Bacterial flagella are formed by protein. Organelles of movement: functions and structure, features of the movement of protozoa. What are the differences between flagellated microorganisms?
Diagram of the structure of a bacterial flagellum.
Bacterial flagella determine motility bacterial cell. Flagella are thin filaments originating from the CPM, having a greater length than the cell itself. The thickness of the flagella is 12-20 nm, length 3-12 µm.
Flagella are composed of a contractile protein such as myosin - flagellina (from lat. flagellum– flagellum), which has antigen specificity. Flagellin subunits are twisted in a spiral.
The flagellum consists of three components - a spiral flagellar thread (filament) of constant thickness, a hook (elbow) and a basal body. The hook to which the flagellar filament is attached is 30-45 nm long and consists of a protein different from flagellin. It is connected to the basal body, which is located in the membrane (in the cell wall and CPM). The flagellar filaments are driven by a membrane hinge-like basal hook. The basal body consists of a central rod enclosed in a system of special rings. The rings act as a “drive disk” and a “bearing” on the inner surface of the peptidoglycan layer. The entire structure performs the function of a chemomechanical converter (flagellin motor).
Gram-negative bacteria have two pairs of rings: outer (L and P rings) and inner (S and M rings). The L and P rings are located inside the cell wall (the L ring is in LPS, and the P ring is in the peptidoglycan layer). They obviously serve as a bushing for the rod. The inner pair (rings S and M) is fixed on the CPM, with the S ring located in the periplasmic space, and the M ring on or in the CPM. The flagella of gram-positive bacteria, which have a thicker homogeneous cell wall, contain only one pair of rings - S and M.
The rotation of the flagellum in the cell wall occurs due to rotational movement rings S and M relative to each other and is provided by the energy of the transmembrane gradient of hydrogen or sodium ions. Thanks to this rotation, bacteria move in the most favorable direction for them. The flagellar apparatus has a special binary switch that allows you to change the direction of rotation of the flagella counterclockwise to the opposite. Thus, bacteria, having received a chemical signal from environment, change the direction of movement and choose optimal living conditions.
Model of flagellum movement.
Number of flagella in bacteria various types varies from one (monotrich) in Vibrio cholerae to tens and hundreds of flagella extending along the perimeter of the bacterium (peritrich) in Escherichia coli, Proteus, etc. Lophotrichs have a bundle of flagella at one end of the cell. Amphitrichy has one flagellum or a bundle of flagella at opposite ends of the cell.
Arrangement of flagella in bacteria.
Flagella are detected using electron microscopy of preparations sprayed with heavy metals, or in a light microscope after treatment special methods, based on etching and adsorption of various substances, leading to an increase in the thickness of the flagella (for example, after silvering). Bacterial motility is determined using phase-contrast or light microscopy of a “crushed” or “hanging” drop).
Vibrio cholerae. Fragments of cells with a polarly located flagellum (G).
The mobility of many protists is ensured by the presence of flagella or cilia. Both are structured the same way. Flagella in both protozoa and flagellar or ciliated cells of multicellular animals and plants are always only part of the locomotor system of the cell, which consists of a kinetosome (or centriole), a flagellum (or undulipodium) and root processes of the kinetosome (or its derivatives). In addition to movement in the water column, flagella and cilia are used for temporary or permanent attachment to the substrate or for creating food flows of water when feeding on suspended particles.
Flagellum- This is a tubular outgrowth of the cell surface, surrounded by a membrane that serves as a continuation of the membrane covering the entire cell. It contains a bundle of protein fibrils, the so-called axoneme. An axoneme or axial filament is a microtubule formation that consists of two central microtubules surrounded by a ring of nine pairs (doublets) of microtubules consisting of subfibrils tightly fused to each other. The fine structure of the flagella of all eukaryotic organisms is surprisingly uniform in its main features.
The most important element of the flagellar system is the basal body or kinetosome. This is a cylinder, the walls of which are formed by nine groups of microtubules, united in groups of three (triplets). Most often, a cell contains two kinetosomes located approximately at right angles to each other. One or two flagella extend from them. The kinetosome does not float in the cytoplasm by itself, since it is secured by a system of roots.
Modern representations about the Protista system are largely based on the structure of the flagellum and its derivatives. The wide distribution of flagella and cilia among them makes it possible to compare almost all taxa with each other, and also makes it possible to use additional characters of the flagellar apparatus, the number of which is already approaching 100, in systematics and phylogeny. Many structural features of flagellates, including body shape, are determined by the presence of this unique system.
