Chemotaxis: what it is, characteristics and biological functions

What is chemotaxis? Let's take a look at this biological phenomenon present in unicellular organisms.

Almost all living beings, however simple or ancestral they may be, move in one way or another at some point in their lives.

Life (in addition to reproductive potential and the presence of at least one cell) implies response to stimuli and, in order to escape from a threat or to search for a food source, directionality towards a specific point is usually necessary.

Thus, we observe almost infinite motor structures in the animal kingdom: from cilia and flagella to vertebrate limbs, each taxon has specialized types of locomotion for its environment and life habits. Even the simplest bacterium you can think of surely has some kind of movement, whether directional or random, with a specific evolutionary purpose.

Today we come to show you the exciting phenomenon of cabs, innate behavioral responses that occur in living beings in the presence of external stimuli. Specifically, we explore the world of chemotaxis we explore the world of chemotaxis, typical in bacteria and other unicellular organisms..

What is cabs?

Before introducing the prefix chemo-, coming from the Greek word khymei (alchemy), it is necessary to understand cabs in general terms.

Cabs is a behavioral response present in unicellular and multicellular organisms towards an external stimuluseither in order to move towards it (attraction) or away from it (repulsion). Cabs can be classified according to the type of stimulus and whether the living being inherently selects it positively or negatively. Some examples are as follows:

• Aerotaxis: the living being is stimulated by the presence of oxygen.
• Electrotaxis: the stimulus is an electric current.
• Magnetotaxis: movement occurs in response to a magnetic field.
• Hydrotaxis: in response to humidity. It is very common.
• Chemotaxis: in response to chemical stimuli.
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As simple as the term may sound, care must be taken. Tropism and kinesis are also types of movement in living things, but they differ from cabs at the conceptual and functional level. Here is a brief description of their differences.

Cabs vs kinesis

The main difference between cabs and kinesis is directionality.. In cabs, the living being directs its movement according to the presence or absence of the sought or repelled stimulus, be it light, water, oxygen or many other environmental parameters.

On the other hand, kinesis is defined by a non-directional movement.. While in both cases the living being is responding to an external stimulus, in kinesis the animal is not moving "towards", but based on its comfort zone.

For example, a bacterium may make undirected movements if its medium is heated to a different comfort zone, but it is not moving anywhere in particular. Generally speaking, if the movement is fast, the living being is looking for its comfort zone, and if it is slow, it has found it.

Cabs vs. tropism

Tropism is typical of plants. It can be defined as a mechanism in response to stimuli that determines the directionality and growth of the organism based on an external stimulus.. If you observe a seed shoot growing in an arched shape in search of a ray of light, you are looking at tropism.

The difference between the two terms is that in cabs the organism has motility. Whether by means of limbs, cilia, flagella or body torsions, the living being is actively moving towards or away from the stimulus. This is not the case of tropism since, as we have said, it is typical in plants (characterized by their lack of movement).

Chemotaxis: a question of chemical concentrations.

Without realizing it, we have defined chemotaxis at multiple points in this space. Generally speaking, it could be described as a type of biological phenomenon common in bacteria (but also present in other uni- and multicellular types) in which they direct their movement according to the concentration of chemical substances present in their environment..

Chemotaxis is a quantifiable phenomenon that has been demonstrated on multiple occasions in the laboratory setting. However, in order for this to occur, certain requirements must be met. Among them, we find the following:

• The concentration of chemical gradients must develop relatively fast and remain for long enough within the biological system.
• Cabs phenomena are distinguished from kinetic phenomena. As previously mentioned, these are two different mechanisms.
• The migration of cells (usually bacteria) must be free outward and along the axis of the concentration gradient.
• The detected responses must be the result of active cell migration.

Chemotaxis allows unicellular beings to find food in the medium (e.g., bacteria). to find food in the medium (e.g. monosaccharides such as glucose) and to flee from chemical toxicants that would cause their death.. Also, although far removed from the main meaning of the term, chemotaxis is useful for animals to be guided towards pheromones produced by their sexual partners, in order to initiate courtship and reproduction.

