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From the Siderophores (from the Greek: ``iron carriers'') are
defined as relatively low molecular weight, ferric ion specific
chelating agents elaborated by bacteria and fungi growing under low
iron stress. The role of these compounds is to scavenge iron from the
environment and to make the mineral, which is almost always essential,
available to the microbial cell. Research in this field began about
five decades ago, and interest in it has accrued with the realization
that most aerobic and facultative anaerobic microorganisms synthesize
at least one siderophore. Siderophores have been related to virulence
mechanisms in microorganisms pathogenic to both animals and plants. In
addition, they have clinical applications and are possibly important in
agriculture. For an introduction to the field, the reader is referred
to one of the comprehensive monographs on the
subject(1, 2) .
Iron in the Environment and in Microbiology The aerobic atmosphere of the planet has caused the surface
iron to become converted to oxyhydroxide polymers of very sparing
solubility. The concentration of free ferric ion at neutral pH is
dictated by the solubility product constant of ferric hydroxide.
Depending on the value selected for this constant, the maximum amount
of uncomplexed ferric ion in solution at biological pH is probably not
greater than 10 It must be stressed that not all microbes require iron,
and siderophores can be dispensed with in these rare cases. Some lactic
acid bacteria are not stimulated to greater growth with iron, they have
no heme enzymes, and the crucial iron-containing ribotide reductase (4) has been replaced with an enzyme using adenosylcobalamin as
the radical generator. Other microbes need iron but grow anaerobically
on Fe(II). While nearly all fungi make siderophores, both budding and
fission yeast appear to be exceptions(3) . Among the
alternative means of assimilating iron are surface reduction to the
more soluble ferrous species, lowering the pH, utilization of heme, or
extraction of protein-complexed metal. Siderophores appear to be
confined to microbes and are not products of the metabolism of plants
or animals, which have their own pathways for uptake of iron.
Detection, Isolation, and Structure Detection of siderophores is most readily achieved in
iron-limited media, which generally means either a synthetic (minimal)
recipe or introduction of a complexing agent that will render the iron
selectively unavailable. Although most siderophores are either
hydroxamates or catechols, earlier tests based on such functional
groups proved unreliable since they are absent from a few siderophores.
The chrome azurol sulfonate assay (5) has become widely used
since it is comprehensive, exceptionally responsive, and more
convenient than microbiological assays which, although sensitive, may
be rigidly specific. The chrome azurol sulfonate assay may be applied
on agar surfaces or in solution. It is based on the color change that
accompanies transfer of the ferric ion from its intense (extinction
coefficient of at least 100,000) blue complex to the siderophore. A
detergent must be present in order to achieve the intense color;
otherwise, only a charge-transfer extinction of a few thousand is
realized. Gram-negative bacteria are impervious to detergents and hence
the chrome azurol sulfonate reagent can be incorporated in the agar
media where it has the potential for isolation of biosynthetic,
regulatory, and transport mutants. For Gram-positive bacteria and
fungi, the toxicity of the reagent must be mitigated in some
way(6) . These qualifications, however, do not compromise use
of the dye in solution or as a spray on chromatograms(5) . Since siderophores differ substantially in structure, no uniform
procedure is available for their isolation. A preliminary examination
by paper electrophoresis should reveal the charge profile as a function
of pH, following which appropriate exchange resins can be applied for
retention and elution of the compound(s). Most are water-soluble, and
it is thus usually expedient to drive the siderophore into an organic
solvent, such as benzyl alcohol or phenol-chloroform, in order to
eliminate salt. The siderophore may be isolated per se or
as its iron chelate. The latter has the advantage of visual color, but
the iron must be removed before any natural product can be
characterized. Vigorous hydrolysis in the presence of iron will destroy
oxidizable moieties, and direct NMR analysis is ruled out by the
paramagnetism of the ferric ion. Structural characterization is best
carried out by a combination of NMR and mass spectroscopy. Both of
these techniques are sensitive and capable of providing absolute
answers. Less than half of the known siderophores will crystallize,
otherwise x-ray diffraction is the method of choice since it affords
the configuration of those molecules containing a chiral
center(7) . Siderophores form high-spin, kinetically labile chelates with
ferric ion which are characterized by exceptional thermodynamic
stability(8, 9) . The formation constant for typical
molecules containing three bidentate ligands is 10 The fact that the siderophore ligand shows strong affinity
for only the higher oxidation state of iron sets this natural
complexing agent apart from molecules such as heme, which serve
effectively as electron shuttles. At the same time, the relatively weak
complexing of Fe(II) affords an efficient means of release, via
reduction, inside the cell. This large discrepancy in the binding
constants for Fe(II) and Fe(III) drives down the oxidation-reduction
potential, and there has been some discussion that the actual value may
be beyond the range of natural reducing agents. This aspect of the
problem requires clarification and elucidation at the enzyme level.
