As evident from its name, Bio means “Living” and Luminescent means “Giving out visible light”, bioluminescence means the production and emission of visible light from a living organism. For humans and other living organisms residing on land, the sun is the only source of light, but deep in the ocean, where the light rays of the sun cannot reach, the organism are able to produce their own light to fulfil their needs such as finding food and hiding from predators. As this phenomena is more common for the water-dwelling organisms, some land invertebrates such as fireflies also show bioluminescence plus some bacterial and fungal species are also able to produce their own light.
History:
Bioluminescence was properly investigated in the nineteenth century but the search for this phenomena started in the time of Aristotle, who showed that the damp wood sometimes give off light. Robert Boyle carried out experiments and showed that the damp wood required air or oxygen to exhibit the phenomena. The other luminous organisms were then identified by many other scientists. In 1753, J. Baker identified Noctiluca as the luminous flagellate, in 1854 a fungal hyphae was recognized as a source of light in dead wood by Johan Heller while Tuckey in 1818 described pellucid, crustaceans and cancers as the organisms displaying the bioluminescent phenomena. The luminous Jelly Fish was observed by Darwin and he wrote in his journal:
“While sailing in these latitude on one very dark night, the sea presented with the most wonderful and beautiful spectacle. There was a fresh breeze and every part of the surface, which during the day is seen as foam, now glowed with a pale light. As far as the eye reached, the crest of every wave was bright, the sky above the horizon, from the reflected glare of these livid flames, was not so utterly obscure, as over the rest of heavens.”
Daniel Pauly commented that Darwin was right in most of his guesses, but regarding this phenomena his guess was quite wrong, as he had little information about biochemistry. Darwin had suggested that the phenomena was a cause of disturbed electrical condition in the atmosphere. A French pharmacologist in the late 19th century, while working on bioluminescence, discovered that the phenomena was the result of oxidation of specific compound and not due to phosphorus, as phosphorus was considered to be one of the causes of giving out light. He named that compound as Luciferin.
To explain the process of bioluminescence, many theories have been suggested, the two being the most common, one suggested by Seliger and the other by Rees at al. Seliger’s theory suggested that as the organisms living in the ocean moves into the depth, natural selection causes the bioluminescent systems to evolve the multi-functional oxygenase called luciferase, which breakdown the pigment molecules in the external tissues and the organism gives off light. While the other theory suggest that luciferins may have evolved to overcome the deadly effects of Reactive Oxygen Species (ROS)
Chemical Reactions:
Bioluminescence occurs as a result of chemical reaction involving three main components: luciferin, the enzyme luciferase and oxygen. Most bioluminescent creatures have these components naturally present while some organism obtain luciferin from the food they eat. Luciferin is the protein-like, light-producing substance, while the enzyme luciferase is found in all the living organisms and catalyzes different chemical reactions and the third component named oxygen is familiar to us! As soon as the oxygen is available, luciferase acts on luciferin, breaks it down and released energy the energy released takes the form of visible light. This is the most generalized form of a reaction. Many organisms require more components to fulfill the reaction. For example, fireflies need Magnesium and ATP while giving off Carbon dioxide as the waste product. The Jelly fish, Aequorea victoria, possesses another protein called photoprotein instead of luciferin. This protein produces short pulses of light as compared to the emission of continuous light by luciferin.
Bioluminescent Organisms:
Almost 80% of the bioluminescent creatures are present in the oceans, including the surface water and in the depth. Here are some of the organism which can emit light.
Jelly Fishes:
More than half of the jelly fish species produce light, mainly to protect themselves from the predators. The most common jelly fish, Aequorea victoria, produces green light around the rim of its bell. The main compound involved is the Green Fluorescent Protein (GFP). The gene encoding this protein has been extracted, grown in lab and is also inserted in some other organisms.
Squid:
Among the bioluminescent organisms, squids are most important. One of them, named as Bobtail squid uses its ability of bioluminescence in a complex way. It has small cavities on the underside of its body which are home to the bioluminescent bacteria. At night, the amount of moon light reaching the body of squid causes these cavities to expand and relax, thus giving out light.
Lantern fish:
These are among the most numerous fishes present in the sea. They have unique light generating organs named photophores, mainly present on the head. The photophores consist of lenses which help to focus the light rays. Recent studies show that lantern fishes are diversifying more rapidly than other bioluminescent organisms in the sea.
Fireflies:
The most common terrestrial creatures that exhibit bioluminescence are fireflies. The reaction takes place in their abdomen and they emit light which lies in the yellow, green and pale red part of spectrum.
Fungi:
Over 70 species of fungi have been known to emit light. Mainly their fruiting body has shown to glow in the dark, but the mycelium may also be bright, lighting up the space where they grow.
Bacteria:
Some bacteria also show the property of bioluminescence, mainly present in the sea or even in freshwater. They may be present as free living or in association with other organisms. In case of symbiosis, the host organism provide them with food and shelter and in turn uses their light-emitting property for camouflage, prey or mate attraction.
Uses:
Different organisms use the ability of bioluminescence for different purposes. However, in some cases the function is unknown, as with some families of earthworm, which produce light when they move.
1-The most important use of bioluminescence is to keep away from the predators. For example a Vampire Squid emit a blast of light to confuse its predator. Glow Worms emit light at night and let the predators think that they are toxic.
2-The Anglerfish has a special fleshy growth on the top of its head which lights up in the dark and help to find food. The Dragon Fish has an advantage for finding food. It emit red light while many small fishes are only able to detect blue light. In this way the small fishes are unable to notice the dragon fish and it can prey on them easily.
3-It can also help some species to reproduce. For example the glow of some mushrooms at night attracts many insects. They carry their spores to the other individuals and help them in reproduction.
4-Fireflies use bioluminescence to attract mates.
Future Prospects:
Bioluminescence is mainly used by the organisms as a matter of protection, but their ability is being used by humans in the areas of genetic engineering. For example the firefly luciferase activity was studied by injecting it in tobacco plant. Most experiments are being designed for the treatment of cancer which involves the bioluminescent activated destruction. Optogenetics (use of light to control the growth of cells in a living tissue) and Biophoton (a photon emitted from living organism and lies in the visible or ultraviolet region) are also on the way. In short, the future of bioluminescence is very bright!
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