Mushroom spores
The spores of the fungi are intended for reproduction. They represent one or several cells with microscopic sizes - from 1 to 100 microns. The spores of most types of fungi contain extremely few nutrients, rare of them survive and, once in favorable conditions, germinate, giving rise to the mycelium of the young fungus. But the death of most disputes is compensated by the formation of a huge number of them. For example, the causative agent of stem rust of cereal plants forms up to 10 billion spores on one barberry bush in the spring and in June, the fruiting body of standard-sized polypores gives up to 30 billion spores, champignons form about 40 billion spores per hour.
The generally accepted classification of disputes by origin and function performed in the life of fungi into two broad groups:
a) spores of asexual reproduction (mitospores);
b) spores of sexual reproduction (meiospores).
During the formation of mitospores, mitotic division of the cell nucleus occurs with the preservation of the number of chromosomes; meiospores - meiosis, characterized by a decrease in the number of chromosomes by half.
Mitospores and meiospores have different functions in the life of fungi. Mitospores are mainly intended for mass dispersal of fungi during the vegetative period, without recombination of hereditary qualities. Meiospores are spores of sexual reproduction. Their appearance is associated with the germination of a zygote - a cell formed during the sexual process from two parental cells. In the process of germination of the zygote and the formation of spores of sexual reproduction, the recombination (redistribution) of the characteristics of the parental organisms takes place, and the diversity of offspring increases.
In many species of fungi, both mitospores and meiospores are formed in the life cycle. For example, in many marsupial fungi - pathogens of ergot, powdery mildew of plants, apple scab and other mitospores are formed throughout the growing season and perform the function of re-infection of plants, and meiospores are formed after wintering and provoke primary infection of plants.
A large group of fungi does not have mitospores in the development cycle, like many cap fungi, tinder fungi, gasteromycetes, and some types of discomycetes (morels, lines). In such cases, meiospores take on the functions of mitospores and serve for the mass dispersal of fungi.
Formation
The formation of mitospores in most forms of fungi occurs inside special cells - sporangia or externally on the branches of aerial mycelium. The first types of spores are called sporangiospores, the second - conidia. Sporangiospores are immobile and passively transferred; they can have flagella and, with their help, move actively in the aquatic environment. Motile spores are called zoospores. Reproduction by zoospores is carried out only in the presence of a droplet-liquid medium.
Sporangiospores, like zoospores, serve for a wide dispersal of fungi. They contain a small amount of nutrients and are not able to maintain their viability for a long time. In one sporangium, up to several tens of thousands of spores can be formed. An increase in the production of sporangiospores is achieved due to additional branches of sporangiophores and an increase in the number of sporangia. Therefore, for the formation of a large sporangium with many sporangiospores, a longer period is needed than for the mass formation of conidia. This explains the fact that asexual reproduction with the help of conidia is widespread in most fungi.
Conidia are formed in higher fungi with cellular mycelium on hyphae of aerial mycelium - conidiophores. They are usually very small (from 1 to 10-15 microns) and are formed in huge quantities. Unlike sporangiospores, conidia can survive for a long time in unfavorable conditions without germinating. Conidia are released both actively and passively as they mature. In the process of evolution, they have formed multiple adaptations that facilitate their distribution. Some conidia have dry surfaces and are easily carried by the wind; others are covered in mucus and are well tolerated by insects or water, etc.
Meiospores, like mitospores, are extremely diverse in fungi. They are formed inside or on the surface of special cells, which are called, respectively, bags and basidia. The bags are found in the fruiting bodies of mushrooms and are well protected from the effects of adverse environmental factors. In fungi from the ascomycete group, ascospores are formed, in basidiomycetes - basidiospores with a different structure.
Spore formation of bacteria
| Parameter name | Meaning |
| Topic of the article: | Spore formation of bacteria |
| Category (thematic category) | Production |
Some rod-shaped bacteria (genus Bacillus and genus Clostridium) can form spores. Spore formation is induced by unfavorable environmental conditions (change in temperature, lack of nutrients, accumulation of toxic metabolic products, change in pH, decrease in moisture content, etc.). Τᴀᴋᴎᴍ ᴏϬᴩᴀᴈᴏᴍ, sporulation is not an obligatory stage in the development of spore-forming bacteria.
There is always only one spore in the cell.
The main stages of sporulation are:
1. Preparatory stage. The process is preceded by a restructuring of the genetic apparatus of the cell: nuclear DNA is stretched out in the form of a thread and concentrated at one of the poles of the cell or in the center, depending on the type of bacteria. This part of the cell is usually called sporogenic zone.
2. Formation of a prospor. In the sporogenic zone, dehydration and compaction of the cytoplasm occurs and the isolation of this zone with the help of a septum formed from the cytoplasmic membrane.
Prospora - a structure located inside the cell and separated from it by two membranes.
