BIOLUMINISCENCE: LIGHT THAT LIGHTS LIFE

BIOLUMINISCENCE: LIGHT THAT LIGHTS LIFE

Nikunja Bihari Sahu

If you happen to come across a Fire-fly flashing its light in a Summer night, you may be assuming it as a meaningless display. However, it is a signal to others to communicate an important message. The phenomenon, called Bioluminescence, is the production and emission of light by living organisms by Chemical reaction which is widely seen in nature. Animals often use the technique to hunt for preys, defend against predators, find mates, and execute other vital activities. Light produced in this way is a survival technique, and hence, means life to many animals around us!

PROTECTION AGAINST ENEMIES

Often animals use a strong flash of light to scare off an impending predator. The bright signal can startle and distract the predator and cause confusion about the location of its target. From small Copepods to the larger Vampire Squids, this tactic can be very useful in the deep-sea. The ‘Green Bomber’ worm (Swima bombiviridis) and four other similar worm species from the polychaeta family that live near the bottom of the sea (the species discovered recently in 2009) release a bioluminescent bomb from their body when in danger.

Many species of Squids flash light to startle predators such as large fishes like Mackerel or Tuna. Like many deep-sea Squids, the Vampire Squid lacks ink sacs. (Squid that live near the ocean surface eject dark ink into water to blind their predators to darkness.). Instead, it ejects a sticky bioluminescent jelly, which can confuse and delay the movement of predators allowing the Squid to have a safe passage.

Some marine species use a technique called ‘Counter-illumination’ to protect them. Many predators, such as Sharks, generally hunt from below. They look above, where the sunlight creates shadows of the prey in the water medium that guide them to reach the prey. Hatchet-fish use counter-illumination technique to evade from its predator. They have light-producing organs that point downward. They adjust the amount of light coming from their undersides to match the light coming from the above. By adjusting their bioluminescence glow, they disguise their shadows and become virtually invisible to the predators looking up.

Some bioluminescent animals, such as Brittle stars, can detach their body parts to distract predators. The predator follows the glowing arm (detached body part) of the Brittle star while the animal crawls away to safety in the dark. Brittle stars, like all Sea stars, can re-grow their lost limbs.

Some animals detach their body parts on other animals too as a means of protection. When threatened, some species of Sea Cucumber can break off the luminescent parts of their bodies to stick onto nearby fishes. The predator generally follows the glow on the fishes while the Sea Cucumber escapes quickly.

Biologists think that some species of Sharks and Whales may take advantage of bioluminescence phenomenon even though they are not bioluminescent themselves. A Sperm Whale, for instance, may seek out a habitat with large communities of bioluminescent plankton which are not part of the Whale's diet. As the planktons predators (fishes) approach the plankton, their glowing alerts the Whale. The Whale’ threatens and eats away the invading fishes. The plankton then turns off their lights.

Some insect larvae (like Glow worm, Millipedes) light up to warn predators that they are toxic. Toads, birds, and other predators evade the prey assuming that consuming the larvae is harmful for them that may lead to death.

FEEDING

Animals can use their lights to lure the prey towards their mouth or even to light up the nearby area where they could see their preys better. Sometimes the prey being lured can be small plankton, like those attracted to the bioluminescence glow around the beak of the Stauroteuthis octupus . But the light can also fool larger animals. Whales and Squids are attracted to the glowing underside of the Cookie-cutter Shark, which grabs a bite out of the animals once they are close.

The most famous predator to use bioluminescence phenomenon for capturing prey is the deep-sea Angler-fish that lures the prey straight to its mouth with a dangling bioluminescent barbel, lit up by glowing bacteria. It has a huge head, sharp teeth, and a long, thin, fleshy outgrowth (called a filament) on the top of its head. On the end of the filament is a ball (called the Esca) that the Angler-fish can light up like a lantern. Smaller fishes, curious about the strange spot of light, swim in for a closer look. By the time the prey sees the enormous dark jaws of the Angler-fish behind the bright Esca, it is often too late for it to escape.

