Bacteria are characterized by division. The main types of bacterial division and factors limiting population growth
22. Bacterial nucleus. Types of bacterial cell division. division process.
Division types:
1. Equal area binary transverse fission, leading to the formation of two identical daughter cells. With this method of division, there is symmetry with respect to the longitudinal and transverse axes. With equal binary fission, the mother cell, dividing, gives rise to two daughter cells and itself, thus, disappears.
2. Unequal binary fission, or budding. When budding, a small outgrowth (bud) is formed at one of the poles of the mother cell, which increases in the process of growth. Gradually, the kidney reaches the size of the mother cell, after which it separates from the latter. The cell wall of the kidney is completely re-synthesized. In the process of budding, symmetry is observed with respect to only the longitudinal axis. When budding, the mother cell gives rise to a daughter cell, and in most cases morphological and physiological differences can be found between them: there is an old mother cell and a new daughter cell.
3. Reproduction by multiple division, characteristic of one group of unicellular cyanobacteria, as a result, small cells are formed, called baeocytes (Greek. bae- small, cyto- cell), the number of which in different species ranges from 4 to 1000. The release of baeocytes occurs by breaking the maternal cell wall. Multiple fission is based on the principle of equal binary fission. The difference lies in the fact that in this case, after binary fission, the resulting daughter cells do not grow, but they again undergo division.
23. Bacterial nucleus. Forms of exchange of genetic information in bacteria. Variation in bacteria.
Forms of exchange of genetic material in bacteria:
1. horizontal
* transformation - the transfer of genetic material, which consists in the fact that the recipient bacterium captures (absorbs) fragments of foreign DNA from the external environment.
A) Induced (artificially obtained) transformation occurs when purified DNA is added to the bacterial culture, obtained from the cultures of those bacteria, the genetic characteristics of which are sought to be transferred to the culture under study.
B) Spontaneous transformation occurs in natural conditions and manifests itself in the emergence of recombinants when genetically different cells are mixed. It occurs due to DNA released by cells into the environment due to their lysis or as a result of active DNA release by viable donor cells.
* sexduction
* transfection - a variant of transformation of bacterial cells lacking a cell wall, carried out by a viral (phage) nucleic acid. With the help of transfection, it is possible to cause a viral infection in such bacteria (without a cell wall). Transfection can also be carried out with other (non-bacterial) cells if foreign DNA is introduced into them, capable of recombining with the DNA of these cells, or reproducing virions, or replicating itself.
* conjugation - the process of exchange of genetic material (chromosomal and plasmid), carried out by direct contact between the cells of the donor and the recipient. This process is controlled only by conjugative plasmids that have a set of genes called the tra-operon (tra - from English, transfer - transfer).
This operon controls the synthesis of the transfer apparatus, conjugative replication, and the surface exclusion phenomenon. The transfer apparatus is a special donor villi, with the help of which contact is established between the conjugating cells. Donor villi are long (1-20 μm) thin tubular structures of protein nature with an inner diameter of about 3 nm.
establishing contact between donor and recipient
pulling a DNA strand from a donor to a recipient
completion of the transferred DNA strand with a complementary strand in the recipient cell
recombination between the transferred chromosome (its fragments) and the chromosome of the recipient cell
merozygote reproduction
the formation of cells bearing the characteristics of the donor and recipient
Conjugative replication of a transferred strand of chromosomal or plasmid DNA is also carried out under the control of plasmid genes. The classic example of a conjugative plasmid is the sex factor, or F-plasmid (from the English . fertility- fertility). The F-plasmid can be both in an autonomous state and integrated into the cell chromosome. Being in an autonomous state, it controls only its own transfer, in which a P~ cell (a cell lacking an F plasmid) turns into a P+ cell (a cell containing an F plasmid). The F-plasmid can integrate into certain regions of the bacterial chromosome, in which case it will control the conjugative transfer of the cell's chromosome.
Thus, conjugation begins with the establishment of contact between the donor and the recipient using the donor villus. The latter merges with the receptor of the cell membrane of the recipient cell. Often such contact is established not only between two cells, but between many cells, forming mating aggregates. It is assumed that the DNA strand is pulled through the canal of the donor villus during conjugation. Since the donor bridge is fragile, the conjugation process can be interrupted at any time. Therefore, during conjugation, either a part of a chromosome or, more rarely, a complete chromosome can be transferred. With the help of F-plasmids, the frequency of gene transfer between bacteria increases significantly.
* transduction - the transfer of genetic material from a donor cell to a recipient cell with the help of bacteriophages. Distinguish between nonspecific and specific transduction.
A) Non-specific transduction - random transfer of DNA fragments from one bacterial cell to another.
B) Specific transduction is carried out only by moderate phages capable of being included in strictly defined regions of the chromosome of a bacterial cell and carrying certain genes.
Molecular mechanisms of bacterial variability
Bacteria, due to the relative simplicity of their organization and short lifespan, undergo variability faster than many other organisms. Their variability is based on mutations and genetic recombinations, especially those occurring with the participation of transposable elements.
