Many naturally occurring organisms are bioluminescent, including insects, fungi, bacteria, jellyfish and dinoflagellates.  The mechanisms of light production appear to have evolved independently, several times.  Bioluminescence has various useful functions, e.g. fireflies flash to attract mates, glowing fungus gnats use light to lure prey into webs, and some marine organisms scare off predators with a flash of light.  Bioluminescent fungi may benefit from attracting insects, which aid in spore dispersal, yet it is often the vegetative mycelium that glows.  It is still a mystery why certain species glow.

Chemistry of bioluminescence

Luciferase is the enzyme that catalyses the oxidation of luciferin, the basic substrate in bioluminescent reactions.

The bioluminescent jellyfish, Aequorea victoria produces flashes of light, in response to mechanical shock.  The luminescent reaction is regulated by a photoprotein called aequorin, which binds Ca2+ and results in a flash of light.   Aequorin is a useful molecular tool for studying calcium-mediated responses.  Green Fluorescent Protein (GFP) is a fluorescent protein, involved in the production of light in Aequorea.  GFP is now extensively used in scientific research as a recombinant fluorescent probe.  GFP has been expressed in many organisms, including the fungus Aspergillus nidulans, allowing us to visualise specific proteins and organelles, e.g. nuclei, mitochondria and vacuolar network in living cells.

Imaging luminescence

Most of the photographs of low-medium level brightness were taken using a "luminograph" photon counting camera attached to a dark-box which contains tungsten lamps for "bright field" conditions.  The camera is controlled by a computer with imaging software to acquire images.  The output is grayscale 256 colour .TIF file, 500x360 pixels.  A Sony PC3 Digital Video camcorder was used to capture animations of dinoflagellates at night and the blue colour is the true colour from the camera.  Infrared illumination was used to capture movies of the firefly.