Factors Affecting Rates of Cell Growth

The rate of cell growth is influenced by temperature, pH, composition of medium, rate of air supply, and other factors. In the case that all other conditions are kept constant, the specific growth rate may be affected by the concentration of a certain specific substrate (the limiting substrate). The simplest empirical expression for the effect ofthe substrate concentration on the specific growth rate is the following Monod equation, which is similar in form to the Michaelis-Menten equation for enzyme reactions  

Several improved expressions for cell growth have been proposed. In the case that cells do not grow below a certain concentration of the limiting substrate, because ofthe maintenance metabolism, a term (h ) corresponding to the substrate concentration required for maintenance is subtracted from the right-hand side of Equation 4.6. Thus, 

Some substrates inhibit cell growth at high concentrations. Equation 4.9, one of the expressions for such cases, can be obtained on the assumption that excess substrate will inhibit cell growth, in analogy to the uncompetitive inhibition in enzyme reactions, for which Equation 3.42 holds  

The products by cell growth, such as ethyl alcohol and lactic acid, occasionally inhibit cell growth. In such cases, the product is considered to inhibit cell growth in the same way as inhibitors do in enzyme reactions, and the following equation (which is similar to Equation 3.41, for noncompetitive inhibition in enzyme reactions) can be applied  

Cell Growth in Batch Fermentors and Continuous Stirred-Tank Fermentors (CSTF) 

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