Bacteria are microscopic single-celled organisms that are found in almost every environment on Earth. One of the most fascinating features of bacteria is their ability to move, and this is often facilitated by the presence of specialized structures called flagella.
The Basics of Bacterial Flagella
Flagella are long, thin, and whip-like structures that extend from the cell body of certain bacteria. These structures are composed of a protein called flagellin, which is secreted and assembled at the tip of the growing flagellum. The number of flagella that a bacterium possesses can vary, with some species having a single flagellum, while others may have multiple flagella.
The Structure of Bacterial Flagella
Bacterial flagella are complex structures that are composed of several key components:
- Filament: The filament is the long, thin, and whip-like structure that extends from the cell body. It is composed of thousands of flagellin subunits that are arranged in a helical pattern.
- Hook: The hook is a short, curved structure that connects the filament to the basal body. It acts as a universal joint, allowing the filament to rotate.
- Basal Body: The basal body is a complex structure that is embedded in the cell membrane and acts as the motor for the flagellum. It is composed of several rings and a central rod that extends through the cell wall.
- Type III Secretion System: The type III secretion system is a specialized protein export system that is responsible for transporting the flagellin subunits from the cytoplasm to the growing tip of the flagellum.
The Growth and Assembly of Bacterial Flagella
The growth and assembly of bacterial flagella is a highly regulated process that is controlled by the type III secretion system. As the flagellin subunits are exported from the cell, they self-assemble at the tip of the growing flagellum, resulting in a rapid rate of growth.
The initial rate of flagellum growth is approximately 1,700 amino acids per second, but this rate decreases as the flagellum becomes longer. Eventually, the growth of the flagellum will stop, even without any other control mechanisms in place.
The Function of Bacterial Flagella
Bacterial flagella serve a critical function in the movement and locomotion of bacteria. By rotating the flagellum, bacteria can propel themselves through their environment, allowing them to seek out nutrients, avoid predators, and colonize new habitats.
The pattern of movement exhibited by bacteria with flagella is often described as a “run-and-tumble” motion. During the “run” phase, the flagella rotate in a coordinated manner, allowing the bacterium to move in a straight line. During the “tumble” phase, the flagella rotate in a more chaotic manner, causing the bacterium to change direction.
The Diversity of Bacterial Flagella
While all bacterial flagella share a common basic structure, there is a significant amount of diversity in the number, arrangement, and characteristics of these structures across different species of bacteria.
Number of Flagella
The number of flagella that a bacterium possesses can vary widely, with some species having a single flagellum, while others may have multiple flagella. The arrangement of these flagella can also vary, with some bacteria having flagella located at one or both ends of the cell, while others may have flagella distributed around the cell body.
Flagellar Arrangement
The arrangement of bacterial flagella can also vary, with some species having a single, polar flagellum (located at one end of the cell), while others may have multiple, peritrichous flagella (distributed around the cell body).
Flagellar Characteristics
In addition to the number and arrangement of flagella, there are also variations in the characteristics of the flagella themselves. For example, some bacterial flagella may be longer or shorter than others, and the rotation speed of the flagella can also vary between species.
The Impact of Flagella on Bacterial Motility
While the number of flagella that a bacterium possesses can affect its overall speed and maneuverability, the relationship between the number of flagella and bacterial motility is not always straightforward.
Bacterial Speed and the Number of Flagella
Contrary to popular belief, bacteria with multiple flagella do not necessarily move faster than those with a single flagellum. The number of flagella has only a small effect on the overall speed of the bacterium, and the pattern of “run-and-tumble” motion is not significantly affected by the number of flagella.
However, the speed of a bacterial cell during the “run” phase may be affected by the number of flagella, with bacteria with more flagella potentially able to move faster. But there is a lack of reliable data on the relationship between the number of flagella and the run velocity of bacterial cells.
Flagella and Bacterial Adhesion
In addition to their role in locomotion, bacterial flagella can also play a role in adhesion to surfaces. Studies have shown that bacterial flagella can explore microscale hummocks and hollows on surfaces, which can help the bacteria to increase their adhesion and colonize new environments.
Conclusion
Bacterial flagella are fascinating structures that play a critical role in the movement and locomotion of many species of bacteria. While the basic structure of bacterial flagella is well-understood, there is a significant amount of diversity in the number, arrangement, and characteristics of these structures across different bacterial species.
Understanding the role of bacterial flagella in motility and adhesion is an important area of research, as it can have important implications for our understanding of bacterial behavior and the development of new strategies for controlling bacterial infections.
References:
- Renault, T. T., Abraham, A. O., Bergmiller, T., Paradis, G., Rainville, S., Charpentier, E., Guet, C. C., Tu, Y., Namba, K., & Keener, J. P. (2017). Bacterial flagella grow through an injection-diffusion mechanism. eLife, 6, e23136. doi:10.7554/eLife.23136.001
- “Do bacteria with multiple flagella move faster than bacteria with a single flagella? Assuming the flagella are at the same length.” Biology Stack Exchange. Retrieved from https://biology.stackexchange.com/questions/41524/do-bacteria-with-multiple-flagella-move-faster-than-bacteria-with-a-single-flagel
- Renault, T. T., Abraham, A. O., Bergmiller, T., Paradis, G., Rainville, S., Charpentier, E., Guet, C. C., Tu, Y., Namba, K., & Keener, J. P. (2017). Bacterial flagella grow through an injection-diffusion mechanism. eLife, 6, e23136. doi:10.7554/eLife.23136.001
- Friedlander, R. S., & Fenno, R. M. (2013). Bacterial flagella explore microscale hummocks and hollows to increase adhesion. Proceedings of the National Academy of Sciences, 110(14), 5460-5465. doi:10.1073/pnas.1219662110
- ScienceDirect. (n.d.). Retrieved from https://www.sciencedirect.com/science/article/pii/S0092867416307241
Hi…..I am Pratyush Das Sarma, I have completed my Master’s in Biotechnology. I always like to explore new areas in the field of Biotechnology.
Apart from this, I like to read and travel.