Probably the significant feature is the oxidation-reduction potential
of the enzyme-ferric siderophore complex rather than the potential of
the free ferric chelate. With few exceptions, the ``hard''
acid ion, Fe(III), is linked to hard base atoms, such as oxygen, which
accounts for the preference for ferric ion. Chirality in the ligand
means that the binding sites for the metal ion are disposed in space in
a particular orientation, and, hence, optical isomers are
possible(10) . Thus, ferrichrome (Fig. 1), in which the
binding sites for the metal ion are mounted on an L-ornithine
derivative, forms
Figure 1:
General
structure of the ferrichromes, prototypical hydroxamate type
siderophores. All Penicillia that have been investigated, and
many other fungal species, synthesize this type of siderophore. Several
bacterial species, including E. coli, maintain a transport
system for utilization of ferrichrome as an iron source. For
ferrichrome, R = R` = R" = H; R‴ = CH
Figure 2:
Ferric enterobactin, a prototypical
catechol-type siderophore. The three catechol rings wrap around the
Fe(III) to afford a right-handed (
The siderophore for which we have the greatest inventory of
information with regard to its anabolism is aerobactin (Fig. 3),
first isolated from Aerobacter aerogenes (12) .
Subsequently, it was detected as a product of pColV-K30, a plasmid
commonly borne by clinical isolates of Escherichia coli. The
aerobactin determinants from the latter source have been cloned and
shown to occur in an operon preceded by a regulatory element (reviewed
in (11) ). Aerobactin, which consists of citrate substituted on
the distal carboxyls with residues of N
Figure 3:
General structure of the
citrate-hydroxamate siderophores. For aerobactin, R =
COOH and n = 4. Aerobactin, a second siderophore from
enteric bacteria, may be coded on plasmids or on the
chromosome.
In constructing a binding agent with requisite
affinity/specificity for Fe(III), nature appears to have exceeded the
free diffusion limit of the outer membrane of Gram-negative bacteria (16) . Thus, enterobactin, the siderophore indigenous to E.
