have even been brought back alive after spending 10 days in the vacuum of space. Magnification: x1000, when printed at 10 centimetres wide. Credit: Steve Gschmeissner / Science Photo Library

Researchers put this ancient critter through a subzero gauntlet to learn more about what happens to their internal clock while surviving the extreme.

Ashleigh Papp: This is Scientific American’s 60-Second Science. Ashleigh Papp is my name.

Papp: Imagine a little critter that isn’t quite an insect or an animal. It measures about one millimeter in height, is shaped like an eight-legged gummy bear, and has tough, almost crunchy-looking scaling. Ladies and gentlemen, it’s the tardigrade!

Jessica Ehmann: They basically look like, more or less, something between a worm and a bear with more legs. Their lumbering gait is what gives them their name: they move from one side to the other when they walk. This is very cute.

Papp: That’s Jessica Ehmann (“ee-mahn”), a research scientist and former student researcher at the University of Stuttgart in Germany, and she’s pretty obsessed with the water bear.

Ehmann: So that’s basically when I fell in love with the tardigrade, because it sat there under my binoculars, and it got up in the front of the body, and it was waving at me.

Papp: Tardigrades have been around for even longer than the dinosaurs–by, like, 200 million years. They’ve also developed some very clever ways to survive in harsh environments over the years. A tardigrade can become dormant for many years if it experiences too much dryness or too little heat.

Ehmann: They take all their arms, and they pull them inside, and you can’t see their arms anymore; they just look like small tongues. They pull in all their extremities. They then slow down their metabolism to a halt.

Papp: And then, when conditions are right again, they wake up and go on with their life, almost like Sleeping Beauty lying asleep for a century before her prince arrives.

Papp: Here’s why that matters. Researchers are very interested in what happens when tardigrades are in that dormant state. They call it “cryptobiosis”. Here’s why.

Papp: A previous study from 2008 by some of Ehmann’s colleagues at Stuttgart investigated how long tardigrades can survive in crazy dry conditions. Ehmann followed a similar approach. Ehmann took a different approach.

Papp: She and her colleagues used tardigrades of the same species and divided them into four groups. The control group was exposed to ambient temperatures. This gave researchers an idea of their survival rates and how long they can live in these conditions.

Papp: The other three groups were put through a gauntlet: the researchers froze these tardigrades at (minus)-30 degrees Celsius, slowly thawed them, counted them to see how many were still alive and then froze them again.

Ehmann: Basically, for those six to eight months, I only froze and thawed and fed and cleaned the tardigrades and noted their survival.

Papp: Overall, the team used about 700 tardigrades and kept up with the freezing-thawing cycles until no more of them reawoke.

Papp: And after evaluating the survival rates for the four groups, the researchers found that the tardigrades that were frozen lived longer than the control group.

Ehmann: When we evaluated the survival of the tardigrades, we actually saw that the tardigrades that were frozen every other week, lived about twice as long as the control group.

Papp: And as long as they were frozen, they didn’t really age.

Ehmann: But which also made the experiments very, very long, because they just lived twice as long as we expected them to (laughing).

Papp: The longest living tardigrade in this experiment, as a reference, was 169 days old when it died! Meanwhile the longest living critter in the control group, the one with water bears that didn’t go in and out of the freezer, was 93 days old. These results were recently published in the Journal of Zoology.

Papp: And this means that the time the tardigrades were frozen didn’t seem to affect their internal clock, almost like it wound down during their dormant phase. This opens up some interesting avenues for human applications.

Ehmann: Now, I guess, many people will start thinking about, like, freezing humans, sending them into space like the sci-fi movies. I don’t think we need to go that far yet. However, I find the application of freezing and thawing cells or tissues to be very interesting. This could be used for medical purposes, or stem cells.

Papp: If a cancer patient was able to have their healthy cells extracted before chemotherapy and put into a tardigradelike state of dormancy, those cells could potentially then be replanted once the harsh treatment was complete, and normal activity–healthy cell or organ function–might resume in much a shorter amount of time.

Papp: We still have a long way to go. We still have a lot to learn about the mechanisms that govern the tardigrades’ transition between dormancy and awake. This work shows that there are solutions to a healthy future, even in the most unlikely of creatures like the tardigrade.

Papp: For Scientific American’s 60-Second Science, I’m Ashleigh Papp.

[The above text is a transcript of this podcast. ]



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