* Mutations are changes in the genotype that are stably inherited. Mutations can be spontaneous or induced.
a) Spontaneous mutations occur without any special effects, they occur as a result of errors in replication and repair. The average frequency of spontaneous mutations is about 1106 (one mutant per 1 million cells).
b) Induced mutations occur with a much higher frequency, they arise as a result of exposure to various mutagens - physical and chemical factors that damage DNA: ionizing radiation, UV irradiation, various analogs of DNA bases, alkylating compounds, acridines, antibiotics
c) Point mutations can be caused by: base substitution, deletion (deletion) of the base, the appearance of an additional base (insert). Point mutations can have three consequences:
1) replacement of one codon by another, and therefore, one amino acid by another;
2) a shift in the reading frame, which will lead to a change in a whole series of sequences of amino acid residues;
3) the emergence of a "meaningless" codon, which will lead to the termination of translation at a given point
protein synthesis can be completely blocked. An altered protein will be synthesized
All this will lead either to the loss of some phenotypic trait in the mutant, or, more rarely, to the appearance of a new trait in it.
Violation of the genome can be a consequence of:
*extended deletions
*inversions (rotation of a chromosome segment by 180°)
* translocation (moving a section of a chromosome from one position to another)
All this will also lead to a change and disruption of various functions of the cell (organism).
A large role in the variability of bacteria and other organisms belongs to the so-called transposable genetic elements, that is, genetic structures that can move intact within a given genome or move from one genome to another, for example, from a plasmid genome to a bacterial one and vice versa. There are three classes of transposable elements: IS elements, transposons, and episomes.
# Insertion sequences (from English, insertion sequence), usually have sizes not exceeding 2 thousand base pairs, or 2 kb. (a kilobase is a thousand base pairs). IS elements carry only one gene, which encodes the protein transposase, with the help of which IS elements are inserted into different regions of the chromosome. They are designated by numbers: IS1, IS2, IS3, etc.
#Transposons are larger segments of DNA flanked by inverted IS elements. They are able to integrate into different parts of the chromosome or move from one genome to another, i.e., they behave like IS elements. In addition to the genes that enable them to move, they also contain other genes, such as drug resistance genes. Transposons have been found in the genomes of plasmids, viruses, prokaryotes, and eukaryotes, and, like IS elements, they are designated by a serial number: Tp1, Tp2, Tp3, etc.
# Episomes include even larger and more complex self-regulating systems containing IS-elements and transposons and capable of replicating in any of their two alternative states - autonomous or integrated - into the chromosome of the host cell. Episomes include various moderate lysogenic phages; they differ from all other transposable elements in having their own protein shell and a more complex reproduction cycle. Episomes themselves are viruses that, like other transposable elements, have the ability to pass from one genome to another in an intact form.
One of the vital functions of prokaryotes, like any other living beings, is reproduction. At its core, the process of reproduction of bacteria can be characterized as an increase in the number of individuals, which occurs due to the division of bacteria.
Modern microbiology has described the schemes of mitosis, meiosis and amitosis - this is how eukaryotes divide, and prokaryotes reproduce by direct division.
Prokaryotes reproduce primarily by dividing the parent bacterial cell into 2 identical daughter cells. Under favorable conditions, binary fission occurs every 20 minutes, and in case of deterioration of environmental conditions, the time required for the cell to grow and divide increases. In case of unfavorable external conditions, prokaryotes stop reproduction for a while or completely.
The very process of dividing the cell in half is preceded by a period of cytoplasm growth and replication (doubling) of the bacterial chromosome, as in the photo.
Replications of the circular bacterial chromosome
The increase in cell size occurs due to a number of coordinated biosynthetic processes that are tightly controlled. The process of bacterial growth is not endless - when prokaryotes reach a given critical size, division occurs.
Mechanism of bacterial DNA replication
When doubling the DNA of a nucleoid (analogous to the nucleus in a bacterial cell), the following scheme is implemented:
- initiation - the beginning of DNA division under the action of a replicon (an enzymatic apparatus, a section of DNA containing information about duplication);
- elongation - elongation, growth of the chromosome chain;
- termination is the completion of chain growth and DNA helixing during replication.
In parallel with DNA replication, the cell itself grows, and the distance between the two new chromosomes attached by means of mesosomes to the cytoplasmic membrane gradually increases. A prokaryotic cell begins to divide some time after replication. Obviously, it is DNA duplication that triggers the separation process.
A similar process is absent for meiosis in eukaryotes. The process of meiosis differs in many ways from the reproduction of prokaryotes. In addition, the division of the mother cell into two parts for gram-positive and gram-negative bacteria has its own characteristics.
Reproduction of gram-negative bacteria
Gram-negative bacteria have a relatively thin cell wall, on which a ring organelle, the septal ring, is located approximately in the center. Separation of bacteria occurs by contraction of the organelle and the formation of a constriction between the daughter cells, as can be seen in the photo.
The septal ring is a complex protein complex, which includes more than 12 different proteins. It is formed by sequential attachment of proteins to each other in a strict sequence.
