Symbiosis, or mutually beneficial cohabitation of two or more organisms, has been known for a long time. But this does not negate the fact that many of the nuances of this phenomenon have not yet been studied or are poorly studied.
For the first time this amazing natural phenomenon was discovered by the Swiss scientist Schwendener in 1877. At that time, he was just researching lichens. To his deepest amazement, it turned out that these organisms are compound, formed by colonies of fungi and unicellular simple algae. The term "symbiosis" in the scientific literature appeared a bit later. More precisely, it was proposed in 1879 by de Paris.
People figured out the concept relatively quickly, but the question remained with the trophy. What do some types of symbiotic organisms eat? In the case of the same lichens, it was clear that algae live off photosynthesis, but where does the fungal component get its nutrients from? If you also do not know the answer to this question, we suggest reading our article.
General information
Modern scientists have found that symbionts are organisms that feed (most often) on what the dominant organism consumes. However, this is a very crude and not too correct definition, and therefore some of the most interesting cases should be described in more detail.
You can certainly give a few examples yourself. So, beneficial bacteria for humans in large quantities are found in acidophilic yoghurts. People give these protozoa an excellent habitat, and bacteria ensure the perfect functioning of our gastrointestinal tract.
By the way, the well-known Kutushov took advantage of this. The symbionts, the cultures of which he sells, provide a significant improvement in the functioning of the gastrointestinal tract, even in the elderly, who often have big problems with this.
Algae as the main symbionts
Biologists have long discovered that no symbiotic pair of organisms can do without algae. And we are talking not only about aquatic, but also about purely terrestrial organisms. They manage to enter into mutually beneficial relations both with each other and with bacteria, fungi,
multicellular organisms. You should be aware that the list of algae that are capable of symbiosis is quite limited.
Thus, representatives of a maximum of five to seven genera are able to establish mutually beneficial relations with fungi, and historically it has developed so that the following symbionts are: nostock (Nostoc), gleocapsa (Gloeocapsa), scytonema (Scytonema) and stigonema (Stigonema).
About algae and sloths
Many people know that in the distant Amazon rainforest lives a remarkable animal in all respects. It became famous for its slowness and leisurelyness. Of course, we are talking about sloths. But far from everyone knows that the color of these animals (dirty green, brown) does not appear as a result of the natural pigmentation of the coat, but thanks to symbiotic algae.
They live right in the wool of sloths and feed on normal photosynthesis. Thanks to them, the sloth gets an excellent camouflage color. Honestly, scientists have never been able to come to a unanimous conclusion that such coexistence gives algae themselves. In this case, symbionts are organisms that feed on substances produced by themselves in the process of photosynthesis.
Unusual forms of relationships of algae with other organisms
Lichens and sloths are an example of a long-term stable relationship between two life forms. But far from always symbiotic bacteria and algae form such strong and long-lasting alliances with other organisms. So, they often just settle on the surface of a living organism. Of course, there is no question of full-fledged symbiosis in this case. This phenomenon is called epiphytosis. The smallest film of the simplest algae often covers not only the shells of mollusks, but also the surface of the body of some waterfowl and marine animals. So, algae-epiphytes in large numbers settle even on giant whales.
Epiphytes - symbionts or parasites?
Scientists still cannot agree on the point of view of the relationship between the epiphyte and the multicellular organism. Some believe that this phenomenon is best taken as a primitive, primary version of a symbiotic relationship.
In fairness, it is difficult to agree with this point of view. Epiphytes do not really cause direct harm to the organisms on the surface of which they inhabit, but the benefits (visible in any case) of them are also not observed.
Harm from epiphytes
Small water insects and mites, whose legs densely cling to epiphytes, become extremely slow, since they simply can not physically melt quickly. Higher aquatic plants, the leaves of which “honored” unicellular algae, often simply die from a lack of sunlight. By the way, every aquarist must have encountered this phenomenon. We can say that in this case the symbionts are parasites, however paradoxical it may sound.
But! The phenomenon of epiphytism has been studied very, very poorly. It is possible that these relationships actually benefit not only algae, but also multicellular organisms. The riddle is still waiting for its explorer. And what do symbionts eat if they live inside the cells of a higher animal or plant?
Intracellular symbionts
It is not so rare that symbionts can live inside the cells of their "master." If we talk about the same algae, then they are called endophytes. They form endosymbioses, which are already much more complicated than the above phenomena. Between partners, in this case, close, strong and long-term ties are already forming. Their main difference is that such simple symbionts are revealed only as a result of sufficiently detailed and complex cytological studies.
