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.
The production of peptide siderophores and the variation in siderophore production among strains of Pseudomonas syringae and Pseudomonas viridiflava were investigated. An antibiose test was used to select a free amino acid-containing agar medium favorable for production of fluorescent siderophores by two P. syringae strains. A culture technique in which both liquid and solid asparagine-containing culture media were used proved to be reproducible and highly effective for inducing production of siderophores in a liquid medium by the fluorescent Pseudomonas strains investigated. Using asparagine as a carbon source appeared to favor siderophore production, and relatively high levels of siderophores were produced when certain amino acids were used as the sole carbon and energy sources. Purified chelated siderophores of strains of P. syringae pv. syringae, P. syringae pv. aptata, P. syringae pv. morsprunorum, P. syringae pv. tomato, and P. viridiflava had the same amino acid composition and spectral characteristics and were indiscriminately used by these strains. In addition, nonfluorescent strains of P. syringae pv. aptata and P. syringae pv. morsprunorum were able to use the siderophores in biological tests. Our results confirmed the proximity of P. syringae and P. viridiflava; siderotyping between pathovars of P. syringae was not possible. We found that the spectral characteristics of the chelated peptide siderophores were different from the spectral characteristics of typical pyoverdins. Our results are discussed in relation to the ecology of the organisms and the conditions encountered on plant surfaces.The species Pseudomonas syringae contains all of the phytopathogenic and oxidase-negative fluorescent pseudomonads except Pseudomonas viridiflava (27,38). P. syringae is divided into 57 pathovars that are pathogenic for numerous monocot and dicot crops (13). P. syringae strains are well adapted to conditions on plant surfaces. A better understanding of the ecological benefits of these pathogens is necessary if new and efficient methods of biological control are to be developed. One of these benefits could be the production of peptide siderophores in iron-deficient environments (8,33). In general, the peptide siderophores produced by fluorescent Pseudomonas strains are pyoverdins (2, 3). All pyoverdins contain the same quinoline chromophore, a peptide chain, and a dicarboxylic acid (or the corresponding amide) connected to the chromophore. The peptide chain is always the same for a given strain but is different in different strains and species (2). Two partially characterized peptide siderophores of P. syringae that have been described (8, 33) have Fe(III)-binding constants at pH 7.0 of about 1 ϫ 10 25 . These values are 10 times higher than the values obtained for pyoverdins produced by saprophytic fluorescent Pseudomonas strains (8, 33). Therefore, it would be interesting to know whether production of these molecules is common in P. syringae strains and whether the molecules are effectively produced on plant surf...
The siderophore and virulence factor yersiniabactin is produced by Pseudomonas syringae. Yersiniabactin was originally detected by high-pressure liquid chromatography (HPLC); commonly used PCR tests proved ineffective. Yersiniabactin production in P. syringae correlated with the possession of irp1 located in a predicted yersiniabactin locus. Three similarly divergent yersiniabactin locus groups were determined: the Yersinia pestis group, the P. syringae group, and the Photorhabdus luminescens group; yersiniabactin locus organization is similar in P. syringae and P. luminescens. In P. syringae pv. tomato DC3000, the locus has a high GC content (63.4% compared with 58.4% for the chromosome and 60.1% and 60.7% for adjacent regions) but it lacks high-pathogenicity-island features, such as the insertion in a tRNA locus, the integrase, and insertion sequence elements. In P. syringae pv. tomato DC3000 and pv. phaseolicola 1448A, the locus lies between homologues of Psyr_2284 and Psyr_2285 of P. syringae pv. syringae B728a, which lacks the locus. Among tested pseudomonads, a PCR test specific to two yersiniabactin locus groups detected a locus in genospecies 3, 7, and 8 of P. syringae, and DNA hybridization within P. syringae also detected a locus in the pathovars phaseolicola and glycinea. The PCR and HPLC methods enabled analysis of nonpathogenic Escherichia coli. HPLC-proven yersiniabactin-producing E. coli lacked modifications found in irp1 and irp2 in the human pathogen CFT073, and it is not clear whether CFT073 produces yersiniabactin. The study provides clues about the