The septal ring proteins perform the following functions necessary for reproduction:
- model the attachment of filaments (ring proteins) in a certain sequence to the Z-ring (immature form of the ring organelle);
- provide binding of the Z-ring to the membrane;
- coordinate the formation of a ring organelle with the segregation (separation) of the chromosome;
- synthesize peptidoglycan - the most significant component of the bacterial cell wall, which provides osmotic protection;
- carry out hydrolysis of peptidoglycan to separate new cells.
The constriction in gram-negative bacteria covers all cell membranes - the cytoplasmic (inner) and outer membranes, as well as a thin layer of peptidoglycan associated with them by lipoprotein.
During eukaryotic meiosis, a similar method of cell division by constriction does not occur.
Reproduction of gram-positive bacteria
The wall thickness of Gram-positive bacteria is more than twice that of Gram-negative bacteria.
The process of reproduction of Gram-positive bacteria is not similar to mitosis and differs from eukaryotic meiosis. At the end of the DNA replication process, Gram-positive bacteria do not create a constriction, but synthesize a transverse septum, as in the photo. In the process of synthesis, as in the formation of a constriction in gram-negative bacteria, mesosomes take part, forming a septum from the edge to the center of the cell structure.
The transverse binary fission of a bacterial prokaryotic cell is always longitudinally and transversely symmetrical, which is another difference between the process and meiosis in the cell structure of eukaryotes.
Under favorable conditions, direct binary fission of bacterial cells can be carried out both in one and in several planes, which is impossible for meiosis. In the case when the cells do not disperse after separation, the formation of associations of various shapes occurs:
- when a cell is cut in one plane, chains of spherical or rod cells are formed (spherical diplococci, a chain of rod-shaped bacteria, as in the photo);
- when separated in different planes, cell clusters of various forms are observed (chains of streptococci, packets of sarcines, bunches of staphylococci).
The variety of forms of prokaryotes, which can be seen in the photo, is completely unrealizable for meiosis of nuclear cells.
Such a transverse separation is typical not only for Gram-positive bacteria, but also for filamentous cyanobacteria.
Multiple division of cyanobacteria
One of the varieties of binary reproduction of prokaryotes is the multiple formation of daughter prokaryotes from the mother cell, which is typical of cyanobacteria, and is completely uncharacteristic of meiosis.
A - reproduction of cyanobacteria of the genus Dermocarpa
B - reproduction of cyanobacteria of the genus Chroococcidiopsis
Initially, cytoplasmic growth and chromosome replication occur. Then, as you can see in the video, successive binary divisions take place inside the additional fibrillar layer of the mother's body, which lead to the formation of baeocytes (small cells). Their number can vary from 4 to 1000 units and is associated with the type of cyanobacteria. Baeocytes are released after the wall of the maternal prokaryote is ruptured, as seen in the video.
In addition to equal division, some bacteria reproduce by budding.
Budding as a special case of binary fission
In photo- and chemotrophs, regardless of the food source (autotrophs or heterotrophs), the possibility of reproduction of the organism by budding is found.
The mechanism of the process is as follows:
- a kidney is formed at the pole of the mother cell;
- the kidney grows to the size of the mother's body (this can be seen in the photo), and a new cell wall is synthesized for the kidney;
- a full-fledged daughter cell is separated from the mother.
If the binary separation process has no limits, as in the case of meiosis
for eukaryotes, then budding depends on the fact of aging of the prokaryote. On average, the mother cell separates no more than 4 kidneys.
Budding has its own specific features:
- only longitudinal symmetry is preserved (clearly visible in the photo);
- after budding, a mother and a daughter cell are obtained, while after a binary division there is no mother cell - there are two equivalent daughter cells;
- the mother and daughter organisms are not identical, the differences between them are clearly visible - the aging process is observed.
Under favorable physical and chemical conditions, prokaryotes are able to divide exponentially and fill the whole world with themselves. However, in reality this does not happen, since there are factors that inhibit bacterial division.
Factors limiting division
With all the species diversity and adaptability, bacteria do not multiply indefinitely. Studies have shown that the growth of the bacterial population occurs in accordance with the law of reproduction of microorganisms and is amenable to numerical and graphical description.
Population growth associated with the division of bacteria consists of several phases:
- lag phase - a period of adaptation, when it takes time to adapt to new living conditions, the division does not have a high value;
- logarithmic phase - the period with the largest number of divisions and exponential population growth;
- stationary phase - the time when the growth of a colony of bacteria tends to zero, the division of bacteria is equalized with the number of deaths due to limited food resources;
- growth retardation - occurs due to a significant reduction in food resources and the accumulation of toxic waste products.
Unfavorable conditions provoke the cessation of bacterial division and, as a result, the inevitable death of the population.
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Bacteria - prokaryotes (non-nuclear) are the simplest forms of organization of living organisms. You can find out what these organisms are from our article.
How bacteria reproduce: ways
There are not so many ways in which bacteria reproduce: simple division, budding, conjugation (some scientists consider it a sexual process in bacteria). Let's dwell on each of them in detail.
The most common method of reproduction in bacteria in the natural environment is equal-sized transverse fission. This means that the mother cell, after doubling the DNA strand and all the organelles, divides in two, forming two daughter cells, in which the genetic material will be similar to the mother. Thus, the bacterium literally clones itself. The process of division occurs by the formation of a constriction or transverse septum in the equatorial part of the cell.
