From Big Medical Encyclopedia

SYMBIOSIS (Greek symbiosis joint life, cohabitation) — the long or constant close cohabitation of organisms of the different types which are in various arose in the course of evolution (from mutually useful to unilaterally harmful) relationship with each other. Such organisms are called symbionts (see).

The page combines three main types of bonds between organisms: mutually advantageous, or a mutualism (many scientists only refer this form of relationship to S.); favorable to one organism and mostly indifferent for another — commensalism (see); favorable to one and more or less harmful to another — parasitism (see). The intermediate position between commensalism and parasitism is occupied by an amensalism or a form of a nakhlebnichestvo, certainly useful to one look — the parasite, but (at least indirectly) harmful to another, napr, the nek-ry arthropods living in holes together with the main owners can be a source to an infection.

The term «symbiosis» was for the first time applied by the German botanist de A. De Bary in 1879 to any characteristic of cohabitation in a broad sense. The nature of mutually advantageous cohabitation was for the first time described by A.S. Famingqing and I. F. Baranetsky in 1867 on the example of the analysis of structure of lichens as forms of existence of a mushroom and seaweed. At the same time the mushroom creates structure of a lichen, promotes deduction of water, absorption of nutrients; the cells of green and blue-green seaweed (tsianbakteriya) located between threads of mushrooms carry out photosynthesis and by that deliver food for both cohabitants. As a result the mushroom and an alga represent the certain new organism created from two components and capable to existence in the most various climatic conditions.

At the same time in all-biological sense of S. includes all three forms of relationship, between to-rymi often there are no strict borders and to-rye under certain conditions can pass one into another. So, the cells of seaweed living in an organism of a one-celled infusorian of Paramecium bursaria can on light due to processes of photosynthesis make enough food both for themselves, and for the owner (i.e. the relations at this stage have mutualistic character); in the dark cells of seaweed behave as commensals — they consume own reserves of nutrients, without giving anything to the owner and without taking away anything from it. Further, when reserves of nutrients are exhausted, these cells begin to behave as parasites, consuming those nutrients, to-rye the owner from the environment gets.

From positions C. also the issue of an origin of ability of cells — eukaryotes is resolved (see. Eukariotny organisms ) — to such forms of division, as mitosis (see) and meiosis (see), and, therefore, question of emergence of metaphytes (hypothesis of A. JI. Takhtadzhyana, 1973). Ideas of cohabitation of the most ancient organisms on cellular (or protocellular) level formed also the basis of one of the most productive hypotheses of their joint development, or a simbiogeneza (the term entered at the beginning of 20 century by K. S. Merezhkovsky). According to J. Bernal (1969), Wilkie and Rudin (D. Wilkie, D. Boodyn, 1970), such major organellas of a cell of all eukaryotes as mitochondrions and chlorolayers, are probably endosymbionts too.

A striking example of a mutualism, i.e. mutually advantageous cohabitation, S. of the termites and flagellar (Hypermastigina) living in back department of intestines of termites serve. Flagellates possess the enzymes digesting wood, eat it and digest it for termites, to-rye are capable to gnaw and eat wood, but because of absence in intestines of necessary enzymes cannot independently acquire it; the friend without friend these organisms perish.

The person on a surface has skin, to a mucous membrane of an oral cavity and a large intestine bacteria live, to-rye, being in the symbiotic relations with the owner (person), promote preservation of protective properties of skin and all organism in general. At the same time under certain conditions (naira., during the weakening of an organism of the owner) they can act as pathogenic microflora.

Commensalism is purely rare since in these or those conditions commensals or can bring nek-ry benefit (and then the relations become mutualpstichesky), or begin to do harm to an organism of the owner. Probably, plants the epiphytes (pineapple and orchids) growing on a surface of trees can be an example of pure commensalism without doing them visible harm. In most cases commensals use an organism of the owner as a habital, but sometimes use also its food waste, becoming in this case parasites of the owner.

Parasitism is considered as a special form of symbiosis, and Sh. D. Moszkowski (1946) and V. A. Dogel (1947) distinguish this form of existence of organisms from symbiosis and carry only those organisms to symbionts, to-rye together react to influences of the environment, without causing to each other harm. It must be kept in mind that true parasites unlike parasitoids, eating at the expense of the owner and (often) breeding with his help, as a rule, do not ubyvat the owner. Selection goes in the area of mutual adaptation, at Krom the owner gains relative stability to a parasite, and the parasite interacts with the owner without special damage for it.

From positions of the space relations of two living together organisms they are subdivided into cases, various on type, «lodger-stva» — sinoykiya (that is uses by one organism of another as the house, a habital). Allocate a simple kvartirantstvo (in this case the organism of the owner is only the house, napr, for the small fishes living among feelers of the owner of the apartment — actinium), an epioykiya (dwelling on a body surface of the owner, napr, the infusorians living on a body surface of crustaceans Cammarus, the crabs of Pinnotheres living in a mantle cavity of lamellibranch of mollusks), and an entoykiya (the cohabitant lives in a cavity of the owner, napr, the small fish of Fieraster living in water lungs of a holothuria). At all forms of a kvartirantst-v, except for simple, the expressed phenomena of commensalism, a mutualism and parasitism can be observed in various degree.

See also Parazitotsenoz .

Bibliography: Bernal Dzh. Emergence of life, the lane with English, M., 1969; D au g e l V. A. General parasitology, L., 1962; P and and N to and AA. Evolutionary ecology, the lane with English, M., 1981; R at d and D. and Wu Yi's N of l to and D. Biogenez of mitochondrions, the lane with English, M., 1970; T and x t and d-I am A. L N. Four kingdoms of the organic world, Nature, No. 2, page 22, 1973; Margulis L. Symbiosis and evolution, Sci. Amer., v. 225, p. 48, 1971.

A. H. Alekseev.