Testing Monod : growth rate as a function of glucose concentration in Saccharomyces cerevisiae

[摘要] ENGLISH ABSTRACT: The complexity of microbial systems has presented serious obstacles to the quantification offermentation processes. Using computer modelling techniques progress has been made inmonitoring, controlling and optimising microbial systems using material balancing techniques andempirical process models. The Monod equation is among the most commonly used models and isbased on empirical findings with no mechanistic basis. Monod presents a simple model to describethe growth of a cell in a defined nutrient environment. The Monod equation is mathematicallyanalogous to the formula that was proposed by Michaelis and Menten to describe enzyme kinetics.Both equations describe a hyperbolic function with a half-saturation constant (K_s in the monodequation and K_m in the Michaelis Menten equation) but the meaning of the two saturation constantsK_s and K_m is different. In number of studies K_s and K_m are used as if they are equivalent. Incontrast to Michaelis-Menten kinetics, which describes a process catalysed by a single enzyme,Monod kinetics describes an overall process involving thousands of enzymes.The Monod equation describes the specific growth rate of a microbial cell as the function of alimiting substrate concentration. The aim of this study was to test this principle, for Saccharomycescerevisiae VIN13 under glucose limited aerobic chemostat conditions. The VIN13 was observed tofollow the Monod description and when compared with other growth kinetic models gave one of thebest fits to the data. A functional relationship between the half-saturation constant, K_s, andMichaelis Menten constant, K_m, was there after derived. This was achieved by using metaboliccontrol analysis (MCA) to explain when K_m of the transporter becomes equal to the K_s. Using thedeductions obtained from MCA a core kinetic model was then formulated to demonstrate that theK_s can either be smaller, equal or higher than the K_m of the transporter, depending on the fluxcontrol distribution in the model.

[发布机构] Stellenbosch University