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Published by Daniel V Guebel and Nester V Darias Studied and Presented by

Optimization of the citric acid production by Aspergillus niger through a metabolic flux balance model. Published by Daniel V Guebel and Nester V Darias Studied and Presented by Alaa Kububja and Meteab Al-Otaibi. Introduction. Leading source of citric acid is aspergillus niger fermentation

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Published by Daniel V Guebel and Nester V Darias Studied and Presented by

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  1. Optimization of the citric acid production by Aspergillus niger through a metabolic flux balance model Published by Daniel V Guebel and Nester V Darias Studied and Presented by Alaa Kububja and Meteab Al-Otaibi

  2. Introduction • Leading source of citric acid is aspergillus niger fermentation • Several efforts made to develop dynamical models • The acid producing stage, Idiophase,

  3. Paper Objective Based on metabolic flux analysis, a mathematical model is developed aiming for: • Better understanding and description of the process of citric acid production • Helping in the design of the best genetic strategies leading to the optimization of citric acid production rate

  4. Idiophase Stages • Early Idiophase 1 mol glucose + 1.5 mol O2 3.81g biomass + 0.62 mol citric acid + 0.76 mol CO2 + 0.37 mol polyols • Medium Idiophase 1 mol glucose + 2.4 mol O2 1.54g biomass + 0.74 mol citric acid + 1.33 mol CO2 + 0.05 mol polyols • Late Idiophase 1 mol glucose + 3.9 mol O2 + 0.42 mol polyols  0.86 mol citric acid + 2.41 mol CO2

  5. Model Development • Hypothesis: existence of a close energetic coupling between the citric acid production and the intracellular pH regulation (due to strong acidic conditions for A. niger, extracellular pH =2) • Focusing at the idiophase stage (80-220 hrs culture time) when the growth drops and acid production becomes the main cellular activity

  6. Model Development (cont.) • Establishing the transient idiophase nature by stoichiometric analysis • Computing the main intracellular fluxes by application of material and physiological constraints at culture time 120 hrs.

  7. Determination of the rate of GABA cycle dNH4+(out)/dt+dNH4+(c) /dt+dNH4+(m)/dt=0 (1) dNH4+(out)/dt=Vgen(out)(NH4+)-Vuptake(c)(NH4+)=0 (2) dNH4+(c) / dt = Vuptake(c)(NH4+) - Vdiss(NH4+ (c)) + Vcatab(AA(c)) - Vuptake(m)(NH4+) = 0 (3) dNH4+(m)/dt = Vuptake(m)(NH4+)-Vdiss(c)(NH4+ (m)) – R14 + Vcatab(AA(m)) = 0 (4) By summation of (2)-(4) R14 = (Vcatab(AA) + Vgen(out)(NH4+ )) – (Vdiss(NH4+ (c)) + Vdiss(NH4+ (m)) = 0 (5) Pyruvate(c) + (1/3) H2O  CO2 + (2/3)NADH2(m) + (1/3) NADH2(c) + (1/3) FADH2(m) +(1/3) H+(m) R14

  8. Determination of the rate of GABA cycle (cont.) dNH3(c) /dt = Vdiss(NH4+ (c)) + Vleak(NH3(m)) - Vleak(NH3(c)) = 0 (6) dNH3(out) /dt = Vleak(NH3(c)) - Vgen(NH4(out)) = 0 (7) dNH3(m)/dt = Vdiss(NH4+ (c)) + Vleak(NH3(m)) = 0 (8) From (6) to (8), we obtain: Vleak(NH3(c)) = Vdiss(NH4+ (c)) + Vleak(NH4+(c)) =0 (9) By substituting (9) in (5) R14 = Vcatab(AA) (10)

  9. Effects on A. niger idiophase synthesis to changes in metabolic processes

  10. Results • Citric productivity would be increased in 45% by • Increase citric acid synthesis rate through: • Increasing glucose uptake • Decreasing biosynthesis rate of by products (polyols) • Decreasing fluxes diverting mass from the the pathway leading to citrate pressure

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