Acquisition and storage of inorganic iron and hemin by the yersiniae

Breaking Iron Homeostasis: Iron Capturing Nanocomposites for Combating Bacterial Biofilm

Given the scarcity of novel antibiotics, the eradication of bacterial biofilm infections poses formidable challenges. Upon bacterial infection, the host restricts Fe ions, which are crucial for bacterial growth and maintenance. Having coevolved with the host, bacteria developed adaptive pathways like the hemin-uptake system to avoid iron deficiency. Inspired by this, we propose a novel strategy, termed iron nutritional immunity therapy (INIT), utilizing Ga-CT@P nanocomposites constructed with gallium, copper-doped tetrakis (4-carboxyphenyl) porphyrin (TCPP) metal-organic framework, and polyamine-amine polymer dots, to target bacterial iron intakes and starve them. Owing to the similarity between iron/hemin and gallium/TCPP, gallium-incorporated porphyrin potentially deceives bacteria into uptaking gallium ions and concurrently extracts iron ions from the surrounding bacteria milieu through the porphyrin ring. This strategy orchestrates a "give and take" approach for Ga3+/Fe3+ exchange. Simultaneously, polymer dots can impede bacterial iron metabolism and serve as real-time fluorescent iron-sensing probes to continuously monitor dynamic iron restriction status. INIT based on Ga-CT@P nanocomposites induced long-term iron starvation, which affected iron-sulfur cluster biogenesis and carbohydrate metabolism, ultimately facilitating biofilm eradication and tissue regeneration. Therefore, this study presents an innovative antibacterial strategy from a nutritional perspective that sheds light on refractory bacterial infection treatment and its future clinical application.

Impact of OmpR on the membrane proteome of Yersinia enterocolitica in different environments: repression of major adhesin YadA and heme receptor HemR

Enteropathogenic Yersinia enterocolitica is able to grow within or outside the mammalian host. Previous transcriptomic studies have indicated that the regulator OmpR plays a role in the expression of hundreds of genes in enterobacteria. Here, we have examined the impact of OmpR on the production of Y. enterocolitica membrane proteins upon changes in temperature, osmolarity and pH. Proteomic analysis indicated that the loss of OmpR affects the production of 120 proteins, a third of which are involved in uptake/transport, including several that participate in iron or heme acquisition. A set of proteins associated with virulence was also affected. The influence of OmpR on the abundance of adhesin YadA and heme receptor HemR was examined in more detail. OmpR was found to repress YadA production and bind to the yadA promoter, suggesting a direct regulatory effect. In contrast, the repression of hemR expression by OmpR appears to be indirect. These findings provide new insights into the role of OmpR in remodelling the cell surface and the adaptation of Y. enterocolitica to different environmental niches, including the host.

Transcriptome changes associated with anaerobic growth in Yersinia intermedia (ATCC29909)

Background

The yersiniae (Enterobacteriaceae) occupy a variety of niches, including some in human and flea hosts. Metabolic adaptations of the yersiniae, which contribute to their success in these specialized environments, remain largely unknown. We report results of an investigation of the transcriptome under aerobic and anaerobic conditions for Y. intermedia, a non-pathogenic member of the genus that has been used as a research surrogate for Y. pestis. Y. intermedia shares characteristics of pathogenic yersiniae, but is not known to cause disease in humans. Oxygen restriction is an important environmental stimulus experienced by many bacteria during their life-cycles and greatly influences their survival in specific environments. How oxygen availability affects physiology in the yersiniae is of importance in their life cycles but has not been extensively characterized.

Methodology/Principal Findings

Tiled oligonucleotide arrays based on a draft genome sequence of Y. intermedia were used in transcript profiling experiments to identify genes that change expression in response to oxygen availability during growth in minimal media with glucose. The expression of more than 400 genes, constituting about 10% of the genome, was significantly altered due to oxygen-limitation in early log phase under these conditions. Broad functional categorization indicated that, in addition to genes involved in central metabolism, genes involved in adaptation to stress and genes likely involved with host interactions were affected by oxygen-availability. Notable among these, were genes encoding functions for motility, chemotaxis and biosynthesis of cobalamin, which were up-regulated and those for iron/heme utilization, methionine metabolism and urease, which were down-regulated.

