Creatures of Light: Nature's Bioluminescence

The Biology of Bioluminescence

Bioluminescence is visible light generated by a living organism through a chemical reaction.

In the presence of oxygen, one type of chemical, known as a luciferin (loo-SIFF-er-in), or “light-bearer,” is acted on by another type of chemical, an enzyme known as luciferase (loo-SIFF-er-ace); other molecules are sometimes involved.

The energy produced by this reaction takes the form of photons, units of light.

Understanding Fluorescence

Fluorescent organisms contain special pigments that become excited when they absorb high-energy light. As the pigments calm down, they release the leftover energy as lower-energy light.

Since light fuels fluorescence, fluorescent objects only glow while illuminated. In most cases, when the light turns off, the fluorescent pigments stop glowing.

Rather than emitting new light right away, some pigments store the energy, and release the lower energy light slowly. This kind of glowing is called phosphorescence.

Firefly Anatomy

For a firefly, the light-producing chemical reaction takes place inside an organ called the lantern. A biochemical reaction takes place here, within specialized cells called photocytes. The reaction releases energy in the form of light.

Lanterns are present in one or more segments of a firefly’s abdomen, depending upon the species and whether the individual is male or female.

Males typically have much bigger eyes than females. Large eyes are an advantage when looking for a female’s flashed response.

Solar Powered

During the day, some dinoflagellates soak up sunlight and use the energy to make chemical compounds—the process known as photosynthesis. At night, they use energy stored in chemicals to make light. The brighter the sunlight during the day, the stronger the flash at night.

Thousands of particles inside a dinoflagellate contain the organism’s luciferin and luciferase. In many dinoflagellate species, these tiny lanterns, known as scintillons (SIN-te-lons), are destroyed at dawn and manufactured again at the end of the day.

Colorful Tool Kit

Naturally occurring fluorescent proteins have become important tools for researchers as they investigate questions like how stem cells specialize or how brains cells communicate.

GFP—green fluorescent protein—was the first to be adapted for broad scientific use. Researchers have employed it to do many jobs, including literally illuminating each neuron’s location in the human brain. By deducing which neurons form a circuit, researchers have constructed a “brain atlas.”

Bioluminescent Bacteria

Although they are among the simplest forms of life, a number of bacteria species make luciferin and luciferase—the chemicals needed for living light.

By studying bioluminescent bacteria, scientists made an intriguing discovery. When bacteria multiply in a petri dish, they don’t glow at first. But when they reach a certain density, their light surges, as if someone flipped a switch.

Why? Studies show that these bacteria communicate by releasing and detecting chemical signals. When they sense enough signals—called a quorum—the genes for their light-making chemicals turn on.

A Difficult Duality

During and after British rule, the Indian princes found themselves in an almost impossible position. They were obliged to live within traditional boundaries and appear as the stereotypical “creatures” when required, but educated by English tutors, they were also encouraged to think along western lines and behave as English gentlemen.

Some refused to countenance these conflicting demands, but most accepted the dominant British model of modernity and were viewed as exotic beings who epitomized India’s role as the crown jewel in Britain’s imperial crown.

Waitomo Glowworm Cave Simulation Glowworms (arachnocampa luminosa larvae)
North Island, New Zealand

In this re-creation of part of New Zealand’s Waitomo cave system, you’ll glimpse a fantastic spectacle above your head: sticky “fishing lines” dropped from the ceiling by glowworms—bioluminescent gnat larvae—which glow more brightly when the larvae are hungry.

When prey fly toward the light, they become tangled in the lines…and the glowworms then reel in and eat their catch.

Vampire Squid Model Vampyroteuthis infernalis
Tropical and temperate oceans

With a name like “vampire squid from hell” (its official name in Latin) you’d guess that this creature lives at depths where the sun never shines. For its size, it has the largest eyes of any animal known, which help it detect the dim light of bioluminescence.

When a predator approaches, a vampire squid thrashes around, waving its bioluminescent arm tips, confusing its attacker and then swimming away. To hide in the dark, it pulls its webbed arms over its head so only the dark inner side of its “cloak” is exposed.

Dinoflagellates

The scientific name of the dinoflagellate species on the left (Pyrodinium bahamense) means “whirling fire creature of the Bahamas.” It rides the waves of the Caribbean Sea and collects in large numbers in sheltered coves.

Up to 30 percent of dinoflagellate species that live in the ocean light up the water when shaken or stirred, creating breathtaking bioluminescent displays, as is seen in the photo on the right.

Bitter Oyster Mushroom Panellus stipticus
Eastern and southern North America

Bioluminescence on land appears in unexpected places. The luminescent glow of mushrooms is often called foxfire, a term coined by early settlers.

This species of bioluminescent mushroom grows in clumps on logs, stumps, and trunks of deciduous trees, especially beech, oak, and birch.

Stoplight Loosejaw Model Malacosteus niger
Northern Hemisphere

The aptly named Stoplight Loosejaw both luminesces and fluoresces. One of its organs produces a blue-green light and contains a fluorescent protein that changes the wavelength of the light to red.

The fish uses this red light (which is nearly invisible to most other sea creatures) to spot red shrimp, then catches the shrimp in its oversized and extendable “loose” jaw. The Stoplight Loosejaw is among the few deep-sea animals that both produce and see red light.

Male Firefly Phausis reticulata
Central and southeastern U.S.

The male firefly modeled here is sometimes called a blue ghost. It makes light but doesn’t flash. Instead, its light slowly strengthens and fades as the blue ghost flies a foot or two above the ground searching for flightless females below.

Scientists think that this type of glowing is an ancient trait among fireflies; the familiar blinking evolved later.