coli, has a molecular weight of 669 while that of ferrichrome,
produced by fungi and utilized avidly by E. coli and other
bacteria, is 740. This exclusion-by-size has required the insertion in
the outer membrane of specialized receptors. In the course of
evolution, these receptors have become ``parasitized'' by
lethal agents such as bacteriophage, bacteriocins (``killer
proteins''), and antibiotics. One of the earliest genetic lesions
studied in E. coli, tonA (``T-one''), now fhuA, was that specifying ability to attach phage T1. This
pore turned out to be the receptor for ferrichrome(17) ,
although it also enables transport of several phages, colicin M, and
albomycin. Similarly, the receptor for ferric enterobactin, FepA, is
the site of penetration of colicins B and D, and the bacteriocin
cloacin utilizes the ferric aerobactin receptor. This is the general
pattern with siderophore receptors; namely, they also act as receptors
for a variety of lethal agents. Thus, the receptor for an
uncharacterized siderophore of Yersinia enterocolitica has
been shown to serve as receptor for pesticin (18) . A second
classical gene in E. coli codes for the TonB protein, required
for phage infection and for iron supply via the many siderophore and
inorganic iron uptake systems of the bacterium(19) . TonB,
located in the cytoplasmic membrane, was viewed as providing some kind
of link to the outer membrane, but clarification, in molecular terms,
had to await sequencing of the genes for the receptors. In an elegant
experiment, the deletion of a particular loop converted FepA into a
nonspecific diffusion channel(20) . A similar finding was
reported for ferrichrome transport in FhuA(21) . Apparently,
these bacteria have evolved a sophisticated mode of active iron
transport in which the energy of the cytoplasmic membrane has been
linked to the outer membrane siderophore receptors. It has been known for many years that all components of
siderophore systems are derepressed at low levels of iron. The first
report on the molecular genetics of the process came with work on Salmonella typhimurium. Chemical mutagenesis identified a
gene, designated fur (ferric uptake regulation), which
controlled expression of the siderophore, again enterobactin, and a
brace of large outer membrane proteins, one of which is the equivalent
of FepA of E. coli(22) . In the latter organism, the
gene was cloned and sequenced, and the product was isolated and shown
to act as a classical negative repressor of transcription (reviewed in (23) ). Although any first row divalent transition element will
``organize'' Fur to bind the operator, Fe(II) is thought to
be the natural activator because of the relative abundance of iron. The
``iron box'' or ``fur box'' consensus sequence in
the operator is GATAATGATAATCATTATC, an array which occurs with some
variation in the regulatory DNA of iron-affected systems in many
microbial species. Polymerization of Fur around the operator has been
suggested as the mode of binding(24) , and this is supported by
observations with the electron microscope(25) . On the other
hand, both Fur and ArcA, the latter the repressor for the sodA
gene coding for manganese-superoxide dismutase, bind at the same site.
Footprinting experiments demonstrated polymerized binding in the
-10 to -35 region of the promoter but suggested interaction
with one face of the double helix(26) . The interaction of
metallo-Fur with DNA was reinvestigated, and it was concluded that the
repressor, which lacks the classic helix-turn-helix motif, contacts one
face of the DNA across almost three successive major
grooves(27) . Earlier it was established that the N-terminal
region of Fur recognizes DNA while other domains of the repressor are
involved in separate functions such as binding metal or
polymerization(28) . A still baffling aspect is the fact
that a number of genes seemingly unrelated to iron acquisition, in
addition to that for superoxide dismutase, are also part of the Fur
regulon. A Fur titration assay has been proposed as a means of
identifying all genes regulated by the repressor(29) . In
contrast to the straightforward regulatory mechanism of the aerobactin
operon by ferrous-Fur, regulation of the fur gene itself seems
considerably more baroque. As well as an iron box, sites for binding of
CAP have been identified(30) . The negative regulation
scheme with Fe(II) as co-repressor for a small, Fur-like protein
appears valid in many other bacterial species such as in the
iron-regulated formation of toxin by Corynebacterium
diphtheriae(31) . Some variation in the structure of the
repressor and the operator can be anticipated. However, in
pseudomonads, a positive mechanism may underlie the observed
overproduction of the fluorescent siderophores variously known as
pseudobactins and pyoverdines(32) . The fur mutants
of E. coli grow poorly(23) , possibly because of
oxidative stress(33) . The mutation appears to be lethal in Neisseria spp.(34) . A role for iron in the virulence mechanism of several
microbes attacking man and other animals is well established. An
adequate iron supply for many pathogenic species is critical since
transferrin has a very high affinity for the metal and the protein is
normally only about one-third saturated with iron. Strains of E.
coli causing disseminating infection were found to harbor ColV
plasmids carrying the aerobactin synthesis and transport genes
(reviewed in (35) ). The siderophore system of Y.
enterocolitica is correlated with the virulence of the
organism(18) . On this vast topic, we can only refer to a
monograph on iron and infection (36) and to two excellent
reviews documenting the elaborate host defense systems based on the
principle of withholding of iron(37, 38) . Regarding phytopathogens, it should be recalled that the
virulence-associated iron chrysobactin uptake apparatus of Erwinia
chrysanthemi involves an operon encoding transport and
biosynthetic functions(39) . As naturally occurring chelating agents for iron,
siderophores might be expected to be somewhat less noxious for
deferrization of patients suffering from transfusion-induced siderosis.
