In vitro metabolism of ginsenosides by the ginseng root pathogen Pythium irregulare

• Published in: Phytochemistry (Oxford) 2006-08, Vol.67 (16), p.1740-1749
• Main Authors: Yousef, Lina F., Bernards, Mark A.
• Format: Article
• Language: English
• Subjects: Araliaceae; Biological and medical sciences; Carbohydrate Sequence; Culture Media; dammarane; ergosterol; Ergosterol - pharmacology; Extracellular glycosidase; Fundamental and applied biological sciences. Psychology; Fungal plant pathogens; Ginseng; Ginsenosides; Ginsenosides - chemistry; Ginsenosides - metabolism; glucose; Glucose - pharmacology; glycosidases; Glycoside Hydrolases - metabolism; Magnetic Resonance Spectroscopy; Panax - parasitology; Panax quinquefolius; Panax quinqufolius; Pathology, epidemiology, host-fungus relationships. Damages, economic importance; Phytopathology. Animal pests. Plant and forest protection; plant pathogenic fungi; Plant Roots - parasitology; protopanaxadiol; Pythium - enzymology; Pythium - growth & development; Pythium - metabolism; Pythium irregulare; secondary metabolites; Spectrometry, Mass, Fast Atom Bombardment; Trichoderma hamatum; triterpenoid saponins
• ISSN: 0031-9422; 1873-3700
• DOI: 10.1016/j.phytochem.2005.06.030

Cultures of the ginseng root pathogen Pythium irregulare selectively metabolize 20( S)-protopanaxadiol ginsenosides (e.g., Rb 1, Rb 2, Rc and Rd) into a single compound, ginsenoside F 2, via an extracellular glycosidase(s). The role of ginseng saponins (ginsenosides) as modulators or inhibitors of disease is vague, but our earlier work supports the existence of an allelopathic relationship between ginsenosides and soilborne microbes. Interestingly, this allelopathy appears to significantly promote the growth of the important ginseng pathogen, Pythium irregulare while inhibiting that of an antagonistic non-pathogenic fungus, Trichoderma hamatum. Herein we report on the apparent selective metabolism of 20( S)-protopanaxadiol ginsenosides by an extracellular glycosidase from P. irregulare. Thus, when P. irregulare was cultured in the presence of a purified (>90%) ginsenoside mixture, nearly all of the 20( S)-protopanaxadiol ginsenosides (Rb 1, Rb 2, Rc, Rd, and to a limited extent G-XVII) were metabolized into the minor ginsenoside F 2, at least half of which appears to be internalized by the organism. No metabolism of the 20( S)-protopanaxatriol ginsenosides (Rg 1 and Re) was evident. By contrast, none of the ginsenosides added to the culture medium of the non-pathogenic fungus T. hamatum were metabolized. The metabolism of 20( S)-protopanaxadiol ginsenosides by P. irregulare appears to occur through the hydrolysis of terminal monosaccharide units from disaccharides present at C-3 and/or C-20 of ginsenosides Rb 1, Rc, Rb 2, Rd and G-XVII to yield one major product, ginsenoside F 2 and one minor product (possibly G-III). A similar transformation of ginsenosides was observed using a crude protein preparation isolated from the spent medium of P. irregulare cultures.