The number of flagella, their relative and absolute length, the place and method of attachment of the flagella, the nature of their movement, their direction are very diverse in different groups, but are constant within individual groups of related organisms.
There are usually 4 morphotypes of flagellates.
Isokonts have from 2 to 8 flagella of equal length, directed in one direction, with the same beating patterns. These include most of the motile cells of green algae.
Anisokonts have 2 flagella of unequal length, directed in one direction, differing in the method of beating. Such flagella are characteristic of colorless flagellates.
U heterokontnyh there are 2 flagella of unequal length (one directed forward, the other backward), differing in the way they beat. They are characteristic of motile algae cells, so-called zoosporic fungi, and colorless flagellates.
Stefanokonty have a corolla of flagella at the anterior end of the cell. This is typical for multiflagellate gametes and zoospores of some green algae.
Uniflagellate forms are usually not distinguished in special group. Many of them are considered to be individuals that have lost their flagellum for the second time, since the vast majority have another flagellated kinetosome.
The main function of the flagellum is movement. IN active work The driving force of the flagellum is the peripheral microtubules and their handles, which have ATPase activity. The central microtubules have a supporting role. The forms of movement of the flagellum are different, but usually it is a helical movement, allowing the flagellum to “screw in” into the water, making up to 40 revolutions per second. In ciliates and multiflagellate protists, the movement of cilia is organized according to the type of metachronal waves. Flagella and cilia are often used for nutrition. Among flagellates, there are species that spend most of their life cycle in an attached state. During this period, the flagellum loses its usual function of movement and turns into an attachment organelle, stalk or stalk. Another function of the flagellum is that with its movements it cleans the surface of the body from small foreign particles adhering to it.
Endoplasmic organelles
The endoplasm of protists contains one or more nuclei, as well as all organelles and structures characteristic of a eukaryotic cell: ER, ribosomes, Golgi apparatus, mitochondria, peroxisomes, hydrogenosomes, plastids (in autotrophic protists), lysosomes, digestive vacuoles. Some protists also have organelles specific to them.
Extrusomes. These organelles are special vacuoles surrounded by a membrane, which in mature extrusomes is usually in contact with the plasmalemma. In response to various external irritations (mechanical, chemical, electrical, etc.), they throw out their contents. In terms of their structure, they are mucopolysaccharides (complex compounds of carbohydrates and proteins). Known 10 different types extrusion. Some contain toxic substances that can immobilize and kill the victim (protozoa and other small organisms). Others perform a protective function or facilitate movement by secreting mucus.
Plastids. Plastids are present in phototrophic and related protists and are represented by chloroplasts and leucoplasts. The main pigments of chloroplasts are chlorophylls. Different groups of phototrophic protists are characterized by certain sets of chlorophylls. Of the secondary pigments in algae, there are carotenes and xanthophylls, which in high concentrations can mask green chlorophyll and give chloroplasts a variety of colors from yellow-green to reddish-brown.
The Golgi apparatus has been found in almost all protist species studied. Most often, the Golgi apparatus is located adjacent to the nucleus and is represented by one or several stacks of flat cisterns (dictyosomes) surrounded by small vesicles. However, in some protists the Golgi apparatus is formed by single cisternae. The absence of dictyosomes is usually interpreted as a primitive feature. However, the absence of dictyosomes in modern protists cannot unambiguously indicate their primitiveness, since the formation and disassembly of dictyosomes largely depends on external influences on the cell (for example, a decrease in oxygen concentration in the environment) or from physiological changes in the protist itself (transition to encystment).
Lysosomes and other organelles and inclusions. In the cells of protists, as in the cells of multicellular animals, lysosomes are present. These cytoplasmic bodies in the form of small vesicles (primary lysosomes) are formed in the Golgi apparatus. Digestive hydrolytic enzymes are localized in them. Secondary lysosomes, or digestive vacuoles, are well expressed only in heterotrophic protists that feed by phagocytosis.
In the endoplasm of different protists, reserve nutrients used in metabolic processes are present in greater or lesser quantities. Most often these are various polysaccharides (glycogen, starch, amyloplectin, etc.), often lipids and other fatty inclusions. The amount of reserve substances depends on the physiological state of the protozoan, the nature and amount of food, and the stage of the life cycle and varies widely. However, some large groups of protists store specific substances. For example, euglenoids store paramyl, which is not found in other protists.