A siderophore from Streptomyces pilosus, desferrioxamine B, is
marketed as the mesylate salt under the trade name Desferal and is
advocated for removal of excess iron resulting from the supportive
therapy for thalassemia. The drug must be injected, however, and an
oral replacement is needed(40) . The potency of common
antibiotics has been elevated by building into the molecules the
iron-binding functional groups of siderophores(41) . The
objective here is to take advantage of the high affinity,
siderophore-mediated iron uptake system of the bacteria. Fluorescent pseudomonads form a line of siderophores
comprised of a quinoline moiety, responsible for the fluorescence, and
a peptide chain of variable length bearing hydroxamic acid and
Siderophores are common products of aerobic and facultative
anaerobic bacteria and of fungi. Elucidation of the molecular genetics
of siderophore synthesis, and the regulation of this process by iron,
has been facilitated by the fact that E. coli uses its own
siderophores as well as those derived from other species, including
fungi. Overproduction of the siderophore and its transport system at
low iron is in this species well established to be the result of
negative transcriptional repression, but the detailed mechanism may be
positive in other organisms. Siderophores are transported across the
double membrane envelope of E. coli via a gating mechanism
linking the inner and outer membranes.
Volume 270,
Number 45,
Issue of November 10, 1995 pp. 26723-26726
©1995 by The American Society for Biochemistry and Molecular Biology, Inc.
INTRODUCTION
Iron in the Environment and in Microbiology
Detection, Isolation, and Structure
Coordination Characteristics
Biosynthesis
Transport
Regulation
Siderophores and Virulence
Clinical Applications
Agricultural Interest
Summary
FOOTNOTES
REFERENCES
M(3) .
Microorganisms growing under aerobic conditions need iron for a variety
of functions including reduction of oxygen for synthesis of ATP,
reduction of ribotide precursors of DNA, for formation of heme, and for
other essential purposes. A level of at least one micromolar iron is
needed for optimum growth. These environmental restrictions and
biological imperatives have required that microorganisms form specific
molecules that can compete effectively with hydroxyl ion for the ferric
state of iron, a nutrient which is abundant but essentially
unavailable.
, or
greater. The affinity for gallium is also high, but the attraction for
aluminum and for all divalent ions is substantially less. Thus, the
siderophore ligand can be said to be ``virtually specific''
for Fe(III) among the naturally occurring metal ions of abundance.
Synthetic man-made elements in the actinide series are also firmly
bound.
complexes, while with enterobactin (Fig. 2) the oxygens linked to iron are derived from
2,3-dihydroxybenzoyl-L-serine and
chelates result. These
correspond, respectively, to left- and right-hand coordination
propellers. Geometrical isomers, cis and trans, are
also possible, except in the two archetypal siderophores just cited
steric restraints confine the isomers to the cis form.
.
Ferrichrome biosynthesis in the basidiomycetous fungus Ustilago
maydis is initiated by gene sid 1, the product of which
bears sequence homology to the
lysine-N
-hydroxylase of E. coli (43).
) coordination propeller with
the highest known binding constant for ferric ion(9) .
Enterobactin is produced generally by enteric
bacteria.
-hydroxyacetyl lysine, is fabricated in sequence
by oxidation of L-lysine, followed by acetylation and
condensation, in a particular order, of two of these side chains with
citrate. Four gene products are required for the biosynthesis. Work has
centered on the gene encoding the monooxygenase since this enzyme
catalyzes the first step in the pathway and is a logical target for
chemotherapeutic intervention aimed at blocking aerobactin synthesis.
