Another amazing tardigrade survival skill is discovered.
- Apparently, some water bears can even beat extreme UV light.
- It may be an adaptation to the summer heat in India.
- Special under-skin pigments neutralize harmful rays.
Many of us consider ourselves tardigrade, or "water bear" fans. These microscopic buggers — actually not bugs at all but their own distinct phylum with over 1,000 members — are unbelievably hardy in spite of their diminutive stature: They range from just 0.5 to 1 millimeter in length.
Tardigrades survive in all sorts of conditions that should really spell their doom. They're basically found everywhere on Earth, and last spring an Israeli lunar lander may have inadvertently dumped a bunch of them on the moon where they may well be happily going about their water bear business.
Almost nothing kills them, except for super-extreme blasts of ultraviolet (UV) light that would be deadly to most organisms. Or so it seemed, until researchers came across some reddish-brown eutardigrades living in moss on a wall in Bengaluru, India. These, it turns out, don't care that much about even staggering amounts of germicide-level UV. The scientists concluded that what they were dealing with was an undocumented member of the Paramacrobiotus genus.
Score one more for our wee heroes.
The research is published in the Royal Society Biological Letters.
3D illustration of a tardigrade
Credit: Dotted Yeti/Shutterstock
It seems at times like scientists enjoy playing the "let's see if this kills them" game with tardigrades, a game that humans usually lose. After searching the campus of the Indian Institute of Science, researchers gathered some water bears and brought them back to the lab to see what they could handle.
The scientists found that after they exposed Hypsibius exemplaris tardigrades to very high doses — 1 kilojoule (kJ) per square meter — of UV light for about 15 minutes, they would in fact die over the next 24 hours. However, when they aimed the same blasts at the reddish-brown tardigrades…nothing. The humans even quadrupled the UV intensity and, nope, they tracked the water bears for 30 days, and a majority of them, 60 percent, were still fine.
As is often the case with tardigrades, the question is how?
Turning deadly light blue
Tardigrade's normal appearance (left), and under inverted fluorescence (right)
Credit: Suma et al., Biology Letters (2020)
When the researchers examined the tardigrades under an inverted fluorescence microscope they found that when they were exposed to UV light, they became blue. The researchers' hypothesis is that these tardigrades carry fluorescent pigments beneath their skin that they deploy as necessary to transform UV light into simple benign, blue light. It may be that this ability has emerged as an evolutionary response to southern tropical India's often-extreme heat. The study says that typical summer-day UV levels in this region are about 4kJ per square meter.
Of the 40 percent of the reddish-brown tardigrades that had died before 30 days — mostly after about 20 days — the scientists concluded they had less pigment with which to neutralize UV light.
When the scientists extracted the pigment from the UV champions and coated some Hypsibius exemplaris tardigrades with the stuff, their resistance to UV exposure was also enhanced, boosting their survival rate to almost twice that of their uncoated brethren.
Autofluorescence has been found in other animals — parrots, scorpions, chameleons, and frogs, among others — so it's not completely unheard of. In parrots, for example, autofluorescence is hypothesized to be involved in tweaking coloration during mating rituals. Still, surprise, tardigrades seem to be putting it to unusual use by employing it for UV protection.
Freeze it, boil it, or expose it to radiation. The water bear shrugs it off. Now we know why.
The tardigrade, also known as the moss piglet or water bear, is a bizarre, microscopic creature that looks like something out of a Disney nightmare scene: strange but not particularly threatening. The pudgy, eight-legged, water-borne creature appears to be perpetually puckering. It's the farthest thing from what you'd expect an unstoppable organism to look like.
Yet, water bears can withstand even the vacuum of space, as one experiment showed. A sort of microscopic Rasputin, tardigrades have be frozen, boiled, exposed to extreme doses of radiation, and remarkably still survive. How they do this has been a mystery to science, until now.
Being a water-borne creature, scientists in this experiment examined how it survived desiccation, or being completely dried out. When it senses an oncoming dry period, the critter brings its head and limbs into its exoskeleton, making itself into a tiny ball. It'll stay that way, unmoving, until it's reintroduced into water.
It's this amazing ability that piqued Thomas Boothby's interest. He's a researcher at the University of North Carolina, Chapel Hill. Boothby told The New York Times, “They can remain like that in a dry state for years, even decades, and when you put them back in water, they revive within hours." After that, “They are running around again, they are eating, they are reproducing like nothing happened."
Originally, it was thought that the water bear employed a sugar called trehalose to shield its cells from damage. Brine shrimp (sea monkeys) and nematode worms use this sugar to protect against desiccation, through a process called anhydrobiosis. Those organisms produce enough of the sugar to make it 20% of their body weight.
Not the water bear. Trehalose only takes up about 2% of its entire system, when it's in stasis. Though employing a sugar to preserve one's body sounds strange, the newly discovered process that the water bear goes through is even more bizarre. It turns itself into glass.
In this study, tardigrades were placed into a drying-out chamber, which mimicked conditions the organisms would encounter in a disappearing pond. As the water bears underwent anhydrobiosis, scientists examined what genes were activated. These genes produced a certain protein, which they named tardigrade-specific intrinsically disordered proteins (TDPs).
When the genes which produce TDPs were blocked, the water bears died. “If you take those genes and put them into organisms like bacteria and yeast, which normally do not have these proteins, they actually become much more desiccation-tolerant," Boothby said.
Water bear under a microscope. Flickr.
It's when the drying out process begins that such genes are activated, flooding the water bear's system with the protective protein. The process occurs in much the same way as trehalose preserves sea monkeys, according to Boothby. This is an example of convergent evolution, when two unrelated organisms develop the same trait for survival.
Usually, proteins are formed in orderly, 3D chains of amino acids. But TDPs operate differently, in a kind of random, somewhat disorganized manner. Dr. Boothby said, “It's a really interesting question about how a protein without a defined three-dimensional structure can actually carry out its function in a cell." Another question, is this protein used by any other organisms?
When desiccation begins and TDP is activated, it engages a process known as vitrification. Boothby said, “The glass is coating the molecules inside of the tardigrade cells, keeping them intact." From there, it goes into a form of stasis until it detects water. When that occurs, the protein is dissolved into the liquid and the tardigrade is revived.
There could be some practical uses to this discovery. For instance in medicine, vaccines often require refrigeration. But in the developing world, it isn't always available, which makes delivering vaccines to vulnerable, rural communities difficult.
Dr. Boothby believes that we may be able to use TDP to sort of freeze-dry vaccines or medications, for easy storage and transport. What about putting humans in stasis for space travel or when they have terminal diseases, to await a cure? No word on that, yet. Scientists have years of research ahead of them already, just to understand the inner-workings of TDP.
Some believe tardigrades may have “alien" DNA. To find out more, click here: