Summary
Maximization of microbial two-step conversion of 9α-fluorohydrocortisone to Δ1-dehydro-16α-hydroxy-9α-fluorohydrocortisone (triamcinolone) in a mixed culture of two microorganisms, Arthrobacter simplex and Streptomyces roseochromogenus, was attempted by a digital simulation, to optimize an operational parameter, pH, during batch cultivation.
A mathematical model of the steroid transformation in the mixed culture was constructed with nine differential equations. The kinetic parameters other than the Michaelis-Menten constants in the mathematical model varied with pH of the culture medium. The mathematical model facilitated the simulation of the effect of pH on steroid conversion in the mixed culture. A modified Simplex method of direct search was applied to optimize the switching time and the combination of pH values in the batch culture with several step-changes of pH. Varied-pH processes showed much higher conversion yields than the constant pH process. A process of 3-phase pH change is expected to be advantageous in practical operation because of its lower susceptibility to pH perturbation, though the yield is almost the same as that of the 2-phase process.
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Abbreviations
- a :
-
rate constant in the logistic model (l/h)
- b :
-
saturation constant in the logistic model (g/l)
- E :
-
volumetric enzyme activity (unit/l)
- f :
-
activity coefficient of an enzyme or an inhibitor (-)
- I :
-
volumetric inhibitor activity (unit/l)
- k m :
-
Michaelis-Menten constant (g/l)
- p :
-
yield factor of 16-hydroxylation by S. roseochromogenus (-)
- q :
-
first-order decay constant of an enzyme or an inhibitor (l/h)
- s :
-
steroid concentration (g/l)
- X :
-
cell concentration (g/l)
- α:
-
constant in the growth-associated term of the Luedeking model (unit/g)
- β:
-
constant in the non-growth-associated term of the Luedeking model (unit/g · h)
- γ:
-
inhibition coefficient for the growth of A. simplex (l/unit)
- δ:
-
repression coefficient for 20-ketoreductase synthesis (l/g)
- ε:
-
inhibition coefficient for 20-ketoreductase activity (l/g)
- μ:
-
specific growth rate (l/h)
- 1:
-
9α-fluorohydrocortisone (F2)
- 2:
-
Δ1dehydro-9α-fluorohydrocortisone (Δ1F2)
- 3:
-
Δ1dehydro-16α-hydroxy-9α-fluorohydrocortisone (F4)
- d :
-
Δ1-dehyrogenase
- h :
-
16α-hydroxylase
- i :
-
inhibitor
- k :
-
20-ketoreductase
- r :
-
Streptomyces roseochromogenus
- s :
-
Arthrobacter simplex
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Yoshida, T., Sueki, M., Taguchi, H. et al. Modeling and optimization of steroid transformation in a mixed culture. European J. Appl. Microbiol. Biotechnol. 11, 81–88 (1981). https://doi.org/10.1007/BF00518048
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DOI: https://doi.org/10.1007/BF00518048