The gene has been sequenced(13) , and fusions with
-galactosidase were used as a means of solubilizing the
enzyme(14) . Lysine-N-hydroxylase, which
carries loosely bound FAD, oxidizes the substrate at the expense of
NADPH and molecular oxygen(15) .
-hydroxy acid functions. Capacity to form these pseudobactin or
pyoverdine type siderophores has been associated with improved plant
growth either through a direct effect on the plant, through control of
noxious organisms in the soil, or via some other route. Nitrogenase can
be said to be an iron-intensive enzyme complex and the symbiotic
variety, as found in Rhizobium spp., may require an intact
siderophore system for expression of this exclusively prokaryotic
catalyst upon which all life depends. These topics are explored in a
recent volume dealing with siderophores in the plant
world(42) .
©1995 by The American Society for Biochemistry and Molecular Biology, Inc.
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R. E. Moore, Y. Kim, and C. C. Philpott The mechanism of ferrichrome transport through Arn1p and its metabolism in Saccharomyces cerevisiae PNAS, May 13, 2003; 100(10): 5664 - 5669. [Abstract] [Full Text] [PDF]
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C. W. Dorsey, M. E. Tolmasky, J. H. Crosa, and L. A. Actis Genetic organization of an Acinetobacter baumannii chromosomal region harbouring genes related to siderophore biosynthesis and transport Microbiology, May 1, 2003; 149(5): 1227 - 1238. [Abstract] [Full Text] [PDF]
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M. de Chial, B. Ghysels, S. A. Beatson, V. Geoffroy, J. M. Meyer, T. Pattery, C. Baysse, P. Chablain, Y. N. Parsons, C. Winstanley, et al. Identification of type II and type III pyoverdine receptors from Pseudomonas aeruginosa Microbiology, April 1, 2003; 149(4): 821 - 831. [Abstract] [Full Text] [PDF]
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K. N. Raymond, E. A. Dertz, and S. S. Kim Bioinorganic Chemistry Special Feature: Enterobactin: An archetype for microbial iron transport PNAS, April 1, 2003; 100(7): 3584 - 3588. [Abstract] [Full Text] [PDF]
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S. R. Shouldice, D. R. Dougan, R. J. Skene, L. W. Tari, D. E. McRee, R.-h. Yu, and A. B. Schryvers High Resolution Structure of an Alternate Form of the Ferric Ion Binding Protein from Haemophilus influenzae J. Biol. Chem., March 21, 2003; 278(13): 11513 - 11519. [Abstract] [Full Text] [PDF]
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C. K. Vanderpool and S. K. Armstrong Heme-Responsive Transcriptional Activation of Bordetella bhu Genes J. Bacteriol., February 1, 2003; 185(3): 909 - 917. [Abstract] [Full Text] [PDF]
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Z. Cao, P. Warfel, S. M. C. Newton, and P. E. Klebba Spectroscopic Observations of Ferric Enterobactin Transport J. Biol. Chem., January 3, 2003; 278(2): 1022 - 1028. [Abstract] [Full Text] [PDF]
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P. N. Diouf, N. Delbarre, D. Perrin, P. Gerardin, C. Rapin, J. P. Jacquot, and E. Gelhaye Influence of Tropolone on Poria placenta Wood Degradation Appl. Envir. Microbiol., September 1, 2002; 68(9): 4377 - 4382. [Abstract] [Full Text] [PDF]
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L. G. Mikael, P. D. Pawelek, J. Labrie, M. Sirois, J. W. Coulton, and M. Jacques Molecular cloning and characterization of the ferric hydroxamate uptake (fhu) operon in Actinobacillus pleuropneumoniae Microbiology, September 1, 2002; 148(9): 2869 - 2882. [Abstract] [Full Text] [PDF]
