Tardigrades: Microorganisms on the Edge of Things

Written by Kyra Ezikeuzor

Imagine living life on the edge, literally; just like living in the most acidic of environments (such as the Picrophilus torridus) or in a deep-sea hydrothermal vent with debilitating heat and pressure (like the Pompeii worm). Or in saltwater (like brine shrimp halophiles). Or in space. Well, look no further to the microorganisms known as extremophiles: the organisms living on the edge of things. Unlike other microorganisms studied in microbiology, extremophiles are classified as animals, not bacterium or protists.

A notable extremophile is the tardigrade, also known as the water bear. Tardigrades are considered polyextremophiles; namely, organisms that can tolerate multiple extreme environmental conditions. They’re indestructible as they can thrive in environments of extreme temperature, radiation, and the space vacuum. In fact, these organisms can survive pressures exceeding 1,200 times atmospheric levels (Ingemar Jönsson et al. 2008).

While resilient, these microorganisms, as the name suggests, are incredibly small; in fact, tardigrades are as small as a grain of salt: measuring about 0.2 to 1.2 millimeters in length; yet, they’re big enough to be seen with the naked eye (Zia 2024).

The tardigrade was discovered in 1773 by German naturalist Johann August Ephraim Goeze when he examined samples of moss under a microscope. He documented his discovery, coining it the “little water bear” (Zia 2024). Regarding their physiology, tardigrades look a bit similar to bears with their plump torsos and stout legs. Interestingly, tardigrades have a brain, muscles, and a digestive system. Evolutionarily, they are classified as panarthropods, a clade of animals that also includes arthropods such as insects and crustaceans, velvet worms (onychophorans), and long-extinct worm-like ancestors known as lobopodians.

Additionally, regarding the tardigrade’s geography, there are terrestrial tardigrades (living in vegetation and desert environments) and aquatic tardigrades living in fresh and saltwater biomes (Zia 2024).

Moreover, many studies have been done to observe the tardigrade’s resistance to extreme environments, especially with respect to extreme temperatures. In 2019, University of Stuttgart scientist Ralph Schill proved that when a water bear is frozen, its aging process pauses. He froze 500 tardigrades at –30 °C, then thawed, counted, and fed them before subjecting them to additional freeze and thaw cycles until all of the microorganisms died. When he compared the characteristics of the repeatedly frozen tardigrades with non-frozen ones (his control group), they were identically the same. He concluded that:

“even in ice, tardigrades stop their internal clocks” (Mayer-Grenu 2022).

The tardigrade’s resilience to extreme temperatures is due to cryptobiosis, their ability to shut down their metabolic processes to survive temperatures from -271°C to more than 150°C.

However, the tardigrade is resilient to radiation for a different reason. Tardigrades can “withstand hundreds of times the amount of radiation that would kill a human” (Bittel 2016). This is because they contain a protective protein known as Dsup, meaning damage suppressor. This protein coats their DNA, giving them resistance.

In a study, scientists used human cells to mimic parts of the tardigrade’s inner workings to figure out which of these cells were providing the tardigrades with their resilience. They found that the Dsup protein shielded the tardigrade’s DNA from radiation and oxidative stress (Bittel 2016). In fact, scientists think this damage suppressor protein can explain why tardigrades can survive in the vacuum of space.

In a 2007 experiment, tardigrades were shown to survive in low space orbit. This experiment was performed in the Biopan-6 experimental platform through the European Space Agency during the FOTON M3 mission. The microorganisms were exposed to both the space vacuum, different spectral ranges of UV, and ionizing solar and galactic cosmic radiation (Ingemar Jönsson et al. 2008), surviving the space vacuum exposure.

Scientists hope to extend the tardigrade’s resilience to humanity, as these fascinating creatures present exciting potential advancements in biotechnology and astrobiology. We hope to biomimic their resilience by studying the proteins that make them indestructible, with the purpose of fine-tuning our lives on earth so we can also exist with a bit of the fortitude of a little water bear.

References:

1. Bittel, J. (2016, September 20). Tardigrade protein helps human DNA withstand radiation. Nature News. https://www.nature.com/articles/nature.2016.20648
2. Eden, L. (2024, July 25). Unusual labmates: Meet tardigrades, the crafters of nature’s ultimate survival kit. MIT Department of Biology. https://biology.mit.edu/unusual-labmates-meet-tardigrades-the-crafters-of-natures-ultimate-survival-kit/
3. Mayer-Grenu, A. (2022, October 7). How tardigrades survive freezing temperatures. https://phys.org/news/2022-10-tardigrades-survive-temperatures.html
4. Science Direct. (n.d.). Initial conditions for radiation analysis: Models of galactic cosmic rays and solar particle events — sciencedirect. https://www.sciencedirect.com/science/article/abs/pii/S0273117706004315
5. Williams, M. (2025, April 7). Phys.org — news and articles on science and Technology. Want to know how to survive in space? Ask a tardigrade. https://phys.org/news/2025-04-survive-space-tardigrade.html