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.