According to the classification, the yeast belongs to the microscopic fungi of the kingdom Mycota. They are single-celled immobile microorganisms of small size - 10-15 microns. Despite the outward resemblance of yeast to large species of bacteria, they are classified as fungi due to their ultrastructure of cells and methods of reproduction.
Rice. 1. Type of yeast on a Petri dish.
Often in natural conditions, yeast is found on substrates rich in carbohydrates and sugars. Therefore, they are found on the surface of fruits and leaves, berries and fruits, on wound juices, in the nectar of flowers, in dead plant matter. In addition, they are found in soils (as an example, in litter), water. Yeast organisms of the genera Candida or Pichia are often found in the intestines of humans and many animal species.
Rice. 2. Habitat of yeast.
Yeast cell composition
All yeast cells contain about 75% of water, 50-60% is bound intracellular, and the remaining 10-30% is released. The dry matter of the cell, depending on age and condition, on average contains:
- nitrogen 45-60%;
- sugar 15-40%;
- fat 2.5-13%;
- minerals 7-11%.
In addition, cells include a number of important components necessary for their metabolism - enzymes, vitamins. Yeast enzymes are catalysts different types fermentation and respiratory processes.
Rice. 3. Cells of yeast organisms.
Yeast cells have different shapes: ellipses, ovals, rods, balls. The dimensions are also different: often the length is 6-12 microns, and the width is 2-8 microns. It depends on the conditions of their habitation or cultivation, nutritional components and environmental factors. Young yeasts are the most stable in their properties, therefore, the characteristics and description of the species are carried out precisely according to them.
Yeast organisms have all the standard components found in eukaryotic cells. However, in addition to this, they have unique distinctive properties of fungi and combine the features of the cellular structures of plants and animals:
- the walls are rigid, like those of plants,
- there are no chloroplasts and there is glycogen, like in animals.
Rice. 4. Variety of yeast types: 1 - baker's (Saccharomyces cerevisiae); 2 - the most beautiful swordsmanship (Metschnikowia pulcherrima); 3 - ground candida (Candida humicola); 4 - sticky rhodotorula (Rhodotorula glutinis); 5 - red rhodotorula (R. rubra); 6 - golden rhodotorula (R. aurantiaca); 7 - Debaryomyces cantarelli; 8 - cryptococcus laurel (Cryptococcus laurentii); 9 - oblong nadsonia (Nadsonia elongata); 10 - sporobolomyces pink (Sporobolomyces roseus); 11 - sporobolomyces holsaticus (S. holsaticus); 12 - Rhodosporidium diobovatum.
- core;
- Golgi apparatus;
- Cell mitochondria;
- ribosomal apparatus;
- fatty inclusions, grains of glycogen, and valutin.
Some species contain pigments. In young yeast, the cytoplasm is homogeneous. In the process of growth, vacuoles appear inside them (containing organic and mineral components). In the process of growth, the formation of granularity is observed, an increase in vacuoles occurs.
As a rule, the shells include several layers with included polysaccharides, fats and nitrogen-containing components. Some of the species have a mucus membrane, so often the cells are glued together and form flakes in liquids.
Rice. 5. The structure of the cell of yeast organisms.
Respiratory processes of yeast
For respiratory processes, yeast cells need oxygen, but many of their types (facultatively anaerobic) can be dispensed with temporarily and without it and receive energy from fermentation processes (oxygen-free breathing), while forming alcohols. This is one of their main differences from bacteria:
among yeast there are no representatives capable of living absolutely without oxygen.
Respiration with oxygen is energetically more beneficial for yeast, therefore, when it appears, the cells complete fermentation and switch to oxygen respiration, while emitting carbon dioxide, which contributes to faster cell growth. This effect is called Pasteur. Sometimes, with a high content of glucose, the Crabtree effect is observed, when even if there is oxygen, yeast cells ferment it.
Rice. 6. Respiration of yeast organisms.
What yeast feeds on
Many yeasts are chemoorganoheterotrophic and use organic nutrients to provide energy for nutrition and energy.
In anoxic conditions, yeast prefers to use carbohydrates such as hexose and oligosaccharides synthesized from it. Some species can also assimilate other types of carbohydrates - pentose, starch, inulin. With access to oxygen, they are capable of consuming a wider range of substances, including fatty, hydrocarbon, alcohol and others. Such complex types of carbohydrates, such as lignins and cellulose, are not available for assimilation. Sources of nitrogen for them, as a rule, are ammonium salts and nitrates.
Rice. 7. Yeast under the microscope.
What does yeast synthesize
Most often, yeast is produced during metabolism different kinds alcohols - most of them are ethyl, propyl, isoamyl, butyl, isobutyl types. In addition, the formation of volatile fatty acids was detected, for example, the synthesis of acetic, propionic, butyric, isobutyric, isovaleric acids was revealed. In addition, during their vital activity, they can release a number of substances into the environment in small concentrations - fusel oils, acetoins, diacetyls, aldehydes, dimethyl sulfide and others. It is with such metabolites that the organoleptic properties of the products obtained from their use are often associated.
Yeast propagation processes
A distinctive feature of yeast cells is their ability to propagate vegetatively, when compared with other fungi, which occurs both from the budding of spores or, for example, zygotes of cells (such as those of the genera Candida or Pichia). Some yeast can realize the processes of sexual reproduction, containing mycelial stages, when the formation of a zygote is observed and its further transformation into a "bag" of spores. Some yeasts that form mycelium (for example, the genera Endomyces or Galactomyces) are capable of breaking down into individual cells - arthrospores.
