The rate of multiplication gets decreased and ceases altogether in due course as the exponential phase is no longer possible.
Now the cells pass into the stationary phase.
A stable number of cells can be reached by the establishment of an equilibrium between the rates of growth and death which is possible theoretically.
But the common situation is one in which neither growth nor death occurs but the cells remain in a state of suspended animation.
Some metabolic activity will be going on though the normal metabolism and growth no longer exists.
This metabolism is called endogenous metabolism which provides the cell with energy and intermediates required to maintain life.
Cessation of growth is due to the exhaustion of essential nutrients and accumulation of toxic waste products.
Various factors may induce the beginning of stationary phase, due to which cells can exhibit a corresponding variation in morphology and physiology between themselves and in comparison with exponential phase cells.
Stationary phase cells may have high levels of intracellular storage polymers such as polysaccharides (glycogen) and lipids (poly-beta-hydroxybutyrate) which are often virtually absent in exponential phase cells.
Gram positive organism may become gram negative in this phase.
Many secondary metabolites are produced by bacterial species at the onset of this phase that have stopped dividing.
Secondary metabolites are diverse in nature and each kind has a restricted taxonomic distribution.
Antibiotics and endotoxins are produced as secondary metabolites.
The initiation of sporulation generally occurs at the end of exponential phase or early in the stationary phase in case of spore forming species.
Since, many of the antibiotics and exotoxins producing bacteria are spore forming organisms, there may be the relation between sporulation and production of these metabolites.
The cells in a culture begin to die after a variable period of time in stationary phase.
They become incapable of growth when taken to a fresh medium.
There will be an increasing divergence between the total count (living and dead cells) and viable counts (living cells only).
There are various reasons for this death or loss of viability which might also have cause the cessation of growth at the onset of stationary phase.
There may be a brief stationary phase followed by a rapid death rate if the reason of cessation of growth is due to accumulation of toxic wastes.
There will be rapid fall in the total and viable count in some cases which is due to the lysis and liberation of cytoplasmic contents into the environment as microorganism are very prone to digest themselves.
This process is called autolysis which is the reason for the occurrence of bizzare cell shapes quite different from the normal range seen in exponential growth.
Some microorganisms may stay in the stationary phase for some days despite of the rapid degeneration and death.
The rapidity of the onset of death phase is an important factor that may influence the spread of infection.
Duration of this phase varies from a few hours to a few days.