Bioluminescence is a specific form of chemiluminescence in which the chemical energy that is produced in a chemical reaction is converted into radiant energy. In bioluminescence the reaction originates in a wide variety of living organisms, including a small number of plants. It should not be confused with fluorescence or phosphorescence, both of which do not involve a chemical reaction.
In either of the former cases the energy from a source of light, not from a chemical reaction, is basically absorbed and then re-emitted in some form of another photon. The chemical reactions that lead to bioluminescence release energy in the form of light.
Unlike the light bulb, in which electrical energy is converted into light, with some of this energy lost in the form of heat, a bioluminescent reaction is 100 percent efficient and converts all the emitted energy into light. Because there is no heat released, bioluminescence is also known as "cold light."
Species and Habitats
Bioluminescence is primarily marine in nature and is the only source of light in the deep ocean, which is the largest habitable biome of the earth. The phenomenon rarely occurs in any source of fresh water. Bioluminescent organisms include ctenophores, annelid worms, mollusks, insects, and fish.
|Species and Habitats|
There are several bioluminescent fungi that are not marine in nature, occurring primarily in the tropics. These fungi appear in different colors. The most common is Panellus stiptucus,which is a small decay fungus that is mostly restricted to North America. The jack-o’-lantern mushroom (Omphalotus olearius) glows brightly, especially when fresh. A few Armillaria species are also reported to glow mildly. No luminous tree or plant is known, however.
Mechanisms of Bioluminescence
Bioluminescence occurs only when two different species are in contact and, almost exclusively, when oxygen is present. The two species are luciferin, which produces the light, and luciferase, a protein that triggers and catalyzes the reaction. The mechanism involves the loss of two electrons, also known as oxidation, by luciferin, a process achieved only through the intervention of luciferase to yield oxyluciferin.
Occasionally luciferin, luciferase, and a cofactor such as oxygen are bound together in a single moiety called photoprotein, which leads to light formation upon contact with a positively charged species, such as the calcium cation. The mechanism appears to involve a peroxide decomposition with free radical intervention.
Dinoflagellates known as Pyrrhophyta, or fire plants, are the most common sources of bioluminescence at the surface of the ocean. They are a group of marine algae that produce light upon mechanical, chemical, or temperature changes. The phenomenon was first observed in the genus Noctiluca in the nineteenth century and has since been observed to occur within other species.
Generally, three types of stimuli can cause bioluminescence in dinoflagellates: mechanical, chemical, and temperature stimulation.
For example, as a copepod approaches the dinoflagellate, agitation of the seawater stimulates light flashes which a small fish, the secondary predator, uses to pinpoint the position of the copepod and eventually consume it. It appears that the mechanical stimulation deforms the cell membrane to create a short flash as little as one one-hundredth of a second.
Dinoflagellate luciferin is thought to derive from the similarly structured chlorophyll, which is found in most plants. The molecule is protected from luciferase at slightly basic medium by a luciferin-binding protein. However, once the acidity increases, the free luciferin reacts, and light is emitted.
The light produced by a single dinoflagellate is only six to eight photons in energy, and the flashing may last only one-tenth of a second. Larger organisms, such as jellyfish, provide flashes that may last up to tens of seconds. Temperature lowering in some dinoflagellate species also creates bioluminescence.
Purpose and Applications
The disappearance of the flash, once oxygen is consumed, has suggested that the bioluminescent reaction was originally used to remove toxic oxygen from primitive types of bacteria that developed at a time when oxygen was not available.
Bioluminescence has also played a crucial role in the direct studies of several cellular and biochemical processes, such as in the formation of ultimate carcinogens from benzoapyrene. The phenomenon has served scientists in many ways.
Calcium levels are monitored via the jellyfish biochemical system, adenosine triphosphate (ATP) measurements are achieved through the firefly, and the gene activity of organisms can be detected by splicing known bioluminescent proteins.