banner by Margaret Perry

The Science and Application of Bioluminescence

by Margaret Perry

Maybe you have this memory: catching fireflies in a backyard when you were a kid, securing them in bell jar containers with punctured plastic wrap and a rubber band. There was always something fascinating in the way they lazily blinked their yellow-green light at you, unlike any other bugs you encountered.

In a way, fireflies are otherworldly. They are bioluminescent—meaning they emit visible light—and are one of the few cases of this phenomenon we witness in our lives. Most other bioluminescent organisms live in more extreme environments, deep within caves or in the ocean. You might have seen pictures of glowing jellyfish or blue-stained algae waves in a desktop background.   

Bioluminescence has yet to be fully explored. With many of the cases existing in extreme environments, it is difficult for researchers to study organisms in their natural habitat. What scientists have discovered is that bioluminescence is the result of a chemical reaction that occurs within organisms. Its main ingredients are the light-emitting pigment luciferin and its enzyme, luciferase. In the presence of oxygen, luciferase catalyzes the oxidation of luciferin, and its end products are a chemical called oxyluciferin and its byproduct, light.

While this is the simplest version of the reaction, depending on the organism, bioluminescence can also involve the protein aequorin (as in the well-known jellyfish Aequorea victoria), or cofactors, such as magnesium and calcium ions. Although sometimes incorrectly used as synonyms, fluorescence and phosphorescence are different from bioluminescence and involve different chemical reactions. The former is the immediate reemission of modified light, and the latter is the longer-lasting type of fluorescence found in glow-in-the-dark products. In contrast, the molecules for bioluminescence are found within an organism. These molecules are replenished through the organism’s diet or internal processes.

Researchers believe that bioluminescence evolved in organisms for a number of reasons. Similar to how the scarlet kingsnake mimics the appearance of its venomous cousin, the Eastern coral snake, many organisms use their bioluminescence for defensive purposes. For example, the squid Watasenia scintillans uses counterillumination camouflage to blend in with varying light levels in the ocean—it adjusts its appearance, so predators lurking below cannot distinguish it from the environment. A crustacean called the sea-firefly uses bioluminescence to its advntages by leaveing glittering blue trails to confuse predators in its escape.

Bioluminescence is also used for communication. In many scale worms and jellyfish, it serves as a type of aposematism, an organism’s signal to predators that they are inedible or unappealing as prey. On the other hand, in the firefly, bioluminescence is a mating call. Similar to a peacock’s colorful plumage, males’ and females’ glowing abdomens serve as signals to attract a mate. Depending on the type of light—steady glows, flashing, or other variations of signaling—fireflies can broadcast their quality as a potential reproductive partner.

Interestingly enough, bioluminescence has been interacting with us long before we have understood it. Bioluminescence was only first studied seriously in the 1920s with the publishing of zoologist E. Newtown Harvey’s book, “The Nature of Animal Light,” and it was not until the late 1900s when its chemical reaction was understood. However, it has been fascinating sailors and scientists for millennia.

Although bioluminescence has appeared in folklore for most of human history, the first substantial mention was in the writings of Greek philosopher Aristotle (384-322 BC), who noticed odd glowing in dead fish. Other early records of bioluminescence appear in the notebooks of Charles Darwin. On his passage around Cape Horn in 1833, the famous naturalist took notice of glowing algae along his ship. The way he described it in his journal was with child-like wonder,

Although he did not know it at the time, he was seeing bioluminescent algae, which produces a glow when stirred by activity in the water.

During World War I, a German submarine was sunk due to location in this way. On Nov. 9, 1918, the German U-boat, U-34, stirred up a cloud of bioluminescent algae off the coast of Gibraltar. The algae betrayed their location, and Allied ship HMS Privet sunk the submarine. All 38 of its crewmembers were lost. During its life, the U-34 had gone on 17 missions and sunk an impressive total of 119 Allied ships. Not only was the incident a victory for Allied forces, which had been struggling to locate the infamous U-boats, but it also opened the possibility of an exciting new naval strategy. During the subsequent global conflicts, World War II and the Cold War, the United States Navy would become increasingly interested in utilizing bioluminescence’s potential for locating enemy watercraft.

The potential of bioluminscence continues to be exciting today. The United States Navy still wants to militarize bioluminescence to be able to both detect and avoid detection by enemy vessels. As they study bioluminescent algae’s reactions to movement in the water, they work to develop a navigation aid for their submarines. Outside the military, scientists are engineering other ways to utilize bioluminescence on a daily and commercial basis. One student from Cambridge wants to see if bioluminescent trees can one day replace streetlights and road signs to save on energy costs. Farmers hope to use bioluminescence in their crops so they can detect dehydration, malnutrition, and disease earlier in plants.

Arguably, most exciting is bioluminescence’s role in drug and cancer research. In addition to being a test for toxins and pesticides in liquid compounds, which disrupt bioluminescence’s chemical reaction and lead to reduced light output, bioluminescence is also now being used to locate tumors.

In a growing field called color-coded surgery, bioluminescence can locate malignant tumors in cancer patients for more effective surgical extraction. A compound injected into the patient’s bloodstream during this surgery contains three crucial components: polycation, which sticks to tissues in the body; polyanion, which neutralizes the former; and a bioluminescent molecule. Tumors, unlike normal tissues in the body, possess molecular scissors that can “cut” this compound in half. When this happens, the polycation breaks from the polyanion and sticks to the tumor’s surface, activating the bioluminescence. With the tumor as a beacon, a surgeon can more easily locate where the tumor begins and remove anything malignant.

This field is only the beginning of bioluminescent engineering. Encouraged by the promise of color-coded surgery, chemical engineers hope to extend the development to other tasks like tracking pathways of cells in the body or locating viruses in patients. Given continued success, bioluminescence may lead to more thorough and less invasive options for patients, and higher rates of success. With so much unexplored and this much potential, the possibilities are bright!