Glowing Sharks: A Team of Graduate Center Scientists Shines Light on a Deep-Ocean Mystery

Gruber shark
Five years ago, while deep diving off the coast of California, Professor David F. Gruber (GC/Baruch, Biology/Natural Sciences) identified a new species of fluorescent sharks. The discovery launched an investigation into how sharks — specifically catsharks and swell sharks that appear brown and gray to the human eye — are able to take in the ocean’s blue light and transform it into green light that illuminates their deep-sea environment.
Gruber recently published the answer in a study that has received widespread coverage from The New York Times, PBS, and The Guardian, among many other media outlets. Unlike other biofluorescent sea creatures Gruber has studied, the sharks’ glow — visible to each other, and to humans who use a light filter — derives from a molecule that is present in their skin, which sets off a series of chemical reactions that converts blue light to green.
These findings are yet another clue in what Gruber calls the “evolving mystery story” of the ocean, and could lead to advances in medical imaging. Understanding how jellyfish and corals use green fluorescent protein to illuminate their surroundings revolutionized experimental biology, Gruber notes. Scientists use the protein to see inside cells and observe genes interacting in real-time.
Together, these discoveries have also radically altered our understanding of what the bottom of the ocean looks like, from the point of view of marine life itself — rather than completely dark, this world contains a vibrant array of blues and greens. “We’re finding an increasing diversity of fluorescent organisms in the blue ocean,” says Gruber, who was also the first to discover fluorescent eels, sea turtles, scorpion fish, seahorses, and stingrays.

Professor David F. Gruber filming fluorescent sharks

Reaching that point required an interdisciplinary approach that included Professor Jean Gaffney (GC/Baruch; Biology, Chemistry/Natural Sciences), whom Gruber describes as a tenacious chemical detective. Gaffney, who’d previously purified fluorescent eel proteins for Gruber’s lab, was able to determine that sharks were using a small molecule, rather than a protein, to create light.
“We initially had trouble solubilizing the shark fluorescent material,” Gaffney says. “Once we found harsher conditions were all that worked, it clued me into the fact it might not be a protein. These basic discovery science projects are amazing to be a part of, because we get to find the unknown.” 
Gruber also brought in Jason Crawford of Yale University, whose lab specializes in these types of small molecules, to identify the specific chemical reactions. Sara Rose Krivoshik (Biology), a third-year Ph.D. student in the Molecular, Cellular, and Developmental Biology subprogram, did further work on the molecules to confirm that the compounds were responsible for the sharks’ fluorescence.
The paper is Krivoshik’s first major publication. “As a graduate student, the process of submitting a paper for publication is still new to me,” she says. “It has been very rewarding to observe the process and see the end result, and it’s exciting to be part of such an interesting and novel study at this point of my career.”
Gruber is now moving into whale research and has recently published the first paper that applies advanced machine learning techniques to sperm whale bioacoustics. “This is all part of the general theme of our laboratory to apply the best available and most current technology to better understand marine organisms from their perspective,” he says.

Submitted on: SEP 10, 2019

Category: Biology | Faculty | General GC News