Rice. 8. Reproduction of yeast.
What determines the growth of yeast
Growth processes of yeast organisms depend on various environmental factors - temperature, humidity, acidity, osmotic pressure. Most yeast prefer medium temperature, among them there are practically no extremophile species that prefer too high or, conversely, low temperatures. The existence of species capable of withstanding adverse environmental conditions is known. It is possible to suppress the growth and development of some yeast organisms using antibiotics.
Rice. 9. Yeast production.
Why yeast is good for you
Yeast is often used in the household or industry. Man has long begun to use them for his life, for example, in the preparation of bread and drinks. Today, their biological abilities are used in the synthesis of useful substances - polysaccharides, enzymes, vitamins, organic acids, carotenoids.
Rice. 10. Wine is a product obtained through the activity of yeast.
The use of yeast in medicine
Yeast is used in biotechnological processes in the production of medicinal substances - insulin, interferon, heterologous proteins. Doctors often prescribe brewer's yeast for weakened people with allergic diseases. They are also used for cosmetic purposes to strengthen hair, nails, and improve the condition of the skin.
Molds appeared on our planet about 200 million years ago. Mold can both take life and save you from death. The mold looks beautiful, but at the same time it does not cause other feelings, except disgust. Molds are a variety of fungi that form branching mycelium without large fruiting bodies. Mold belongs to micromycetes. These are mushrooms and mushroom-like, having microscopic sizes. Molds are widespread in nature, they develop almost everywhere. Large colonies grow on nutrient media at high temperatures and high humidity, and mold growth is not limited, provided food is available. Molds are distinguished by their unpretentiousness to the environment and food.
Fig. 1. The structure of the mycelium and vegetative reproductive organs of mold fungi
1 - unicellular (mucor); 2 - multicellular (penicillium); 3 - a-conidiophoid penicillium with conidia; b - conidiophores of Aspergillus with conidia; c - sporangiophoid carrier of mucor with sporangia filled with sporesIn the structure of molds, branching hyphae are distinguished, forming a mycelium, or mycelium. Mold mushrooms are extremely diverse, but they all have typical features. The mycelium (mycelium) of molds is the basis of their vegetative body and looks like a complex of branching thin filaments (hyphae). The hyphae of the fungus are located on the surface or inside the substrate on which the fungus has settled. In most cases, molds form large myceliums that occupy a large area. The lower fungi have a non-cellular mycelium, while in most molds the mycelium is divided into cells.
Reproduction of molds
Mushrooms are able to reproduce different ways... The simplest, characteristic of all mushrooms, is reproduction by parts of the mycelium. Each part of the mycelium (mycelium), once on a new site of the substrate, under favorable circumstances becomes independent and develops as whole organism, and the part of the mycelium, which is immersed in the nutrient substrate, plays a major role in providing the body of the mold with nutrients, moisture and minerals. The air part, which rises above the surface of the substrate, as a rule, serves to form various bodies, with the help of which molds multiply (oidia, spores, conidia, etc.).
Oidia are little bodies that are parts of the mycelium. They are formed by some multicellular fungi, in which the mature mycelium breaks down into many small areas that acquire a dense shell.
Disputes - bodies of various shapes, up to several microns in size; usually found at the ends of the hyphae of the aerial part of the mycelium, inside special formations of an oval and semicircular shape - sporangia.
Spores of angiospores are formed by the disintegration of the multinucleated cytoplasm of a young sporangium into many separate areas, which are gradually covered with their own membrane and turn into spores.
Filaments of aerial mycelium carrying sporangia are called sporangiophores. This spore formation is characteristic of unicellular fungi. In multicellular organisms, the so-called exospores are formed, that is, external, or external, which are more often called conidia, and the aerial hyphae carrying them are conidiophores. Conidia are formed by separating directly from conidiophores or special cells located at their apex. These cells are usually oblong in shape and are called sterigmas. Conidia are located on conidiophores (or sterigmata) singly, in chains, etc.
Sporangiophores and conidiophores on the surfaces of materials affected by fungi form a visible fluffy bloom. Its various colors (green, black, olive, pink, white, gray, etc.) depend on the color of conidia, spores, oidia, which are formed in enormous quantities when the fungi reach physiological maturity. The mycelium of fungi is usually colorless.
Many fungi, reproducing in one way or another vegetative way, under suitable conditions of development, can reproduce sexually. This process is not the same for different mushrooms. However, in this case, special fruiting bodies are always formed, in some cases reaching enormous sizes (cap, lamellar, tubular and other mushrooms found in nature are the fruiting bodies of molds).
Sexual spores are located on plates or in containers - bags. An example of the latter is various types of raincoats, stitching. Fungi that can reproduce Chlamydospores and fungal sclerotia sexually are called perfect. Some mushrooms do not reproduce sexually at all. They are classified as imperfect. Knowledge of the structural features of the mycelium, organs of vegetative reproduction, and the structure of fruiting bodies is necessary in practical work to recognize specific pathogens of certain processes.
When unfavorable conditions occur, many fungi are capable of forming dormant stages in the form of so-called sclerotia. They are strong, hard on the surface, usually dark, and inside are white nodules of various sizes and shapes, formed from tightly intertwined hyphae. Sclerotia, falling into favorable conditions for development, germinate and form certain (depending on the type of fungus) reproductive organs. They often form in the ears of cereals. Chlamydospores are another resting stage. When they are formed, the cytoplasm inside the hyphae gathers in the form of lumps, forming a new membrane, usually thick and colored, and the hyphae become like chains or beads consisting of chlamydioepores. Sometimes chlamydospores are formed only at the ends of the hyphae. The multicellular structure, the differentiation of vital functions between the parts of the fungus - air and deep mycelium - indicate that mold fungi are more highly organized, complex organisms in comparison with bacteria.