Another method of reproduction that bacteria use in nature and the human body is budding, which is slightly different from division. So, the mother cell does not divide “in half”, but “grows” a daughter cell (kidney) at one of its poles. The mother cell most often can grow up to 4 daughter cells, after which it ages and dies. Budding, like division, produces genetic clones of the mother cell.
The sexual process in bacteria
Another way of reproduction of bacteria, in which the simplest sexual process is present, is conjugation. Most often, bacteria living in the human or animal body resort to it. They, unlike eukaryotes (nuclear organisms), do not form gametes and do not merge germ cells (gametes).
In the course of such reproduction, two bacterial cells come into contact, form a conjugation bridge and exchange genes, resulting in the formation of genetically new cells. This process is also called genetic recombination. Bacteria such as E. coli (Escherichia coli) and some other gram-negative and gram-positive bacteria reproduce sexually.
Page 2
The main way bacteria reproduce is by dividing the cell in two (binary fission). In this case, the plasma membrane and wall invaginate and lace it in half. Invagination of the membrane occurs between the points of attachment of the two daughter circular DNA molecules, as a result of which the daughter cells are provided with copies of the maternal chromosome. Bacteria have the ability to form endospores. Some endospores have dense multilayered membranes, are resistant to aggressive environmental factors and retain the ability to germinate for a long time.
The sexual process in bacteria is the transfer of DNA from one cell to another, followed by genetic recombination. The exchange of hereditary material can occur by conjugation (direct cell contact), transduction (transfer of DNA by a bacteriophage virus), or transformation (absorption of DNA fragments from outside). However, mutations are a universal source of variability. In combination with the rate of reproduction of bacteria, they provide these organisms with a high ability to adapt to environmental conditions.
Various types of bacteria can use almost any organic compound as an energy source - not only nutrients, such as sugars, amino acids and fats, but also waste products, such as urea and uric acid contained in urine, and substances that make up excrement. One type of bacteria can even use penicillin as a nutrient substrate, which kills many bacteria.
see also
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Genetic Engineering
Introduction Genetic engineering is a field of biotechnology that includes the actions of rearranging genotypes. The essence of genetic engineering comes down to understanding that any organism, be it ...
Asepsis in biotechnology
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Some microorganisms reproduce by sporulation (actinomycetes and fungi) and budding (yeast), some microorganisms reproduce sexually, but most of them reproduce asexually (vegetatively). Under favorable conditions, reproduction proceeds with unusual speed - every 20-30 minutes, the mother bacterial cell divides into two daughter cells. The daughter cell eventually becomes the mother cell and also divides. Thus, the division of bacteria goes exponentially. If such a division proceeded unhindered, then in 48 hours one bacterium could give rise to hundreds of billions of cells, and in five days such a mass that would fill the basins of all the seas and oceans. However, this does not happen, because microorganisms are affected by various environmental factors.
Cell division is preceded by a uniform increase in total nitrogen, RNA and protein in the cytoplasm. Then replication (doubling) of DNA occurs. In a dividing cell, hydrogen bonds are broken between the DNA helices and single daughter DNA helices are formed (Fig. 25).
Rice. 25. The process of binary fission of rod-shaped prokaryotes
3 - stretching of the cell;
- formation of a partition;
5 - cell division.
Immediately after DNA replication, cell elongation and the formation of a transverse septa begin due to two layers of the cytoplasmic membrane protruding towards each other. Most often, a septum is formed in the middle of the mother cell, as a result of which the daughter cells are approximately the same size. Between the layers of the septum, the formation of a cell wall takes place.
In the process of reproduction, one of the halves of the cell constantly retains flagella. At the final stage of bacterial reproduction, flagella-tics grow in the other half.
The growth and reproduction of microorganisms depends on various environmental factors and species characteristics. Observation of the development of microorganisms cultivated in a liquid nutrient medium in closed tanks shows that biomass growth requires an energy source, the presence of components necessary for biomass synthesis, the absence of inhibitors in the medium that inhibit cell growth, maintenance of the environment of the necessary physico-chemical conditions. Under these conditions, the growth of microorganisms can be conditionally divided into several successive phases or periods (Fig. 26):
1. lag phase (eng. lag - delay) - the period between the sowing of bacteria and the start of reproduction. During this period, the bacterial culture adapts to the nutrient medium. It manifests itself in the accumulation of the optimal amount of the necessary enzymes, in the inactivation of some inhibitor present in the environment, in the germination of spores, etc. Under favorable conditions, the bacteria increase in size and prepare for division. The lag phase can last from 10 minutes to several hours, but on average it is 4-5 hours.
3. The phase of logarithmic or exponential growth is the period of the most intensive division of bacteria. Bacteria divide every 20-40 minutes. During this phase, bacteria are especially vulnerable, which is explained by the high sensitivity of growing cells to environmental factors. The duration of exponential growth depends on the concentration of nutrients in the substrate and averages 5-6 hours.