evolution and dispersion of yersiniabactin genes. It describes methods to detect and study yersiniabactin producers, even where genes have evolved.Iron is essential for life in nearly all microorganisms. However, it is not readily available because the solubility of ferric ions at neutral pH is very low, and generally iron exists precipitated or chelated to iron-binding proteins in a host and to various compounds in the environment (7,34,48,67). A frequent mechanism used by bacteria to meet their needs for iron is the secretion of low-molecular-mass iron chelating compounds called siderophores. Siderophores are able to solubilize iron and translocate it back to the bacterial cytosol via a specific outer membrane receptor and via transport proteins located in the periplasm and in the inner membrane (7, 67).Yersiniabactin (YBT) is a bacterial siderophore with a very high stability constant for iron (4 ϫ 10 36 ) that was characterized in Yersinia pestis and Yersinia enterocolitica (15,24,33,63). It has been extensively studied because it is a virulence factor widespread among human-and animal-pathogenic enterobacteria. In Yersinia spp. (14, 64), the YBT iron uptake system, called the YBT locus (ϳ30 kb), is located in the 36-kb (Yersinia pseudotuberculosis and Y. pestis) or 43-kb (Y. enterocolitica) genomic high-pathogenicity island (HPI). The YBT locus contains one regulatory gene, three genes involved in transport, and the YBT synthesis genes (review...
Toxin-based identification procedures are useful for differentiating Pseudomonas syringae pathovars. A biological test on peptone-glucose-NaCl agar in which the yeastRhodotorula pilimanae was used proved to be more reliable for detecting lipodepsipeptide-producing strains of P. syringae than the more usual test on potato dextrose agar in which Geotrichum candidum is used. A PCR test performed with primers designed to amplify a 1,040-bp fragment in the coding sequence of the syrD gene, which was assumed to be involved in syringomycin and syringopeptin secretion, efficiently detected the gene in pathovars that produce the lipodepsipeptides. Comparable results were obtained in both tests performed with strains of the syringomycin-producing organisms P. syringae pv. syringae,P. syringae pv. atrofaciens, and P. syringaepv. aptata, but the PCR test failed with a syringotoxin-producingPseudomonas fuscovaginae strain. The specificity of the test was verified by obtaining negative PCR test results for related pathovars or species that do not produce the toxic lipodepsipeptides.P. syringae pv. syringae was detected repeatedly in liquid medium inoculated with diseased vegetative tissue and assayed by the PCR test. Our procedure was also adapted to detect P. syringae pv. morsprunorum with a cfl gene-based PCR test.
The relationship of pyoverdins produced by 41 pathovars of Pseudomonas syringae and by phytopathogenic Pseudomonas species was investigated. A high-performance liquid chromatography method for analyzing the culture medium proved to be superior to isoelectric focusing for detecting pyoverdin production, for differentiating slightly different pyoverdins, and for differentiating atypical from typical Fe(III)-chelated pyoverdins. Nonfluorescent strains were found in Pseudomonas amygdali, Pseudomonas meliae, Pseudomonas fuscovaginae, and P. syringae. Pseudomonas agarici and Pseudomonas marginalis produced typical pyoverdins. Among the arginine dihydrolase-negative fluorescent Pseudomonas species, spectral, amino acid, and mass spectrometry analyses underscored for the first time the clear similarities among the pyoverdins produced by related species. Within this group, the oxidase-negative species Pseudomonas viridiflava and Pseudomonas ficuserectae and the pathovars of P. syringae produced the same atypical pyoverdin, whereas the oxidase-positive species Pseudomonas cichorii produced a similar atypical pyoverdin that contained a glycine instead of a serine. The more distantly related species Pseudomonas asplenii and Pseudomonas fuscovaginae both produced a less similar atypical pyoverdin. The spectral characteristics of Fe(III)-chelated atypical pyoverdins at pH 7.0 were related to the presence of two -hydroxyaspartic acids as iron ligands, whereas in typical pyoverdins one of the ligands is always ornithine based. The peptide chain influenced the chelation of iron more in atypical pyoverdins. Our results demonstrated that there is relative pyoverdin conservation in the amino acids involved in iron chelation and that there is faster evolution of the other amino acids, highlighting the usefulness of pyoverdins in systematics and in identification.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.