They are alive and glowing

I kept a large bunch of these zoophytes in a vessel with salt water…
When I rubbed some part of a branch in the dark, the whole animal
it began to phosphoresce strongly with green light;
I don't think I've ever seen anything more beautiful in this kind.
Charles Darwin,
Voyage on the ship "Beagle" Currently, about 800 species of luminous living creatures are known.

Most of them live in the sea, more often in deep waters. These are bacteria, unicellular flagellate algae, radiolarians, fungi, planktonic and attached coelenterates, siphonophores, sea feathers, combworms, echinoderms (ophiura, starfish, holothurias and sea lilies), worms, mollusks, crustaceans, fish. Some of the most brightly glowing animals are pyrosomes (fireflies); other tunicates – primitive chordates (salps, appendicularies) are also able to glow. Of the freshwater bioluminescent species, only the New Zealand gastropod mollusk Latia neritoides and several species of bacteria are known. Among terrestrial organisms, individual species of fungi, earthworms, snails, millipedes and insects glow.

At the level of the microcosm, a very weak glow, which we can register only with the help of highly sensitive photometers, is a side effect of the neutralization of reactive oxygen species by enzymes, which are necessary, but toxic to the cells of participants in the glucose oxidation process. They also supply the energy necessary for chemiluminescence to various phosphor proteins.

One of the first bacterial lamps – a flask with a culture of glowing bacteria – was entertained by the Dutch botanist and microbiologist Martin Beyerink more than 100 years ago. In 1935, such lamps even illuminated the great hall of the Paris Oceanological Institute, and during the war, the Soviet microbiologist A.A.Egorova used glowing bacteria for prosaic purposes – to illuminate the laboratory. And you can set up a similar experiment: put raw fish or meat in a warm place, wait a week or two, and then come up at night (from the windward side!) and look what happened – it is likely that the bacteria that populated the nutrient medium will glow with an otherworldly light.

In bacteria, phosphor proteins are scattered throughout the cell, in unicellular eukaryotic (having a cell nucleus) organisms, they are located in membrane-surrounded vesicles in the cytoplasm. In multicellular animals, light is usually emitted by special cells – photocytes, often grouped into special organs – photophores. Photocytes of coelenterates and other primitive animals, as well as photophores working due to symbiotic photobacteria, glow continuously or for several seconds after mechanical or chemical irritation. In animals with a more or less developed nervous system, it controls the work of photocytes, turning them on and off in response to external stimuli or when the internal environment of the body changes. In addition to intracellular, deep-sea shrimps, octopuses, cuttlefish and squid have a secretory glow: a mixture of the secretion products of two different glands is ejected from the mantle or from under the shell and spreads in the water like a shining cloud, blinding the enemy.

Another classic example of bioluminescence is wood rot. It is not the tree itself that glows in them, but the mycelium of an ordinary open. And in the higher fungi of the genus Mycena, also growing on a rotting tree, but in warm places like Brazil and Japan, fruit bodies glow – what are usually called mushrooms (although mold, yeast and other fungi are also fungi, only lower). One of the species of this genus is called M.lux-coeli, "mycena is the light of heaven".

Those who are lucky enough to swim in the sea at night during its glow will remember this enchanting sight for the rest of their lives. Bacteria, mainly of the genera Photobacterium and Vibrio, and multicellular planktonic organisms glow in the sea, but the main light source is one of the largest (up to 3 mm!) and complexly arranged unicellular organisms, flagellate algae Noctiluca.

In some years, usually in autumn, their number increases so much that the whole sea glows – where the water moves at least a little. If you are unlucky and you find yourself on the shores of warm seas at the wrong time, try pouring seawater into a jar and adding a little sugar there. Noctiluces will react to this by increasing the activity of the luciferin protein. (The luciferin complex is the most common of about 30 known bioluminescence mechanisms.) Shake the water and admire the bluish glow. And when you get enough of it, you can remember that you are looking at one of the unsolved mysteries of nature: the ambiguity of the evolutionary mechanisms of the appearance of the ability to glow in a variety of taxa was noted by Darwin in a separate chapter of the Origin of Species, and since then scientists have not been able to shed the light of truth on this question.

