bioluminescence

bioluminescence

[bahy-oh-loo-muh-nes-uhns]
bioluminescence, production of light by living organisms. Organisms that are bioluminescent include certain fungi and bacteria that emit light continuously. The dinoflagellates, a group of marine algae, produce light only when disturbed. Bioluminescent animals include such organisms as ctenophores, annelid worms, mollusks, insects such as fireflies, and fish. The production of light in bioluminescent organisms results from the conversion of chemical energy to light energy. In fireflies, one type of a group of substances known collectively as luciferin combines with oxygen to form an oxyluciferin in an excited state, which quickly decays, emitting light as it does. The reaction is mediated by an enzyme, luciferase, which is normally bound to ATP (see adenosine triphosphate) in an inactive form. When the signal for the specialized bioluminescent cells to flash is receive, the luciferase is liberated from the ATP, causes the luciferin to oxidize, and then somehow recombines with ATP. Different organisms produce different bioluminescent substances. Bioluminescent fish are common in ocean depths; the light probably aids in species recognition in the darkness. Other animals seem to use luminescence in courtship and mating and to divert predators or attract prey.

Emission of light by an organism or biochemical system (e.g., the glow of bacteria on decaying meat or fish, the phosphorescence of protozoans in tropical seas, the flickering signals of fireflies). It occurs in a wide range of protists and animals, including bacteria and fungi, insects, marine invertebrates, and fish. It is not known to exist naturally in true plants or in amphibians, reptiles, birds, or mammals. It results from a chemical reaction that produces radiant energy very efficiently, giving off very little heat. The essential light-emitting components are usually the organic molecule luciferin and the enzyme luciferase, which are specific for different organisms. In higher organisms, light production is used to frighten predators and to help members of a species recognize each other. Its functional role in lower organisms such as bacteria, dinoflagellates, and fungi is uncertain. Luminous species are widely scattered taxonomically, with no clear-cut pattern, though most are marine.

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Bioluminescence is the production and emission of light by a living organism as the result of a chemical reaction during which chemical energy is converted to light energy. Its name is a hybrid word, originating from the Greek bios for "living" and the Latin lumen "light". Adenosine triphosphate (ATP) is involved in most instances. The chemical reaction can occur either inside or outside the cell. In bacteria, the expression of genes related to bioluminescence is controlled by an operon called the Lux operon. Bioluminescence has appeared independently several times (up to 30 or more) during evolution.

Bioluminescence occurs in marine vertebrates and invertebrates, as well as microorganisms and terrestrial animals. Symbiotic organisms carried within larger organisms are also known to bioluminesce.

Characteristics

Bioluminescence is a form of luminescence, or "cold light" emission; less than 20% of the light generates thermal radiation. It should not be confused with fluorescence, phosphorescence or refraction of light.

Ninety percent of deep-sea marine life is estimated to produce bioluminescence in one form or another. Most marine light-emission belongs in the blue and green light spectrum, the wavelengths that can transmit through the seawater most easily. However, certain loose-jawed fish emit red and infrared light and the genus Tomopteris emits yellow bioluminescence.

Non-marine bioluminescence is less widely distributed, but a larger variety in colours is seen. The two best-known forms of land bioluminescence are fireflies and glow worms. Other insects, insect larvae, annelids, arachnids and even species of fungi have been noted to possess bioluminescent abilities.

Some forms of bioluminescence are brighter (or only exist) at night, following a circadian rhythm.

Adaptations for bioluminescence

There are five main accepted theories for the evolution of bioluminescent traits:

Camouflage

Attraction

Bioluminescence is used as a lure to attract prey by several deep sea fish such as the anglerfish. A dangling appendage that extends from the head of the fish attracts small animals to within striking distance of the fish. Some fish, however, use a non-bioluminescent lure.

The cookiecutter shark uses bioluminescence for camouflage, but a small patch on its underbelly remains dark and appears as a small fish to large predatory fish like tuna and mackerel. When these fish try to consume the "small fish", they are eaten by the shark.

Dinoflagellates have an interesting twist on this mechanism. When a predator of plankton is sensed through motion in the water, the dinoflagellate luminesces. This in turn attracts even larger predators which will consume the would-be predator of the dinoflagellate.

The attraction of mates is another proposed mechanism of bioluminescent action. This is seen actively in fireflies, which use periodic flashing in their abdomens to attract mates in the mating season. In the marine environment this has only been well-documented in certain small crustaceans called ostracod. It has been suggested that pheromones may be used for long-distance communication, and bioluminescent used at close range to "home in" on the target.

Repulsion

Certain squid and small crustaceans use bioluminescent chemical mixtures or bioluminescent bacterial slurries in the same way as many squid use ink. A cloud of luminescence is expelled, confusing or repelling a potential predator while the squid or crustacean escapes to safety. Every species of firefly has larvae that glow to repel predators.

Communication

Bioluminescence is thought to play a direct role in communication between bacteria (see quorum sensing). It promotes the symbiotic induction of bacteria into host species, and may play a role in colony aggregation.

Illumination

While most marine bioluminescence is green to blue, the Black Dragonfish produces a red glow. This adaptation allows the fish to see red-pigmented prey, which are normally invisible in the deep ocean environment where red light has been filtered out by the water column.

Biotechnology

Bioluminescent organisms are a target for many areas of research. Luciferase systems are widely used in the field of genetic engineering as reporter genes. Luciferase systems have also been harnessed for biomedical research using bioluminescence imaging.

Vibrio symbiosis with numerous marine invertebrates and fish, namely the Hawaiian Bobtail Squid (Euprymna scolopes), are key experimental model for symbiosis, quorum sensing, and bioluminescence.

The structure of photophores, the light producing organs in bioluminescent organisms, are being investigated by industrial designers.

Some proposed applications of engineered bioluminescence include:

  • Christmas trees that do not need lights, reducing danger from electrical fires
  • glowing trees to line highways to save government electricity bills
  • agricultural crops and domestic plants that luminesce when they need watering
  • new methods for detecting bacterial contamination of meats and other foods
  • bio-identifiers for escaped convicts and mental patients
  • detecting bacterial species in suspicious corpses
  • novelty pets that bioluminesce (rabbits, mice, fish etc.)

Organisms that bioluminesce

All cells produce some form of bioluminescence within the electromagnetic spectrum, but most are neither visible nor noticeable to the naked eye. Every organism's bioluminescence is unique in wavelength, duration, timing and regularity of flashes. Below follows a list of organisms which have been observed to have visible bioluminescence.

Terrestrial organisms

Fish

Marine invertebrates

Microorganisms

See also

References

External links

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