In the laboratory, bacteria are typically grown in broth contained in a tube or flask, or on an agar plate. These are considered closed or batch systems because nutrients are not renewed, nor are waste products removed. Under these conditions, the cell population increases in number in a predictable fashion and then eventually declines. As the population in a closed system grows, it follows a pattern of stages, called a growth curve. This growth pattern is most distinct in a shaken broth culture, because all cells are exposed to the same environment. In a colony, cells on the outer edge of a colony experience very different conditions from those at the center.
To maintain cells in a state of continuous growth, nutrients must be continuously added and waste products removed. This is called an open system, or continuous culture.
102 Chapter 4 Dynamics of Prokaryotic Growth
This growth curve is characterized by five distinct stages—the lag phase, the exponential or log phase, the stationary phase, the death phase, and the phase of prolonged decline (figure 4.17).
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