When the medium has just been inoculated with some bacteria, there is a first phase (lag phase) when there is no apparent growth. During that phase, there are few cell divisions, and the number of cells does not increase. This phase can last a few hours. After that, the cell division rate rises to reach an exponential rate (this is the log phase) when the number of cells in the medium doubles every 20 minutes. This phase lasts a few hours, until the resources of the medium become scarce, or when the cells receive signals that the medium is too populated. The culture then enters a static phase when there is no modification of the number of cells (stationary phase). Normal depletion of the resources, and intoxication of the medium then leads to the death phase, when the number of cells decreases in the medium.
This is illustrated in the Figure 1.
View : Dr Chromo's lecture on 'Transformation'.
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