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B. Pelletier, J. Beaudoin, Y. Mukai, and S. Labbe Fep1, an Iron Sensor Regulating Iron Transporter Gene Expression in Schizosaccharomyces pombe J. Biol. Chem., June 14, 2002; 277(25): 22950 - 22958. [Abstract] [Full Text] [PDF]
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 J. H. Crosa and C. T. Walsh Genetics and Assembly Line Enzymology of Siderophore Biosynthesis in Bacteria Microbiol. Mol. Biol. Rev., June 1, 2002; 66(2): 223 - 249. [Abstract] [Full Text] [PDF]
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R. K. Tokala, J. L. Strap, C. M. Jung, D. L. Crawford, M. H. Salove, L. A. Deobald, J. F. Bailey, and M. J. Morra Novel Plant-Microbe Rhizosphere Interaction Involving Streptomyces lydicus WYEC108 and the Pea Plant (Pisum sativum) Appl. Envir. Microbiol., May 1, 2002; 68(5): 2161 - 2171. [Abstract] [Full Text] [PDF]
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O. Ardon, H. Bussey, C. Philpott, D. M. Ward, S. Davis-Kaplan, S. Verroneau, B. Jiang, and J. Kaplan Identification of a Candida albicans Ferrichrome Transporter and Its Characterization by Expression in Saccharomyces cerevisiae J. Biol. Chem., November 9, 2001; 276(46): 43049 - 43055. [Abstract] [Full Text] [PDF]
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C. K. Vanderpool and S. K. Armstrong The Bordetella bhu Locus Is Required for Heme Iron Utilization J. Bacteriol., July 15, 2001; 183(14): 4278 - 4287. [Abstract] [Full Text] [PDF]
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W. M. Yuan, G. D. Gentil, A. D. Budde, and S. A. Leong Characterization of the Ustilago maydis sid2 Gene, Encoding a Multidomain Peptide Synthetase in the Ferrichrome Biosynthetic Gene Cluster J. Bacteriol., July 1, 2001; 183(13): 4040 - 4051. [Abstract] [Full Text] [PDF]
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L. L. Guan, K. Kanoh, and K. Kamino Effect of Exogenous Siderophores on Iron Uptake Activity of Marine Bacteria under Iron-Limited Conditions Appl. Envir. Microbiol., April 1, 2001; 67(4): 1710 - 1717. [Abstract] [Full Text]
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R. Penyalver, P. Oger, M. M. López, and S. K. Farrand Iron-Binding Compounds from Agrobacterium spp.: Biological Control Strain Agrobacterium rhizogenes K84 Produces a Hydroxamate Siderophore Appl. Envir. Microbiol., February 1, 2001; 67(2): 654 - 664. [Abstract] [Full Text]
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G. Cabrera, A. Xiong, M. Uebel, V. K. Singh, and R. K. Jayaswal Molecular Characterization of the Iron-Hydroxamate Uptake System in Staphylococcus aureus Appl. Envir. Microbiol., February 1, 2001; 67(2): 1001 - 1003. [Abstract] [Full Text]
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E. E. Zheleznova, J. H. Crosa, and R. G. Brennan Characterization of the DNA- and Metal-Binding Properties of Vibrio anguillarum Fur Reveals Conservation of a Structural Zn2+ Ion J. Bacteriol., November 1, 2000; 182(21): 6264 - 6267. [Abstract] [Full Text]
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C. Sprencel, Z. Cao, Z. Qi, D. C. Scott, M. A. Montague, N. Ivanoff, J. Xu, K. M. Raymond, S. M. C. Newton, and P. E. Klebba Binding of Ferric Enterobactin by the Escherichia coli Periplasmic Protein FepB J. Bacteriol., October 1, 2000; 182(19): 5359 - 5364. [Abstract] [Full Text]
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A. Stintzi, C. Barnes, J. Xu, and K. N. Raymond Microbial iron transport via a siderophore shuttle: A membrane ion transport paradigm PNAS, September 19, 2000; (2000) 200318797. [Abstract] [Full Text]
