The Biology of Bioluminescence.
In Europe, long before safety and effective electric lamps, miners used bottles filled with fireflies to illuminate dark coal mines. They avoided to use candles because of the high risk of sparking explosions.
That little insects, fireflies, belong to a group of living creatures which illuminate light. Perhaps you have seen or at least heard about them — one of the most wondrous creatures often found in woods.
The phenomenon of light production and emission by a living organisms, known as bioluminescence, is caused by a certain chemical reactions taking place inside the living organism.
Bioluminescence was considered to be seldom phenomenon in nature till the depths of oceans have been explored. It reveals that this phenomenon occurs most widely in marine, less in terrestrial life forms. Thus it is common for fish, jellyfish, bacteria, fungi, worms, larva, arachnids, dinoflagellates and other types of organisms. So let’s find out how they produce light.
How Does Bioluminescence Occur?
Bioluminescent reaction involves a light-emitting pigments: photoproteins (luciferin, aequorin, coelenterazine etc..). The reaction also involves enzyme luciferase that catalyzes the reaction, oxygen, additional factors such as Ca++/Mg++ charged ions and ATP molecules that contain enough energy to occur the reaction.
Note!
ATP- adenosine triphosphate molecules store and transport energy in most living organisms, including the human body.
Reactions can be initiated by some neurological, mechanical, chemical or as-yet-undiscovered triggers. In firefly luminescence, ATP initially reacts with firefly luciferase, ionic magnesium, and firefly luciferin to form a luciferase-luciferyl-adenylate complex and pyrophosphate. That complex then reacts with molecular oxygen to emit light. Enough energy is liberated in the last step to convert the electronic configuration of the luciferase-luciferyl-adenylate complex from a low-energy ground state to a high-energy excited state. The high-energy complex then loses energy by radiating a photon of visible light and returns to the ground state. In spite of radiant results it generates almost no heat as nearly 100% of the energy consumed in the reaction. So it’s sometimes known as cold light.
Depending on the species of the bioluminescent life form luciferin & luciferase molecules are produced in a different way. For example, dinoflagellates that obtain food through photosynthesis use a luciferin that resembles chlorophyll. That is why heir luminescence is brighter after very sunny days.
Note!
Chlorophyll is a green pigment which is responsible for photosynthesis.
Some shrimp and fish appear to manufacture their luciferin from the food they eat. Deep-sea fish possess the most complicated light organs; they consist of photogenic cells, reflector, lens body, and, in certain cases, colour filters.
Light organs (photophores) are usually present at the end of the tentacles, over other surfaces of the body or under the eyes. Photophores are under fish’s nervous control as after death the ability to luminesce disappears swiftly.
The nervous system doesn’t directly control the photocytes. The flash triggering nerve impulse goes to non-luminescent cells next to the photocytes. The impulse ends up triggering nitric oxide production. The nitric oxide is what stimulates the light production. It turns on the flash by temporarily stopping the oxygen consumption of the photocyte’s mitochondria. Oxygen can then diffuse farther into the interior of the photocyte, where it triggers the light-producing reaction between luciferin and luciferase. The flash turns off as the nitric oxide is used up and the mitochondria start to consume oxygen again.
Some species like angler fish host bioluminescent bacteria instead. These bacteria live in a light organ in the host organism’s body. The bacteria produce light all the time. In order to turn their lights on and off, some animals can drag their light organs into their bodies. Others cover them with pieces of skin similar to eyelids. Some organisms also use a fluorescent substance, like green fluorescent protein (GFP), to adjust the color of the light they create. The fluorescent substance absorbs the blue-green light and emits it as a different color. Therefore, animals can either house these substances in their own bodies or develop a symbiotic relationship with light-producing bacteria.
Note!
A pigmented layer of cells surrounds the light organs internally to absorb stray light. Reflector layer consists of reflecting material that redirects the light towards the lens. The generated light passes through the lens whose pigments filter the emitted light and adjust its spectrum. Matrix represents the space between the photogenic chamber and other structures. The right half of the photogenic chamber represents an intrinsic light organ with photocytes (firefly). The left half of the photogenic chamber represents a symbiotic light organ with transverse section of tubules filled with luminous bacteria (angler fish).
The Purpose of Bioluminescence.
As you see from demonstration bioluminescence can be used for defensive, offensive and mating purposes. Let me give you a few interesting examples.
Arachnocampa luminosa
or luminescent glow worm found in the Waitomo Glowworm Caves in New Zealand (the pic. is above) is endemic. In their larval stage they dangle silken threads to attract flying insects with glowing bluish-green light.
Angler fish lives in the lonely, lightless bottom of Atlantic and Antarctic oceans.
In order to find her prey females use a luminescent lure to attract other fish. The light produced by symbiotic bacteria living in their bulb-like light organ.
However male angler fish are smaller in size, without spooky teeth in a big mouth and attractive luminous bulb.
It reveals that males follow pheromones and bioluminescent lure to find their preys: females. When he finds her he bites into her belly and latches on until his body fuses with hers. Their skin joins together, and so do their blood vessels, which allows the male to take all the nutrients he needs from his host/mate’s blood. The two fish essentially become one. Taking food from her they provide sperm whenever she’s ready to spawn.
Ostracods (“blue tears”) are up to 1 inch in size. During World War II they were used as convenient light source for reading maps and papers.
While it is eaten by cardinalfish it gives off light making the fish to spit it out. Otherwise the fish itself will be visible for its predators.
Some squid and shrimp produce a luminescent glowing cloud similar in function to the ink cloud of squid in daylight to escape from their predators.
Jellyfish produce bright flashes or release thousands of glowing particles into the water as a mimic of small plankton to confuse or startle a predator. Others produce a glowing slime that can stick to a potential predator and make it vulnerable to its predators.
The best known example of communication is the bioluminescence of fireflies, where there is an exchange of flashes between males and females. Females respond to the flashes of flying males, with the eventual result that the male approaches the female for the purpose of mating. To avoid confusion between members of different types of fireflies, the signals of each species are coded in a unique temporal sequence of flashing.
Every time the Nature surprises us with its wondrous creatures. Let’s be wise and protect it.
Questions to muse on before Googling!
* The most marine bioluminescent creatures produce blue light. Why?
* What is the difference between bioluminescence and biofluorescence?
REFERENCES:
1. TED-Ed The brilliance of bioluminescence
2. @TED Talks that will help you to know more about bioluminescence.
I hope this article has been useful 😊. If so, please Clap 👏 as much as you want. If you have something to say, please comment below. We will muse on things together.
