How many types of yeast fungi are there. Yeast, their structure and reproduction

The boundaries of the group are not clearly outlined: many mushrooms that can reproduce vegetatively in a unicellular form and are therefore identified as yeasts, at other stages of the life cycle form a developed mycelium, and in some cases, macroscopic fruiting bodies. Previously, such fungi were classified as a separate group of yeast-like fungi, but now they are usually considered together with yeasts. Studies of 18S rRNA showed a close relationship with typical yeast species capable of growing only in the form of mycelium.

Yeast cells are typically 3-7 µm in diameter. There is evidence that some species are able to grow up to 40 microns.

Yeast is of great practical importance, especially baker's or brewer's yeast ( Saccharomyces cerevisiae). Some species are facultative and opportunistic pathogens. To date, the yeast genome has been completely deciphered. Saccharomyces cerevisiae(they became the first eukaryotes whose genome was completely sequenced) and Schizosaccharomyces pombe.

Story

The Russian word "yeast" has a common root with the words "tremble", "tremble", which were used to describe the foaming of a liquid, often accompanying the fermentation carried out by yeast. English word " yeast" (yeast) comes from Old English " gist», « gyst", which means "foam, boil, give off gas".

Yeast is probably one of the most ancient "household organisms". For thousands of years people have used them for fermentation and baking. Among the ruins of ancient Egyptian cities, archaeologists have found millstones and bakeries, as well as images of bakers and brewers. It is assumed that the Egyptians began to brew beer in 6000 BC. e., and by 1200 BC. e. mastered the technology of baking yeast bread along with baking unleavened bread. To start the fermentation of a new substrate, people used the remains of the old. As a result, yeast selection took place in various farms for centuries and new physiological races were formed that were not found in nature, many of which were even initially described as separate species. They are the same products of human activity as varieties of cultivated plants.

Louis Pasteur - scientist who established the role of yeast in alcoholic fermentation

• Saccharomycotina
• Taphrinomycotina
  • Schizosaccharomycetes

• Urediniomycetes
  • Sporidiales

Features of metabolism

Yeasts are chemoorganoheterotrophs and use organic compounds both for energy and as a source of carbon. They need oxygen for respiration, however, in its absence, many species are able to obtain energy through fermentation with the release of alcohols (facultative anaerobes). Unlike bacteria, there are no obligate anaerobes among yeasts that die in the presence of oxygen in the environment. When air is passed through the fermentable substrate, the yeast stops fermentation and begins to breathe (because this process is more efficient), consuming oxygen and releasing carbon dioxide. It accelerates the growth of yeast cells ( Pasteur effect). However, even with oxygen access, in the case of a high glucose content in the medium, yeast begins to ferment it ( Crabtree effect).

Yeast is quite demanding on nutritional conditions. Under anaerobic conditions, yeast can only use carbohydrates as an energy source, mainly hexoses and oligosaccharides built from them. Some species ( Pichia stipitis, Pachysolen tannophilus) also metabolize pentoses, such as xylose. Schwanniomyces occidentalis And Saccharomycopsis fibuliger capable of fermenting starch, Kluyveromyces fragilis- inulin. Under aerobic conditions, the range of digestible substrates is wider: in addition to carbohydrates, there are also fats, hydrocarbons, aromatic and one-carbon compounds, alcohols, organic acids. Many more species are able to use pentoses under aerobic conditions. However, complex compounds (lignin, cellulose) are not available for yeast.

Ammonium salts can be nitrogen sources for all yeasts, about half of the species have nitrate reductase and can assimilate nitrates. Urea uptake pathways are different in ascomycetes and basidiomycetes yeasts. Ascomycetes first carboxylate it, then hydrolyze, basidiomycetes - immediately hydrolyze with urease.

For practical use, the products of the secondary metabolism of yeast, released in small quantities into the environment, are important: fusel oils, acetoin (acetylmethylcarbinol), diacetyl, butyric aldehyde, isoamyl alcohol, dimethyl sulfide, etc. The organoleptic properties of the products obtained with the help of yeast depend on them.

