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Bioluminescence is the production and emission of light by a living organism. It is a form of chemiluminescence. Bioluminescence occurs widely in marine vertebrates and invertebrates, as well as in some fungi, microorganisms including some bioluminescent bacteria, and terrestrial arthropods such as fireflies. In some animals, the light is bacteriogenic, produced by symbiotic bacteria such as those from the genus Vibrio; in others, it is autogenic, produced by the animals themselves.
In a general sense, the principal chemical reaction in bioluminescence involves a light-emitting molecule and an enzyme, generally called luciferin and luciferase, respectively. Because these are generic names, luciferins and luciferases are often distinguished by the species or group, e.g. firefly luciferin. In all characterized cases, the enzyme catalyzes the oxidation of the luciferin. In some species, the luciferase requires other cofactors, such as calcium or magnesium ions, and sometimes also the energy-carrying molecule adenosine triphosphate (ATP). In evolution, luciferins vary little: one, in particular, coelenterazine, is found in 11 different animal phyla, though in some of these, the animals obtain it through their diet. Conversely, luciferases vary widely between different species, which is evidence that bioluminescence has arisen over 40 times in evolutionary history.
Both Aristotle and Pliny mentioned that damp wood sometimes gives off a glow. Many centuries later Robert Boyle showed that oxygen was involved in the process, in both wood and glowworms. It was not until the late nineteenth century that bioluminescence was properly investigated.
Bioluminescence has several functions in different taxa, namely: defensive functions of startle, counter-illumination (camouflage), misdirection (smoke screen), distractive body parts, burglar alarm (making predators easier for higher predators to see), and warning to deter settlers; offensive functions of lure, stun or confuse prey, illuminate prey, and mate attraction/recognition. It is much easier for researchers to detect that a species can produce light than to analyze the chemical mechanisms or to prove what function light serves. In some cases, the function is unknown, as with species in three families of earthworms, where the coelomic fluid produces light when the animal moves.
Most marine light-emission is in the blue and green light spectrum. However, some loose-jawed fish emit red and infrared light, and the genus Tomopteris emits yellow light. The most frequently encountered bioluminescent organisms are the dinoflagellates in the surface layers of the sea, which are responsible for the sparkling phosphorescence sometimes seen at night in disturbed water. A different effect is the thousands of square miles of the ocean which shine with the light produced by bioluminescent bacteria, known as mareel or the milky seas effect.
Bioluminescent organisms are a target for many areas of research. Luciferase systems are widely used in genetic engineering as reporter genes, each producing a different colour by fluorescence, and for biomedical research using bioluminescence imaging. For example, the firefly luciferase gene was used as early as 1986 for research using transgenic tobacco plants. Bioluminescent activated destruction is an experimental cancer treatment. Researchers are also investigating the possibility of using bioluminescent systems for street and decorative lighting, and a bioluminescent plant has been created.