However, once the NRPS enzymatic template is in place then it is an extremely efficient method for synthesizing short peptides, STAT inhibitor consuming significantly less ATP per peptide bond formed than ribosomal mechanisms [60]. It might therefore be useful to have a backup siderophore in place that can be expressed immediately in response to iron starvation
and provide the cell with small amounts of iron while the NRPS template for the more efficient primary siderophore is established. As the phenotypes of our mutant strains indicate that achromobactin is only important when pyoverdine is not available, it is possible that achromobactin likewise serves as a ‘first response’ siderophore to cope with a sudden onset of iron starvation in P. syringae 1448a. Our investigation into the timing and regulation of pyoverdine and achromobactin synthesis in P. syringae 1448a is ongoing. Conclusions P. syringae see more 1448a appears to have the genetic capacity to produce three different siderophores however only two of these, pyoverdine and achromobactin, were detectable as active siderophores under the various conditions examined. An essential role for five NRPS genes in pyoverdine synthesis was confirmed by gene deletion and complementation studies, and the in silico assignation of substrate specificity for each NRPS module was found to be congruent
with a structure for P. syringae 1448a pyoverdine inferred from MS/MS data. Surprisingly, this data also indicated that P. syringae 1448a produces a second, heavier,
isoform of pyoverdine, which may contain an extra alanine residue located between the chromophore and the lysine residue of the peptide side chain. Although pyoverdine was shown to be a substantially more effective siderophore than achromobactin, neither siderophore was found to play a definitive role in the ability of P. syringae 1448a to cause halo blight, indicating that these siderophores are not promising Ketotifen targets for development of novel antibiotics to protect bean crops. Methods Bioinformatics and computer programs Adenylation domain specificities for putative pyoverdine NRPS modules were predicted using the NRPS/PKS predictor currently online at http://nrps.igs.umaryland.edu/nrps/, based on the 8 amino acid model of A domain prediction [32]. Specificities were also predicted using the TSVM method [33] with congruent results. For analysis of the pyoverdine cluster of P. syringae 1448a, inferred amino acid sequences of known pyoverdine genes from P. aeruginosa PAO1 (as described in [6, 8]) were aligned against the P. syringae 1448a genome using the default BLASTP settings of the Pseudomonas genome database http://www.pseudomonas.com[27]. Genes were taken to be orthologs if they were annotated as being in the same COG group; up to 5 matches were recorded where orthologous genes were not clearly present in the known pyoverdine locus and/or had a shared amino acid identity under 40%.
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