Spreading

Yeast habitats are mainly associated with sugar-rich substrates: the surface of fruits and leaves, where they feed on intravital plant secretions, flower nectar, plant wound juices, dead phytomass, etc., however, they are also common in the soil (especially in the litter and organic horizons) and natural waters. Yeast (b. Candida, Pichia, Ambrosiozyma) are constantly present in the intestines and passages of xylophages (wood-eating insects), rich yeast communities develop on leaves affected by aphids. Representatives of the genus Lypomyces are typical soil inhabitants.

Life cycle

A distinctive feature of yeast is the ability to reproduce vegetatively in a unicellular state. When compared to the life cycles of fungi, this looks like spore or zygote budding. Many yeasts are also capable of a sexual life cycle (its type depends on affinity), which may include mycelial stages.

In some yeast-like fungi that form mycelium, it can disintegrate into cells (arthrospores). This is childbirth Endomyces, Galactomyces, Arxula, Trichosporon. In the latter two, arthrospores begin to bud after formation. Trichosporon also forms vegetative endospores inside mycelial cells.

Ascomycete yeast cycles

Life cycle of ascomycete haplo-diploid yeasts.

The most characteristic type of vegetative reproduction for unicellular ascomycete yeasts is budding, only Schizosaccharomyces pombe do not reproduce by budding, but by binary fission. The site of budding is an important diagnostic feature: polar budding, due to the formation of budding scars, leads to the formation of apicular (lemon-shaped, Saccharomycodes, Hanseniaspora, Nadsonia) and pear-shaped ( Schizoblastosporion) cells; multilateral does not modify the shape of the cell ( Saccharomyces, Pichia, Debaryomyces, Candida). At childbirth Sterigmatomyces, Kurtzmanomyces, Fellomyces budding occurs on long outgrowths (sterigmas).

Budding in ascomycete yeast is holoblastic: the cell wall of the mother cell softens, bends outward and gives rise to the cell wall of the daughter cell.

Common, especially in ascomycete yeast genera Candida And Pichia, the cells after budding do not diverge and form a pseudomycelium, which differs from the true one by clearly visible constrictions at the site of the septa and shorter compared to the previous end cells.

Yeasts can change their mating type through DNA recombination. This change in cells occurs at a frequency of approximately 10-6 per cell. In addition to the mat locus, the cell also has a copy of the genes mat a And matα: respectively HMR(Hidden MAT Right) and HML (Hidden MAT Left). But these loci are in a silent state. The cell replaces the working locus mat for a copy. In this case, a copy is made from that locus, which is in the opposite allelic state. The gene is responsible for this process. BUT. This gene is only active in the haploid state. It codes for endonucleases that cut DNA at the mat locus. Exonucleases then remove the mat region and a copy of HMR or HML is replaced in its place.

Application

Some types of yeast have long been used by humans in the preparation of bread, beer, wine, kvass, etc. In combination with distillation, fermentation processes underlie the production of strong alcoholic beverages. The beneficial physiological properties of yeasts allow them to be used in biotechnology. Currently, they are used in the production of xylitol, enzymes, food additives, and for cleaning oil pollution.

Yeasts are also widely used in science as model organisms for genetic research and in molecular biology. Baker's yeast was the first eukaryote to have a fully sequenced genomic DNA. An important area of ​​research is the study of prions in yeast.

Traditional processes

bakery

Main article: bakery

Granular dry active yeast - a commercial product for bakery

The preparation of baked yeast bread is one of the oldest technologies. This process mainly uses Saccharomyces cerevisiae. They carry out alcoholic fermentation with the formation of many secondary metabolites, which determine the taste and aromatic qualities of bread. Alcohol evaporates during baking. In addition, bubbles of carbon dioxide form in the dough, causing it to “rise” and after baking, giving the bread a spongy texture and softness. A similar effect is caused by adding soda and acid (usually citric acid) to the dough, but in this case flavor compounds are not formed.

Flour is usually poor in fermentable sugars, so eggs or sugar are added to the dough. For getting more flavoring compounds, the dough is pierced or stirred, releasing carbon dioxide, and then left to "rise" again. However, there is a risk that the yeast does not have enough fermentable substrate.

Winemaking

Grapes with a layer of yeast on them.

Yeast is naturally present on the surface of grape fruits, often they are visible as a light coating on berries, formed mainly Hanseniaspora uvarum. Although "wild" epiphytic yeasts can produce unpredictable fermentation results, they usually do not compete with wine barrel-dwelling fermenters.

