Dinoflagellates called Noctiluca scintillans glow on the shores of Hong Kong. Credit: Kim Cheung / AP

By Grace Finnell-Gudwien


It was a dimly moonlit night in January 2020 when University of Illinois freshman Lauren Bartels and her sister boarded a tandem kayak in Laguna Grande, Puerto Rico, for a tour. Paddling through a canal, they saw ahead something quite extraordinary — a light show in the water. Bioluminescent dinoflagellates — tiny, microscopic plankton that can produce their own light through a chemical reaction — were the performers. Bioluminescence, it turns out, is a ubiquitous natural phenomenon, both on land and sea, and has myriad potential applications in the laboratory for the sciences of human health and sustainability.

As Bartels glided across the bioluminescent bay, every stroke of her paddle disturbed the dinoflagellates, causing them to light up. Reaching her hand into the water had the same effect. The tour guides made them shine even brighter by throwing a tarp over the paddlers to create an area of complete darkness. Inside this void, kayakers could “splash around” and really experience bioluminescence; she described it as a “pulse” or a “firework that would stay around a second longer than usual.”

Clear bottom kayaks allowed tourists to see the dinoflagellates right under their noses. As Bartels described it, this “really cool” boat allowed you to feel that you were among the dinoflagellates. While the dinoflagellates need to be disturbed to glow, she explained that paddling pushed just enough water under the kayak for them to sparkle. They looked like “little specks of dirt,” she joked, “but not dirt because it was light.”

Many, many years earlier, in 1832, Charles Darwin experienced a similar phenomenon aboard the HMS Beagle. Darwin described his observations in his journal, mentioning a “luminous” sea and the water “giving out sparks” when collected in a bottle near the Canary Islands.

Although both Bartels and Darwin were struck with wonder in the face of living light, bioluminescence is actually quite common in the ocean, especially in deep waters. The National Oceanic and Atmospheric Administration’s (NOAA) Ocean Exploration and Research website states that 80 percent of the animals that live between 200 and 1,000 meters (or about one-eighth to three-quarters of a mile) deep in the ocean can produce light. Terrestrial organisms that can generate “living light” include fireflies and some species of fungi. While not all dinoflagellates bioluminesce, the Latz Laboratory at the University of California San Diego states that dinoflagellates are one of “the most common sources of bioluminescence at the surface of the ocean.”

Glowing waters like those Bartels and Darwin witnessed are signs of populations that have overproduced, so that a massive amount of the microbes all live in the same water. Under these circumstances, according to the Latz Lab, they become a “red tide.” Named for the rusty red shade that the organisms color the water during the day, these collections of “blooms” arise from extra nutrients in the ocean; according to Philip Weinstein of the University of South Australia, these spots of high nutrients can form naturally due to upwelling, the overturning of the ocean water that brings nutrients deeper in the water column up to the top. Paradoxically, some red tides sparkle a bright blue at night.

A red tide bloom of Noctiluca scintillans in New Zealand. Credit: M. Godfrey

“Red tide” is a familiar danger to coastal dwellers, for the color often signifies HABs, or harmful algae blooms, that release toxins affecting both marine life and the humans who eat seafood. Although algae blooms can be naturally produced, they are also often an effect of agricultural runoff, especially fertilizers that leach into the ocean. Yet dinoflagellates are critical to supporting a healthy ocean. When dinoflagellates are harmed, “dark events” occur, where the microbes do not produce light. Protectores de Cuencas, an organization dedicated to protecting Puerto Rico’s ecosystems, explains that coastal erosion and water pollution are hurting dinoflagellates at the well-known tourist destination Puerto Mosquito and other bioluminescent bays. Kelly Thompson of the Vieques Insider described a months-long dark event at the tourist bay Puerto Mosquito that started in January 2014. She explained that this lack of light occurred because the concentration of nutrients and materials in the water was harmful to the dinoflagellates. This imbalance in the water stems from coastal erosion depositing sediment and pollution from agricultural runoff, or pesticides used on farm fields. The water may be further polluted if humans swim during their visits and their sunscreen, insect repellent, and other cosmetics wash off in the bays. While Lauren’s tour group did allow visitors to place their hands in the water, they were not allowed to swim in the bays.