5. The stationary growth phase is caused by gradual depletion of the medium, accumulation of lytic enzymes in it, chemical inhibition of microbial cell growth by metabolic products. This phase differs from the previous one by the increased resistance of bacteria to many chemical and physical factors. By the beginning of this phase, the number of viable cells reaches its maximum level and remains at this maximum for several hours, depending on the type of microorganisms and the characteristics of their cultivation. At the end of this phase, some microorganisms experience the process of sporulation.
6. The final phase of the reproduction process - the phase of aging and death - is characterized by the death of bacteria due to the depletion of the nutrient medium and the accumulation of metabolic products in it. Autolysis of microorganisms is observed as an extreme manifestation of cell instability after growth stops. The duration of this phase can be from several hours to several weeks.
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Bacteria, like all living organisms, reproduce. This happens most often by simple transverse division in different planes. In this case, various combinations of cells are formed: paired connections, single cells, clusters, chains, packages, etc.
Some microorganisms reproduce by sporulation (actinomycetes and fungi) and budding (yeast), some microorganisms reproduce sexually, but most of them reproduce asexually (vegetatively).
Under favorable conditions, reproduction proceeds with unusual speed - every 20-30 minutes, the mother bacterial cell divides into two daughter cells. The daughter cell eventually becomes the mother cell and also divides.
Thus, the division of bacteria goes exponentially. If such a division proceeded unhindered, then in 48 hours one bacterium could give rise to hundreds of billions of cells, and in five days such a mass that would fill the basins of all the seas and oceans. However, this does not happen, because microorganisms are affected by various environmental factors.
Cell division is preceded by a uniform increase in total nitrogen, RNA and protein in the cytoplasm.
Then replication (doubling) of DNA occurs. In a dividing cell, hydrogen bonds are broken between the DNA helices and single daughter DNA helices are formed (Fig. 25).
25. The process of binary fission of rod-shaped prokaryotes
1 — formation of single helices of DNA;
2 — doubling (replication) of DNA;
3 - stretching of the cell;
- formation of a partition;
4 - the end of the formation of the partition and the formation of a convex cell wall;
5 - cell division.
Immediately after DNA replication, cell elongation and the formation of a transverse septa begin due to two layers of the cytoplasmic membrane protruding towards each other.
Most often, a septum is formed in the middle of the mother cell, as a result of which the daughter cells are approximately the same size. Between the layers of the septum, the formation of a cell wall takes place.
The single helix of DNA in new cells serves as a template for creating a second helix, resulting in the formation of a double helix of DNA with restored hydrogen bonds and the formation of a new nucleoid.
In the process of reproduction, one of the halves of the cell constantly retains flagella.
At the final stage of bacterial reproduction, flagella-tics grow in the other half.
The growth and reproduction of microorganisms depends on various environmental factors and species characteristics. Observation of the development of microorganisms cultivated in a liquid nutrient medium in closed tanks shows that biomass growth requires an energy source, the presence of components necessary for biomass synthesis, the absence of inhibitors in the medium that inhibit cell growth, maintenance of the environment of the necessary physico-chemical conditions.
Under these conditions, the growth of microorganisms can be conditionally divided into several successive phases or periods (Fig. 26):
Rice. 26. Typical growth curve of a population of microorganisms 1 - lag phase;
2 - phase of accelerated growth; 3 - phase of logarithmic (exponential) growth;
4 - phase of growth retardation; 5 - phase of stationary growth; 6 - phase of aging and dying.
lag phase (eng. lag - delay) - the period between sowing bacteria and the start of reproduction. During this period, the bacterial culture adapts to the nutrient medium. It manifests itself in the accumulation of the optimal amount of the necessary enzymes, in the inactivation of some inhibitor present in the environment, in the germination of spores, etc. Under favorable conditions, the bacteria increase in size and prepare for division.
The lag phase can last from 10 minutes to several hours, but on average it is 4-5 hours.
2. The phase of accelerated growth is observed after the lag phase and is characterized by an increase in the rate of division of microorganisms and the accumulation of biomass.
3. The phase of logarithmic or exponential growth is the period of the most intensive division of bacteria.
Bacteria divide every 20-40 minutes. During this phase, bacteria are especially vulnerable, which is explained by the high sensitivity of growing cells to environmental factors. The duration of exponential growth depends on the concentration of nutrients in the substrate and averages 5-6 hours.
4. The deceleration phase is the transitional period from exponential growth to the stationary growth phase. During this phase, there is a depletion of the nutrients of the substrate and the accumulation of metabolic products in it, which reduces the intensity of reproduction of microorganisms.
The stationary growth phase is caused by gradual depletion of the medium, accumulation of lytic enzymes in it, and chemical inhibition of microbial cell growth by metabolic products. This phase differs from the previous one by the increased resistance of bacteria to many chemical and physical factors. By the beginning of this phase, the number of viable cells reaches its maximum level and remains at this maximum for several hours, depending on the type of microorganisms and the characteristics of their cultivation.
At the end of this phase, some microorganisms experience the process of sporulation.
6. The final phase of the reproduction process - the phase of aging and death - is characterized by the death of bacteria due to the depletion of the nutrient medium and the accumulation of metabolic products in it. Autolysis of microorganisms is observed as an extreme manifestation of cell instability after growth stops.
