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.

3.

4.

Log Phase Stationary Phase 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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