Growth of a Bacterial Cell

Growth of a Bacterial Cell

It can be defined as orderly increase in  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 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 population of a bacterial cell for determining the growth curve. The population of a bacterial cell is obtained by innoculating  a small number of innoculum 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 logarithm of cell number against time.

A bacterial cell undergoes four different growth phases and they are as follows:-

  1. Lag phase
  2. Log phase
  3. Stationary phase
  4. Death phase

Graphical representation of a growth phases of bacterial cell.

Growth Phases of Bacterial population
Growth Phases of Bacterial population

Where,On X axis L is equal to logarithm of number of cell.

On Y Axis T is equal to time in hours

Growth phases of a bacterial cell

1.Lag phase

Initially when we innoculate a 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 other 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 starts to multiply and cells enter in 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 in most of the biochemical and biological studies bacterial cells from this exponential growth phase are used.

If we plot a graph of logarithm of cell number against time on X axis it result in a straight line with positive slope.The multiplication rate and generation time of bacterial cell varies 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.

3.Stationary phase

As the cells enter in stationary phase the number of cells remain constant because generation time of 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 this 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 starts to die.Here death rate is higher than the growth rate and the death rate increases to 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 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.

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