The “wonder” of bioluminescent organisms is chemically produced, though scientists continue to work on understanding how. At the most general level, the mechanism of bioluminescence is similar for all living things. J. Woodland Hastings, in the Cell and Physiology Source Book, explains that bioluminescence is a specific form of chemiluminescence, which is when light is produced by a chemical reaction. Thus, fireflies, fungi, dinoflagellates, and even the anglerfish in Finding Nemo contain chemicals used to glow. For a bioluminescent reaction to occur, a substrate generically called luciferin must be present and react. This chemical substrate is specifically named by the type of organisms, such as “bacterial luciferin” or “firefly luciferin.” A second chemical involved is the enzyme luciferase, which is also a generic name. Enzymes connect into substrates like jigsaw puzzle pieces and regulate the speed of a chemical reaction, and luciferase is this puzzle piece in bioluminescent reactions.

At the same time, though, the process has evolved independently in specific organisms through evolution; some organisms are understood better than others. Illinois Natural History Survey Principal Mycologist Andrew Miller explained, for example, that currently fireflies’ chemicals are better understood than those in fungi. Scientists “(don’t) really know for sure in fungi” how the chemical reaction works. Nor are they entirely sure why different organisms have evolved to glow.

Hastings posits that dinoflagellates sparkle to scare away predators, but fireflies shine to attract mates. A writer for National Geographic speculates that a form of bioluminescence, counterillumination, helps some organisms hide from sharks. Since sharks hunt from deeper in the ocean and look up toward the surface for prey, some bioluminescent fish, such as the hatchet fish, hide in plain sight. These fish will swim near the top of the surface where sharks are looking, but they have the ability to control how much light they emit from their undersides. By emitting the same amount of light that penetrates into the ocean from the sun, they fool the sharks, who cannot determine that a hatchet fish swims above them; they will just see a continuous sea of light overhead.

Beyond helping themselves, bioluminescent creatures offer humans many uses. Some of these applications of living light are simply utilitarian, such as putting fireflies in a jar for light; you may have even done this yourself as a child. In an article for Health & Safety International, Andrew Watson tells of how miners sometimes collected fireflies to light their mines before the invention of the oil lamp. More peculiarly, miners were also known to use dried fish skin to produce light. This skin was “crawling with bioluminescent bacteria,” explained Ferris Jabr in Hakai Magazine.

Foxfire bioluminescence from Panelluses stipticus in Mt. Vernon, Wisconsin (long exposure). Credit: Wikipedia Commons

Jabr also describes how in 17th century Indonesia, Indigenous Peoples used glowing fungi as “flashlights in the forest” to light their paths. While some of these fungi can be seen in central Illinois, such as the Jack-O-Lantern and honey mushrooms, Miller explains that because fungi in the tropics glow much brighter, we should not expect to be guided by the light of fungi in Illinois. Often, he elaborates, fungi in the woods are “fungal mycelium,” or more colloquially “fungal roots,” that live inside of rotting wood called “foxfire.” Interestingly, Miller says that when these mushrooms are outside of the wood and producing spores, they do not bioluminesce. Since the hypothesized reason that fungi glow is to “attract insects to transport spores” for reproduction, it is uncertain why these foxfire fungi glow at all.

The light from bioluminescent dinoflagellates has also been used in naval warfare. In 1918, during World War I, the British found and sank a German U-boat by detecting the glow of the water churned up by the nearby submarine. Research about locating submarines and other underwater weapons and vessels became prevalent during World War II and the Cold War, and similar studies have been done until recently by the United States Navy.

Fighter pilot and Apollo 13 astronaut-to-be James Lovell is thankful for bioluminescence. Jabr tells Lovell’s story, explaining how one night in 1954 Lovell’s fighter jet short-circuited during training, leaving the pilot without light or the ability to use the jet’s technological maps to land. Lovell then noticed a mysterious green glow in the dark ocean below, and realizing that it was bioluminescence caused by the wake of the aircraft carrier he needed to find, he used the glow to safely land.

A firefly’s light is used to attract prey and members of the opposite sex and to warn off predators. Scientists have also found research uses for the chemicals that cause firefly bioluminescence. Credit: tomosang / Getty Images

Other uses of bioluminescence are more scientific. Sara Lewis, author of Silent Sparks: The Wonderous World of Fireflies, explains that the firefly luciferase and luciferin can be used to detect when food is contaminated with bacteria. The chemicals cause ATP, an energy molecule found in every living cell, to glow. Since food poisoning-inducing bacteria like salmonella and E. coli are living organisms, their cells possess ATP. Thus, when luciferase and luciferin are added to food with “bad” bacteria, these chemicals can cause the bacteria to glow, literally bringing light to a potentially dangerous situation. This knowledge has been around since the 1960s, but more recently scientists have turned to synthetic luciferase and luciferin. These man-made chemicals work significantly faster than the ones from fireflies (minutes instead of days), but the idea to create chemicals to detect bacteria in dairy, meat, soda, and other consumables was certainly influenced from nature’s own living light.

