Generally applicable fed‐batch culture concept based on the detection of metabolic state by on‐line balancing

Abstract

In many microorganisms, flux limitations in oxidative metabolism lead to the formation of overflow metabolites even under fully aerobic conditions. This can be avoided if the specific growth rate is controlled at a low enough value. This is usually accomplished by controlling the substrate feeding profile in a fed-batch process. The present work proposes a control concept which is based on the on-line detection of metabolic state by on-line calculation of mass and elemental balances. The advantages of this method are: 1) the check of measurement consistency based on all of the available measurements, 2) the minimum requirement of a priori knowledge of metabolism, and 3) the exclusive use of simple and established on-line techniques which do not require direct measurement of the metabolite in question. The control concept has been linked to a simple adaptive controller and applied to fed-batch cultures of S. cerevisiae and E. coli, organisms which express different overflow metabolites, ethanol and acetic acid, respectively. Oxidative and oxidoreductive states of S. cerevisiae and E. coli cultures were detected with high precision. As demonstrated by the formation of acetic acid in E. coli cultures, metabolic states could be correctly distinguished for systems for which traditional methods, such as respiratory quotient (RQ), are insensitive. Hence, it could be shown that the control concept allowed avoidance of overflow metabolite formation and operation at maximum oxidative biomass productivity and oxidative conversion of substrate into biomass. Based on mass and elemental balances, the proposed method additionally provides a richness of additional information, such as yield coefficients and estimation of concentrations and specific conversion rates. These data certainly help the operator to additionally evaluate the state of the process on-line.

Control of yeast fed-batch process through regulation of extracellular ethanol concentration

“…The control strategy can also be based upon a calorimetric quotient by substituting the oxygen uptake rate with the heat production rate [23][24][25][26][27]. Alternatively, when the bioreactor is sufficiently instrumented, on-line mass balances can be constructed, from which a control strategy can be formulated [28,29]. However, note that for all of these approaches at least two measurements are required, versus only one when the overflow metabolite concentration is used.…”

Simple control of specific growth rate in biotechnological fed-batch processes based on enhanced online measurements of biomass

“…In addition, the biosynthesis of many products is closely dependant on reaching and maintaining the appropriate growth profiles [3][4][5][6]. In processes involving strains prone to metabolic bottlenecks, such as E. coli or S. cerevisiae, controlling the growth rate below a critical value is also necessary to prevent the formation of overflow metabolites causing decreased biomass productivity [7][8][9][10]. Hence, the ability to closely monitor and maintain the desired growth rate at various stages of a fed-batch process is essential in order to maximize productivity and ensure consistent product quality.…”

Real-time monitoring and control of microbial bioprocesses with focus on the specific growth rate: current state and perspectives

“…The latter approach has been explored by Bastin and Dochain (1986). Jobe et al (2003), Dabros et al (2010) , Fig. 3 Excerpt of a fed-batch culture of E. coli where the specific growth rate was maintained at a sufficiently low level to avoid overflow metabolite production.…”