CHEMOTACTICISM: WHAT IT IS, EXAMPLES - BIOLOGY - 2025

The chemotaxis is a biological process in which the movement or displacement of some cells to be attracted to the chemotactic agents (chemicals) occurs. 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, and it is important that it be carried out during the different phases of embryonic and fetal development.

Source: Gabriel Bolívar

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 movement vary according to the organs of locomotion that the organisms possess.

What is chemotacticism?

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.

Bacteria movement

A bacterium swims in a straight line by rotating the flagella in an anti-clockwise direction. At certain intervals, there is a change in the direction of the flagella; which 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; whereas 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 produces the non-oriented or random movement of an organism.

Types

Considering the sense or direction of the movement of the cells in relation to the attractant factor, the existence of two types of chemotacticism is described: positive and negative.

Positive chemotacticism

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 the places where there is a greater 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.

Negative chemotacticism

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.

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.

In addition to 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 (NO ₃ ^-).

Examples

-Chemotacticism in bacterial nutrition

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 chemotaxis.

The attractant chemotactic factors cause a transient inhibition of demethylation, whereas the repellent factors stimulate demethylation.

-In fertilization and embryonic development

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 in the fallopian tube.

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; as are the growth factors.

-Chemotacticism in inflammation

Factors produced by microorganisms

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 to numerous phagocytic host cells.

Chemotactic factor generated by complement

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 leukocytes and monocytes. 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.

Chemotactic factors generated by cells

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 immune reactions.

-Alteration of chemotacticism in infectious diseases

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.

References

1. Annual Reviews. (1975). Chemotaxis in Bacteria. Recovered from: nemenmanlab.org
2. Brooks, G.; Butel, J. and Morse S. (2005). Jawetz, Melnick and Adelberg Medical Microbiology. (18th ed.) Mexico: The Modern Manual
3. Spermatozoa Chemotaxis. Sea Urchin Spermatozoa Chemotaxis. Recovered from: embryology.med.unsw.edu.au
4. Wikipedia. (2018). Chemotaxis. Recovered from: en.wikipedia.org
5. Williams & Wilkins (1994). Microbiology Mechanisms of infectious diseases. (2nd. Ed.) Buenos Aires: Panamericana