Growth Curves of S. elongatus under salt stress and low carbon

When liquid media is inoculated with bacteria and the cell population is counted at intervals, it is possible to plot a typical bacterial growth curve that shows the increase in the number of cells over time. Such growth curves show four distinct phases of growth:

• Lag phase: There is slow growth or lack of growth due to the physiological adaptation of cells to culture conditions or the dilution of exoenzymes (due to initial low cell densities).
• Log or exponential phase: Optimal growth rates are seen in this phase. Cell numbers double at discrete time intervals known as the mean generation time.
• Stationary phase: During this phase, the growth (cell division) and death of cells occur at the same rate, resulting in the number of cells being constant. The reduced growth rate is usually due to a lack of nutrients and/or a buildup of toxic waste constituents.
• Decline or death phase: Here, the death rate exceeds the growth rate, resulting in a net loss of viable cells.

This is one of the simplest methods used to analyze trends in growth because it uses a spectrophotometer to track changes in the optical density (OD) over time. In other words, as the number of cells in a sample increases, the transmission of light through the sample will decrease.

Growth curves for certain freshwater cyanobacterial species are carried out under salt stress to account for sucrose production in the particular strain. This is because sucrose is naturally produced intracellularly in these strains to balance the osmotic pressure of a saline environment.