The duration of this phase can be from several hours to several weeks.
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Reproduction of microorganisms - binary division of unicellular microorganisms (bacteria, rickettsia, protozoa, yeast), as a result of which two new daughter full-fledged individuals are formed, endowed with the genetic information of the mother cell. Yeast-like fungi can reproduce by budding, spores; Molds and actinomycetes usually reproduce by spores.
bacteria
They reproduce by simple transverse division.
Bacteria are haploid cells. The composition of a bacterial cell includes a capsule, cell wall, cytoplasmic membrane, cytoplasm, where mesosomes, ribosomes, nucleoid, and inclusions are located. Some bacterial cells have flagella and form spores.
Unlike animal cells, such internal structures of a bacterial cell as mesosomes, ribosomes, and nucleoid do not have membranes separating them from the cytoplasm.
According to the method of nutrition, bacteria are divided into autotrophs and heterotrophs, according to the method of respiration - into aerobes and anaerobes.
actinomycetes
They reproduce by spores and transverse division (lacing) of hyphae.
Occupy an intermediate position between fungi and bacteria. Among the radiant fungi, there is a network of pathogenic species - the causative agents of actinomycosis. Many actinomycetes are producers of antibiotics. (cm.
antibiotics). In Burgey's "Determinant" actinomycetes are called streptomycetes.
Yeast
There are 2 types of yeast reproduction - vegetative (asexual) and sexual with the formation of spores. In most yeast species, vegetative propagation is carried out by budding, rarely by division (Schizosaccharomyces). Asporogenic. Yeast reproduces only by budding. Sexual reproduction occurs under unfavorable conditions, when the yeast stops budding and turns into bags (asci) with spores - ascospores.
The sexual process consists in the copulation (fusion) of 2 vegetative cells by bringing them together and forming a copulatory canal, in which parts of the plasma and the cell nucleus merge, called karyogamy, with the formation of a diploid zygote representing 2 cells connected by a copulation canal.
Reduction division, or meiosis, accompanied by a halving of the number of chromosomes, occurs immediately, without a sexual process, and the zygote turns into an ask with 4 haploid spores, so the vegetative generation of such spores is haploid. Spores germinate without copulation. This is how the yeast Zygosaccharomyces reproduces. In the yeast Saccharomyces, the sexual process occurs when spores or cells germinated from them merge to form a diploid zygote, which immediately begins to bud, forming diploid offspring.
Meiosis occurs just before spore formation.
mold mushrooms
Fungi have vegetative, sexual and asexual reproduction.
Vegetative propagation can be carried out by separating from the main mass of the mycelium of its parts, which can develop independently, as well as by budding of the mycelium or individual cells in yeast fungi.
Sexual reproduction consists in the fusion of germ cells, resulting in a zygote.
Asexual reproduction is carried out with the help of special formations called spores. Spores can develop inside special spores or at the ends of special outgrowths of the mycelium - conidiophores.
The main method of reproduction of mold fungi is with the help of spores. Mold grows incredibly fast.
In ordinary bread mold, small black dots can be distinguished - sporangia, in which spores are formed. One sporangium contains up to 50,000 spores, each of which is capable of reproducing hundreds of millions of new spores in just a few days! And if the conditions are favorable, mold will quickly appear on a book, shoes, or a fallen tree in the forest.
Bacteria: The vital activity of bacteria is characterized by the growth- formation of structural and functional components of the cell and an increase in the bacterial cell itself, as well as reproduction- self-reproduction, leading to an increase in the number of bacterial cells in the population.
bacteria multiply by binary fission in half, less often by budding.
Actinomycetes, like fungi, can reproduce by spores. For one group of unicellular cyanobacteria, multiple division has been described (a series of rapid successive binary divisions, leading to the formation of 4 to 1024 new cells). Actinomycetes, being branching bacteria, multiply by fragmentation of filamentous cells. Gram-positive bacteria divide by growing the synthesized division partitions into the cell, synthesize a transverse partition from the periphery to the center with the participation of mesosomes.
and gram-negative - by constriction (at the site of division, a gradually increasing curvature of the CPM and the cell wall inward is found.), as a result of the formation of dumbbell-shaped figures, from which two identical cells are formed. When budding, a kidney is formed and grows at one of the poles of the mother cell, the mother cell shows signs of aging and usually cannot produce more than 4 daughter cells.
In other bacteria, in addition to reproduction, a sexual process is observed, but in the most primitive form.
The sexual process of bacteria differs from the sexual process of eukaryotes in that bacteria do not form gametes and cell fusion does not occur. However, the main event of the sexual process, namely the exchange of genetic material, occurs in this case as well. This is called genetic recombination.
Cell division is preceded by the replication of the bacterial chromosome according to a semi-conservative type (the double-stranded DNA chain opens and each strand is completed by a complementary strand), leading to the doubling of the DNA molecules of the bacterial nucleus - the nucleoid. DNA replication occurs in three stages: initiation, elongation, or chain growth, and termination.
