By Soha Aggarwal
Perhaps the most exciting thing about bioluminescence is that it is found only in the lower branches of the “tree of life”. None of the birds, reptiles, or mammals could boast of bioluminescent jerks, whereas several other groups of organisms—fungi, bacteria, insects, fish – have been able to possess light-generating abilities truly in every possible way. Even some of the most simple animals in the world, such as marine plankton, exhibit light-generating capabilities lost in higher vertebrates. They have bioluminescent cells that contain a unique chemical, luciferin, which reacts with oxygen to produce light.
What is Bioluminescence?
Bioluminescence is a phenomenon that refers to the light emitted by living things due to a chemical reaction in their bodies. The most common display of bioluminescence is in fireflies, which produce light through a chemical reaction taking place in their abdomens. Similarly, sea-scapes glow and glitter due to the light-producing abilities of various marine organisms. Bioluminescence can also be used by fish to attract a mate. Additionally, squids might produce a bioluminescent liquid instead of ink to confuse their predators .
While humans believe that the light produced by them is in response to a physical disturbance such as a wave or a moving boat hull, the reality is starkly different. This property, created due to the chemical reaction, helps the creatures to attract and repel mates. It is also efficient in facilitating communication, which would otherwise become difficult in the vast ocean. Such a phenomenon catches one's eye through its wonderful appearance, however, one must understand that it is a masked beauty—a protective and deceptive coat creatures have painted as a part of their survival strategy. The mechanism of bioluminescence allows one to unravel this deception and find out what lies inside in reality.
Bioluminescent Jellyfish in Ocean
The Inner Workings of Bioluminescence
Delving deeper into the science behind Bioluminescence, there is a chemical reaction that occurs in which the enzyme luciferase catalyzes the pigment luciferin. The genesis of the names Luciferase and Luciferin are from Latin, with their root word being light. Luciferin is the compound that produces light. In a chemical reaction, it is referred to as a substrate. While some bioluminescent organisms synthesize luciferin, some absorb it from other organisms, either as food or from a symbiotic relationship.
The enzyme luciferase catalyzes this reaction in the presence of luciferin and oxygen. The process results in the formation of the byproduct, oxyluciferin. After being restored to its lowest energy level, the unstable oxyluciferin formed emits light. Furthermore, the wavelength of light generated depends on the kind of luciferin and luciferase involved in the reaction. For example, fireflies emit yellow- green light at a wavelength of 560 nanometres. Jellyfish, on the other hand, emit blue or green light in order to aid in defense.
Diagrammatic Representation of Bioluminescent Reaction
Bioluminescence has developed gradually with different luciferins and luciferases. Coming back to fireflies, they have evolved varieties of luciferases that belong to bioluminescent beetles. The biosynthesis of luciferin requires its specialized enzymatic pathways and unique chemical transformations. There are far fewer luciferins than luciferases. Some species tend to have unique luciferases, while others even share the same ones. Of the nearly twenty groups of bioluminescent organisms in the world, a luciferin called coelenterazine is the light-emitter in nine of them (2009). Yuichi Oba, a professor of biology at Chubu University in Japan, states that these species do not make the coelenterazine themselves (2009). Instead, they get it from their diets. Species can also acquire it through their symbiotic relationships. For instance, marine animals such as squid, house bioluminescent bacteria in their light organs. These bacteria live inside the host, where they are sheltered and even fed by the host animal. Therefore, the bacteria and squid have a symbiotic relationship. In organisms such as Midshipman fish, this phenomenon can be seen. Midshipman fish have cyprinid luciferin which acts as a substrate in their own luminescent reactions.
Case Studies of Bioluminescence
Bioluminescence has been used to attract prey for multiple centuries. Citing the example of Anglerfish, one may note that the creature uses a light organ inhabited by bacteria which hangs from its forehead to attract its prey. When the prey gets near this fish, it gets entirely engulfed. Similarly, the adult versions of glow-worms do not possess wings, instead exhibit structures on their abdominal and thoracic areas, where the organs emit light. Even fungi such as mushrooms are bioluminescent and glow to attract insects which is regulated by a circadian clock controlled by the external temperature.
In adult fireflies, bioluminescence is used to lure and attract prey. The phenomenon may also be utilized as a hunting tool. Furthermore, Black Dragonfish inhabit the seas and possess special organs, known as photophores, to produce light. While the blue-green color emitted by them is used to attract prey and camouflage themselves, the red light emitted enables them to find prey in the dark. Some squids and shrimp produce a luminescent cloud similar in function, to the ink cloud of squid in daylight. Animals living in the great depths of the oceans, where the sunlight is very dim, use bioluminescence to camouflage themselves.
Bioluminescence can also be used as a tool for communication. This is seen in fireflies, where flashes get exchanged between males and females. The latter responds to the flashes of the male variant, eventually resulting in the male approaching the female with the intention of mating. To avoid confusion in the signals between the different species of fireflies, each species has a unique temporal sequence of flashing.
Evolution of Bioluminescence and its Human Application
‘The sea was luminous in specks and the wake of the vessel, of a uniform slightly milky color. When the water was put into a bottle, it gave out sparks…’
This is the first entry of Charles Darwin in his zoological notebook. Darwin had observed flickering bioluminescent creatures, glinting light in response to a physical disruption. However, Darwin failed to understand why this phenomenon occurred in different species in a seemingly random fashion. Today, we know that bioluminescence has evolved independently at least forty times in land and sea. Their diversity is also unparalleled, with species occupying both coastal waters to the deep sea and polar to the tropical regions. Their ecological array is matched by diversity in their bioluminescent colors, and widely different chemical patterns, reactions and kinetics. Through the last several years, there has been a shift of research interest from chemistry and biology into genetic biotechnology. Due to the high detectability and rapid speed of bioluminescent spectroscopy, it has made advancements in molecular biology. These properties allow for the monitoring of biological processes longitudinally in clinical, diagnostic and drug delivery applications. The bioluminescence reaction is also now routinely used for gene assays, detection of protein-protein interactions, high-throughput screening in drug discovery, analysis of pollution in ecosystems and in vivo imaging of small mammals.
There are also several applications of biotechnology. For example, bioluminescent systems are now being considered as green alternatives to outdoor lighting and public spaces in agriculture. The French start-up company Glowee was founded in 2014, and it has used bioluminescent bacteria to develop lamps as a form of sustainable lighting. The company has managed to increase the lifespan of the bacteria, and hence the lamps from three days up to one month.
Bioluminescence is under threat due to a range of human-induced challenges such as pollution primarily from plastics, chemicals and oil spills which pose a major threat to bioluminescent organisms. Rising sea temperatures and ocean acidification, caused by excessive carbon dioxide emission also might affect bioluminescent species. The United Nations Food and Agriculture Organization estimates that 33 percent of global fish stocks are overfished, depleting the ocean biodiversity, and affecting the availability of prey for bioluminescent species.
Conclusion
In conclusion, bioluminescent reactions are extremely important to organisms. Their chemical reaction involves the presence of luciferin, luciferase and oxygen to produce oxyluciferin. Bioluminescence is crucial for many organisms and serves functions such as attracting prey, facilitating communication and helping in hunting. It holds immense potential for scientific advancements in the fields of biomedical imaging, the environment and biotechnology. However, it is also essential to recognize the importance of conserving the diversity of bioluminescent organisms. The implementation of robust conservation efforts is necessary to protect these organisms' habitats, prevent overexploitation, and preserve their genetic diversity. Such efforts will not only safeguard these fascinating organisms but also ensure that their potential contributions to science and technology are not lost.
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