Harvested grapes are crushed to obtain juice (must, grape must) with 10-25% sugar. To obtain white wines, a mixture of seeds and peel (pulp) is separated from it, it remains in the must for red wines. The sugars are then converted to ethanol by fermentation. Secondary metabolites of yeast, as well as compounds obtained from them during the maturation of wine, determine its aroma and taste. To obtain a number of wines (for example, champagne), already fermented wine is fermented a second time.

The cessation of fermentation is associated either with the depletion of sugar reserves (dry wine), or with the achievement of the threshold of ethanol toxicity for yeast. Sherry yeast, unlike ordinary yeast (which dies when the alcohol concentration in solution reaches 12%), is more stable. Initially, sherry yeast was known only in the south of Spain (in Andalusia), where, thanks to its properties, strong wine - sherry (up to 24% with long aging) was obtained. Over time, sherry yeast was also found in Armenia, Georgia, Crimea, etc. Sherry yeast is also used in the production of some strong beers.

Brewing and kvass

barley malt

In brewing, grain (most often barley) is used as a raw material, containing a lot of starch, but little sugar fermentable by yeast. Therefore, starch is hydrolyzed before fermentation. For this, amylases are used, which are formed by the grain itself during germination. Germinated barley is called malt. The malt is ground, mixed with water, and boiled to produce a must, which is subsequently fermented by yeast. There are bottom-fermenting and top-fermenting brewer's yeasts (this classification was introduced by the Dane Christian Hansen).

Top-fermenting yeast (eg. Saccharomyces cerevisiae) form a "cap" on the surface of the must, prefer temperatures of 14-25°C (which is why top fermentation is also called warm) and tolerate higher alcohol concentrations. Bottom (cold) fermentation yeast ( Saccharomyces uvarum, Saccharomyces carlsbergensis) have an optimum development at 6-10°C and settle to the bottom of the fermenter.

The use of yeast in modern biotechnology

Industrial production of alcohol

Alcoholic fermentation is a process leading to the formation of ethanol (CH 3 CH 2 OH) from aqueous solutions of carbohydrates (sugars), under the action of some types of yeast (see fermentation) as a type of metabolism.

In biotechnology, sugar cane, feed corn and other cheap sources of carbohydrates are used to produce alcohol. To obtain fermentable mono- and oligosaccharides, they are destroyed by sulfuric acid or fungal amylases. Then fermentation and distillation of alcohol is carried out to a standard concentration of about 96% vol. . Yeast of the genus Saccharomyces were genetically modified to ferment xylose, one of the main monomers of hemicellulose, which makes it possible to increase the yield of ethanol when using vegetable raw materials containing, along with cellulose, significant amounts of hemicellulose. All this can reduce the price and improve its position in the competition with hydrocarbon fuels.

Nutritional and feed yeast

However, in the 1990s, due to the emerging hygienic and environmental problems in the production and use of microbial protein, as well as the economic crisis, production dropped sharply. The accumulated data testified to the manifestation of a number of negative effects of the use of paprin in fattening poultry and animals. For environmental and hygienic reasons, interest in this industry has also decreased worldwide.

Nevertheless, various yeast extracts are now produced and sold in the West: vegemite, marmite, bovril, tsenovis. There are similar productions in Russia, but their volumes are small. To obtain extracts, either yeast autolysates are used (the cells are destroyed and the protein becomes available due to the enzymes of the cells themselves), or their hydrolysates (destruction by special substances). They are used as food additives and to add flavor to dishes; in addition, there are cosmetic products based on yeast extracts.

Deactivated (killed by heat treatment) but not destroyed nutritional yeast is also sold, especially popular with vegans due to its high content of protein and vitamins (especially group B), as well as low amounts of fat. Some of them are enriched with vitamin B 12 of bacterial origin.

Theodor Schwan (1810-1882) named the yeast cells Zuckerpilz, Sugar Mushrooms, and this name further developed into Saccharomyces, the genus to which all yeasts belong.

Yeasts belong to the kingdom of fungi, are divided into two large types: basidomycetes, bud-forming yeasts, so named because they divide to form buds; and ascomycetes having a rod-shaped form and dividing by elongation of one of the ends.

