- Several species of bacteria can emit light, a process called bioluminescence.
- Most bioluminescent bacteria have been classified in the genera Photobacterium and Vibrio, but a few species are found also in Shewanella, a genus of primarily marine bacteria, and in Photorhabdus, a genus of terrestrial bacteria.
- Members of the genus Vibrio (e.g., V. fischeri) emit light only as free-living organisms whereas members of the Photobacterium, e.g., P. phosphoreum function also as symbionts in the light organs of fish.
- Light emission is usually observed only in dense cultures.
- The biochemical mechanism of light emission by bacteria is different from the one in fireflies or in those luminous fish that have photophores and produce their own light.
- In addition to the enzyme called bacterial luciferase, FMNH2, 02, and a long-chain aliphatic aldehyde such as hexadecanal (palmitaldehyde) are required.
- Bacterial bioluminescence is strictly 02-dependent.
- Substrate oxidation via the tricarboxylic acid cycle yields NADH that is used to reduce FMN.
- Bacterial luciferase then forms a complex with all the components involved.
- An excited state of this complex decays and, coupled to oxidation reactions, light is emitted.
- Bacterial bioluminescence is a very interesting process. Its advantage for those organisms that live in symbiosis with fish is apparent; the advantage is less apparent for free-living bacteria.
- Most bioluminescent bacteria inhabit the marine environment and some species colonize specialized light organs of certain marine fishes and squids, producing light that the animal uses for signaling, avoiding predators, and attracting prey.
- When living symbiotically in light organs of fish and squids, or saprophytically, for example, on the skin of a dead fish or parasitically in the body of a crustacean, luminous bacteria can be recognized by the light they produce.