Bioluminescence: Light Emission by Organisms

• Bioluminescence is the production and emission of light by a living organism
• It is a type of chemiluminescence, which is simply the production of light by a chemical reaction

Occurrence

• Bioluminescence occurs widely in marine vertebrates and invertebrates, as well as in some fungi, microorganisms and terrestrial invertebrates such as fireflies
• Most marine bioluminescence is produced by bacteria, dinoflagellates, crustaceans, molluscs, fish, and cnidarians

Mechanism

• Bioluminescence arises from enzyme-catalyzed chemiluminescence reactions
• These reactions involve a light-emitting molecule (a luciferin) and a luciferase enzyme
• Luciferins are a class of light-emitting molecules which undergo oxidation
• Luciferases are enzymes that catalyze the reaction of luciferins
• The general reaction involves luciferin + O2 --(luciferase)--> oxyluciferin + light
• ATP, cofactors such as calcium, or other proteins may sometimes be required
• Different organisms use different luciferin-luciferase systems
• Light is emitted when the luciferin molecule returns to its ground state
• The color of light produced depends on the luciferin, luciferase and other factors such as pH and ions

Luciferins

• The most common luciferin is coelenterazine, found in many aquatic organisms
• Firefly luciferin is common among insects
• Dinoflagellate luciferin is found in dinoflagellates
• Bacterial luciferin is found in bacteria

Luciferases

• Luciferases are the enzymes that catalyze the oxidation of luciferins
• They are specific to their luciferin substrate
• Luciferases differ in structure among organisms, even when using the same luciferin

Bacterial Bioluminescence

• Several marine bacteria species exhibit bioluminescence
• Common genera include Vibrio, Photobacterium, and Shewanella
• The lux operon regulates bacterial bioluminescence
• The lux operon includes genes for luciferase (luxAB), fatty acid reductase complex (luxCDE), and a regulatory protein (luxR)
• Bioluminescence is often expressed at high cell densities through quorum sensing

Bioluminescence in Dinoflagellates

• Dinoflagellates are a type of plankton
• They are a major source of bioluminescence in surface waters
• Bioluminescence is controlled by a circadian clock
• Light emission occurs upon mechanical stimulation
• Luciferin is bound to a luciferin-binding protein
• At pH 8, luciferin is released and reacts with luciferase

Bioluminescence in Fish

• Many deep-sea fish have bioluminescent organs called photophores
• Photophores contain bioluminescent bacteria or produce light themselves
• Light production may be controlled by hormones or nerves
• Bioluminescence help fish attract prey, escape predators, or communicate

Bioluminescence in Insects

• Fireflies are the most well-known bioluminescent insects
• Light is produced in the abdomen
• Luciferin, luciferase, ATP, magnesium ions, and oxygen are required for the reaction
• The color of light varies among species
• Bioluminescence functions in mate attraction

Fungi Bioluminescence

• Some fungal species exhibit bioluminescence in their mycelia or fruiting bodies
• Luciferin is hispidin
• Bioluminescence may attract insects to help disperse spores

Functions of Bioluminescence

• Camouflage: Counterillumination to avoid detection by predators
• Mate attraction: To signal potential mates
• Predation: To lure prey
• Defense: Startling predators or misdirecting them
• Communication: Signaling between individuals
• Illumination: Providing light in the deep sea

Applications of Bioluminescence

• Scientific research: Reporter gene assays, in vivo imaging
• Environmental monitoring: Detecting pollution and toxins
• Medical diagnostics: Detecting pathogens and diseases
• Commercial applications: Novel lighting, tourism

Bioluminescence is the production and emission of light by a living organism, a type of chemiluminescence. It occurs widely in marine and terrestrial life, with bacteria, dinoflagellates, and fireflies being common examples. The process involves luciferins, luciferases, and sometimes ATP or other cofactors.