Bioluminescence, a fascinating natural phenomenon

25/11/2020

Without a doubt, one of the most fascinating phenomena of nature is that of bioluminescence, which at first sight we might consider inexplicable, but as we shall see, the latter is not so.

This phenomenon is generalized in marine habitats, it is estimated that 90% of the organisms in the depths present it, while on land it is only observed in fungi and invertebrates. In general, we can find it in plants, animals, bacteria, and fungi.

Bioluminescence is a process that occurs in some living organisms, where a chemical reaction is created that produces light. Most of the time we can see it at night on the beaches, on the shore, where the waves break, which is the time when daylight does not prevent us.

But how is it produced, since we said that it is given thanks to the energy generated by a chemical reaction and this manifests itself as light? For this, the enzyme luciferase, the protein luciferin, oxygen, and the nucleotide adenosine triphosphate (ATP) intervene. Luciferase catalyzes the oxidation of a substrate of luciferin and with the ATP the cellular energy is obtained that allows to produce that light emission.

There are basically three types of bioluminescence: intracellular, extracellular, and symbiosis with luminescent bacteria.

Intracellular bioluminescence is that which is generated by specialized cells, either in unicellular or pluricellular organisms. The dinoflagellates are an example of unicellular organisms with this condition; in the case of the pluricellular ones we have as an example the fireflies that carry out a more complex process through urate crystals they possess; or, some fish through guanine plates; other organisms that present it are the squids.

Extracellular bioluminescence occurs from this chemical reaction that we commented on, but outside the organism. Once synthesized, luciferase and luciferin are stored separately in various glands in the skin or under it, so that when the time comes, they are expelled simultaneously mixing outwards and consequently producing luminous clouds. This type of luminescence is common in many crustaceans and some cephalopods.

The symbiosis with luminescent bacteria, this phenomenon is known only in marine animals such as celestial (actinias, hydras, corals, jellyfish, anemones, and polyps), worms, mollusks, echinoderms, and fish, mainly in abyssal fish (this is how those that live at great depths are called).

This modality seems to be the most extended, the organisms that present it have small bladders called photophores, where they keep luminescent bacteria, same that present the chemical reaction already commented. There are species that can control at will the intensity of the light emitted and even neutralize it through structures connected to their nervous system.

As for the usefulness of luminescence for organisms, there are several: as a camouflage to blend in with the ambient lighting; it is also thought that for some it can serve as a defense tool, since it dissuades possible predators or, on the contrary, it can serve as a lure to attract prey; for others as a distraction, such is the case of squids that instead of ink release a bioluminescent cloud that gives them the opportunity to escape; another usefulness is communication; and finally, lighting, especially in abyssal organisms.

In the case of fungi, it is not yet known exactly, but it is considered that it has an important role in their reproduction by attracting arthropods with positive phototropism (attraction to light), so these, in their mobility, will spread the spores of the fungus thus contributing to its propagation and consequent survival as a species.

There is another particular case of natural lighting, which works differently, the fluorescence, as is the case of some jellyfish as the so-called "crystal gelatin" (Aequorea victoria) that produces the green fluorescent protein or GFP according to its acronym in English (Green Fluorescent Protein), which is capable of capturing light from the range of ultraviolet rays that emit green light.

These jellyfish show a very bright luminescence, on the edge of the outer bell they have a sequence of glowing dots. Professor Osamu Shimomura was the first to isolate GFP in 1962 from the Aequorea Victoria.

In October 2008, Professors Martin Chalfie (American), Osamu Shimomura (Japanese) and Roger Y. Tsien (Chinese American), were awarded the 2008 Nobel Prize in Chemistry for the "Discovery and Development of Green Fluorescent Protein (GFP).

The green fluorescent protein (GFP), which has been modified to emit colors at different wavelengths and together with proteins derived from other organisms offers new varieties of fluorescent proteins, already has and will have an infinite number of applications in everyday use in a wide variety of fields, that is, it has great biotechnological potential.

Since its discovery in 1962, it has undergone many changes; its applications involve all areas of biology. One of the areas that have benefited most from the multiple uses of GFP has been neuroscience. It has been possible to mark neurons in vivo with up to 90 fluorescent colors, which gives the possibility of visualizing the networks of the neural architecture of the same organism.

Confinement causes greater bioluminescence

The decline in human activities due to the confinement has led to the recovery of nature and its expression in phenomena like bioluminescence, which has been observed along the Mexican coast, said David Uriel Hernández Becerril, a researcher at UNAM's Institute of Marine Sciences and Limnology.

"There is no record of the periodicity or places where bioluminescence occurs, but the minimal presence of human activity or lack thereof has made it possible for it to disperse to areas where it was rarely seen before, such as several coasts of Mexico," he said.

It is sad that the coronavirus emergency has shown that human activities such as tourism limit the distribution of species on the planet. Tourism, although it generates economic resources and detonates development, inhibits the growth of marine communities because it contaminates the water, air, and soil.

These phenomena and the sighting of wild animals after quarantine should be an incentive to be aware of the importance of biodiversity, cultural, and natural heritage. "It is likely that these days environmental pollution will continue to decrease and more animals will appear in cities; it is time to reflect on what we are doing wrong".

By Mexicanist, with information from Inecol by Alberto Rísquez