Bacterial flagella determine the motility of the bacterial cell. Flagella are thin filaments originating from the cytoplasmic membrane and are longer than the cell itself. The thickness of the flagella is 12-20 nm, length 3-15 µm. They consist of 3 parts: a spiral filament, a hook and a basal body containing a rod with special disks (1 pair of disks in gram-positive bacteria and 2 pairs of disks in gram-negative bacteria). Flagella are attached to the cytoplasmic membrane and cell wall by discs. This creates the effect of an electric motor with a motor rod that rotates the flagellum. Flagella consist of a protein - flagellin (from flagellum - flagellum); is an H antigen. Flagellin subunits are twisted in a spiral. The number of flagella in bacteria of various species varies from one (monotrich) in Vibrio cholerae to tens and hundreds of flagella extending along the perimeter of the bacterium (peritrich) in Escherichia coli, Proteus, etc. Lophotrichs have a bundle of flagella at one end of the cell. Amphitrichy has one flagellum or a bundle of flagella at opposite ends of the cell.
Pili (fimbriae, villi) are thread-like formations, thinner and shorter (3-10 nm x 0.3-10 µm) than flagella. Pili extend from the cell surface and consist of the protein pilin, which has antigenic activity. There are pili responsible for adhesion, that is, for attaching bacteria to the affected cell, as well as pili responsible for nutrition, water-salt metabolism and sexual (F-pili), or conjugation pili. Pili are numerous - several hundred per cell. However, there are usually 1-3 sex pili per cell: they are formed by so-called “male” donor cells containing transmissible plasmids (F-, R-, Col-plasmids). A distinctive feature of the sex pili is the interaction with special “male” spherical bacteriophages, which are intensively adsorbed on the sex pili.
Spores are a peculiar form of resting firmicute bacteria, i.e. bacteria with a gram-positive type of cell wall structure. Spores are formed when unfavorable conditions existence of bacteria (drying, nutrient deficiency, etc.. One spore (endospore) is formed inside a bacterial cell. The formation of spores contributes to the preservation of the species and is not a method of reproduction, like fungi. Spore-forming bacteria of the genus Bacillus have spores that do not exceed the diameter of the cell. Bacteria , in which the size of the spores exceeds the diameter of the cell, are called clostridia, for example, bacteria of the genus Clostridium (lat. Clostridium - spindle). The spores are acid-resistant, therefore they are stained red by the Aujeszky method or the Ziehl-Neelsen method, and the vegetative cell is stained blue.
The shape of the spores can be oval, spherical; location in the cell is terminal, i.e. at the end of the stick (in the causative agent of tetanus), subterminal - closer to the end of the stick (in the causative agents of botulinum, gas gangrene) and central (in the anthrax bacillus). The spore persists for a long time due to the presence of a multilayer shell, calcium dipicolinate, low water content and sluggish metabolic processes. Under favorable conditions, spores germinate, going through three successive stages: activation, initiation, germination.
8. Basic forms of bacteria
Globular bacteria (cocci) They are usually spherical in shape, but can be slightly oval or bean-shaped. Cocci can be located singly (micrococci); in pairs (diplococci); in the form of chains (streptococci) or grape bunches (staphylococci), in a package (sarcins). Streptococci can cause tonsillitis and erysipelas, while staphylococci can cause various inflammatory and purulent processes.
Rod-shaped bacteria the most common. The rods can be single, connected in pairs (diplobacteria) or in chains (streptobacteria). The rod-shaped bacteria include Escherichia coli, the causative agents of salmonellosis, dysentery, typhoid fever, tuberculosis, etc. Some rod-shaped bacteria have the ability to form disputes. Spore-forming rods are called bacilli. Spindle-shaped bacilli are called clostridia.
Sporulation is a complex process. Spores are significantly different from an ordinary bacterial cell. They have a dense shell and a very small amount of water, they do not require nutrients, and reproduction completely stops. Spores are able to withstand drying, high and low temperatures for a long time and can remain in a viable state for tens and hundreds of years (spores of anthrax, botulism, tetanus, etc.). Once in a favorable environment, the spores germinate, that is, they turn into the usual vegetative propagating form.
