the horizontal gene transfer

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Evolution and Bacterial Chemotaxis

Evolution is known as the mechanism by which species adapt to their surroundings, and it is said to occur in tiny, normally imperceptible changes. Changes are present in all living species, and they can occur through changes to the genetic code or through adjustments to characteristics (such as behavior and enzyme levels) that do not include genetic changes. The subject of bacterial chemotaxis is investigated in this article. It is preferable to describe simple concepts before delving into the subject. Chemotaxis is a combination of two words: chemo and taxis. The name refers to an organism's movement in response to a certain chemical stimulus. It is essential to note that somatic cells, single-celled microorganisms such as bacteria, as well as multicellular organisms usually direct their movements regarding the direction of particular chemicals found in their environment. Bacteria chemotaxis, therefore, is the movement of bacteria in response to specific chemicals found in the environment. Bacterial chemotaxis as an adaptive feature is essential as it enables bacteria to find food such as glucose by swimming towards regions where it is highly concentrated and also escapes poisons or harmful chemicals such as phenols.

Significance of Bacterial Chemotaxis

The topic of bacterial chemotaxis is not only exciting but also significant in the understanding of how bacteria respond to stimuli. With such knowledge, one is better placed to fathom the underlying reasons for the presence of bacteria in different regions of the environment. Similarly, the concept of bacterial chemotaxis offers researchers an opportunity to learn how diseases are transmitted by bacteria as they move from one point to the other in response to chemicals in the environment. Besides, through gaining an understanding of this topic, one learns how to get rid of bacteria, i.e., use of harmful chemicals that will scatter the unicellular organisms away.

Experiments on Bacterial Chemotaxis

The project identifies two experiments about bacterial chemotaxis. There is also an evaluation of various aspects that are being described in the studies. The paper will describe the aims of the two experiments. In this section, there will be an evaluation of what body of knowledge each analysis contributes as well as the gaps in the literature that the studies attempt to fill. Nonetheless, it is essential to stress that the aim would be assessing the essence of chemotaxis in bacteria, i.e., how it helps the organisms find food and also escape harm in the environment. The first experiment is titled 'Robustness in bacterial chemotaxis' by Alon, Surette, Barkai, and Leibler (1999). This experiment is on how the response of living cells is influenced by networks of interacting proteins. Particularly, the issue is addressed in experiments using Escherichia coli's chemotaxis. The paper will assess how the response, as well as adaptation to signals, varies when there is a change in the intracellular levels of the constituents of the chemotaxis system. The second experiment is 'Ecology and Physics of Bacterial Chemotaxis in the Ocean' by Stocker and Sermour (2012). This experiment reviews the occurrence, various features, and also consequences of bacterial chemotaxis in the ocean environment.

Results and Analyses

Experiment One: Robustness in bacterial chemotaxis

This research attempts to explain the mechanism through which bacteria, Escherichia coli in this case, move towards and away from chemicals. The sensory network of the bacteria dictates the migration of E. coli towards chemical attractants and far away from repellants through translating temporal alterations in the concentration of chemical stimuli into the regulation of the swimming direction of the cell (Alon et al., 1999). The chemotaxis system of E. coli has been used as a model for realizing how the interactions between individual constituents cause processes at the network level. The figure below characterizes the protein network that causes the chemotaxis.

Figure 1: Chemotaxis system of E. coli

Source: (Alon et al., 1999)

Description of the System

The swimming motion of bacteria such as E. coli is dependent on the chemicals present, i.e., they move towards specific attractants and avoid repellants. The experiment by Alon et al. (1999) equates the movement (swimming) of bacteria to a random walk that is characterized by periods of smooth swimming that is interrupted by short-term tumbles that changes alter the direction of movement. Chemotaxis is achieved by regulation of the frequency of such obstacles.

When bacteria are swimming up a gradient of attractants, they come across high levels of positive chemicals that increases with time. Consequently, E. coli tumbles less quickly; thus they chose to continue moving up the gradient (Alon et al., 1999). The bacterial action of swimming is biased by the type of chemical it encounters. Therefore, it may either decide to proceed to move towards the chemical if beneficial, i.e., glucose, which is food. Nonetheless, when the chemical is poisonous, the bacteria experiences increased tumbling frequency, forcing them to move away (Alon et al., 1999).

Experiment Two: Ecology and Physics of Bacterial Chemotaxis in the Ocean

The experiment seeks to understand both the ecological and physical processes that supporting bacterial movement (swimming) and chemotaxis in the ocean. There is also a description of the available knowledge pertaining to chemotaxis in marine bacteria. The experiment asserts that the essence of bacteria chemotaxis as a micro-scale behavior is not readily seen, especially in the vast, turbulent ocean. As a result, the process of bacterial chemotaxis has been overlooked by most ocean ethnographers (Stocker & Seymour, 2012).

Essence of Bacterial Chemotaxis

Nonetheless, chemotaxis, as performed by marine bacteria, is essential in that it offers the motile species (organisms) with competitive advantages under favorable conditions such as when there is the availability of food. The figure below shows a bacterium (red) chasing a swimming phytoplankton (cyan).

Figure 2: A bacterium (Pseudoalteromonas haloplanktis) (shown in red markings) chasing a swimming phytoplankton cell (Pavlora lutheri) (cyan)

Source: (Stocker & Seymour, 2012)

Also, chemotaxis establishes and also ensures there is the maintenance of pathogenic and symbiotic relations between bacteria and other micro- and macro-organisms in the ocean. Another impact of such swimming of marine bacteria is that it influences the directions and rates of various processes of cycling chemicals, and in so doing, it influences the productivity of the ocean (Stocker & Seymour, 2012). Similarly, it affects the biogeochemical connections between the ocean and the surface, thus a concern for global climate. According to Stocker and Seymour (2012), marine bacteria outshine E. coli in chemotaxis, but there is little knowledge and insights into why and how.


The paper has evaluated the concept of chemotaxis, with particular emphasis on chemotaxis of the bacteria. As has been shown, chemotaxis, or the ability to sense and direct motility in response to chemical gradients (Stocker & Seymour, 2012), is significant for the survival and adaptation of bacteria. The movement helps the motile species to move to access food when the gradient favors them, and also to evade danger in the case of harmful chemicals. The topic is of great significance as it helps one in learning about the reasons behind the presence of bacteria in different parts of the environment at different times.


Alon, U., Surette, M. G., Barkai, N., & Leibler, S. (1999). Robustness in Bacterial Chemotaxis. Nature, 397 (6715), 168-171.

Stocker, R., & Seymour, J. R. (2012). Ecology and Physics of Bacterial Chemotaxis in the Ocean. Microbiology and Molecular Biology Reviews, 76 (4), 792–812.

December 08, 2022



Biology Scientist Genetics

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Evolution Charles Darwin Gene

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