Bioluminescence

• Categories: Algae; cellular biology; fungi; physiology; water-related life

Bioluminescence is a specific form of chemiluminescence, which is a phenomenon in which the chemical energy that is produced in a chemical reaction is converted into radiant energy. In bioluminescence, the reaction is a natural function that originates in a living organism. It should not be confused with fluorescence or phosphorescence, neither of which involves a chemical reaction. Instead, fluorescence and phosphorescence are both products of spontaneous emission, in which photons are absorbed and then later re-emitted.

Bioluminescence also involves the emission of photons, but this is caused by the oxidation of a light-emitting compound called luciferin. When the oxidized luciferin, or oxyluciferin, returns to its ground state, its excess energy is released as a photon. Unlike the light bulb, in which electrical energy is converted into light and some of the energy is lost in the form of heat, a bioluminescent reaction is 100 percent efficient, converting all the emitted energy into light. Because there is no heat released, bioluminescence is also known as “cold light.”

Species and Habitats

Bioluminescence occurs in a wide range of organisms. It is most common among marine organisms and is the only source of light in the deep ocean, which is the largest habitable biome of the earth. Few freshwater organisms exhibit bioluminescence. Bioluminescent organisms include certain ctenophores (comb jellies), annelids (segmented worms), mollusks, arthropods (insects and myriapods), and fish. The most common manifestations of this phenomenon on land are glowing fungi on wood and luminous insects such as fireflies. Bioluminescence can serve as a means of species recognition in the darkness as well as courtship, preying, and mating.

There are more than seventy-five species of bioluminescent fungi, primarily occurring in tropical regions, although some species are found in temperate climates. All known species of bioluminescent fungi to date are wood decayers, meaning that they digest wood and cause it to rot. Among the most common is Panellus stiptucus (bitter oyster), a small fungus that is mostly restricted to North America. Omphalotus olearius (jack-o’-lantern mushroom) glows brightly, especially when fresh. A few Armillaria species are also reported to glow mildly. No luminous tree or plant species is known to exist.

Mechanisms of Bioluminescence

Bioluminescence occurs when light-emitting compounds called luciferins react with oxygen molecules. This chemical reaction cannot proceed without the presence of an enzyme called luciferase to act as a catalyst. During the reaction, the luciferin is oxidized, losing two electrons to become a compound known as oxyluciferin. When the oxyluciferin decays back into luciferin, it releases a photon of light—the light produced by bioluminescence.

Occasionally luciferin, luciferase, and a cofactor such as oxygen are bound together in a single moiety called a photoprotein, which leads to light formation upon contact with a positively charged species, such as the calcium cation. The mechanism appears to involve a peroxide decomposition with free-radical intervention.

Dinoflagellates

Dinoflagellates, a phylum of single-celled protists, are the most common sources of bioluminescence at the surface of the ocean. Not all dinoflagellate species are bioluminescent, but many are. The phenomenon was first observed in the genus Noctiluca in the nineteenth century and has since been observed to occur within other species.

Generally, three types of stimuli can cause bioluminescence in dinoflagellates: mechanical, chemical, and temperature stimulation. Mechanical forms of stimulation, such as the stirring of water from a moving boat, a swimming fish, or a breaking wave, are prevalent in many dinoflagellates. The light appears to serve as a “burglar alarm” against grazing predators, which are then being seen through the flash by a larger second predator. For example, as a copepod approaches the dinoflagellate, agitation of the seawater stimulates light flashes which a small fish, the secondary predator, uses to pinpoint the position of the copepod and eventually consume it. It appears that the mechanical stimulation deforms the cell membrane to create a short flash as little as one one-hundredth of a second.

Dinoflagellate luciferin is thought to derive from the similarly structured chlorophyll, which is found in most plants. The molecule is protected from luciferase at slightly basic medium by a luciferin-binding protein. However, once the acidity increases, the free luciferin reacts, and light is emitted. The light produced by a single dinoflagellate is only six to eight photons in energy, and the flashing may last only one-tenth of a second. Larger organisms, such as jellyfish, provide flashes that may last up to tens of seconds. Temperature lowering in some dinoflagellate species also creates bioluminescence.

Purpose and Applications

Bioluminescence serves a wide range of functions in nature, including defense (bright flashes to startle, counterillumination for camouflage, etc.), offense (luring, stunning, or illuminating prey), and communication (primarily for mating purposes). Steven H. D. Haddock and colleagues estimated in 2010 that bioluminescence has independently evolved "a minimum of 40 times, and likely more than 50 times, among extant organisms."

Bioluminescence has played a crucial role in the direct studies of several cellular and biochemical processes, such as in the formation of ultimate carcinogens from benzoapyrene. The phenomenon has served scientists in many ways. Calcium levels are monitored via the jellyfish biochemical system, adenosine triphosphate (ATP) measurements are achieved through the firefly system, and the gene activity of organisms can be detected by splicing known bioluminescent proteins. In addition, scientists have investigated the possibility of using bioluminescence as a source of sustainable natural lighting.

Bibliography

"Bioluminescence." Smithsonian National Museum of Natural History, ocean.si.edu/ocean-life/fish/bioluminescence. Accessed 9 Jan. 2025.

Burkenroad, M. D. “A Possible Function of Bioluminescence.” Journal of Marine Research, vol. 5, 1943, pp. 161–64.

Connor, Steve. “How Research into Glowing Fungi Could Lead to Trees Lighting Our Streets.” The Guardian, 3 July 2016, www.theguardian.com/science/2016/jul/03/fungi-glow-dark-luminscent-mushrooms-conservation-enviroment-bioscience. Accessed 19 Apr. 2017.

Fleisher, Kellie J., and James F. Case. “Cephalopod Predation Facilitated by Dinoflagellate Luminescence.” Biological Bulletin, vol. 189, no. 3, 1995, pp. 263–71.

Ganeri, Anita. Creatures That Glow. Harry N. Abrams, 1995.

Haddock, Steven H. D. “Bioluminescence in the Sea.” Annual Review of Marine Science, vol. 2, 2010, pp. 443–93.

Hamman, J. P., and H. H. Seliger. “The Mechanical Triggering of Bioluminescence in Marine Dinoflagellates: Chemical Basis.” Journal of Cellular Physiology, vol. 80, no. 3, 1972, pp. 397–408.

Shimomura, Osamu. Bioluminescence: Chemical Principles and Methods. Rev. ed., World Scientific, 2012.

Wilson, Thérèse, and J. Woodland Hastings. Bioluminescence: Living Lights, Lights for Living. Harvard UP, 2013.