GROWTH CURVE

 GROWTH CURVE

Growth curve is a plot between cell mass and fermentation time in a fermentation reaction. The significance of this curve is that it shows the increase in the cell mass with respect to the time of the fermentation reaction. Growth curve is drawn when an inoculum (initial mass of required microbes) is added to the nutrient media in the fermentor.

Growth curve can be divided into 4 phases:-

-          Lag phase

-          Log/exponential phase

-          Stationary phase

-          Decline/ death phase

LAG PHASE:-

-          In this phase the inoculum is added.

-          Whenever a microbe is added to a nutrient medium, the microbes do not consume the nutrients in the medium and grow at the very beginning, but every microbe need some time to adjust itself to the new environment.

-          It is the lag phase in which these microbes adjust themselves to the environment.

-          Hence there is absolutely no increase in the cell mass in this phase.

-          Lag phase ends as microbes adjust themselves to the external environment.

LOG/EXPONENTIAL PHASE:-

-          In this phase microbes are completely ready to consume the nutrients from the medium and reproduce.

-          Microbes reproduce exponentially (1 to 2....... 2 to 4 ....... 4 to 8 and so on).

-          Hence in this phase there is a drastic increase in the cell mass, the reaches a maximum point.

-          In this phase the cell birth > cell death.

-          In the lag phase microbes produce the products of our interest.

-          This phase ends when the nutrients are almost exhausted.

STATIONARY PHASE:-

-          In this phase the microbes compete for nutrients and space.

-          As a result of this stress microbes produce secondary metabolites.

-          Secondary metabolites are of great importance to the pharmaceutical industry.

-          In this phase cell birth = cell death.

-          Hence there is neither increase nor decrease in the cell mass. Hence the graph looks like a plateau.

-          This phase ends when all the nutrients of the medium are exhausted.

DECLINE/DEATH PHASE:-

-          In this phase microbes are deprived of nutrients and start dying.

-          So we can say that cell birth < cell death.

-          Hence there is a sharp fall in the cell mass and in the slope of the graph too.