Optimization of bioconversion conditions for vitamin D3 to 25-hydroxyvitamin D using Pseudonocardia autotrophica CGMCC5098

Abstract

The optimal culture conditions for bioconversion of vitamin D3 to calcifediol (25(OH)D3) were investigated by varying carbon and nitrogen sources, metal salt concentrations, initial pH, temperature, solvents, surfactants, and agitation speed. In the process of this microbial hydroxylation, the timing of the addition of vitamin D3, which is dissolved in ethanol, is of critical importance. Besides, the concentration of ethanol in zymotic fluid is the key factor to get high conversion ratio of vitamin D3. In particular, the optimal culture conditions were 1.5% glucose, 1.5% soybean cake meal, 0.5% yeast extract, 0.5% corn steep liquor, 0.3% CaCO3, 0.1% NaCl, 0.2% KH2PO4, pH 7.2 at 27 °C and the timing of the addition of vitamin D3 dissolved in 5% (v/v) ethanol was 48 h followed by the inoculation of seed culture broth. Under the optimized conditions, the conversion of vitamin D3 (1 g/L) by Pseudonocardia autotrophica CGMCC5098 in 50 L fermenter resulted in about 61.31% bioconversion ratio (639 mg/L) of 25(OH)D3 on the 5th day.