Important! Scientists have proven relatively long ago that the most important cellular organoids - mitochondria in animals and chloroplasts in plants - were formed in time immemorial due to symbiotic relationships. Once they were independent organisms.
At some point, these intracellular symbionts switched to a completely “settled” existence inside a living cell, and then completely became dependent on it, transferring control of their genome to its core (partially). So, we can safely say that all currently known life forms that strive for a mutually beneficial existence have all chances to someday become one with those organisms with which they today have partnerships.
How do symbionts get inside a cell?
How do microorganisms end up in the cells of higher animals and plants? Some species have specially designed mechanisms for this. And often they are not available at the symbiont itself, but at the “receiving side”. There is such a small water fern - azolla (Azolla). On the lower cavity of its leaves there are narrow passages that lead to caverns specializing in mucus secretion. It is in these cavities that the blue-green algae anabenas (Anahaena azollae) fall, which float into the caverns along with the flow of water.
Fern grows, canals overgrow, algae remain in complete isolation. Scientists have long tried to create colonies of other species on the basis of azolla, but they have not achieved any success. It is safe to say that the formation of a symbiotic bond is possible only if a complete coincidence of a number of parameters. In addition, such a union is distinguished by pronounced species specificity.
Thus, symbionts are organisms that feed thanks to processes specific to their species (nitrogen-fixing microorganisms), share valuable substances with a partner, but at the same time they need certain conditions that only he can provide.
What is the benefit of such coexistence?
Note that there are many nitrogen compounds inside the azolla cavities. Blue-green algae, which enter the fern organism, not only actively absorb them, but also completely lose their ability to independently fix atmospheric nitrogen. Symbiotic organisms reciprocate, supplying the fern with oxygen and some organic substances.
It should be noted that these symbionts undergo practically no changes in their internal organization. However, this is not the case in all cases of intracellular symbiosis. Most often, those algae that enter into mutually beneficial cooperation with other organisms are distinguished by a complete reduction of the cell membrane. For example, this happens in blue-green algae, which form a symbiotic relationship with some types of sea sponges.
Termites and intracellular symbionts
For a relatively long time, all scientists were at a loss, reflecting on the digestion processes of termites. How does this species manage to thrive on wood alone? Relatively recently, it was nevertheless found that the smallest symbionts-bacteria, which are the symbionts of protozoa that live in the intestines of the termites themselves, are responsible for the direct processing of wood pulp. Such a complicated, but very effective scheme.
But the researchers still did not understand where insects get enough energy from: after all, cellulose in any case is not particularly nutritious. In addition, they need a huge amount of nitrogen. There is no such volume in the digested wood of trees simply by definition. Recently, scientists from Japan came to a phenomenal result, which they obtained by carefully studying the genome of symbionts of flagellates living in the gastrointestinal tract of termites.
What turned out to be in their genome?
There are many interesting things. In particular, scientists were able to detect not only those genes that are responsible for the production of an enzyme for breaking down cellulose, but also those that are responsible for nitrogen fixation. The latter is a very complex process of binding atmospheric nitrogen with the formation of those forms that can be absorbed by a plant or animal organism. This is extremely important, since the nitrogen obtained in this way is used by termites and their flagella for protein synthesis.
Simply put, in this case, symbionts are organisms that feed on the wood consumed by termites. Symbionts of symbionts (nitrogen-fixing bacteria of flagellates) are responsible for the fixation of nitrogen, without which neither the termite nor its "guests" can live.
Legumes and symbionts
Since we remembered nitrogen-fixing bacteria, we cannot but say about legumes. They, as anyone who has studied botany remembers, are characterized by a strikingly high content of vegetable protein. This circumstance has also long been extremely surprising for scientists. Beans managed to form a sufficient amount of protein even in those conditions when there was practically no nitrogen in the soil!
It turned out that its entry was provided by symbionts. Yes, they were all the same nitrogen-fixing bacteria, conveniently living in nodules on the roots of all leguminous plants. They extract precious nitrogen from the air, converting it into a highly digestible form.
Commercial use of symbionts
It is not surprising that physicians have long cultivated beneficial bacteria for humans. At first, this happened in the form of the production of yoghurts and other lactic acid products, but today research has reached a whole new level.
The symbionts of Kutushov have become especially famous today. What it is? Currently, under this brand name, cultures of fermented milk organisms are sold that improve digestion processes.
All Kutushov's symbionts (more precisely, their cultures) are based solely on ancient Mongolian recipes for fermented milk products. So they are really capable of improving your overall well-being and even appearance.
Developed by their scientist Kutushov. The symbionts in the cultures are carefully selected, they provide the human body with valuable amino acids and trace elements. It is due to this that a positive effect is achieved.