Bioluminescence is the production and emission of light by a living organism. Bioluminescence is a naturally occurring form of chemiluminescence where energy is released by a chemical reaction in the form of light emission. Some creatures produce the chemicals luciferin (a pigment) and luciferase (an enzyme). The luceferin reacts with oxygen to create light. The luciferase acts as a catalyst to speed up the reaction, which is sometimes mediated by cofactors such as calcium ions or ATP. The chemical reaction can occur either inside or outside the cell. In bacteria, the expression of genes related to bioluminescence is controlled by an operon called the Lux operon. Based on its diversity and phylogenetic distribution, it is estimated that bioluminescence has arisen independently as many as 30 times in the course of evolution.
The Vibrionaceae are a family of Proteobacteria, given their own order. Most bioluminescent bacteria belong to this family, and are typically found as symbiotes of deep-sea animals. Bioluminescence is most common in living creatures that has an habitat in pitch black darkness. Eerie white to blue-green bioluminescent bacteria and fungi is seen in the images of a cave in Russia.
Amazing: Bioluminescent Organisms Light Up Russian Caves