We dedicate these last lines to explore some of the chemotactic phenomena that go a little further than a bacterium searching for food. Don't miss them.

1. Chemotaxis and the immune system

The migration of white Blood cells (e.g. macrophages, neutrophils and lymphocytes) into infected or inflamed body tissues is a chemotaxis phenomenon that underpins the basis of the immune system in humans.

In laboratory environments (in vitro) it has been demonstrated how these cell bodies have the ability to move directionally based on the concentration of certain chemical compounds.. While this is a conglomerate of 3 different types of movement: random, kinetic and chemotactic, the latter has been shown to be essential for immune responses to occur at the local level.

For example, phagocytes (free circulating cell that has the property of trapping and destroying pathogens) move entirely based on chemotactic stimuli. These move to a certain location in response to concentrations of substances such as interleukin-I, thrombin, growth factor, immunoglobulins, leukotrienes and many others.. Once the pathogen is located, adhesion, endocytosis, destruction and elimination phenomena occur.

2. Chemotaxis and pheromones

Pheromones are chemical substances secreted by living beings, whose purpose is to provoke responses in other individuals of the same species, whether of the same or opposite gender. These are volatile chemical signals in liquid form that are dispersed in the environment..

This is a clear example of chemotaxis, although it is nothing like the typical definition of a bacterium using its cilia to approach a source of glucose in the environment. For example, if a bear rubs itself against a tree, it is probably not only relieving the itch it feels from the parasitic agents on its back (which it also does), but it is probably secreting pheromones that alert the rest of the males in the area to its presence and physical superiority.

Thus, the other males respond directionally to that particular stimulus, either by moving away from the territory (to avoid confrontation) or by moving closer to the source of the pheromone to challenge the dominant male and increase their chances of reproduction, if they manage to defeat him in a confrontation. Because of the directionality of the response and the chemical basis of the response, pheromone-mediated behaviors are considered chemotactic.

Summary

Cabs is an exciting phenomenon because it is an intrinsic behavioral response that allows living things to survive in the environment based on a very simple premise: based on the presence of a stimulus, I either approach (attraction) or move away (avoidance).. There are many types of cabs, since any environmental or biotic factor can modify the environment, thus changing the directionality of the movement of the living being studied.

In particular, chemotaxis is of growing interest in the clinical setting. By studying the chemotactic mechanisms of bacteria in infectious processes, it is possible to devise drugs that inhibit their mobile response to external agents, which would reduce the range of infection and its progress. Undoubtedly, this is a fascinating subject, from both a medical and biological point of view.

Bibliographic references:

• Acosta, E. A., & Venegas, A. A. (2006). BIOPHYSICAL MODEL TO EXPLAIN THE CHEMOTAXIS PROCESS. Colombian Journal of Physics, 38(2).
• Castellanos, N. P., Lombardo, D., Makarov, V. A., Velarde, M. G., & Arena, P. (2011). Chemotaxis, Infotaxis and Memotaxis: strategies for exploration and survival. Spanish journal of physics, 22(3).
• Galicia-Jiménez, M. M., Sandoval-Castro, C., Rojas-Herrera, R., & Magaña-Sevilla, H. (2011). Bacterial chemotaxis and flavonoids: perspectives for the use of probiotics. Tropical and subtropical agroecosystems, 14(3), 891-900.
• Nápoles, M. C., Gutiérrez, A., & Varela, M. (1998). Chemotaxis of Bradyrhizobium japonicum ICA 8001 towards organic acids and soybean seed exudates. Tropical Crops, 19(2), 27-29.
• Rojas-Dotor, S., Pérez-Ramos, J., & Rico-Rosillo, M. G. (2009). Chemotaxis and disease. Revista Médica del Instituto Mexicano del Seguro Social, 47(1), 51-56.
• Cabs, biologyonline.com. Retrieved February 2 from https://www.biologyonline.com/dictionary/taxis#:~:text=Taxis%20is%20a%20behavioral%20response,organism%20to%20an%20external%20external%20stimulus.