Kinetics of Microbial Growth

Transcription

1 Kinetics of Microbial Growth Unlimited growth Assuming t d 0.33 h, in 48 h, one cell would become 2.33 X cells If a cell weighs g, then the total would be 2.23 X g This would be 4000 times the weight of the earth! This obviously does not happen. Prof. Dr. Clem Kuek QAU Bioprocess/GrowthKinetics.doc 1

2 Factors Determining Growth & ynthesis of Products Absolute Factors Nutrients; ph; Temperature; Oygen Rate-Determining Factors Temperature; ph; Mass Transfer; Energy Transfer Prof. Dr. Clem Kuek QAU Bioprocess/GrowthKinetics.doc 2

3 Kinetics of Batch Culture Growth Rate, r Δ Δt or as t becomes infinitesimally small d Units e.g. g cells ml dt -1 h -1 pecific Growth Rate, r Units e.g. g g -1 cells ml -1 h -1 Prof. Dr. Clem Kuek QAU Bioprocess/GrowthKinetics.doc 3

4 Kinetics of Batch Culture 2 Phases of growth in batch culture pecific Growth Rate Ln Population ize Lag Acceleration Eponential Deceleration Maimum population Death ma Time Prof. Dr. Clem Kuek QAU Bioprocess/GrowthKinetics.doc 4

5 Kinetics of Batch Culture 3 The eponential phase may be described by where d dt (2.1) [microbial biomass] t time (h) specific growth rate (h -1 ) Cell Number Eponential Phase Time Prof. Dr. Clem Kuek QAU Bioprocess/GrowthKinetics.doc 5

6 Kinetics of Batch Culture 4 Integrating equation 2.1 gives t 0 e t (2.2) where o [original biomass] t [biomass after time t] e base of natural log Taking natural log, equation 2.2 becomes ln t ln 0 + t Log Cell Number Eponential Phase Thus, plot of ln X vs. t gives straight line in the eponential phase, slope of which Tim Prof. Dr. Clem Kuek QAU Bioprocess/GrowthKinetics.doc 6

7 Determining r from data Time (h) X (g L -1 ) (g L -1 ) Prof. Dr. Clem Kuek QAU Bioprocess/GrowthKinetics.doc 7

8 Determining r from data 2 Growth Rate, r 1. Hand-drawn tangent r y 2. Numerical differentiation Difference between values on either side of data point r 2 t t Curve fitting r 2 ln ln t 3 t 1 [ ] Prof. Dr. Clem Kuek QAU Bioprocess/GrowthKinetics.doc 8

9 Determining from data Using the values for growth determined as described previously, pecific Growth Rate may be estimated by the relationship r However, in batch culture, does not remain constant. ma pecific Growth Rate ubstrate concentration is a major affecting factor. ubstrate concentration Prof. Dr. Clem Kuek QAU Bioprocess/GrowthKinetics.doc 9

10 Determining ma from data 1. By tabulation of values for through the eponential phase of the culture. Time (h) (g L -1 ) r (h -1 )* r / ma *r via numerical differentiation. Prof. Dr. Clem Kuek QAU Bioprocess/GrowthKinetics.doc 10

11 Prof. Dr. Clem Kuek QAU Bioprocess/GrowthKinetics.doc 11 Determining ma from data 2 2. Lineweaver-Burke plot K r K dt d r s m m s + + Taking the reciprocal and since r m m m m m K K K r s s s

12 Determining ma from data 3 Compare Ks + m m with y m + c Thus, when 1 is plotted against 1, we get 1 Note large number of points in this area Intercept 1 ma lope K s ma 1 Prof. Dr. Clem Kuek QAU Bioprocess/GrowthKinetics.doc 12

13 Yield factor Y Y the ratio of product or cell quantity resulting from a certain quantity of input e.g. Y /s Yield of cell weight per unit weight substrate utilized Y p/n Yield of product weight per unit weight of nitrogen utilized Determination of Yield Factor on carbon substrate, Y /s r rs ms s + Y s rs Y r 1 + m s s where r s rate of consumption of carbon substrate m s maintenance coefficient on carbon substrate Prof. Dr. Clem Kuek QAU Bioprocess/GrowthKinetics.doc 13

14 Determination of Yield Factor on carbon substrate, Y /s 2 Thus, when r s is plotted against r, we get r s Note large number of points in this area Intercept m s lope 1 Y /s r Prof. Dr. Clem Kuek QAU Bioprocess/GrowthKinetics.doc 14

15 The Importance of ma For processes where maimal growth rates are diserable, attainment of ma in culture is important. ince ma is determined by the genetics of the microorganism conditions of culture Attainment of ma has implications for both determinants. For other processes, identification of ma is important so that it can be avoided e.g. in the production of secondary metabolites. Prof. Dr. Clem Kuek QAU Bioprocess/GrowthKinetics.doc 15

16 The Importance of the Yield Factor Y Y indicates the degree of efficiency of the conversion of substrates into desired products. Attainment of efficient Y translates directly into economic efficiency, and thus productivity. ince Y is determined by the genetics of the microorganism conditions of culture nature of the input (substrate) Attainment of an efficient Y has implications for the determinants. Prof. Dr. Clem Kuek QAU Bioprocess/GrowthKinetics.doc 16