Regulation of iron transport related genes by boron in the marine bacterium Marinobacter algicola DG893.
ABSTRACT While there has been extensive interest in the use of boron isotope ratios as a surrogate of pH in paleoclimate studies in the context of climate change-related questions, the high (0.4 mM) concentration and the depth-independent (conservative or non-nutrient-like) concentration profile of this element have led to boron being neglected as a potentially biologically relevant element in the modern ocean. Here we report that boron affects the expression of a number of protein and genes in the "algal-associated" Gram-negative marine bacterium Marinobacter algicola DG893. Most intriguingly, a number of these proteins and genes are related to iron uptake. In a recent separate publication we have shown that boron regulates one such iron transport related protein, i.e. the periplasmic iron binding protein FbpA via a direct interaction of the metalloid with this protein. Here we show that a number of other iron uptake related genes are also affected by boron but in the opposite way i.e. they are up-regulated. We propose that the differential effect of boron on FbpA expression relative to other iron transport related genes is a result of an interaction between boron and the global iron regulatory protein Fur.
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ABSTRACT: This report describes a method to purify the major iron-regulated protein (MIRP) expressed by N. gonorrhoeae and N. meningitidis. This purification procedure involves maximal expression of the MIRP by growing the organisms on iron-limited media; cellular disruption by sonication followed by centrifugal fractionation; selective solubilization of the MIRP with the cationic detergent hexadecyltrimethylammonium bromide; cation-exchange chromatography in the presence of this detergent; and gel filtration chromatography. The MIRP purified by this technique migrates as a single band when analyzed by SDS-PAGE. The purified MIRP displayed an unusually basic isoelectric point, this value being greater than 9.35. Further biochemical analysis revealed the highly conserved nature of this protein isolated from the two pathogenic species of the genus Neisseria. For example, the amino acid composition of the meningococcal and gonococcal MIRPs were nearly identical and amino terminal sequence analysis showed that both shared the identical primary sequence through residue 48. Surprisingly, the first five NH2-terminal residues of the MIRPs exhibited homology with the first five residues of the gonococcal porin, protein I. Purified preparations of the MIRP exhibited a characteristic pink color reminiscent of the basic iron-binding protein lactoferrin. This observation coupled with the property of iron-regulation prompted us to analyze purified MIRP for iron-content. Approximately 0.5 mol iron per 1 mol of MIRP was detected. This study is the first to show that iron is associated with the MIRP, a property that may implicate this protein as playing a direct role in neisserial iron assimilation. While the precise function of the MIRP is not known, the availability of this protein in pure and biologically relevant quantities will allow further studies to elucidate its pathobiologic function.Journal of Experimental Medicine 05/1987; 165(4):1041-57. · 13.21 Impact Factor
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ABSTRACT: The bioluminescent marine bacterium Vibrio harveyi controls light production (lux) by an elaborate quorum-sensing circuit. V. harveyi produces and responds to two different autoinducer signals (AI-1 and AI-2) to modulate the luciferase structural operon (luxCDABEGH) in response to changes in cell-population density. Unlike all other Gram-negative quorum-sensing organisms, V. harveyi regulates quorum sensing using a two-component phosphorylation-dephosphorylation cascade. Each autoinducer is recognized by a cognate hybrid sensor kinase (called LuxN and LuxQ). Both sensors transduce information to a shared phosphorelay protein called LuxU, which in turn conveys the signal to the response regulator protein LuxO. Phospho-LuxO is responsible for repression of luxCDABEGH expression at low cell density. In the present study, we demonstrate that LuxO functions as an activator protein via interaction with the alternative sigma factor, sigma54 (encoded by rpoN). Our results suggest that LuxO, together with sigma54, activates the expression of a negative regulator of luminescence. We also show that phenotypes other than lux are regulated by LuxO and sigma54, demonstrating that in Vibrio harveyi, quorum sensing controls multiple processes.Molecular Microbiology 06/2000; 36(4):940-54. · 5.03 Impact Factor
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ABSTRACT: Cell-cell communication in bacteria is accomplished through the exchange of extracellular signalling molecules called autoinducers. This process, termed quorum sensing, allows bacterial populations to coordinate gene expression. Community cooperation probably enhances the effectiveness of processes such as bioluminescence, virulence factor expression, antibiotic production and biofilm development. Unlike other autoinducers, which are specific to a particular species of bacteria, a recently discovered autoinducer (AI-2) is produced by a large number of bacterial species. AI-2 has been proposed to serve as a 'universal' signal for inter-species communication. The chemical identity of AI-2 has, however, proved elusive. Here we present the crystal structure of an AI-2 sensor protein, LuxP, in a complex with autoinducer. The bound ligand is a furanosyl borate diester that bears no resemblance to previously characterized autoinducers. Our findings suggest that addition of naturally occurring borate to an AI-2 precursor generates active AI-2. Furthermore, they indicate a potential biological role for boron, an element required by a number of organisms but for unknown reasons.Nature 02/2002; 415(6871):545-9. · 38.60 Impact Factor