Tardigrades are microscopic animals that look like a cross between a caterpillar and a naked mole rat. These aquatic invertebrates are almost impossible to kill. They can withstand the most extreme conditions such as the vacuum of outer space, 30 years in a freezer, boiling temperatures, pressures six times greater than the deepest ocean, several years of dehydration, and radiation lethal to pretty much every other living species on this earth.
One newly discovered species, eutardigrade belonging to the genus Paramacrobiotus, protects itself from ultraviolet (UV) radiation with naturally occurring fluorescent pigments. In a recent study, published on October 14 in Biology Letters, these pigments were glowing blue under a fluorescence micrograph. This is the first-ever experimental evidence of fluorescent molecules protecting species from UV radiation.
Sandeep Eswarappa, one of the study’s authors, said:
Tardigrades’ tolerance for stress is extraordinary, but the mechanisms behind their resistance is not known in most species.
Eswarappa and his team investigated these mechanisms in Paramacrobiotus specimen that the scientists identified and then raised in the laboratory after plucking samples from a mossy wall. They found that similar to other tardigrades; these Paramacrobiotus are resistant to UV radiation.
The team placed the specimen under a germicidal UV lamp for 15 minutes, which is enough time to kill most microbes; all Paramacrobiotus sp. survived, seemingly unharmed or bothered by the ordeal. The answer to how these water bears survived eluded Eswarappa and his team until they noticed a tube of the tardigrades in a UV transilluminator, used to visualize fluorescence. The tube was glowing blue, “it was our mini-eureka moment,” Eswarappa recalled.
The team found that individual Paramacrobiotus varied in how much they glowed, and more fluorescent tardigrades were more UV-resistant. After one hour of UV exposure, all less-fluorescent specimens died within 20 days, while 60% of strongly fluorescent individuals survived over 30 days.
The scientists conducted another set of tests to link fluorescence with protection even further, which involved soaking roundworms and non-UV-resistant tardigrade species in a bath of glowing Paramacrobiotus extract. Remarkably, both animals were more UV-resistant compared with individuals soaked in only water.
The results plainly show that the pigments are “a mechanism for UV tolerance in these animals, and that’s a nice step forward,” says tardigrade expert Paul Bartels, who wasn’t involved in the study.
Eswarappa suggests that the fluorescent pigments absorb UV rays while emitting harmless blue light. The team doesn’t know precisely how the pigments offer protection. For example, the glow may be an ancillary effect of the pigments and have nothing to do with UV shielding. However, Eswarappa suspects that the glowing pigments may help these tardigrades survive in regions where UV levels are extreme, such as southern India, in the summertime.
Another species of tardigrade, Ramazzottius variornatus, which is thought to be among the toughest tardigrade species, was investigated by a research team at the University of Tokyo in 2016. They found that the tardigrade’s resilience can be transferred to human cells’ cultures, which could help make it possible for humans to travel even deeper into space.
These findings also may one day protect workers from radiation in nuclear facilities and open up the possibility of improving human cells’ stress resistance, which could benefit people undergoing radiation therapies.