Mushroom nutrition
Fig. 2. Fungus aspergillus fumigatus molds
Many types of mold are found in nature, for example, Penicillium spp, Mycorales, Aspergillus, Fusarium, Dematiaceae, Saccharomycetaceae, etc. Mushrooms of the genus Penicillum are of great importance to humans. Penicillus is a green mold that grows on plant substrates, including food. Penicill produces the antibiotic penicillin, the world's first antibacterial drug. It is also important for humans to use in the household yeast related to saccharomycete fungi. Yeasts are fungi that do not form the classic mycelium, but their vegetative cells multiply by budding or division. Yeast mushrooms can live as separate single cells throughout their entire life cycle. Since ancient times, yeast has been widely used by humans, since these mushrooms are involved in the process of alcoholic fermentation. This property of yeast is used in the production of alcohol and alcohol-containing products, winemaking, bakery, confectionery, production of fodder protein for livestock nutrition.
Many types of molds have pathogenic properties, that is, they can provoke diseases in humans, animals, plants. Other types of mold harm a person's household because they spoil foodstuffs, including vegetables and fruits, when long-term storage, cause damage to timber, fabrics.
Yeast, their structure and reproduction
Yeasts are unicellular, immobile organisms. They can be of various shapes: elliptical, oval, spherical and rod-shaped. Cell length ranges from 5 to 12 microns, width - from 3 to 8 microns. The shape and size of yeast cells are variable and depend on the genus and species, as well as on the cultivation conditions, the composition of the nutrient medium and other factors. Young cells are more stable, therefore, young cultures are used to characterize yeast. A yeast cell consists of a cell membrane, an adjacent cytoplasmic membrane, cytoplasm or protoplasm, inside which organelles and inclusions (storage substances) are located in the form of fat droplets, grains of glycogen and volutin.
Fig. 3. Yeast cell structure diagram
1 - fissile nucleus; 2 - glycogen; 3 - volutin; 4 - mitochondria
Yeast belongs to the class of marsupial mushrooms (Ascomycetes) to the subclass of the simplest marsupials (Protoascales). The classification of yeast is based on the method of reproduction and some physiological characteristics. The main systematic feature is the ability to form spores. On this basis, yeast is divided into two groups: sporogenic yeast - yeast that can form spores, and asporogenic yeast - non-spore-forming, that is, not having sexual reproduction.
According to some researchers, the second group of yeasts should be attributed to the class of imperfect fungi (Fungi imperfecti - imperfect fungi), although the loss of the ability to reproduce sexually is secondary, and they can also be attributed to marsupials. The classification of sporogenic fungi was proposed in 1954 by V. I. Kudryavtsev. It is based on the method of vegetative reproduction. V. I. Kudryavtsev proposes to combine all yeast into one order of unicellular fungi (Unicellomycetales - unicellomycetes).
He divides sporogenic yeast into three families based on vegetative propagation:
Family Saccharomycetaceae (Saccharomycetaceae) - reproduce by budding. This family includes the genera Saccharomyces (saccharomyces), which is of the greatest practical importance, Pichia (pihia), Nasenula (ganzenula), and others (17 genera in total). They differ in the form of spores and the way of their formation and germination.
Family Schizosaccharomycetaceae (schizosaccharomycetaceae) - reproduce by division. This family includes two genera: Schizosaccharomyces (schizosaccharomyces) and Octosporomyces (octosporomyces).
Family Saccharomycodaceae (saccharomycodace) - reproduction begins by budding and ends with division. The main genera of this family are Saccharomycodes (saccharomycodes) and Hanseniasrora (Hanseniaspora).
Asporogenic yeast is classified according to the system of J. Lodder and Kroeger van Riy, proposed in 1952. The classification is based on the ability of microorganisms to form false mycelium and the ability to ferment. The main genera of this group are Candida (Candida) and Torulopsis (Torulopsis).
Yeast can reproduce vegetatively (by budding or division) and by spores. When budding, a tubercle appears on the mother cell - a kidney that grows and, having reached a certain size, is separated from the mother cell. Under favorable conditions, the budding process lasts about 2 hours. In some yeasts, the daughter cells are not separated from the mother cells, but remain connected, forming a false mycelium (filmy yeast).
In most yeasts, under unfavorable conditions, for example, with a sharp transition from good nutrition to poor nutrition, spore formation occurs, although there are asporogenic yeasts that never form spores (Candida, Torulopsis). Spores are mostly formed asexually, although the cell nucleus undergoes reduction division before this, so that spores have a haploid (single) set of chromosomes.
In the cell, from 2 to 8 ascospores arise, which, when mature, can continue to multiply by budding, giving a weakened haploid generation. As a result of the fusion of two haploid ascospores, a diploid zygote is formed, which subsequently gives a normal generation. The formation of sexual spores is observed in the yeast Zigosaccharomyces (zygosaccharomyces). In them, the formation of spores is preceded by cell fusion (copulation).
