Bioluminescence in the Living World

Bioluminescence is a process in which living organisms produce light. The light is used for communication, for attracting prey or other creatures, or for defense. Bioluminescent organisms produce a cold light that is accompanied by very little heat. A wide variety of organisms produce bioluminescence, including some kinds of animals, fungi, protists and bacteria. Most bioluminescent organisms - but not all of them - live in the ocean.

Bioluminescent organisms contain a pigment molecule called luciferin. An enzyme known as luciferase causes the luciferin to react with oxygen to produce light. ATP is required in this process. There are several kinds of luciferin. The name comes from the Latin word “lucifer”, which means “light bearer.” Different organisms may produce different colors during bioluminescence, including green, blue, yellow and red.

Many bioluminescent organisms are found in deep, dark ocean water far from sunlight. In fact, scientists think that about ninety percent of animals in water from 200 meters to 1000 meters deep are bioluminescent. Marine organisms usually produce light with a blue-green color, which is the color of light that travels best under water. The eyes of underwater animals detect blue light better than light of other colors.

The flashlight fish is one deep-water inhabitant that produces light. The light-producing organ of the fish (called a photophore) is located beneath each of its eyes. The light is actually produced by bioluminescent bacteria that live in the photophores. The fish can flash its light on and off by covering the organ with a flap of skin which acts somewhat like an eyelid. The video below shows the flashlight fish when illuminated by a video light and then when the video light is turned off.

The deep sea angler fish has a bioluminescent lure attached to a moveable spine extending from its head. As in the flashlight fish, the bioluminescence is produced by bacteria. When the angler fish needs to eat, it lowers its “fishing rod” and flicks the glowing end to attract prey. The rest of the fish is hard to see in the darkness. The angler fish grabs hold of its prey with its strong jaws. Since the stomach of the angler fish can expand dramatically, it is able to eat large prey animals when they are available.

The stoplight loosejaw fish and some related fishes produce a red light, which allows them to see in the ocean depths. The animals that they feed on cannot see red light, allowing the loosejaw to be an invisible predator.

The firefly squid is a tiny creature with a big light display. It reaches a length of only three inches but its entire body, including the tentacles, is covered by photophores that produce blue light. The photophores may all emit light at the same time or the light may be released non-synchronously in a pattern. The complex light patterns are believed to have several functions. They may be a signal to rivals and mates and may confuse predators.

Some deep sea squids can release a bioluminescent mucus to confuse predators.

Noctiluca scintillans, also known as sea sparkle, is a bioluminescent dinoflagellate. It lives near the ocean surface and feeds on plankton. The body of Noctiluca scintillans consists of just one cell, but the cell is large compared to the bodies of other unicellular organisms. Organelles inside the cell produce the bioluminescence. The light is produced when the dinoflagellates are mechanically stimulated, such as by the actions of nearby predators. One theory is that the bioluminescence has developed in order to distract the predators.

Probably the best known example of land organisms that exhibit bioluminescence is the firefly, also called a lightning bug. Fireflies are nocturnal beetles. There are about 2000 different species of fireflies. Their light-producing organs are located at the end of their bodies on the bottom of their abdomens.

Fireflies generally release their light in a series of flashes. The flashes help fireflies find mates, and may also protect the insect by warning potential predators that the fireflies taste bad. In addition, scientists have discovered that the flashes may be used to attract prey. Certain female fireflies can imitate the light flash pattern of the female of another firefly species. The male of the other species is attracted by the mating signal and is eaten by the attracting female.

It’s not known for certain how the firefly is able to turn its light on and off, but it’s thought that the firefly is able to control how much oxygen is available to react inside the light organ. When oxygen is available, the light is turned on. When oxygen is unavailable, the light is turned off.

Oxygen availability may be determined by the presence of nitric oxide. According to this theory, when nitric oxide is present, it inhibits mitochondria in the light organs from using oxygen. The oxygen is therefore available for light production. When nitric oxide is absent, the mitochondria are no longer inhibited and use oxygen for cellular respiration. The oxygen is therefore unavailable for light production.

The term “glow worm” is used to refer to the bioluminescent, worm-like larvae of certain beetles, or to adult bioluminescent beetles that have a worm-like appearance.

Certain fungi produce light as they digest wood, a phenomenon sometimes known as foxfire. In some species, only the cap or the gills of the mushroom release light, while in other species only the stem glows. Sometimes only the mycelium that produces the mushroom is bioluminescent. The light is continually being released, but shows up best in the dark. One theory to account for the mushroom glow is that the fungi are attracting animals to aid in spore dispersal.

There are only almost no bioluminescent organisms in fresh water. So far only some insect larvae and one kind of limpet have been found to release light in fresh water.

Bioluminescence plays a very important role in the lives of many creatures, but no bioluminescent plant, amphibian, reptile, bird or mammal has yet been discovered. However, scientists are investigating how luciferase systems can benefit humans. These systems are already being used in some technologies, and researchers are investigating other possible uses.