| Summary: | <p>Abstract</p> <p>Background</p> <p>Pyoverdines (PVDs) are high affinity siderophores, for which the molecular mechanisms of biosynthesis, uptake and regulation have been extensively studied in <it>Pseudomonas aeruginosa </it>PAO1. However, the extent to which this regulatory model applies to other pseudomonads is unknown. Here, we describe the results of a genomic, genetic and structural analysis of pyoverdine-mediated iron uptake by the plant growth-promoting bacterium <it>P. fluorescens </it>SBW25.</p> <p>Results</p> <p><it>In silico </it>analysis of the complete, but un-annotated, SBW25 genome sequence identified 31 genes putatively involved in PVD biosynthesis, transport or regulation, which are distributed across seven different regions of the genome. PVD gene iron-responsiveness was tested using '<it>lacZ </it>fusions to five PVD loci, representative of structural and regulatory genes. Transcription of all fusions increased in response to iron starvation. <it>In silico </it>analyses suggested that regulation of <it>fpvR </it>(which is predicted to encode a cytoplasmic membrane-spanning anti-sigma factor) may be unique. Transcriptional assays using gene expression constructs showed that <it>fpvR </it>is positively regulated by FpvI (an extracytoplasmic family (ECF) sigma factor), and not directly by the ferric uptake regulator (Fur) as for PAO1. Deletion of <it>pvdL</it>, encoding a predicted non-ribosomal peptide synthetase (NRPS) involved in PVD chromophore biosynthesis confirmed the necessity of PvdL for PVD production and for normal growth in iron-limited media. Structural analysis of the SBW25 PVD shows a partly cyclic seven residue peptide backbone, identical to that of <it>P. fluorescens </it>ATCC13525. At least 24 putative siderophore receptor genes are present in the SBW25 genome enabling the bacterium to utilize 19 structurally distinct PVDs from 25 different <it>Pseudomonas </it>isolates.</p> <p>Conclusion</p> <p>The genome of <it>P. fluorescens </it>SBW25 contains an extensively dispersed set of PVD genes in comparison to other sequenced <it>Pseudomonas </it>strains. The PAO1 PVD regulatory model, which involves a branched Fpv signaling pathway, is generally conserved in SBW25, however there is a significant difference in <it>fpvR </it>regulation. SBW25 produces PVD with a partly cyclic seven amino acid residue backbone, and is able to utilize a wide variety of exogenous PVDs.</p>
|
|---|