BACTERIAL GROWTH CURVE: MAIN CHARACTERISTICS - BIOLOGY - 2025

The bacterial growth curve is a graphical representation of the growth of a bacterial population over time. Analyzing how bacterial cultures grow is crucial to be able to work with these microorganisms.

For this reason, microbiologists have developed tools that allow them to better understand its growth.

Between the 1960s and 1980s, the determination of bacterial growth rates was an important tool in various disciplines, such as microbial genetics, biochemistry, molecular biology, and microbial physiology.

In the laboratory, the bacteria are generally grown in a nutrient broth contained in a tube or on an agar plate.

These crops are considered closed systems because nutrients are not renewed and waste products are not removed.

Under these conditions, the cell population predictably increases in number and then decreases.

As the population in a closed system grows, it follows a pattern of stages called a growth curve.

The 4 stages of bacterial growth

Bacterial growth period data typically produces a curve with a series of well-defined phases: adaptation phase (lag), exponential growth phase (log), stationary phase, and death phase.

1- Adaptation phase

The adaptation phase, also known as the lag phase, is a relatively flat period on the graph, in which the population appears not to grow or is growing at a very slow rate.

Growth is delayed mainly because inoculated bacterial cells require a period of time to adapt to the new environment.

In this period the cells prepare to multiply; This means that they must synthesize the molecules necessary to carry out this process.

During this delay period, enzymes, ribosomes, and nucleic acids necessary for growth are synthesized; energy is also generated in the form of ATP. The length of the lag period varies somewhat from one population to another.

2- Exponential phase

At the beginning of the exponential growth phase, all the activities of bacterial cells are directed towards increasing cell mass.

During this period, cells produce compounds such as amino acids and nucleotides, the respective building blocks of proteins and nucleic acids.

During the exponential or logarithmic phase, cells divide at a constant rate and their numbers increase by the same percentage during each interval.

The duration of this period is variable, it will continue as long as the cells have nutrients and the environment is favorable.

Because bacteria are more susceptible to antibiotics and other chemicals during this time of active multiplication, the exponential phase is very important from a medical point of view.

3- stationary phase

In the stationary phase the population enters a survival mode in which cells stop growing or grow slowly.

The curve evens out because the rate of cell death balances the rate of cell multiplication.

The decrease in growth rate is caused by depletion of nutrients and oxygen, excretion of organic acids and other biochemical contaminants in the growth medium, and a higher density of cells (competition).

The length of time cells remain in the stationary phase varies depending on the species and environmental conditions.

Some populations of organisms remain in the stationary phase for a few hours, while others remain for days.

4- Death phase

As limiting factors intensify, cells begin to die at a constant rate, literally perishing in their own waste. The curve now slopes down to enter the death phase.

The speed with which death occurs depends on the relative hardiness of the species and how toxic the conditions are, but is generally slower than the exponential growth phase.

In the laboratory, refrigeration is used to delay the progression of the death phase, so that the cultures remain viable for as long as possible.

References

1. Hall, BG, Acar, H., Nandipati, A., & Barlow, M. (2013). Growth Rates Made Easy. Molecular Biology and Evolution, 31 (1), 232–238.
2. Hogg, S. (2005). Essential Microbiology.
3. Nester, EW, Anderson, DG, Roberts, EC, Pearsall, NN, & Nester, MT (2004). Microbiology: A Human Perspective (4th ed.).
4. Talaro, KP, & Talaro, A. (2002). Foundations in Microbiology (4th ed.).
5. Zwietering, M., Jongenburger, I., Rombouts, F., & Van Riet, K. (1990). Modeling of the Bacterial Growth Curve. Applied and Enviromental Microbiology, 56 (6), 1875–1881.