home Zoology What is the function of flagella in a bacterial cell? Bacterial flagellum. Laboratory diagnosis of bacterial motility

What is the function of flagella in a bacterial cell? Bacterial flagellum. Laboratory diagnosis of bacterial motility

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Most bacteria move using flagella. The flagella can only be seen with an electron microscope. In a light microscope without special processing methods, individual flagella are not visible.

According to the location and number of flagella on the cell surface, bacteria are divided into:

On the monotrichous- have one flagellum (for example, bacteria of the genera Caulobacter and Vibrio);

. lophotrichous - have a bunch of flagella on one or both poles of the cell (for example, bacteria of the genera Pseudomonas, Chromatium);

. amphitrichous- have a flagellum at both poles of the cell (for example, bacteria of the genus Spirillum);

. peritrichous- a large number of flagella located over the entire surface of the cell (for example, bacteria of the species E.coli and kind Erwinia) (Fig. 1).

Flagella are spirally twisted filaments, consisting of a specific protein flagellin . Flagellin is built from relatively low molecular weight subunits. Subunits are arranged in a spiral around the internal free space. Amino acid composition of flagellin different types bacteria can vary.

Monotrich Lofotrich

Amphitrich Peritrich

Figure 1 - Types of flagella in bacteria

The flagellum consists of three parts: a filament, a hook, and a basal body (Fig. 2). With the help of the basal body, which includes the central rod and rings, the flagellum is fixed in the cytoplasmic membrane and cell wall. The number of rings in gram-negative and gram-positive bacteria is different. Gram-negative bacteria have four rings: L, P, S, M. Of these, L and P are the outer pair of rings; S and M inner pair of rings. The L-ring is anchored in the outer membrane, P in the peptidoglycan layer of the cell wall, S in the periplasmic space, and M in the cytoplasmic membrane. Gram-positive bacteria have a simpler basal body. It consists of only two rings: S and M, i.e., only from the inner pair of rings that are located in the cytoplasmic membrane and cell wall.

The flagella of bacteria are similar to a ship's propeller by the nature of their work. If the cell has many flagella, they gather into a bundle during movement, which forms a kind of propeller. A bunch of flagella, rapidly rotating counterclockwise, creates a force that makes the bacterium move in an almost straight line. After the direction of rotation of the flagella changes, the bundle unwinds and the cell stops, instead of forward movement it begins to rotate randomly, its orientation changes. At the moment when all the flagella of the bacterium begin to rotate synchronously counterclockwise again, forming a propeller pushing the bacterium, the direction of its forward movement will differ from the initial one. In this way, the bacterium can change the direction of its movement.

Figure 2 - The structure of the flagellum

Since gram-positive bacteria do not have an outer pair of rings, it is believed that only the inner pair (S and M rings) is necessary for flagella rotation. These rings, connected to a rotating rod protruding outward, form the so-called electric motor that ensures the movement of the flagellum (Fig. 2). At the periphery of the M ring are MotB proteins. MotA proteins are embedded in the cytoplasmic membrane and are adjacent to the edges of the M and S rings. Torque arises due to the interaction of MotB protein subunits with MotA protein subunits. MotA protein subunits have two proton half-channels. Through these proton half-channels, protons are transferred from the periplasmic space to the cytoplasm of bacteria (similar to the proton channel of ATP synthase). As a result of the transfer of protons through the MotA and MotB proteins, the M ring rotates. It has been established that one complete turn of the M ring is associated with the transfer of about 1000 protons across the membrane. Thus, the proton-motive force arising in the cytoplasmic membrane is used as an energy source for the rotation of the flagella.

Motile bacteria are characterized taxis , i.e., a directed motor reaction in response to a certain factor. Depending on the nature, there are chemotaxis, phototaxis, magnetotaxis and viscositaxis.

Chemotaxis- the movement of bacteria relative to the source of the chemical. For every microorganism chemical substances in this regard, they can be divided into two groups: inert and causing taxis, or effectors. Among the effectors are: attractants - substances that attract bacteria; Repellents are substances that repel bacteria.

