04 monod chemostat

04 monod chemostat - CEE 266 ENVIRONMENTAL BIOTECHNOLOGY...

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Unformatted text preview: CEE 266 ENVIRONMENTAL BIOTECHNOLOGY Lecture 4 (Monod Growth and Chemostat Kinetics) Typical Growth Curve for a Bacterial Population Batch culture: a closed-system microbial culture of fixed volume. Figure 6.10 Exponential Phase Growth   Log phase growth is first order   Growth rate ∝ to population size   lnX vs. t is linear, slope = µ   µ units are 1/t (i.e. hr-1) Monod Growth Kinetics  Relates specific growth rate, µ, to substrate concentration  Empirical---no theoretical basis—it just “fits”!  Have to determine µmax and Ks in the lab  Each µ is determined for a different starting S µmax S µ= Ks + S € Monod Growth Kinetics   Looks like Michaelis-Menten, but variable is different   First-order region, S << KS, the equation can be approximated as µ = µmaxS/Ks   Center region, Monod “mixed order” kinetics must be used S << KS mixed order µmax µ, 1/hr   Zero-order region, S >> KS, the equation can be approximated by µ = µmax S, mg/L S >> KS Michaelis Menten vs. Monod   Michaelis Menten   Kinetic expression derived (theoretical)   Monod   Empirical expression   Enzyme concentration increases with time   Constant enzyme pool   Pure enzymes   Growing microbes   Non-growing microbes   Relates growth rate to S   v vs. S where v is velocity   µ vs S   Km is half saturation constant   Ks is half saturation constant Cell Growth and Binary Fission Figure 6.1 The Rate of Growth of a Microbial Culture Figure 6.8 Calculating Microbial Growth Parameters Figure 6.9 Doubling Time N0 initial population (@t=0) Nt = N0 x 2n Nt population at time t log Nt = log N0 + nlog 2 n number of generations n = (log Nt – log N0)/log 2 g generation (doubling) time = (log Nt – log N0)/log 2 K growth rate constant = 3.3 (log Nt-log N0) * g is measured only in exponential phase! The Mathematics of Exponential Growth   Increase in cell number in an exponentially growing bacterial culture is a geometric progression of the number 2   Relationship exists between the initial number of cells present in a culture and the number present after a period of exponential growth: N = No2n where N is the final cell number, No is the initial cell number, and n is the number of generations during the period of exponential growth The Mathematics of Exponential Growth   Generation time (g) of the exponentially growing population is g = t/n where t is the duration of exponential growth and n is the number of generations during the period of exponential growth   Specific growth rate (k) is calculated as k = 0.301/g Example Question   You determine that a coconut cream pie has 1 million (106) Staphylococcus aureus cells in it. You estimate that the food preparer did not wash hands and probably inoculated the cream with 1000 S. aureus.   If the pie was made 5 hours ago, how many generations have occurred? How long is each generation?   If the pie was refrigerated for the first 2 hours, how many cells would you have counted? Solution Without refrigeration: g = 0.5 hr With refrigeration: N = 64,000 Continuous Culture: The Chemostat   Continuous culture: an open-system microbial culture of fixed volume   Chemostat: most common type of continuous culture device   Both growth rate and population density of culture can be controlled independently and simultaneously   Dilution rate: rate at which fresh medium is pumped in and spent medium pumped out   Concentration of a limiting nutrient Schematic for Continuous Culture Device (Chemostat) Figure 6.11 Continuous Culture: The Chemostat   In a chemostat   The growth rate is controlled by dilution rate   The growth yield (cell number/ml) is controlled by the concentration of the limiting nutrient   In a batch culture growth conditions are constantly changing; it is impossible to independently control both growth parameters The Effect of Nutrients on Growth Figure 6.12 Continuous Culture: The Chemostat   Chemostat cultures are sensitive to the dilution rate and limiting nutrient concentration   Too high a dilution rate, the organism is washed out   Too low a dilution rate, the cells may die from starvation   Increasing limiting nutrient concentration results in greater biomass but same growth rate Steady-State Relationships in the Chemostat Figure 6.13 ...
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