The Siderophore Pyoverdine of Pseudomonas syringae pv. tabaci 6605 Is an Intrinsic Virulence Factor in Host Tobacco Infection

ABSTRACT To investigate the role of iron uptake mediated by the siderophore pyoverdine in the virulence of the plant pathogen Pseudomonas syringae pv. tabaci 6605, three predicted pyoverdine synthesis-related genes, pvdJ, pvdL, and fpvA, were mutated. The pvdJ, pvdL, and fpvA genes encode the pyoverdine side chain peptide synthetase III l-Thr-l-Ser component, the pyoverdine chromophore synthetase, and the TonB-dependent ferripyoverdine receptor, respectively. The ΔpvdJ and ΔpvdL mutants were unable to produce pyoverdine in mineral salts-glucose medium, which was used for the iron-depleted condition. Furthermore, the ΔpvdJ and ΔpvdL mutants showed lower abilities to produce tabtoxin, extracellular polysaccharide, and acyl homoserine lactones (AHLs), which are quorum-sensing molecules, and consequently had reduced virulence on host tobacco plants. In contrast, all of the mutants had accelerated swarming ability and increased biosurfactant production, suggesting that swarming motility and biosurfactant production might be negatively controlled by pyoverdine. Scanning electron micrographs of the surfaces of tobacco leaves inoculated with the mutant strains revealed only small amounts of extracellular polymeric matrix around these mutants, indicating disruption of the mature biofilm. Tolerance to antibiotics was drastically increased for the ΔpvdL mutant, as for the ΔpsyI mutant, which is defective in AHL production. These results demonstrated that pyoverdine synthesis and the quorum-sensing system of Pseudomonas syringae pv. tabaci 6605 are indispensable for virulence in host tobacco infection and that AHL may negatively regulate tolerance to antibiotics.

Characterization of a Gene Encoding an Acetylase Required for Pyoverdine Synthesis in Pseudomonas aeruginosa

ABSTRACT Strains of Pseudomonas aeruginosa secrete one of three pyoverdine siderophores (types I to III). We have characterized a gene, pvdY II (for the pvdY gene present in type II P. aeruginosa strains), that is only present in strains that make type II pyoverdine. A mutation in pvdY II prevented pyoverdine synthesis. Bioinformatic, genetic, and biochemical approaches indicate that the PvdYII enzyme catalyzes acetylation of hydroxyornithine. Expression of pvdY II is repressed by the presence of iron and upregulated by the presence of type II pyoverdine. Characterization of pvdY II provides insights into the molecular basis for production of different pyoverdines by different strains of P. aeruginosa.