Characterization of ginsenoside-converting bacteria isolated from soil of ginseng field

Abstract

Screening of novel bacterial strains metabolizing ginsenosides was performed in the ginseng field soil. Through four round screenings, 20 novel strains were found to be able to transform major ginsenosides into minor ginsenosides. The phylogenetic analysis based on the 16S rRNA gene sequences revealed that, three of these isolates, designated as strains Gsoil 202, Gsoil 3054 and Gsoil 3082, were novel species of the genus Arthrobacter in the Actinobacteria, Rhodanobacter in the Gammaproteobacteria and Terrabacter in the Actinobacteria, respectively, and they were characterized by a polyphasic approach to clarify their taxonomic positions. On the basis of the results obtained in this study, we propose that these three strains represent novel species of genus Arthrobacter, Rhodanobacter and Terrabacter, and the names Arthrobacter ginsenosidimutans sp. nov., Rhodanobacter ginsenosidimutans sp. nov. and Terrabacter ginsenosidimutans sp. nov are proposed. The investigation on the biotransformation pathway of ginsenoside Rb1 revealed that strain Gsoil 202 could transform ginsenoside Rb1 to Rg3, via ginsenoside Rd as an intermediate, by hydrolyzing terminal glucose and consecutively inner glucose at the C-20 position. Strain Gsoil 3054 could hydrolyze not only major ginsenoside Rb1, but also other major ginsenosides Rb2 and Rc, to ginsenoside Rd, by cleaving the β-(1→6)-glucosidic linkage at C-20 of Rb1, the -O-β-D-glucose-(6→1)-α-L-arabinopyranoside linkage attached to the hydroxyl group at the C-20 site of Rb2 and the -O-β-D-glucose-(6→1)-α-L-arabinofuranoside linkage attached to the hydroxyl group at the C-20 site of Rc, respectively. Strain Gsoil 3082 could mainly transform Rb1 to Rg3 via ginsenoside Rd by hydrolyzing terminal glucose and consecutively inner glucose at the C-20 position. Moreover, minor of ginsenoside F2 was produced by the strain Gsoil 3082 via gypenoside XVII by being hydrolyzed one molecule of terminal glucose at the C-20 and the other term...