Conclusions/Significance

This is the first transcriptome analysis of a non-pathogenic Yersiniaspp. and one of few elucidating the global response to oxygen limitation for any of the yersiniae. Thus this study lays the foundation for further experimental characterization of oxygen-responsive genes and pathways in this ecologically diverse genus.

Yersinia pseudotuberculosis mntH functions in intracellular manganese accumulation, which is essential for virulence and survival in cells expressing functional Nramp1

Manganese has an important yet undefined role in the virulence of many bacterial pathogens. In this study we confirm that a null mutation in Yersinia pseudotuberculosis mntH reduces intracellular manganese accumulation. An mntH mutant was susceptible to killing by reactive oxygen species when grown under manganese-limited conditions. The mntH mutant was defective in survival and growth in macrophages expressing functional Nramp1, but in macrophages deficient in Nramp the bacteria were able to survive and replicate. In Galleria mellonella, the mntH mutant was attenuated. Taken together, these data suggest a role for manganese in Y. pseudotuberculosis during macrophage intracellular survival, protecting the bacteria from the antimicrobial products released during the respiratory burst.

Distribution of serotypes and virulence-associated genes in pathogenic Escherichia coli isolated from ducks

The objective of the present study was to investigate the serotypes and virulence-associated genes of avian pathogenic Escherichia coli (APEC) isolated from duck colibacillosis cases. Two hundred and fifty-four APEC isolates from duck colibacillosis cases were serotyped and amplified for 12 known virulence-associated genes and the betA gene (encoding choline dehydrogenase) by polymerase chain reaction assays. One hundred and forty-three E. coli isolates from cloacal swabs of healthy ducks were also amplified for the same genes. A total of 53 O-serogroups were found in 254 APEC isolates, among which O93, O78 and O92 were predominant serogroups. Polymerase chain reaction results showed that Shiga-toxin-producing E. coli distributed in only 2.4% of ducks compared with 49.2% of the APEC isolates harbouring the irp2 gene, and 44.9% the fyuA gene, respectively. The ibeA gene was only present in 27 APEC isolates and was not found in healthy ducks. The rfaH gene was detected in 20.5% of APEC isolates, whereas 5.6% was found in healthy ducks. A total 79.5% of APEC isolates harboured the betA gene, which was significantly higher than in healthy ducks (16.1%), suggesting that betA may be associated with virulence.

Comparative analysis of the Photorhabdus luminescens and the Yersinia enterocolitica genomes: uncovering candidate genes involved in insect pathogenicity

Background

Photorhabdus luminescens and Yersinia enterocolitica are both enteric bacteria which are associated with insects. P. luminescens lives in symbiosis with soil nematodes and is highly pathogenic towards insects but not to humans. In contrast, Y. enterocolitica is widely found in the environment and mainly known to cause gastroenteritis in men, but has only recently been shown to be also toxic for insects. It is expected that both pathogens share an overlap of genetic determinants that play a role within the insect host.

Results

A selective genome comparison was applied. Proteins belonging to the class of two-component regulatory systems, quorum sensing, universal stress proteins, and c-di-GMP signalling have been analysed. The interorganismic synopsis of selected regulatory systems uncovered common and distinct signalling mechanisms of both pathogens used for perception of signals within the insect host. Particularly, a new class of LuxR-like regulators was identified, which might be involved in detecting insect-specific molecules. In addition, the genetic overlap unravelled a two-component system that is unique for the genera Photorhabdus and Yersinia and is therefore suggested to play a major role in the pathogen-insect relationship. Our analysis also highlights factors of both pathogens that are expressed at low temperatures as encountered in insects in contrast to higher (body) temperature, providing evidence that temperature is a yet under-investigated environmental signal for bacterial adaptation to various hosts. Common degradative metabolic pathways are described that might be used to explore nutrients within the insect gut or hemolymph, thus enabling the proliferation of P. luminescens and Y. enterocolitica in their invertebrate hosts. A strikingly higher number of genes encoding insecticidal toxins and other virulence factors in P. luminescens compared to Y. enterocolitica correlates with the higher virulence of P. luminescens towards insects, and suggests a putative broader insect host spectrum of this pathogen.

