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HAVE you seen glowing fi refl ies fl i ing about in the dark? The light

in these fi refl ies is the result of a natural phenomenon called Bioluminescence. This phenomenon is found in a wide array of organisms such as vertebrates, invertebrates, bacteria and fungi. Some eukaryotes perform this function by their own as they have evolved a specifi c mechanism in the course of evolution. While others illuminate with the help of luminescent bacteria present in their bodies.

During the pre-electricity era, jars of fi refl ies used to be the source of light. Dried skins of luminescent fi shes were used in Britain and Europe as weak light sources before the invention of safety lamps.

This phenomenon sometimes also creates magnifi cent illumination of disturbed sea waves in the night and is called the Milky Sea Eff ect. This eff ect is caused due to the presence of a large number of luminescent dinofl agellates and luminescent bacteria on the surface of the sea. Darwin recorded the fi rst observation of the milky seas.

In 1667, Robert Boyle, an Anglo-Irish philosopher, chemist and physicist studied the mechanism involved in this process and found that air is required for this phenomenon to occur. Today, we know that it is oxygen that is required. Later, Raphael Dubois extracted the two key components of a bioluminescent reaction and coined the terms “Luciferine” and “Luciferase”.

It is the chemical reaction that generates the light. The reaction comprises two major components: Luciferase (enzyme to catalyze the reaction) and Luciferin (light emi ing pigment). The reaction of Luciferin with oxygen generates light; other cofactors and components are also the part of this reaction.

Bioluminescence plays a very important role in the life cycle of these luminescent organisms.

Communication: Molecular commu-nication, also called Quorum Sensing, plays a very important role in the regulation of bioluminescence in many bacterial species. Some inducers are released by the organisms which when

UDIT MALIK

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Prey a raction: The glowworms of New Zealand’s Waitomo Cave secrete slimy threads that refl ect their own bioluminescence. The tail grows as the worm gets more hungry. This glowing light a racts the insects that get entangled in the glowing slimy tail.

Mate a raction: Firefl ies glow to a ract

the mates and also to a ract other insects so that they can a ack them easily.

Spore Dispersal: Many fungi emit light. One such example is Panellus stipticus, wood decay fungi of the division Basidiomycota. Some of its species are bioluminescent. The luminescence is localized near the fruiting body of the fungi to a ract the arthropods that help in the dispersal of its spore.

Exploiting a Natural Phenomenon In the twentieth century, J. Woodland Hastings explored the phenomenon further and made discoveries of Quorum Sensing and Green Fluorescent Proteins (GFP). These revolutionary discoveries have laid the foundation for modern day applications of this very interesting phenomenon of bioluminescence.

The bioluminescence phenomenon is today being used in medicine, diagnosis of diseases, detection of pollutants, gene detection and many more. With understanding of biological clock regulation, even display screens have been constructed. Let us take a look at some inventions based on this phenomenon.

they reach a threshold level, activates the genes of luminescence. This is the major form of luminescence in the bacteria. Some organisms use this phenomenon to communicate within the colony, for example, Pyrosomes, the colony of the zooides. Light emission by individual zooides helps the colony in various activities such as swimming in the same direction.

Defense: Luminescence in several organisms is also used as defense mechanism against predators. For instance, Dinofl agellates glow when they have a fear of a predator. When they glow they a ract the predators of a higher level, which then feed on the predators of Dinofl agellates.

This phenomenon sometimes also creates magnifi cent illumination of disturbed sea waves in the night and is called the Milky Sea Effect. This effect is caused due to the presence of a large number of luminescent dinofl agellates and luminescent bacteria on the surface of the sea. Darwin recorded the fi rst observation of the milky seas.

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Biopixel: An LCD like screen illuminated by millions of bacteria. The story was fi rst presented before the world in 2008, when researchers from the University of California, San Diego claimed to have built a bacterial cell that could tell other bacteria when to illuminate. And in another paper published in 2010, the same team claimed that they had managed to regulate millions of bacteria in a colony to illuminate in unison. Thus establishing the base of the Biopixel.

The biologist and bioengineers (Arthur Prindle, Phillip Samayoa, Ivan Razinkov, Tal Danino Lev S. Tsimring and Jeff Hasty) of the University of California, San Diego, used millions of recombinant and programmed E. coli cells, to form a biological microcircuit. In the circuit, the cells illuminate in a regulated and synchronized order to generate a decided signal using the natural phenomenon of Quorum Sensing.

In liquid media, Quorum Sensing is a slow process because of slow diff usion rate of chemical molecules. But faster communication can take place in a gaseous medium. A large-scale coherent illumination of millions of bacteria in the bacterial colony is not feasible with gaseous phase medium. So, the team constructed a microfl uidic array that coupled the redox signal of hydrogen peroxide gas produced by colonies and the native redox machineries of E. coli cell for eff ective and effi cient Quorum Sensing. This led to the synchronized and consistent illumination of the colonies thus producing the desired signal on the screen. The team has tried to modify the organism and circuit to use the invention as an arsenic detection sensor and the

results are promising.

Philips Biolight Concept: A novel way of using bioluminescence as house light has been developed by the Dutch electronics giant Philips. They have created a lighting system that generates light by using house bio-waste and luminescent bacteria.

A kitchen digester is used as the source of methane that decomposes the organic house waste to generate the methane. The methane released from the digester is connected to the base of the reservoir of bacteria (made of hand blown glass material) using silicon tubes. As long as the media is provided to the bacteria, it illuminates. The advantage is that no heat is generated from this light. But it is not enough to illuminate the whole room. The company proposes to use it as a dim light source for entertainment purposes or as a warning strip.

Recombinant plants with bioluminescence: Many experiments have been conducted to incorporate the genes of luminescent protein into plants. And some of them have been successful. This is a progressive step in understanding plant biology. Researchers have also modifi ed plants with luminescent genes that glow when they require water and nutrients.

Bioluminescence Imaging: It is a non-invasive technique that allows the study of ongoing biological processes in small laboratory animals. The cells are fi rst transfected with the luciferase genes

and are then grown in the media or are introduced in the laboratory animals. The luciferin is provided externally. The expression of luciferase is measured by measuring the luminescence. The intensity of luminescence is measured using the imaging process. This technique is being widely used to study cancer, Parkinsons’ disesase, identifying drug resistant cells, etc. This technique has been recently used to study the connection between placenta and foetus.

Diagnosis and detection: Bioluminescent proteins now have a huge market. They are being used as markers to detect the analyte in question. The luminescent protein, for example, Green Fluorescent Protein (GFP) or others can be a ached to antibodies that glow when they bind to the analyte of interest thus giving an easy and safe way of detection as compared to radioactive based detection techniques.

Drug discovery is also an aspect that is being exploited with the help of luminescent proteins. It could even be possible to replace street lights by luminescent trees that could sense the diff erence between day and night and illuminate in the dark. There is a lot more to come.

Udit Malik is an MSc in Microbiology and has worked in the Intellectual Property industry. Address: WZ-47, Rajeev Nagar, Opp.Sec-22, Rohini, New Delhi 110086; Email: uditmalik20@gmail.com

A novel way of using bioluminescence as house light has been developed by the Dutch electronics giant Philips. They have created a lighting system that generates light by using house bio-waste and luminescent bacteria.