BIOLUMINESCENCE NATURE’S LIGHT SHOW:

By ANNE SUNDERMANN

"BIOLUMINESCENCE IS NOT A RARE OCCURRENCE, OR UNIQUE TO ONE SPECIES. ON THE CONTRARY, IT IS WIDESPREAD WITHIN SEVERAL ECOLOGICAL NICHES, AND IS FOUND IN DIVERSE AND DISPARATE ORGANISMS"

The warm saltwater of Lough Hyne, Co. Cork offer visitors a spectacular vision of shimmering waves full of bioluminescent plankton. Offshore, nature’s fireworks are regularly displayed by bioluminescent organisms that light up the waters of Ireland’s oceans and seas.

Bioluminescence is not a rare occurrence, or unique to one species. On the contrary, it is widespread within several ecological niches, and is found in diverse and disparate organisms. From microscopic plankton to jellyfish and squid to sharks, researchers have found that more than three quarters of marine creatures in the water column have bioluminescence capabilities. Bottomdwelling sea creatures and freshwater species are less likely to produce light.

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Less common on land, bioluminescence is restricted to invertebrates such as insects and fungi. Fireflies, click beetles, and glow worms use their light to lure prey, deflect predators, and attract mating partners. Up to 70 species of fungi are bioluminescent while no light-producing plants species have been found.

A Cold Light

Organisms can emit several different types of light: fluorescence, which is light emitted from external source material; phosphorescence, where external light is absorbed and emitted at a different wavelength; and chemiluminescence, which is light created from a chemical reaction.

Bioluminescent light is, then, a form of chemiluminescence, generated internally through chemical or biological processes rather than via excitation from external sources of light. According to Martini & Haddock (2017), bioluminescence is “an active ability to communicate, in contrast to the passive traits of fluorescence or phosphorescence in which photons are absorbed by a tissue or structure and then re-emitted at a different wavelength.”

The luminescent product is considered a cold light, that is, less than 20 percent of emissions are heat producing. The emitted light tends toward blues and greens in a marine environment, wavelengths that travel best through water, but there is a variety across the light spectrum including yellows and, rarely, reds.

Bringer Of Light

Luciferin is the base compound, or substrate, for bioluminescence. Basically, an enzyme [luciferase] catalyses the luciferin (primarily with oxygen, but also other compounds), which emits coloured light as a way of releasing energy from the reaction. Luciferin, derived from the term light bringer, is found in the food chain and is also manufactured by some organisms. For example, a modified form of dinoflagellate luciferin may have evolved in concert with that found in a few species of shrimp, which may point to a dietary connection. Another research team has determined that the luciferin-luciferase combination for several bioluminescent fungi suggests a single bioluminescent system. Regardless of its origins, researchers have not detected much change in the basics of bioluminescence over time.

EAT, PREY, LOVE

Bioluminescence is used by organisms to attract potential food sources, and to escape from becoming prey themselves, particularly as camouflage. Lighted patterns also serve as a means of intraspecies communication, notably during mating.

The visual component of bioluminescence can be quite artistic. Several organisms spew or splatter their light emissions, á la Jackson

Pollack. Others create their glow up by lining their bodies with specialized cells called photophores, while others create a pulsing light, using bacteria growing in pouches that open and close. There is a worm species that lights up an appendage, which breaks away as a diversion to attack.

Foxfire, a blue-green light created by several fungi species, has been the stuff of legend since the 19th century. The fungi emit light in damp and rotting wood, creating eerie night-time landscapes. Once scientists started researching this phenomenon, they found bioluminescence that was based on a biological circadian rhythm. The researchers suspect that “the circadian control of light might be used to optimize energy for attracting insects to spread spores.”

Although most bioluminescent organisms provide their own source of light, many team up symbiotically with bacteria. For example, the female anglerfish Diceratias pileatus, is known for the bright lure dangling above its gaping tooth-filled mouth, an attractant for prey and a beacon for the much smaller male. The fish has a mutualistic symbiotic relationship with the bioluminescent bacteria that live inside the globular appendage; the bacteria provide the fish with potential mate and prey in the darkness of the deep sea, while the fish offers a secure home for the light-producing bacteria.

Evolutionary Spotlight

The ability to create light serves many purposes in nature and its widespread occurrence, as well as the high diversity of organisms with this capability, support the theory that bioluminescence serves a variety of ecological roles.

With its many roles in nature, it’s no wonder that there is commercial interest in bioluminescence, primarily as biosensors or markers for monitoring conditions such as blood clots and drug effectiveness, and other forms of biomedical and environmental monitoring. A jellyfish Aequorea victoria has both bioluminescent and fluorescent properties and contains protein that gives off a green light, known as green fluorescent protein (GFP). The cloned version of the GFP is used as a marker to track proteins in living cells, which is helpful to gauge the efficacy of cancer treatments, determine the changes in pH and oxygen levels, and many other uses.