Abstract:The production process for Arthrobacter simplex with high specific hydrocortisone A'-dehydrogenase activity was improved by medium optimization in parallel shake flask experiments. Using a genetic algorithm, the concentrations of 12 medium components (mineral salts and amino acid) were optimized within 144 experiments to give maximum specific hydrocortisone A'-dehydrogenase activity and biomass yield (full experimental plan: 1.5 x loL4 experiments). The specific hydrocortisone A'-dehydrogenase activity was improved by a factor of 4.5 to 1800 U g-'. With the optimized medium composition in a stirred tank reactor for batch production of A. simplex, a specific hydrocortisone A'-dehydrogenase activity of 2000-3000 U g -' dry biomass was achieved depending on harvest time (previously reported data: 18-37 U g-').
The transformation of microcrystalline hydrocortisone by free and immobilized cells of Arthrobacter simplex resulted in formation of prednisolone. The effect of medium composition, non-ionogenic surfactants and exogenous electron acceptors on the delta 1-dehydrogenase activity of free and immobilized cells is described.
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