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Bright blue helps protect this tardigrade from harmful ultraviolet light

When it explodes with ultraviolet radiation, a newly discovered tardigrade species is protected by a blue glow.

The backward, microscopic animals also known as water bears or moss piglets, are the last survivor of nature. They are resistant to temperatures below –270 ° Celsius and up to 150 ° C and can withstand the vacuum of space, and some are especially resistant to harmful UV radiation (SN: 14/07/17). A new species shields itself from that UV radiation with bright pigments, a new study suggests. It is the first experimental evidence of fluorescent molecules that protect animals from radiation, the researchers reported on Oct. 14 in Biology Letters.

"The tolerance of aliens to stress is extraordinary," says Sandeep Eswarappa, a biochemist at the Indian Institute of Science in Bangalore, India, "but the mechanisms behind its resistance are not known in most (species)."

He and his colleagues investigated these mechanisms in a new tardigrade species of the genus Paramacrobiotus that scientists identified and then grew in the lab after plucking specimens from a mossy wall of campus. Eswarappa found that, like many other tardigrades, these Paramacrobiotus are resistant to ultraviolet radiation. After sitting under a germicidal UV lamp for 15 minutes, long enough to kill most microbes and give a skin lesion to humans, all Paramacrobiotus specimens survived, seemingly baffled by the ordeal.

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The secret of how these water bears persisted eluded Eswarappa and his team until one day researchers accidentally saw a tube of earth tardigrades in a UV transilluminator, used to visualize fluorescence in the lab. To the team's surprise, the tube glowed blue. “It was our mini-eureka moment,” Eswarappa says.

Molecules fluoresce when they absorb higher-energy light and release lower-energy light. Some biologists have suggested that fluorescent pigments could protect against ultraviolet radiation from certain animals, such as comb jellies or corals, although such powers had not been shown in the laboratory (SN: 17/11/17).

tardigrade under normal lightThe researchers suspect that the reddish brown spots of this microscopic Paramacrobiotus tardigrade, which are seen here under normal light, absorb harmful ultraviolet rays and in turn emit harmless blue light.H.R. Sum

The individual Paramacrobiotus varies in the amount of fluorescence, the equipment found, and later fluorescent gradients are more resistant to UV light. After one hour of UV exposure, 60 percent of the highly fluorescent individuals survived more than 30 days, while all less fluorescent specimens died at 20 days.

To further link fluorescence to protection, the researchers soaked the worms and individuals of a tardigrade species that is not resistant to UV light in a bright Paramacrobiotus extract bath. Thus endowed, both animals were more tolerant of UV rays compared to individuals immersed only in water.

Experiments clearly show that pigments are "a mechanism of ultraviolet tolerance in these animals, and that's a good step forward," says Paul Bartels, an invertebrate zoologist and tardigrade expert at Warren Wilson College in Asheville, NC. participated in the study. "It's a very cool study."

Eswarappa was surprised to find that the brightness of tardigrades played a role in UV protection, as "the finding of fluorescence was serendipitous." It suggests that fluorescent pigments absorb UV rays, emitting harmless blue light, although the study cannot say exactly how the pigments confer protection. Brightness itself, for example, may simply be an auxiliary effect of pigments and not be involved in UV protection. Eswarrapa speculates that bright pigments can help these water bears survive in southern India, where UV levels can be extreme.

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