Perhaps the most unexpected use of bioluminescence is its ability to aid in tagging and tracking genes. In 1962, Osamu Shimomura discovered a green glowing protein in the bioluminescent jellyfish Aequorea victoria; the Green Fluorescent Protein (GFP) was used in study genetic processes in ways that garnered Shimomura, Martin Chalfie, and Roger Y. Tsien the 2008 Nobel Prize in Chemistry. In his study about GFP tagging, Peter J. Clyne describes some of the glowing protein’s abilities in more detail; GFP is a fusion protein, a kind of macromolecule that can determine the specific location of a gene on a strand of DNA. It can even specify between different variants of the same gene.

Natalie Kofler, former visiting scholar at Illinois and now an advisor and curriculum lead at Harvard Medical School, has plenty of experience with the GFP. Trained in molecular biology, Kofler explained that GFP is “a really, really common tool” that she and her lab researchers used “in tons of different contexts.” One of these contexts is at the cellular (or even subcellular) level. “You can use GFP on different sorts of proteins to be able to see different compartments of cells or just use it more generally just to watch the movement or functions of cells,” Kofler said. This is done by linking the GFP into the DNA of another cell or organism, a process called transgenics. For example, to see the entire surface of a cell, scientists can link GFP to a protein on the cell membrane and literally make the cell’s border glow. Other options include linking GFP to a protein in the nucleus, cytoplasm, or any other organelle in order to see those specific cell parts.

While she is not actively performing lab work, in the past Kofler has used GFP to observe cell migration. By forcing the cells to glow, she could “really clearly” see how they spread throughout a culture as well as “take interesting pictures” under a microscope. The fluorescence makes simply counting cells from under the microscope easier, too.

At a larger level, GFP can be used in mouse models to see how neurons move throughout a mouse’s brain. Kofler detailed how if a scientist creates mouse models where a specific gene is linked to GFP, then every time that gene creates a protein, that protein will also have that genetic connection to GFP. With this ability, scientists can observe neurons grow and move in a living mouse, or they can “sacrifice the mouse and remove a tissue and look at where the neurons are.” To see the neuron in removed tissue, scientists shine a light on the tissue, which causes the fluorescence to show where the GFP-linked neurons are located as well as what other kinds of cells express the GFP-linked gene.

GFP, as well as similar fluorescent markers, are also used in immunohistochemistry. In this branch of science, GFP is linked to antibodies that target specific proteins. When a scientist stains a piece of tissue with these GFP-linked antibodies, the antibodies’ stain will glow under a microscope. Since these antibodies migrate to certain proteins, wherever the antibodies’ stain is visible is where the desired proteins to study can be found. Kofler cited the example of using GFP-linked antibodies to look at layers and different cell types in skin. Oftentimes, though, immunohistochemistry uses antibodies to find disease- or cancer-causing proteins and toxic substances in cells, called antigens. As Kofler so clearly stated: “The point is, we just use GFP all the time.”

Another side of transgenics and bioluminescence intrigues Kofler as well: bioluminescent trees. Currently, scientists are working on genetically engineering trees to produce their own light with the end goal of using these trees to replace streetlights. Detailed in a Smithsonian Magazine interview of entrepreneur Antony Evans, who works with biologists Omri Amirav-Drory and Kyle Taylor, these trees would produce a dimmer, more spread-out, and “much more beautiful light.” Plus, using natural light over electricity is significantly more sustainable.

Unfortunately, trees take a long time to grow, making the research move slowly. This example of biomimicry, though, or the idea of how we can copy nature to engineer better things, is fascinating. “How can we create urban environments that are still functional in the ways we need that feel more natural and more generative?” Kofler asks. “That’s something that I’ve always been super interested about.” This question is the direction science is headed, and new answers come every day. Many of them are coming from bioluminescence, but only time will tell.

Regardless of whether trees will someday glow or not, bioluminescence is something to keep in the limelight. As a tourist attraction, an ecological marker, a lifesaving source of light, or a biomedical tool, bioluminescence is certainly important. In the future, perhaps the phenomenon will become an everyday part of people’s lives, but until then, humans can marvel at the uses, beauty, and mystery of bioluminescence.

About the Author …

Grace Finnell-Gudwien is a senior studying Earth, Society, and Environmental Sustainability with a minor in Ecology and Conservation Biology and certificates in certificates in Geographic Information Sciences and Environmental Writing. She is currently applying to graduate school and plans to pursue a Master’s in Environmental Journalism.

This piece was written for ESE 498, the CEW capstone course, in Spring 2021.