The bacteria life cycle consists of the lag phase, the log or exponential phase, the stationary phase and the death phase. Factors that influence bacterial growth bear heavily on this cycle.
Bacteria do not grow during the lag phase. However, they do adjust to their environment and metabolize, that is, produce vitamins and amino acids needed for division. They begin making copies of their DNA, and if the environment supplies plenty of nutrients, the lag phase may be very short. Then the bacteria will proceed to the next phase of their life.
Log or Exponential Phase
During the log or exponential phase, bacteria multiply rapidly, even exponentially. The time it takes for a culture to double is called "generation time," and under the best conditions, the fastest bacteria can double in about 15 minutes. Other bacteria take days.
Within a bacterium, the DNA copy drifts to the opposite side of the membrane. The bacterium then pulls apart, creating two identical "daughter cells," which begin dividing anew. This process is called binary fission.
During the stationary phase, bacteria growth dwindles. Due to accumulating waste and a lack of space, bacteria cannot maintain the clip of the log or exponential phase. If the bacteria moves to another culture, however, rapid growth may resume.
During the death phase, bacteria lose all ability to reproduce, which becomes their death knell. Like the log or exponential phase, bacterial death may occur as rapidly as their growth.
Factors that Influence Growth
Temperature, acidity, energy sources and the presence of oxygen, nitrogen, minerals and water all affect bacterial growth, thus affecting the bacteria life cycle. Optimal growing conditions depend on the bacteria. Psychrophiles, for example, thrive in arctic conditions while hyperthermophiles grow best in hot environments, such as ocean vents. Allaliphiles require highly acidic environments while neutrophiles prefer places that are neither acidic nor basic. Of course, these are only two of many possible examples.