How luciferin brought living light to folklore and science

Bioluminescent glows have fuelled myths and legends for thousands of years. Jennifer Tsang explores how cultures around the world have interpreted luciferin's glow. 

 Illustration by Ben Coy

Illustration by Ben Coy

I stepped outside one summer evening at my childhood home in Austin, Texas not suspecting a thing. It was about sunset and warm. A yellow glow jumped out right in front of me for just a split second. I thought my eyes were playing tricks on me, but it happened again, and again. Were these really the mysterious fireflies I thought were fictional for the first 18 years of my life? I had heard stories about catching fireflies in a jar to make a living lamp, but I thought these were just fairy tales to entertain a child’s imagination. Since I had never seen it before, surely it couldn’t be real? Little did I know that bioluminescence was part of reality. I collected some of the fireflies, put them in a jar sealed with a paper towel on top, and turned off the lights, mesmerised by their ephemeral glow.

In the darkness of the night, bioluminescent insects or mushrooms reveal themselves, oceans light up when disturbed, and the world turns into a hauntingly beautiful place. One could imagine this sight as frightful or surreal, and bioluminescence may even resemble ghosts or spirits to some. Bioluminescence has held a folkloric charisma since ancient times. Does this sentiment still hold true? In our modern time, how many people walk through life now without witnessing bioluminescence? After all, I never observed bioluminescence in the first 18 years of my life.

Bioluminescence occurs when light is released through a chemical reaction. Generally, two things are involved: the enzyme luciferase and the pigment luciferin. Luciferase gives an electron to luciferin to create oxyluciferin. Oxyluciferin releases light, causing the green-yellow glow that we see. In the ocean under the moonlight, in the forest, or in dark caves, many creatures glow because this chemical reaction happens within their bodies. In addition to luciferin and luciferase, some organisms require other cofactors or specific conditions to glow.

 
  Diagram showing bioillumination in the firefly squid ( Watasenia scintillans ).   Chiswick Chap/Wikimedia Commons  (CC BY-SA 4.0)

Diagram showing bioillumination in the firefly squid (Watasenia scintillans). Chiswick Chap/Wikimedia Commons (CC BY-SA 4.0)

 

Many organisms only glow at night, such as the bobtail squid, which uses symbiotic bioluminescent bacteria to camouflage itself against the moonlight. Dinoflagellates, unicellular organisms suspended in the ocean, only glow when they are disturbed. Bioluminescent fungi dimly illuminate the forests in the night. In fish alone, bioluminescence has evolved on at least 27 separate occasions. Bioluminescence has evolved in animals for all sorts of purposes, from attracting mates to luring in prey to scaring away predators. So many creatures have the power to emit light, but this ability has eluded humans. Is this why bioluminescence is held in such a mythical or even divine regard? 

Since ancient times, light and dark have played contrasting roles. White and black, day and night, this contrast became a symbol of good and evil. Light has been deified by ancient people who worshipped the fire god or the sun god, for instance. Gods, angels, fairies, and saints radiate light or halos. The terms luciferase and luciferin are derived from the Latin term lucem ferre, which means “light bearer.” Not by coincidence, “Lucifer” once meant “the morning star,” “the planet Venus,” or “light-bringing.” With the rise of Christianity, the role of Lucifer began to change from a morning star, to a defiant angel, and finally to the devil and the Prince of Darkness. When we think about light, we often associate it with heat, fire, and the sun. Because bioluminescence is a cool light without fire or heat, it tended to hold a mysterious, supernatural, or divine fascination throughout history. Like the contrasting meanings of “Lucifer,” bioluminescence has played parts in both good and evil for thousands of years. Bioluminescent organisms were viewed as divine or possessing healing powers, but bioluminescence was also met with fear and repulsion. 

Because of the lack of writing and documentation technologies in much of antiquity, historians have a hard time tracking early accounts of bioluminescence. The first mentions of bioluminescence probably came in the form of poetry and folk songs. The first written evidence of bioluminescence was dated to around 1500-1000 BC in the Thirteen Classics of Confucian tradition. But the oldest surviving detailed account on bioluminescence comes from Aristotle. In De Anima (circa 350 BC), a treatise on the nature of living things, Aristotle wrote, “Not everything is visible in light, but only the colour proper to each thing; for some things are not seen in the light but bring about perception in the dark, e.g. those things which appear fiery and shining (and there is no one name for them), such as fungus, horn, the heads, scales, and eyes of fish; but in none of these is the proper colour seen.” Aristotle realised that these organisms are different from the organisms that had colour and can be seen during the day.

