Microbial growth in Closed Cultivation Systems Open Cultivation

Microbial growth in: • Closed Cultivation Systems • Open Cultivation Systems • Semi-Open Cultivation Systems

Closed Cultivation Systems • Operates in a closed system. • All materials are added to the system at the start of the process, the system is then closed and products removed only when the process is complete. • Also called Batch Cultivation Process/System • The most widely used system for growing microorganism.

Open Cultivation Systems • It allows continuous processing with substrate (nutrients in medium) entering and end product leaving out of the system. • Also called Continuous Cultivation Process/System. • Steady state condition is maintained, in which – The rate of increase of cell biomass with time is equal to zero. – The total number of cells are constant and – The total volume in the bioreactor are constant.

Semi-Open Cultivation Systems • Also called semi-batch cultivation • Allows either input of substrate in the system or output of end product from the system but not both.

Maintenance energy and yield concepts, and Estimation of biomass • Stoichiometry – Mass and Molar Relationships between thre reactants consumed and products formed can be determined using Stoichiometric calculations Example. C 6 H 12 O 6 ------- 2 C 2 H 6 O + 2 CO 2 Substrate Products Total mass and Number of atom of each element these two quantities is constant during any Chemical and Biochemical reactions.

Maintenance energy Cell consumed Substrate from the external environment and channel it into different metabolic pathways. Some substrate may be directed into growth and product synthesis and some is used to generate energy for maintenance activities. Substrate requirement for maintenance is different for different organism and culture conditions. The specific rate of substrate uptake for maintenance activities is known as maintenance coefficient , m. A maintenance coefficient is used to describe the specific rate of substrate uptake for cellular maintenance, or m = - [d. S/dt]m /X Unit of maintenance coefficient , m. is kg substrate (kg biomass)-1 S-1

• For product formed in the metabolic pathways which generate ATP, the rate of production is related to cellular energy demand. • Growth is usually the major energy requiring function of cells, therefore if production is coupled to energy metabolism, product will be formed whenever there is growth. • However ATP is also required for other activities known as maintenance or maintenance energy. • For Example – Cell mobility. – Turnover of cellular components. – Adjustment of membrane potential and internal p. H.

Yield Concept • The extent to which reactants are converted to product is expressed as the reaction yield. • Generally yield is the ratio of mass or mole of product formed to the mass or moles of reactant consumed. • If more than one products or reactants is involve in the reaction, the particular compound of interest must be identified. • e. g. The yield of glutamic acid from glucose is 0. 6 g g-1. • are expressed in terms of yield coefficients or yield factors (Y) • Yield coefficients (Y) is used to quantify the nutrient requirement and production characteristics of an organism

The carbon requirement for biomass production under aerobic conditions may be estimated from the cellular yield coefficient (Y) which is defined as:

• The yield is an important term in bioprocess analysis because of the complexity of metabolism or frequent occurrence of side reactions. • Despite this complexity yield principle can be applied to cell metabolism to relate flow of substrate in metabolic pathways to formation of biomass and other products.

Definition of Yield coefficients (Y) can be mathematically generalized as- ΔF YFG = -----ΔG Where, YFG is the yield factor, F and G are substances involved in metabolism, ΔF is the mass or moles of F produced and ΔG is the mass or moles of G consumed. -ve sign shows the consumption of G

• Several yield coefficients or yield factors include– Yield of biomass from substrate (Yxs) – Yield of biomass from oxygen(Yxo) – Yield of product from substrate(Yps) – ------------

• (Yxs) is defined as mass or mole of Biomass produced per unit mass or mole of substrate consumed. • (Yps) is defined as mass or mole of product produced per unit mass or mole of substrate consumed. • (Ypx) is defined as mass or mole of product produced per unit mass or mole of Biomass formed. • (Yxo) is defined as mass or mole of Biomass produced per unit mass or mole of oxygen consumed. • (Ycs) is defined as mass or mole of carbon dioxide produced per unit mass or mole of substrate consumed. • (YATP) is defined as mass or mole of Biomass produced per unit mass or mole of ATP formed.

Parameters of growth and analysis of growth data • • • Nutrient Composition of the medium Temperature Dissolved oxygen p. H of the medium Degree of mixing

Estimation of biomass Total mass and Number of atom of each element These two quantities is constant during any Chemical and Biochemical reactions. Therefore the estimation of biomass can be done by using Stoichiometric calculations with the help of – Biomass Yield – Product Yield

The carbon requirement for biomass production under aerobic conditions may be estimated from the cellular yield coefficient (Y) which is defined as: • (Yxs) is defined as mass or mole of Biomass produced per unit mass or mole of substrate consumed. • (Yps) is defined as mass or mole of product produced per unit mass or mole of substrate consumed. • (Ypx) is defined as mass or mole of product produced per unit mass or mole of Biomass formed. • (Yxo) is defined as mass or mole of Biomass produced per unit mass or mole of oxygen consumed.

• 1. What is the “glucose effect” and why are certain cells affected by it? • 2. What are the problems faced with rapidly metabolising substrate? • 3. Explain the role of water in fermentation media. • 4. Industrial byproducts are used as fermentation substrate. Comment