Transcription
When provided with proper nutrients, a bacterial cell divides into two by the process called binary fission. This multiplication process is also influenced by other factors such as pH, temperature, and oxygen levels. The requirement of these factors varies from species to species.
This is how a bacterial cell divides into two. Two becomes four, four becomes eight, and so on. That means each time the population of bacteria becomes double in number. The time required for a bacterial cell to become double in number is called generation time. For example, the generation time of E. coli is 17 minutes, which means for every 17 minutes, a single cell of E. coli divides into two cells. Generation time depends on the surrounding environmental conditions and differs from species to species. When the division starts with one cell, there will be two cells in the first generation, four in the second generation, eight in the third generation, and so on.
Let's see how to calculate the generation time, but before that, we have to understand the bacterial growth curve and the different phases involved in it. A typical bacterial growth curve looks something like this. The growth curve consists of four different phases: lag phase, exponential or log phase, stationary, and death phase.
When a fresh medium is inoculated with some number of bacterial cells, the cells remain unchanged for some time in the lag phase. The cells start adjusting to the medium environment. The length of this phase depends on the size of inoculum, time required to recover from physical damage, and time required to synthesize enzymes.
The lag phase is followed by the log phase, where the cells multiply at the fastest rate. In this phase, the population doubles at each generation time. Then comes the stationary phase. The exponential phase cannot be continued forever as the nutrients in the medium exhaust after they are completely utilized. In the stationary phase, the cells stop dividing. However, the production of secondary metabolites like antibiotics and formation of spores still exists.
The cells enter into death phase if the incubation is continued after the stationary phase. In this phase, the number of viable cells decrease exponentially. The death of cells is due to the accumulation of lytic enzymes and cell wastes. This is the reason why the growth curve pattern appears low in the beginning as there is no start of growth in the lag phase, and slowly goes up during the log phase as the growth occurs rapidly and reaches the stationary phase where the cells stop dividing. In the death phase, the curve goes down as the cells start losing the viability.
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