FMB LEC FINALS: 2 - GROWTH CHARACTERISTICS OF BACTERIA

• Bacterial growth


  An increase in bacterial numbers
• Bacterial division


  • Binary fission (single cell divides into two identical cells)
  • Budding
  • Aerial spore formation
  • Fragmentation
• Generation time


  The time required for a cell to divide (and its population to double)
• Most bacteria have a generation time of 1 to 3 hours; others require more than 24 hours per generation
• Logarithmic representation of bacterial populations

  Bacterial division occurs according to a logarithmic progression (two cells, four cells, eight cells, and so on)

  
• Phases of growth


  1. Lag phase

  2. Log phase (or exponential growth phase)

  3. Stationary phase

  4. Death phase (or logarithmic decline phase)
• Lag phase


  Little or no change in the number of cells, but metabolic activity is high
• Log phase (or exponential growth phase)


  Bacteria multiply at the fastest rate possible under the conditions provided

  
• Stationary phase


  Equilibrium between cell division and death
• Carrying capacity


  The number of organisms that an environment can support
• Death phase (or logarithmic decline phase)


  The number of deaths exceeds the number of new cells formed
• Direct measurement of microbial growth

  1. Plate counts

  2. Filtration

  3. Most probable number (MPN) method

  4. Direct microscopic count

  
• Plate counts


  Determining the number of bacteria in a sample by counting the number of colony-forming units (CFU) on a solid culture medium

  
• Filtration


  Bacteria are retained on the surface of a membrane filter and then transferred to a culture medium to grow and subsequently be counted
• Most probable number (MPN) method


  A statistical estimation used for microbes that will grow in a liquid medium

  
• Direct microscopic count


  Microbes in a measured volume of a bacterial suspension are counted with the use of a specially designed slide

  
• Estimating bacterial numbers by indirect methods

  1. Spectrophotometry (measuring turbidity)

  2. Measuring metabolic activity

  3. Measuring dry weight

  
• Spectrophotometry


  Determining turbidity by measuring the amount of light that passes through a suspension of cells

  
• Measuring metabolic activity


  Assuming the amount of a certain metabolic product is in direct proportion to the number of bacteria present
• Measuring dry weight


  For filamentous organisms (fungi and bacteria), a convenient method of growth measurement

  
• BACTERIAL DIVISION

  
  

  • an increase in bacterial nos.

  Bacterial growth
• Bacterial growth is an ____________________ in bacterial nos.

  increase
• The normal reproductive method of bacteria is _________ ________________, in which a single cell divides into two identical cells.

  binary fission
• The normal reproductive method of bacteria is binary fission, in which a ___________ cell divides into _______ identical cells.

  single

  two
• Some bacteria reproduce by budding, aerial spore formation (some filamentous bacteria (some actinomycetes) produce chains of conidiospores carried externally at the tip of the filaments), or fragmentation(a few filamentous spp.)
• A diagram of the sequence of cell division

  
• 1 sequence of cell division in bacteria

  Cell elongates

  DNA is replicated
• Cell elongates

  DNA is replicated


  1 sequence of cell division in bacteria
• 2 sequence of cell division in bacteria

  Plasma membrane begins to constrict

  New wall is made
• Plasma membrane begins to constrict

  New wall is made


  2 sequence of cell division in bacteria
• 3 sequence of cell division in bacteria

  Cross-wall forms

  - complete separation of 2 DNA copies
• Cross-wall forms

  - complete separation of 2 DNA copies


  3 sequence of cell division in bacteria
• 4 sequence of cell division in bacteria

  Cells separate

  - 2 identical cells are ganerated
• Cell separate

  - 2 identical cells are generated


  4 sequence of cell division in bacteria
• True of False

  A new cell is generated from binary fission?

  False, the same cell will be produced
• GENERATION TIME

  
  

  • the time required for a cell to divide (and its population to double)

  Generation time
• Generation time is the time required for a cell to ____________ (and its population to ____________)

  divide

  double
• Generation time varies considerably among _________________ and with ____________________ conditions.

  organisms

  environmental
• Most bacteria have a generation time of 1 to 3hours; others require more than 24 hours per generation.
• Visual representation of increase in bacterial no. over five generations. The no. of bacteria doubles in each generation.

  
  

  The superscript indicates the generation; that is, 2(5) = 5 generations.doubles