3. Formation of spore shells. A cortical layer (cortex) is formed between the membranes, which is similar in composition to the cell wall of a vegetative cell. In addition to peptidoglycan - murein, the cortex contains calcium salt dipicolinic acid, which is synthesized by the cell in the process of sporulation. Further, on top of the membrane, a spore shell is synthesized, consisting of several layers. The number and structure of the layers are different for different types of bacteria. The shell is impermeable to water and solutes and provides greater spore resistance to external influences
4. Exit the spore from the cell. After the maturation of the spore, the shell is destroyed, and the spore is released.
The sporulation process takes several hours.
Τᴀᴋᴎᴍ ᴏϬᴩᴀᴈᴏᴍ, dispute - it is a dehydrated cell covered with a multilayer membrane, which contains the calcium salt of dipicolinic acid. The main feature of bacterial spores is their high thermal stability.
Once in favorable conditions, the dispute grows. The process of converting a spore into a growing (vegetative) cell begins with water absorption and swelling. In this case, profound physiological changes occur: respiration intensifies and enzymes are activated. During this period, the spore loses its thermal stability. Further, its outer shell is torn, and a vegetative cell is formed from the formed structure.
Spore formation of bacteria - concept and types. Classification and features of the category "Spore formation of bacteria" 2017, 2018.
There are bacteria in nature that have the unique ability to form spores. How this process takes place, the reader will find out by reading the article.
Spore bacteria are more resistant to freezing, drying, prolonged or short-term boiling, and exposure to chemicals. There are vegetative forms of bacterial formation and sporulation. Examples of the latter: pathogens of diseases such as anthrax, botulism, tetanus and some types of saprophytic soil inhabitants that can be found in manure.
When the spore shell enters a favorable environment for it, it begins to swell. This process continues until the shell is completely destroyed. At the time when the membrane tissue is torn, through this large impulse the young cell enters the external environment.
In this way, the spore grows in aerobic bacteria. Anaerobic bacteria do not lose their outer cell membrane during sporulation. The spore does not come into contact with the external environment, its contact occurs with the cell membrane. When favorable conditions arise, nutrients enter the cell through the sheath. The spore begins to sprout.
Spore formation in bacteria is undesirable during processing and storage of individual products. If this process occurs, it will be difficult to fight the microorganisms. To eliminate spores in canned food, for example, the product must be sterilized, which will greatly reduce its quality. To preserve milk for a long time, it is sterilized, and this leads to the loss of its original properties and vitamin A. For information: the heating temperature during sterilization is 120 degrees.
During pasteurization, in order to preserve the nutrients as much as possible, the milk is heated to only 80-90 degrees. This affects the shelf life: milk quickly deteriorates, since during pasteurization the spores do not die, but on the contrary, when they germinate and begin to multiply rapidly, which is why the product deteriorates.
Spores (endospores) of bacteria are a special type of resting reproductive cells, characterized by a sharply reduced level of metabolism and high resistance.
A bacterial spore forms inside the mother's cell and is called an endospore. The ability to form spores is mainly possessed by rod-shaped gram-positive bacteria of the genera Bacillus and Clostridium; of spherical bacteria, only a few species, for example, Sporosarcina ureae. Typically, only one spore forms inside a bacterial cell.
The main function of spores is to preserve bacteria in adverse environmental conditions. The transition of bacteria to sporulation is observed with depletion of the nutrient substrate, a lack of carbon, nitrogen, phosphorus, accumulation of potassium and manganese cations in the medium, a change in pH, an increase in oxygen content, etc.
Spores differ from vegetative cells by repression of the genome, an almost complete absence of metabolism (anabiosis), a small amount of free water in the cytoplasm, an increase in the concentration of calcium cations in it, and the appearance of dipicolinic (pyridine-2,6-dicarboxylic) acid in the form of Ca-chelate, with which associate the stay of the spores at rest and their thermal stability.
In a light microscope, the spores have the appearance of oval, sometimes rounded, highly refracting light formations 0.8-1.0, 1.2-1.5 microns in size; they can be located centrally (B. anthracis), subterminally - closer to the end (Cl. botulinum), terminal - at the end of rods (Cl. letani). The structure of a mature spore is complex and of the same type in different types of bacteria. Its central part is represented by the core, or sporoplasm, which includes nucleic acids, proteins and dipicolinic acid. It contains a nucleoid, ribosomes, and indistinct membrane structures. The sporoplasm is surrounded by a cytoplasmic membrane, the rudimentary peptidoglycan layer is adjacent to it, then a massive layer of the cortex, or cortex, specific for spores, is located. There is an outer membrane on the surface of the cortex. Outside, the spore is clothed with a multilayer shell. In many bacteria, an exosporium is located around the circumference of the outer layer of the spore membrane.
Sporulation (sporulation) is one of the most complex processes of bacterial cell differentiation, which is controlled by a complex of special genes - sporulon. In many bacilli, polypeptide antibiotics are synthesized during spore formation, which inhibit the growth of vegetative cells.
