In this article we will talk about such interesting microorganisms as yeast. How do they multiply? We have to answer this question. You will learn about the specific features of reproduction of yeast.
Reproduction is the reproduction of a new cell,which is identical with the mother. Its consequence in the main part of unicellular organisms is an increase in the population size. This process in microorganisms is due mainly to the "interconnection" of them with the surrounding nutrient medium. It should create favorable conditions for this, which regulate the action of certain enzymes.
Scientists have found that reducing enzymes -powerful reductants, which are released into the environment, when the growth of the number of yeast cells occurs. They act on the cell membrane (on disulfide protein bonds). Due to this, the shell becomes permeable for the intake of nutrients from the environment. This also ensures the biosynthesis of enzymes, including constitutive ones.
Methods of reproduction of yeast
Let us pass directly to our topic."Yeasts multiply by spores or not?" - the answer to this question is ambiguous. The fact is that the cells of these microorganisms, depending on the conditions of their cultivation, can reproduce in a sexual and vegetative way. The form of the latter is determined by belonging to some biologically independent group (that is, to the family) by division, by budding, and also by means of budding, which ends with division. Currently, four types of vegetative propagation of yeast are described.
The first type of vegetative reproduction
It is noted, for example, in the genus Saccharomyces (infamily Saccharomycetaceae). In this case, the material from which the mother cell membranes consist does not directly pass to the shells of new, daughter cells. In the initial stages of growth, they receive it as a result of the fact that it is synthesized and gradually accumulates at the base of the most forming kidney. In this case, the scars are in the areas of the greatest curvature of the cell membrane. Often they are adjacent to each other, arranged in a spiral or circle.
However, this process is not typical for all microorganisms belonging to the group of unicellular fungi called "yeast." How do other species multiply? Let's continue our story.
The second type
The next type of vegetative reproductionis noted in the yeast of the genera Hanseniaspora and Saccharo-mycodes (family Saccharoinycoaaceae). Its peculiarity is polar budding, while a multiple scar is formed. In this case, the kidney (what the yeast reproduces) is formed as a result of the protrusion of the renal scar that remains from the previous budding, as well as the stretching of the septum between the cells.
The third type
It is observed in the family of yeastSchizosaccharomyceta-seae (for example, the genus Schizosaccharomyces). A characteristic of this type is that the growth of cell membranes is bio-polar. The new material from which the cells are formed is deposited as a ring-shaped outgrowth from the center of the cell to its ends at the point of its division.
Vegetative reproduction: the fourth type
It is characteristic of Endomyces magnusii, theircylindrical cells. In this case, during the division, structural changes are noted on the whole of its shell. If there are many divisions, the sheath is composed of several plates that are parallel and on the rumen are enclosed one in the other.
Mitosis
In the daughter cell from the maternalA certain part of the structural formations of the nucleus and cytoplasm passes through vegetative propagation. Before each cell division, the chromosomes are reproduced once and all at the same time. This ensures their uniform distribution between the daughter and the mother cell. For a given type of nuclear fission, called mitosis, a strictly constant number of chromosomes is observed in cell generations.
Maternal cell nucleation
We found out that the kidney is what multipliesyeast in the vegetative mode. If we consider this process in time, then it can be noted that in about one hour under optimal conditions a daughter cell is completely formed. But she alone can not repeat the process of budding endlessly. The maternal cell during life has an average of 25-30 buds (generic scars). The deterrent of this process is a change in the structure of the cell membrane, which is associated with scar formation. They lead to a decrease in its useful surface, which reduces the metabolism, as well as the content of protein, DNA, RNA in cells and leads, in the end, to death.
One can distinguish another way, noting the question of how yeast reproduces. This process is disputed. This method is called sexual. Let us dwell on it in more detail.
Sexual mode of reproduction
Yeasts, the reproduction of which occurs assexual, and vegetative way, represent a great interest from this point of view. Many scientists have studied the behavior of these microorganisms. They found out that the sexual mode is associated with the sprouting of spores, which are in asces or bags (they are called ascospores) into vegetative cells. How do yeast reproduce by spores? Let's figure it out.
This method is accompanied by the fission of the nucleus withusing meiosis. If during the cultivation of yeast there is a sharp transition from a full medium to a poor nutrient, then if there is sufficient moisture, as well as significant accumulation of reserve substances in the cell and access to oxygen, sporulation occurs. Ascospores appearing as a result of it are resistant to unfavorable environmental conditions (drying, high temperature), but they are less thermostable than bacterial spores. Ascospores die at a temperature of about 60 ° C, while spores of bacteria can withstand higher temperatures - boiling water and even higher.
Ascospores are usually formed as a result of sexualfusion of 2 yeast cells and the subsequent division of the fertilized nucleus. They can be from one to four, and sometimes eight in one ask. If the conditions for vegetative development are favorable, the spores germinate on a fresh nutrient medium and then again become budding cells.
The life cycle of yeast
In yeast, the life cycle is associated with alternationspore formation and vegetative reproduction with different diploid and haploid stages. Yeast-saccharomycetes, in which there is a change in haplo and diplophase, are divided into two groups: homotallic and heterotallic.
Heterotallic strains
Heterotallic strains have a stablehaploid and diploid phases. At the same time, diploid cells can vegetatively reproduce indefinitely, and under adverse conditions, proceed to spore formation. As a result of this, an ascension with haploid spores is formed, each of which relates to one of the 2 types of mating. Copulation is performed only when two ascospores or cells from different haploid strains meet, as a result of which zygotes are formed, and diplase is restored.
Homotallic strains
Homotallic strains from heterotallicdiffer in that they have only a stable diplase. Isolated from asuka haploid spores form a diploid structure. In other words, in the offspring of one spore self-adioidization (fusion of haploid cells) occurs due to the fact that spores can be combined in any combination of maternal or sister haploid cells with their kidney.
And in homotallic yeasts there are typespairing. A.F. Rusnak studied the yeast of the Sacch species. vini, which are used in winemaking. She noted the existence of a large set of races. Analyzing this, the researcher concluded that their nature is predominantly homotallic.
However, some yeast in the haploidfor a long time able to reproduce vegetatively. Examples include Chizosaccharomyces and Zygosaccharomyces. Haploid cells merge before sporulation, a diploid zygote is formed. Then, with the help of meiosis, it divides and gives rise to four or eight haploid spores. They germinate and after a while start to multiply in the haploid state asexually.
Positive moments of sporulation
By studying microorganisms such as yeast (asthey multiply), scientists noticed that the metabolism, as well as the general activity of microorganisms, slowed down during sporulation. This condition ensures their survival in unfavorable for reproduction of vegetative conditions. Therefore sporulation, which combines the process of species conservation and reproduction, should be considered as a positive stage in the development of yeast organisms.
The results of the study of B. Pazogni
B. Pazogni investigated how yeast reproduce.He received interesting results on the effect on the productivity and vital activity of these microorganisms at the stage of sexual reproduction. The cultures of wine yeast that have been sporulated with further spore germination and diploidization process outperform the worts of the culture wort that did not pass these stages. In tests carried out under semi-production conditions, a reduction in the fermentation period from 35 days to 21-31 was noted.
So, you met such interestingmicroorganisms, like yeast. How do they multiply, you now know. We hope you remember what features have two main methods. Yeasts reproduce by spores and budding. Each of these methods is carried out under certain conditions, and each of them has its own peculiarities.