The practical importance of yeast
The yeasts Saccharomyces cerevisiae and Saccharomyces ellipsoideus are of the greatest practical importance. Yeast Sacch. cerevisiae can be round or oval in shape. They are widely used in bakery, brewing, fermentation and alcohol production. Under the influence of environmental conditions, certain types of yeast acquired some distinct characteristics. These yeast varieties are commonly called races. Various industries use their own yeast races. The alcohol industry, for example, uses races XII, XV, II, Ya. M, etc. They have the ability to actively ferment sugars at a temperature of 28-30 ° C and are relatively resistant to alcohol. For brewing beer, races with slow fermentation are used at relatively low temperatures (4-10 ° C), which give the drink an aroma, with a small alcohol content. In baking, races are used that have a speed of reproduction, fermentation energy and lifting force.
Yeast Sacch. ellipsoideus (Sacch.vini). This group of yeast is ellipsoidal. They are most commonly used in winemaking. There are several races with properties to impart to wines characteristic taste and aroma (bouquet). Representatives of the Sacch yeast group. lactis cause alcoholic fermentation in fermented milk products.
Along with useful representatives, there are species from the genus Saccharomyces (for example, Sacch. Pasteurianum, Sacch. Intermedius, Sacch. Validus, Sacch. Turbidans), which are pests of the brewing industry. When developing in beer, they give it an unpleasant taste and smell, the drink turns out to be cloudy. The class of ascomycetes includes a number of yeasts and yeast-like organisms that have lost the ability to sporulate. Some of them cause spoilage of raw materials and finished food products.
Mushrooms belonged to the lowest plants until the end of the 20th century. In 1970, they were finally separated into a separate kingdom of Mushrooms, tk. have a number of features that distinguish them from plants and bring them closer to animals.
general characteristics
The kingdom of mushrooms is one-celled and multicellular organisms. Currently, taxonomists have counted more than 100 thousand species of mushrooms.
Fungi are heterotrophic organisms that do not have chlorophyll. They occupy an intermediate position between animals and plants, as they are characterized by a number of properties that bring them closer to animals and plants.
Common signs of fungi and animals:
- There is chitin in the cell membrane;
- as a spare product, they accumulate glycogen, not starch;
- as a result of the exchange, urea is formed;
- lack of chloroplasts and photosynthetic pigments;
Common signs of fungi and plants:
- Unlimited growth;
- absorbent food, i.e. not swallowing food, but absorption;
- the presence of a pronounced cell wall;
- reproduction by spores;
- immobility;
- the ability to synthesize vitamins.
Mushroom nutrition
Many species of the Kingdom of Fungi live in cohabitation (symbiosis) with algae and higher plants. Mutually beneficial cohabitation of the mycelium of fungi with the roots of higher plants forms mycorrhiza (for example, boletus with birch, boletus with aspen).
Many higher plants (trees, durum wheat and others) cannot grow normally without mycorrhiza. Fungi receive oxygen from higher plants, excretion of roots, and compounds that do not contain nitrogen. Mushrooms "help" higher plants to assimilate hard-to-reach substances from humus, activating the activity of enzymes of higher plants, promote carbohydrate metabolism, fix free nitrogen, which is used by higher plants in a number of compounds, give them growth substances, vitamins, etc.
The Kingdom of Mushrooms is conventionally divided into lower and higher. The basis of the vegetative body of mushrooms is the mycelium, or mycelium. Mycelium consists of thin filaments, or hyphas, similar to fluff. These filaments are found inside the substrate on which the fungus lives.
Most often, the mycelium occupies a large surface. Across mycelium absorption of nutrients occurs by osmosis. The mycelium of lower fungi is either divided into cells, or there are no intercellular septa.
Mono- or multinucleated cells of fungi in most cases are covered with a thin cell membrane. Under it is the cytoplasmic membrane that envelops the cytoplasm.
In the cell of fungi there are enzymes, proteins and organelles (lysosomes) in which proteins are cleaved by proteolytic enzymes. Mitochondria are similar to those in higher plants. Vacuoles contain reserve nutrients: glycogen, lipids, fatty acids, fats, etc.
Edible mushrooms are rich in vitamins and minerals. Approximately 50% of the dry mass of mushrooms are nitrogenous substances, of which proteins account for about 30%.
Mushrooms reproduce asexually:
- Specialized cells - spores;
- vegetatively - by parts of the mycelium, by budding.
The process of sporulation may be preceded by the sexual process, which is very diverse in fungi. A zygote can form as a result of the fusion of somatic cells specialized in gametes and sex cells - gametes (formed in the genitals - gametangia). The resulting zygote germinates immediately or after a dormant period and gives rise to hyphae with organs of sexual sporulation, in which spores are formed.
Controversy various mushrooms spread by insects, various animals, humans and air currents.
The value of mushrooms in nature and human life
Molds inhabit food, soil, vegetables and fruits. They cause spoilage of benign products (bread, vegetables, berries, fruits, etc.). Most of these fungi are saprophytes. However, some molds are the causative agents of infectious diseases in humans, animals and plants. For example, the trichophyton fungus causes ringworm in humans and animals.
Everyone is well aware of the single-celled mushroom mucor, or white mold, which settles on vegetables, bread and horse dung. Initially, white mold has a fluffy bloom, and over time it turns black, since round heads (sporangia) form on the mycelium, in which a huge number of dark-colored spores are formed.
Antibiotics are obtained from a number of genera of mold (penicillin, aspergillus).
14 ..
4.4 Yeast. Their shapes, sizes. Yeast propagation. Yeast classification principles
Yeast is a higher fungus that has lost the ability to form mycelium and, as a result, have turned into single-celled organisms.
Yeast cells are oval, ovoid and elliptical in shape (Figure 4.4). Cylindrical (rod-shaped), pear-shaped and lemon-shaped yeasts are somewhat less common.