Other fishes, such as a type of Dragon fish, also use bioluminescence for hunting and feeding. They are adapted to emit red light. As most fishes can see only blue light, the Dragon fish has an enormous advantage when they light up a surrounding area. That means, they only can see their prey, but their prey can't see them!

ATTRACTING MATES

The male Caribbean Ostracod, a tiny crustacean, uses bioluminescent signals on its upper lips to attract females. Syllid fire-worms generally live on the sea floor; but with the onset of full moon they move to the open waters where the females of some species, like Odontosyllis enopla, use bioluminescence signals to attract their males while moving around in circles. Angler-fish, Flash-light fish and Pony-fish all are thought to luminesce in order to communicate for mating.

CHEMISTRY OF BIOLUMINISCENCE

Traditional light bulbs create light by a process called Incandescence. In this process, a filament inside the bulb gets heated to a very high temperature due to the passage of electricity and emits light. However, this process of producing light is not very efficient as enormous amount of energy is dissipated in the form of heat leaving a little to be converted to useful light.

However, glowing animals typically create light by a chemical reaction (called Luminescence) that produces light energy within the organism’s body which is far more efficient than Incandescence. It neither requires nor generates much heat, and hence, sometimes known as cold light.

The reaction (as given below) takes place in the presence of a molecule called Luciferin which reacts with Oxygen of air to produce light. Many organisms also produce an enzyme called Luciferase, which acts like a catalyst to speed up the reaction. The reaction may be mediated by cofactors like Calcium (Ca²⁺) or Magnesium (Mg²⁺) ions.

As seen from the above reaction, Carbon dioxide (CO₂), Adenosine Mono Phosphate (AMP) and Phosphate groups (PP) are released as waste products along with Light energy.

DISTRIBUTION

Animals exhibiting Bioluminescence occur mostly in the open sea. These include, fish , jellyfish, comb jellies, crustaceans, and cephalopod mollusks. Most marine light emission is in the blue and green part of the spectrum However, some loose jawed fish emit red and infra-red light and the genus Tomopteris emits yellow light.

Among the micro-organisms, some species of Fungi and Bacteria also exhibit bioluminescence. The most frequently encountered bioluminescent organisms may be the Dinoflagellates present in the surface layers of the sea which are responsible for the sparkling phosphorescence of the seas sometimes seen at night in disturbed waters. A different effect that needs special mention is the thousands of square miles of the ocean surface which shine with light produced by bioluminescent bacteria commonly known as the Milky Seas Effect. This is sometimes visible from the satellite.

Terrestrial bioluminescence is less diverse and widespread as the two well known examples are the Fireflies and the Glow worms. Other invertebrates including some insect larvae, annelids and arachnids possess bioluminescent abilities.

SCOPES AND RESEARCH

Bioluminescent organisms are a target for many areas of research in the field of Biology and Medicine. Luciferase systems are widely used in Genetic engineering as reporter genes (each producing a different colour by fluorescence) and for biomedical research using bioluminescence imaging technique. For example, the firefly luciferase gene was used as early as 1986 for research using transgenic tobacco plants. Vibrio bacteria, in symbiosis with marine invertebrates such as the Hawaiian Bobtail Squid (Euprymna scolopes), are key experimental models for bioluminescence. Bioluminescent activated destruction is an emerging cancer treatment method which is under research.

The structures of the light producing organs in bioluminescent organisms (called Photophores) are being investigated by industrial designers. Engineered bioluminescence could perhaps one day be used to reduce the need for street lighting or for decorative purposes. In this method, it may be possible to produce light that is both bright enough and can be sustained for long periods at a workable price. In an experiment, the gene that makes the tails of fireflies glow was added to mustard plants. The plants glow faintly for an hour when touched, but a sensitive camera is needed to see the glow. University of Wisconsin-Madison is researching the use of genetically engineered bioluminescent E.coli bacteria, for use as a light bulb. Research is also under way to create bioluminescent plants!

Because Luciferin is consumed in the light-producing reaction, the reaction cannot be sustained for a long period of time. A team from Cambridge is working in this area to develop a genetic biotechnology part that codes for a luciferin regenerating enzyme from the North American firefly that would help to strengthen and sustain the light output.