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Bioluminescence is the ability of living organisms to glow with their own proteins or with the help of symbiotic bacteria.
Today, about 800 species of luminous living creatures are known. Most of them live in the sea. These are bacteria, unicellular flagellate algae, radiolarians, fungi, planktonic and attached coelenterates, siphonophores, sea feathers, ctenophores, echinoderms, worms, molluscs, crustaceans, fish.
Some of the most brightly glowing animals are pyrosomes (fire beetles). Among freshwater bioluminescent species, the New Zealand gastropod mollusk Latia neritoides and a number of bacteria are known. Among terrestrial organisms, certain species of fungi, earthworms, snails, millipedes and insects glow.
At the microscopic level, 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 cells - participants in the glucose oxidation process. They also supply the energy required for chemiluminescence to various phosphor proteins.
One of the first bacterial lamps - a flask with a culture of luminous bacteria - was entertained more than a hundred years ago by the Dutch botanist and microbiologist Martin Beijerink. In 1935, such lamps even illuminated the large hall of the Paris Oceanological Institute, and during the war the Soviet microbiologist A.A. Egorova used luminous bacteria for prosaic purposes - to illuminate the laboratory.
And you can carry out 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 see what happens - it is likely that the bacteria inhabiting the nutrient medium will glow with an otherworldly light. Bacteria, mainly of the genera Photobacterium and Vibrio, and multicellular planktonic organisms (pictured) glow in the sea, but the main source of light is one of the largest (up to 3 mm!) And complex unicellular organisms - flagellate algae of the night light.
In bacteria, phosphor proteins are scattered throughout the cell, in unicellular eukaryotic (with a cell nucleus) organisms, they are located in membranes surrounded by a membrane 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 that work due to symbiotic photobacteria, glow continuously or for several seconds after mechanical or chemical stimulation. 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 the intracellular one, in deep-sea shrimps, octopuses, cuttlefish and squid, there is a secretory type of glow: a mixture of 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 ordinary honey fungus.
And in the higher fungi of the genus Mycena, also growing on a rotting tree, but in warm regions like Brazil and Japan, fruiting bodies glow - what are usually called mushrooms (although molds, yeasts and other fungi are also mushrooms, only lower ones). One of the species of this genus is called M. lux-coeli, "mycene - heavenly light."
The most striking application of bioluminescence is the creation of transgenic plants and animals. The first mouse with the GFP gene inserted into chromosomes was created in 1998.
Glowing proteins are needed to work out techniques for introducing foreign genes into the chromosomes of various organisms: if it glows, it means that the method works, you can use it to introduce a target gene into the genome. The first luminous fish - the transgenic zebrafish (Brachydanio rerio) and the Japanese medaka rice fish (Orizias latipes) - went on sale in 2003.
Those who are lucky enough to swim in the sea at night during its glow will remember this enchanting sight for a lifetime. Most often, the cause of the glow is the flagellate algae of the night light (Noctiluca). In some years, their number increases so much that the whole sea glows. If you are unlucky and find yourself on the shores of warm seas at the wrong time, try pouring seawater into a jar and add a little sugar there.
Noctylists will react to this by increasing the activity of the luciferin protein. Shake up the water and admire the bluish glow. And when you stop to admire, you can remember that you are looking at one of the unsolved mysteries of nature: the lack of clarity of the evolutionary mechanisms of the emergence of the ability to glow in various taxa was noted in a separate chapter of "The Origin of Species" by Darwin, and since then scientists have not been able to shed it on this question is the light of truth.
Luminescence could have developed in organisms living in good light conditions, based on pigment compounds that perform a light-protecting function.
But the gradual accumulation of a trait - one photon per second, two, 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 on the naked location looks impossible too. And even the functions of the glow in many species remain incomprehensible.
Why are they glowing?
Glowing bacterial colonies and fungi attract insects that spread germs, spores, or mycelium. Insectivorous larvae of the New Zealand mosquito Arachnocampa weave a trapping net and illuminate it with their own body, attracting insects.
Flashes of light can scare away predators from jellyfish, comb jelly and other helpless and gentle creatures. For the same purpose, corals and other colonial animals growing in shallow water glow in response to mechanical stimulation, and their neighbors, which no one touched, also begin to flicker. Deep-sea corals convert the weak short-wavelength light that reaches them into radiation with a longer wavelength, possibly to allow the symbiotic algae inhabiting their tissues to photosynthesize.
Fishing rod with light bulb
The order of anglerfish (Lophiiformes) is the most diverse (16 families, over 70 genera and over 225 species) and, perhaps, the most interesting of deep-sea fish. (Many are familiar with sea anglers not from the zoology textbook, but from the cartoon "Finding Nemo").
Angler females are predators with large mouths, powerful teeth, and a highly distendable stomach. Sometimes dead anglerfish are found on the surface of the sea, choking on fish more than twice their size: the predator cannot release it due to the structure of its teeth. The first ray of the dorsal fin is transformed into a "fishing rod" (illicium) with a luminous "worm" (eska) at the end. It is a mucus-filled gland that contains bioluminescent bacteria. Due to the expansion of the walls of the arteries that feed the escu with blood, the fish can arbitrarily cause the luminescence of bacteria that need an oxygen supply for this, or stop it, narrowing the vessels.
Usually, the glow occurs in the form of a series of flashes, individual for each species. Illicium in the species Ceratias holboelli is able to move forward and retract into a special channel on the back. Luring prey, this angler gradually moves the luminous bait to its mouth until it swallows the prey. And Galatheathauma axeli has the bait right in the mouth.
The location of the phosphors and even the nature of the blinking of the glowing 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 their males not for amorous, but for gastronomic purposes.
Off the coast of Japan, mass weddings are celebrated by the umitohara (sea fireflies) - tiny, 1-2 mm long, crustaceans of the genus Cypridina - and the squid Watasenia scintellans. Vatazenia bodies about 10 cm long, together with 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 school of these squids!
In many deep-sea cephalopods, the body is painted with a pattern of multi-colored light spots, and the photophores are very complex, like a searchlight 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 ventral 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.