Phototaxis- movement towards or away from a light source, characteristic of phototrophic bacteria.

magnetotaxis- the ability of bacteria to move along lines of force magnetic field earth or magnet. Found in bacterial cells containing magnetosomes and common in various types of aquatic ecosystems.

A number of bacteria have viscositaxis - the ability to respond to changes in the viscosity of the solution and move in the direction of its increase or decrease. Specific receptors are responsible for the sensitivity of bacteria to the concentration gradient of certain factors. The receptor responds to the effector and transmits a certain type of signal to the basal body of the flagellum.

Villi (or fimbriae)

Villi, or fimbriae, are surface structures that consist of pilin protein and do not perform the function of movement. In size, they are shorter and thinner than flagella. The number of fimbriae on the cell surface ranges from 1-2 to several thousand; both coccoid and rod-shaped bacteria have them. There are two types of fimbriae: general and specific.

fimbriae of general type perform the function of attaching the cell to the surface of the substrate. The possibility of their participation in the entry of large molecular compounds into the cytoplasm of the cell is not ruled out.

Specific villi- sex pili found in cells of the so-called donors, i.e., in cells containing the sex factor (F-plasmid) or other donor-specific plasmids. If a sex factor is present in a bacterial cell, then one or two sex F-pills per cell are synthesized on their surface. They have the appearance of hollow protein tubes from 0.5 to 10 microns in length. F pili play a decisive role in the formation of conjugation pairs during the transfer of genetic material from a donor cell to a recipient cell.

For movement in the aquatic environment, some microorganisms use a flagellate organ - the “flagellum”. This organ, built into the cell membrane, allows the microorganism to move at will in the direction it chooses at a certain speed.

The male sex cells also use the flagellum for locomotion.

For a certain time, scientists knew about flagella. However, knowledge about them structural features, which have appeared only in the last decade or so, came as a huge surprise to them. It was found that the flagellum moves through a very complex "organic motor", and not a simple vibrating mechanism, as previously thought.

This motor is formed according to the same mechanical principles as the electric motor. It has two main parts: the moving part ("rotor") and the stationary part ("stator").

The bacterial flagellum differs from all organic systems that make mechanical movements. The cell does not use the available energy stored in ATP molecules. Instead, it has a special energy resource: the microorganism uses the energy of the flow of ions through their outer membranes. The internal structure of the engine is extremely complex. About 240 different proteins are involved in the creation of the flagellum. Each of them occupies a certain place. Scientists have found that these proteins conduct signals that turn the engine on and off, form connections that facilitate movement at the atomic level, and activate other proteins that attach the flagellum to cell membrane. The models developed to summarize the operation of the system are sufficient to describe the complex structure of the system. (one)

The complex structure of the bacterial flagellum by itself is already enough to refute the theory of evolution, since the flagellum has an irreducibly complex structure. Even if one single molecule of this incredibly complex structure were to disappear or be damaged, the flagellum would neither function nor be of benefit to the microorganism. The flagellum must work perfectly from the very first moment of its existence. This fact once again emphasizes the absurdity of the theory of evolution's assertion of "gradual development".

Even those creatures that evolutionists consider "simplest" have amazing structure. The bacterial flagellum is one of countless examples. This microorganism moves in water, moving this organ on its shell. when they were studied internal system of this well-known organ, scientists around the world were surprised to find that the microorganism has an extremely complex electric motor. This electric motor, which includes about fifty different molecular subunits, has a rather intricate structure, as shown below.

The bacterial flagellum is clear evidence that even supposedly "primitive" creatures have unusual structure. As humanity becomes more and more aware of the details, it becomes clear that those organisms that 19th century scientists, including Darwin, considered the simplest, are in fact just as complex as others. In other words, with the advent of understanding about the perfection of creation, the futility of trying to find an alternative explanation for creation becomes obvious.

The microorganism swims in a viscous liquid medium, rotating spiral-shaped propellers called flagella.

The bacterial flagellum is a nanomachine consisting of 25 different proteins, ranging from a few to tens of thousands. It consists of a collection of this large number of proteins, each of which in different parts performs a specific function, such as motor rotation, insulation, drive shaft, governor switching sequence, universal bundle, helical propeller, and rotary amplifier for self-assembly.

