How do bacteria multiply under favorable and unfavorable conditions?

The smallest organisms on our planet -prokaryotic bacteria cells. Probably, their size is one of the reasons why they are capable of a colossal increase in the number. It is estimated that the normal reproduction of bacteria occurs every 20-30 minutes. Naturally, the number of cells is simply incredible! For a day in the translation to the mass of offspring from one individual will be about 5 tons.

However, due to various limiting factors, this increase does not occur. What is the cause of such a rapid multiplication of these organisms? Let's try to understand this question.

Methods of reproduction of bacteria

There are several of them. The main factor that determines this or that variant of the process of reproduction is the external conditions. How do bacteria multiply under favorable conditions? There are two ways:

• vegetative (asexual);
• by budding.

These are faster, simple and evolutionarily ancient methods. However, with such methods, there is no exchange of genetic information, so the children are an exact maternal copy.

But how do bacteria multiply, if the parametersexternal sphere are unfavorable? Then comes a special process, which has the same basis as sexual multiplication of multicellular - the exchange of genetic information due to the recombination of DNA segments of neighboring nucleoids in cells.

Let's consider each of these options in more detail and find out the features of artificial cultivation of populations of microorganisms.

Asexual reproduction and its features

Each bacterial cell performs all the vital processes:

• breathes;
• eats;
• Moves;
• absorbs and spends energy;
• grows;
• develops.

The result of all life is the process of asexual reproduction, as a result of which the mother cell gives rise to new individuals and gradually dies.

Process description

The way the bacteria grows vegetatively can be briefly described in several paragraphs.

1. The bacterium reaches a certain size and a reserve of nutrients. As a result, it is ready to start the process.
2. Then the cell begins to stretch out longitudinally, that is, to lengthen.
3. In this middle, a transverse septum (constriction) is formed, which begins to converge towards the center of the cell, squeezing it.
4. Inside, the process of replication of the DNA molecule takes place, that is, the division of the nucleoid.
5. The genetic material at both ends of the molecule is attached to the walls of the bacterial cell.
6. The main and replicated DNA diverges at different poles.
7. The constriction closes and the cell is split in half. So two children are formed.
8. Missing structures (flagella, mucus capsules and so on) are completed in each representative separately.
9. The nucleotide of the cell is divided first, and after it occurs cytokinesis.

Obviously, the growth and multiplication of bacteria by this type is a very simple and quick process that does not require preparation and some specific features.

However, in some species (for example, in the haybacillus bacteria), the process does not end there. Two daughter cells form a bridge between them, through which DNA freely passes from one to the other. Meeting each other, nucleic acid molecules exchange sites, which leads to the appearance of mutations. After this, the DNA returns to its cage, only already changed, with new sections built into the chain. The bridge collapses, each individual begins an independent existence.

Types of cell division

There are a few more peculiarities in how the bacteria multiply asexually. When the process is completed, three variants of the development of events are possible.

1. Cytokinesis and division of a nucleoid occurs earlier,than have time to form constrictions, and the cells disperse by two structures. Therefore, in these cases, formation of diplococci, streptococci, staphylococci, rod-shaped multicellular formations and other combined forms occurs.
2. Normal separation. In this case, a timely and harmonious vegetative division of both the cells themselves, and the genetic material and cytoplasm occurs. As a result, two normal daughter cells are obtained from one maternal cell.
3. The ongoing division of genetic material is much faster than the separation of the cells themselves. As a result, multinucleoid forms are formed.

After the formation of any of the above colonies, cells in many of them also tend to separate from each other and independent existence.

Methods of detachment of cells from each other

The peculiarities of bacterial multiplication by the vegetative method include different cell separation options. In total, there are three of them.

1. Cells break the cytoplasmic bridge between them and repel each other (breaking separation). Example: anthrax rods.
2. Accurate separation by sliding one individual over the surface of another. Example: Escherichia.
3. Section. The way in which one cell describes another around the shape of V. Example: diphtheria bacteria.
   

On this peculiarity of asexual (vegetative) reproduction of bacterial species ends.

Sexual reproduction: features

How does the reproduction of bacteria by sexualway, it was established only in 1946. Before that, only the option we had already considered was known. It was believed that the answer to the question of how the real bacteria multiply is unambiguous: only asexual division of the cell in two.

However, experiments on Escherichia coli strainsshowed that its cells are capable of conjugation. This is the name of a special process of exchange of genetic material. And this is already a direct sign of sexual reproduction.

As such, female and male cells amongno bacteria. However, there is always one that contains the initial DNA (male) and the one that will receive it (female). The whole process is as follows.

1. Two cells approach each other and establish contact.
2. The place of contact is called a saw, and it is a hollow fibrous tube. It is produced by a "male" cell.
3. Then, through the formed channel, the transfer of the DNA of the father to the mother cell begins.
4. Here, the genetic material is recombined, that is, it exchanges patches. Each molecule completes the missing chain.
5. The process is very slow, so during its passage, the "male" cell is capable of replicating its DNA several times.
6. As a result, new individuals are formed that have a recombinant genetic material with signs of both male and female cells. And also there are several initial paternal cells.

Growth of bacterial colonies

In order to study how growth andmultiplication of bacteria, prepare special nutrient media suitable for each species. They are sown strains and, observing certain sterile conditions, in order to avoid competition when other microorganisms are being colonized, they observe the changes that are taking place and the growth of whole colonies.

If this process is not limited by limiting factors, then the population growth proceeds in a logarithmic progression. The death of cells by natural means is only in the arithmetic.

Spore formation

Hearing that microbes are capable of forming special structures - disputes, many people think that this is another variant of how the bacteria multiply. However, it is not.

Spore is only a temporary state of resta cell in which she is able to experience unfavorable environmental conditions. Sometimes even tens of years. With the processes of reproduction of offspring this is in no way connected.