6, 7, 8. Microbial growth rates

Question 1

what is the pattern of microbial growth rate?

Answer 1

• primary metabolism trophophase
  – low cell mass, limiting nutrient
• secondary metabolism idiophase
  – hugh cell mass, secondary metabolite

Question 2

what are the phases of growth?

Answer 2

• lag phase
  – intermediate accelerating phase
• exponential phase
• stationary phase
  – intermediate deceleating pahse
• death phase

Question 3

what is the lag phase?

Answer 3

• period of adjustment to new conditions
• little/no cell division (no population increase)
• may last from 1 hour to several days
• growth rate =(est)= 0

Question 4

what happens when multiple lag phases occur?

Answer 4

• diauxic growth

Question 5

what is the exponential phase?

Answer 5

• cells divide and generations times at minumum
• most rapid growth period
• cells have highest metabolic activity
• most susceptible to adverse environmental factors (radiation / antibiotics)
• primary metabolites produced
• biomass productivity can be calculated

Question 6

what is the stationary phase

Answer 6

• population size stabilises
• no. cells produced = no. cells dying
• overall cell number doesn’t increase
• cell divisions begin to slow down
• production of secondary metabolites

Question 7

what is the death phase?

Answer 7

• population size decreases
• no. cells dying > no. cells produced
• cell no. decreases at logarithmic rate
• cells lose ability to divide
• few cells remain alie for long period of time

Question 8

what are the different modes of operation?

Answer 8

• batch mode
• fed-batch mode
• continuous mode

Question 9

explain the modes of operation

Answer 9

• batch
  – all nutrients provided from start of fermentation with no extra feeding
• fed-batch
  – extra nutrients added at time intervals during fermentation to obtain higher cell densities / switch metabolism to produce specific product
  – no overflow / outlet to reactor so volume increases
• continuous
  – inlet and outlet benefit, steady state production ahcieved for long term production
  – chemostat
  – turbidostat
  – perfsion

Question 10

draw the graphs of the operation processes

Answer 10

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Question 11

what is an example of the primary metabolite?

Answer 11

• biomass and ethanol from baker’s yeast
• product accumulates in direct proportion to biomass

Question 12

what is an example of secondary metabolite? **

Answer 12

• penicillin

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Question 13

what are the characteristics to batch growth?

Answer 13

(C(x) = biomass concentration)
(u = specific growth rate)
(k(d) = death rate constant)

• lag phase
  – u = 0
• exponential phase
  – dC(x)/dt = u(max)C(x)
• declining growth phase
  – dC(x)/dt = uC(x)
• stationary phase
  – u = k(d)
• death phase
  – dC(x)/dt = -k(d)C(x)

Question 14

how to calculate u

Answer 14

• u = (dC(x)/dt)/C(x)
• Xt - XoE^(ut)
• ln(Xt) = ln(Xo) + u(delta)t
• u = (lnXt - lnXo)/(delta)t