Whole‐cell biotransformation of oleanolic acid by free and immobilized cells of <i>Nocardia iowensis</i>: Characterization of new metabolites

Abstract

In this study, Nocardia iowensis was used to transform oleanolic acid (OA) into oleanane derivatives. The first derivative, which was found after 24 h of cultivation, was the known and already described OA methyl ester. After 1 week, two other derivatives (oleanonic acid methyl ester and an unknown metabolite) were identified as new products of a biotransformation by N. iowensis . These oleanane metabolites were characterized by HPLC, HPLC‐ESI‐MS, and HPLC‐ 1 H NMR spectroscopy. The biotransformation was performed by suspended and immobilized cells (ICs) of N. iowensis . Cells immobilized in alginate beads were used in order to prepare a continuous process. The substrate uptake of free and ICs was similar, whereas the peak area of OA methyl ester of the ICs was only about 10% of the native cells. However, the final product (oleanonic acid methyl ester) concentrations were similar in both approaches, whereas the unknown metabolite 3 was only detected transiently in the medium of ICs. Based on these results, a new biosynthetic pathway for the biotechnological production of oleanonic acid methyl ester is proposed.