In the world of bioluminescence, it’s common for organisms to get luciferin—the small molecule needed to make light—from their diet. Scientists have hypothesized that bioluminescent fish make their own luciferase, the enzyme that catalyzes the reaction that causes luciferin to glow. But in a study published this week (January 8) in Science Advances, researchers showed that a species of coastal fish generates light using both luciferin and luciferase captured from its bioluminescent prey, a small crustacean known as an ostracod.
This work “challenges our view of how we perceive fish bioluminescence,” says David Gruber, a marine biologist at City University of New York who was not involved in the study. “In the past, we thought either the fish made both of the components of bioluminescence themselves or just one of the components, but this is an example of them making neither of them and getting them both from their diet. I always love it when a paper comes out that shows us an angle that we hadn’t known before.”
As a graduate student at Nagoya University in Japan, Manabu Bessho-Uehara had set out to study the evolution of bioluminescence. He says that there are more than 200 genera of fish that glow, and a 2016 study indicated that bioluminescence has arisen independently at least 27 times in marine fishes. “What’s funny is nobody identified luciferase genes from any of the fish, so that’s where I wanted to start,” Bessho-Uehara, who is now a postdoc at the Monterey Bay Aquarium Research Institute in California, tells The Scientist.
Previous work had shown that fish in the genus Parapriacanthus, shallow-water fish found off the coast of the west Pacific and Indian Oceans, sequester luciferin from their prey in their light organs, but it was believed that they were making their own luciferase enzyme. So when Bessho-Uehara and his colleagues in Japan looked for a luciferase gene in the Parapriacanthus ransonneti genome, they expected to find a fish gene encoding a fish protein. Instead, they discovered that the luciferase protein in the light organs that run along the underside of the fish was identical to the enzyme produced by the ostracods these fish eat.
The researchers found no gene encoding luciferase in the fish genome, indicating that the animals instead sequester the protein from their diet. To test this hypothesis, the research team fed the fish non-glowing food for up to a year, resulting in a loss of their luminescence. Then they fed the fish a different species of glowing ostracods. After a few weeks on the new diet, the fish were again capable of glowing. The researchers also found peptides that matched the newly introduced ostracods’ luciferase in their light organs.
“When I first heard about it I was kind of skeptical, but they make a very convincing story that this [fish] really is using the luciferase stolen from their prey,” says Edith Widder, the founder of the Ocean Research & Conservation Association who did not participate in the study. She explains that it’s surprising that the luciferase enzyme, which is a fairly large, complex molecule, can be taken up by the digestive system and not degraded to the point where it’s no longer functional, an observation that the authors highlight as well.
“That’s why I was initially so skeptical when I heard about this because I couldn’t quite imagine how that was possible,” she says. “They’ve convinced me that that’s what’s going on here and so it opens up a lot of other questions about how this is actually happening. It’s just a phenomenal evolutionary innovation.”
In the future, Bessho-Uehara and his colleagues will continue the search for fish luciferase genes. They also plan to investigate how the protein gets into the fish’s cells and whether or not other bioluminescent fish use a similar strategy.
“Because this has evolved independently so many times, the mechanisms by which this is working can be quite different from one lineage to another lineage,” says Matt Davis, a biologist at St. Cloud State University in Minnesota who did not participate in the work. “It just goes to show that even though we know a lot about which lineages are producing and emitting the light, we still have a lot to learn about how this actually works.”
M. Bessho-Uehara et al., “Kleptoprotein bioluminescence: Parapriacanthus fish obtain luciferase from ostracod prey,” Science Advances, doi:10.1126/sciadv.aax4942, 2020.
Abby Olena is a freelance journalist based in Alabama. Find her on Twitter @abbyolena.