ABSTRACT
Bioluminescence has evolved independently many times, so that the responsible genes are unrelated in bacteria, unicellular algae, coelenterates, beetles, fishes, and others. Chemically, all involve exergonic reactions of molecular oxygen with different substrates (luciferins) and enzymes (luciferases), resulting in photons of visible light (~50 kcal). Several factors determine the color of the emissions, such as the amino acid sequence of the luciferase (in beetles) or the presence of accessory proteins, notably GFP, discovered in coelenterates and now used as a reporter of gene expression and a cellular marker. The mechanisms used to control the intensity and kinetics of luminescence, often emitted as flashes, also vary. Bioluminescence is credited with the discovery of how many bacteria, luminous or not, sense their density and regulate specific genes by chemical communication, as in the fascinating example of symbiosis between luminous bacteria and a squid.