Reproduction of spirochaetes: transverse cell division-cell division in bacteria, in which the mother cell gives rise to two daughter cells. It is carried out in three stages:
1) replication of the DNA molecule of the circular chromosome attached to the mesosome, which is also divided into two parts;
2) dilution with the help of mesosomes of two daughter ring chromosomes;
3) division of the cytoplasm by a transverse septum, which is formed from the periphery to the center of the cell.
Mushroom breeding:
Most fungi are capable of vegetative, asexual and sexual reproduction proper.
Pleomorphism is characteristic - the presence of several types of sporulation at the same time, for example, asexual and sexual.
Vegetative propagation
- parts of the mycelium.
- Specialized formations: arthrospores (oidia) with thin walls or chlamydia spores with thick ones, they are formed, with some differences, when the mycelium breaks apart, and then give rise to a new one.
- Budding of hyphae or individual cells (for example, in yeast).
Ascospores in marsupials and basidiospores in smuts also bud. The resulting buds gradually separate, grow and eventually begin to bud themselves.
asexual reproduction
Actually asexual reproduction occurs through spores.
Depending on the method of formation, endogenous and exogenous spores are distinguished.
- Endogenous spores(sporangiospores) are characteristic of lower fungi.
They are formed inside special cells called sporangia.
- Exogenous disputes commonly called conidia, they are found in higher and some lower fungi.
They are formed on the tops or on the side of special hyphae - vertically oriented conidiophores, which can be simple or branched.
They are covered with a dense shell, so they are quite stable, but motionless. They can be picked up by air currents or animals and carried over considerable distances. When germinating, they give a growth tube, and then hyphae.
sexual reproduction
gamete conjugation
For lower fungi, the fusion of haploid gametes is characteristic by isogamy, anisogamy (heterogamy), or oogamy.
In the case of oogamy, the genital organs develop - oogonia(female) and antheridia(male). During fertilization, the formation oospores- this is a zygote that is covered with a thick shell, spends some time at rest, and then germinates.
The rate and phases of bacterial reproduction under stationary conditions.
When growing bacteria on a liquid nutrient medium, near-bottom, diffuse, or surface (in the form of a film) culture growth is observed.
The growth of a periodic culture of bacteria grown on a liquid nutrient medium is divided into several phases, or periods:
1. lag phase;
2. phase of logarithmic growth;
3. phase of stationary growth, or maximum concentration of bacteria;
4. phase of bacterial death.
These phases can be depicted graphically as segments of the bacterial reproduction curve, which reflects the dependence of the logarithm of the number of living cells on the time of their cultivation.
Lag phase - the period between sowing bacteria and the start of reproduction.
The duration of the lag phase is on average 4-5 hours. At the same time, bacteria increase in size and prepare for division; the amount of nucleic acids, protein and other components increases.
The phase of logarithmic (exponential) growth is a period of intensive division of bacteria. Its duration is about 5-6 hours. Under optimal growth conditions, bacteria can divide every 20-40 minutes.
During this phase, bacteria are the most vulnerable, which is explained by the high sensitivity of the metabolic components of a rapidly growing cell to inhibitors of protein synthesis, nucleic acids, etc.
Then comes the phase of stationary growth, in which the number of viable cells remains unchanged, constituting the maximum level (M-concentration). Its duration is expressed in hours and varies depending on the type of bacteria, their characteristics and cultivation.
The process of bacterial growth is completed by the death phase, which is characterized by the death of bacteria under conditions of depletion of the sources of the nutrient medium and the accumulation of metabolic products of bacteria in it. Its duration varies from 10 hours to several weeks. The intensity of growth and reproduction of bacteria depends on many factors, including the optimal composition of the nutrient medium, redox potential, pH, temperature, etc.
The growth rate of bacteria depends both on external conditions and on the physiological characteristics of the cell itself.
In the presence of favorable conditions, the growth of a bacterial cell ends with reproduction. The main way most bacteria reproduce is by simply dividing the cell in half. Division is preceded by replication (doubling) of the chromosome. These two processes are closely related. The frequency of replication is regulated by the rate of cell growth. Replication of the bacterial chromosome is carried out in the manner described earlier (see section 3.2.5).
The study of the uniform distribution of genetic material between daughter cells formed as a result of the division of the mother cell allowed G. Jacob, S. Brenner and T. Cousin (1963) to formulate the concept of replicon. A replicon is a unit of replication; it is a section of DNA containing the regulatory elements necessary for independent replication. In bacteria, these are the chromosome and plasmids. Each replicon contains at least two loci involved in the control of replication: a structural replicator gene (initiator gene) that determines the synthesis of the initiator protein and a special replicator site that recognizes signals for the start of chromosome duplication.
After a certain period of growth, the cell reaches a certain physiological state. From the cytoplasmic membrane, the replicon receives signals about the need for chromosome replication and the readiness of the cell for division. Under the influence of signals, the activity of the structural gene is activated and the initiator protein is synthesized.
It, acting on the replicator, starts replication.
There is a coordinated interaction between the chromosome replication system and cell division: cell division is always preceded by chromosome doubling. Once replication is complete, cell division begins. In gram-positive bacteria and cyanobacteria, this is accomplished by the formation of a transverse septum that separates the mother cell into two equivalent daughter cells.