Most yeasts use a bud-forming type of division. Although simple growth on a culture medium of cells of the species saccharomyces cerevisiae, like most other yeast species, produces a limited number of buds, about 20. However, only half of the cells divide in culture, and very few produce up to 20 buds. Poisoning, mutations, temperature and other factors affect the viability of yeast. Toward the end of the fermentation, a lot of the yeast clumps together, a phenomenon known as flocculation. The process of flocculation is not completely understood, but it is known to be caused by divalent ions such as magnesium, calcium, and manganese.

Biology

Yeast - living organisms formed by a single cell. Each cell, spherical or egg-shaped, is a mushroom, not exceeding 6-8 thousandths of a millimeter in size.

Yeast, like any other living organism, lives thanks to the presence of oxygen (aerobiosis). But they have the ability to adapt to an oxygen-deprived environment (anaerobiosis).

To provide themselves with energy, they can use different carbohydrate substrates, mainly sugars:

• glucose is the most preferred food for Saccharomyces cerevisiae
• sucrose - immediately converted to glucose and fructose by yeast enzymes
• maltose is the main endogenous substrate of French bread fermentation
• many other sugars

In his interesting scientific work, Vern J. Elliot showed how yeast uses different types of sugars. If you look at the graph, you can see the growth rate of yeast over time when fed with different sugars.

Since 250 types of yeast were studied in the experiment, different types of yeast showed similar results: sucrose led to the fastest growth. It can be assumed that your yeast will give a similar result.

What does it mean? If you use less yeast and more cane sugar (sucrose), you can get a long-term release of CO 2 . On the other hand, the amount and duration of CO 2 release depends more on the type of yeast than on the type of sugar. There are specific mutated yeast species. Also, the lifespan of a yeast culture before it dies out due to poisoning depends more on the amount of alcohol produced than on the type of sugar. Acidity plays a less significant role than is commonly thought. In general, it is most reasonable to use sucrose, although this is not necessary.

Depending on the environmental conditions, yeast starts two types of metabolism: aerobic, anaerobic.

Aerobic state

In the presence of oxygen, yeast produces carbon dioxide, water and a huge amount of energy from sugar and oxygen. This metabolic process is called respiration. Under these conditions, glucose oxidation occurs completely (Krebs cycle):

Glucose + Oxygen -> Carbon Dioxide + Water + Energy.

All the energy contained in glucose is released. This energy is necessary for yeast to live. They are also able to synthesize organic matter for growth and reproduction. This is if they find the necessary nutrients in the environment, in particular nitrogen.

Anaerobic state

Without oxygen, yeast can also use sugar for energy in the quantities necessary for life. This metabolic process is called fermentation (glycolysis). Sugars are converted into carbon dioxide and alcohol. Glucose is not completely oxidized:

Glucose -> Carbon Dioxide + Alcohol + Energy
or
C 6 H 12 O 6 + Saccharomyces cerevisiae \u003d 2C 2 H 5 OH + 2CO 2!

The alcohol that is formed as a result of this transformation still contains a huge amount of energy. This is only a fraction of the energy contained in the glucose molecule, one-twentieth of the energy produced by breathing. This process provides a minimum of energy for life, but does not allow rapid division.

Description of yeast types

baker's yeast

Baker's yeast is the most readily available. You can probably buy them in the nearest supermarket. This is dried active yeast. Most of them are sold in small bags.

Pressed yeast

Also called confectionery. Pressed yeast consists of approximately 30% dry matter and 70% wet content. They spoil very quickly and should be stored in the freezer.

Pressed yeast has a lifespan of approximately two weeks from production and unpacking if stored at 23°C. At a temperature of 0-5°C, compressed yeast loses approximately 10% of its gas generating capacity every 4 weeks. At 7°C they lose 4% of activity per week. At a temperature of 35 ° C, half of the activity is lost in 3-4 days. They can be stored for two months at -1 °C, then CO 2 production can be obtained from yeast stored for two months.

For pressed yeast, use warm water.

active dry yeast

Active dry yeast is approximately 92% solids and 8% mixture. They are stored in a cool dry place at a temperature not exceeding 25 °C. The life time of active dry yeast at room temperature is about 2 years from the date of production. Opened yeast should preferably be stored in an airtight container in the refrigerator where it will remain active for about 4 months.

