Light Up the Dark: Bioluminescence in Organisms

Priasha Dutta, Amity University Kolkata

Bioluminescence can be undoubtedly regarded as one of the most stunningly beautiful and captivating abilities that Mother Nature has bestowed to some of its beings on this planet. This rather unique property is possessed and depicted by a comparatively small population of organisms on the planet. It is the phenomenon where certain biochemical reactions occurring inside the system of an organism, leads to the production and emission of light. This is observed in organisms whose habitats are often amidst comparatively darker and low-lighted surroundings. Bioluminescence is exhibited by mostly marine and freshwater organisms like some algae, crustaceans, jellyfish, squids, anglerfish; as well as by many bacteria, glow worms, fireflies, corals, mushrooms, etc. In fish alone, there are about 1,500 known species that exhibit some form of bioluminescence. In some cases, animals take in bacteria or other bioluminescent creatures to light themselves up.

How does it work?

There are over forty bioluminescent systems and the molecular components of only seven light-emitting reactions are known to us, while the others are yet to be discovered. Luciferins are small molecules which depict the characteristic emission of light upon oxidation. These have been procured by evolution from various unrelated biochemical pathways. Oxidation of luciferins is catalysed by enzymes called luciferases to form bioluminescent systems. It is characterized by a series of light-emitting reactions that differ in colour and varies based on catalysis rates and thermostability of luciferases, cellular localisation, environmental factors like pH and temperature and dependence on ATP, NADH, ions and other metabolites.

Types of bioluminescent systems-

• Coelenterazine is the most common type of luciferin found amongst the majority of these organisms. All coelenterazine dependent pathways emit blue light except in some cases where the colour is changed if a different bioluminescent protein interacts with a luciferase. Gaussia luciferase, Nanoluc luciferase and Renilla luciferase act in this coelenterazine dependent system.
• D-luciferin is another important compound which produces a yellow or orange light in bioluminescent beetles, worms, fireflies, etc. Emission of D-luciferin is dependent on ATP concentrations and thus is used as an ATP indicator in studies related to cancer metabolism or monitoring bacterial contaminants in water. Important enzymes from D-luciferin dependent systems are Firefly luciferases (most popular with easy discovery and very high quantum yield of bioluminescence) and click beetle luciferases.
• Other common bioluminescent systems include bacterial, fungal and based on Cypridina luciferin.

Types of emission:

The unique feature of bioluminescence is that it does not need the initial absorption of sunlight or other electromagnetic radiations produced by any molecule, or pigment, to emit light and it produces light genetically. This light is emitted in wavelengths between that of 400nm and 720 nm, from violet to the near-infrared range. Although the majority of marine organisms emit blue light (410–550 nm) the wavelengths of the light often change based on the habitat of the organism as follows:

• violet and blue (420–500 nm) in the deep sea
• blue-green (460–520 nm) in shallow waters
• green-yellow (520–580 nm) on land

There can also be various emission patterns such as:

• flashes in squids, fireflies and dinoflagellates (responsible for the well-known glow in some oceans);
• blinking in some bacteria;
• continuous glow in some bacteria and fungi;
• ability to switch on and off the emission in Anglerfish.
• Bioluminescent earthworms glow in the presence of some external stimuli like potassium chloride.

Applications and Current research:

Typically bioluminescence is used to warn predators by dazzling them, to lure prey, to attract the opposite gender for mating, propagation and even for communication between the same species. The mechanisms of each of them are still quite new to us as more and more of such unique functions are still being discovered to this day. Luciferase, luciferins, and the genes that code for them are being used extensively in the field of biomedical and biotechnological research like drug screenings, bioassays, environmental monitoring, food testings etc. 

Also read: Designing Special RBCs for the delivery of Therapeutic Proteins

REFERENCES-

1. Fleiss, A., & Sarkisyan, K. S. (2019). A brief review of bioluminescent systems (2019). Current Genetics, 65(4), 877–882. https://doi.org/10.1007/s00294-019-00951-5
2. Ch. Ramesh and R. Mohanraju. 2015. A review on bioluminescence and its applications. International Journal of Luminescence and Applications (ISSN: 2277-6362) Vol. 5, No. 1, February 2015. Article ID: 050. pp.45-46 https://www.researchgate.net/publication/321162295_A_review_on_bioluminescence_and_its_applications

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