His exalted name, “Light,” touches the darkness
and everywhere is filled with light.
The letters written from a brilliant world
are revealed to the hearts;
Then the Divine command,
“Read in the name of your Lord!”
descends and becomes our intentions.

We look around the Earth and believe that we start to sail into the dark upon reaching the depths of the skies, the land, and the oceans. But if we look with care, we may notice that the inhabitants of those places often inform us of the beauties they are created with.

The depths of the oceans, especially, are where what we see leave us amazed. From microscopic bacteria to giant squids, and from tiny lighted jellyfish to spiny skin, many creatures, from ascidians to some sharks and stingrays, turn on their lights, literally, illuminating the darkness of the deep sea. This biological light-producing process in the body of some animals is called bioluminescence. It is astounding that these creatures can emit biological light with no change in their body temperature. Normally, light is formed by emitting heat. This basic principle applies to some of the most common sources of light that we know of, such as campfires and electrical lightbulbs.

A mechanism that produces light without heat has been created in some insects living under the sea as well as those on land. The basis of biological light production is generally the oxidation of luciferin, i.e. its conversion to oxyluciferin. The enzyme necessary for this chemical reaction to occur is luciferase.

Most living creatures that can produce bioluminescence live in deep, dark areas of the world’s various seas and oceans. Some of the inhabitants of these depths emit strong blue (secondarily green) light at an average wavelength of 475 nm. An interesting note is that underwater life forms are often created with sensitivity to the wavelengths of blue-green lights mentioned above. In rare cases, there are also sea creatures that emit light in the yellow-red wavelength range.

Animals with the ability to emit light are also usually given excellent control mechanisms so that they can use their equipment as a weapon. They can turn their lights on and off in a flash and can utilize complex chemical and neurological mechanisms that provide functions such as adjusting the intensity, color, and direction of the light. Creatures that produce light underwater sometimes do not need to use the light in order to see where they are going. Instead, they tend to use these marvelous gifts in a variety of strategic ways. Some will try to attract the attention of their prey; others will attempt to ward off predators and aggressors; still others will use their lights to indicate that they are ready for reproduction. It is even possible for some creatures to utilize several of these functions at the same time.

Let us now examine some specific species and how they employ bioluminescence.

Light vomiting shrimp

One of the most interesting examples of bioluminescence in animals is the light-emitting deep-sea shrimp Acanthephyra purpurea. This shrimp will actually vomit light from its mouth as a last-ditch effort to deter predators. The intent is to disorient, confuse, and even temporarily blind other creatures, similar to the effect of a flashbang grenade, so that the shrimp can retreat into the dark. As a result of their research on the shrimps, marine biologist Edith Widder states that the chemical substances sprayed are not blue when they are in the body and that the blue light production occurs when the luciferin substance in the sprayed liquid comes into contact with the oxygen in water.

Loosejaw fish

There are at least 42 recorded families of bony fish that have bioluminescent properties. One of them is the Photostomias guernei, or the “loosejaw fish”. This fish has a remarkable organ that emits light on the sides of its eyes. These lights, which resemble the headlight lamps of our cars, are not constantly lit, in order to avoid waste. When hunting, the fish illuminates the way ahead with the light it produces, and it can turn these lights off when they are no longer needed. A wonderful feature of this organ is that, just like headlights, a highly reflective layer is created behind the main center of the light. The reason that the fish is able to turn the light off may be because its black velvety body is contrasted by the light color of the organ and would thus attract much unwanted attention.

Deep sea hatchetfish

Bioluminescent systems were also given to creatures in order to act as a means of camouflage. They work phenomenally for both hunting and survival in situations where blending in with the environment is paramount for catching prey or evading predators. In the depths of the underwater world, the silhouette of an animal bathing in light is an easily recognizable target. One of the best examples of this phenomenon is the deep-sea hatchetfish. The fish has been created with its eyes on top of its body and its mouth facing upwards, making it easier to hunt. It also emits bioluminescence from its abdomen to provide camouflage against more aggressive, larger fish that swim lower than itself. The color of the light emitted makes it difficult to recognize the fish from below as it perfectly matches the color intensity of the environment. In the meantime, if the sunlight that hits the sea is interrupted in any way, the fish will turn off its lights and the camouflage will continue.

