Bacterial Growth II

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Bacterial Growth II

• Diauxic Growth
• Growth Rate Constant

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Bacterial Growth II
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Bacterial Growth II
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Diauxic Growth

• Key features of diauxic growth
• Microbes have a choice of carbon source in the
  medium
• They will utilise first the one which is closest
  to the one they were using before inoculation, or
• They will use the simplest structure first
  (usually glucose)

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Diauxic Growth

• Key features of diauxic growth
• Initially the growth curve is the same as a
  standard growth curve
• The stationary phase is in fact another lag phase
• In this second lag phase new enzymes are being
  synthesised by the bacteria to utilise the
  secondary carbon source

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Diauxic Growth

• Key features of diauxic growth
• The second lag phase is then followed by a second
  exponential phase followed by the stationary
  phase and death phase

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Growth Rate Constant

• During exponential growth
• The number of microorganisms doubles at regular
  intervals.
• The time taken for the population to double is
  called the generation time
• The number of generations per hour is called the
  exponential growth rate constant, represented as
  K.

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Growth Rate Constant

• The growth rate constant and the generation time
  for a culture can be found as follows

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Growth Rate Constant

• Two measurements of the population size (N) are
  taken during the exponential phase t hours apart
• We call the first measurement N0, and the second
  Nt.
• During time t. there were a certain number of
  divisions (or generations) which we will call n.

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Growth Rate Constant

• Then
• n log10 Nt - log10 N0
• log10 2

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Growth Rate Constant

• As log10 2 is always equal to 0.301
• n log10 Nt - log10 N0
• 0.301
• YOU ARE NOT EXPECTED TO KNOW HOW THIS EQUATION IS
  DERIVED OR TO MEMORISE IT BUT WILL BE REQUIRED
  TO USE IT!

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Growth Rate Constant

• Once we know there are n generations in t hours,
  we can find the growth rate constant, K (number
  of generations per hour)
• K n / t generations-1
• We can also find the generation time, which is
  equal to 1 / K hours, or 60 / K minutes

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Growth Rate Constant

• A students counts the number of bacteria in a
  liquid culture at 10 am, and again at 3 pm. Her
  cells counts are as follows
• 10am 25 000 cell cm-3
• 3 pm 200 000 cell cm-3
• Calculate the growth rate constant (K) and the
  generation time for this culture.