Some red tides, foxfire, and fireflies are examples of remarkable biological chemical reactions. Bioluminescence is light produced within a living organism, usually by the chemical reaction of luciferin with luciferase. Named for Lucifer, the light-bearer, the compounds produce an eerie yet fascinating glow.
Fireflies and certain fungi show bioluminescence on land, while some sharks, octopuses, jellies, squids, microscopic organisms, and the vast majority of the inhabitants of the ocean depths show bioluminescence in the sea. Their light can be a result of microscopic organisms held within the tissues of a larger host, or it can be produced by the creature itself, in special cells called photophores.
In the photophore organs of bioluminescent organisms, or within tiny organisms living within a larger creature or free-living, luciferin is converted to oxyluciferin. The process is called oxidation, and can be thought of as a controlled burning or rusting. The luciferin, once it is changed to oxyluciferin, cannot produce more light, any more than ashes can produce fire.
Luciferase is a catalyst in the oxidation process. It promotes the production of light, while remaining essentially unchanged. The organism must synthesize more luciferin though, or ingest it.
Phosphorescence, florescence, chemiluminescence, and bioluminescence
Not every glow is bioluminescence. Phosphorescence is the glow emitted when something absorbs light energy, and then later reemits it. Some diamonds, though not all, are phosphorescent, and glow after they are removed from light.
Florescence is the property of immediately emitting absorbed energy, though at a less energetic wavelength than was absorbed. Florescent lights rely on phosphors that absorb ultraviolet light and emit visible light. Chemiluminescence is light emitted as a result of a chemical reaction, like the glowsticks seen at parties. which light up when the substances within them are mixed to produce a chemical reaction.
Bioluminescence is the form of chemiluminescence seen in organisms. It occurs when one of the types of luciferin is oxidized within an organism, with the reaction speeded up by luciferase. The reaction produces light, but relatively little heat.
Luciferin occurs within fireflies and glowworms, certain snails, bacteria that live within some cephalopods like the Hawaiian bobtail squid, fungi, algae and other tiny marine organisms, jellies, sea worms, earthworms, fish, and some shrimp. There are glowing sea spiders, and centipedes and millipedes that glow.
Purpose of Bioluminescence
Some organisms use bioluminescence to advertise. Fireflies, for example, announce their species and their gender with their flashing or steady glow. The ostracods, tiny seed shrimp, have an elaborately lit courtship display that brings together partners of the correct species. Fireworms use luciferin for brilliant mating displays in and near the Bahamas.
Other organisms use a tuned glow to hide. Counterillumination is used by some squids to illuminate their undersides so they are perfectly matched to the changing ocean background. Their bioluminescence makes them essentially invisible to predators.
Some organisms hunt by bioluminescence. Most deep water organisms see in a band that includes blue light. They cannot see red light, which does not travel far through water anyway. The malacosteidae, though, the Loosejaws, transmit red light.
The blue light manufactured in their photophores is immediately absorbed by a florescent pigment, and reemitted as red light. Then a filter restricts the light to a particular part of the red spectrum. This way, the fish is able to spotlight its prey with a light they cannot see, and take them unaware. Of course, the malacosteidae can do this because they also evolved retinas that can see red light.
Light can be a lure, as well. The dragonfish of the ocean depths has a long lure attached near its sharp-fanged mouth. It flashes and waves this photophore-tipped lure to attract passing food-fish. When they come too close, it snaps them up, in a maneuver beautifully adapted to its circumstances. Foxfire, bioluminescence produced by fungi in rotting wood, may attract insects to spread fungal spores.
Bioluminescence can also be a warning. The Jack-O-Lantern Mushroom is poisonous. It is orange in color, and appears in fall on rotting wood. By daylight it is orange, but to a dark-adapted eye the gills of the underside emit an ominous blue-green glow. In California, the mushroom may appear right around Halloween. Similar species are found in the eastern U.S. and in Japan. The evolutionary advantage of this bioluminescence seems to be that it warns animals not to eat it, thus preserving the spores to produce the nest generation.
Scientific uses of bioluminescence
Though bioluminescence appears supernatural, science uses it in genetic engineering. Adding genes that produce a glow to a snip of the genetic code allows biotech researchers to easily see if the sequence they have spliced into an organism’s DNA has been successfully integrated.
Researchers also use Vibrio, a genus of bacteria mostly found in salt water. Some Vibrio are deadly, while others have bioluminescence. Scientists use the glow of some genera of vibrio to study quorum sensing and related ideas. Vibrio communicate with one another, deciding when they are gathered in enough numbers for it to be worthwhile to turn on their bioluminescence. Quorum sensing is a fascinating new field that may help fight the problem of antibiotic resistance in medicine.
Bioluminescence is useful and beautiful. It serves as a warning and a guide, while it lures the curious to beaches and forests where they can rediscover the magic of the natural world.