Bioluminescence is the ability of an organism to produce light through a chemical reaction. This phenomenon occurs in many types of living things, such as marine animals (both with and without backbones), land insects like fireflies, certain fungi, and tiny organisms like some bacteria and dinoflagellates. In some animals, the light is created by bacteria that live in partnership with the organism, such as those in the Vibrio genus. In others, the light is produced directly by the animal itself. Bioluminescence has developed independently at least 94 times, with its first known appearance in octocorals around 540 million years ago.
Most bioluminescence involves a chemical reaction between a substance called luciferin and an enzyme called luciferase. These names are general, so scientists often specify the type based on the species, such as "firefly luciferin" or "cypridina luciferin." In all known cases, the enzyme helps oxidize luciferin, creating a substance called oxyluciferin in an excited state. When this substance returns to its normal, stable state, it releases visible light.
In some species, the luciferase enzyme needs additional helpers, such as calcium or magnesium ions, or a molecule called ATP that stores energy. Over time, luciferin has changed little, with one example, coelenterazine, found in 11 different animal groups. However, some of these animals get coelenterazine from their food. In contrast, luciferase varies greatly between species. Bioluminescence has developed over 40 times in evolutionary history.
Both Aristotle and Pliny the Elder observed that wet wood sometimes glows. Many years later, Robert Boyle discovered that oxygen plays a role in the glowing process in wood, fish, and glowworms. It was not until the late 1800s that scientists began studying bioluminescence seriously. This ability is common in many animal groups, especially in ocean environments. On land, it is found in fungi, bacteria, and some invertebrates, such as insects.
Animals use bioluminescence for purposes like counterillumination camouflage, mimicking other animals to attract prey, and communicating with members of their own species, such as finding mates. In laboratories, systems based on luciferase are used in genetic engineering and medical research.
History
Before the invention of the safety lamp for use in coal mines, dried fish skins were used in Britain and Europe as a weak light source. This method avoided the danger of using candles, which could cause explosions of firedamp, a gas found in mines. In 1920, the American zoologist E. Newton Harvey published a detailed report titled The Nature of Animal Light, summarizing early research on bioluminescence. Harvey noted that Aristotle wrote about light from dead fish and flesh, and both Aristotle and Pliny the Elder mentioned light from damp wood in their writings. He recorded that Robert Boyle studied these light sources and showed that both they and glowworms needed air to produce light. Harvey also noted that in 1753, J. Baker identified the flagellate Noctiluca as a luminous animal visible to the naked eye, and in 1854, Johann Florian Heller identified fungi’s thread-like parts, called hyphae, as the source of light in dead wood.
James Hingston Tuckey, in his 1818 book Narrative of the Expedition to the Zaire, described catching animals that caused luminescence. He mentioned pellucida, crustaceans (which he linked to the milky color of water), and cancers (shrimps and crabs). Under a microscope, he observed the "luminous property" in the brain, describing it as "a brilliant amethyst about the size of a large pin’s head."
Charles Darwin noticed bioluminescence in the sea and wrote about it in his Journal. He described a luminous "jellyfish of the genus Dianaea" and noted that bright green sparks in waves were likely caused by tiny crustaceans. He also suggested that a disturbed electrical condition in the atmosphere might be responsible. Daniel Pauly later noted that Darwin’s guess was incorrect because the science of biochemistry was not yet understood, and the complex evolution of marine life was not fully known at the time.
Bioluminescence became important to the United States Navy during the Cold War because submarines could be detected by their bright wakes in some waters. A German submarine was sunk during World War I after being spotted in this way. The Navy wanted to predict when such detection might occur to help its submarines avoid being seen.
One story about using bioluminescence for navigation involves Jim Lovell, an astronaut on Apollo 13. As a Navy pilot, he once used the glowing wake of his aircraft carrier, the USS Shangri-La, to find his way back to the ship when his navigation systems failed.
In the late 1800s, the French pharmacologist Raphaël Dubois studied bioluminescence. He examined click beetles (Pyrophorus) and a marine bivalve mollusk, Pholas dactylus. He disproved the old idea that bioluminescence came from phosphorus and showed that it involved a compound called luciferin, which reacts with an enzyme. He sent preserved parts of the mollusk to Harvey, who had become interested in bioluminescence after visiting the South Pacific and Japan and observing glowing organisms. Harvey studied the phenomenon for many years, aiming to prove that luciferin and the enzymes involved in light production were shared among species, suggesting a common ancestor for all bioluminescent organisms. However, he found this idea to be false, as different organisms had major differences in their light-producing proteins. He spent the next 30 years studying these components, but it was the Japanese chemist Osamu Shimomura who first obtained crystalline luciferin in 1957. He used the sea firefly Vargula hilgendorfii, and it took another ten years before he discovered the chemical’s structure and published his paper Crystalline Cypridina Luciferin. Shimomura, Martin Chalfie, and Roger Y. Tsien won the 2008 Nobel Prize in Chemistry for their work on green fluorescent protein, a tool used in biological research.