Active dry yeast should be dissolved in four volumes of warm water, 10 minutes after dissolution, they must be mixed. The water should not be hot, not warmer than 35 °C.

Instant Active Dry Yeast

Instant active yeast consists of 96% solids and 4% mixture. I would recommend storing them in a cool, dry place below 25°C.

The life time of instant yeast at room temperature is about 2 years from the date of manufacture. Opened instant yeast can be stored in an airtight container in the refrigerator where it will remain active for up to 4 months. To dissolve this yeast, they must be poured with five volumes of warm water, wait 10 minutes and mix.

It doesn't matter how you store your yeast in the refrigerator, but if you freeze it, you extend its shelf life. The only argument against freezing is temperature fluctuations in the refrigerator when opening and closing doors and defrost cycles. Temperature fluctuations destroy yeast cells.

After defrosting, the yeast should be allowed time to warm to room temperature before dissolving it in tepid water. Otherwise, the temperature shock can destroy the yeast cells.

Brewer's yeast

This is a specific type of yeast used in brewing. There are many types of yeast that are used in the preparation of different types of beer with very different flavor profiles. This is not "... pure mountain water ...", or "... favorite hands of a beer master ...". This is what the yeast does. Using different types of yeast, different tastes of beer are obtained. Saccharomyces cerevisiae, and Saccharomyces uvarum are dark and light beers, respectively.

Primary yeast cultures produce beer all over the world. Ale yeast is a special strain of S. cerevisiae that is better adapted to higher alcohol content. Most of these live cultures are in liquid form and do not require a dissolution process like dry yeast.

Wine or champagne yeast

They can ferment over a higher temperature range and are more tolerant of high alcohol levels in solution, which are toxic to most other yeasts.

This yeast settles to the bottom, unlike bread and brewer's yeast, which accumulate near the surface in a sticky mass. Champagne yeast usually does not foam on the surface. That is, when used in aquarium yeast generators, there are much fewer problems with yeast getting into the tubes.

What to Consider

The nature of yeast is such that it can withstand drying, crushing, pressing. The basic rule when working with fermentation is cleanliness. Yeast may not survive with other bacteria and should be kept as clean and sterile as possible.

Sterility

Rinse yeast generators thoroughly with hot water, do not use soap. Keep spare bottles tightly closed. Boil the water you want to use, sterilize the lids. Scald your two liter bottle with a funnel. While the water is hot, add sugar and close tightly with a sterile lid. Shake it. until the sugar dissolves. This will sterilize the bottle, water and sugar, do not open the bottle until the water has cooled to room temperature and you are ready to add the yeast.

dry yeast activation

If you plan to use dry yeast, you must activate the culture first. As previously discussed, yeasts need an aerobic environment to start, after which they readily switch to anaerobic conditions. Many skip this step and pour the mixture directly into the bottle. Many yeasts die due to the fact that they did not have time to complete their aerobic phase of life before changing it to an anaerobic one and due to the destruction of cell walls.

(yeast mushrooms)

- mushroom type

✎ What are yeast fungi?

Mushroom yeast (yeast mushrooms) is a non-taxonomic position of unicellular fungi from the group of imperfect fungi that have lost their classical (mycelial) structure due to the transition of their habitat to liquid or semi-liquid, rich in organic substances, substrates.
They unite approximately 1,500 species, which belong mainly to the class of ascomycetes and less often to basidiomycetes.

✎ Features of Mushroom Yeast

Mushroom yeast(not to be confused with thermophilic yeast) is such a prefabricated type of fungus that does not have a typical mycelium and exists in the form of divided budding or dividing cells. They exist throughout their life, or most of it, in the form of completely separate single cells. And, due to their unicellular structure, they have a much higher metabolic rate than ordinary mycelial species, due to the relatively larger surface area of ​​\u200b\u200btheir cells. Therefore, they grow and multiply always at an incredible rate.
Historically, such species have always been studied separately from others, due to the fact that the methods of their identification were more similar to bacteriological than to mycological. Well, according to the ability of sexual reproduction, these species are divided into subgroups located in different classes of fungi:

in the class Ascomycetes and Basidiales these are:

• tubular,
• lamellar,

in the class of deuteromycetes, in which the sexual cycle is not found, these are:

• pycnidal,
• melanconial,
• hyphomycetes.

