BIOLOGICAL NANOMACHINE: BACTERIAL FLAGELLUM

Prof. Dr. Selahattin SERT, Expert Mehmet YÜKSEL
1 Atatürk University. Faculty of Agriculture, Food Engineering Department, Erzurum
2 Atatürk University, Hınıs Vocational School, Food Processing Department, Erzurum
[email protected]

The living beings that we cannot see with the naked eye but that can be seen after being magnified hundreds or thousands of times under the microscope are called "microorganisms" or "microbes" in short. It became possible to see microorganisms with the microscope made by Leeuwen Hoek of the Netherlands in 1674. This researcher saw microorganisms with a microscope, drew their shapes, and called all of them "animalcules", meaning small animals. However, about seven centuries before this date, the great Islamic scholar Avicenna (Ibn Sina) (980-1037) indicated microorganisms with the following statement: "Every disease is caused by a worm; unfortunately, we do not have a device to see it. Cleanliness prevents the diseases caused by worms like that". [1]

The bacterial flagellum, which is an excellent biological motor, rotates at between several hundred and 1,000 revolutions per second.

In the same years, the theory of biogenesis was put forward against the idea that living things came into being “spontaneously or by chance”as a result of the degradation of inanimate substances (the theory of abiogenesis), that is, “the theory spontaneous generation”. Scientific discussions on this subject continued for a long time; finally Pasteur demolished this theory of spontaneous generation in 1861 through his experiments. [2]

Bacteria are found almost everywhere in nature. Some of the bacteria are harmful. They cause disease in humans and animals, and lead to yield loss in plants. However, the benefits of bacteria outweigh their harms because they play an important role in the degradation of organic substances and their transformation into soil, making them ready for the plants to use. If bacteria were not given the task of degrading the dead bodies of plants and animals, the earth would be covered with the remains of dead animals and plants, and perhaps life would end. It is understood from this fact that bacteria were given a very important task in the continuation of life. Also, bacteria are widely utilized in the food and feed industry. For instance, the transformation of milk into yogurt, the production of cheese, vinegar and pickle are realized thanks to bacteria. Bacteria also play a role in transforming olives into an edible state. Bacteria play a role in the production of some food additives and preservatives, in the preservation of fresh feed throughmaking silage for a long period of time. [3]

Although bacteria are small in size (0.2-20 micrometers), they have a complex structure. One of these complex structures is the organelle called flagellum (whip), which enables the movement of some bacteria. The flagellum basically allows the bacterium to respond to the needs of the food, oxygen and light, and to avoid toxic substances. In this article, the perfect structure and functioning of the flagellum is discussed; it will be mentioned how its mechanism, which is explained by irreducible complexity, is a miracle of creation.

The Structure and Movement Mechanism of Bacterial Flagellum

Evolutionists argue that origin of life comes from a primitive bacterium that came into being by chance. However, those claims were refuted when the complex structures of bacteria were understood in recent years,. One of those structures is the flagellum.

About 250 pieces forming the flagella are made up of 25 different proteins. The flagellum filament is made up of approximately 30,000 protein units and is placed in place with a flawless mechanical design.

The flagella of bacteria have been known for a long time. However, recent observations have revealed the detailed structure of the flagellum and amazed the scienceworld. It was found that the flagellumdid not work with a simple vibration mechanism as previously thought, but with a very complex "biological molecular motor". [4]

Flagella are thin, wavy strands of 3-20 µm in length. Its chemical structure is a protein called "flagellin". They are seen as spiral in the electron microscope. The flagellum consists of a filament, a hook and a basal body (Figure 1). In bacteria, movement occurs when the hook transfers the movement from the basal body to the filament. The filament makes a rotational motion like a wheel and moves the bacterium forward.

Figure 1.General structure of bacterial flagellum. [5]

About 250 pieces forming the flagella are made up of 25 different proteins. The flagellum filament is made up of approximately 30,000 protein units and is placed in place with a flawless mechanical design. [6]

 Scientists found that those proteins, which form the flagellum, send signals to turn the engine off and on, enable them to move at atomic size, and activate the proteins that attach the flagellum to the cytoplasmic membrane. Even the model systems designed to explain the operation of the engine bysimplifying it were insufficient to understand the complexity of the flagellum (Figure 2).

Figure 2. Model mechanism for the engine of bacterial flagellum. [7]

While the energy requirements of other molecular motors are provided by ATP hydrolysis, the energy of the flagellar motor is provided by the mechanism called protonmotive force (PMF) directly through the plasma membrane by ATP stimulation. This mechanism involves the electrochemical orientation of H⁺ or Na⁺ protons. PMF is basically a metabolic process. Proton pumps are involved in this process. [8] However, the mechanism of this movement that takes place through chemical and mechanical systems has not been fully understood yet. [9]

Escherichia coli and Salmonella entericatyphimurium are the two bacteria in which the structure and functioning of the bacterial flagellum is understood best. In studies on these bacteria, it was determined that approximately 50 genes were involved in the formation and control of the flagellar motor. About a dozen of those genes are responsible for the chemical structure of the flagellum: 17 for the physical structure, and the rest for the coordination of the movement of the flagellum. [10]

The bacterial flagellum, which is an excellent biological motor, rotates at between several hundred and 1,000 revolutions per second. This movement is two-way. For instance, the anticlockwise movement in the E. coli bacterium pushes the bacterium forward, and the clockwise movement changes the direction of the bacterium by making it flip. Thus, the bacterium gains the ability to move in the form of both displacement and orientation. [11]

Some bacteria can be displaced in liquid medium at a rate of 100 μm per second. That is, a bacterium of 2 μm length travels 3000 times its length per minute. However, even the cheetah, one of the fastest running animals, can travel only 1,500 times its body length per minute. [12]

Conclusion

The flagellar motor, which is millions of times smaller than the smallest artificial engine, has been created in a structure that cannot be simplified in any way. This irreducibility of simplicity has recently been explained by the term ‘irreducible complexity’. That is, if even one of the parts of the flagellum is missing or defective, the flagellum cannot work and hence will not be of any use to the bacterium. The bacterial flagellum created in the form of an extraordinarily perfect nanomachine, and the mechanism of this perfectly operated molecular motor is just a small example of creation.

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[1] Sert, S. (2011). Genel mikrobiyoloji. Atatürk Üniversitesi, Ziraat Fakültesi Yayınları. Erzurum.
[2] Sert, S. ibid.
[3] Sert, S. ibid.
[4] Erhardt, M., Namba, K., & Hughes, K. T. (2010). Bacterial nanomachines: the flagellum and type III injectisome. Cold Spring Harbor perspectives in biology, 2(11), a000299
[5] Belas, R. (2014). Biofilms, flagella, and mechanosensing of surfaces by bacteria. Trends in microbiology, 22(9), 517-527.
[6] Vonderviszt, F., & Namba, K. (2013). Structure, function and assembly of flagellar axial proteins.
[7] Berry, R. M. (2005). Bacterialflagella: flagellar motor. eLS.
[8] Berry, R. M. ibid.
[9] Çakmakçı, M. L., Karahan, A. G., Çakır, İ., 2008. Mikrobiyoloji. Bizim Büro Basımevi, Ankara. 227 p.
[10] Coulton JW and Murray RGE (1978) Cell envelope associations of Aquaspirillum serpens flagella. Journal of Bacteriology 136: 1037–1049.
[11] Manson, M. D. (2010). Dynamic motors for bacterial flagella. Proceedings of the National Academy of Sciences, 107(25), 11151-11152.
[12] Sert, S. ibid.