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L. L. Guan, H. Onuki, and K. Kamino Bacterial Growth Stimulation with Exogenous Siderophore and Synthetic N-Acyl Homoserine Lactone Autoinducers under Iron-Limited and Low-Nutrient Conditions Appl. Envir. Microbiol., July 1, 2000; 66(7): 2797 - 2803. [Abstract] [Full Text]
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Z. Ye and J. R. Connor Identification of iron responsive genes by screening cDNA libraries from suppression subtractive hybridization with antisense probes from three iron conditions Nucleic Acids Res., April 15, 2000; 28(8): 1802 - 1807. [Abstract] [Full Text] [PDF]
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 A. D. Anbar, J. E. Roe, J. Barling, and K. H. Nealson Nonbiological Fractionation of Iron Isotopes Science, April 7, 2000; 288(5463): 126 - 128. [Abstract] [Full Text]
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C.-W. Yun, T. Ferea, J. Rashford, O. Ardon, P. O. Brown, D. Botstein, J. Kaplan, and C. C. Philpott Desferrioxamine-mediated Iron Uptake in Saccharomyces cerevisiae. EVIDENCE FOR TWO PATHWAYS OF IRON UPTAKE J. Biol. Chem., March 31, 2000; 275(14): 10709 - 10715. [Abstract] [Full Text] [PDF]
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B. E. Britigan, G. T. Rasmussen, O. Olakanmi, and C. D. Cox Iron Acquisition from Pseudomonas aeruginosa Siderophores by Human Phagocytes: an Additional Mechanism of Host Defense through Iron Sequestration? Infect. Immun., March 1, 2000; 68(3): 1271 - 1275. [Abstract] [Full Text] [PDF]
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A. Xiong, V. K. Singh, G. Cabrera, and R. K. Jayaswal Molecular characterization of the ferric-uptake regulator, Fur, from Staphylococcus aureus Microbiology, March 1, 2000; 146(3): 659 - 668. [Abstract] [Full Text]
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 M. V. Panchenko, H. W. Farber, and J. H. Korn Induction of heme oxygenase-1 by hypoxia and free radicals in human dermal fibroblasts Am J Physiol Cell Physiol, January 1, 2000; 278(1): C92 - C101. [Abstract] [Full Text] [PDF]
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 A. O. Tzianabos, R. L. Cisneros, J. Gershkovich, J. Johnson, R. J. Miller, J. W. Burns, and A. B. Onderdonk Effect of Surgical Adhesion Reduction Devices on the Propagation of Experimental Intra-abdominal Infection Arch Surg, November 1, 1999; 134(11): 1254 - 1259. [Abstract] [Full Text] [PDF]
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N. Bsat and J. D. Helmann Interaction of Bacillus subtilis Fur (Ferric Uptake Repressor) with the dhb Operator In Vitro and In Vivo J. Bacteriol., July 15, 1999; 181(14): 4299 - 4307. [Abstract] [Full Text]
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O. Dussurget, J. Timm, M. Gomez, B. Gold, S. Yu, S. Z. Sabol, R. K. Holmes, W. R. Jacobs Jr., and I. Smith Transcriptional Control of the Iron-Responsive fxbA Gene by the Mycobacterial Regulator IdeR J. Bacteriol., June 1, 1999; 181(11): 3402 - 3408. [Abstract] [Full Text]
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A. Segura, P. V. Bünz, D. A. D'Argenio, and L. N. Ornston Genetic Analysis of a Chromosomal Region Containing vanA and vanB, Genes Required for Conversion of Either Ferulate or Vanillate to Protocatechuate in Acinetobacter J. Bacteriol., June 1, 1999; 181(11): 3494 - 3504. [Abstract] [Full Text]
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E. S. Henle, Z. Han, N. Tang, P. Rai, Y. Luo, and S. Linn Sequence-specific DNA Cleavage by Fe2+-mediated Fenton Reactions Has Possible Biological Implications J. Biol. Chem., January 8, 1999; 274(2): 962 - 971. [Abstract] [Full Text] [PDF]