Black dragonfish

Diversity in the light organs of the scaleless black dragonfish (Melanostomias bartonbeani)

This species of black dragonfish (Melanostomias bartonbeani) takes advantage of luminescence in a number of ways. An illuminated area next to the eyes is used to find prey and send signals to its mates. The black dragonfish’s chin also has an illuminated extension that dangles in the waves as bait for naive prey. In addition, a set of small organs of light arranged along its abdomen play a role in concealing its silhouette. Furthermore, light-emitting pocket-like structures surrounded by a gelatinous capsule embedded in the skin are used as alarm systems. The bioluminescent systems within this creature are immensely complex and beautiful, and when observed in detail reveal the dazzling splendor of the world that we live in.

Fish with 3 different types of illumination

The Northern Stoplight Loosejaw (Malacosteus niger) has three different types of light organs, the complex use of which cannot be possible without top engineering skills. The wide, drop-shaped, illuminated organ under its eyes emits a red light at a wavelength of 702 nm as if it knows the laws of optics under the sea. This red light is not visible to most deep-sea creatures, for it is quickly absorbed in water. Yet, with this red light this fish is able to have vision in a close proximity while remaining largely undetected. This is similar to infrared binoculars soldiers use for night vision without giving away their position. The loosejaw is thus a dangerous hunter that has an edge over its prey. There also exists a blue light-emitting oval section, behind the organ, that emits red light and is usually larger in males. A third light organ is round and smaller and is located between the eyes and the red-light organ.

Angler fish

The angler fish is one of the most iconic fish of the deep ocean due to its famous rod and bioluminescence. The angler fish does not actually produce its light on its own: the light is credited to bioluminescent symbiotic bacteria that inhabit the end of the rod on their forehead. This illuminated part, which resembles a worm-like bait, is very attractive to small fish. These fish are thus lured to the angler expecting a quick snack, but instead the angler swallows them whole with its massive mouth. While doing their task of helping the angler hunt small fish, the bacteria maintain a symbiotic relationship with the fish and also find an environment in which to proliferate. In this way, they form a good example of cooperation and solidarity. One may wonder: how can such a mutual agreement come into fruition between a fish and some bacteria which are deprived of a nervous system, mind, and consciousness?

One of the reasons that marine biologists are interested in light-emitting bacteria is the wide-lit regions called the “Milky Seas.” These can be observed in satellite images of Earth. Recently, satellites helped detect a bioluminescent area of roughly 5,946 sq. mi in the Indian Ocean; scientists wondered if some bioluminescent bacteria or Dinoflagellate-type flame-colored algae may be the cause of the phenomenon.

Alarming jellyfish

The luminescence of some marine life serves as an alarm or distress siren. A remarkable example of this is the Atolla jellyfish (Atolla wyvillei), an elegant inhabitant of deep waters. This jellyfish produces blue lights that are spread in circles in the water when it is attacked. Thanks to these lights, it tries to draw the attention of larger and stronger animals than the initial attacker in order to escape from harm’s way.

As can be observed in some species that we are familiar with, such as fireflies, the bioluminescence feature that is full of wisdom granted to some living beings is a thought-provoking biological miracle which does not only make us ponder where they got these abilities from but also reveals how so many intricate patterns are found in nature.

