Differences in Bacterial Growth Curves

Bacterial growth is defined as the division of one bacterium, resulting in two identical cells, in a process called binary fission, thereby doubling the bacteria population. All three cells are genetically identical. The bacteria population goes through exponential growth, in order to survive and grow. In the natural environment conditions are not always viable for the bacteria growth curve; however, in labs scientists create a perfect habitat, in which bacteria grow predictably, showing the bacteria growth curve.

Significance

• Bacteria are all around us and pose health threats, such as infection. When a bacterium is exposed to good growing conditions, a new cell wall grows through the center of the bacterium, forming two new cells. The two new cells may then divide into four new cells. In the optimum environment within a lab, including the necessary energy source, nutrients, pH, and correct temperature, the bacteria will grow predictably along the growth curve. This gives scientists knowledge of how certain bacteria behave and how to suppress their growth.

Lag Phase

• Lag phase is the first phase in the bacteria growth curve. Lag phase is the phase in which bacteria will adapt to certain growth conditions, such as moisture or heat, in their surrounding habitat. It is also the phase where the bacteria are maturing. When in lag phase, bacteria do not have the ability to divide and grow slowly. It is during the lag phase of the bacterial growth cycle that synthesis of RNA and enzymes occurs.

Exponential Phase

• Exponential phase, which is commonly referred to as the log phase, is the phase known for cell doubling. The metabolic machinery is now running, so the bacteria start multiplying exponentially, doubling in number every few minutes. Doubling will continue at a constant rate to ensure that both the number of cells and the rate of population increase double with each consecutive time period. The actual rate of growth depends upon the growth conditions, which affect the frequency of cell division and the probability of both cells surviving.

Stationary Phase

• Stationary phase, the third phase on the bacteria growth curve, is when the growth rate begins to slow due to nutrient depletion and increased toxicity. The bacteria begin to run out of the resources used to multiply. In the stationary phase, the rate of bacterial growth is equal to the rate of bacterial death. The growth is stabilized at this point.

Death Phase

• The death phase is the last phase in the bacteria growth cycle. Toxic waste products build up through the stationary phase and once the bacteria enter into death phase, the food is completely depleted, killing the bacteria. Bacterial growth can be suppressed with bacteriostats, any chemical that stops bacteria from reproducing, without necessarily killing the bacteria. In nature, where more than one bacterial species is present, the growth of microbes is more dynamic and continual, making the death phase sometimes nonexistent for certain bacteria.