Characterization of Fluorescent and Nonfluorescent Peptide Siderophores Produced by Pseudomonas syringae Strains and Their Potential Use in Strain Identification

Abstract

Nonfluorescent highly virulent strains of Pseudomonas syringae pv. aptata isolated in different European countries and in Uruguay produce a nonfluorescent peptide siderophore, the production of which is iron repressed and specific to these strains. The amino acid composition of this siderophore is identical to that of the dominant fluorescent peptide siderophore produced by fluorescent P. syringae strains, and the molecular masses of the respective Fe(III) chelates are 1,177 and 1,175 atomic mass units. The unchelated nonfluorescent siderophore is converted into the fluorescent siderophore at pH 10, and colors and spectral characteristics of the unchelated siderophores and of the Fe(III)-chelates in acidic conditions are similar to those of dihydropyoverdins and pyoverdins, respectively. The nonfluorescent siderophore is used by fluorescent and nonfluorescent P. syringae strains. These results and additional mass spectrometry data strongly suggest the presence of a pyoverdin chromophore in the fluorescent siderophore and a dihydropyoverdin chromophore in the nonfluorescent siderophore, which are both ligated to a succinamide residue. When chelated, the siderophores behave differently from typical pyoverdins and dihydropyoverdins in neutral and alkaline conditions, apparently because of the ionization occurring around pH 4.5 of carboxylic acids present in ␤-hydroxyaspartic acid residues of the peptide chains. These differences can be detected visually by pH-dependent changes of the chelate colors and spectrophotochemically. These characteristics and the electrophoretic behavior of the unchelated and chelated siderophores offer new tools to discriminate between saprophytic fluorescent Pseudomonas species and fluorescent P. syringae and P. viridiflava strains and to distinguish between the two siderovars in P. syringae pv. aptata.

Impact of Siderophore Production by Pseudomonas syringae pv. syringae 22d/93 on Epiphytic Fitness and Biocontrol Activity against Pseudomonas syringae pv. glycinea 1a/96

“…syringae 22d/93. It has been known for a long time that plant-associated P. syringae isolates produce pyoverdin, a peptide-type siderophore that causes the green fluorescence responsible for the term "fluorescent pseudomonads" (7,9,25). However, the hypoth- esis that one bacterial isolate produces one type of siderophore has been revised due to the increased availability of genome sequence information so that it is now acknowledged that there is great redundancy in iron uptake systems, which includes the presence of multiple of siderophore receptors in, and the production of several different siderophores by, a single bacterium (18).…”

Salicylic Acid, Yersiniabactin, and Pyoverdin Production by the Model PhytopathogenPseudomonas syringaepv. tomato DC3000: Synthesis, Regulation, and Impact on Tomato andArabidopsisHost Plants

“…tomato DC3000 likely synthesizes the yellow-green fluorescent siderophore Pvd, based on the presence of the required biosynthetic genes in its genome (11) and the synthesis of Pvd by other P. syringae pv. tomato strains (13,14). Therefore, we first wanted to determine whether DC3000 produces Pvd under iron-limiting conditions.…”

“…syringae B301D (18) and present in numerous Pseudomonas syringae strains, including P. syringae pv. tomato LMG5093 (13,15). This Pvd pss contains the 2,3-diamino-6,7-dihydroxy-quinoline chromophore characteristic of all Pvd in addition to a heptapeptide consisting of two ␤-hydroxyaspartic acids, two serines, two threonines and one lysine (18).…”

Taxonomic heterogeneity, as shown by siderotyping, of strains primarily identified as Pseudomonas putida

“…As a general rule, strains belonging to a given species produce an identical pyoverdine, whereas strains belonging to different species produce different pyoverdines (Meyer, 2000;Bultreys et al, 2001;Meyer et al, 2002;Meyer & Geoffroy, 2004). To be valid, however, this rule should also apply to well-defined species, i.e.…”