Bioluminescence, the emission of visible light by living organisms, is known to occur in many distantly related phyla, including the fungi. Although written observations of this phenomenon in fungal species are reported to date as far back as Aristotle (384-322 BC) and Pliny the Elder (23-79 AD), and detailed studies have been conducted with many other organisms (i.e., insects, fish, dinoflagellates, bacteria), we know surprisingly little about the nature of the chemical reactions responsible for fungal bioluminescence, or even why this phenomenon occurs in fungal species.
Like all other organisms in which it occurs, bioluminescence in fungi is an oxygen-dependent reaction involving substrates generically termed luciferans, which is catalyzed by one or more of an assortment of unrelated enzymes referred to as luciferases. In fungi, both the luciferans and luciferases involved remain largely unidentified. During the luciferan-luciferase reaction, unstable chemical intermediates are produced. As these intermediates decompose excess energy is released as light emission, causing the tissues in which this reaction occurs to glow or luminesce. Although the older literature reports some fungal species as producing white or blue light, all recent studies and observations indicate that bioluminescent fungi emit a greenish light with a maximum around 520-530 nm.
Fungal luminescence has been hypothesized to attract invertebrates that aid in spore dispersal, which may be a suitable explanation for those species with luminescent basidiomes, but not for those in which only the mycelium emits light. Additional hypotheses include the attraction of predators of mycetophagous invertebrates, and even the function of emitted light as a warning to nocturnal heterotrophs that might consume the fungus or its substrate, similar to warning colorations observed in other organisms.
It is also possible that bioluminescence in these fungi is nothing more than the by-product of some other metabolic process. Because the reaction is oxygen-dependent, it has been hypothesized that bioluminescence may have evolved as a method to consume excess oxygen produced in the cells of organisms during other metabolic processes (i.e., an antioxidant).