Tardigrades are practically indestructible, capable of surviving in radiation conditions, extreme temperatures (at minus 150 °C and 150 °C perfectly), in the vacuum of space and even without eating or drinking for a long time. Precisely how tardigrades survive without water is what a team of scientists has just discovered.
These tiny animals expel water from the body and transform into a ball that seems lifeless. Thus, in this state of desiccated suspended animation, they can survive for decades without needing to eat or drink. How is this possible?
A new study published in PLOS Biology has just revealed the key to the matter. Those responsible for the animal not dying, even if it does not drink a drop of water, are proteins that only they have and that turn the inside of the cells into gel, preventing the cell membranes from wrinkling and collapsing. This is a very different strategy from those that have been observed in animals that survive periods of drought.
The secret of the tardigrades
Tardigrades or water bears are microscopic extremophilic animals, that is, they are capable of surviving in extreme conditions: they can live in the vacuum of space, they can withstand freezing and boiling temperatures for an hour. Under the microscope, tardigrades have chubby bodies and eight legs with very delicate claws.
In nature there are animals that remain alive after long periods of drought. One of them is brine shrimp , which use sugars called trehalose to freeze their cells. This strategy, which leaves the cells as if they were glass, protects their function until they come into contact with water again.
Tardigrades, however, do not have much trehalose. What they do have are proteins that are not present in any other animal. A 2017 study found that some of these proteins promoted a crystal-like state of trehalose in desiccated tardigrades.
These proteins that appear to be unique to tardigrades are known as cytoplasmic abundant heat-soluble (CAHS) proteins . CAHS float in the cytoplasm, the fluid that fills cells. From previous studies, it was known that these proteins were involved in the survival of tardigrades during desiccation, but until now it was not known how they acted.
Kunieda and her team dehydrated CAHS-bearing cells to see what happened. What happened was that when the cells were threatened with desiccation, the proteins condensed, forming a network of filaments. These filaments propped up the cell, turning the cytoplasm into something gel-like and preventing the cell from collapsing as water seeped out. The condensation was a matter of minutes and when rehydrating the process was reversed just as quickly. Specifically, 6 minutes after rehydration, the cell functioned normally again.
In experiments, the researchers found that CAHS could make insect cells more resistant to desiccation, but they weren’t as resistant as tardigrade cells, so CAHS must act in concert with something else.
Researchers have also discovered that tardigrades have more than 300 proteins that react to stress , that is, to adverse conditions, so there is still work to be done. In the future, the findings could be used to develop better preservatives to improve the shelf life of drugs and vaccines, the scientists say.
Referencia: Tanaka, A., Nakano, T, et. al. 2022. Stress-dependent cell stiffening by tardigrade tolerance proteins that reversibly form a filamentous network and gel. Plos Biology. DOI: https://doi.org/10.1371/journal.pbio.3001780