Tardigrades, small aquatic creatures known as water bears, can survive extreme heat, radiation, and even the vacuum of space – conditions that would kill most animals. Now, scientists have discovered a new species of tardigrade that can withstand ultraviolet (UV) light so lethal that it can be used regularly to get rid of hard-to-kill viruses and bacteria.
The discovery was made by accident: researchers from the Indian Institute of Science scoured their campus for aquatic bears and then exposed them to extreme conditions. They happened to have a germicidal UV lamp in the lab, so they hit their samples with it. The dose of 1 kilojoule per square meter, which killed bacteria and nematodes after only 5 minutes, was lethal to Hypsibius examples tardigrade to 15 minutes; most died after 24 hours. But when they hit a strange reddish-brown species with the same dose, they all survived. Additionally, when the researchers increased the dose four times, about 60 percent of reddish brown bears lived for more than 30 days.
The researchers realized they had found a new species of tardigrade, part of the Paramacrobiotus kind. To understand how the new species, which was found in moss on a concrete wall in Bengaluru, India, survived, scientists examined it with an inverted fluorescence microscope. To their surprise, under the UV light, the reddish tardigrades turned blue (above). The fluorescent pigments, likely located under the skin of the tardigrades, turned the UV light into harmless blue light, the team reports today in Biology letters. In contrast, Paramacrobiotus with less pigment it died about 20 days after exposure.
Next, the researchers extracted the fluorescent pigments and used them to coat H. examples and many Caenorhabditis elegans earthworms. Animals with jury-rigged shields survived almost twice as fast as animals without shields. It is likely, the scientists say, that tardigrades developed fluorescence as a means of tolerating the high doses of UV typical of hot summer days in South India.