Let us imagine for a moment that we are in a place where there is no light, not a single speck of it to see what is around us, the perpetual darkness of the deep ocean for example – where not a single ray of light had ever breached it’s numerous layers. Where the night is an unfaltering and unceasing occurrence.
Quite morose, right?
But it is these never ending dark depths of the ocean where some of the brightest and most beautiful bioluminescent organisms are found, lightning up their own paths when there is no one else to do so.
Bioluminescence:
In simple terms, bioluminescence is a chemical reaction that produces light within an organism. But it is vastly different from any other light known in nature for two major reasons:
For one, bioluminescent lights are “Cold lights” which means almost negligible amount of heat is produced during the emission of such a light by the organisms which is important in order to maintain the general metabolism processes of the animals.
And for another, bioluminescence, is a type of chemiluminescence – where the reaction of two unique molecules namely Luciferin and Luciferase, that leads to the production of light.
Bioluminescence is seen in a wide array of organisms – starting from the most basic terrestrial bacteria, phytoplanktons, fungi and fire flies to marine animals like angler fish, lantern fish some squids and the well known jelly fishes to name a few.
The reaction behind bioluminescence:
The name of the molecule, Luciferin is derived from the word ‘Lucifer’, named after an angel who fell from grace and later became the Satan according to some popular mythologies.
But in literal sense, it translates to ‘The light bringer’ in Latin. Since the function of this molecule is to produce light.
Luciferase on the other hand is the enzyme that catalyzes the oxidation of luciferin in the presence of some co factors like ATP, thus leading to the production of a byproduct oxylucifersae that emits light.
In some cases an enzyme named, phototropin instead of Luciferase catalyzes this oxidation reaction and requires ions like that of calcium for it’s function.
Why bioluminescence is needed?
Bioluminescence has a wide array of different functions, in different organisms – starting from predation to attracting mates and sometimes even protection.
The predatory lights:
The best known bioluminescent predator is perhaps the Angler fish. A teleost fish found in the murky depths of Antarctic and Atlantic oceans with a wide body, sharp teeth and a long fleshy filament dangling down, from the top of it’s head.
At the end of this hanging filament, there’s a pouch called ‘Esca’ filled with bioluminescent bacteria that lights up the tip of this filament. These fishes uses this glowing esca as a bait to lure in small fishes and prey on them.
The cookie cutter shark: Popularly known as the cigar shark, has it’s whole ventral side covered by photophores – cells that produces light. Since, like most sharks this fish circles near the surface of the water, small fishes, crustaceans and squids gets to see the glowing bluish photophores from below and are attracted towards them. Leading them to be killed and eaten by these sharp predators.
Dragon fish: Also known as loosejaws are deep sea fishes that uses their barbels to produce red spectrum light, instead of blue like most of the other bioluminescent organisms.
Since, only lights of the blue spectrum are visible to most of the marine animals these dragon fishes can easily depict it’s prey in the water while remaining invisible itself.
The defensive lights:
Vampire squid: Named so, because of it’s blood red color and the skin that joins it’s eight arms forming a graceful cape like structure.
This squid uses bioluminescence to deceive it’s predators, and makes an quick escape. It ejects a sticky bioluminescent mucus upon it’s predator and all around it, to confuse and startle the organism to get enough time to elope.
Railroad worm : This larva produces not one but two types of bioluminescent lights. It’s long tubular body glows yellowish-green while it’s head glows bright red, thus, making itself look like an poisonous (Since most terrestrial poisonous species are brightly colored) and unpalatable species and warns off the nocturnal predators.
Counter-illumination: This is a protective mechanism used by some of the marine bioluminescent organisms for camouflaging themselves against the predators.
For example, the Hatchet fish – uses counter illumination in order to make itself invisible, by adjusting it’s bioluminescence in such a manner that it could loose itself in the color of the sea.
Some organisms has another peculiar way of deceiving their predators. As seen in Brittle stars – when they are cornered by a predator, they often detach the glowing arm from their body and let it float away in ocean, causing the predator to get distracted and making them follow the glowing arm, while the star creeps away silently in the dark.
