The chemotacticism It is a biological process in which the movement or displacement of cells occurs when they are attracted by chemotactic agents (chemical substances). The cells can be prokaryotic or eukaryotic; for example, bacteria and leukocytes.
This phenomenon occurs in unicellular and multicellular organisms, which have organs of locomotion that allow them to move. It is extremely important for all living things. It is required from the moment a new being is engendered, being important that it is carried out during the different phases of embryonic and fetal development.
Chemotacticism is vital to carry out the normal functions of multicellular organisms; for example, nutrition and defense of the body.
Bacterial chemotaxis was discovered by Engelmann and Pfeffer more than a century ago. It was determined that these microorganisms can present different types of chemotaxis, depending on whether the stimulus is attraction or repulsion towards a chemotactic agent..
The way in which the chemotactic response occurs or the characteristics of the displacement, vary according to the organs of locomotion that the organisms possess..
Chemotacticism is a response presented by prokaryotic or eukaryotic cells, unicellular or multicellular organisms that are mobile. The gradient or difference in concentration of a chemical substance influences the direction of its movement, since it responds to this gradient present in its environment.
Chemotactic factors are inorganic or organic substances. In the cell membrane of organisms there are chemotaxis proteins, which function as receptors by detecting the different types of chemical gradients of these substances..
A bacterium swims in a straight line by rotating the flagella counterclockwise. At certain intervals, there is a change in the direction of the flagella; what is manifested in movements of the bacteria such as jumping or jumping.
In general, the chemotactic signals of the medium influence the movement of the bacteria. When the bacterium approaches an attractant, it swims in a straight line for longer, occasionally showing jumps; while when it moves away from a chemical factor, it does so with more jumps.
Chemotacticism differs from chemokinesis or chemokinesis, in that the gradient alters the probability of movement in only one direction; that is, in chemokinesis the chemical substance produces the non-oriented or random movement of an organism.
Considering the sense or direction of the movement of cells in relation to the attracting factor, the existence of two types of chemotacticism is described: positive and negative.
The movement of the organism occurs towards a higher concentration of the chemical substance found in its environment.
For example: when bacteria move or swim attracted to places where there is a higher concentration of carbon in the form of glucose.
This type of chemotacticism is represented in the image. The organism moves to the regions where there is greater concentration of the beneficial substance for it; while in negative chemotacticism, the opposite occurs: nothing towards the region where the concentration of the harmful substance is lower.
It occurs when the movement of an organism occurs in the opposite direction of the site where there is a greater concentration of a diffusible chemical substance.
An example of this type of negative chemotacticism occurs when bacteria can move away from certain chemicals that are harmful to them. They withdraw, flee from the place where there are substances, such as phenol, which is a poison for them.
Apart from the chemotaxis described, there is another classification of movement that is generated in response to the type of modification that occurs in the environment:
-Aerotaxis, which is the movement of cells towards the site where there is an optimal concentration of oxygen.
-Phototaxis, or the movement of bacteria to places where there is a greater amount of light.
-The taxi. The latter consists of the movement of bacteria to places where there are electron acceptors; for example, the nitrate ion (NO3-).
The presence of a chemotactic factor or chemical attractant, such as a sugar or an amino acid, is captured by the specific receptors for that substance located on the bacterial membrane..
Methylation and demethylation of specific membrane proteins mediated by cyclic guanosine monophosphate (cGMP) has been described as one of the mechanisms that causes bacteria to carry out different types of chemotacticism.
Attractive chemotactic factors cause a transient inhibition of demethylation, while repellent factors stimulate demethylation.
Chemotacticism is responsible for fertilization. In this case, the concentration gradient is due to progesterone released by glomerular cells (which surround the zona pellucida of the oocyte). This causes sperm to travel to the egg located in the fallopian tube ampulla..
During the different stages of embryonic development, and during organogenesis, cells migrate and organize themselves in response to a large number of specific chemotactic factors; how are growth factors.
In the inflammatory reactions produced in response to an infection, the same microorganisms, such as bacteria, produce chemotactic substances. They induce chemotacticism, the rapid migration or arrival of polymorpho-nuclear leukocytes to the site where the infection is occurring..
Bacterial peptides initiate with N-formyl-methionine, which are chemo attractants of numerous phagocytic host cells.
Complement is a set of serum proteins that have a defense function in the body and is activated by a series of proteolytic reactions in a sequential or cascade manner..
This complement can be activated when it comes into contact with infectious microorganisms or with antigen-antibody complexes; among the active fragments generated is C5a.
The main function of the complement fragment C5a is chemotaxis, by which it attracts neutrophilic and monocyte leukocytes. These cells by diapédesis cross the vascular endothelium and reach the infected tissue or mucosa to effect phagocytosis or ingestion of pathogens or foreign particles.
Some cells, such as monocytes and macrophages, produce chemotactic substances, including leukotrienes and various interleukins. B and T lymphocytes also release chemotactic cytokines, the effects of which enhance immunity reactions..
In general, chemotaxis is modified in patients with infectious diseases such as AIDS and brucellosis.
Chemotacticism can decrease in several syndromes in which phagocytosis is inhibited. This can occur in inflammatory diseases such as arthritis, tumor metastasis, asbestos poisoning, among other conditions.