bioluminescence

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The emission of light by living organisms that is visible to other organisms. The enzymes and other proteins associated with bioluminescence have been developed and exploited as markers or reporters of other biochemical processes in biomedical research. Bioluminescence provides a unique tool for investigating and understanding numerous basic physiological processes, both cellular and organismic.

Although rare in terms of the total number of luminous species, bioluminescence is phylogenetically diverse, occurring in many different groups (see table). Luminescence is unknown in higher plants and in vertebrates above the fishes, and is also absent in several invertebrate phyla. In some phyla or taxa, a substantial proportion of the genera are luminous (for example, ctenophores, about 50%; cephalopods, greater than 50%). Commonly, all members of a luminous genus emit light, but in some cases there are both luminous and nonluminous species.

Bioluminescence is most prevalent in the marine environment; it is greatest at midocean depths, where some daytime illumination penetrates. In these locations, bioluminescence may occur in over 95% of the individuals. Where high densities of luminous organisms occur, their emissions can exert a significant influence on the communities and may represent an important component in the ecology, behavior, and physiology of the latter. Above and below midocean depths, luminescence decreases to less than 10% of all individuals and species; among coastal species, less than 2% are bioluminescent. Firefly displays of bioluminescence are among the most spectacular, but bioluminescence is rare in the terrestrial environment. Other terrestrial luminous forms include millipedes, centipedes, earthworms, and snails, but the display in these is not very bright.

While not metabolically essential, light emission can confer an advantage on the organism. The light can be used in diverse ways. Most of the perceived functions of bioluminescence fall into four categories: defense, offense, communication, and dispersal to enhance propagation.

Bioluminescence does not come from or depend on light absorbed by the organism. It derives from an enzymatically catalyzed chemiluminescence, a reaction in which the energy released is transformed into light energy. One of the reaction intermediates or products is formed in an electronically excited state, which then emits a photon. See also Chemiluminescence.

Bioluminescence originated and evolved independently many times, and is thus not an evolutionarily conserved function. It has been estimated that present-day luminous organisms come from as many as 30 different evolutionarily distinct origins. In the different groups of organisms, the genes and proteins involved are unrelated, and it may be confusing that the substrates and enzymes, though chemically different, are all referred to as luciferin and luciferase, respectively. To be correct and specific, each should be identified with the organism.

Luminous bacteria typically emit a continuous light, usually blue-green. When strongly expressed, a single bacterium may emit 10⁴ or 10⁵ photons per second. A primary habitat where most species abound is in association with another (higher) organism, dead or alive, where growth and propagation occur. Luminous bacteria are ubiquitous in the oceans and can be isolated from most seawater samples. The most exotic specific associations involve specialized light organs (for example, in fish and squid) in which a pure dense culture of luminous bacteria is maintained. In teleost fishes, 11 different groups carrying such bacteria are known, an exotic example being the flashlight fish.

Of the approximately 70,000 insect genera, only about 100 are classed as luminous. But their luminescence is impressive, especially in the fireflies and their relatives. Fireflies possess ventral light organs on posterior segments; the South American railroad worm, Phrixothrix, has paired green lights on the abdominal segments and red head lights; while the click and fire beetles, Pyrophorini, have both running lights (dorsal) and landing lights (ventral). The dipteran cave glow worm, in a different group and probably different biochemically, exudes beaded strings of slime from its ceiling perch, serving to entrap minute flying prey, which are attracted by the light emitted by the animal. The major function of light emission in fireflies is for communication during courtship, typically involving the emission of a flash by one sex as a signal, to which the other sex responds, usually in a species-specific pattern. The time delay between the two may be a signaling feature; for example, it is precisely 2 s in some North America species. But the flashing pattern is also important in some cases, as is the kinetic character of the individual flash (duration; onset and decay kinetics).

The firefly system was the first in which the biochemistry was characterized. In 1947 it was discovered that adenosine triphosphate (ATP) functions to form a luciferyl adenylate intermediate from firefly luciferin. This then reacts with oxygen to form a cyclic luciferyl peroxy species, which breaks down to yield CO₂ and an excited state of the carbonyl product (thus emitting a photon). Luciferase catalyzes both the reaction of luciferin with ATP and the subsequent steps leading to the excited product.

Bioluminescence and chemiluminescence have come into widespread use for quantitative determinations of specific substances in biology and medicine. Luminescent tags have been developed that are as sensitive as radioactivity, and now replace radioactivity in many assays. The biochemistry of different luciferase systems is different, so many different substances can be detected. One of the first, and still widely used, assays involves the use of firefly luciferase for the detection of ATP. The amount of oxygen required for bioluminescence in luminescent bacteria is small, and therefore the reaction readily occurs. Luminous bacteria can be used as a very sensitive test for oxygen, sometimes in situations where no other method is applicable. An oxygen electrode incorporating luminous bacteria has been developed.

Luciferases have also been exploited as reporter genes for many different purposes. Analytically, such systems are virtually unique in that they are noninvasive and nondestructive: the relevant activity can be measured as light emission in the intact cell and in the same cell over the course of time. Examples of the use of luciferase genes are the expression of firely and bacterial luciferases under the control of circadian promoters; and the use of coelenterate luciferase expressed transgenically (in other organisms) to monitor calcium changes in living cells over time. Green fluorescent protein is widely used as a reporter gene for monitoring the expression of some other gene under study, and for how the expression may differ, for example at different stages of development or as the consequence of some experimental procedure.

Chemoluminescence occurring in living cells.

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Flying and glowing Photinus pyralis, a firefly.