Yeast cell sizes range from 2.5 to 10 µm in diameter and 4 to 20 µm in length. On average, the mass of a yeast cell is about 510–11 g. The shape, size, and mass of yeast cells change depending on the conditions of the environment in which they develop and on the age of the cells.
Yeast cell structure is described in section 2.4.
Rice. 4.4 - Form of yeast cells:
a - arrow-shaped, b - sickle-shaped, c - lemon-shaped,
d - oval, ovoid, d - cylindrical, e - pear-shaped
Yeast propagation depends on the living conditions of the yeast cell and the type of yeast.
1. Vegetative reproduction
It occurs by budding, less often by division or budding division.
Budding- this is the process of formation of a small tubercle on the cell - a kidney, which gradually increases in size. At the junction of the kidney with the mother cell, a constriction is gradually formed - a constriction. When the kidney reaches about one third of the size of the mother cell, the nucleus moves into the constriction and here it divides into 2 nuclei. One of the nuclei passes into the kidney, while the other remains in the mother's cell. Gradually, the constriction limits the daughter cell from the mother, then the layers of the septum are separated, leaving a kidney scar on the mother cell. Oval yeast usually grows by budding.
Binary fission yeast cell occurs through the emergence of a transverse septum, which, developing, leads to the formation of two daughter cells, identical to the parent. Cylindrical yeast propagates by division.
Budding division typical for lemon-shaped yeast. First, a kidney appears at the pole, which, after the division of the nucleus, is limited from the mother cell by a septum.
2. Sexual reproduction
Some types of haploid yeast multiply in this way. Before sporulation, such haploid cells merge, resulting in the formation of a diploid cell, the nucleus of which divides by meiosis to form four or eight ascospores. Sexual reproduction of yeast takes place under unfavorable conditions.
Yeast classification
Yeast belongs to the kingdom of fungi (Mycota), the division of true fungi (Eumycota). Depending on whether the yeast is able to reproduce sexually, they can be attributed to 2 classes: the class of ascomycetes and the class of deuteromycetes. A small part of the yeast belongs to the class of Basidiomycetes.
Since yeasts differ in their cultural properties from fungi, there are separate classifications.
So, there is a separate classification of perfect (sporogenic) yeast - Kudryavtsev's classification. According to this classification, yeast belongs to the class of ascomycetes, the order of unicellular fungi - yeast, which includes three families: saccharomycetes, schizosaccharomycetes and saccharomycods. Families differ in the shape of the cells, the method of vegetative reproduction.
Saccharomycetes family
Representatives of this family have an oval or ovoid shape, reproduce vegetatively by budding. A particularly important role belongs to the genus Saccharomyces.The main biochemical feature of this yeast is that it ferments sugars to form ethyl alcohol and carbon dioxide. The yeast used in industry is called cultural yeast. So, in the bakery and in the production of alcohol, riding yeast of the genus Saccharomyces cerevisiae. Saccharomyces minor yeast found application in production rye bread and kvass. Brewing uses grass-fed yeast Saccharomyces carlsbergensis ... Saccharomycetes yeast have an oval shape, reproduce vegetatively by budding, under unfavorable conditions they reproduce sexually with ascospores.
Cultural yeast is acidophilic, that is, it grows in an acidic environment, the optimum pH value for yeast is 4.5-5.0. Under aerobic conditions, they actively grow and multiply, and under anaerobic conditions, they carry out alcoholic fermentation (Pasteur effect).
Yeast is sensitive to high concentrations of substances dissolved in the environment. At a high concentration of sugar in the environment, the vital activity of yeast ceases, since this increases the osmotic pressure of the environment and plasmolysis of the cells occurs. The value of the limiting sugar concentration for different yeast races is not the same.
Distinguish between top and bottom fermentation yeast. Top-fermented yeast in the stage of intensive fermentation, they are distributed on the surface of the fermentation medium in the form of a rather thick layer of foam and remain in this state until the end of fermentation. These yeasts include alcoholic and baker's yeast. Bottom-fermented yeast , developing in the fermented liquid, do not pass into the surface layer - foam, quickly settle at the end of fermentation, forming a dense layer at the bottom of the fermentation tank. Bottom-fermented yeast is brewer's yeast. Such differences in the fermentation of liquid media by top-fermented yeast and bottom-fermented yeast are due to the fact that top-fermented yeast belongs to pulverized yeast that do not stick to each other, and bottom-fermented yeast belongs to flaky yeast, since they have sticky membranes, which leads to agglutination and rapid cell sedimentation.
Schizosaccharomycete family
Cells are rod-shaped, multiply by division, in unfavorable conditions - by sporulation. Representatives of this family of the genus Schizosaccharomyces cause alcoholic fermentation and are used in countries with hot climates for the production of beer, Cuban rum.
Family of saccharomycodes
Cells are lemon-shaped, multiply by budding division, and in unfavorable conditions - by sporulation. Yeasts of the genus Saccharomycoides cause alcoholic fermentation, but are pests in winemaking, as they form products that give wines an unpleasant sour smell. Such yeast is called wild yeast.
According to the classification of J. Lodder and Kroeger Van Riy imperfect yeast, unable to reproduce sexually, as well as having lost the ability to alcoholic fermentation, are budding or dividing cells, some of them form pseudomycelium (elongated cells). The classification is based on the following systematic features: the ability to form false mycelium and the relationship to sugars. Yeast of the genera Candida, Torulopsis, Rhodotorula (wild yeast) are asporogenic.
