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Log Phase

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Bacterial Growth Curve

Bacterial growth is defined as the increase in the population of bacteria by the proliferation of one bacterium into two daughter cells. A typical bacterial growth curve shows the preparation, division, growth and death of the bacterial cells.

The growth of microbes such as bacteria, yeasts or protozoa in batch culture could be shaped into four stages –

  • Lag phase
  • Log phase
  • Stationary phase
  • Death phase

Here, let’s look at bacterial growth in a log phase.

Log phase Overview

Log phase definition 

It is a growth period of a cluster of cells in a culture medium. During this phase, there is an exponential increase in the number indicated by a section of the growth curve. This section is a straight line segment when the logarithm of numbers is plotted against time.

Log phase, also referred to as the exponential phase or logarithmic phase, is one of the phases observed in a bacterial growth curve. The striking feature of this phase is the property of cell doubling through binary fission. The count of bacteria (new) that appear each time is proportionate to the current population. For any species of bacteria, there is a genetic determination of the generation time under specific growth conditions such as pH, temperature, nutrition, etc. This generation time is the intrinsic growth rate.

Doubling remains constant if growth is not restricted. Hence, the rate of population increases and the number of cells doubles with every sequent time period. The relationship between the number of cells and time in this phase is exponential. Consequently, a straight line is the outcome in this case of growth when the natural log of cell number is plotted against the factor of time. The specific growth rate of an organism is obtained from the slope of the straight line. This growth rate is a quantification of the count of divisions per cell per unit time. The bacterial growth curve is usually plotted on a semi-logarithmic graph imparting its appearance of a linear relationship.

However, the actual or the definite rate of such growth in a bacterial growth curve is dependent on the conditions of growth affecting the regularity of cell division occurrences and the prospect of daughter cells to survive. Bacteria (cyanobacteria) under favourable controlled criteria multiply their population quadruple times every day, furthermore can increase their population by threefold. This type of growth fails to sustain perpetually. This environment is soon deprived of nutrition and supplemented with wastes.

As cells in this log phase exhibit constant growth rate and a steady/consistent metabolic activity, the cells are preferred to be consumed for industrial applications and for research purposes. This stage is also the phase wherein bacteria are highly susceptible to the activity of antibiotics and disinfectants affecting cell-wall synthesis, DNA and protein.

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Frequently Asked Questions

What is the log and lag phase?

Lag phase is the phase where the cells grow in size and prepare for cell division. Next comes, the log phase where the cells divide in an exponential manner.

How do you extend the log phase?

The log phase can be extended by increasing the supply of nutrients.

Why is it important to use cells in the log phase?

Biologists prefer to use microbial culture in the log phase because at that stage the cells are the most healthy.

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