In the ever-dark depths of our ocean, a huge variety of organisms have developed different strategies to enlighten their environment. Among them are even deep-sea corals. The production of light is referred to as “bioluminescence”. In essence, bioluminescence is the product of an oxidative reaction in which energy is released in the form of light. The production of light is essential for many organisms in order to communicate with each other, scare their enemies or attract theirfood. Some organisms have evolved fluorescent proteins to convert light into different colours. This is for example the case in the jellyfish Aequorea victoria. The discovery of its green fluorescent protein has revolutionised modern biology, helping for instance in the development of therapeutics against viruses. Unfortunately, the deep-sea is under threat – not only by our way of living on land, but also by the emergence of companies pushing the boundaries for the ruthless –instead of sustainable- exploitation of the deep-sea. By destroying the deep-sea, we deprive ourselves of the chance of discoveries that will improve everyone’s life.
Woods Hole is a tiny fishing village in Cape Cod in New England, which every summer is filled with enthusiastic biology students, spending hours until the late night or even until sunrise to study marine organisms. At the beginning of my PhD I had the chance to accompany my professor to Woods Hole to perform experiments on starfish oocytes, an interesting story that however should not be part of this exploration. Woods Hole is a place where ground-breaking discoveries are being made that have lead already to multiple nobel prices. Upon arrival, some scientists told me with glowing eyes that during some nights, when the water is warm enough, you can go swimming with sparkling stars in the sea at Stony Beach. I feverishly waited for that moment until the rumours spread that now was the time to go. With a whole bunch of scientists we went into the sea and got enchanted by the sparkling bluish light that appeared every time you agitated the water. That night you heard so many “woooh”, “aaahhhhs” and “ooohs” that the police came and fished us out of the water with their overly bright torches, because we apparently disturbed the neighbours.
The source of the light we saw were dinoflagellates, which are tiny marine plankton. They belong to a huge group of organisms that is capable of producing light. We call the production of light by organisms “bioluminescence”. If we think about light-producing organisms, “fireflies” and maybe the bizarre-looking anglerfish come to our mind. Thinking that organisms that play around with light are rare is however completely misleading. In fact, almost all taxonomic groups have evolved species that produce light – flowering plants, and terrestrial vertebrates like birds, amphibians and mammals are the few prominent lineages that have not evolved bioluminescence. Most of the bioluminescent organisms live where the production of light makes most sense: in the crystal-clear, ever-dark deepness of the oceans. Here, light coming from a tiny organism can be spotted from miles away. This allows communication between organisms, searching for a mating partner, andit can attract bait or repel predators. Light made by life is so prominent in the deep-sea, that many transparent organisms have evolved pigmented stomachs to hide the light coming from their ingested prey to remain hidden in the dark and not attract to much attention from their own enemies. As you can see in the next video, even coral make use of bioluminescence.
How do all these different organisms manage to glow or flash in the dark? In the species tree, we find bioluminescence in different organisms that are not necessarily closely related. Therefore, bioluminescence has evolved many times during evolution. Bioluminescence is the result of a chemical reaction in which a compound, that is called luciferin, is oxidised. During this oxidation, energy is released in the form of a photon which we recognise in the form of light. Of course, these reactions do not take place spontaneously. You need a catalyser that allows the reaction to take place. For this, the organisms use an enzyme, which is generally called luciferase. Interestingly, bioluminescent organisms have different strategies to use bioluminescence: most organisms can produce luciferin and luciferase themselves, because they possess the genes in their own genomes to do so (e.g. the bacterium Vibrio fisheri), sometimes they ingest organisms that produce luciferin and luciferase and accumulate these compunds (e.g. golden sweeper fish) and again others sometimes develop specialised organs in which they cultivate bacteria (e.g. angler fish) that are bioluminescent.
A revolution in biology thanks to discoveries made in jellyfish
One of the nobel laureats anchored in Woods Hole, Osamu Shimomura, was especially fascinated by the glow of the jellyfish Aequorea victoria, which lives usually in shallow waters. His work revolutionised biological research. In principal, he found that Aequorea victoria first produces bluish light by bioluminescence. However, Aequorea victoria also emits greenish light. How can this be? For this, Aequorea victoria uses a special trick: fluorescence. Fluorescence is fundamentally different from bioluminescence: In bioluminescence, a chemical reaction produces light by the emission of a photon. In fluorescence, you need a light source that transfers electrons on a more energy-intensive orbit where they circulate around their nuclei. As soon as these electrons fall back on the orbit which is of lower intensity, light is emitted. This process is very quick, so that you see fluorescence only if you already shine light on the fluorescent compound (in contrast to bioluminescence where it can be totally dark and then there is light appearing). The light for activation is of higher energy (bluish) than the emitted light (reddish). In the case of Aequorea victoria, it produces first bluish light by bioluminescence that is then converted to greenish light by fluorescence using green fluorescent protein (GFP).
In modern biology, GFP and other fluorescent proteins that emit light of a different colour are used extensively. If we like to know where a protein is localised in the cell or how it moves and behaves in a cell, we will basically attach GFP to this protein by genetically modifying the cells. Then, by using a microscope and shining light on the cell, we can observe live what the protein is doing. The discovery of GFP in combination with the possibility for us to tag a protein by genetic engineering has revolutionised our understanding in virtually all fields of biological research, helping us to understand for example the way a virus takes through an infected cell and based on this todevelop therapeutic compounds. Have a look on the following video to see what kind of beautiful movies we are able to make thanks to the discovery of GFP:
This shows again how all countries of our world need to work together to use our oceans sustainably. The United Nations had declared 2021 – 2030, as the decade of ocean science for sustainable development. Let’s work together to make it indeed a decade of sustainable development and not a decade of ruthless exploitation.
The decade of ocean science for sustainable development
To continue reading the scientific articles:
Haddock SH, Moline MA, Case JF. Bioluminescence in the sea. Ann Rev Mar Sci. 2010;2:443-93. doi: 10.1146/annurev-marine-120308-081028. PMID: 21141672
Weblink to the official website about the “decade of ocean science for Sustainable development”: https://www.oceandecade.org
Thanks to Trevor McKinnon for providing the photo on unsplash.
„Biolumineszenz“Fluoreszenz
Das Problem von der Entstehung des Lichts in der Tiefsee wurde sehr verständlich erklärt. Dies gilt insbesondere auch für den Unterschied zwischen Biolumineszenz und Fluoreszenz. Der Text ist ohne
chemische und biologische Kenntnisse zu verstehen. Die Gefahren für diese faszinierende Welt werden gut beschrieben