Efficient biotransformation of ginsenoside Rb1 to Rd by isolated Aspergillus versicolor, excreting β-glucosidase in the spore production phase of solid culture.

Ginsenosides are the major pharmacological components in ginseng. Microorganisms from a ginseng field were isolated to identify transformation of ginsenosides. Based on HPLC and LC-MS analysis, strain LFJ1403 showed strong activities to transform ginsenoside Rb1 to Rd as the sole product. Phylogenetic analysis of 18S rDNA indicated that LFJ1403 belonged to Aspergillus versicolor. Through comparing four systems of transforming Rb1 to Rd, strain LFJ1403 was found to secrete ginsenoside-converting enzymes in the spore production phase of plate culture. This result suggested that the enzyme could be directly obtained from the plate. The spore suspension, which contained the exocrine enzyme, was easy to prepare and efficient for biotransformation of ginsenoside Rb1 to Rd. Further study showed that the maximum bioconversion rate was 96% (w/w) in shake flasks when a spore suspension system was used with optimized biotransformation conditions. Scale-up of this system to 2L resulted in an 85% conversion rate. The ginsenoside Rb1 converting enzyme was separated by gradient HPLC with Q-Sepharose column, and its β-glucosidase activity and Rb1-converting ability was assayed by the 4-Nitrophenyl-β-D-glucopyranoside (PNPG) method and HPLC with C18 column, respectively. We obtained 130 U ml(-1) enzymatic activity with the purified β-glucosidase. This is the first report on efficiently converting ginsenoside using extracellular enzyme directly from the fungus spore production phase of solid culture.