Proteobactin and a yersiniabactin-related siderophore mediate iron acquisition in Proteus mirabilis

Proteus mirabilis causes complicated urinary tract infections (UTIs). While the urinary tract is an iron-limiting environment, iron acquisition remains poorly characterized for this uropathogen. Microarray analysis of P. mirabilis HI4320 cultured under iron limitation identified 45 significantly upregulated genes ( P  ≤  0.05) that represent 21 putative iron-regulated systems. Two gene clusters, PMI0229-0239 and PMI2596-2605, encode putative siderophore systems. PMI0229-0239 encodes a non-ribosomal peptide synthetase-independent siderophore system for producing a novel siderophore, proteobactin. PMI2596-2605 are contained within the high-pathogenicity island, originally described in Yersinia pestis , and encodes proteins with apparent homology and organization to those involved in yersiniabactin production and uptake. Cross-feeding and biochemical analysis shows that P. mirabilis is unable to utilize or produce yersiniabactin, suggesting that this yersiniabactin-related locus is functionally distinct. Only disruption of both systems resulted in an in vitro iron-chelating defect; demonstrating production and iron-chelating activity for both siderophores. These findings clearly show that proteobactin and the yersiniabactin-related siderophore function as iron acquisition systems. Despite the activity of both siderophores, only mutants lacking the yersiniabactin-related siderophore have reduced fitness in vivo . The fitness requirement for the yersiniabactin-related siderophore during UTI shows, for the first time, the importance of siderophore production in vivo for P. mirabilis .Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/79111/1/MMI_7317_sm_FigS1-S2_TabS1-S3.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/79111/2/j.1365-2958.2010.07317.x.pd

Rhamnolipids Mediate an Interspecies Biofilm Dispersal Signaling Pathway

Bacterial biofilms are problematic in natural and anthropogenic environments, and they confer protective properties on their constituent cells, making them difficult to treat with conventional antibiotics. Antibiofilm strategies, therefore, represent a promising direction of research for treating biofilm infections. Natural autodispersal and interspecies dispersal signaling pathways provide insight into cell–cell communication mechanisms, species dynamics in mixed communities, and potential targets for infection therapies. Here, we describe a novel interspecies dispersal signaling pathway between <i>Pseudomonas aeruginosa</i> and <i>Escherichia coli</i>. <i>E. coli</i> biofilms disperse in response to compounds in <i>P. aeruginosa</i> culture supernatant. Two components of the <i>P. aeruginosa</i> Las and Rhl quorum sensing systems, N-(3-oxo-dodecanoyl) homoserine lactone (3oxoC12HSL) and rhamnolipids, are found to act cooperatively to disperse <i>E. coli</i> biofilms. Our results indicate that rhamnolipids do not affect growth, biofilm development, or dispersal in <i>E. coli</i> but instead complement 3oxoC12HSL signaling by inducing selective permeability of the <i>E. coli</i> membrane. The increased target cell permeability is consistent with rhamnolipid-mediated removal of lipopolysaccharide from <i>E. coli</i> membranes and appears to selectively increase the permeability of lipophilic acyl homoserine lactones. This work suggests that rhamnolipids play a critical role in <i>P. aeruginosa</i>–<i>E. coli</i> interspecies signaling. Rhamnolipids and other biosurfactants may have similar effects in other intra- and interspecies chemical signaling pathways

Baulamycins A and B, Broad-Spectrum Antibiotics Identified as Inhibitors of Siderophore Biosynthesis in Staphylococcus aureus and Bacillus anthracis

Siderophores are high-affinity iron chelators produced by microorganisms and frequently contribute to the virulence of human pathogens. Targeted inhibition of the biosynthesis of siderophores staphyloferrin B of Staphylococcus aureus and petrobactin of Bacillus anthracis hold considerable potential as a single or combined treatment for methicillin-resistant S. aureus (MRSA) and anthrax infection, respectively. The biosynthetic pathways for both siderophores involve a nonribosomal peptide synthetase independent siderophore (NIS) synthetase, including SbnE in staphyloferrin B and AsbA in petrobactin. In this study, we developed a biochemical assay specific for NIS synthetases to screen for inhibitors of SbnE and AsbA against a library of marine microbial-derived natural product extracts (NPEs). Analysis of the NPE derived from Streptomyces tempisquensis led to the isolation of the novel antibiotics baulamycins A (BmcA, 6) and B (BmcB, 7). BmcA and BmcB displayed in vitro activity with IC(50) values of 4.8 µM and 19 µM against SbnE and 180 µM and 200 µM against AsbA, respectively. Kinetic analysis showed that the compounds function as reversible competitive enzyme inhibitors. Liquid culture studies with S. aureus, B. anthracis, E. coli and several other bacterial pathogens demonstrated the capacity of these natural products to penetrate bacterial barriers and inhibit growth of both Gram-positive and Gram-negative species. These studies provide proof-of-concept that natural product inhibitors targeting siderophore virulence factors can provide access to novel broad-spectrum antibiotics, which may serve as important leads for the development of potent anti-infective agent