References

• Steven H.D. Haddock, Mark A. Moline and James F. Case. 2010. Bioluminescence in the Sea, Article in Annual Review of Marine Science, DOI:10.1146/annurev-marine-120308-081028 Source: PubMed.
• Edith A. Widder. 2001. Harbor Branch Oceanographic Institution, Fort Pierce, Florida, Marine Bioluminescence, Bioscience Explained, vol 1, no 1, pp. 1-9.
• Edith A. Widder. 2010. “Bioluminescence in the Ocean: Origins of Biological, Chemical, and Ecological Diversity,” Science, vol. 328, pp. 704-708.
• www.wired.com/2012/01/glow-little-spewing-shrimp-glow/ March 28, 2018.
• en.wikipedia.org/wiki/Malacosteus_niger / April 1, 2018.
• Harold, A. 2015. Malacosteus niger. The IUCN Red List of Threatened Species 2015: e.T190149A21909439. http://dx.doi.org/10.2305/IUCN.UK.2015-4.RLTS.T190149A21909439.en.
• https://www.iucnredlist.org/species/190149/21909439

You need to read “The Very Lonely Firefly,” a story book delighting children of all ages by Eric Carle (1) to get the answer. In the mean time, you can read this article to have better insight into the enchanting world of the firefly. Are they just a pleasure to our eyes, during their short lives in the summer, or do they live on in children’s books?

Fireflies, or lightning bugs, belong to the Lampyridae family. There are thousands of firefly species all over the world and none of them are actually flies. Then what are they? Well, they are beetles, who get the names “firefly” and “lightning bug” because of the flashes of light emanating from their bodies, a process called bioluminescence (2). This “cold light” does not heat up or burn its producer through infrared or ultraviolet frequencies, and is formed by the action of an enzyme called luciferase in the lower abdomen of the firefly. It may be yellow, green, or pale red, with wavelengths from 510 to 670 nanometers. The enzyme luciferase acts on the luciferin, in the presence of magnesium ions, ATP, and oxygen to produce light (3). According to Vieira et al., 2012, in the Journal of Photochemistry and Photobiology, the firefly’s luciferase is the most important and studied bioluminescence system in scientific research(4). The firefly luciferase was cloned and isolated for the purpose of constructing bioassay systems in the late 1980s (5). Since then, due to very interesting characteristics, this system has been used in numerous biomedical, pharmaceutical and bioanalytical applications (4).

In biomedical research, the ability to visualize a biological process is very important because it offers the most direct method to support or disprove any scientific claim (6). Therefore, firefly luciferase is very desirable as a reporter in this area. Typically, the luciferase gene is cloned with a DNA sequence of interest into cells and then the cells are assayed by measuring its bioluminescence. Fusing a protein with luciferase is like putting a reflective vest on a cyclist in the dark to be able to watch him. Because the firefly luciferase lights up, it helps screening for chemical biology and drug discovery applications in academia and the pharmaceutical industry (5). For example, the firefly luciferase gene was used as a reporter to screen tumor-specific promoters in lung cancer (7). Another example showing how beneficial the firefly is for scientific research is a rapid in vivo (Latin for within the living) assessment of drug efficacy against Mycobacterium tuberculosis, which is the causative agent of most cases of tuberculosis, using an improved firefly luciferase (8). In this study, Andreu et al., 2013, used a Mycobacterium tuberculosis strain carrying a red-shifted derivative of the firefly luciferase gene to infect mice, and they monitored disease progression in living animals by bioluminescence imaging before and after treatment with a frontline anti-tuberculosis drug. Furthermore, firefly luciferase was used in a research about anti-malaria drugs, an illness which affects about 5% of the world’s population and brings a death toll of 0.5–2.5 million each year (9).

Firefly luciferase is not only used in biomedical research, but also in molecular plant biology. In the early ’90s, plant scientists were already able to show the bioluminescence of a promoter fragment fused to the firefly luciferase gene and its regulation by phytochrome (a pigment that plants use to detect light) and the circadian clock (a roughly 24 hour cycle in the physiological processes of living beings) (10) in plants. Some examples for the great usage of this system among many others include a firefly luciferase complementation assay that was used to reveal the interacting partners of Open Stomata 1 protein, which is critical for plant drought responses in Brassica oleracea (cabbage) (11) and the characterization of the promoter region of an important gene encoding a copper chaperone for the copper/zinc superoxide dismutase that is involved in oxidative stress protection of the potato plant (12).

