Tardigrades, also known as water bears, are microscopic animals capable of surviving in harsh environmental conditions. Takuma Hashimoto, a biologist at the University of Tokyo designed experiments to verify if a protein unique to the water bear will protect human DNA from X-ray damage.
Human cells nicknamed “Dsup” for “damage suppressor” were cultured from the newly discovered protein. When the cells were blasted with radiation, they underwent only half as much decay as normal cells. Referring to the tardigrade derived protein, Hashimoto said that he found it remarkable that a single gene is enough to improve the radiation tolerance of human cultured cells.
Water bears have amazing superpowers of survival that has long fascinated scientists. Looking as if they belong in a Sci-Fi movie, they are hardly the size of a grain of sand, and seemingly eyeless. With a vacuum cleaner nozzle of a snout and eight puffy legs with bear like claws, their bodies resemble hazmat suits.
When the the tardigrade Ramazzottius varieornatus encounters dryness, their body water characteristically drops down to 2.5% wt./wt. accompanied by body shrinkage. The contracted dry animal, referred to as a tun, shows no visible signs of life, but it can resume their activity if a drop of water is added. Video credit: Daiki D. Horikawa.
Their diet consists of moss and lichen although some feed on other water bears. These primitive water dwellers can survive environments more dangerous than anything Nature can think of to throw at them. Being frozen at temperatures slightly above absolute zero, or being plunged into scalding liquids does not faze them in the least.
In previous experiments, water bears were bathed in -253 degree Celsius (-423 degree Fahrenheit) liquid nitrogen for 26-hours. The coldest temperature ever recorded on Earth was in Antarctica at −89.2 C (−128.6 F). Amazingly, the creatures sprang back to life when put in a few drops of water.
Of the approximately 1,000 known tardigrade species, some can handle devastating pressures at least six times greater than found at the seven mile (11 kilometer) deep Mariana Trench in the Pacific Ocean.
The devastations of outer space doesn’t seem to faze them either. Thousands of water bears were attached to a satellite in 2007. During their journey through space, they were directly exposed to deadly space radiation in vacuum conditions and then returned to Earth. Many of the travelers survived the trip. Some females even laid eggs, which yielded healthy offspring afterwards.
Water bears can slip into a state of suspended animation in which their metabolism slows to 10,000 times below the normal rate and they lose almost all the liquid in their bodies. They do this to survive extreme conditions, and scientists still have no idea how they do it.
Many studies done on water bears over the years reach the conclusion that they have an increased ability to repair damaged DNA, especially as they emerge from a state of extreme dehydration, which can last for decades. Hashimoto and colleagues’ experiments with human cells showed that using the tardigrade’s Dsup protein actually act as a shield to protect DNA, especially from harm done by X-rays.
A tardigrade that is walking on a moss. Video credit: Kunieda.
Last December another team of researchers published the first complete genome of a tardigrade in the US. They used the species Ramazzottius hypsibius and found that nearly a fifth of its DNA actually came from other plants and animals. This is viewed as a new record for horizontal gene transfer between species in the animal kingdom. The team postulated that this accounted for the remarkable resistance of water bears to environmental factors.
A controversy erupted when other scientists disagreed with the conclusions, and argued that the high percentage of foreign DNA found was more likely the result of sample pollution. Hashimoto’s results may resolve this controversy as his findings suggest the critics were right.
The genome of a different species, R. varieoranatus, was sequenced with a precision 100 times greater than was done with the previous research. Foreign genes accounted for only 1.2 percent of the result. R. varieoranatus is believed to be the hardiest of all tardigrades and Hashimoto argues that based on this result, horizontal gene transfer is not a major cause of tolerability.
The study was published in the journal Nature Communications.