1. Bacterial growth curve consists of four phases: lag phase, log/exponential phase, stationary phase, and death phase. 2. During the lag phase, bacteria adapt to their environment and prepare for reproduction through metabolic activity without cell division. 3. The exponential phase is characterized by rapid, exponential cell division until nutrients are exhausted or toxic byproducts accumulate.

1. BACTERIAL GROWTH
CURVE

19. BACTERIAL
GROWTH CURVE

20. BACTERIAL GROWTH CURVE
Bacterial growth curve is a curve that represents the different phase of bacterial growth.A
Characteristic growth curve obtained in batch culture (culture in which no fresh nutrients
are added) consists of four phases.
1. Lag phase: During this phase bacteria adapt themselves to growth conditions. It is a
phase of intense metabolic activity in which bacteria prepare for reproduction;
synthesizing DNA, enzymes and other macromolecules needed for cell division.
Therefore, during this phase there may be increase in size (volume) but no increase in
cell number. The length of this phase depends on type of bacteria, quality of culture
medium in which bacteria is growing.
2. Log phase or Exponential phase: This phase is characterized by cell doubling. During
this phase the bacteria multiply at maximum rate and their number increases
exponentially or by geometric progression: 1,2,4,8, etc. or 2º,2¹,2²,2³……2ⁿ (where n=
number of generations) with time. For this type of exponential growth , plotting the
natural logarithm of cell number against time produces a straight line.

21. Since the bacteria is growing in a constant medium of batch culture (no fresh
nutrients added) therefore the duration of this phase is limited because of
exhaustion of nutrients, accumulation of toxic metabolic end products, decrease in
oxygen tension and increase in cell density.
3. Stationary phase: During this phase the growth rate slows down as a result of
nutrients depletion and accumulation of inhibitory end (toxic) products. Sooner
or later, the bacterial cells start dying and number of such cells balances the
number of new born cells. In other words growth rate becomes equal to death
rate in this phase.
4. Death or decline phase: During this phase death exceeds reproduction rate and
thus number of viable bacterial cells start declining. Finally after a variable
period, the entire bacterial population dies and culture becomes sterile.