The growth of a Bacterial Cell
It can be defined as an orderly increase in the quantity of all cell components of a cell.The cell increases in its size, shape and weight and further undergoes cell division.The bacterial cell undergoes different growth phases.This growth phases of the bacterial cell can be studied by plotting a growth curve.
As we know studying growth pattern of an individual bacterial cell is impossible due to its small size so here we use the population of a bacterial cell for determining the growth curve. The population of a bacterial cell is obtained by inoculating a small number of inoculum from old culture to a suitable fresh culture media and growth of a cell is monitored at regular interval of time.The growth curve is plotted by using the logarithm of cell number against time.
A bacterial cell undergoes four different growth phases and they are as follows:-
- Lag phase
- Log phase
- Stationary phase
- Death phase
Graphical representation of growth phases of the bacterial cell.
Where On X-axis L is equal to the logarithm of a number of the cell.
On Y Axis T is equal to the time in hours
Growth phases of a bacterial cell
Initially, when we inoculate an old bacterial cell to a new fresh medium the bacterial cell does not carry out immediate cell division and the inoculated population remains steady.As the bacterial cell get exposed to a new fresh medium these cells try to adjust in the new environment like present nutrients, pH, temperature as well as on another hand this cell synthesize amino-acids, protein, RNA, enzyme and intermediate metabolic products which are further necessary for growth and cell division.
The time of lag phase may vary from species to species due to various environmental factor. At the end of lag phase, the bacterial cells start to multiply and cells enter in the logarithmic phase of growth.
2. Logarithmic phase
This log phase is also called as exponential growth phase.In this growth phase of bacterial all cell multiply and carry out cell division.Cell division in this growth phase is constant and maximum.Here the number of cells increases exponentially with time.In this growth phase, all bacterial cells are small in size and biologically active as they are constantly dividing so into most of the biochemical and biological studies bacterial cells from this exponential growth phase are used.
If we plot a graph of the logarithm of cell number against time on X axis it results in a straight line with positive slope.The multiplication rate and a generation time of bacterial cell vary from species to species under different environmental condition.At the end of log phase the growth rate decrease that is generation time of cell increases.After the end of log phase, the bacterial cell enters in stationary phase.
As the cells enter in stationary phase the number of cells remain constant because generation time of a cell is very low.It occurs due to various factors like depletion of nutrients, accumulation of toxic waste products, change in pH etc. Due to all these factors in this phase the growth rate is equal to death rate and the total number of cells till the end of stationary phase remains constant.
If we plot a graph of log of cell number against time a straight line parallel to X-axis is formed with the end of this phase the death phase starts.
4. Death phase
In death phase of growth, the bacterial cells start to die.Here death rate is higher than the growth rate and the death rate increases to a maximum at the end of death phase. There are various factors responsible for this phase like exhaustion of nutrients, accumulation of toxic waste products.drastic changes in pH etc.
If we plot a graph of log of a number of cells against time on X axis a straight line with negative slope will be observed.Here with the death phase the bacterial growth curve end.
These are the growth phases of a bacterial cell.