m/z Relative abundance Reference spectrum [M+H] + Acquired spectrum Supplemental Figure 1. Identification of enantio-pyochelin. Top panel: MS/MS spectrum for the [M+H] + ion identified as enantio-pyochelin, bottom panel: reference MS/MS spectrum of pyochelin from GNPS database

Supplemental Figure 2A. LC-MS-analysis of the 2 nd size exclusion fraction of the XAD-4 crude extract of P. fluorescens BBc6R8. The middle panel shows the extracted UV-chromatogram ( nm) with four groups of pyoverdine congeners. The peaks of the four main groups are color-coded correlated with the observed quasi molecular ion [M+H] + peak in the corresponding mass spectra recorded at the same time (top and bottom panels). Abbreviations: Pyo = pyoverdine; Glu = glutamic acid; Suc = succinic acid; Suca = succinic acid amide; Mal = malic acid; Kgl = alpha-ketoglutaric acid. Pyo-Suc Pyo-Kgl Pyo-Glu Pyo-Suca Pyo-Mal

Supplemental Figure 2B. Extracted UV-Spectra from the identified pyoverdine derivatives. The color code refers to the peaks marked in Figure 2A. R = peptide moiety of the Pf-BBc6R8-pyoverdine. Abbreviations: Pyo = pyoverdine; Glu = glutamic acid; Suc = succinic acid; Suca = succinic acid amide; Mal = malic acid; Kgl = alpha-ketoglutaric acid. Pyo-Mal Pyo-Suca Pyo-Glu Pyo-Suc Pyo-Kgl

Supplemental Figure 3. HR-ESI-TOF-MS of viscosin. Bottom panel: measured HR-MS [M+Na] + m/z Top panel: calculated HR-MS spectrum for the formula C 54 H 95 N 9 O 16 Na, the theoretical pseudomolecular ion of viscosin ( , Δ +0.8 ppm)

Supplemental Figure 4. Result of the white line agar assay demonstrating that the biosurfactant produced by P. fluorescens BBc6R8 is viscosin. A. White line agar assay between P. tolaasii and P. reactans (WLIP producer). The arrow points at the white line indicating the production of WLIP by P. reactans. B. White line agar assay between P. tolaasii and P. fluorescens SBW25 (viscosin producer). C.. White line agar assay between P. tolaasii and P. fluorescens BBc6R8 A B C

Supplemental Figure 5. 1 H NMR spectrum of viscosin (250 MHz, d 4 -MeOH).

Supplemental Fig 6. Effect of P. fluorescens BBc6R8 WT and of the mutant ∆viscB -P448 on the radial growth of L. bicolor S238N on KB agar medium. Similar result was obtained with mutant ∆viscB -P450 (data not shown). Open squares: L. bicolor S238N alone, black squares: L. bicolor S238N co-cultivated with P. fluorescens BBc6R8 WT, grey triangles: L. bicolor S238N co-cultivated with ∆ viscB. Each point is the mean value of 7 biological replicates +/- SD. The experiment was reproduced three times independently and similar results were obtained each time.

Reference spectrum [M+H] + Acquired spectrum m/z Relative abundance Supplemental Figure 7. Top panel: MS/MS spectrum for the [M+H] + ion identified as desferrioxamine E, bottom panel: reference MS/MS spectrum of desferrioxamine E from GNPS database.