Fig. 4: Bacillibactin siderophore is key to mobilizing pulcherrimin-bound Fe.

a Conceptual framework in MSgg showing the possible route of Fe recovery. Pulcherrimin could be uptake as a complex (siderophore), or Fe trapped in pulcherrimin could be remobilize by a stronger siderophore (BB) based of affinity constant. A foreign species (Pf-5) could strip Fe from pulcherrimin and used it as an Fe source. b, B. subtilis WT growth was monitored (by absorbance at OD₆₀₀) in MSgg medium. Optical density was measured every 6 h starting at 12 h post-inoculation (12 h, 18 h, 24 h, 30 h, and 36 h) in presence of no added Fe (control), 50 µM FeCl₃, and 50 µM pulcherrimin as Fe sources. c The growth of ∆dhbF was monitored as in (a). d The competitive strain P. protegens Pf-5 growth was evaluated as in (a). e Pellicle formation assays were performed to evaluate the biofilm robustness in the presence of no added Fe, 50 µM FeCl₃, and 50 µM pulcherrimin as Fe sources. Pellicles were cultivated in a 24-well plate and pictures were taken 24 h later. Scale bar (top upper right—5 mm). All experiments were performed in three biological replicates with three technical replicates. Representative experiments and pictures are presented. Data are presented as mean values ±SD, n = 3. Source data are provided as a Source Data file.