Explained: Why scientists study tardigrades, tiny eight-legged ‘water bears', in space

Indian Express

2 days ago

Among the scientific experiments astronaut Shubhanshu Shukla will undertake during his two week stay at the International Space Station (ISS) is one that will examine the revival, survival, and reproduction of tardigrades in space.
What is the Voyager Tardigrades experiment? And why do scientists study these microscopic, eight-legged organisms?
First, what are tardigrades?
Tardigrades, also known as 'water bears', are robust aquatic animals that have been around for roughly 600 million years, 400 million years before dinosaurs walked the planet. They have survived all the five major mass extinction events to have taken place thus far, and scientists believe they could be around long after humanity has died out.
Typically about 0.5 mm long when fully grown, tardigrades have four pairs of legs, with 4-6 claws on each foot. They also have a specialised mouth which helps them suck nutrients from plant cells, algae, and other small invertebrates.
Tardigrades can be found almost everywhere — from the highest mountains to the deepest oceans. Their most common habitat, however, is the thin film of water found on mosses and lichens, which bestows upon these animals the moniker of 'moss piglets'.
Why do scientists study tardigrades?
Although these micro-animals were discovered in 1773 by German zoologist Johann August Ephraim Goeze, they have become a subject of intensive research in the past few decades.
This is because tardigrades are remarkably resilient creatures, known to survive in the harshest of conditions. Water bears have been known to withstand temperatures as low as minus 272.95 degrees Celsius or as high as 150 degrees Celsius; endure ultraviolet radiation of space and pressures of 40,000 kilopascals (equivalent to what can be experienced at a depth of 4 km under the ocean's surface); and live after being stored in a freezer for 30 years, according to a report by Front Line Genomics.
A better understanding of tardigrades' survival mechanisms can potentially have several applications: from helping scientists develop more resilient crops to creating advanced sunscreens to preserving human tissues and organs for transplantation.
Why are tardigrades so resilient?
Siddharth Pandey, an affiliate research scientist with US-based Blue Marble Space Institute of Science, told The Indian Express that tardigrades owe their incredible resilience to cryptobiosis, a state in which organisms bring their metabolism to a near-complete standstill in the face of adverse environmental conditions. Tardigrades can reduce their metabolism to less than 0.01% of normal, and drop their water levels by more than 95%, a state called anhydrobiosis.
Both anhydrobiosis and cryptobiosis result in the emergence of a durable shrunken state, called tun, in which tardigrades are able to withstand extreme conditions.
Also, these animals produce unique proteins such as cytoplasmic-abundant heat soluble (CAHS) proteins which are key to their resilience.
'These [proteins] form a gel-like matrix within their cells, vitrifying and protecting essential cellular components from destruction. This allows them to withstand extreme temperatures, radiation, and the vacuum of space,' Pandey said.
What does the Voyager Tardigrades experiment seek to do?
Scientists will take tardigrades to the ISS in a state of tun, before reviving them and examining the effects of space radiation and microgravity on their biological processes.
The primary objective of the experiment is to identify the genes that are responsible for making these animals resilient. In other words, scientists hope to pinpoint the specific molecular machinery that enables tardigrades' survival and DNA repair in space.
This will help scientists develop strategies to protect astronauts during long-duration space missions, and preserve biological materials for extended space travel.
For instance, the survival mechanisms of tardigrades can be used to come up with strategies that better shield astronauts from space radiation, or counteract muscle and bone density loss experienced during lengthy space stays.
Have tardigrades been taken to space before?
Tardigrades have been a part of space missions since 2007, when some 3,000 moss piglets hitched a ride to space aboard the European Space Agency's Foton-M3 mission.
The tardigrades, in a state of tun, were kept in a little round box on the side of the spacecraft whose lid was opened in space. Upon returning to Earth, they were rehydrated and examined. The German and Swedish scientists undertaking the experiment found that not only did many water bears survive the harsh space environment, some were also able to reproduce successfully.
'While exposure to UV radiation did cause some damage and reduce survival rates slightly, the experiment confirmed that the vacuum of space alone was not a barrier to their survival, solidifying their status as one of Earth's most durable organisms,' Pandey said.
The experiment also made tardigrades the first animal to survive exposure to space. Before water bears, animals had only survived space in the safety of a spaceship or space suit.