2D image quantification of microbial iron chelators (siderophores) using diffusive equilibrium in thin films method.

Siderophores are natural metal chelating agents that strongly control the biogeochemical metal cycles such as Fe in the environment. This article describes a new methodology to detect and quantify at the micromolar concentration the spatial distribution at millimetre scale of siderophores within the root's system. The "universal" CAS assay originally designed for bacterial siderophores detection and later designed for fungus was adapted here for diffusive equilibrium in thin film gel techniques (DET). The method was calibrated against the marketed desferrioxamine mesylate (DFOM) siderophore and applied with experiments performed with sunflower (Helianthus annuus) and wheat (Triticum aestivum) cultivated on free iron agar medium plates. We present here the first results with 2D images of the siderophores distribution in the vicinity of the root system of plants. With this technique we detected (i) the production of siderophores on bacteria inoculated (Pseudomonas fluorescens) environments, (ii) hotspots of natural iron binding ligands production up to 50 µM in the wheat rhizosphere. The lower detection limit in our experiment was 2.5µmol/L. This new technique offers a unique opportunity to investigate the siderophore production in 2 dimensions in a wide range of applications from laboratory experiments to natural systems very likely using an in situ and non-destructive tool.