Tardigrades survive deadly radiation by glowing in the dark

By Michael Marshall

This tardigrade uses fluorescence to resist deadly UV radiation

Harikumar R. Suma & Sandeep M. Eswarappa

A tiny tardigrade can withstand intense ultraviolet radiation for an hour by glowing in the dark. "It acts like a shield," says Sandeep Eswarappa of the Indian Institute of Science in Bangalore.

Tardigrades, also called water bears, are animals about 1 millimeter long. They are known to withstand extreme conditions that would kill most organisms, such as being completely dehydrated.

When Eswarappa and his colleagues were studying moss on their institute's campus, they realized that it may be a new type of tardigrade, although they don't yet have enough information to formally describe it. At the moment they call it Paramacrobiotus BLR, short for Bangalore.


“We found this particular tardigrade in many places, especially places that are well lit with sunlight,” says Eswarappa. The researchers brought some of the animals to their laboratory and began examining them.

Their first experiment was to expose the animals to a germicidal UV lamp. A control animal, a worm named Caenorhabditis elegans, died within 5 minutes, but Paramacrobiotus BLR survived for an hour.

"The next step happened by accident," says Eswarappa. While looking at how the tardigrades could survive the UV light, he left a tube near a UV source and noticed that the tube had started to glow.

Further experimentation revealed that the tardigrade contained a fluorescent chemical. "It absorbs the UV light and emits harmless visible light in the blue range," says Eswarappa.

The team was able to transfer the fluorescent chemical to another tardigrade, Hypsibius exemplaris, and to C. elegans, both of which are sensitive to ultraviolet radiation. This protected them from 15 minutes of UV exposure.

The team does not yet know exactly what the fluorescent shield is made of because simple methods of identifying the chemicals have not produced clear results. "It's not an easy connection," says Eswarappa.

Once the chemical is known, Eswarappa hopes to manufacture it in large quantities and to study whether it can be used in sunscreens. "We want to patent it and see if we can mass-produce it," he says.

Journal reference: Biology Letters, DOI: 10.1098 / rsbl.2020.0391

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