Optimization of culture conditions for the bioconversion of vitamin D3 to 1α,25-dihydroxyvitamin D3 usingPseudonocardia autotrophica ID 9302

We assessed the ability of aPseudonocardia sp. from soil samples to bioconvert vitamin D₃. The optimal culture conditions for the bioconversion of vitamin D₃ to active 1α,25-dihydroxyvitamin D₃ were investigated by varying the carbon and nitrogen sources, the metal salt concentrations, the initial pH, and the temperature. Microbial transformations were carried out with the addition of vitamin D₃ dissolved in ethanol. They were sampled by extraction with methanol-dichloromethane and the samples were examined by HPLC. Optimum culture conditions were found to be 0.4% yeast extract, 1% glucose, 3% starch, 1% fish meal, 0.2% NaCl, 0.01% K₂HPO₄, 0.2% CaCO₃, 0.01% NaF, and pH 7.0 at 28°C. The optimal timing of the addition of vitamin D₃ for the production of calcitriol byPseudonocardia autotrophica ID 9302 was concurrent with the inoculation of seed culture broth. Maximum calcitriol productivity and the yield of bioconversion reached a value of 10.4 mg/L and 10.4% respectively on the 7th day in a 75 L fermenter jar under the above conditions.