The smallest organisms on the planet - prokaryotic cells of bacteria.Perhaps their size - this is one of the reasons that they are capable of tremendous increase in the number.It is estimated that the normal bacterial growth occurs every 20-30 minutes.Naturally, the number of cells forming incredible!During the day, in terms of the mass of the offspring of one individual will be about 5 tons.
However, due to various limiting factors of such growth is not happening.What caused such a rapid reproduction of these organisms?Let's try to sort out this issue.
method of reproduction of bacteria
there are several.The main factor that determines one or another variant of the process of reproduction - is the external environment.As the bacteria multiply under favorable conditions?Two Ways:
- vegetative (asexual);
- budding.
It is faster, simpler and evolutionarily ancient techniques.However, when such methods are not exchanged genetic information, so the individual subsidiaries are exact copy of the parent.
But as the bacteria multiply if the parameters of the external sphere unfavorable?Then comes a special process, having the same basis as the sexual reproduction of multicellular - the exchange of genetic information through recombination of DNA molecules in the cells adjacent nucleoid.
Let us consider each of these options in more detail and explain the features of the artificial cultivation of microorganism populations.
Asexual reproduction and its features
Each bacterial cell performs all the vital processes:
- breathing;
- powered;
- moves;
- absorbs and spending power;
- growing;
- develops.
up the whole of life becomes the process of asexual reproduction, resulting in the mother cell gives rise to new individuals, and gradually dies.
Process Description
How bacteria multiply vegetatively, can be briefly described in a few paragraphs.
- bacteria reach a certain size and nutrient storage.As a result, it is ready to start the process.
- then the cell starts to extend longitudinally, that is to lengthen.
- This transverse wall is formed in the middle (waist), which begins to converge towards the center of the cell, squeezing it.
- inside while the process of replication of the DNA molecule, ie the division of the nucleoid.
- genetic material of both ends of the molecule is attached to the bacterial cell wall.
- primary and replicated DNA differ on different poles.
- Padding closes and is a division of the cells in half.Since forming two daughter individuals.
- missing structures (flagella, capsules and slime, etc.) are being completed each representative separately.
- first divided nucleoid cells, and cytokinesis occurs after him.
It is obvious that the growth and multiplication of bacteria by this type - a very simple and fast-moving process that requires no training and some specific features.
However, in some species (eg, hay rod-shaped bacteria), the process does not end there.Two daughter cells form together a bridge through which DNA freely move from one to another.Facing each other, exchanged nucleic acid portions, giving rise to mutations.The DNA was returned to its cage has only changed with a new integrated circuit portions.Bridge collapses, each individual begins an independent existence.
types of cell division
There are a few features of how bacteria reproduce asexually.When making process there are three possible scenarios.
- Cytokinesis nucleoid and division occurs before the time to form the waist and cells differ two structures.Therefore, in these cases, it is the formation of diplococci, streptococci, staphylococci, rod-like multicellular structures and other forms of joint.
- normal separation.Thus there is a timely and balanced vegetative division of both the cells and genetic material and the cytoplasm.As a result of a normal parent obtained two daughter cells.
- division genetic material is happening much faster than the separation of the cells themselves.As a result, formed mnogonukleoidnye form.
Once formed, any of these colonies, cells in many of them also tend to separate from each other and independent existence.
can disconnect the cells from each other
Features bacterial growth vegetatively provide different options for cell separation.In total they can name three.
- Cells break cytoplasmic bridge between them and repel each other (separation breaks).Example: the anthrax bacillus.
- Careful separation by means of a slip on the surface of another individual.Example: Escherichia.
- section.The way in which one cell describes around another figure in the form of V. Example: diphtheria bacteria.
In this particular asexual (vegetative) reproduction of bacterial species to an end.
Sexual reproduction: features
How is the multiplication of bacteria sexual way, it has been found only in 1946.Before this was known only have we considered an option.It was believed that the answer to the question of how to reproduce these bacteria is clear: only asexually dividing cells in half.
However, experiments with strains of Escherichia coli showed that its cells are capable of conjugation.So-called special process of exchange of genetic material.And this is a direct indication of just sexual reproduction.
As such female and male cells in the bacteria there.However, there is always the one that contains the initial DNA (male), and one that will be its host (female).The entire process takes place as follows.
- two cells come together with each other and make contact.
- drinking place called the contact, and it is hollow fibrous straw.Produced "male" cell.
- then formed on the channel starts to happen the transmission of DNA in the mother cell's father.
- where genetic material is recombined, ie exchanges of land.Each molecule itself completes the missing chain.
- process is very slow, so for the time of his passing, "male" cells capable of several times to replicate its DNA.
- As a result, new individuals are formed with recombinant genetic material with signs of both male and female cells.And are some initial paternal cells.
growth of bacterial colonies
In order to study how the growth and reproduction of bacteria, prepare special nutrient medium suitable for each kind.They are planted strains and observing certain sterile conditions to avoid competition in shares, other microorganisms, watching the changes taking place and the growth of entire colonies.
If you do not limit the limiting factors this process, the growth of the population is in a logarithmic progression.The death of cells in a natural way - just arithmetic.
Spore formation
heard that bacteria are able to form a special structure - the controversy, many people think that this is another version of how bacteria multiply.However, it is not.
argue - this is only a temporary state of rest cells in which it is able to survive adverse environmental conditions.Sometimes even decades.With the process of procreation is in no way connected.