Self-test questions
1. What are the similarities and differences between mushrooms and plants, with animals?
2. What is "mycelium", "hyphae"?
3. What type of cellular organization do most fungi have?
4. What is the difference between higher and lower mushrooms?
5. What is the difference between perfect mushrooms and imperfect ones?
6. What signs are used as the basis for the classification of mushrooms?
7. Describe the class of Ascomycetes. What are the most important representatives of this class?
8. Describe the class of deuteromycetes. Which of the representatives of deuteromycetes are the causative agents of spoilage of fruits and vegetables?
9. What is the structure of sporangiophores, conidiophores?
10. What methods of propagation of mushrooms do you know?
11. What are "oidia", "chlamydospores"?
12. List the main stages of sexual reproduction of fungi.
13. What is formed as a result of sexual reproduction in phycomycetes, ascomycetes, basidiomycetes?
15. What are the shapes and sizes of yeast cells?
16. What is the structure of a yeast cell?
17. How does yeast multiply?
18. What signs are the basis for the classification of Kudryavtsev's sporogenic yeast?
19. Describe the family of yeast-schizosaccharomycetes.
20. What signs are used as the basis for the classification of asporogenic yeast by J. Lodder and Kroeger Van Riy?
21. What is cultured and wild yeast?
22. Describe the bottom and top fermentation yeast.
In what conditions is sexual reproduction of yeast - ascomycetes carried out?
Literature
1. Schlegel G. General Microbiology. - M .: Mir, 1987 .-- 500 p.
2. Churbanova I.N. Microbiology. - M .: Higher school, 1987 .-- 240 p.
3. Mudretsova-Wyss K.A., Kudryashova A.A., Dedyukhina V.P. Microbiology, sanitation and hygiene - Vladivostok: Publishing house of the Far Eastern State Aviation University, 1997. - 312 p.
4. Asonov N.R. Microbiology.- 3rd edition, revised. and additional - M .: Kolos, 1997. - 352 p.
Fungi are ancient heterotrophic organisms that occupy a special place in the general system of living nature. They can be both microscopically small and reach several meters. They settle on plants, animals, humans or dead organic remains, on the roots of trees and grasses. Their role in biocenoses is large and varied. In the food chain, they are decomposers - organisms that feed on dead organic residues, subjecting these residues to mineralization to simple organic compounds.
In nature, mushrooms play a positive role: they are food and medicine for animals; by forming a fungus root, they help plants to absorb water; As a component of lichens, fungi create a habitat for algae.
Mushrooms are chlorophyll-free lower organisms, uniting about 100,000 species, from small microscopic organisms to such giants as tinder fungus, giant slicker and some others.
In the system of the organic world, fungi occupy a special position, representing a separate kingdom, along with the kingdoms of animals and plants. They are devoid of chlorophyll and therefore require ready-made organic matter for nutrition (they belong to heterotrophic organisms). By the presence in the metabolism of urea, in the cell membrane - chitin, a reserve product - glycogen, and not starch - they approach animals. On the other hand, by the way of feeding (by absorbing, not swallowing food), with unlimited growth, they resemble plants.
Fungi also have characteristics that are characteristic only of them: in almost all mushrooms, the vegetative body is a mycelium, or mycelium, consisting of filaments - hyphae.
These are thin tubes, like filaments, filled with cytoplasm. The filaments that make up the mushroom can intertwine tightly or loosely, branch out, grow together with each other, forming films like felt or bundles visible to the naked eye.
In higher fungi, hyphae are divided into cells.
Fungal cells can contain from one to several nuclei. In addition to nuclei, cells also contain other structural components (mitochondria, lysosomes, endoplasmic reticulum, etc.).
Structure
The body of the overwhelming majority of fungi is built of thin filamentous formations - hyphae. Their combination forms the mycelium (or mycelium).
Branching out, the mycelium forms a large surface, which ensures the absorption of water and nutrients. Conditionally, mushrooms are divided into lower and higher. In lower fungi, hyphae do not have transverse septa and the mycelium is one highly branched cell. In higher fungi, hyphae are divided into cells.
The cells of most fungi are covered with a hard shell, which is absent in zoospores and the vegetative body of some of the simplest fungi. The cytoplasm of the fungus contains structural proteins and enzymes, amino acids, carbohydrates, and lipids that are not associated with cell organoids. Organoids: mitochondria, lysosomes, vacuoles containing storage substances - volutin, lipids, glycogen, fats. There is no starch. A mushroom cell has one or more nuclei.
Reproduction
In fungi, vegetative, asexual and sexual reproduction are distinguished.
Vegetative
Reproduction is carried out by parts of the mycelium, special formations - oidia (formed as a result of the disintegration of hyphae into separate short cells, each of which gives rise to a new organism), chlamydospores (formed in about the same way, but have a thicker dark-colored shell, tolerate adverse conditions well), by budding of mycelium or individual cells.
For asexual vegetative reproduction, special adaptations are not needed, but not many descendants appear, but few.
With asexual vegetative reproduction, the filament cells, no different from the neighboring ones, grow into a whole organism. Sometimes, animals or movement of the environment will tear the hypha to pieces.
Sometimes, when unfavorable conditions occur, the thread itself disintegrates into individual cells, each of which can grow into a whole mushroom.
Sometimes growths form on the thread, which grow, fall off and give rise to a new organism.
Often, some cells build up a thick membrane. They can withstand drying and remain viable for up to ten years or more, and germinate in favorable conditions.
During vegetative reproduction, the DNA of the offspring does not differ from the DNA of the parent. Such reproduction does not require special devices, but the number of offspring is small.