The division is as follows.
At the beginning
a bilayer cytoplasmic membrane is synthesized. Then two tubercles form on the inner side of the cell wall. They grow intensively and, penetrating ring-shaped inside the cell between the layers of the formed cytoplasmic membrane, form a double septum dividing the cell in half.
Division of most grammer meticulous bacteria
occurs through constriction. In this case, the genomes diverge along the poles of the cell, the cytoplasmic membrane and the cell wall are stretched, protruding from the periphery to the center of the cell until they come into contact with each other. As a result, the cell is laced into two daughter cells. Cell division by the formation of a septum or constriction is called binary in connection with the formation of two identical daughter cells.
In addition to the described binary fission, bacteria have another method of reproduction - budding. Bacteria of the genera Hyphomicrobium, Pedomicrobium and others, united in the group of budding bacteria, reproduce by budding.
These organisms look like elongated sticks (0.5 x 2 microns), sometimes pear-shaped, ending in hyphae, or prosthesis (outgrowths).
Reproduction in these bacteria begins with the formation of a kidney at the end of a hyphae or directly on the mother cell.
The kidney grows into a daughter cell, forms a flagellum and separates from the mother cell. Upon reaching the mature state, the flagellum is lost and the development process is repeated.
In contrast to binary fission, during budding, the original cell remains the parent cell, and the newly formed cell remains the daughter cell.
There are morphological and physiological differences between them.
Actinomycetes reproduce by fragments of mycelium and spores. In some (the genus Micromonospora), single spores are formed on the hyphae of the vegetative mycelium, in others (the genus Streptomyces, etc.), chains of spores are formed at the ends of the hyphae of the aerial mycelium, the so-called conidiophores.
Fragments of mycelium and spores germinate under favorable conditions of humidity and temperature and give rise to new organisms.
Filamentous cyanobacteria, in addition to binary fission, reproduce in patches of trichomes and hormogonia. The latter are shortened threads, consisting of small vegetative cells of the same shape and size. When the middle cells of the trichome (filaments) die, the hormogonia slip out of the sheath of the mother trichome, grow, divide, forming new trichomes.
Hormogonia, unlike the maternal trichome, do not have heterocysts and are never sheathed.
Regardless of which way the process of reproduction of bacteria goes, the speed of this process is enormous: in 24 hours as many generations can change as a person has in five thousand years.
The rate of reproduction depends on many conditions and is different for each type of bacteria. In the presence of the necessary nutrients in the medium, favorable temperature and acidity of the medium, the division of each cell can be repeated after 20-30 minutes (E. coli). At such a reproduction rate, 472 * 1019 cells (273, 72 generations) can be formed from one cell per day.
Intensive reproduction is of great biological importance for bacteria. It ensures the preservation of microorganisms on the earth's surface. When unfavorable conditions occur, they die in masses, but it is enough for a few cells to survive somewhere, as under suitable conditions they will give a large progeny of cells.
Microbial populations in natural habitats, such as soil or water, are constantly changing in line with changing living conditions.
But in laboratory conditions on nutrient media, the change in the population of microorganisms occurs in a natural way.
And also in the section "PRODUCTION OF BACTERIA"
actinomycetes(Actinomyces) translated from Latin - radiant fungus, a separate group of microorganisms with a number of morphological features of the lowest species of fungus and non-spore-forming bacteria.
Morphology of actinomycetes
The structure of actinomycytes has similar features with filamentous fungi, mycelial vultures have an average thickness of 0.7 microns, varying within 0.5-1.2 mm, which is much less than that of mushrooms.
For threads, straight or slightly curved, without transverse partitions, monopodial or, in some cases, whorled branching is characteristic. The cell membrane in composition has a number of features of gram-positive bacteria.
Reproduction of actinomycetes
Actinomyces reproduce by substratum mycelium germinating in the substrate and aerial mycelium growing from sporangiophores.
Fruit-bearers, depending on the species, have a different shape of curls from a twisted shape to straight or wavy.
Some species of actinomycetes have spore-bearing branches arranged in whorls or bundles, often they hang monopodially on mycelium threads.
Spore formation occurs by fragmentation or segmentation.
Fragmentation- this is the process of crushing the protoplast of the spore-bearing branch into one hundred or more small lumps containing basophilic and nuclear substance.
Lumps, turning into spores, are located in a long chain in the spore-bearing plant.
Segmentation- this is the process of dividing the spore-bearing segments into rod-shaped segments, with the help of transverse partitions, they are rounded and converted into spores.
The shells of spores in different species have a smooth, sometimes bumpy, serrated, spiny, hairy surface. The outgrowths on the surface of the shells are clearly visible through an electron microscope.
In most cases, actinomycetes are aerophiles and mesophiles, but thermophiles have also become widespread, many of their species are able to form pigments of different colors.
Actinomycetes, having a diverse set of enzymes, are able to synthesize various substances and release them in large quantities into the environment. Among these substances with high physiological activity, there are many vitamins, some amino acids, toxins, carotenoids, phytohormones and others.
It is also worth mentioning the ability of actinomycetes to form various types of antibiotics.
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