Contenders for the world's toughest animals come in a range of sizes—rhinoceroses and cockroaches included. But these animals are marshmallows compared to the tardigrade, or the so-called water bear.
This microscopic beast only reaches a maximum of 1.5 mm long and seems to have near superpowers, Rachel Feltman reports for The Washington Post. Tardigrades typically live in water but can dehydrate, shriveling up for decades. During this state, they reduce their metabolism to 0.01 percent normal conditions until they rehydrate, popping back to life. They can survive at 212 degrees Fahrenheit and 459 degrees below zero. Even more impressive, the eight-legged creatures can survive in the vacuum of space and endure ten days of intense cosmic radiation.
Now, a new study of the tardigrade genome identifies the genes that help the hardy water bear survive such extremes and may have implications for future human space travel.
Researchers from the University of Tokyo looked at the genome of Ramazzottius varieornatus, one of the hardier tardigrade species, reports George Dvorsky for Gizmodo. Through this analysis, they found several unique properties of the genome, including more copies of an anti-oxidant enzyme and a protein repair gene than found in any other animal. The gene of particular interest, however, is coded to produce a protein unique to the species that likely protects it from radiation. The protein, called Dsup, not only protects the DNA in tardigrade cells from direct radiation, but it also helps repair radiation damage. They published their results this week in the journal Nature Communications.
When the researchers transferred Dsup to cultured human cells, it initially appeared not to make a difference, lead author Takuma Hashimoto explains in a press release. “However, we left them in the incubator for a while in the hope that a key property of Dsup lay hidden somewhere in that miniscule difference, and that the difference would eventually become quite distinct," he says. "To our great surprise, when we checked the cells under the microscope some time later, their shape and number had changed significantly, far beyond our expectations."
In other words, the Dsup helped repair the damaged DNA over time. This could be an important step forward in protecting human astronauts that will be subjected to large amounts of cosmic radiation during future trips to Mars and other planets. “Once Dsup can be incorporated into humans, it may improve radio-tolerance,” geneticist Takekazu Kunieda, co-author of the study tells Dvorsky. “But at the moment, we’d need genetic manipulations to do this, and I don’t think this will happen in the near future.”
He also points out that the protein only produces about half the protection needed, and suspects the tardigrade uses other strategies to protect itself from radiation as well.
The study also puts to bed a controversy that erupted last year when a team from the University of North Carolina, Chapel Hill, released a paper claiming tardigrades had collected about 6,000 genes from bacteria, plants, fungi and Archaea—about one-sixth of their total genome. The idea was that the water bear had “stolen” the genes that give it its superpowers from other species through a process known as horizontal transfer. After a back-and-forth with another team who challenged the results, however, the researchers soon determined most of those genes were a result of contamination during the study.
This new study also analyzed genes acquired by horizontal transfer and used extra precautions to prevent contamination. They determined that roughly 1.2 percent of tardigrade genes come from other species, which is not unique in the animal kingdom. In fact, it makes the tardigrade even more impressive, Kunieda tells Dvorsky. Tardigrades evolved most of these extreme abilities all on their own.