Microbial growth kinetics

Monod(40) proposed the use of a saturation-isotherm type of equation to relate the growth rate of a micro-organism culture to the prevailing feed concentration. This has become known as the Monod equation and is usually expressed as  

The graphical significance of the constants in the Monod equation are identical to the corresponding constants in the Michaelis-Menten relationship for enzyme kinetics (see Section 5.4.4). The specific growth rate initially increases with increas- 

Two possible explanations can be readily put forward as to why this form of equation should be suitable for describing the dependence of microbial growth rate on feed concentration. The first of these is that the equation has the same form as the theoretically based Michaelis-Menten equation used to describe enzyme kinetics. The chemical reactions occurring inside a microbial cell are generally mediated by enzymes, and it would be reasonable to suppose that one of these reactions is for some reason slower than the others. As a result the growth kinetics of the micro-organism would be expected to reflect the kinetics of this enzyme reaction, probably modified in some way, but in essence having the form of the Michaelis-Menten equation. 

The maximum growth rate in this instance does not occur at the highest substrate concentration, but rather at some intermediate value. Differentiation of equation 5.65 with respect to S and setting the result equal to zero enables the maximum growth rate to be determined. The maximum rate, Umax is shown to occur when  

The success with which this equation predicts the specific growth rate of a substrate-inhibited fermentation is somewhat varied. Typically, the constants may be adjusted to represent the experimental data with a fair degree of accuracy at low substrate values, but at substrate concentrations above IKSK, the predicted growth rate tends to be slightly greater than that observed in practice. 

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For those pesticides which are utilized as microbial growth substrates, sigmoidal rates of biodegradation are frequentiy observed (see Fig. 2). Sigmoidal data are more difficult to summarize than exponential (first-order) data because of their inherent nonlinearity. Sigmoidal rates of pesticide metabohsm can be described using microbial growth kinetics (Monod) however, four kinetics constants are required. Consequentiy, it is more difficult to predict the persistence of these pesticides in the environment. 

Panikov, N. S., 1995, Microbial Growth Kinetics. Chapman and Hall, London. 

D. Ramkrishna Statistical Models of Cell Populations. - Sh. Nagai Mass and Energy Balances for Microbial Growth Kinetics. -M.Moo-Young J. M. Scharer Methane Generation by Anaerobic Digestion of Cellulose-Containing Wastes. - B.Metz, N. W.F.Kossen,... 

KiMM is given the subscript, MM, to remind us that it reflects Michaelis-Menten enzyme kinetics as distinguished from KiM used above to model microbial growth kinetics (see Monod cases above). Note, is the same as KE in Box 12.2 when it s value represents the reciprocal of the equilibrium constant for the binding step. 

Table 5.17 shows some of the different expressions which have been used to describe microbial growth kinetics. (Note that the constants used in the table may not fulfill the same function and their units may be different, the table being intended to give some indication of the breadth of forms which have been employed.)... 

The domination of microbial growth kinetics by the Monod equation has led to the development of techniques to determine the constants Ks and fim used in that equation. Whilst n is in fact dependent on other parameters, such as temperature and pH, in the usual case these are specified, and a design procedure requires values of the Monod constants under these conditions. The yield coefficient Y will also be required in order to link calculations of microbial growth to substrate concentrations. 

Button, D. K. (1978). On the theory of control of microbial growth kinetics by limiting nutrient concentration. Deep-Sea Res. 25, 1163—1177. 

More extensive discussions of the theoretical aspects of chemostat culture have been published elsewhere (e.g. Herbert et al, 1956 Pirt, 1975 Bailey Ollis, 1977). Many of the theoretical principles apphed to microbial chemostat cultures can be applied successfully to animal cell cultures, although there are a number of instances where the behaviour of animal cells has been reported to deviate from the models used to describe microbial growth kinetics (Tovey, 1980 Boraston et al, 1984 Miller et al., 1988). 

As we shall see later in this chapter, this rectangular hyperbolic expression provides a useful model for microbial growth kinetics. At this point we should examine the two constants that determine the shape of the V versus [S] curve. The value of Vmax is the maximum rate of reaction, that is, the rate attained at high values of [S], When is reached, further increases in [S] have no effect on reaction rate. 

Mitchell DA, Stuart DM, Tanner RD (1999) Solid-state fermentation - microbial growth kinetics. In Flickinger MC, Drew SW (eds) The encyclopedia of bioprocess technology fermentation, biocatalysis and bioseparation, vol 5. WUey, New York, p 2407 Saucedo-Casteneda G, Gutierrez-Rojas M, Bacquet G, Raimbault M, Viniegra-Gonzalez G (1990) Biotechnol Bioeng 35 802... 

Button DK (1993) Nutrient-limited microbial growth kinetics overview and recent advances. Antonie Van Leeuwenhoek 63 225-235... 

In this connection it might be mentioned that Monod (1942) originally regarded the relationship that he proposed for microbial growth kinetics (based on an analogy to enzyme kinetics) as equally valid for continuous and discontinuous processes. One was here dealing with formal kinetics and a case of parameter fitting (Ks instead of K ). 

The connection between enzyme and microbial growth kinetics is... 

The present-day theory of microbial growth kinetics stems from, and is still dominated by, Monod s formulation (1942, 1949) of the function fi = /x(s), given in Equ. 2.54. Also, this relation is a homologue of the Michaelis-Menten equation Monod derived it empirically, and thus this is a formal kinetic equation. The consequence is a different interpretation of the parameters and K. The microbial growth rate is... 

Monod kinetics An unstructured model used to describe the correlation of substrate concentration with microbial growth kinetics. The model is based on enzymatic Michaelis-Menten kinetics ... 

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