Early accounts of bioluminescence mostly involved fireflies, glowworms, and luminescent fungi on trees. Both the Chinese and the Japanese wrote ancient stories about mysterious lights in the waters, fields and mountains crediting it to dragons or gods. In India, glowworms grazed holy writings. Fireflies have also been found in early Buddhist text from India and China. Bioluminescence in the oceans, likely due to dinoflagellates, has captivated us especially as we learnt to sail and explore the seas. The Romans, always on the lookout for omens, saw bioluminescence of the sea as a premonition. Roman historian Titus Livius noticed that as dictator Quintus Fabius Maximus became consult, “this year the sea appeared to be on fire.” Aristotle characterised bioluminescence in the ocean as “exahalations of fire from the sea” and, in later centuries, ocean bioluminescence was called “burning of the seas.”  

In contrast to the association of bioluminescence to the gods or the supernatural, bioluminescence has also been associated with death and decay. Luminescent bacteria and fungi would cover human bodies left unburied, illuminating them in the night. The Chinese once called it “devil lights of the outer wilderness.” In Li-Chi (Notes on Ancient Rites, circa 400-100 BC) decaying grass was implicated as the origin of fireflies. Fireflies were feared in the Middle Ages in Italy and were met with a superstitious dread because they embody spirits of their departed ancestors.

It wasn’t until the Scientific Revolution when we began to uncover the science behind bioluminescence. Robert Boyle (known for Boyle’s law) and his assistant Robert Hooke created an air pump and chamber to study the properties of air. They noticed that when the chamber was depleted of air, the glowworms inside dimmed. But when air was allowed to enter into the chamber, the worms began to glow again. Though Boyle and Hooke did not know this at the time, it is oxygen that is essential for bioluminescence. 

 
  Dinoflagellates glow blue in the surf beneath a night sky.   Mike/  Wikimedia Commons  (CC BY-SA 2.0)

Dinoflagellates glow blue in the surf beneath a night sky. Mike/Wikimedia Commons (CC BY-SA 2.0)

 

With improvements to rudimentary microscopes, scientists were able to observe bioluminescence of individual dinoflagellates. Macartney observed that dinoflagellates glowed when poked and prodded and thought that light emission served a protective function. Being able to observe the organisms under the microscope meant scientists were able to see where exactly the light was coming from. In the dinoflagellates, bioluminescence was localised to distinct locations in the cell.

Soon, the first chemiluminescence reaction (emission of light due to a chemical reaction) was discovered in 1877 in lophine. This discovery lead the pharmacologist Raphaël Dubois to wonder whether bioluminescence is a chemical reaction occurring inside a living organism. He made a paste out of bioluminescent clams in cold water and split this glowing concoction into two parts. He heated one part and watched the glow disappear rapidly. The part that was not heated eventually dimmed. By mixing the cold sample and the cooled hot sample, luminescence was restored. Dubois concluded that bioluminescence is a chemical reaction requiring a heat stable molecule which he named luciferin and a heat labile molecule which he thought could be an enzyme and called luciferase.

Aside from my brief experience with fireflies that one summer night, I have not witnessed the magic of bioluminescence. With the bustle of the city and the bright streetlights, how often do we notice these living lights today? If it wasn't for that one summer night, the only place I would have seen bioluminescence is in a David Attenborough documentary, or in Avatar, a movie so infused with fantasy that it gives bioluminescence a dreamlike charm, perhaps reminiscent of the stories told during ancient times. Avatar brings us to a world where its humanoid inhabitants live in harmony with the plants and animals among them and worship a Mother Earth through the Tree of Souls. The luminescent seeds from this tree resemble half dandelion and half jellyfish and they believe them to be pure and sacred spirits. The portrayal of the bioluminescent in Avatar reveals a fascination with living light even to this date.

Over the past 3,000 years, we have learnt quite a bit about bioluminescence. As science advanced, luminescence has been harnessed for biological experiments. Scientists introduce bioluminescence genes into bacteria to monitor their movement inside hosts. Luminescence is used to detect proteins from cells. Though luminescence is considered commonplace in the lab, it is still inherently magical and beautiful. Still, our first view of bioluminescence may have us mesmerised by such an unusual sight despite our understanding of the science behind it. We may not hold bioluminescence to such godlike esteem or fear nowadays, but glimpses of bioluminescence may make us ponder our place in the world and how such a beautiful sight could have come to be.

Edited by Diana Crow