A Unique Enzyme Gives Bermuda Fireworms Their Glow

A new study reveals the secret to the invertebrates’ dazzling mating ritual

Dr. James B. Wood

On the third night after the full moon in summer and fall, at 22 minutes after sunset, tiny marine invertebrates known as Bermuda fireworms light up the Caribbean in a bioluminescent mating ritual. And now, as Brandon Specktor reports for Live Science, researchers have unlocked the secret to the fireworms’ green glow: a special enzyme that has not been seen in any other bioluminescent animals.

The spectacular and precisely timed mating habits of the Bermuda fireworm have been historically well documented. It is believed that Christopher Columbus and his crew caught a glimpse of the amorous creatures on October 11, 1492, as they approached San Salvador island; in his diaries, Columbus mentions “the flame of a small candle alternately raised and lowered” in the dark waters.

In the 1930s, scientists realized that Columbus’ mysterious sighting aligned with the mating behavior of the Bermuda fireworm (Odontosyllis enopla), which lives throughout the Caribbean. Mark Siddall, a curator at the American Museum of Natural History’s Division of Invertebrate Zoology and co-author of a new study published in PLOS One, describes the arresting sight of the critters’ copulation:

“The female worms come up from the bottomnd swim quickly in tight little circles as they glow, which looks like a field of little cerulean stars across the surface of jet black water,” Siddall explains in a statement. “Then the males, homing in on the light of the females, come streaking up from the bottom like comets—they luminesce, too. There’s a little explosion of light as both dump their gametes in the water.”

But just why the fireworms produce light shows wasn’t so clear to modern-day researchers. Some thought the key was luciferase, an enzyme that produces light in several animals, including fireflies and jellyfish. Other scientists posited, however, that photoproteins were driving the fireworms’ glow.

Hoping to bring some clarity to the debate, Siddall and his fellow researchers plucked 12 female fireworms from the waters of Ferry Reach, a channel in northeastern Bermuda, at the moment of their bioluminescence and froze them. The team then analyzed the full set of RNA molecules, or transcriptome (which essentially gives researchers a laundry list of details about genes, like which ones are active in which cells), in three of the 12 fireworms. RNA molecules are involved in encoding the proteins linked to bioluminescence, reports Michelle Starr of Science Alert.

The researchers discovered that the fireworms’ glow can indeed be attributed to the presence of luciferase, but the specific type of luciferase that is present in Bermuda fireworms appears to be wholly unique. The researchers compared it to luciferase genes logged in databases, and were not able to find any matching proteins.

The new study revealed additional genetic secrets to the fireworms’ dazzling mating ritual. Researchers identified certain enzymes that make fireworms’ eyes grow larger so they are more sensitive to bioluminescent glow as well as others that modified the nephridia—an organ that stores and releases gametes—during the breeding period.

These new insights into fireworm RNA don’t reveal how the creatures know to mate at such specific times. But the study’s findings could have important implications for medical research, says Michael Tessler, a biologist at the Natural History Museum’s Sackler Institute for Comparative Genomics.

“It’s particularly exciting to find a new luciferase,” Tessler says in the statement, “because if you can get things to light up under particular circumstances, that can be really useful for tagging molecules for biomedical research.”

Get the latest stories in your inbox every weekday.