Log Phase

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

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 exponential phase or logarithmic phase, is one of the phases observed in the bacterial growth. The striking feature of this phase is the property of cell doubling through binary fission. The count of bacteria (new) that appear each unit 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 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 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 nutrition deprived soon 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 is highly susceptible to the activity of antibiotics and disinfectants affecting cell-wall synthesis, DNA and protein.

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