TAXIS

From Big Medical Encyclopedia

TAXIS (Greek taxis creation, an arrangement) — motor reactions of freely mobile inferior plants, the elementary animals, separate cells of metaphytes (spermatozoa, leukocytes, zoospores) and microorganisms in response to action of an irritant. The movement towards an irritant is called to positive T., from an irritant — negative; the movement which is not oriented in relation to an irritant is designated as fobotaksis or the movement of «fright». Change of force of action of an irritant or condition of an organism can change T. Razlichayut's character of the movement on a concentration gradient of oxygen (aerotaxis), various chemical substances (chemotaxis), temperatures (thermotaxis), feedstuffs or particles (trophotropism), on an electrochemical gradient (galvanotaxis). The movement depending on the provision of a light source is called a phototaxis, and concerning the sun — a heliotaxis. Movement against current of liquid received the name of a rheotaxsis. T. have adaptive value, promoting moving of an organism to rather comfortable zone in Wednesday, heterogeneous on a certain factor.

A chemotaxis at bacteria — the active movement of bacterial cells on a concentration gradient of nek-ry chemical substances (amino acids, carbohydrates, inorganic ions, molecular oxygen, etc.), as a result to-rogo they move to areas of concentration, optimum for them. The chemotaxis is known at mobile, hl. obr. flagellar forms of bacteria of various taxonomical groups (Enterobacteriaceae, Pseudomonadaceae, Bacillaceae, Rhizobiaceae, Bdellovibrio, etc.). The bacteria possessing the sliding type of the movement have data on existence of a chemotaxis. At pathogenic bacteriums the chemotaxis can play a role of a factor of virulence.

Reactions of a chemotaxis observe under a microscope in the drug «the crushed drop» or in glass capillaries. The substances causing accumulation of bacteria in zones of high concentration call attractants, and reaction — a positive chemotaxis. At a negative chemotaxis of a bacterium gather in zones of the minimum concentration of substance, a cut in this case call a repellent. Different types of bacteria are characterized by various sets chemical: the substances causing a chemotaxis.

The touch system providing a chemotaxis includes the chemoceptors which are components of a bacterial cover and in some cases identified with the proteins in a periplasm connecting nutritious substrate; receptors (it is identified apprx. 30) are selectively sensitive to one or several chemical substances and directly are not tied with flagellums. Transfer of information from them on flagellums is carried out by specialized proteinaceous molecules, methylation or demetili-rovaiy to-rykh serves as a signal to change of sign of rotation of flagellums according to what the nature of the movement of a cell («somersaults» or the directed movement) changes.



Bibliography: Poglazov B. F., Metl and N and A. L. and N about in and to about in V. V. Modern ideas of the mechanism of the movement of bacteria, Izv. Academy of Sciences of the USSR, it is gray. biol., No. 5, page 672, 1981, bibliogr.; With t e fi-@ e r R., Edelberg E. and Ingram D. The world of microbes, the lane with English, t. 2, page 126, M., 1979; Adler J. The behavior of bacteria, on the mechanism of sensory transduction in bacterial che-motaxis, Johns Hopk. med. J., v. 144, p. 121, 1979.

Century of H. Yarygin; S. S. Belokrysenko (bakt.).

Яндекс.Метрика