Conclusion

A set of factors shared by the two pathogens was identified including those that are involved in the host infection process, in persistence within the insect, or in host exploitation. Some of them might have been selected during the association with insects and then adapted to pathogenesis in mammalian hosts.

Relative Reinforcing Effects of Cocaine, Remifentanil, and Their Combination in Rhesus Monkeys

Human polydrug abusers often take combinations of opioids and stimulants, but it is not clear why. Behavioral economics with demand curve analysis is uniquely able to separate two of the possibilities: that the drug combination increases the reinforcing potency of the component drugs or that the drug combination is a more effective reinforcer than either drug alone. Rhesus monkeys self-administered a range of doses of cocaine, remifentanil, and combinations of the drugs through indwelling intravenous catheters; the number of responses required for each drug infusion increased across drug-availability sessions. Combining small doses of cocaine and remifentanil that by themselves resulted in very low rates of responding yielded rates of responding that were higher than the maximum maintained by any dose of the constituent drugs. Nevertheless, demand curve analysis demonstrated that the drug combination was equally elastic as the component drugs, indicating that it was not more effective as a reinforcer than either cocaine or remifentanil alone. This suggests that enhanced self-administration of this particular drug combination is due primarily to the drug enhancement of the potency of the other drug.

Complete DNA sequence of Yersinia enterocolitica serotype 0:8 low-calcium-response plasmid reveals a new virulence plasmid-associated replicon

The complete nucleotide sequence and organization of the Yersinia enterocolitica serotype 0:8 low-calcium-response (LCR) plasmid, pYVe8081, were determined. The 67,720-bp plasmid encoded all the genes known to be part of the LCR stimulon except for ylpA. Eight of 13 intact open reading frames of unknown function identified in pYVe8081 had homologues in Yersinia pestis plasmid pCD1 or in Y. enterocolitica serotype 0:9 plasmid pYVe227. A region of approximately 17 kbp showed no DNA identity to pCD1 or pYVe227 and contained six potential new genes, a possible new replicon, and two intact insertion sequence (IS) elements. One intact IS element, ISYen1, was a new IS belonging to the IS256 family. Several vestigial IS elements appeared different from the IS distribution seen in the other LCR plasmids. The RepA proteins encoded by Y. enterocolitica serotype 0:8 pYVeWA and pYVe8081 were identical. The putative pYVe8081 replicon showed significant homology to the IncL/M replicon of pMU407.1 but was only distantly related to the replicons of pCD1 and pYVe227. In contrast, the putative partitioning genes of pYVe8081 showed 97% DNA identity to the spy/sopABC loci of pCD1 and pYVe227. Sequence analysis suggests that Yersinia LCR plasmids are from a common ancestor but that Y. enterocolitica serotype 0:8 plasmid replicons may have evolved independently via cointegrate formation following a transposition event. The change in replicon structure is predicted to change the incompatibility properties of Y. enterocolitica serotype 0:8 plasmids from those of Y. enterocolitica serotype 0:9 and Y. pestis LCR plasmids.

Isolation of pathogenic yersiniae from wild animals in Bulgaria

Pathogenic Yersinia strains were isolated between December 1998 and April 1999 from 37 wild animals: rabbit (Lepus europeus), boar (Sus scrofa scrofa), asiatic jackal (Canis aureus), red fox (Vulpes vulpes), mouflon (Ovis musimon), european river otter (Lutra lutra), beech marten (Martes foina), polecat (Musleta putorius) and wild cat (Felis silvestris). It was established that among the wild animals Y. enterocolitica strains of serotype 0:3 predominated, accompanied by Y. pseudotuberculosis strains of serotype 0:3. In one sample from asiatic jackal and one sample from rabbit, Y. enterocolitica serotype 0:8 was isolated. Yersinia enterocolitica and Y. pseudotuberculosis strains were isolated from tonsils and tongues as well as from the viscera--lung, liver, heart, spleen, kidney and lymph nodes, mainly in young animals (1-2 years of age). The results showed that wild animals are a possible natural reservoir for pathogenic Y. enterocolitica and Y. pseudotuberculosis and are included in the epidemiological chain of yersinioses.

