In Figure 1b, green-fluorescent protein from the hydromedusa Aequorea is being excited by blue light.
The molecules are not stable in this excited state and as they return to their ground state, the energy is almost immediately re-emitted in the form of a longer wavelength photon. Excitation occurs as the material is being hit by incident light of particular wavelengths. Bioluminescence can be considered a subset of chemiluminescence: light produced when such a chemical reaction occurs within a living organism. Excitation and the resultant light production come as the result of a chemical reaction, as in glow-sticks (Figure 1a). Three involve excitation of a material in such a way that it emits light:
There are many terms describing optical phenomena which may be confused with bioluminescence. All of the photos below show something other than bioluminescence. One way to describe it is to describe what it is not. In this way selection acts primarily through the genes coding for the proteins, specifically the luciferase or photoprotein. Part of this convergence may be explained by dietary links, where an organism receives its luciferin from its diet, but evolves its own enzyme and photocyte system to control the emission of light. Most phyla use one of four light-emitting substrates, with coelenterazine being the most widely distributed. Despite this huge diversity of luminous phyla, most of which are thought to have evolved luminescence independently, there is low diversity of luciferins in the sea. In fact, in this region, it has been estimated that 90% of the fish and crustacean species are capable of making light, and the numbers for jellies are even higher.Īlthough it is sometimes assumed that these animals get their luminescence from bacteria, the surprising truth is that nearly all of them (with some notable exceptions) produce at least one of the chemicals required to glow. This is especially true in the dimly-lit midwater zone (100-1000 meters deep) where biologically produced light can outshine what light has filtered down from the surface. The Diversity of Light-Producing Marine OrganismsĪlthough there are some well-known examples of terrestrial bioluminescence, such as fireflies and "foxfire" (fungus glowing on wood), the vast majority of luminous organisms make their home in the ocean.
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