The glow could develop in organisms living in conditions of good illumination, based on pigment compounds that perform a light-protective function. But the gradual accumulation of the trait – one photon per second, then two, then ten – both in them and in their nocturnal and deep-sea relatives could not affect natural selection: such a weak glow is not felt even by the most sensitive eyes, and the appearance of ready-made mechanisms of intense glow in a bare place also looks impossible. And even the functions of the glow in many species remain completely incomprehensible or hypothetical.

Glowing colonies of bacteria and fungi attract insects that spread germs and spores or mycelium of fungi. Insectivorous larvae of New Zealand mosquitoes Arachnocampa weave a fishing net and highlight it with their own body, attracting small insects. Light flashes can scare away predators or just fast-moving animals from jellyfish, combfish and other helpless and gentle creatures. For the same purpose, corals and other colonial animals growing in shallow water glow in response to mechanical irritation, and their neighbors, who have not been touched, also begin to flicker. Deep–sea corals convert the weak short-wave light reaching them into radiation with a longer wavelength - perhaps in order to enable photosynthesis of symbiotic algae living in their tissues.

The location of phosphors and even the nature of the flashing of luminous spots can serve for communication – for example, to attract a partner. And the females of the American firefly Photuris versicolor, after mating, begin to "beat off the morse code" of females of another species, attracting its males not with amorous, but with gastronomic purposes. Off the coast of Japan, mass weddings are celebrated by umitoharu (sea fireflies) – tiny, 1-2 mm long crustaceans of the genus Cypridina, and squid Watasenia scintellans (shimmering). The body of the watazenia is about 10 cm long, along with the tentacles are dotted with photophore pearls and illuminate an area with a diameter of 25-30 cm - imagine what the sea looks like with a whole shoal of these squids!

In many deep-sea cephalopods, the body is painted with a pattern of multicolored light spots, and the photophores are very complicated, like a spotlight shining only in the right direction with reflectors and lenses (sometimes double and colored).

Many deep-sea planktonic shrimp have the ability to glow. On the limbs, along the sides and on the abdominal side of the body, they have up to 150 photophores, sometimes covered with lenses. The location and number of photophores for each species is strictly constant and in the darkness of the ocean depths helps males to find females and all together – to gather in flocks. In some species of shrimp, the organs of the Pestle glow – areas of the liver that are clearly visible through a thin translucent shell. Some shrimps, mainly from the genus Systellaspis, emit a jet of glowing liquid and use a "fire curtain" to hide from enemies.

Many people are familiar with sea anglers not from a zoology textbook, but from the cartoon "In Search of Nemo". The order of anglerfish (Lophiiformes) is the most diverse (16 families, over 70 genera and over 225 species) and, perhaps, the most interesting of the deep–sea fish.

Female anglers are predators with a large mouth, powerful teeth and a highly stretchable stomach. Sometimes dead anglers are found on the surface of the sea, choking on fish that exceed their size by more than twice: the predator cannot release it because of the structure of its teeth. The first ray of their dorsal fin is turned into a "fishing rod" (illytion) with a glowing "worm" (esca) at the end. It is a gland filled with mucus, which contains bioluminescent bacteria. Due to the expansion of the walls of the arteries feeding the esc with blood, the fish can arbitrarily cause the glow of bacteria that need an influx of oxygen for this, or stop it by narrowing the vessels. Usually the glow occurs in the form of a series of flashes, individual for each species. The illition in the species Ceratias holboelli is able to extend and retract into a special channel on the back. Enticing prey, this angler gradually moves the glowing bait to his mouth until he swallows the victim. And in Galatheathauma axeli, the bait is located right in the mouth.

In addition to bizarre shapes and hunting tools, anglers are characterized by unusual relationships between the sexes. The largest females (Ceratias holboelli) grow up to 1.2 m; the length of males in different species is only 1.5–4.5 cm. In their youth, they have well-developed eyes and large olfactory organs. This allows them to find brides in the still water of great depths by the smell of pheromones. Approaching the female, the male recognizes her species by the structure of the eka or by the color and frequency of flashes. Then the male clings to the side of his wife with sharp teeth, fuses with her lips and tongue, and his jaws, teeth, eyes and intestines are reduced, so that in the end he turns into a process that produces sperm. The male feeds at the expense of the female's blood: their blood vessels also fuse. Up to three males can simultaneously parasitize on one female.

