Generation time or doubling time is the unit of me sure of bacterial growth; it is the time it takes for the size of a bacterial population to double.

Bacterial Growth Curve

When a bacterium is inoculated into a new culti medium, it exhibits a characteristic pattern or chan in cell numbers. This pattern is called a growth cur (FIG. 10-4). The normal growth curve of bacteria h four phases, the lag phase, the log or exponent growth phase, the stationary phase, and the dea phase. During the lag phase there is no increase cell numbers. Rather, the lag phase is a period adaptation during which bacteria are preparing f reproduction: synthesizing DNA, RNA, other stn tural macromolecules, and the various enzym needed for cell division.

After the lag phase, the bacteria begin to multip by binary fission, doubling in number every tin they divide. This is the log phase of growth, al called the exponential phase. It is so named becau the logarithm of the bacterial cell numbers increas linearly with time. During this phase, bacterial repr duction occurs at a maximal rate for the specific set growth conditions. It is during this period that tl generation time of the bacterium is determined.

After some period of exponential growth, the st tionary growth phase is reached. The stationai phase often occurs when the maximum populatic density that can be supported by the available в sources is reached. Once the stationary growth phas is reached, there is no further net increase in bacterii cell numbers. During the stationary phase the growt

FIG. 10-4 Growth curve for bacteria has four distinct phases: lag, exponential (log), sta­tionary, and death.

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