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Mirobial / Nutrition / Environmental factors on growth / Control of…

- - - - Increasing of cell number or cell number or cell mass not cell size
    - - cell devides cells (asexual reproduction) Some bacteria increase number by budding or fragmentation
      - The time required to divide from 1 ->2 cells called doubling time or generation time
  - - - type of microbes
      - growth conditions
  - - - There are numerous factors affecting growth
      - A typical growth curve in closed system
        
        Bacterial Growth Curve : Lag Phase
        
        ✓ The population remained unchanged
        
        ✓ A period of adjustment to new environments and preparation for
        new cells
        
        ✓ No cell division occurs but increasing of cell mass and metabolic activity
        
        synthesizing cell components, nutrients
        
        replicating the chromosome
        
        ✓ The length of lag phase is dependent on
        
        species
        
        new conditions (media and physical)
        
        inoculum size, age
        
        Bacterial Growth Curve : Log Phase
        
        ✓ Number of cell increase exponnentially (Generation time can be calculated from this stage)
        
        ✓ Cells divide at a constant rate with a maximum activity (max growth rate)
        
        ✓ At the end of log phase, some cells stop dividing brcause depletion of nutrient and accumulation of toxic waste in the media and also not enough space.
        
        ✓ Also called “exponential phase"
        
        ✓ Most metabolically active and cells are sensitive to adverse conditions
        
        calculation of generation time
        
        g = t/n N = N0 x 2^n
        
        Bacterial Growth Curve : Stationary Phase
        
         Cell numbers become constant
        
         Cells stop growing because
        
        1) depletion of nutrients, space
        
        2) accumulation of toxic products
        
         Cells are resistance to adverse conditions
        
         Produce secondary metabolites e.g. antibiotics, pigments
        
         Spore formation occur in this phase
        
        Bacterial Growth Curve : Death Phase
        
         Death rate > Growth rate
        
         Autolysis may be occurred
        
         An exponential decrease in viable cell numbers
        
         Some growth measurement methods cannot observe death phase
      - In closed system, bacteria does not double endlessly
    - -  It is an open system in which contaminations can be occur.
      -  It is a type of fermentation in which constant addition and flow of
        solution occur.
      -  Yield is more than batch system.
      -  Microorganisms and sterile nutrients are added continuously and the nutrient solutions and microbes are transformed simultaneously.
  - - - Plate counts ( pour plate / spread plate)
      - Filtration
      - Direct microscopic count
      - Most probable number (MPN)
    - - Metabolic activity
      - Dry weight
      - Turbidity
- - - - several group of substances
        
        alcohol
        
        phenol
        
        iodine
        
        chlorine
    - - Conditions influencing antimicrobial activity; number of MO, type of MO, physical state of MO, concentration of antimicrobial agent, temperature, pH, duration of exposure
    - - cold
      - desiccation
      - heat
      - osmotic
      - pressure
      - filtration
      - radiation