The term bioluminescence refers to any source of light generated by living organisms. For the purposes of this article, the light in question is the visible spectrum, or wavelengths from 400 to 800 nm. Most people are familiar with animal species capable of generating light, especially fireflies and certain aquatic species like deep sea fish. Scientists think the main functions of bioluminescence are attracting mates and prey as well as confusing predators with a sudden flash of light. As it turns out, however, the animal kingdom is not the only domain of bioluminescent organisms. Bacteria algae, and certain fungi are capable of bioluminescence as well.
In the realm of fungi, some species emit a faint glow, visible on dark, moonless nights. The fungal species most familar to science is the foxfire, sometimes called will o’ the wisp or fairy fire. This particular fungus is a saprophyte that grows on rotting tree bark. It is particularly noticeable in the fall as deciduous trees shed their leaves.
Light generating reactions
Although many variations exist, photoemission tends to follow this basic pattern:
Luciferin + Oxygen + ATP -> Oxyluciferin + ADP + Pi + Water + Light
In almost all bioluminescent organisms, the generation of light depends on an enzyme called luciferase.
This enzyme catalyzes a series of reactions which utilize a molecular substrate (luciferin) in an unoxidized form, a source of oxygen, and, in most cases, adenosine triphosphate (ATP). ATP supplies the free energy that drives the oxidation reaction forward. The enzyme hydrolyzes ATP, using this energy to combine oxygen with luciferin. When molecular oxygen binds to this substrate, photons are released. Some bioluminescent jellyfish contain a protein called aqueorin, which emits light when calcium ions bind to it.
Scientists are unsure as to why some species of fungus are bioluminescent. One possibility is that the faint glow attracts insects, which proceed to disperse fungal spores. Thus, in the case of fungi bioluminescence may serve as a form of reproductive assistance.
Other bioluminescent fungi
Over 40 species of bioluminescent fungi have been identified, mostly in tropical regions of the world. The main reason for this geographic distribution may be the abundant insect species in the tropics. Attracting a wider variety of insects may, in turn, lead to more effective spore dispersal. Scattering of spores remains the most plausible theory for fungal bioluminescence; after all, most fungi are seldom eaten and spore formation itself usually occurs asexually. The debate continues…
