Chapter 3 Efficiency of growth and product formation 3.0 Introduction In order to develop a rational approach to improving rates of metabolite production, it is necessary to consider the fate of the nutrients that are required for its synthesis. However, overcoming the major flux control points within a metabolic pathway may not lead to metabolite overproduction if the energetic consequences of the alteration are unfavourable to the organism. nergetics In this chapter we will consider growth and product formation from an energetics perspective perspective. In the first part of the chapter, the stoichiometry of growth is considered in some detail. The relationships between product formation and growth are then described, together with approaches to determining key parameters of growth efficiency. Finally, classes of metabolites are defined, according to the relationships petween energy and metabolite synthesis. Examples of commercially significant products in each class are also discussed cquations describing growth and product formation stoichiometry are presented in this pter. These are intended to illustrate a quantitative approach to the study of efficiency of growth and product formation. You are not expected to recall all details of the equations rather the factors that need to be considered in such a quantitative analysis. If this approach is entirely new to you, we recommend Chapters 8-10 of the BIOTOL text Bioprocess Technology: Modelling and Transport Phenomena, which deals with the modelling of growth and product formation 3.1 Growth stoichiometry 3.1.1 Yield coefficients In any quantitative ass of growth and /or pro on, it is essential to link formation of microbial biomass and products with the utilisation of substrate and nutrients. In the case of microbial biomass production, the total amount of cell mass comew formed is often proportional to the mass of substrate utilised. Mathematically this is as the com responding ratio, or yield coefficient: △X x/s △s AX= amount of biomass produced As=amount of substrate consumed36 Chapter 3 Efficiency of growth and product formation 3.0 Introduction In order to develop a rational approach to improving rates of metabolite production, it is necessary to consider the fate of the nutrients that are required for its synthesis. However, overcoming the major flux control points within a metabolic pathway may not lead to metabolite overproduction if the energetic consequences of the alteration are unfavourable to the organism. In this chapter, we will consider growth and product formation from an energetics perspective. In the first part of the chapter, the stoichiometry of growth is considered in some detail. The relationships between product formation and growth are then described, together with approaches to determining key parameters of growth efficiency. Finally, classes of metabolites are defined, according to the relationships between energy and metabolite synthesis. Examples of commercially significant products in each class are also discussed. Since process technologists rely on quantitative relationships, many seemingly complex equations describing growth and product formation stoichiometry are presented in this chapter. These are intended to illustrate a quantitative approach to the study of efficiency of growth and product formation. You are not expected to recall all details of the equations, rather the factors that need to be considered in such a quantitative analysis. If this approach is entirely new to you, we recommend Chapters 8-10 of the BIOTOL text ‘Bioprocess Technology: Modelling and Transport Phenomena’, which deals with the modelling of growth and product formation. energetics perspective 3.1 Growth stoichiometry 3.1.1 Yield coefficients In any quantitative assessment of growth and/or product formation, it is essential to link formation of microbial biomass and products with the utilisation of substrate and nutrients. In the case of microbial biomass production, the total amount of cell mass formed is often proportional to the mass of substrate utilised. Mathematically this is expressed as the corresponding ratio, or yield coefficient: yield coefficient where AX = amount of biomass produced AS = amount of substrate mnsumed