Twisted bacteria can be in the form of a comma - vibrios, with several curls - spirilla, in the form of a thin twisted stick - spirochetes. Vibrios include the causative agent of cholera, and the causative agent of syphilis is a spirochete.
9. Features of the morphology of rickettsia and chlamydia
Rickettsia are small gram-negative microorganisms characterized by pronounced polymorphism - they form coccoid, rod-shaped and filamentous forms (Fig. 22). The size of rickettsia varies from 0.5 to 3-4 microns, the length of filamentous forms reaches 10-40 microns. They do not form spores or capsules and are stained red according to Zdrodovsky.
Chlamydia are spherical, ovoid or rod-shaped. Their sizes range from 0.2-1.5 microns. The morphology and size of chlamydia depend on the stage of their intracellular development cycle, which is characterized by the transformation of a small spherical elementary formation into a large initial body with binary fission. Before dividing, chlamydia particles are enveloped in a formation resembling a bacterial capsule. Chlamydia are stained* according to Romanovsky-Giemsa, are gram-negative, and are clearly visible in intravital specimens with phase-contrast microscopy.
10. Structure and biology of mycoplasmas.
The class Mollicutes includes only one order, Mycoplasmatales. Representatives of this order - mycoplasma -
They differ from bacteria in that they lack a cell wall. Instead, they contain a three-layer lipoprotein cytoplasmic membrane. The sizes of mycoplasmas range from 125-250 microns. They have the shape of round, oval or filamentous formations, gram-negative
Mycoplasmas reproduce by binary fission, like most bacteria, especially after the formation of small coccoid formations (elementary bodies, EB) in filamentous structures.
Mycoplasmas are capable of budding and segmentation. The minimum reproducing unit is considered to be the ET (0.7-0.2 µm). The main component of the cell membrane is cholesterol. Mycoplasmas are not capable of producing cholesterol and utilize it from tissues or nutrient media supplemented with their addition. The Gram stain is negative, but the best results are obtained by Romanowsky-Giemsa stain. Mycoplasmas are demanding regarding cultivation conditions: native serum, cholesterol, nucleic acids, carbohydrates, vitamins and various salts must be added to the nutrient media. On dense media they form characteristic small translucent colonies with a raised granular center, giving them a “fried egg” appearance. On media containing blood, some types of mycoplasmas produce a- and beta-hemolysis. In semi-liquid media, mycoplasmas grow along the injection line, forming dispersed, crumbly colonies. In liquid media they lead to slight turbidity or opalescence; some strains are capable of forming a thin oily film. In humans, representatives of the genera Mycoplasma, Ureaplasma and Acholeplasma are isolated, including pathogenic and saprophytic species
Flagella (1, 2, 4, 8 and more - up to several thousand) originate from the anterior pole of the body. If there are many of them, they can cover the entire body of the protozoan (for example, in the order Hypermastigina and the order Opalinina), thereby resembling ciliates. The length of flagella varies widely - from a few to several tens of micrometers. If there are two cords, then often one performs the locomotor function, and the second stretches motionlessly along the body and performs the function of the steering wheel. In some flagellates (genus Trichomonas, genus Trypanosoma), the flagellum runs along the body (Fig. 19) and is connected to the latter using a thin cytoplasmic membrane. In this way, an undulating membrane is formed, which causes the forward movement of the protozoan through wave-like vibrations.
The details of the mechanism of operation of flagella are different, but basically it is a helical movement. The simplest is, as it were, “screwed” into the environment. The flagellum makes from 10 to 40 rps.
The ultrastructure of flagella is very complex and shows striking constancy throughout the animal and flora. All flagella and cilia of animals and plants are built according to a single plan (with a few deviations) (Table I).
Each flagellum is composed of two sections. Most of it is a free area, extending outward from the surface of the cell and being the actual locomotor area. The second section of the flagellum is the basal body (kinetosome) - a smaller part immersed in the thickness of the ectoplasm. On the outside, the flagellum is covered with a three-layer membrane, which is a direct continuation of the outer membrane of the cell.
Inside the flagellum there are 11 fibrils arranged in a strictly regular manner. There are 2 central fibrils along the axis of the bundle (Fig. 20), originating from the axial granule. The diameter of each of them is about 25 nm, and their centers are located at a distance of 30 nm. Along the periphery, under the shell, there are 9 more fibrils, each consisting of two closely welded tubes. The locomotor activity of the flagellum is determined by the peripheral fibrils, while the central fibrils play a supporting function and may represent a substrate along which excitation waves propagate, causing movement of the flagellum.