In 1957, Harvey wrote a detailed historical account of all types of luminescence. A more recent book on bioluminescence, covering the 20th and early 21st centuries, was also published.
Evolution
In 1932, E. N. Harvey was one of the first scientists to explain how bioluminescence might have developed over time. In his early work, he proposed that early bioluminescence could have come from proteins in the respiratory system that contain fluorescent groups. This idea was later shown to be incorrect, but it sparked interest in studying how bioluminescence began. Today, two main theories about the origin of bioluminescence (both related to marine life) are those proposed by Howard Seliger in 1993 and Rees et al. in 1998.
Seliger’s theory suggests that enzymes called luciferases played a key role in the evolution of bioluminescent systems. He believed that these enzymes originally helped break down certain molecules as part of a process called oxidation. As early ancestors of many species moved into deeper, darker waters, natural selection favored animals with better eyesight and stronger visual signals. If a mutation occurred in an enzyme involved in breaking down pigment molecules (which are often used for attracting mates or confusing predators), it could have led to light being produced outside the body.
Rees et al. studied a molecule called coelenterazine, a type of luciferin found in marine life. They suggested that natural selection might have favored the use of luciferins to protect ocean organisms from harmful substances called reactive oxygen species, such as hydrogen peroxide and oxygen. Over time, as early species moved deeper into the ocean, the need for protection from these harmful substances decreased because there was less exposure to them. This change may have allowed luciferins to shift from being used for protection to being used for producing light.
Although Seliger’s theory was popular at first, it has been questioned because of new biochemical and genetic evidence studied by Rees and others. What is clear, however, is that bioluminescence has evolved separately at least 40 times. In fish, bioluminescence appeared by the Cretaceous period. Around 1,500 fish species are known to be bioluminescent, and this ability evolved independently at least 27 times. In 17 of these cases, fish obtained light-producing bacteria from the water, while in the others, they created light through chemical reactions inside their bodies. These fish have become very diverse in the deep ocean and use their nervous systems to control their light, which helps them attract prey, avoid predators, and communicate.
All bioluminescent organisms share a common process: a molecule called luciferin reacts with oxygen, and this reaction is sped up by an enzyme called luciferase to produce light. In 1962, McElroy and Seliger suggested that the bioluminescent reaction may have evolved to help remove harmful oxygen from cells, similar to how photosynthesis works in plants.
Bioluminescence has evolved independently at least 94 times. It first appeared in octocorals (a type of coral) about 540 million years ago. Within ray-finned fish, it evolved separately 27 times. The earliest known examples among fish are Stomiiformes and Myctophidae. In sharks, bioluminescence evolved only once. Studies of octocoral DNA suggest that their ancestor was already bioluminescent as far back as 540 million years ago.
Chemical mechanism
Bioluminescence is a type of light production that happens when a chemical reaction releases energy as light. This reaction uses a light-emitting substance called luciferin and an enzyme called luciferase. Because there are many different types of luciferin and luciferase, the chemical processes involved vary widely. However, a common feature in most systems is the use of molecular oxygen, and often carbon dioxide (CO₂) is released during the reaction. For example, the reaction in fireflies requires magnesium and ATP, and produces CO₂, adenosine monophosphate (AMP), and pyrophosphate (PP) as waste. Other reactions may need additional helpers, such as calcium ions for a photoprotein called aequorin, or magnesium ions and ATP for firefly luciferase. The creation of light always involves breaking down organic peroxides. In general, the luciferin/luciferase reaction can be described as:
Instead of using luciferase, the jellyfish Aequorea victoria uses a type of protein called a photoprotein, specifically aequorin. When calcium ions are added, a quick chemical reaction causes a brief flash of light, which is different from the longer-lasting glow made by luciferase. Later, in a slower step, luciferin is restored from its oxidized form (oxyluciferin), allowing it to recombine with aequorin for another flash. Photoproteins are enzymes, but they work in unusual ways. Additionally, some of the blue light from aequorin is absorbed by a green fluorescent protein, which then releases green light through a process called energy transfer.
