In studies of how to survive in space and in hostile environments, there is often no better a scientific specimen than the tardigrade, the so-called water bear. This is due to its capability to survive in such scenarios and far more besides. Even exposure to the vacuum of space doesn’t do much to deter it.
The Amazing Tardigrades
It is because of these traits that tardigrades are so heavily studied, in order to figure out the genetics behind these extraordinary capabilities. From experiments conducted in simple labs around the world to the International Space Station, these water bears are highly sought out for anyone studying extremophile environments, but wanting to make it possible for non-extremophile organisms to survive in them.
Because tardigrades are not extremophiles. They are not adapted to live in such environments. Eventually, it will kill them, but that doesn’t change the fact that they can continue to live far longer than practically any other organism studied in such conditions, other than the adapted extremophiles themselves.
How they do it is something scientists desperately want to figure out. How is it that we can find various tardigrade species in the most remote of environments, from the high slopes of the Himalaya mountains to the depths of the ocean? What exactly in their genetics and their physiology makes them capable of living in such places?
As of yesterday, at least one question in regards to tardigrades has been discovered: how they survive in high heat or low water environments without drying out.
In a collaborative study by researchers from the University of North Carolina, North Carolina State, the University of California (Berkeley), and the University of Modena and Reggio Emilia in Italy, they were able to identify a class of proteins known as IDPs, intrinsically disordered proteins.
In general, these proteins are, as their name suggests, disordered. They don’t maintain any particular three-dimensional shape and have what is called conformational flexibility. Examples of these sorts of proteins include membrane proteins that form cell wall channels and globular proteins that form into spherical shapes to create water soluble colloid mixtures.
This intrinsic disorder is characterized by what types of amino acids make up the proteins. The hydrophilic and charged group of amino acids inherently have more disorder and a likelihood to form into other complexes with molecules. Meanwhile, the uncharged, hydrophobic amino acids are very structured and ordered. Then there’s also a couple amino acids that can be either, depending on the circumstances.
As you might guess, it is a higher propensity of the former that makes up these IDPs and allows them to fluidly change their shape as needed. But how does this factor into protecting tardigrades from drying out?
A Simple Matter Of Checking
First off, let’s discuss how they were discovered. It was known that the genes that protect tardigrades are similar to those found in bacteria that also protect them from desiccation. The trehelose sugar was at one point a suspect, but further testing showed no connection to the ability, at least in tardigrades since they don’t have the capability to make it.
The researchers then decided to look into what genes are up-regulated when a tardigrade is going through the process of desiccation. This almost immediately revealed the IDPs as involved. To confirm this, the scientists also looked at two other species and found similar genes being up-regulated there as well, confirming their involvement in the process.
The final step was to insert these genes into yeast and other test bacteria to see if they conferred the ability as well. In short, they did, case closed. All in all, a very straightforward experiment with useful and interesting results. If only most experiments turned out that way.
A final facet of IDPs they found was that they were capable, similar to trehelose sugars, of forming “glass-like solids” around the organisms, which is how they protected them from losing all their water. If this covering was interfered with, then the tardigrades would die.
With that understood, IDPs may have a number of possible uses in the future as drought protection, among other things. Crops may be able to be protected and water stores in general may have a new way to prevent water loss over time. There are even possibilities for usage in space travel, as these proteins likely also played a role in protecting tardigrades when exposed to space itself.
But, for now, just knowing these facts about the proteins gives us far more information about the tardigrade and its capabilities. There are many more things that need to be discovered about them, which may offer even new methods to be applied to other fields.
All thanks to the lowly water bear.
Photo CCs: SEM image of Milnesium tardigradum in active state from Wikimedia Commons