Bacterial Growth Curve

Bacterial Growth

Bacteria are unicellular organisms that tend to reproduce asexually by the means of binary fission. Bacterial growth is the increase in the number of bacterial cells rather than the increase in their cell size. The growth of these bacterial cells takes place in an exponential manner, i.e., one cell divides into 2, then 4, then 8, 16, 32 and so on.

The time taken for a bacterial cell to double is called generation time. The generation time varies among different species of bacteria based on the environmental conditions they grow in. Clostridium perfringens is the fastest growing bacteria that has a generation time of 10 minutes while Escherichia coli has a doubling time of 20 minutes. Mycobacterium tuberculosis is one of the slowest growing bacteria, taking about 12 to 16 hours to double.

Growth Curve

In a closed system with enough nutrients, a bacteria shows a predictable growth pattern that is the bacterial growth curve. It consists of four different phases. Read on to learn about the phases in detail.

Phases of the Bacterial Growth Curve

Upon inoculation into a new nutrient medium, the bacteria shows four distinct phases of growth. Let us dive into each of the phases in detail –

Lag Phase

The bacteria upon introduction into the nutrient medium take some time to adapt to the new environment. In this phase, the bacteria does not reproduce but prepares itself for reproduction. The cells are active metabolically and keep increasing in size. The cells synthesise RNA, growth factors and other molecules required for cell division.

Log Phase

Soon after the lag phase, i.e., the preparation phase, the bacterial cells enter the log phase. The log phase is also known as the exponential phase. This phase is marked by the doubling of the bacterial cells. The cell number increases in a logarithmic fashion such that the cell constituent is maintained. The log phase continues until there is depletion of nutrients in the setup. The stage also comes to a stop if toxic substances start to accumulate, resulting in a slower growth rate. The cells are the healthiest at this stage and researchers prefer to use bacteria from this stage for their experimental processes.

Plotting this phase on the bacterial growth curve gives a straight line. Upon calculation of the slope of this line, the specific growth rate of the organism is obtained. It is the measure of divisions per cell per unit of time.

Stationary Phase

In the stationary phase, the rate of growth of the cells becomes equal to its rate of death. The rate of growth of the bacterial cells is limited by the accumulation of toxic compounds and also depletion of nutrients in the media. The cell population remains constant at this stage. Plotting this phase on the graph gives a smooth horizontal linear line.

Death Phase

This is the last phase of the bacterial growth. At this stage, the rate of death is greater than the rate of formation of new cells. Lack of nutrients, physical conditions or other injuries to the cell leads to death of the cells.

This sums up all about the bacterial growth curve. Stay tuned to BYJU’S Biology for more updates.

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Frequently Asked Questions

What are the 4 phases of the bacterial growth curve?

The bacterial growth progresses in four phases namely – lag phase, log phase, stationary phase and death phase.

What does the bacterial growth curve show?

The bacterial growth curve shows the preparation, division, growth and death of the bacterial cells.

What are the things bacteria need to grow?

Bacteria require optimum temperature, pH, moisture, oxygen, carbon source, nitrogen source and other nutrients.

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