Under ideal conditions, the growth of a population of bacteria occurs in several stages termed lag, log, stationary, and death.
During the lag phase, active metabolic activity occurs involving synthesis of DNA and enzymes, but no growth.
Geometric population growth occurs during the log, or exponential phase, when metabolic activity is most intense and cell reproduction exceeds cell death.
Following the log phase, the growth rate slows and the production of new cells equals the rate of cell death. This period, known as the stationary phase, involves the establishment of an equilibrium in population numbers and a slowing of the metabolic activities of individual cells. The stationary phase reflects a change in growing conditionfor example, a lack of nutrients and/or the accumulation of waste products.
When the rate of cell deaths exceeds the number of new cells formed, the population equilibrium shifts to a net reduction in numbers and the population enters the death phase, or logarithmic decline phase. The population may diminish until only a few cells remain, or the population may die out entirely.