The necrotrophic plant pathogenic bacteriumDickeya solaniemerged in the potato agrosystem in Europe. All isolated strains ofD.solanicontain several large polyketide synthase/non-ribosomal peptide synthetase (PKS/NRPS) gene clusters. Analogy with genes described in other bacteria suggests that the clustersoocandzmsare involved in the production of secondary metabolites of the oocydin and zeamine families, respectively. A third cluster namedsolwas recently shown to produce an antifungal molecule. In this study, we constructed mutants impaired in each of the three secondary metabolite clusterssol,ooc, andzmsto compare first the phenotype of theD.solaniwild-type strain D s0432-1 with its associated mutants. We demonstrated the antimicrobial functions of these three PKS/NRPS clusters against bacteria, yeasts or fungi. The clustersol, conserved in several otherDickeyaspecies, produces a secondary metabolite inhibiting yeasts. Phenotyping and comparative genomics of differentD.solaniwild-type isolates revealed that the small regulatory RNA ArcZ plays a major role in the control of the clusterssolandzms. A single-point mutation, conserved in someDickeyawild-type strains, including theD.solanitype strain IPO 2222, impairs the ArcZ function by affecting its processing into an active form.