Bioluminescence

Bioluminescence is the production of light by an organism as the result of a chemiluminescence reaction. It occurs in a wide variety of organisms, including marine vertebrates and invertebrates, terrestrial arthropods such as fireflies, some fungi, and microorganisms such as some bacteria and dinoflagellates. 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. Bioluminescence has evolved independently at least 94 times, first emerging in octocorals some 540 million years ago.

In most cases, the principal chemical reaction in bioluminescence involves the reaction of a substrate called luciferin and an enzyme, called luciferase. Because these are generic names, luciferins and luciferases are often distinguished by the species or group, e.g. firefly luciferin or cypridina luciferin. In all characterized cases, the enzyme catalyzes the oxidation of the luciferin resulting in excited state oxyluciferin, which is the light emitter of the reaction. Upon their decay to the ground state they emit visible light.

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. Bioluminescence has arisen over 40 times in evolutionary history.

Both Aristotle and Pliny the Elder mentioned that damp wood sometimes gives off a glow. Many centuries later Robert Boyle showed that oxygen was involved in the process, in wood, fish, and glowworms. It was not until the late nineteenth century that bioluminescence was properly investigated. The phenomenon is widely distributed among animal groups, especially in marine environments. On land it occurs in fungi, bacteria and some groups of invertebrates, including insects.

The uses of bioluminescence by animals include counterillumination camouflage, mimicry of other animals, for example to lure prey, and signaling to other individuals of the same species, such as to attract mates. In the laboratory, luciferase-based systems are used in genetic engineering and biomedical research.