Functional characteristics and optimum fermentation condition of a siderophore-producing bacteria from the rhizosphere of Trifolium repens

In order to fully utilize the resources of the plant growth promoting rhizobacteria associated with wild forages in Guizhou Province, the siderophore-producing bacterial strain TSQA26-3 was isolated from the rhizosphere soil of wild Trifolium repens and used as the research object in this study. Morphological observation, VITEK-2, and 16S rRNA gene sequence analysis were used to identified the strain. The growth-promoting characteristics of the strain were investigated, and the suitable fermentation medium for the siderophore produced by the strain was optimized using single factor and orthogonal experiments. The result showed that the strain TSQA26-3 was identified as Pseudomonas putida and had the ability to dissolve inorganic phosphorus, produce IAA, and fix nitrogen. Mannitol-Glutamine was proven to be the optimal medium for siderophore production. The fermentation medium formula and cultivation conditions were as follows: 25.0 g·L⁻¹ Mannitol, 2.5 g·L⁻¹ L-Glutamine, 1.0 g·L⁻¹ K₂HPO₄, 0.25 g·L⁻¹ MgSO₄·7H₂O, initial pH 7.0, 170 r·min⁻¹, temperature 30 ℃, and medium volume 70 mL in 250 mL conical flask.