Female of Lampyris noctiluca, the Common Glowworm.

Bioluminescence is the production and emission of light by a living organism. Its name is a hybrid word, originating from the Greek bios for "living" and the Latin lumen "light". Bioluminescence is a naturally occurring form of chemiluminescence where energy is released by a chemical reaction in the form of light emission. 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)^[vague] during evolution.^[1]

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.

Contents 1 Characteristics 2 Adaptations for bioluminescence 2.1 Counterillumination camouflage 2.2 Attraction 2.3 Repulsion 2.4 Communication 2.5 Illumination 3 Biotechnology 3.1 Proposed applications of engineered bioluminescence 4 Bioluminescent organisms 4.1 Terrestrial organisms 4.2 Fish 4.3 Marine invertebrates 4.4 Microorganisms 5 See also 6 References 7 External links

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:

Counterillumination camouflage

Further information: Camouflage

In some squid species bacterial bioluminescent is used for counterillumination so the animal matches the overhead environmental light seen from below.^[2] In these animals, photoreceptive vesicles have been found that control the contrast of this illumination to create optiminal matching.^[2] Usually these light organs are separate from the tissue containing the bioluminescent bacteria. However, in one species Euprymna scolopes these light organs make up an integral component of the animal's light organ.^[3]

Attraction

Firefly larva

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 swimming beneath it. When these fish try to consume the "small fish", they are bitten by the shark, which gouges out small circular "cookie cutter" shaped chunks of flesh from its hosts.

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 bioluminescence 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.^[4]

Biotechnology

Artistic rendering of bioluminescent Antarctic krill (watercolor by Uwe Kils)

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.

Proposed applications of engineered bioluminescence

Some proposed applications of engineered bioluminescence include:^[5][6]

• Glowing trees to line highways to save government electricity bills
• Christmas trees that do not need lights, reducing danger from electrical fires
• 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.)

Bioluminescent organisms

Omphalotus nidiformis

Example of a bioluminescent species of mushroom...

...glowing with the lights off.

Firefly (species unknown) with and without flash.

The fungus Panellus Stipticus displaying bioluminescence.

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

• certain arthropods
  • fireflies
  • glow worms
    • railroad worms
  • certain mycetophilid flies
  • certain centipedes
  • certain millipedes
• annelids
• Mushrooms (see Foxfire)
  • Jack O'Lantern mushroom (Omphalotus olearius)
  • ghost fungus (Omphalotus nidiformis)
  • Honey mushroom
  • Panellus stipticus
  • several species of Mycena
• a terrestrial mollusc
  • Dyakia striata

Fish

• Cookie-cutter shark
• Marine hatchetfish
• Anglerfish
• Flashlight fish
• Pineconefish
• Porichthys
• Gulper eel
• Many rattails

Marine invertebrates

• many cnidarians
  • Sea pens
  • coral
  • Aequorea victoria, a jellyfish
• certain Ctenophores or "comb jellies"
• certain echinoderms (e.g. Ophiurida)
• certain nudibranchs
• certain crustaceans
• certain chaetognaths
  • ostracods
  • krill
• certain molluscs
  • clams
  • Octopus
    • Bolitaenidae
  • the order Teuthida
    • Colossal Squid
    • Mastigoteuthidae
    • Sepiolidae
    • Sparkling Enope Squid
    • Vampire squid

Microorganisms

• Dinoflagellates
• Vibrionaceae (e.g. Vibrio fischeri, Vibrio harveyi, Vibrio phosphoreum)
• Fungi species - A total of 71 species are bioluminescent^[7] including species of Armillaria, Omphalotus, Mycena, Gerronema, Pleurotus.

See also

• Biophoton
• De Phenomenis in Orbe Lunae
• Foxfire
• Bioluminescence imaging
• List of light sources
• Milky seas effect

References

1. ^ Hastings,J.W. Biological diversity, chemical mechanisms, and the evolutionary origins of bioluminescent systems. J. Mol. Evol. 19,309 (1983)
2. ^ ^{a b} Young RE, Roper CF. (1976). Bioluminescent countershading in midwater animals: evidence from living squid. Science. 191(4231):1046–8. PMID 1251214
3. ^ Tong D, Rozas NS, Oakley TH, Mitchell J, Colley NJ, McFall-Ngai MJ.Evidence for light perception in a bioluminescent organ. Proc Natl Acad Sci U S A. 106: 9836–9841 PMID 19509343
4. ^ Long-wave sensitivity in deep-sea stomiid dragonfish with far-red bioluminescence: evidence for a dietary origin of the chlorophyll-derived retinal photosensitizer of Malacosteus niger. by R.H. Douglas, C.W. Mullineaux, and J.C. Partridge
5. ^ Bioluminescent fireflies light way by Ron McAdow
6. ^ Bioluminescence Questions and Answers
7. ^ Bryner, Jeanna (05 October 2009). "Glow-in-the-Dark Mushrooms Discovered". Live Science. http://www.livescience.com/strangenews/091005-glowing-mushrooms.html. Retrieved 2009-10-06. 

External links

Wikimedia Commons has media related to: Bioluminescence

• Bioluminescence web page
• Lights Alive! at San Diego Natural History Museum
• Bioluminescent fireflies light way
• Glow in the Dark Shark has Killer Smudge article describing cookie-cutter shark adaptation
• Glow with the Flow article from Scripps Institution of Oceanography
• Gonyaulax Bioluminescence at Monterey Bay Aquarium Research Institute
• glow-worms on the UF / IFAS Featured Creatures Web site

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