Implementation of a Specific Rate Controller in a Fed-Batch E. Coli Fermentation

Abstract

The specific growth rate is one of the most important process variables characterizing the state of microorganisms during fermentations mainly because the biosynthesis of many products of interest is often related with the values assumed by this parameter. In the particular case of the fed-batch operation of Escherichia coli for the production of recombinant proteins, it is important to maintain the specific growth rate below a certain threshold in order to avoid the accumulation of acetic acid throughout the fermentation and, additionally, it is often argued that both pre-and the post-induction specific growth rates should be closely controlled in order to achieve maximum productivities of the desired recombinant protein. In a previous work the authors have developed and validated by simulations a strategy for the automatic control of the specific growth rate in E. coli fed-batch fermentations based on an asymptotic observer for biomass and on developed estimators for the specific growth rates. The main purpose of the present work was to implement experimentally the developed observer, estimator and controller in a real fed-batch fermentation process. For that purpose a data acquisition and control program was developed in LabVIEW that allows the acquisition of the necessary on line data (off gas and dissolved oxygen concentration and culture weight) and the calculation of the feeding rates using the developed equations. The feedforward-feedback controller developed was able to keep the culture growing in an exponential phase throughout the fermentation without accumulation of glucose and acetate.

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

“…The specific growth rate (μ) is an essential process variable above all because it is characteristic of the physiological state of microorganisms and related to the biosynthesis of many products of interest (Rocha et al 2008). With regard to bioprocesses, μ has an influence on four main aspects: biomass production, product quantity, cellular state, and product quality.…”

Applying a Metabolic Footprinting Approach to Characterize the Impact of the Recombinant Protein Production in Escherichia coli

“…Fermentation conditions were monitored and controlled via a computer supervisory system. A closed-loop feeding control algorithm was employed to maintain the growth rate (µ) constant in the fed-batch culture [17]. The algorithm is based on a Monod kinetic model using glucose as the only growthlimiting substrate and can be represented by the following equation:…”

Adaptive Control of Biomass Specific Growth Rate in Fed-Batch Biotechnological Processes. A Comparative Study

“…The biomass specific growth rate (SGR), defined as the ratio of the biomass growth rate and the amount of biomass in culture broth, is the most important variable in biotechnological processes. It influences the physiological state of a microbial culture, production of cell biomass and desired products, quantity and quality of products [6][7][8], as well as the rate of product synthesis. Because of the control mode, fed-batch processes overcome substrate inhibition and overflow effects and allow high cell density and product concentrations [9].…”