Asexual
With asexual spore reproduction, the filament of the fungus forms special cells that create spores. These cells look like twigs unable to grow and separating spores from themselves, or like large bubbles in which spores form. Such formations are called sporangia.
With asexual reproduction, the DNA of the offspring does not differ from the DNA of the parent. Less substances are spent on the formation of each spore than on one offspring during vegetative reproduction. Asexually, one individual produces millions of spores, so the fungus is more likely to leave offspring.
Sexual
With sexual reproduction, new combinations of traits appear. During this reproduction, the DNA of the offspring is formed from the DNA of both parents. In fungi, DNA unification occurs in different ways.
Different ways to ensure DNA unification during sexual reproduction of fungi:
At some point, the nuclei merge, and then the DNA strands of the parents, exchange pieces of DNA and separate. In the DNA of the offspring, there are sections obtained from both parents. Therefore, the descendant is somewhat similar to one parent, and in some ways - to the other. A new combination of traits can decrease and increase the vitality of the offspring.
Reproduction consists in the fusion of male and female reproductive gametes, resulting in the formation of a zygote. In fungi, iso-, hetero- and oogamy are distinguished. The reproductive product of lower fungi (oospore) grows into the sporangium, in which spores develop. In ascomycetes (marsupials), as a result of the sexual process, bags (asci) are formed - unicellular structures, usually containing 8 ascospores. Bags formed directly from the zygote (in the lower ascomycetes) or on the ascogenous hyphae developing from the zygote. In the bursa, the nuclei of the zygote merge, then the meiotic division of the diploid nucleus and the formation of haploid ascospores. The pouch is actively involved in the distribution of ascospores.
For basidiomycetes, the sexual process is characteristic - somatogamy. It consists in the fusion of two cells of the vegetative mycelium. The sexual product is a basidium, on which 4 basidiospores are formed. Basidiospores are haploid, they give rise to a haploid mycelium, which is short-lived. By fusion of the haploid mycelium, a dikaryotic mycelium is formed, on which basidia with basidiospores are formed.
In imperfect fungi, and in some cases in others, the sexual process is replaced by heterokaryosis (heteronucleus) and the parasexual process. Heterokaryosis consists in the transition of genetically heterogeneous nuclei from one segment of the mycelium to another by the formation of anastomoses or fusion of hyphae. In this case, the fusion of nuclei does not occur. The fusion of nuclei after, their transfer to another cell is called a parasexual process.
Fungus filaments grow by transverse division (filaments do not divide along the cell). The cytoplasm of neighboring cells of the fungus is a single whole - there are holes in the partitions between the cells.
Nutrition
Most mushrooms look like long filaments that suck up nutrients from the entire surface. Mushrooms absorb the necessary substances from living and dead organisms, from soil moisture and water of natural reservoirs.
Mushrooms release substances that break the molecules of organic substances into pieces that the fungus can absorb.
But under certain conditions, it is more useful for the body to be a thread (like a mushroom), and not a lump (cyst) like a bacterium. Let's check if this is so.
Let's trace the bacteria and the growing filament of the fungus. Strong sugar solution is shown in brown color, weak sugar solution is shown as light brown, water without sugar is shown in white.
We can conclude: a filamentous organism, growing, may end up in places rich in food. The longer the thread, the greater the supply of substances that the saturated cells can spend on the growth of the fungus. All hyphae behave as part of one whole, and parts of the fungus, once in food-rich places, feed the entire fungus.
Mold fungi
Mold fungi settle on moist plant residues, less often animals. One of the most common molds is mucor, or capitate mold. The mycelium of this fungus in the form of the finest white hyphae can be found on stale bread. Mucor hyphae are not separated by partitions. Each hypha is one highly branched cell with several nuclei. Some branches of the cell penetrate into the substrate and absorb nutrients, while others rise up. At the top of the latter, black rounded heads are formed - sporangia, in which spores are formed. Ripe spores are spread by air currents or by insects. Once in favorable conditions, the spore grows into a new mycelium (mycelium).
The second representative of mold fungi is penicillus, or blue-gray mold. The mycelium of the penicillus consists of hyphae, divided by transverse septa into cells. Some hyphae rise up, and at the end of them branching, resembling tassels, is formed. At the end of these ramifications, spores form, with the help of which the penicillus multiplies.
Yeast mushrooms
Yeast is single-celled, immobile organisms of an oval or elongated shape, 8-10 microns in size. They do not form a true mycelium. The cell has a nucleus, mitochondria, many substances (organic and inorganic) accumulate in vacuoles, redox processes take place in them. Yeast accumulates volutin in cells. Vegetative propagation by budding or division. Spore formation occurs after repeated reproduction by budding or division. It occurs more easily with an abrupt transition from abundant nutrition to an insignificant one, when oxygen is supplied. In a cell, the number of spores is paired (usually 4-8). In yeast, the sexual process is also known.
Yeast fungi, or yeast, are found on the surface of fruits, on plant debris containing carbohydrates. Yeast differs from other fungi in that it does not have mycelium and is single, in most cases oval cells. In a sugary environment, yeast causes alcoholic fermentation, as a result of which ethanol and carbon dioxide:
C 6 H 12 O 6 → 2C 2 H 5 OH + 2CO 2 + energy.
This process is enzymatic, proceeds with the participation of a complex of enzymes. The released energy is used by yeast cells for life processes.
Yeast reproduces by budding (some species by division). When budding, a bulge is formed on the cell, resembling a kidney.
