The Model

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The model illustrates the main growth phases the B. subtilis undergoes. These are identified as the lag phase, the exponential phase and the stationary phase. The death phase is a constitutive event and it is possible that it exerts an influence on the three phases discussed below. However, to simplify a complicated model, it is less relevant in this case and therefore is not included in this model. The M-file used to generate the model below is located in the Appendices section, its link can be found at the bottom of this page.


Key Phases of Bacterial Growth


During the lag phase, the rate of growth is slow due to two main reasons, B. subtilis is absorbing nutrients in the medium and the replication machinery is being switched on. The higher the concentration of nutrients in the medium, the faster the rate of bateria growth.

As a result, the volume of the bacteria increases, followed by an increase in the number of bacteria.


Both colony number and cell volume increase exponentially during this phase. Our model assumes concentration of the nutrients inside the bacteria is constant.


The growth of the colony ceases in number and in volume due to a finite concentration of nutrients, hence it does not have a gradient. Other causes may be death and cell division.

According to the model, the maximum growth of the bacteria is determined by the concentration of nutrients available initially.

To further enhance the accuracy of the model, the following information will be extracted from experimental data:

  • Time span of lag phase, stationary phase and exponential phase
  • The growth rate


Dry lab hub

Growth Curve

Genetic Circuit



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