GROWTH AND
PHYSIOLOGY OF BACTERIA
Mrs.Rashmi.S
GROWTH
 Defined as the orderly increase in the
quantity of the cellular components or
structures, followed by cell division

Bacteria divide by binary fission
Generation Time
The time required for a cell to
divide or for the population to
double .
1
2
4
8
16
Two types of bacterial counts

Total count: Total number of cells in the
sample

Viable count: Number of living cells
capable of multiplication
Total count is obtained by:

Direct Microscopic counting.

Coulter counter.

Nephalometer.

Determination of the Cell Mass.

Measurement of cell Nitrogen.
Viable count:
1.
Determination of cells by Plate Count
2.
Membrane Filter method
BACTERIAL GROWTH CURVE
Bacterial counts are made at intervals and plotted
in relation to time.
Curve exhibits following phases
1.
Lag Phase
2.
Log Phase
3.
Stationary Phase
4.
Phase of decline
GROWTH CURVE
LAG PHASE:
 Characterized by a period during which there
is no increase in the number of cells.
 Cells enlarge ,as enzymes and metabolic
intermediates are built up
 Duration of Lag phase varies with the Spp.,
size of the inoculum, nature of the culture
medium and environmental factors .
LOG OR EXPONENTIAL PHASE:

Cells start dividing

Number increase exponentially by geometric
progression with time.

If log of number of cells plotted against time,
results in a straight line
STATIONARY PHASE :

Cell division stops due to depletion of
nutrients and accumulation of toxic products.

Balance is maintained between cell division
and cell death

Viable count remains stationary for some time.
PHASE OF DECLINE :

Phase of decrease in the cell number due to
cell death

Total count continues with out decline.

Viable count decreases
Continuous culture
Maintaining microbial population
in logarithmic phase of growth in
a constant environment.
Methods of Continuous culture

CHEMOSTAT

TURBIDOSTAT
Bacterial Nutrition
Bacteria are classified nutritionally into:




PHOTOTROPHS
CHEMOTROPHS
AUTOTROPHS
HETEROTROPHS
Based on Oxygen requirements bacteria are
classified into:
AEROBES (Eg: Vibrio)
ANAEROBES (Eg: Clostridium)
MICROAEROPHILLIC (Eg: Helicobacter)
Based on Temperature requirements bacteria are
classified into

MESOPHILLIC

THERMOPHILLIC

PSYCHROPHILLIC
BACTERIAL METABOLISM

OXIDATION

FERMENTATION

O-R POTENTIAL
FACTORS INFLUENCING
BACTERIAL GROWTH







Carbondioxide
Temperature
Moisture and Drying
H+ ion concentration
Light
Osmotic Effect
Mechanical and Sonic Stress
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