The nucleus of the mother cell divides, and one of the daughter nuclei becomes a bulge. The bulge grows rapidly, turns into an independent cell and separates from the mother. With very rapid budding, the cells do not have time to separate and, as a result, short fragile chains are obtained.
At least ¾ of all fungi are saprophytes. The saprophytic way of feeding is associated mainly with products of plant origin (the acidic reaction of the environment and the composition of organic substances of plant origin are more favorable for their life).
Fungi-symbionts are associated mainly with higher plants, bryophytes, algae, less often with animals. An example would be lichens, mycorrhiza. Mycorrhiza is the cohabitation of the fungus with the roots of a higher plant. The fungus helps the plant to assimilate hard-to-reach humus substances, promotes the absorption of mineral nutrition elements, helps with its enzymes in carbohydrate metabolism, activates the enzymes of a higher plant, binds free nitrogen. From a higher plant, the fungus obviously receives nitrogen-free compounds, oxygen and root secretions, which facilitate the germination of spores. Mycorrhiza is very common among higher plants; it is not found only in sedge, cruciferous and aquatic plants.
Ecological groups of mushrooms
Soil mushrooms
Soil fungi are involved in the mineralization of organic matter, the formation of humus, etc. In this group, fungi are isolated that enter the soil only at certain periods of life, and fungi of the rhizosphere of plants living in the zone of their root system.
Specialized soil mushrooms:
- coprophylls- mushrooms that live on soils rich in humus (manure heaps, places where animal droppings accumulate);
- keratinophylls- mushrooms that live on hair, horns, hooves;
- xylophytes- fungi that decompose wood, among them there are destroyers of living and dead wood.
House mushrooms
House mushrooms - destroyers of wooden parts of buildings.
Aquatic mushrooms
The group of mycorrhizal symbiont fungi also belongs to them.
Fungi growing on industrial materials (metal, paper and products from them)
Hat mushrooms
Hat mushrooms settle on humus-rich forest soil and get water from it, mineral salts and some organic matter. They get some of the organic matter (carbohydrates) from trees.
The mycelium is the main part of every mushroom. Fruit bodies develop on it. The cap and the leg are made of tightly fitting mycelium threads. In the leg, all the threads are the same, and in the cap they form two layers - the upper one, covered with a skin colored with different pigments, and the lower one.
In some mushrooms, the bottom layer consists of numerous tubes. Such mushrooms are called tubular. In others, the bottom layer of the cap consists of radially arranged plates. Such mushrooms are called lamellar. Spores form on the plates and on the walls of the tubes, with the help of which the fungi multiply.
The mycelium hyphae entwine the roots of trees, penetrate them and spread between the cells. Between the mycelium and the roots of the plants, a cohabitation that is beneficial for both plants is established. The fungus supplies plants with water and mineral salts; replacing root hairs on the roots, the tree gives up some of its carbohydrates to it. Only with such a close connection of the mycelium with certain tree species is the formation of fruiting bodies in cap mushrooms possible.
Dispute formation
In the tubes or on the plates of the cap, special cells are formed - spores. Ripe small and light spores spill out, they are picked up and carried by the wind. They are carried by insects and slugs, as well as squirrels and hares that eat mushrooms. The spores are not digested in the digestive organs of these animals and are thrown out along with the droppings.
In moist, humus-rich soil, fungal spores germinate, from which mycelium threads develop. A mycelium arising from a single spore can form new fruiting bodies only in rare cases. In most species of fungi, fruiting bodies develop on myceliums formed by fused filament cells originating from various spores. Therefore, the cells of such a mycelium are dual-core. The mycelium grows slowly, only having accumulated reserves of nutrients, it forms fruiting bodies.
Most of the species of these fungi are saprophytes. They develop on humus soil, dead plant residues, some on manure. The vegetative body consists of hyphae, which form the mycelium located underground. In the process of development, umbrella-like fruit bodies grow on the mycelium. The stump and the cap consist of dense bundles of mycelium filaments.
In some mushrooms, on the underside of the cap, plates radiate radially from the center to the periphery, on which basidia develop, and in them spores are hymenophores. Such mushrooms are called lamellar. Certain types of fungi have a veil (a film of infertile hyphae) that protects the hymenophore. When the fruiting body ripens, the veil breaks and remains in the form of a fringe along the edges of the cap or a ring on the leg.
In some fungi, the hymenophore is tubular. These are tubular mushrooms. Their fruiting bodies are fleshy, quickly rot, easily damaged by insect larvae, and eaten by slugs. Cap mushrooms reproduce by spores and parts of mycelium (mycelium).
The chemical composition of mushrooms
V fresh mushrooms water makes up 84-94% of the total mass.
Proteins of mushrooms are absorbed only by 54-85% - worse than proteins of other plant products. The assimilation is hampered by poor solubility of proteins. Fats, carbohydrates are absorbed very well. Chemical composition depends on the age of the fungus, its condition, species, growing conditions, etc.
The role of mushrooms in nature
Many fungi grow together with the roots of trees and grasses. Their cooperation is mutually beneficial. Plants provide the mushrooms with sugar and proteins, and the fungi destroy the dead plant residues in the soil and suck in the water with the minerals dissolved in it through the entire surface of the hyphae. The roots that have grown together with fungi are called mycorrhiza. Most trees and grasses form mycorrhiza.
Fungi play the role of destroyers in ecosystems. They destroy dead wood and leaves, plant roots and animal corpses. They convert all dead residues into carbon dioxide, water and mineral salts - into what plants can assimilate. While feeding, mushrooms gain weight and become food for animals and other mushrooms.
