Model-Based Optimization of Mannitol Production by Using a Sequence of Batch Reactors for a Coupled Bi-Enzymatic Process—A Dynamic Approach

Abstract

Multi-enzymatic reactions can successfully replace complex chemical syntheses, using milder reaction conditions, and generating less waste. The present model-based analysis compares the performances of several optimally operated Batch Reactors (BR) with those of an optimally operated serial Sequence of BRs (SeqBR). In multi-enzymatic systems, SeqBR could be more advantageous and flexible, allowing the optimization of costly enzymes amounts used in each BR in the series. Exemplification was made for the bi-enzymatic reduction of D-fructose to mannitol by using MDH (mannitol dehydrogenase) and the NADH cofactor, with the in situ continuous regeneration of NADH at the expense of formate degradation in the presence of FDH (formate dehydrogenase). For such coupled enzymatic systems, the model-based engineering evaluations are difficult tasks, because they must account for the common species’ initial levels, their interaction, and their dynamics. The determination of optimal operating modes of sole BR or of a SeqBR turns into a multi-objective optimization problem with multiple constraints to be solved for every particular system. The study presents multiple elements of novelty: (i) the proof of higher performances of an optimal SeqBR (including N-BRs) compared to a sole optimal BR operated for N-number of runs and (ii) the effect of using a multi-objective optimization criteria on SeqBR adjustable dynamics.

Concepts and Tools to Model GRCs, and Some Essential CCM Pathways in Living Cells 1. Generalities

“…As proved in the literature, the in-silico (math/kinetic modelbased) numerical analysis of biochemical or biological processes by using MSDKM or HSMDM models are proved to be not only an essential but also an extremely beneficial tool for engineering evaluations aiming (i) to determine with a higher accuracy the optimal operating policies of complex multi-enzymatic reactors, [5,[19][20][21][22][23], or of bioreactors including the biomass adaptation to the variable bioreactor environment over hundreds of cell cycles [2,9,[24][25][26], or even (ii) to easier and quickly simulate and analyse the performances/ characteristics of various GMO-s alternatives, by using the "metabolic flux analysis" (MFA), [26][27][28][29][30], together with the gene-knock-out technique) [9,10,14,[30][31][32].…”

“…Even if the multi-enzymatic systems are advantageous, the engineering part used to optimize such a complex process is not an easy task because it must account for the interacting enzymatic reactions, enzymes deactivation kinetics (if significant), multiple and often opposed optimization objectives, technological constraints, and uncertainties coming from multiple sources (model / constraints inaccuracies, disturbances in the control variables), and a highly nonlinear process dynamics [2,19,20,[22][23][24][33][34][35]. All these parametric/model/data uncertainties require updating (with a certain frequency) the enzymatic process model, the optimal operating policies of the reactor being determined by using rather deterministic (model-based) optimization rules [36].…”

“…All these parametric/model/data uncertainties require updating (with a certain frequency) the enzymatic process model, the optimal operating policies of the reactor being determined by using rather deterministic (model-based) optimization rules [36]. Multi-objective criteria, including economic benefits, operating and materials costs, product quality, etc., are used to off-line, or to on-line derive feasible optimal operating/control policies for various bioreactor types [34] by using specific numerical algorithms [20,22,23,25,32,35,[37][38][39].…”

“…The current (default) approach to solve the model-based design, optimization and control problems of industrial biological reactors is the use of unstructured models of Monod type (for cell culture reactors) [3] or of Michaelis-Menten type (if only enzymatic reactions are retained) [21,22,23,35,51,52] that ignores detailed representations of cell processes. The applied engineering rules are similar to those used by the CBE and inspired from the NSCT [25,34,53,[54][55][56][57][58][59][60].…”

Tryptophan Production Maximization in a Fed-Batch Bioreactor with Modified E. coli Cells, by Optimizing Its Operating Policy Based on an Extended Structured Cell Kinetic Model

“…Over the last few decades, there has been a continuous trend to develop more and more effective bioreactors [ 1 , 2 ] “to industrialize important biosyntheses for producing fine chemicals used in the food, pharmaceutical, or detergent industry, by using free-suspended or immobilized cell cultures (or enzymes) in suitable bioreactors (or enzymatic reactors)”, as reviewed by Maria [ 3 ]. The batch (BR), semi-batch (fed-batch, FBR), a serial sequence of BRs [ 4 ], and the continuously operated fixed-bed or three-phase fluidized-bed bioreactors (with immobilized biocatalyst) are successfully used to conduct biosyntheses aimed at replacing complex chemical and energetically intensive processes, as well as those generating toxic wastes [ 5 , 6 ].…”