The process of spore formation goes through a number of successive stages:
- preparatory. Metabolism changes, DNA replication is completed, and all condensation occurs. The cell contains two or more nucleoids, one of them is localized in the sporogenic zone, the rest in the cytoplasm of the sporangium. Dipicolinic acid is synthesized at the same time;
- pre-dispute stage. From the side of the cytoplasmic membrane of the vegetative cell, an ingrowth of a double membrane, or septum, occurs, separating the nucleoid from a section of compacted cytoplasm (sporogenic zone). As a result, a prospore is formed, surrounded by two membranes;
- the formation of shells. First, a rudimentary peptidoglycan layer is formed between the membranes of the prospore, then a thick peptidoglycan layer of the cortex is deposited above it, and a spore membrane is formed around its outer membrane;
- maturation of the spore. The formation of all structures of the spore ends, it becomes thermally stable, acquires a characteristic shape and occupies a certain position in the cell.
When exposed to favorable conditions, spores germinate into vegetative cells. This process begins with the absorption of water and the hydration of the spore structures. At the same time, enzymes are activated and the energy of respiration increases sharply. Lytic enzymes destroy the integument of the spore and peptidoglycan of the cortex, dipicolinic acid and calcium salts are released outside. At the site of the rupture of the spore membrane, a growth tube arises and a vegetative cell is formed. Spore germination lasts about 4-5 hours.
Bacterial spores are resistant to high temperatures, chemical compounds, including organic solvents and surfactants; can exist for a long time (tens, hundreds of years) in a dormant state.
Some types of bacteria simultaneously form spores (tarasporic bodies, which are not elements or components of a bacterial cell, are described in B.anthracis, B.cereus, etc. On the surface of spores, in B. thuringiensis cells, parasporic bodies are formed in the form of large protein crystals, which are toxic and are used for the preparation of a preparation used in the fight against harmful insects.
There are some types of bacteria that produce round or oval bodies that are highly refractive. These formations are called endospores. Spore formation is one of the stages of the development cycle of certain microorganisms in response to the adverse effects of the external environment, developed in the process of evolution in the struggle to preserve the species. Lack of nutrients causes different reactions in some microorganisms, ensuring the preparation of the cell for a long period during which nutrients are unavailable. The transition to sporulation is observed with depletion of the nutrient substrate, with a lack of carbon, nitrogen or phosphorus, a change in the pH of the medium, etc. Spore formation is inherent mainly in rod-shaped microorganisms (bacilli and clostridia, and is relatively rarely observed in cocci (Sarcina urea, Sarcina lutea) and convoluted forms (Desulfovibrio desulfuricans).
Spore formation occurs in the external environment, on nutrient media and is not observed in human and animal tissues. The sporulation process is divided into seven successive stages, characterized by various cytological changes (Fig. 12).
Preparatory stages(stages 0 and I). At these stages, there are still no morphologically visible changes in the cell, but the amount of water decreases and the cytoplasm becomes denser.
Prospore stage(stage II) is the first morphologically recognizable sporulation stage. It is characterized by the appearance of a prospore septum, which divides the cell into a small prospore and a large mother cell. This is a key step in sporulation.
During stages of absorption of prospora(stage III) there is a spatial separation of a small spore, which passes into the cytoplasm of the mother cell. A double membrane structure is formed outside the spore.
Pre-dispute stage characterized by the formation of a cortex (dense spore membrane) inside the membrane structure of the prospore (stage IV) and the condensation of proteins on its surface (stage V).
On the ripening stage(stage VI) the spore membrane develops further and becomes resistant to chemical agents and heat. The formed spore occupies about 1/10 of the mother cell.
The final stage is release mature dispute from the mother cell (stage VII). The spore formation process lasts 18-20 hours.
Due to the presence of a dense multilayer shell with a lamellar structure, a minimum amount of water and a high content of calcium, lipids and dipicolinic acid, spores are highly resistant to environmental factors and disinfectants. They can withstand relatively high and low temperatures, prolonged drying, exposure to radiation, toxic substances, etc. They can persist for decades in adverse conditions.
Once in favorable conditions, the spores germinate and again turn into vegetative forms. The spore germination process begins with the absorption of water. They swell, increase in size. From the shell at the pole, in the center, or between the pole and the center, an appendix appears, from which the stick is drawn. The spore germination process is much faster and takes 4 - 5 hours.
By the nature of localization in the body of microorganisms, the spores are located:
1. Central (anthrax bacillus, anthracoid bacillus, etc.).
2. Subterminally - towards the end (causative agent of botulism, etc.).
3. Terminal - at the end of the stick (tetanus causative agent).
In some types of spore-forming microorganisms, the spore diameter exceeds the diameter of the bacterial cell. If the spores are localized subterminally, the bacteria take the form of a spindle. These include clostridia of butyric acid fermentation. In some clostridia, for example, in the causative agent of tetanus, the spores are located terminally, their cell resembles a drumstick (Fig. 13).
Rice. 13. Forms and location of spores in bacilli.
The ability to sporulate is used in the taxonomy of microbes, as well as in the choice of methods for disinfecting objects, rooms, food products, and various products.
