This article will discuss interesting microorganisms such as yeast. How do they breed? We have to answer this question. You will learn about the features of the breeding yeast.
Reproduction is the reproduction of a new cell, which is identical to the mother. Its consequence in the main part of unicellular organisms is an increase in population. This process in microorganisms is mainly due to their "interconnection" 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 are powerful reducing agents that are released on Wednesday when growth retardation of the number of yeast cells occurs. They act on the cell membrane (on disulfide protein bonds). Due to this, the membrane becomes permeable to the ingestion of nutrients from the medium. This ensures the biosynthesis of enzymes, including constitutive ones.
Methods of Propagation of Yeast
We proceed directly to our topic. "Yeast reproduce 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 sexually and vegetatively. The form of the latter is determined by belonging to a biologically independent group (i.e., a family) by division, budding, and also by budding, ending with division. At present, four types of vegetative propagation of yeast have been described.
The first type of vegetative propagation
It is noted, for example, in the genus Saccharomyces (in the family Saccharomycetaceae). In this case, the material of which the shells of the mother cells are composed does not directly transfer to the shells of new daughter cells. In the initial stages of growth, they get it as a result of the fact that it is synthesized and gradually accumulates at the base of the very forming kidney. Moreover, scars are located in areas of greatest curvature of the cell membrane. Often they adjoin each other, are arranged in a spiral or circle.
However, this process is not characteristic of all microorganisms belonging to the group of unicellular fungi called "yeast". How do their other species breed? We continue our story.
Second type
The next type of vegetative propagation is observed in yeast of the genera Hanseniaspora and Saccharo-mycodes (family Saccharoinycoaaceae). Its peculiarity is polar budding, while a multiple scar forms. In this case, the kidney (what yeast reproduces) is formed as a result of protrusion of the renal scar, which remained from the previous budding, as well as stretching of the septum between the cells.
Third type
It is observed in the Schizosaccharomyceta-seae yeast family (for example, the genus Schizosaccharomyces). Characteristic of this type is that the growth of cell walls is biopolar. The new material from which the cells are formed is deposited in the form of an annular outgrowth from the center of the cell to its ends at the site of its division.
Vegetative propagation: the fourth type
It is characteristic of Endomyces magnusii, their cylindrical cells. In this case, during division, structural changes are noted throughout its shell. If there are many divisions, the shell consists of several plates that are located in parallel and are enclosed in one on the other.
Mitosis
A certain part of the structural formations of the nucleus and cytoplasm passes into the daughter cell from the mother cell during the vegetative propagation. In this case, before each cell division , the chromosomes are reproduced once and all at once. This ensures their uniform distribution between the daughter and mother cells. With this type of nuclear division, called mitosis, a strictly constant number of chromosomes is observed in generations of cells.
Maternal cell budding
We found out that the kidney is what the yeast reproduces in the vegetative way. If we consider this process in time, it can be noted that in about one hour, under optimal conditions, a daughter cell is completely formed. But she alone cannot repeat the process of budding endlessly. The mother cell during life has an average of 25-30 buds (birth scars). The restraining factor of this process is a change in the structure of the cell membrane, which is associated with the formation of scars. It is they that lead to a decrease in its useful surface, which reduces the metabolism, as well as the content of protein, DNA, RNA in the cells and leads, in the end, to death.
One more method can be distinguished, noting the question of how the yeast reproduces. Disputes carry out this process. This method is called sexual. Let us dwell on it in more detail.
Sexual reproduction method
Yeast, the reproduction of which occurs both sexually and vegetatively, is of great interest from this point of view. Many scientists have studied the behavior of these microorganisms. They found that the sexual method is associated with the germination of spores that are found in askeys or bags (called ascospores) into vegetative cells. How does yeast reproduce by spores? Let's figure it out.
This method is accompanied by nuclear fission using meiosis. If during the cultivation of yeast there is a sharp transition from a full-fledged environment to poor in nutrients, then in the presence of sufficient moisture, as well as a significant accumulation of spare substances in the cell and access to oxygen, spore formation occurs. The ascospores resulting from it are resistant to adverse environmental conditions (drying, high temperature), however, they are less thermostable than bacterial spores. Ascospores die at a temperature of about 60 ° C, while bacterial spores can withstand higher temperatures - boiling water and even higher.
Ascospores are usually formed as a result of sexual fusion of 2 yeast cells and subsequent fission of the fertilized nucleus. There 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.
Yeast life cycle
In yeast, the life cycle is associated with the alternation of spore formation and vegetative propagation with different durations of the diploid and haploid stages. Saccharomycetes yeast, in which there is a change in haplo- and diplo-phases, are divided into two groups: homotallic and heterotallic.
Heterotallic strains
Heterotallic strains have stable haploid and diploid phases. In this case, diploid cells are able to vegetatively multiply indefinitely, and under adverse conditions go on to spore formation. As a result of this, asks with haploid spores are formed, each of which belongs to one of 2 types of mating. In this case, copulation occurs only when 2 ascospores or cells from various haploid strains meet, as a result of which zygotes are formed, and diplophase is restored.
Homotallic strains
Homotallic strains from heterotallic ones differ in that they have only stable diplophase. Haploid spores isolated from asca form a diploid structure. In other words, self-diploidization (fusion of haploid cells) occurs in the offspring of one spore due to the fact that spores can combine in any combination of maternal or sister haploid cells with their kidney.
And homotallic yeast has mating types. A.F. Rusnak studied the yeast species Sacch. vini, which are used in winemaking. She noted the existence of a large set of races. After analyzing this, the researcher concluded that their nature is predominantly homotallic.
Nevertheless, some yeast in the haploid state can reproduce vegetatively for a long time. Examples include Chizosaccharomyces and Zygosaccharomyces. Haploid cells merge before spore formation, a diploid zygote is formed. Then, with the help of meiosis, it is divided and gives rise to four or eight haploid spores. They germinate and after some time begin to multiply in the haploid state asexually.
Positive spore formation
Studying microorganisms such as yeast (how they reproduce), scientists noticed that the metabolism, as well as the general vital activity of microorganisms, are slowed by spore formation. This condition ensures their survival in unfavorable vegetative conditions for reproduction. Therefore, spore formation, which combines the process of conservation of species and reproduction, should be considered as a positive stage in the development of yeast organisms.
The results of the study B. Pazoni
B. Pazoni investigated how yeast multiplies. He obtained interesting results on the effect on the productivity and vital activity of these microorganisms at the stage of sexual reproduction. Cultures of wine yeast that underwent sporulation with further germination of spores and the process of diploidization are superior in speed to fermentation of wort cultures that did not pass these stages. In tests carried out in semi-production conditions, a decrease in the fermentation period was noted from 35 days to 21-31.
So, you met such interesting microorganisms as yeast. How do they breed, you now know. We hope you remember what features have two main ways. Yeast reproduces by spores and budding. Each of these methods is carried out under certain conditions, and each of them has its own characteristics.