In vertebrates more highly organized than fish, bioluminescence does not occur (rumors about luminous spots on the sides of the Trinidad lizard have not been confirmed). Only Homo sapiens has learned to use this phenomenon, and then only recently. In the early 1960s, American scientists Johnson and Shimomura isolated the first luminescent protein, equorin, from the jellyfish Aequorea victoria. With its help, many discoveries have been made, primarily in electrophysiology: equorin glows in the presence of calcium ions, which plays a major role in the formation of action potentials of muscle cells and nerve impulses. The introduction of a calcium concentration indicator into the cells helped to trace the mechanisms of their activity.

From the same A.victoria in 1992 isolated and cloned a gene for green fluorescent protein (GFP). By combining the GFP gene into a single block with other genes, it is possible to make visible in a fluorescent microscope the sites of synthesis of proteins encoded in these genes, to trace the growth of pathogenic bacteria and cancer cells, to observe the reproduction of viruses.

For many studies, a label of only one color is not enough, and soon a gene encoding a red fluorescent protein (RFP) was isolated from a Discosoma marine coral.

Green and red fluorescent proteins are molecules with a very complex structure capable of absorbing ultraviolet or blue photons and transferring their energy to the fluorophore part hidden inside, which emits photons with a longer wavelength.

The efficiency of such a system is strikingly high: only 20% of the absorbed light energy is converted into heat, and the remaining 80% is converted into visible light.

Now there are several dozen natural and modified genes whose proteins fluoresce in all parts of the visible spectrum, from blue-green to ruby-red. But most often, scientists use the most studied of them, GFP and RFP, both in a variety of biological studies and in genetic engineering.

The brightest and most interesting application of bioluminescence for non–specialists is the creation of transgenic plants and animals. The first mouse with the GFP gene embedded in chromosomes was created in 1998. But the glow is most often not the main thing here. Glowing proteins are needed to work out techniques for introducing foreign genes into the chromosomes of a variety of organisms: glowing means that the method works, you can use it to introduce a target gene into the genome. To control the success of the experiment, a virus, a bacterial plasmid or a gene gun is charged with a construction of three genes: GFP – the target gene – RFP, and organisms glowing both green and red are selected for further work: in this case, the gene carrying the sign scientists need probably got into the chromosome.

Back in 2000, at the University of Oregon (Portland, Oregon, USA), the first and so far the only GFP monkey Andy was born (ANDi, read the opposite abbreviation "inserted DNA" – "inserted DNA"). After processing 224 eggs with the viral vector, 40 began to divide, and only five embryos reached birth. Two monkeys were born dead, and only one of the survivors turned out to be glowing. But when cloning and creating transgenic animals, such (unchanged since the time of the unforgettable Dolly) results can be considered good.

In May 2001, the Taiwanese scientist Dr. Gong (Zhiyuan Gong) presented to the public the fruits of his labors – three colored forms of danio rerio, red, orange and green (orange and yellow are obtained by simultaneous synthesis of GFP and RFP proteins in muscle tissue).

The first luminous fish – transgenic danio (Brachydanio rerio) and Japanese rice fish medaka (Orizias latipes) – appeared on sale in 2003, first in Taiwan and other Asian countries, and then in the USA.

The official producers of these fish, the Taiwanese Taikong Corporation (fish with unethical names TK-1, TK-2 and TK-3) and the American company Yorktown Technologies (GloFish), supply only sterilized fish to the market – not so much to appease environmentalists, as trying to maintain a monopoly.

This constrains the pace of production, but demand generates supply, and rumors that all transgenic fish on sale are infertile have not been confirmed. So in Russian and Ukrainian pet stores, these fish are not so rare.

It is simply impossible to list everything that genetic lighting engineers have done in some ten years. Only in the last few months, scientists from different countries have reported the birth of red-glowing frogs (August 2007) and kittens (December 2007). You won't surprise anyone with green pigs anymore, but GFP piglets of the second generation, children of a transgenic pig and a simple Chinese boar, have just been born (January 2008). Maybe while this issue of the magazine is being prepared for publication, we will learn about another living and glowing miracle.

Alexander Chubenko,
portal "Eternal youth" www.vechnayamolodost.ruAn abridged version of the article, but illustrated with luminescent pictures, was published in the magazine "Popular Mechanics" No. 4-2008.