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They have been sighted from mountaintops to the deep sea, from tropical rain forests to the Antarctic.
Tardigrades are notable for being perhaps the most durable of known organisms; they are able to survive extreme conditions that would be rapidly fatal to nearly all other known life forms. They can withstand temperature ranges from 1 K (−458 °F; −272 °C) to about 420 K (300 °F; 150 °C), pressures about six times greater than those found in the deepest ocean trenches, ionizing radiation at doses hundreds of times higher than the lethal dose for a human, and the vacuum of outer space. They can go without food or water for more than 10 years, drying out to the point where they are 3% or less water, only to rehydrate, forage, and reproduce. They are not considered extremophilic because they are not adapted to exploit these conditions. This means that their chances of dying increase the longer they are exposed to the extreme environments, whereas true extremophiles thrive in a physically or geochemically extreme environment that would harm most other organisms.
Usually, tardigrades are about 0.5 mm (0.020 in) long when they are fully grown. They are short and plump with four pairs of legs, each with four to eight claws also known as "disks". The first three pairs of legs are directed ventrolaterally and are the primary means of locomotion, while the fourth pair is directed posteriorly on the terminal segment of the trunk and is used primarily for grasping the substrate.
Tardigrades are prevalent in mosses and lichens and feed on plant cells, algae, and small invertebrates. When collected, they may be viewed under a very low-power microscope, making them accessible to students and amateur scientists. Tardigrades form the phylum Tardigrada, part of the superphylum Ecdysozoa. It is an ancient group, with fossils dating from 530 million years ago, in the Cambrian period.
[video=youtube_share;cjV2WP0wkvo]http://youtu.be/cjV2WP0wkvo[/video]
These ultimate survivors can handle everything from the vacuum of space to 600 times the normal atmospheric pressure. And new research is revealing how they manage one of their party tricks, turning to glass when there is not enough water to maintain normal life processes.
Tardigrades usually live in wet places like ponds or on moss. When things dry out they respond by entering a state of suspended animation, in which they can last for decades without food or water, before restoring themselves when the rains come.
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At the annual meeting of the American Society for Cell Biology, the University of North Carolina's Dr. Thomas Boothby reported on how they achieve this remarkable resurrection.
Tardigrades, Boothby said, produce proteins that are disordered when in a liquid solution. However, as water is lost, the proteins form a sort of glass glaze that protects the parts of cells that otherwise would be damaged by the absence of water. The glass dissolves when water returns, allowing the tardigrades to restore their functions.
These proteins are essential to tardigrades' capacity to survive drying out; reduced concentrations make the tiny creatures vulnerable. However, they are not the sole cause of micro-animals' exceptional survival skills. Boothby told Science News that lower concentrations do not affect another of tardigrades' traits, the capacity to survive extreme cold, a capacity that has allowed them to survive even in Antarctica.
Boothby, who was the lead author of a (now disputed) paper last month reporting that almost a sixth of tardigrade DNA comes from other sources, had HeLa tumor cells produce the same proteins. When wet, proteins diffused within the cells, but then became concentrated in certain parts of the cell when dried out. Boothby suggested this is to protect those areas. “We found in vitro these proteins formed biological glasses when dried,” he said, with some irony, since in vitro literally means "within glass."
When the proteins were expressed in bacteria and yeast, which were then dried out, they maintained their capacity, producing glassy materials that protected the single-celled organisms against the effects of water loss. Further research is being done to learn how they do this, and how it can be extended to other circumstances.
Even before this discovery, tardigrade anti-desiccation molecules were inspiring the creation of substances that blend the characteristics of glass and crystals in ways that could be useful for making better solar cells and light-emitting diodes.
“Understanding desiccation tolerance promises to contribute to many applications, such as engineering of drought tolerant plants and the stabilization of biomaterials,” Boothby noted. Moreover, medicines and vaccines that currently require refrigeration – very expensive in parts of the developing world – might be preserved using similar methods.
Another reason to wish to be a water bear.
