BBC science program The Infinite Monkey Cage interviewed a man who had gone 5km deep in a bathysphere. Even in the pitch back of the deep, he found light coming from the bio-luminescence of tiny bacteria. This is surprisingly common in the deep ocean, with the most common color being blue as this light penetrates farthest in the water.
Illustration of an Angler Fish
The fearsome angler fish uses a bioluminescent lure on top of its head to attract prey. Most squids have bioluminescence at various parts of their body. Often, the squid uses this to match the light coming from above so that predators underneath can’t see it’s outline. Some squids also use luminescent material the way an octopus uses ink. When attacked, they release a jet of luminescent chemicals confusing their attacker while the squid escapes.
But its not just animals, there are also bioluminescent mushrooms such as the Omphalodotus Nidiformis.
Omphalodotus Nidiformis with the lights on and off
The key to all this is a class of molecules called luciferin which react with oxygen to create light. The same kind of luciferin sometimes occurs in many different types of animals. For example, corals, crustaceans, mollusks, comb jellies and protozoa all use the molecule coelenterazine. Some species make their own luciferin while others rely on bacteria living inside them to make it for them.
In biological research, the bio-luminescence is commonly used to tag genes. On a visit to the National Center for Biological Sciences in Bangalore, a researcher showed me some fruit flies she was working on which were tagged with a gene that made them glow in the dark. The idea is that the geneticist changes one set of genes and tags it with a marker gene. So when the animal grows up and the modified genes become active, the marker gene also gets activated (causing the fly to glow). This way, the researcher knows easily in which animals, the modified gene has got activated. One of the most common marker genes is the one that encodes the green bio-luminescence in jellyfish.
Luciferin from a small crustacean called the sea-firefly was used in World War 2 by the Japanese Military as a source of light during secret operations.
Trials on mice for a new treatment for cancer are underway where cells are changes so that when a cell turns cancerous, its starts producing bio-luminescent luciferin to create light. A photosensitizing agent is added which makes these cells very vulnerable to the light causing them to die without harming nearby tissue.