✎ How are yeast fungi arranged?

The body of yeast fungi is very different from all the others due to the fact that it consists of only one cell and therefore does not form mycelium (mycelium). And their reproduction is a very interesting phenomenon. A small protrusion appears on the cell, which grows, forming the so-called kidney and gradually turns into an independent cell, which is able to separate and, ultimately, separates. This process is called budding.

✎ The role of yeast in nature and everyday life

Mankind has long used yeast mushrooms in bread baking and for the preparation of alcoholic beverages. In many languages ​​of the world, their name is associated with the fermentation process that they cause. Their Russian name comes from the word "shiver" and it accurately characterizes the state of the fermented wort or rising dough.
As already noted, about 1,500 species of imperfect fungi are known in nature, and we encounter many of them in everyday life. They are divided into:

• bakery,
• beer,
• wine.

For example, in baking, baker's yeast is used to make the dough rise and baking become "fluffy", while in winemaking and brewing, wine and brewer's yeast are used, respectively, for the fermentation process. Thus, an indisputable fact becomes obvious: yeast mushrooms were, are and will be constant companions and friends of man.

Yeast is a fungus whose cells are microscopic in size (about 5 microns) and bud, forming a kind of colony. Yeast usually does not form mycelium. The shape of yeast cells is spherical.

In nature, yeast lives on the surfaces of fruits, flowers, they are present in the surface layers of the soil, the digestive tract of some insects, etc.

Yeasts are not a single taxonomic group of fungi. Yeasts include individual representatives of two divisions of fungi - ascomycetes and basidiomycetes. Yeast can be considered a special life form that has arisen in different types of fungi. There are more than 1000 types of yeast in total.

Yeasts are considered secondary unicellular organisms. This means that their ancestors were multicellular forms of fungi, which later became single-celled. Currently, there are peculiar "transitional" forms. So some fungi at some stages of the life cycle have signs of yeast, and at others they form a multicellular mycelium.

Budding is essentially the vegetative reproduction of yeast, i.e., the formation of spores. A bulge forms on the parent cell, which gradually grows, turns into an adult cell and can be separated from the parent cell. When the cells bud, the yeast looks like branching chains.

In addition to vegetative reproduction, yeast has a sexual process, when two yeast cells merge, a diploid cell is formed, which subsequently divides, forming haploid spores.

Yeast-ascomycetes differ from yeast-basidiomycetes in their life cycle, synthesized substances, features of budding, etc.

Nutrition of yeast cells is mainly carried out by the fermentation of low molecular weight carbohydrates (sugars). Sugars are fermented by yeast to alcohol and carbon dioxide. In this case, energy is released that goes to the vital processes of yeast.

Fermentation is anaerobic respiration, that is, obtaining energy without oxygen. However, yeast can also breathe oxygen. Thus, their anaerobicity is facultative (optional). When yeast breathes oxygen, it releases carbon dioxide but does not ferment sugars to alcohols. However, if there are a lot of sugars, then the yeast will ferment it even in the presence of oxygen.

The yeast fermentation process is used by man. In baking, the carbon dioxide formed by yeast makes the dough more porous. The formation of alcohol by yeast is used in winemaking and brewing. Also, in the course of their metabolism, yeast forms other substances (various oils, alcohols, etc.), which give the finished food products a special taste.

Man has learned to use yeast since ancient times. Their use in ancient Egypt is noted. However, the fact that these microscopic fungi provide the rise of the test or the formation of alcohol, people then did not know. Yeast was first observed by A. Leeuwenhoek (in 1680), then they were described by Charles Cagnard de La Tour (1838). However, only in 1857, L. Pasteur finally proved that organisms provide fermentation in raw foods, and this is not just a chemical reaction.

Certain types of yeast can cause disease.

Human life is impossible without microorganisms, which are of great benefit. They live nearby, although they are not visible to the naked eye. This article looks at how yeast and other microorganisms reproduce.

