Shortly after the sun dips below the horizon, puffs of sparkling green light glow beneath the ocean’s surface. This alluring spectacle, which occurs two days before the quarter moon and lasts from 20 to 30 minutes, has long mesmerized voyaging sailors. What they may not know, however, is that the source of this radiance is a tiny worm, shorter in length than a single fingernail.
Odontosyllis phosphorea, the luminescent fireworm, lives on the seafloor of tropical and temperate oceans and is known for its mating swarms: Female worms swim to the surface and secrete a bioluminescent mucus that attracts males for spawning.
This mucus emits the green light, which has been observed by kayakers and seafarers in waters as nearby as Mission Bay. Dr. Dimitri Deheyn and Dr. Michael Latz, marine biologists at’ Scripps Institution of Oceanography, are working to uncover the different purposes of the worm’s bioluminescence, as well as the protein responsible for the light itself.
‘Hundreds of years ago, locals would say that this was the ‘spirit of the ocean,” Deheyn said. ‘It has been reported many times, but few studies have been done regarding the biology of the light.’
Through their research, the scient
ists have already discovered that juvenile worms are able to produce the light as an internal flash, rather than the secretion of mucus. Because sexually immature worms are able to achieve bioluminescence, the scientists propose that this internal light cannot be for the sole purpose of mating.
‘We hypothesize that the bioluminescence could therefore have two purposes,’ Deheyn said. ‘One is as a means of defense in the small worms, and the other as a visual signal for mating in the adults.’
In order to identify the protein responsible for the light, the team must isolate the protein in the mucus generated by the worms.
Fifty to 60 years ago, scientists would collect the worms by finding the mating swarms and using a dip net, Latz said. They would then take the bodies of the worms, grind them and then extract the chemicals responsible for the glow.
Deheyn and Latz take a different approach. They gather worms from their tubular seafloor homes instead. When the worms swarm near the surface, they easily deplete their mucus; collecting them from their resting place ensures that the worms’ ability to glow hasn’t been diminished.
In the lab, worms are exposed to potassium chloride, which artificially triggers secretion.
In general, a chemical reaction resulting in bioluminescence requires oxygen; based on previous studies, if oxygen is removed, no light should be produced. However, by testing solely the mucus, Deheyn and Latz were able to trigger a glow without adding oxygen, which led them to speculate that the protein responsible for the light is a photoprotein ‘mdash; a protein that contains oxygen within it.
‘When they studied the worm 50 years ago, the lack of oxygen would have reduced the bioluminescence,’ Latz said. ‘They used the full worm, indicating that they might have analyzed the internal flash instead of the mucus itself.’
The scientists said that isolating the particular protein responsible will be a very difficult process. They will need to determine the amino-acid structure of the protein through column chromatography and gel electrophoresis, a standard method for separating proteins based on their size and charge.
Latz said that a successful identification of the protein could prove extremely useful to biomedicine.
‘We hope to have it as a new tool for bioengineering and biomedical applications,’ Latz said. ‘It is important because light is a really easy signal to measure. It could be used to indicate changes in gene expression, ATP ‘mdash; a common energy source used by cells ‘mdash; and protein. In general, there is tremendous interest in identifying and characterizing new bioluminescent chemicals, which is the reason why we are doing the project itself.’
Today, the protein responsible for the bioluminescence in jellyfish is a valuable tool used in biomedical research.
According to Deheyn, over 30,000 scientific papers have been published to date regarding this protein, discovered by Noble Prize laureate Dr. Osamu Shimomura. The protein that Deheyn and Latz are trying to identify could possibly complement other existing fluorescent proteins.
Joy Leilei Shih, who recently finished her master’s degree in marine biodiversity and conservation at UCSD, has been a research assistant in Deheyn’s lab for one year. She studies a different species, known as chaetopterus, or parchment worm.
Like the fireworm, this worm releases bioluminescent mucus and can glow internally. However, it does not swim to the surface of the water for spawning, as does the fireworm. Instead, its light is thought to deter predators and repel other animals looking for a dark place to hide.
Shih said identifying the protein responsible for bioluminescence in the fireworm’s mucus could be significant in future medical research, and would build off previous studies.
‘In the long run, if we are able to identify, isolate and get a good understanding of this protein, it would be very helpful in the medical field, such as with things like cancer research,’ Shih said. ‘The other thing that’s exciting is that previously it was thought that what makes it glow was an enzyme-substrate reaction. But based on their experiments, we think that it is a photoprotein that creates the glow. It’s like thinking that the world is flat and then figuring out that it’s round.’
Laura Enzor, who just received her master’s degree from the University of West Florida, also studies the parchment worm in Deheyn’s lab.
‘I think that the research is significant simply because it’s interesting to find out how animals work and why they do what they do,’ Enzor said. ‘This is a really interesting adaptation, and we should look at why they do it, how they do it and what helps them do it ‘mdash; namely the protein. Just learning about these animals is reward enough; you don’t necessarily have to be looking for a cure to something.’
Currently, Deheyn and Latz are still working to identify and isolate the protein in question.
‘The enzyme in the protein is not found anywhere else in the living kingdom,’ Latz said. ‘That is what’s special and also what makes it difficult to isolate. There is no framework for what it could be.’
Readers can contact Danielle Crawford at [email protected].