Acquisition, transport, and storage of iron by pathogenic fungi

Iron is required by most living systems. A great variety of means of acquisition, avenues of uptake, and methods of storage are used by pathogenic fungi to ensure a supply of the essential metal. Solubilization of insoluble iron polymers is the first step in iron assimilation. The two methods most commonly used by microorganisms for solubilization of iron are reduction and chelation. Reduction of ferric iron to ferrous iron by enzymatic or nonenzymatic means is a common mechanism among pathogenic yeasts. Under conditions of iron starvation, many fungi synthesize iron chelators known as siderophores. Two classes of compounds that function in iron gathering are commonly observed: hydroxamates and polycarboxylates. Two major responses to iron stress in fungi are a high-affinity ferric iron reductase and siderophore synthesis. Regulation of these two mechanisms at the molecular level has received attention. Uptake of siderophores is a diverse process, which varies among the different classes of compounds. Since free iron is toxic, it must be stored for further metabolic use. Polyphosphates, ferritins, and siderophores themselves have been described as storage molecules. The iron-gathering mechanisms used by a pathogen in an infected host are largely unknown and can only be posited on the basis of in vitro studies at present.

Sequence and genetic analysis of the hemin storage (hms) system of Yersinia pestis

We have sequenced a region from the pigmentation (pgm) locus of Yersinia pestis KIM6+ that is identified with the exogenous hemin storage (Hms+) phenotype in cells grown at 26 but not at 37 degrees C. The hmsHFRS locus encodes a putative polycistronic operon, with hmsH encoding an outer membrane protein with a deduced molecular mass of 93.4/89.5 (unprocessed/processed) kDa. The mature HmsH 788 aa polypeptide has a pI of 4.99. The hmsF gene has an open reading frame of 654 aa, encoding a 74.6/72.2 kDa OM protein with a pI of 5.16 when processed. A deduced 423 aa, 52 kDa protein with a pI of 10.83 is encoded by hmsR. HmsR has a basic, hydrophilic, and alpha-helical carboxyl terminus; 13 aa at the amino-terminal end and a 'KRKRAR' sequence at the carboxy-terminal end are essential for an Hms+ phenotype. The hmsS gene encodes a hypothetical 155 aa, 17.5 kDa protein with a pI of 6.68. Hms- Y. pestis strain M23-2 transformed with the cloned hmsHFRS locus developed an Hms(c) phenotype (Hms+ at 26-37 degrees C) due to mutations in genes outside the pgm locus.

Genetic organization of the yersiniabactin biosynthetic region and construction of avirulent mutants in Yersinia pestis

We have identified an approximately 22-kb region of the pgm locus of Yersinia pestis KIM6+ which encodes a number of iron-regulated proteins involved in the biosynthesis of the Y. pestis cognate siderophore, yersiniabactin (Ybt), and which is located immediately upstream of the pesticin/yersiniabactin receptor gene (psn). Sequence analysis and the construction of insertion and deletion mutants allowed us to determine the putative location of the irp1 gene and the positions of irp2, ybtT, and ybtE within the ybt operon. Mutations in the irp1, irp2, or ybtE gene yielded strains defective in siderophore production. Mutant strains were unable to grow on iron-deficient media at 37 degrees C but could be cross-fed by culture supernatants from yersiniabactin-producing strains of Y. pestis grown under iron-limiting conditions. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis of whole-cell extracts from Ybt+ and Ybt- strains grown in iron-deficient media revealed that expression of ybt-encoded proteins is not only iron regulated but also influenced by the presence of the siderophore itself. Finally, Y. pestis strains with mutations in either the psn or irp2 gene were avirulent in mice when inoculated subcutaneously.

