Dickeya solani D s0432-1 produces an arsenal of secondary metabolites with anti-prokaryotic and anti-eukaryotic activities against bacteria, yeasts, fungi, and aphids

Abstract

SUMMARYThe necrotrophic plant pathogenic bacterium Dickeya solani is a new invader of potato agrosystem in Europe. All isolated strains of D. solani contain several large polyketide/fatty acid/non-ribosomal peptide synthetase clusters. Analogy with genes described in other bacteria, suggests that two clusters are involved in the production of secondary metabolites of the oocydin and zeamine family. In this study, we constructed by an approach of reverse genetics mutants affected in the three secondary metabolite clusters ssm, ooc and zms in order to compare the phenotype of the D. solani strain D s0432-1 with its derived mutants. We demonstrated that the zeamine cluster zms inhibits growth of gram-positive and gram-negative bacteria. It is also implicated in a toxicity against aphids. The oocydin cluster ooc inhibits growth of fungi of the phylum Ascomycota. Finally, we unveiled the function of a new secondary metabolite cluster ssm (for solani secondary metabolite), only conserved in some Dickeya species. This cluster produces a secondary metabolite inhibiting yeasts. D. solani therefore produces several molecules that are toxic to a wide range of living and potentially interacting organisms, from bacteria to insects. The expression of these secondary metabolite pathways could contribute to the rapid spread of D. solani in Europe.