Flagellar proteins are synthesized inside the cell body and transported along a long, narrow central channel in the flagellum to its peripheral (outer) end, where they, using the flagellar tip as a setting motor, can effectively and independently create complex nanoscale structures. The rotary motor, whose diameter is only 30 to 40 nm, rotates the flagellum at a frequency of about 300 Hz and a power of 10-16 W, with an energy conversion efficiency close to 100%.

Structural designs and functional mechanisms found in the complex mechanism of the bacterial flagellum could provide mankind with many groundbreaking technologies that will form the basis for future nanotechnology, for which we can find many useful ways applications.(2)

Cells can move with the help of specialized organelles, which include cilia and flagella. Cell cilia are always numerous (in protozoa, their number is in the hundreds and thousands), and the length is 10-15 microns. Flagella are most often 1-8, their length is 20-50 microns.

The structure and functions of the organelles of movement

The structure of cilia and flagella, both in plant and animal cells, is similar. Under an electron microscope, it was found that cilia and flagella are non-membrane organelles consisting of microtubules. Two of them are located in the center, and around them along the periphery lie another 9 pairs of microtubules. This entire structure is covered by a cytoplasmic membrane, which is a continuation of the cell membrane.

Flagella and cilia provide not only the movement of cells in space, but also the movement of various substances on the surface of the cells, as well as the entry of food particles into the cell. At the base of the cilia and flagella are basal bodies, which also consist of microtubules.

It is believed that the basal bodies are the center of formation of microtubules of flagella and cilia. Basal bodies, in turn, often originate from the cell center.

A large number of unicellular organisms and some multicellular cells do not have special organelles of movement and move with the help of pseudopodia (pseudopodia), which is called amoeboid. It is based on the movement of molecules of special proteins, called contractile proteins.

Features of the movement of protozoa

Unicellular organisms are also able to move (ciliates slipper, green euglena, amoeba). To move in the water column, each individual is endowed with specific organelles. In protozoa, such organelles are cilia, flagella, pseudopods.

Euglena green

Euglena green is a representative of the protozoa of the flagellate class. The body of the euglena is spindle-shaped, elongated with a pointed end. The organelles of the movement of Euglena green are represented by a flagellum, which is located at the blunt end. Flagella are thin outgrowths of the body, the number of which varies from one to dozens.

The mechanism of movement with the help of a flagellum differs in different species. Basically, this is a rotation in the form of a cone, the top of which is facing the body. The movement is most effective when the cone apex angle reaches 45°. The speed ranges from 10 to 40 revolutions per second. Often observed in addition to the rotational movement of the flagellum, also its wavy swaying.

This type of movement is characteristic of uniflagellate species. In polyflagellates, the flagella are often located in the same plane and do not form a cone of rotation.

The microscopic structure of flagella is quite complex. They are surrounded by a thin shell, which is a continuation of the outer layer of ectoplasm - the pellicle. The internal space of the flagellum is filled with cytoplasm and longitudinally arranged threads - fibrils.

The peripherally located fibrils are responsible for the implementation of the movement, and the central ones perform the supporting function.

Infusoria slipper

The ciliate shoe moves due to cilia, carrying out wave-like movements with them. It is directed forward with a blunt end.

The cilia move in the same plane and make a direct blow after full extension, and a return blow in a curved position. The blows go sequentially one after another with a slight delay. During swimming, the infusoria performs rotational movements around the longitudinal axis.

The shoe moves at a speed of up to 2.5 mm / s. The direction changes due to the bends of the body. If there is an obstacle on the way, then after the collision, the ciliate begins to move in the opposite direction.

All cilia of ciliates have a similar structure to the flagella of Euglena green. The cilium at the base forms a basal grain, which plays an important role in the mechanism of movement of the body.

In some ciliates, the cilia are interconnected and thus allow for greater speed.

Ciliates are highly organized protozoa and their motor activity they do it with abbreviations. The shape of the body of the simplest can change, and then return to its previous state. Rapid contractile movements are possible due to the presence of special fibers - myonemes.

amoeba vulgaris

Amoeba - the simplest pretty large sizes(up to 0.5mm). The shape of the body is polypodial, due to the presence of multiple pseudopodia - these are outgrowths with internal circulation of the cytoplasm.