In evolution, luciferins change little over time. One example, coelenterazine, is the light-emitting substance used by nine groups of very different organisms, including polycystine radiolaria, Cercozoa (Phaeodaria), protozoa, comb jellies, cnidaria (like jellyfish and corals), crustaceans, molluscs, arrow worms, and vertebrates (such as ray-finned fish). Not all these organisms make coelenterazine themselves; some get it from their food. In contrast, luciferase enzymes differ greatly and are usually unique to each species.
Distribution
Bioluminescence is common among many animals, especially in the open sea. These include fish, jellyfish, comb jellies, crustaceans, and cephalopod molluscs. It is also found in some fungi and bacteria, as well as in many land-dwelling insects, mostly beetles. In marine coastal areas, about 2.5% of organisms are bioluminescent. In deep-sea areas of the eastern Pacific, about 76% of major deep-sea animal groups can produce light. Over 700 animal genera have species that create light. Most marine light is blue or green. Some loose-jawed fish produce red or infrared light, and the genus Tomopteris emits yellow light.
Dinoflagellates, a type of tiny ocean plankton, are often seen in the top layers of the sea. They cause the glowing effect sometimes seen in disturbed water at night. At least 18 types of these plankton can produce light. These organisms live in warm, shallow areas like lagoons and bays with narrow connections to the ocean. Another phenomenon is the "milky seas effect," where large areas of the ocean glow due to bioluminescent bacteria.
Bioluminescence is most common in the open ocean, especially in the deep, lightless areas and in surface waters at night. Many of these organisms move vertically through the water column during the day and night, spreading bioluminescent species throughout the open ocean. This movement is thought to be influenced by the need to avoid predators and the lack of hiding places in open water. In the deep sea, where sunlight does not reach, bioluminescence is important for organisms to keep their eyes functional for detecting light.
Most organisms create their own light, though some rely on bacteria that live inside them. These bacteria form a partnership with their host, such as fish, squids, or crustaceans. While many glowing bacteria live freely in the ocean, most are found in symbiotic relationships with other animals. The most common glowing bacteria in the sea are types called Photobacterium and Vibrio.
In these partnerships, the bacteria gain food and a place to grow, while the host benefits from the light. Hosts may obtain these bacteria from the environment, through reproduction, or through long-term evolutionary changes with their bacterial partners. Hosts have developed specific body parts to support certain types of glowing bacteria, showing how these partnerships have evolved over time.
Bioluminescence is well studied in the mesopelagic zone, but the benthic zone (the ocean floor) at similar depths is less understood. Even deeper areas of the ocean floor are poorly studied due to the difficulty of exploring them. Unlike the open ocean, where light is visible, bioluminescence is less common on the ocean floor. This is because light may be blocked by the seafloor or other structures. Visual signals used in the open ocean, like counter-illumination, may not work in the deep ocean floor. Research on bioluminescence in deep-sea floor species remains limited because of the challenges of collecting samples from such depths.
Uses in nature
Bioluminescence serves many purposes in different living things. Steven Haddock and others (2010) identified several clear functions in ocean animals, including: using light to startle predators, blending in with the environment (counterillumination), creating a false target (misdirection), having parts that draw attention away from the body, warning predators that the animal is not easy to eat, and attracting mates. Researchers often find it easier to see that an animal can make light than to understand how or why it does so. In some cases, the purpose of bioluminescence is unknown, such as in certain earthworms, like Diplocardia longa, where body fluid produces light when the animal moves. The functions listed are well understood in the named animals.
In the deep sea, many animals, including some squid, use bacterial bioluminescence to blend in with their surroundings. This happens through counterillumination, where the animal matches the light coming from above. Light-sensitive cells control the brightness of the light to match the background. These light-producing organs are usually separate from the bacteria that make the light. However, in Euprymna scolopes, the bacteria are part of the animal’s light organ.
Bioluminescence is used in many ways. For example, the cirrate octopus Stauroteuthis syrtensis emits light from structures on its arms. These structures evolved from the typical suckers of an octopus but no longer help in grasping. Instead, they are used to attract prey. The light is placed near the mouth, suggesting it helps catch food.
