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Chemists find source of shark fluorescence

Brominated metabolites make sharks glow and have antibiotic properties

by Laura Howes
August 11, 2019 | A version of this story appeared in Volume 97, Issue 32


A photo of a shark with green patterns on its skin.
Credit: David Gruber
The skin of the chain cat shark has green fluorescent markings that can be seen by other chain cat sharks.
The structure of fluorescence molecule 8-bromo-kynurenine yellow.

When a fluorescent eel photobombed David Gruber’s film of fluorescent corals, the Baruch College marine biologist realized that undersea fluorescence might be more common than he thought. The more he looked, the more examples he found, including swell sharks and chain catsharks. He asked Yale University chemist Jason Crawford—a fellow lover of the mysteries of the deep—to help work out how these sharks glow. The team compared fluorescent and nonfluorescent skin from both shark species to find the source of the fluorescence: brominated tryptophan-kynurenine metabolites including 8-bromo-kynurenine yellow. These small molecules are produced through a pathway that also makes antibiotic compounds (iScience 2019, DOI:10.1016/j.isci.2019.07.019). “We didn’t actually know what kind of molecules to detect up front,” Crawford says. “But as a small-molecule-metabolism lab, we were delighted that they were small molecules.” Siouxsie Wiles of the University of Auckland says new fluorescent molecules are always fascinating, but these new compounds are particularly interesting to her because of their antimicrobial properties. “Wouldn’t it be really neat,” she asks, “if new antibiotics were developed based on studying why sharks glow?”


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