Whole cell bioconversion of vitamin D₃ to calcitriol using Pseudonocardia sp. KCTC 1029BP

Abstract Calcitriol is an important drug used for treating osteoporosis, which can be produced from vitamin D₃. The current method of producing calcitriol from vitamin D₃ during cultivation of microbial cells results in low yields of calcitriol and high purification costs. Therefore, in this study, the steps of cell cultivation and bioconversion of vitamin D₃ to calcitriol were separated. Cells of Pseudonocardia sp. KCTC 1029BP were utilized as a whole cell catalyst to produce a high level and yield of calcitriol from vitamin D₃. In addition, the effects of bioconversion buffers, cyclodextrins, and metal salts on the production of calcitriol were comparatively examined and selected for incorporation in the bioconversion medium, and their compositions were statistically optimized. The optimal bioconversion medium was determined as consisting of 15 mM Trizma base, 25 mM sodium succinate, 2 mM MgSO₄, 0.08 % β-cyclodextrin, 0.1 % NaCl, 0.2 % K₂HPO₄, and 0.03 % MnCl₂. Using this optimal bioconversion medium, 61.87 mg/L of calcitriol, corresponding to a 30.94 % mass yield from vitamin D₃, was produced in a 75-L fermentor after 9 days. This calcitriol yield was 3.6 times higher than that obtained using a bioconversion medium lacking β-cyclodextrin, NaCl, K₂HPO₄, and MnCl₂. In conclusion, utilizing whole cells of Pseudonocardia sp. KCTC 1029BP together with the optimal bioconversion medium markedly enhanced the production of calcitriol from vitamin D₃.