In the amoeba, the common pseudopodia is also called pseudopodia. Directing the pseudopods in different sides, the amoeba develops a speed of 0.2 mm / minute.

The organelles of protozoan movement do not include the cytoplasm, nucleus, vacuoles, ribosomes, lysosomes, EPR, Golgi apparatus.

There are a large number of microbes with flagella. Bacterial flagella are their characteristic features, and according to this principle they are combined into taxonomic units. Thanks to the processes, these organisms are able to make cell contractions and thus move.

These structural elements of the cell determine its mobility. Most often, these are thin threads that originate from the cytoplasmic membrane. Some types of microbes have a significantly larger flagellum than the host cell itself.

The processes are able to push the cell in a liquid medium. The structure of the flagellum is such that it can quickly move the body-cell, and at the same time it will cover relatively large distances. These movements are made on the principle of a propeller. To move, microbes use one or more processes.

In some microbes, processes can be an additional factor of pathogenicity (pathogenicity). This can be explained by the fact that it contributes to the approach of a pathogenic microorganism to a healthy cell.

What are flagella made of

These parts of the microorganism are spirally twisted threads. They have different thickness and length, as well as the amplitude of the coil. Some bacteria with flagella have several varieties of these organs at once.

These elements of the cell consist of a special protein - flagellin. It has a relatively low molecular weight. This allows the subunits of molecules to be arranged in a spiral and thus form the structure of a process of a certain length.

In addition to the thread, the tourniquet has a hook near the cell surface, as well as a basal body. With the help of such a body, it is securely fixed in the cell.

What are villi

Villi are otherwise called pili. They are present in different organisms. The location of these structural elements bacterial cell is different. Usually these are cylinders of protein nature, having a length of up to 1.5 micrometers and a diameter of up to 1 micrometer. In one microorganism, there can be several types of pili.

The functions of these formations have not yet been fully determined. It is known that certain types of microbes have villi. The most obvious role played by pili is attachment to the substrate and locomotion in the environment.

Most of the data collected about Escherichia coli, which have pili villi. However, there is a huge number of microscopic organisms in which the structure of the villi has not yet been fully determined. In any case, bacterial pili promote efficient cell movement.

What are the differences between flagellated microorganisms

Depending on the number and method of location, all microscopic organisms are divided into the following types:

Monotrichs. These are bacteria with one flagellum.
Lophotrichous. These cells have a bunch of processes at the end.
Peritrichs. Such microbes have many processes over the entire surface.
Amphitrichs. These microorganisms have a bilateral, or bipolar arrangement of flagella.

Flagella of prokaryotes

In prokaryotic bacteria, such elements consist of only one section of flagellin subunits. One or two-sided arrangement of such elements is possible. To a large extent, such parts of the cell can be determined by differences in the life cycle.

Some prokaryotic bacteria may have pili. The number of these structural elements allows the bacteria to move or attach to the substrate.

Most prokaryotes have excellent adaptations to move around in a liquid environment and thereby increase survival under adverse environmental factors.

eukaryotic flagella

Flagella in eukaryotic microorganisms have a much greater thickness, as well as a complex structure. Unlike prokaryotes, these flagellar bacteria can rotate on their own. Pili in such organisms give them the opportunity to additionally attach to the substrate, as well as perform complex movements.

In some microorganisms, flagella have a more complex structure - in the form of microtubules. Such a tube has densely packed strands of protein molecules. They are great for moving around. different environment. Microtubules appear to have originated in late stages evolution of microorganisms.

How to identify flagella

Conventionally, flagella can be determined by direct and indirect methods.

Observation of a bacterium under a microscope is a direct detection of these elements. To make them more visible, staining is applied. special methods. Flagella are even better visible in an electron microscope.

Indirectly, bacteria are determined by the fact of cell motility. This is best detected with a "crushed drop" preparation when the glass slide is covered with a coverslip. Often, in order for the processes to be more visible, the field of view is artificially darkened.

The study of flagella bacteria and their functions allows microbiologists to find ways to combat pathogens, as well as a field for their application.

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