Hydrolysis of [17,17-2H2]gibberellin A20-glucoside and [17,17-2H2]gibberellin A20-glucosyl ester by Azospirillum lipoferum cultured in a nitrogen-free biotin-Based chemically-defined medium

Azospirillum lipoferum strain USA 5b, a gibberellin producing bacterium, was cultured in a nitrogen-free biotin-based chemically-defined medium in the presence of the glucosyl ester or the 13-O-glucoside of [17,17-²H₂]-gibberellin A₂₀. The [17,17-²H₂]-gibberellin A₂₀ conjugates were added at both the stationary phase of the cultures and at the beginning of the growth curve. Metabolism of the conjugates was examined after 72 h of incubation using capillary gas chromatography-mass spectrometry, with identification by full scan mass spectra. Metabolites identified were [17,17-²H₂]-gibberellin A₂₀, [17,17-²H₂]-gibberellin A₁ and [17,17-²H₂]-gibberellin A₃. Also, in the Azospirillum cultures fed at the beginning of the growth curve, gibberellin A₅ and gibberellin A₂₀ were characterized as endogenous by mass spectrometry/full spectrum. These results support the concept that the growth promotion in plants that is induced by Azospirillum infection may occur by a combination of both gibberellin production and gibberellin-glucoside/glucosyl ester deconjugation by the bacterium.