Understanding Bacterial Growth Curve: Phases | Biology Blog

                                    Bacterial Growth Curve 

In any biological system growth can be defined as the orderly increase of all chemical component . Increase of mass weight not really reflect growth curve because of the cells could be simply increasing their content of storage product such as glycogen . The idea of the bacterial growth curve was developed through careful observations and experiments done by early scientists in the late 1800s. They studied how bacteria grow and divided their growth process into different stages.Bacterial growth in batch culture can be modeled with four different phases -       

                      

•       Lag Phase 
  
  
•       Exponential Growth Phase
  
  
•       Stationary Phase   
  
  
•        Death Phase           

                                                                  

•              Figure of Growth Curve
  
                                                                 

1. Lag Phase -     During Lag Phase , bacteria adapt themselves to growth condition . It is the period where the individual bacteria are maturing and not yet able to divide . During this period of bacterial growth cycle synthesis of RNA , Enzymes and other molecules occur .
   
   
2. Exponential Growth Phase -  This phase is also known by another name called Log Phase . It is a period characterize by  cell doubling . The number of new bacteria appearing per unit time is proportional to the present population . If growth is not limited , doubling will continue at a constant rate , so both the number of cell and the rate of population increases double with each consecutive time period . For this type of exponential growth , plotting the natural logarithmic of   cell number against time produces a straight line .
   
   
3. Stationary Phase -   The growth rate slow as a result of   nutrient depletion and accumulation of toxic product . This phase is reached as the bacteria begin to exhaust the resources that are available to them . This phase is a constant value as the rate of bacterial growth is equal to the rate of bacterial death .
   
   
4. Death Phase -      Bacteria run out of nutrient and die . Death result from a number of factor ;  an important one is depletion of the cellular reserves of energy . like  growth , death  is a exponential function and hence in a logarithmic plot , the death phase is a linear decrease in number of viable cells with time . 

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