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P. Thulasiraman, S. M. C. Newton, J. Xu, K. N. Raymond, C. Mai, A. Hall, M. A. Montague, and P. E. Klebba Selectivity of Ferric Enterobactin Binding and Cooperativity of Transport in Gram-Negative Bacteria J. Bacteriol., December 15, 1998; 180(24): 6689 - 6696. [Abstract] [Full Text]
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S. Yu, E. Fiss, and W. R. Jacobs Jr. Analysis of the Exochelin Locus in Mycobacterium smegmatis: Biosynthesis Genes Have Homology with Genes of the Peptide Synthetase Family J. Bacteriol., September 1, 1998; 180(17): 4676 - 4685. [Abstract] [Full Text]
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H. Y. Kang and S. K. Armstrong Transcriptional Analysis of the Bordetella Alcaligin Siderophore Biosynthesis Operon J. Bacteriol., February 15, 1998; 180(4): 855 - 861. [Abstract] [Full Text]
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S. M. C. Newton, J. S. Allen, Z. Cao, Z. Qi, X. Jiang, C. Sprencel, J. D. Igo, S. B. Foster, M. A. Payne, and P. E. Klebba Double mutagenesis of a positive charge cluster in the ligand-binding site of the ferric enterobactin receptor, FepA PNAS, April 29, 1997; 94(9): 4560 - 4565. [Abstract] [Full Text] [PDF]
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C.-W. Yun, J. S. Tiedeman, R. E. Moore, and C. C. Philpott Siderophore-Iron Uptake in Saccharomyces cerevisiae. IDENTIFICATION OF FERRICHROME AND FUSARININE TRANSPORTERS J. Biol. Chem., May 19, 2000; 275(21): 16354 - 16359. [Abstract] [Full Text] [PDF]
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C.-W. Yun, M. Bauler, R. E. Moore, P. E. Klebba, and C. C. Philpott The Role of the FRE Family of Plasma Membrane Reductases in the Uptake of Siderophore-Iron in Saccharomyces cerevisiae J. Biol. Chem., March 23, 2001; 276(13): 10218 - 10223. [Abstract] [Full Text] [PDF]
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A. M. Romeo, L. Christen, E. G. Niles, and D. J. Kosman Intracellular Chelation of Iron by Bipyridyl Inhibits DNA Virus Replication. RIBONUCLEOTIDE REDUCTASE MATURATION AS A PROBE OF INTRACELLULAR IRON POOLS J. Biol. Chem., June 22, 2001; 276(26): 24301 - 24308. [Abstract] [Full Text] [PDF]
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D. C. Scott, Z. Cao, Z. Qi, M. Bauler, J. D. Igo, S. M. C. Newton, and P. E. Klebba Exchangeability of N Termini in the Ligand-gated Porins of Escherichia coli J. Biol. Chem., April 13, 2001; 276(16): 13025 - 13033. [Abstract] [Full Text] [PDF]
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O. Protchenko, T. Ferea, J. Rashford, J. Tiedeman, P. O. Brown, D. Botstein, and C. C. Philpott Three Cell Wall Mannoproteins Facilitate the Uptake of Iron in Saccharomyces cerevisiae J. Biol. Chem., December 21, 2001; 276(52): 49244 - 49250. [Abstract] [Full Text] [PDF]
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D. E. Ehmann, C. A. Shaw-Reid, H. C. Losey, and C. T. Walsh The EntF and EntE adenylation domains of Escherichia coli enterobactin synthetase: Sequestration and selectivity in acyl-AMP transfers to thiolation domain cosubstrates PNAS, March 14, 2000; 97(6): 2509 - 2514. [Abstract] [Full Text] [PDF]
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A. Stintzi, C. Barnes, J. Xu, and K. N. Raymond Microbial iron transport via a siderophore shuttle: A membrane ion transport paradigm PNAS, September 26, 2000; 97(20): 10691 - 10696. [Abstract] [Full Text] [PDF]
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