Stimulation, purification, and chemical characterization of siderophores produced by the rhizospheric bacterial strain Pseudomonas putida

Most of the microorganisms generate siderophores in iron deficient condition. Siderophores are low-molecular-weight chelating agents produced by microorganisms and higher plants to encourage take-up of iron. It is reported that heavy metals in the milieu influence siderophores biosynthesis by microorganisms. In this study, we evaluated the effect of zinc ions, in the case of iron deficiency, on the siderophores generation by an array of rhizobacteria. Sixteen strains were specifically isolated from the rhizosphere of ginseng plant (Panax schinseng). The siderophores-producing rhizobacteria were investigated using chrome azurol S (CAS)-liquid media provided with various concentrations of ZnSO4 of (50-250 µg mL−1). The siderophore-producing strain Pseudomonas KNUK9 indicated high identity (99% using 16S-rRNA sequencing) to P. putida and showed potent antagonistic effect in vitro against the phytopathogenic fungal strain Aspergillus niger. The Sephadex LH-20 purified siderophore of Pseudomonas KNUK9 strain was chemically investigated using UV, FTIR, and MALDI-TOF-MS spectra. Results demonstrated that the pyoverdine is the iron-binding compound produced by Pseudomonas KNUK9 strain, and it's greatly influenced by the presence of Zn2+ ions in the medium. 100 µg mL−1 Zn2+ ions concentration improved the siderophores production in all siderophores-producing bacterial strains.