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 number 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.
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