Most microorganisms produce siderophores when they are faced with iron-limiting conditions. Fluorescent pseudomonads produce a yellow-green, fluorescent siderophore, called pyoverdine. Besides pyoverdine, sev-eral other secondary siderophores, which have a relatively lower affinity for iron, have been identified in Pseu-domonas spp. Examples are pyochelin, pseudomonine and thioquinolobactin (Cornelis and Matthijs 2002). An atypical set of secondary siderophores, due to their lipopeptidic nature, are the siderophores corrugatin (Risse et al., 1998), ornicorrugatin (Matthijs et al., 2008) and histicorrugatin (Matthijs et al., 2016). These siderophores consist out of an 8 amino acid long peptide which is linked to octanoic acid, an eight-carbon saturated fatty acid. They differ from each other by having 1 or 2 amino acid changes in the peptide chain. The phylogenetic distribution of Pseudomonas strains producing one of these 3 siderophores throughout the Pseudomonas genus, represented by more than 700 strains, was studied by means of PCRs with primers spe-cific for the receptor and/or the biosynthetic genes of histicorrugatin, ornicorrugatin and corrugatin, and by means of mass analysis to identify the siderophore produced. In addition, sequenced genomes were screened in silico for biosynthetic or uptake genes of histicorrugatin, ornicorrugatin or corrugatin. Well-defined subclusters of Pseudomonas strains producing one of these siderophores have been identified in the P. fluorescens group. Remarkably, when looking at the biological origin of the producing strains it was found that the ability to produce histicorrugatin, ornicorrugatin or corrugatin is almost exclusively found in Pseudomonas strains isolated from plants. To gain insight in the role of histicorrugatin, ornicorrugatin or corrugatin in the interaction of Pseudomonas with the plant, the effect of one of these siderophores is being investigated. As a model system Pseudomonas fluo-rescens C7R12 and Arabidopsis thaliana have been chosen. C7R12 produces pyoverdine (PYOC7R12) and or-nicorrugatin. The impact of PYOC7R12 on Arabidopsis thaliana plants facing iron deficiency, has already been studied (Trapet et al., 2016). Under this condition, apo-PYOC7R12 modulated the expression of around 2000 genes, it positively regulated the expression of genes related to development and iron acquisition/redistribution while it repressed the expression of defense-related genes (Trapet et al., 2016). This mechanism being dependent on the expres-sion of the iron uptake-related genes IRT1 and FRO2 (Trapet et al., 2016). The impact of ornicorrugatin is now being studied using purified ornicorrugatin and ornicorrugatin-negative mutants. REFERENCES Cornelis P. and Matthijs S. (2002) Diversity of siderophore-mediated iron uptake systems in fluorescent pseudomonads: not only pyover-dines. Environ Microbiol 4: 787-798. Risse D., Beiderbeck H., Taraz K., Budzikiewicz H., Gustine D. (1998) Corrugatin, a lipopeptide from Pseudomonas corrugata. Z Naturforsch C 53: 295-304. Matthijs S., Brandt N., Ongena M., Achouak W., Meyer J.-M., Budzikiewicz H. (2016) Pyoverdine and histicorrugatin-mediated iron acquisi-tion in Pseudomonas thivervalensis Biometals 29: 467-85. Matthijs S., Budzikiewicz H., Schäfer M., Wathelet B., Cornelis P. (2008) Ornicorrugatin, a new siderophore from Pseudomonas fluorescens AF76. Z Naturforsch 63c, 8-12. Trapet P., Avoscan L., Klinguer A., Pateyron S ., Citerne S., Chervin C., Mazurier S., Lemanceau P., Wendehenne D. and Besson-Bard A. (2016) The Pseudomonas fluorescens siderophore pyoverdine weakens Arabidopsis thaliana defense in favour of growth in iron-deficient conditions. Plant Physiol. 171: 675-693.