Bacterial growth is the asexual reproduction, or cell division, of a bacterium into two daughter cells, in a process called binary fission. Providing no mutational event occurs the resulting daughter cells are genetically identical to the original cell. Hence, "local doubling" of the bacterial population occurs. Both daughter cells from the division do not necessarily survive. However, if the number surviving exceeds unity on average, the bacterial population undergoes exponential growth.
Factors Required for Bacterial Growth
The requirements for bacterial growth are:
(A)) Environmental factors affecting growth, and
(B) Sources of metabolic energy.
A. Environmental Factors affecting Growth
1. Nutrients. Nutrients in growth media must contain
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Exponential Phase or Logarithmic (Log) Phase. The cells multiply at the maximum rate in this exponential phase, i.e. there is linear relationship between time and logarithm of the number of cells. Mass increases in an exponential manner. This continues until one of two things happens: either one or more nutrients in the medium become exhausted, or toxic metabolic products, accumulate and inhibit growth. Nutrient oxygen becomes limited for aerobic organisms. In exponential phase, the biomass increases exponentially with respect to time, i.e. the biomass doubles with each doubling time. The average time required for the population, or the biomass, to double is known as the generation time or doubling time. Linear plots of exponential growth can be produced by plotting the logarithm of biomass concentration as a function of time. Importance : Antibiotics act better at this phase.
3. Maximal Stationary Phase. Due to exhaustion of nutrients or accumulation of toxic products death of bacteria starts and the growth cease completely. The count remains stationary due to balance between multiplication and death rate. Importance: Production of exotoxins, antibiotics, metachromatic granules, and spore formation takes place in this phase.
4. Decline phase or death phase. In this phase there is progressive death of cells. However, some living bacteria use the breakdown products of dead bacteria as nutrient and remain as