Sea cumber is another such example – which when threatened detaches the glowing part of it’s body onto another organism like a fish. So that now the predator starts following the glowing fish, letting the sea- cucumber creep away in the dark.
The attractive lights:
One of the best known bioluminescent organism to us, is perhaps the fire fly. The small glowing bugs that could be often seen on a warm summer’s night twinkling like miniature golden stars outside our windows, under the open sky.
But these yellow lights are neither produced to attract preys, nor to deceive the predators. Instead fireflies twinkle in order to attract the opposite sex and to find a mate. The pattern of their flashing is code to what species they belong to. Since every species of fireflies has a different pattern of flashing, females could differentiate and depict between their own species and a forerign one.
Found in the bathypelagic zone of open ocean, the angler fishes lives at the depths of 2000 meters below the water surface in the complete absence of any kind of light, except it’s own.
The female angler fish has a fleshy filament hanging from the top of it’s head that had bioluminescent bacterias in the pouch at it’s tip, called esca. So, these glowing escas not only help them in hunting preys and finding food, but also acts as the organ that attracts the small male angler fish towards her.
The male angler fishes on the other hand, has no bioluminescent organ, no hunting instinct, in fact it barely has an functional digestive tract because it’s sole purpose of life is to find a mate and get attached to her for life. If it fails to do so within a limited period of time, it will soon die.
But those few lucky ones, that succeed in finding a mate and successfully get attached to their ventral side aren’t actually that lucky either – because as soon as they attach with their mates, their body starts disintegrating, fusing into the body of the female, until they become one.
After a while, nothing is left of them bar the testicles.
The female carries 4-6 males on it’s back like permanent saddle bags of sperms to be used at a later date.
So, blue light, it seems is not something you would want to follow.
Bioluminescent phytoplanktons:
If you have ever been to the picturesque Caribbean islands, or if you are planning to – you must surely know about the phenomenon of glowing water.
People from all over the globe flock here, at the beaches of Caribbean islands of Purto Rico at night – to watch the whole surface of sea glow in a mystical blueish light that could take one’s breath away.
This is due to the single celled dinoflagellates that live within, at such high numbers that with a very little disturbance, the water starts to appear like the sky with thousands upon thousands of stars spread upon it’s dark canvas.
But as the old saying goes : Not all that glitters is gold. This maybe true in case of bioluminescence as well.
Just like the Purto Rican bay of glowing water, the waters surrounding the Taiwan’s Matsu island of China also glows in a mystic blue color, every summer’s night.
It attracts tourists from all over China’s mainland to see this phenomenon known as, China’s “Blue tears”.
Caused by the single- celled dinoflagellates , known as Noctiluca Scintillans, the phenomenon may seem spectacular and romantic to some but in reality, they are immensely toxic. And is growing year by year.
It can poison the marine life, affecting one and all – from fishes to sea turtle and even humans. The dinoflagellates N. Scintillans aren’t toxic themselves, but they poison the ocean only when they are present in high numbers, feeding upon other toxic algae and end up releasing ammonia and other harmful chemicals in the water. Along with utilizing a large amount of oxygen present in water, thus leaving little to nothing for the rest of the organisms.
Thus, “Blue tears” seems to be an appropriate name for such a tragic phenomenon.
What it means to us?
From the last decade, studies to understand the circumstances leading to bioluminescence and the chemical reactions involved in it has been a major research project for bioengineers, so that in the near future, one can utilize this natural process for our own benefit.
For example, a synthetic analogue of D-luciferin found in fireflies, has been created- known as Akalumine. Which produces a much higher wavelength of light at 677nm as compared to the natural D-luciferin, it can easily penetrate the tissues of most of the animals and can even cross the blood- brain barrier. Akalumine have proved itself as a very important analogue to study bioluminescence. Nicotiana tabaccum – a tobacco plant, has been the first plant to be genetically engineered, utilizing fungal bioluminescence system of Neonohopanus nambi (a poisonous mushroom). If this line of research succeeds in the upcoming decades, and that if we ever succeed to create trees that are fully functional bioluminescents – imagine, what a revolutionerizing development that would be, replacing the need of electrical lights with natural eco friendly ones.