Bioluminescence has inspired myths and folklore throughout the centuries. The oldest surviving written text on bioluminescence comes from Aristotle – in De Anima Aristotle wrote in 350 BC, “not everything is visible in light, but only the color proper to each thing, for some things are not seen in the light but bring about perception in the dark, e.g. those things which appear fiery and shining (and there is no one name for them), such as fungus, horn, the heads, scales and eyes of fish, but in none of these the proper color is seen”. But what is bioluminescence and how did it come to be?

What Is Bioluminescence?

Bioluminescent animals can glow in complete darkness. The most commonly seen occurrence of bioluminescence is when we see fireflies flashing green at night. However, many other organisms are also capable of making their own light, including fish, algae, bacteria and even viruses, both on land and under the sea. Bioluminescence is the production of light by a living organism, due to two chemicals reacting with each other, yielding a high energy compound that releases energy in the form of light.

Bioluminescence is the result of a chemical process named “chemiluminescence”, which is when light is produced due to a chemical reaction. Two chemicals interact with each other, yielding an unstable high energy compound. This unstable energy is then released as light to reach a stable state. When this light is produced by a living organism, we call it “bioluminescence”.

The Chemical Reaction

The two chemicals reacting with each other in bioluminescence are an organic compound called Luciferin, and an enzyme called Luciferase. Luciferin, when combined with oxygen, becomes oxidized in an enzymatic reaction that is catalyzed by Luciferase. This reaction yields oxyluciferin, and light is produced. The presence of a molecule called ATP (Adenosine Triphosphate) also seems vital to the production of light. Most bioluminescent organisms produce light in this way, although the presence of the Luciferase enzyme is not always necessary to produce light. Some reactions use photo-proteins to create light.

Photo-proteins are a variant of the Luciferase enzyme, and are able to produce light when combined with an oxidizing agent. This process is efficient and 100 percent of the chemical energy becomes converted into light. Light produced by bioluminescence is known as “cold light” as very little heat is produced during the chemical reaction.

Some organisms acquire luciferin from their food or a symbiotic relationship with other organisms, although most bioluminescent organisms produce luciferin in their own bodies. The type of luciferin will determine the color of the light produced, with some animals – like squids – being able to produce multiple light colors.

The colors produced by bioluminescence extend across the visible color spectrum. In the ocean, blue light is the most commonly produced color in the deep sea, as it travels the farthest through seawater. Green is the next most common color, found in more coastal species, possibly as the more turbid water scatters blue light and favors longer wavelengths. Pinks and purples, yellow, orange and red rarely occur and their functions remain uncertain.

What Is The Role Of Bioluminescence?

Within the ocean, bioluminescence plays a critical role, especially in deep sea organisms. These organisms produce light which serves several purposes in their dark, sunless habitats.

Bioluminescence can be used to communicate with other animals of the same species, oftentimes to attract mates. It can also be used as a defense mechanism. Certain species of squids, such as the vampire squid, can eject a bioluminescent mucus (instead of ink) which allows the squid to escape from predators. Brittle sea stars detach their glowing arms when hunted to distract their predators.

In the deep sea, bioluminescence is often used as lures to attract prey, or to search for prey in the dark. Stoplight Loosejaws emit a red light, and the deepest sea animals and other fish can only see blue light. This means that the Loosejaw is able to use the red light to successfully search for prey in the dark.

The largest vertebrates able to produce light were discovered off the coast of New Zealand, where three shark species were found to be bioluminescent. The kitefin shark is able to grow to nearly 6 feet in length, making it the largest known bioluminescent vertebrate (giant squids grow larger than this and are able to produce light, but are not vertebrates). According to the scientists studying these sharks, they use their bioluminescence to “disappear”, as the faint light they emit renders them invisible against the light filtering in from above. This protects them from predators swimming below them, as well as making it easier for them to hunt.

Bioluminescence also has an important use in the laboratory. Observing Crystal jellyfish resulted in a major scientific breakthrough when researchers studied their glowing abilities. These jellyfish contain a protein called green fluorescent protein (GFP) which contains about 250 different amino acids which grow green when in contact with UV light. This protein has been used to create “green mice” which glow an eerie green when hit by UV light, by inserting the GFP gene into the mice. This protein is now being widely used as a biological marker that helps scientists find and study genes.

An Evolutionary Miracle

Light production by animals and plants can be considered an evolutionary miracle. Within the deep sea, it is almost understandable that marine organisms would have evolved this ability due to the lack of light. However, on land, insects have not only evolved the ability to glow, but also to turn the light on and off. They are able to convert nearly 100% of their energy into light without wasting any heat (compared to man-made lights that convert 10% of electric energy into light and 90% into heat). Bioluminescence is thus the most efficient system of light emission known to man. The significant molecule that is involved in bioluminescence, ATP, is present in all living organisms, including humans. This implies that there is a possibility of activating bioluminescence in other living creatures, for use in medical research.