(Photo : Wikimedia Commons/Schokraie E, Warnken U, Hotz-Wagenblatt A, Grohme MA, Hengherr S, et al.)
Tardigrades are deemed indestructible after they survive blasts of radiation. Apparently, they can take anything thrown at them and this is due to their DNA.
Tardigrades' DNA Have Repair Genes
A new study uncovered one of the reasons behind tardigrades' ability to survive anything thrown at them. It turned out that these microscopic animals can enable their bodies to repair themselves.
Biologist Courtney Clark Hachtel of the University of North Carolina at Ashton led a team and blasted tardigrades with gamma rays. They observed how tardigrades responded.
"What we saw surprised us," said biologist Bob Goldstein of The University of North Carolina at Chapel Hill. "The tardigrades are doing something we hadn't expected."
For many years, tardigrades' amazing ability to withstand ionizing radiation has been known. They carry on with their meager existence as if nothing had happened, surviving a dose that would be fatal to humans by a factor of 1,000.
For certain tardigrade species, this is assumed to be due in part to the damage suppression protein Dsup. However, not all tardigrade species possess Dsup or a homolog thereof, indicating that alternative ways of survival may be involved.
In order to ascertain the cause, the scientists examined the impact of gamma radiation on the tardigrade species known as Hypsibius exemplaris. They exposed tardigrades to gamma rays produced by the beta decay of cesium-137 by placing the animals in a tabletop irradiator.
They exposed the tardigrades to two distinct doses -- one lower dosage that is within acceptable bounds and another considerably larger median lethal dose --because the amount of radiation is known.
Surprisingly for them, even though H. exemplaris does have Dsup; the radiation exposure didn't trigger it. As a result, the tardigrades' DNA suffered significant radiation damage.
Instead of providing preventive defense, the tardigrades increased the synthesis of DNA repair genes to the point that their byproducts are among the most prevalent in their tiny bodies. The majority of the ionizing radiation-damaged DNA in the tardigrades had been repaired by the time they were 24 hours post-exposure.
In a subsequent experiment, the scientists subjected samples of the bacteria to ionizing radiation and expressed a portion of the tardigrade repair genes in an Escherichia coli culture. DNA repair capacity exhibited by bacteria injected with tardigrade genes was comparable to that observed in H. exemplaris, while untreated E. coli does not exhibit it.
The researchers discovered that this implies that H. Exemplaris is able to withstand amounts of ionizing radiation that would destroy other creatures because it can detect the radiation and mount a defense.
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Why Tardigrades Are Resilient?
Tardigrades possess a long, fat torso and eight stumpy legs. They're often called "water bears," but they actually resemble pigs or bears. Their closest relatives are insects and crustaceans.
According to the Rutland Herald, tardigrades undergo a condition called cryptobiosis that enables them to endure such hostile conditions. They have to draw in all eight legs and almost dry out.
Think of it like freezing fruit to maintain its freshness. When faced with extreme conditions, such as cold temperatures or a shortage of water, tardigrades enter this state.
In these settings, water bears can survive for up to 30 years. When the tardigrade's environment is replenished with water or the pressure reaches a point where survival is possible, their cells regenerate and start operating normally once more.
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