Fireflies use light to find mates. In some species, females flash from their abdomens to attract males, while in others, males fly and send signals that females respond to. Click beetles emit orange light from their bodies when flying and green light from their chest when moving on the ground. The orange light may help attract mates, while the green light could be a warning to predators. The larvae of Pyrophorus nyctophanus live in termite mounds in Brazil and glow green to attract insects they eat.
In the ocean, small shrimp-like creatures called ostracods use bioluminescence to find mates. They may use chemicals for long-distance communication and light for close-range contact. A worm called the Bermuda fireworm glows briefly a few nights after a full moon to attract males.
Bioluminescence can also be used for defense. Some animals startle predators, blend in with their surroundings, create a false target, or release light to distract. The shrimp family Oplophoridae uses light to startle predators. Acanthephyra purpurea can release a glowing substance when threatened, a trait also seen in some fish.
Many squids and crustaceans use bioluminescence like ink to confuse predators. A cloud of glowing material is released, allowing the animal to escape. The deep-sea squid Octopoteuthis deletron can shed glowing parts of its arms to distract predators.
Dinoflagellates may use light to protect themselves from predators. When they sense danger, they glow, possibly drawing attention to predators of their attackers. Other possibilities include confusing predators or warning them of toxicity. Some plankton avoid being eaten because glowing cells could make their predators visible. Deep-sea fish have dark stomachs to prevent swallowed prey from glowing and attracting larger predators.
A small crustacean called the sea-firefly glows when resting but releases a cloud of blue light when disturbed to confuse predators. During World War II, the Japanese military collected and dried these creatures for use as light sources.
Railroad worm larvae have glowing green organs on each body segment, likely for defense. They also have red-light organs on their heads, the only known terrestrial animals to emit red light.
Some animals use bioluminescence to warn predators they are not tasty. Firefly larvae and some millipedes glow for this reason. Marine creatures like scale worms, jellyfish, and brittle stars may also use light this way, though more research is needed. A freshwater snail called Latia neritoides produces glowing mucus, possibly to scare predators. A marine snail, Hinea brasiliana, flashes light through its shell to deter predators.
Bacteria use bioluminescence to communicate when their numbers are high. They release small molecules that signal others to produce light.
Pyrosomes are colonial sea creatures with glowing organs that flash in rhythm. Each individual responds to light from others, helping the group move together.
Some bioluminescent bacteria infect worms that live in caterpillars. When the caterpillars die, the glowing may attract predators, helping spread the bacteria and worms. Similar reasons may explain why some fungi glow.
Biotechnology
Bioluminescent organisms are important in many areas of scientific study. Luciferase systems are often used in genetic engineering as reporter genes and in biomedical research through bioluminescence imaging. For example, the firefly luciferase gene was used in 1986 to study transgenic tobacco plants. Vibrio bacteria form a symbiotic relationship with marine invertebrates, such as the Hawaiian bobtail squid (Euprymna scolopes), and are important models for studying bioluminescence. Bioluminescent activated destruction is an experimental method for treating cancer.
The structures of photophores, the light-producing organs in bioluminescent organisms, are being studied by industrial designers. Engineered bioluminescence might one day help reduce the need for street lighting or be used for decoration if bright, long-lasting light can be produced at a reasonable cost. Scientists added the firefly gene that causes their tails to glow to mustard plants. These plants emit a faint glow for about an hour when touched, but a sensitive camera is needed to see it. Researchers at the University of Wisconsin–Madison are studying genetically engineered E. coli bacteria to use as light sources in light bulbs. In 2011, Philips demonstrated a microbial system for home lighting. A team from Cambridge, England, developed a genetic tool to help reuse luciferin, a compound needed for light production, by creating a luciferin regenerating enzyme from the North American firefly. In 2016, a French company named Glowee began selling bioluminescent lights for shop fronts and street signs. These lights use the bacterium Aliivibrio fischeri and are used between 1 and 7 a.m., when electricity use is restricted by law. However, Glowee’s lights last only three days. In April 2020, scientists engineered plants to glow more brightly by using genes from the bioluminescent mushroom Neonothopanus nambi to convert caffeic acid into luciferin. Another possible use is replacing chemiluminescence with bioluminescent enzymes. A Canadian company, Lux Bio, is working to create long-lasting bioluminescent enzymes for this purpose.
ATP bioluminescence is a process in which ATP is used with other compounds, such as luciferin, to produce light in an organism. This process is useful as a biosensor to detect living microbes in water. Different types of microbes can be identified using various ATP assays with different substrates and reagents. Cell viability tests using Renilla and Gaussia rely on the substrate coelenterazine.