Probably, in nature there are no more tenacious and adapted to the environment organisms than bacteria. These unicellular life forms can tolerate colossal changes in temperature, pressure and acidity. They can do without water for a long time in a drought, and upon the occurrence of favorable environmental factors, they can again return to normal life. How can bacteria survive where other organisms die?
What is a cyst in biology
Bacteria are able to survive adverse conditions through encystation. The essence of this process is that the bacterial cell is surrounded by a thick membrane. Actually, this is the reason why microorganisms are not afraid of drought or temperature changes.
Cysts are a form of bacteria that can survive under the influence of adverse factors. This protective and adaptive structure is characteristic not only for prokaryotic organisms, but also for some protists.
Features of a resting cell
A cyst is a very specific form of bacteria that leads to some transformations within the cell. These features depend on the type of encysting, however, there are some general characteristics of this process. First, a thick protective membrane forms around the cell, which is a barrier to adverse environmental factors.
However, encystation completely or partially blocks the connection of the cell with the environment, so microorganisms must prepare for the formation of a dense shell. First, bacteria store essential substances and enzymes that will work even under encysting conditions. Then the cell loses some of its structures in order to temporarily remove unnecessary current energy costs.
A cyst is one of the stages in the life cycle of many microorganisms. Accordingly, the encystation process is periodic. Some cysts are able to remain viable after 5, or even 10 years. There is evidence that protist cysts can live up to 16 years. This gives the right to call microorganisms the most tenacious on the planet.
Factors contributing to encystation
A study of bacteria in the laboratory shows that cyst is the best device for experiencing adverse conditions. Determination of encysted cells on Petri dishes under the influence of various factors shows the importance of a dense cell membrane. What factors cause the formation of cysts?
1. Temperature differences.
2. The change in the concentration of dissolved substances in this environment.
3. Evaporation of water (drainage of water bodies).
4. Lack or excess of oxygen.
5. Lack of food resources.
The last point is a common cause of encysting microorganisms. If you grow a colony of bacteria on a Petri dish, then after the supply of food has expired, most cells go into the form of a cyst. If the environment is rich in nutrients, the likelihood of encysting is minimal.
In some groups of organisms, cysts also form in other circumstances. For example, in ciliates, this process is necessary for rebuilding the nuclear apparatus inside the cell. The encystation of parasitic cells of eukaryotes occurs in order to get out of the host organism and enter an unsuitable living environment. Some representatives of prokaryotes and eukaryotes use cysts for reproduction.
Types of encystation
For what purposes do microorganisms enter the cyst stage? Here are a few types of encysting that are most common in nature.
1. Cysts of rest.
These forms of bacteria and protists are a typical example of encysting, in which a cell experiences adverse environmental conditions.
2. Reproduction cysts.
This type is characteristic of many representatives of ciliates. In this case, the cysts form a fairly thin shell, and the cell begins to divide many times. As a result, the cyst bursts, and a large number of copies of the mother's body come out.
3. Digestive cysts.
Such cell forms are quite rare in a few types of microorganisms. Here the cyst is a device for the efficient digestion of food. This type of encysting is characteristic of predator organisms, which after “eating” their prey form a shell and begin to actively digest prey.