Preparation of Fe-Siderophore Solutions

To study the suitability of each bacterial media for Fe chlorosis remediation in soil applications, an Fe-siderophore solution (ISS) was prepared by rehydrating to the same volume the previously obtained powders; this procedure allowed to achieve the same initial concentration of siderophores. Then, a soluble salt of Fe(III), FeCl₃.6H₂O (Sigma), was added to the maximum complexation capacity at pH 9.0 (A. vinelandii ≈ 188 µmol L⁻¹ and B. subtilis ≈ 225 µmol L⁻¹) of each solution, which was previously determined (Ferreira et al., 2019b (link)). During the process, the pH of the solution was kept between 7.0 and 9.0, and the final pH was set at 9.0. The solution was allowed to settle overnight and filtered (0.45-µm pore size filter). The initial Fe concentration was then measured by atomic absorption spectroscopy with flame atomization (AAS-FA) using a Perkin-Elmer AAnalyst 400 spectrometer (Norwalk, CT, USA).