Yeast: definition

Yeasts are microorganisms that belong to the fungus family. Their distribution is observed everywhere, they are present even in the air. Yeasts are able to feed. They can produce by-products, reproduce, and also generate energy. Nutrition is sugar, if they are not present, the yeast begins to break down starches. In the process of vital activity of organisms, a by-product is formed - carbon dioxide, which is released in the form of tiny bubbles. They, in turn, are caught by the gluten network, which is a protein substance that flour is rich in.

The shape of yeast cells is oval, ovoid, elliptical, less common cylindrical or rod-shaped, lemon-shaped and pear-shaped. The mass, size, shape of the cells are different. Their parameters are influenced by the habitat and the age of the cells.

Each microorganism has its own way of reproduction. Yeast has several. How do yeast reproduce? This type of unicellular organisms is characterized by such methods as budding and sporulation. But sometimes reproduction occurs as a result of cell division into two parts, that is, in half. To the question of which method of reproduction is characteristic of yeast, the answer is simple - budding. In general, the mode of reproduction is influenced by the conditions of life and the types of unicellular organism.

Reproduction of yeast by budding

How do yeast reproduce? In short - three, but the main one is budding. This method of reproduction is called vegetative and consists in separating the daughter cell from the mother cell. In this case, the yeast is said to reproduce by budding. How does this happen? The mother cell forms a tubercle on its surface, which is called the kidney. Its size increases, and finally it grows. A constriction (channel) separates the kidney and the cell that produces it. It gradually begins to narrow, as a result of which the daughter cell separates, into which the cellular elements from the mother cell pass, but not completely, but part of them.

This method of reproduction is typical for lemon yeast. For its implementation, favorable conditions are needed, under which there will be enough nutrition for the cells, good air access is provided. For the process of yeast propagation, the temperature of 25 ° C is considered optimal. At what rate does yeast multiply? If conditions are favorable, the process can take approximately two hours.

It often happens that the detachment of young cells did not occur, they remained together with the mother. IN this case and the process of budding takes place on them. The result of this division is the formation of a whole cluster of cells connected to each other.

Reproduction of yeast by sporulation

Another way yeast reproduces is by sporulation. Spore formation occurs inside the cell. Their number can be different: from 2 to 12 pieces. How does yeast reproduce? The process can occur in two ways:

• Sexual - sporulation is the result of the fusion of 2 cells.
• Asexual - spores are formed as a result of crushing the cell nucleus into small particles, each of which is surrounded by the substance of the protoplasm and covered by a shell.

yeast spores

In most cases, the spores are round or oval in shape. They are more resistant to external factors than vegetative cells. The formation of spores is facilitated by the unfavorable conditions in which the cell lives. For example, there was a sharp transition in nutrition: from good to bad. Since the formation of spores occurs asexually, they also have one set of chromosomes. But there are yeasts (asporogenic) that do not form spores at all.

How do yeast reproduce? This process can occur both by budding and by sporulation. Such yeast are called "true". Some types of yeast do not have the ability to form spores. The process of their reproduction occurs in only one way - by budding. Such yeast was given another name - "false".

How are yeast classified?

Yeast belongs to the class of ascomycetes according to Kudryavtsev's classification. It consists of three families. Yeast cells of families differ in shape, their reproduction occurs in different ways.

• Saccharomyces family. In such yeast, the shape of the cells can be either oval or ovoid. They reproduce vegetatively by budding. Developing in an unfavorable environment, yeast reproduces sexually with the help of ascospores. The biochemical sign of such yeast is the fermentation of sugar. In industry, yeast is used, which is called "cultural". They need an acidic environment for their development. Their growth and reproduction will be active under conditions called aerobic. Yeasts are very sensitive to substances dissolved in their habitat, which have a high concentration. In this regard, fermentation is distinguished as top and bottom. So, for example, a high concentration of sugar causes the cessation of the vital activity of yeast.
• Schizosaccharomycetes are a family of yeasts whose cells are rod-shaped. Reproduction occurs by division, and under conditions that are unfavorable for cell development, spore formation occurs. Such yeast causes fermentation, which is called alcohol. They are used in the industry of regions with a warm climate, they are used to produce beer and Kuban rum.
• Sugar family. In such yeast, the shape of the cells is lemon-shaped, reproduction is by budding. These yeasts, like the representatives of the previous family, cause fermentation - alcohol. In the wine industry, they are considered pests due to the formation of products due to which the wine acquires an unpleasant smell.