The basal body (kinetosome) is located in the ectoplasm. It has the appearance of a cylindrical body surrounded by a membrane, under which along the periphery there are 9 fibrils, which are a direct continuation of the peripheral fibrils of the tourniquet itself. Here, however, they become triple (Fig. 20, Table II). Sometimes the base of the flagellum continues deep into the cytoplasm beyond the kinetosome, forming a root filament (rhizoplast), which can either end freely in the cytoplasm or be attached to the nuclear membrane.
In some flagellates, a parabasal body is located near the kinetosome. Its shape can be varied. Sometimes it is an ovoid or sausage-shaped formation, sometimes it takes on a rather complex configuration and consists of many individual lobules (
All bacteria are divided into movable and immobile. The organs of movement in bacteria are flagella. They consist of the protein flagellin, which in its structure belongs to the contractile proteins of the myosin type.
Base of flagellum is a basal body, consisting of a system of disks (blepharoplast: 1 disk - the outer side of the cell wall, 2 disk - the inner side of the cell wall, 3 disk - the cytoplasmic membrane), “built in” into the cytoplasmic membrane and the cell wall. The length of the flagellum is greater than the length of the body of the microbe itself.
According to the number of flagella and their location, motile microorganisms are divided into:
1. Monotrichs, which have one flagellum at the end of the body (the most mobile). For example, Vibrio cholerae.
2. Lophotrichs, which have a bundle of flagella at one of the cell poles. For example, Burkholderia (Pseudomonas) pseudomalei is the causative agent of melioidosis.
3. Amphitrichy, which has a flagellum at both poles of the cell. For example, Spirillum volutans.
4. Peritrichs, which have flagella along the entire perimeter of the cell. For example, Escherichia coli, Salmonella typhi.
Identification of flagella. The flagella are very thin, so they can only be detected with special processing. In particular, first, with the help of a mordant, swelling and an increase in their size are achieved, and then the preparation is colored, due to which they become visible under light microscopy. Flagella can be identified by Morozov, Leffler staining, as well as electron microscopy. Flagella can also be detected by the active motility of bacteria.
The movement of microbes is observed in “crushed” and “hanging” drop preparations from living cultures. These preparations are microscoped with a dry or immersion objective in a dark field or in phase contrast. In addition, motility can be determined by the growth pattern of bacteria in semi-solid agar.
They drank from bacteria.
Pili (pili), synonyms: villi, fimbriae, are thin hollow filaments of a protein nature that cover the surface of bacterial cells. Unlike flagella, they do not perform a motor function.
Pili extend from the surface of the cell and are made of protein pilina.
According to their functional purpose they are divided into 2 types.
1) Most bacteria have pili of the first type, which is why they are called “villi” general type"(common pili). They cause the attachment or adhesion of bacteria to certain cells of the host body. Adhesion is the initial stage of any infectious process.
2) Pili of the second type (synonyms: conjugative, or sexual - sex pili) are found only in donor bacteria that have a special plasmid. Their number is small - 1-4 per cell.
Sex saws perform the following functions:
1. Participate in the transfer of genetic material from one cell to another during the conjugation of bacteria.
2. Specific bacterial viruses – bacteriophages – are adsorbed on them
Bacterial spores, conditions of formation, location, mechanism and stages of Aujeszky staining.
Controversy- a peculiar form of resting bacteria with a gram-positive type of cell wall structure.
Sporulation- this is a way of preserving a species (genophore) in the external environment under unfavorable conditions, and not a method of reproduction.
Spores are formed under unfavorable conditions for the existence of bacteria (drying, nutrient deficiency, etc.). A single spore (endospore) is formed inside a bacterial cell.
Stages of sporulation
1. Preparatory. In the cytoplasm of bacteria, a compacted area is formed that does not have free water, called the “sporogenic zone,” which contains the nucleoid.
2. Prespore stage (prospores). A shell of a double cytoplasmic membrane is formed around the sporogenic zone.
3. Formation of a cortex consisting of peptidoglycan and an outer membrane with a high content of calcium salts and lipids.
4. Maturation stage. A spore shell is formed on the outside of the outer membrane, after which the vegetative part of the cell lyses, releasing the spore.