Scientists have found many ways to use the firefly light, but what is the function of it for its real owner? Marc Branham, an assistant professor in the department of entomology and nematology at the University of Florida, explains. “Fireflies seem to flash light for a variety of reasons. The larvae produce short glows and are primarily active at night, even though many species are subterranean (underground) or semi-aquatic. Fireflies produce defensive steroids in their bodies that make them unpalatable to predators. Larvae use their glows as warning displays to communicate their distastefulness. As adults, many fireflies have flash patterns distinctive to their species and use them to identify other members of their species as well as to discriminate between members of the opposite sex. Several studies have shown that female fireflies choose mates depending upon specific male flash pattern characteristics. Higher male flash rates, as well as increased flash intensity, have been shown to be more attractive to females in two different firefly species (13).”

Are there other creatures like fireflies producing light? “Besides fireflies, many other organisms, especially marine creatures, use bioluminescence for sexual selection, attracting prey and as a means of camouflage, and it has been estimated that about 90 percent of deep-sea animals are bioluminescent, according to the Scripps Institution of Oceanography,” says Remy Melina, a staff writer for “Life’s Little Mysteries.”(14)

A firefly’s glow is a theme of summer nights, romantic poems, and childhood adventures and books. However, when you enjoy a firework show done by fireflies next time, please look at them more carefully by thinking that they have more than that to offer humanity, including thrilling scientific inventions done with just a single protein from them. Who knows what else they have waiting to be discovered by us? How amazing it is that, like everything else created on earth, a firefly is also a very precious art piece decorated with intricate features, and even though it is very tiny, its service to humanity is, in many ways, enormous.

References

http://www.barnesandnoble.com/sample/read/9780399227745
National Wildlife Federation
http://en.wikipedia.org/wiki/Firefly
Vieira J, Pinto da Silva L, Esteves da Silva JC (2012) Advances in the knowledge of light emission by firefly luciferin and oxyluciferin. J Photochem Photobiol B. 117:33-9.
Thorne N, Inglese J, Auld DS (2010) Illuminating insights into firefly luciferase and other bioluminescent reporters used in chemical biology. Chem Biol. 17(6):646-57>
Brogan J, Li F, Li W, He Z, Huang Q, Li CY (2012) Imaging molecular pathways: reporter genes Radiat Res. 177(4):508-13.
Xu R, Guo LJ, Xin J, Li WM, Gao Y, Zheng YX, Guo YH, Lin YJ, Xie YH, Wu YQ, Xu RA (2013) Luciferase assay to screen tumour-specific promoters in lung cancer.Asian Pac J Cancer Prev. 14(11):6557-62.
Andreu N, Zelmer A, Sampson SL, Ikeh M, Bancroft GJ, Schaible UE, Wiles S, Robertson BD (2013) Rapid in vivo assessment of drug efficacy against Mycobacterium tuberculosis using an improved firefly luciferase. J Antimicrob Chemother. 68(9):2118-27.
Che P, Cui L, Kutsch O, Cui L, Li Q (2012) Validating a firefly luciferase-based high-throughput screening assay for antimalarial drug discovery. Assay Drug Dev Technol. 10(1):61-8.
Millar AJ, Short SR, Chua NH, Kay SA (1992) A novel circadian phenotype based on firefly luciferase expression in transgenic plants. Plant Cell.4(9):1075-87.
Wang M, Yuan F, Hao H, Zhang Y, Zhao H, Guo A, Hu J, Zhou X, Xie CG (2013) BolOST1, an ortholog of Open Stomata 1 with alternative splicing products in Brassica oleracea, positively modulates drought responses in plants. Biochem Biophys Res Commun. 442(3-4):214-20.
Trindade LM, Horvath BM, Bergervoet MJ, Visser RG (2003) Isolation of a gene encoding a copper chaperone for the copper/zinc superoxide dismutase and characterization of its promoter in potato. Plant Physiol. 133(2):618-29.
http://www.scientificamerican.com/article/how-and-why-do-fireflies/
http://www.livescience.com/32677-what-makes-fireflies-light-up.html