What is the importance of yeast?

The practical use of yeast is an integral part of the production of bakery products, alcohol. They are used in brewing, as well as for making kvass. The living conditions of yeasts have a strong influence on them, as a result of which some of their varieties have acquired characteristics called isolated. Such yeasts are called "races".

For the manufacture of products, each industry uses its own race. For example, for the production of alcoholic beverages, yeast is needed with a high ability to actively ferment sugar at high temperatures (up to 30 ° C). Beer is prepared using a slow-fermenting race. Baking bread and buns is carried out using a race that multiplies rapidly, accumulates energy and lift. This is why flour products look fluffy.

However, there are yeasts that are harmful to beer production. Developing in the product, they contribute to an unpleasant taste and smell. Such yeasts and yeast-like organisms are not able to form spores. Moreover, their presence spoils the raw materials and the finished product.

mold mushrooms

Their appearance on planet Earth belongs to the distant past: 200 million years ago. Mold has unlimited possibilities. It can take a life from a person, or it can save a person in difficult times. The mold looks very beautiful, but despite this, it is disgusting. This type of organism tends to form a branching mycelium, the size of which is microscopic. Mushrooms, as well as similar organisms, are widely distributed in nature.

They develop in any environment, forming large colonies, and settle on a feeding environment. Especially favorable for the development of fungi is high temperature, as well as high humidity. Notably, mold growth is almost impossible to stop if food is present. Mushrooms are unpretentious to the habitat and food.

Mold mushrooms: structure

This type of microorganisms has many varieties, but they are all characterized by typical features. The basis of the vegetative body is mycelium or mycelium - thin threads (hyphae) that can strongly branch. The location of the hyphae is the surface or the inner part of the substrate in the area of ​​the fungus settlement. Molds, forming mycelium, occupy large areas. The mycelium of lower fungi has a non-cellular structure, while in molds it is divided into cells.

How do fungi reproduce?

Fungi and yeast reproduce in different ways. For yeast, budding and sporulation are the main ones, and for fungi, the easiest way is with the help of parts of the mycelium. The mycelium, once in a new area, begins to develop independently, forming a single organism, and the mycelium, immersed in the substrate, provides the mold with moisture, nutrition and substances of mineral origin. On the air part of the mycelium, located above the surface of the substrate, the formation of bodies occurs, due to which the mold fungus multiplies.

Under unfavorable conditions, the fungus can form a dormant stage called sclerotium. These are strong nodules, the surface of which is hard. They are formed by intertwined hyphae. Under favorable conditions, the sclerotium germinates, forming separate organs intended for reproduction.

There is another resting stage - chlamydospores. Their formation entails the collection of cytoplasm into lumps. This is how a new shell is formed. It is thick and colored. Such hyphae are like a chain. Molds, having a multicellular structure, are highly organized, complex organisms.

bacteria

These are microorganisms that consist of a single cell. Their size reaches 10 microns. In shape, they are divided into rod-shaped, spherical, convoluted. The parameters of bacteria change when the external factors of their habitat change.

How do bacteria, molds, yeast reproduce? Mushrooms reproduce by mycelium, yeast by buds and spores, and bacteria by simple transverse fission asexually, although they can reproduce in other ways. Bacteria rarely reproduce by budding, but sexually it occurs at a primitive level.

Bacterial cells consist of capsules, cytoplasmic membranes, cell walls, cytoplasm, in which ribosomes, mesosomes, inclusions, and nucleoid are located. Some bacterial cells are characterized by the presence of flagella and the formation of spores. Cells differ in the way they feed. According to this feature, bacteria are autotrophs, heterotrophs. Their breathing patterns also differ. In this regard, bacteria are distinguished as aerobes and anaerobes.

How do yeast reproduce? Single-celled organisms - yeast - reproduce in many ways, including cell division. An interesting fact: the division of one cell can occur 20-25 times. This means that a single cell is able to create new ones in an amount equal to the number of its division. One generation of cells does not live long, approximately one to seven hours. The duration of its existence is influenced by the environment, as well as the age of the mother cell.