Bacterial growth

As bacterial growth is defined as the growth of the bacterial cells through cell division, that is, the increase in the number of bacteria, the growth of the bacterial population. The rate of growth is dependent on the number of divisions per unit time, the so-called rate of cell division.

Phases of bacterial growth in static cultures

According to the growth of the population ecology of the bacteria can be divided into a static bacterial culture into four phases: lag phase (lag ); exponential phase (log ); stationary phase; Death phase.

Start-up phase (lag )

In the initial phase, also known as latency phase (or phase was English ) refers to, there is the analysis of the available materials in the nutrient medium by receptors in the cell membrane of the bacteria. Depending on this, the expression of genes turned on, which encode enzymes that make the reduction of the substances present in the culture medium possible. This takes a certain amount of time, which may differ depending on the bacterial species and composition of the nutrient medium. The metabolism of nutrients is the basis for cell growth and division. Further, in many cases the properties of the culture medium for cell growth and cell division improves the metabolism, for example by lowering the redox potential.

Exponential phase (log )

After adjustment of the metabolism and possibly also of the medium, the bacterial culture is transferred in exponential growth. The generation time remains the same here over several cycles of cell division. The human gut bacterium Escherichia coli has under ideal conditions in laboratory cultures a generation time of about 30 minutes: From the example in the table below it can be seen that the number of bacterial cells ( starting at 1) doubles every 30 minutes.

Stationary phase

The system approaches the capacity limits of the available space and nutrients, the number of bacterial cells in the medium no longer. A dynamic equilibrium is that in which the number of dying and adventitious bacteria by cell division are balanced.

Death phase

When the nutrients are substantially depleted in the medium, and the tolerance value of the population density of the bacteria of each species has been reached, a the death phase. The bacterial cells starve or die of excretion products of their own metabolism that are present at this stage in high concentration. Furthermore, separate bacteria from toxins, thus the competition is reduced by nutrients through representatives of their own or other species. The concentration of these toxins also increases with increasing population density.

Cultivation of bacteria in the laboratory

The cultivation of bacteria takes place in the laboratory, usually in liquid nutrient media, or jelly-like nutrient media, rather than, for example, on the basis of an agar gel. The growth curve as described above can be observed only in bacteria pure cultures in liquid media under ideal conditions in the laboratory. To the ideal conditions, including, inter alia, optimum temperature, nutrient composition of the medium, the oxygen supply. The optimum of all of these factors are species- dependent. These conditions are never achieved in nature.

Very few species of bacteria can be cultured in the laboratory in this way, many species need significantly more complex conditions of life, and also the interaction with one to numerous other creatures to multiply.

Suppress bacterial growth

To slow down the bacterial growth, or to stop, various measures are employed. Plays a role, inter alia, in the preservation of foods and similar materials. In medicine, antibiotics may be used to suppress the often important functions of the bacterial anabolism. Eukaryotes are not affected by antibiotics, as their construction material change is fundamentally different from that of prokaryotic bacteria.