Bacterial Growth Curve

What is the Bacterial growth curve?

  • A characteristic curve, also known as a bacterial growth curve or growth cycle, is produced when the growth of a microbial population is periodically monitored by graphing the logarithm of the number of viable bacteria against time on a graph.
  • The growth curve of the microbial population is hyperbolic as a result of the exponential growth pattern of bacteria.
  • In batch culture, there is an early period of no growth (lag phase), followed by a period of rapid development (exponential growth), a period of leveling off (stationary phase), and eventually a period of declining viable cell count (death or decline phase).
  • There is a transition stage in between each of these phases (curve portion).

What are the phases of bacterial growth?

                Even while comprehending the differences between the lag, log, stationary, and death phases of a cell growth curve despite the fact that it may appear like elementary biology content, using that knowledge in active cell culture reveals a deeper understanding of microbiological processes.

              By paying great attention, those of us who are knowledgeable about cell culture can successfully scale up production with less stress and heartache or optimize growth circumstances. The little things that the uninformed could overlook are significant. . Knowing what they are is critical, but understanding what they are secret is much more crucial.

Lag Phase:

  • The Lag phase is the time after the addition of microorganisms to a new culture medium when there is typically no quick doubling of the population.
  • This phase is also known as the adaptation phase because microorganisms do not grow or divide rapidly during this time; instead, they require some time to adapt to their surroundings.
  • However, this does not imply that the cells are dormant; on the contrary, during this period, each cell grows larger than usual.
  • Microorganisms are well prepared for cell division at the phase’s conclusion.

Exponential Phase:

  • In the exponential phase, microbial cells divide as quickly as they can give their genetic capacity, the characteristics of the medium, and the circumstances of their growth.
  • During this phase, microbial growth is steady and their numbers regularly double.
  • This phase of microbial growth is balanced, which implies that the production rates of all the components of the cells are constant.
  • Plotting the log of the number against the results of the time during this period results in a straight line.
  • Population in this stage of growth is very homogenous in terms of metabolic activity, cellular chemical makeup, and physiological characteristics

  Stationary phase:

  • The stationary phase is the period of bacterial growth when there is no longer a net rise in the population.
  • The population expansion of microorganisms eventually stops during this phase due to a closed system, and the growth curve becomes horizontal.
  • Due to an equilibrium between the rate of reproduction and death, or when population growth stops but metabolic activity continues, the population remains constant.
  • Increased bacterial cell density, nutrient depletion, oxygen restriction, the slow development of microorganisms, and the buildup of hazardous secondary metabolites are only a few of the factors that cause the microbial population to reach stationary environments.

Death and Decline Phase:

  • The number of viable cells falls exponentially at a constant pace during the death phase.
  • As bacteria proliferate at various rates, so do their rates of death.
  • It was believed that many environmental factors, such as the depletion of vital nutrients and the accumulation of harmful wastes, kill microorganisms.

What is an open system in the bacterial growth phase?

                        A continuous culture (Open system) system maintains stable environmental conditions by supplying nutrients continuously and removing waste regularly. By inserting a new, sterile media in this instance, the cell volume and cell concentration are kept constant.

What are the types of open systems?

Two major types of an open systems are commonly used;


          A microbial culture is continually fed nutrients at a predetermined rate while also being harvested concurrently to maintain the culture volume. This procedure is known as a chemostat.


         The turbidostat is a continuous culture device in which the specific growth rate (r) of the bacterial population becomes a dependent variable while the population density of an organism (or its food) remains constant. Turbidostat cultures are effective instruments for determining the biological constraints on population expansion.

What is a closed system in the bacterial growth phase?

                     In a closed culture, the system is not supplemented with additional nutrients or cleaned of waste. Closed systems have predicted growth curves that cultures will adhere to.


Rimsha Bashir
Rimsha Bashir

Rimsha Saith is a highly knowledgeable microbiologist with a keen interest in the field. Her expertise and passion are in her writing for Microbiology. As a writer, Rimsha has authored numerous articles that have been well-received by both health and medical students and industries.

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