Bacterial Growth Curve

Bacteria are a large group of single-celled microorganisms. They reproduce asexually by binary fission. These microorganisms grow rapidly and exponentially under favorable conditions. When grown in culture, predictable growth patterns develop in bacterial populations. This pattern can be represented graphically as the number of viable cells within the population over time and is known as a bacterial growth curve.

Bacterial growth curve is divided into four different phases of growth that is, Lag phase, Log Phase , Stationary phase and Death phase. Let us study in detail.

Lag Phase (1-4 hours)

Bacteria adapt to grow in the new environment. This is the time when individual bacteria have matured and are not yet able to multiply. The slope of this line is the organism's specific growth rate, measured as the number of cell divisions per unit time. Actual growing conditions vary depending on growing conditions.

Log Phase Or Exponential (6-8 hours)

Period characterized by doubling of cells. The number of newly emerging bacteria per unit time is proportional to the current population.

When growth is unrestrained, doubling continues at a constant rate, so both cell number and population percentage increase with each successive period.

The slope of this line is the organism's specific growth rate, a measure of the number of cell divisions per unit time. This actual rate depends on the frequency of cell division events and growth conditions that affect the chances of both daughter cells to survive.

Stationary Phase (hours to days)

Stationary phase is due to growth limiting factors. This is most often due to nutrient depletion or inhibitor formation. such an organic acid.
newly formed cells per minute = dying cells per minute The
cell death as a function of time is rather unpredictable and very difficult to explain. Another explanation for the stationary phase is not enough space in the cell.

Death Phase (Hours to Days)

Bacteria run out of nutrients and die, but cell numbers remain constant. The depletion phase is brought about by nutrient depletion, toxic build-up and autolytic enzymes. A few surviving cells may persist for months after most of the cells have died. These few viable cells may grow at the expense of released nutrients.