Cloning and characterization of bacteriophage-like DNA from Haemophilus somnus homologous to phages P2 and HP1

In an attempt to identify and characterize components of a heme uptake system of Haemophilus somnus, an Escherichia coli cosmid library of H. somnus genomic DNA was screened for the ability to bind hemin (Hmb+). The Hmb+ phenotype was associated with a 7,814-bp HindIII fragment of H. somnus DNA that was subcloned and sequenced. Thirteen open reading frames (orfs) were identified, all transcribed in one direction, and transposon mutagenesis identified orf7 as the gene associated with the Hmb+ phenotype. Orf7 (178 amino acids) has extensive homology with the lysozymes of bacteriophages P-A2, P21, P22, PZA, phi-29, phi-vML3, T4, or HP1. The orf7 gene complemented the lytic function of the K gene of phage P2 and the R gene of phage lambda. A lysozyme assay using supernatants from whole-cell lysates of E. coli cultures harboring plasmid pRAP501 or pGCH2 (both of which express the orf7 gene product) exhibited significant levels of lysozyme activity. The orf6 gene upstream of orf7 has the dual start motif common to the holins encoded by lambdoid S genes, and the orf6 gene product has significant homology to the holins of phages HP1 and P21. When expressed from a tac promoter, the orf6 gene product caused immediate cell death without lysis, while cultures expressing the orf7 gene product grew at normal rates but lysed immediately after the addition of chloroform. Based on this data, we concluded that the Hmb+ phenotype was an artifact resulting from the expression of cloned lysis genes which were detrimental to the E. coli host. The DNA flanking the cloned lysis genes contains orfs that are similar to structural and DNA packaging genes of phage P2. Polyclonal antiserum against Orf2, which is homologous to the major capsid precursor protein (gpN) of phage P2, detected a 40,000-M(r) protein expressed from pRAP401 but did not detect Orf2 in H. somnus, lysates. The phage-like DNA was detected in the serum-susceptible preputial strains HS-124P and HS-127P but was absent from the serum-resistant preputial strains HS-20P and HS-22P. Elucidation of a potential role for this cryptic prophage in the H. somnus life cycle requires more study.

Characterization of hemin binding activity of Streptococcus pneumoniae

Streptococcus pneumoniae is a causative agent of bacterial pneumonia, otitis media, meningitis, and bacteremia. It causes considerable morbidity and mortality throughout the world, especially among children, the elderly, and immunocompromised individuals. We have demonstrated previously that the growth of S. pneumoniae is limited under iron-depleted conditions and can be restored by the addition of either hemin or hemoglobin. In the present study, we showed that S. pneumoniae had the ability to bind hemin and that the level of hemin binding activity was not affected by supplementation of the growth medium with iron. Approximately 70 to 80% of the hemin binding activity was mediated by proteinase-resistant components, and the remainder was mediated by proteins. Hemin binding proteins were located in both soluble extract and envelope fractions of pneumococcal cells. By batch affinity chromatography, a major hemin binding polypeptide with an apparent molecular mass of 43 kDa was identified in the cell lysate of S. pneumoniae. Polyclonal antibodies against this polypeptide were raised. By immunoblot analysis, this hemin binding polypeptide was localized in the envelope and did not exhibit any variation in molecular weight among all serotypes tested. The subcellular distribution of hemin binding activity may have functional implications.

Yersinia pestis--etiologic agent of plague

Plague is a widespread zoonotic disease that is caused by Yersinia pestis and has had devastating effects on the human population throughout history. Disappearance of the disease is unlikely due to the wide range of mammalian hosts and their attendant fleas. The flea/rodent life cycle of Y. pestis, a gram-negative obligate pathogen, exposes it to very different environmental conditions and has resulted in some novel traits facilitating transmission and infection. Studies characterizing virulence determinants of Y. pestis have identified novel mechanisms for overcoming host defenses. Regulatory systems controlling the expression of some of these virulence factors have proven quite complex. These areas of research have provide new insights into the host-parasite relationship. This review will update our present understanding of the history, etiology, epidemiology, clinical aspects, and public health issues of plague.

Iron uptake and iron-repressible polypeptides in Yersinia pestis

Pigmented (Pgm+) cells of Yersinia pestis are virulent, are sensitive to pesticin, adsorb exogenous hemin at 26 degrees C (Hms+), produce iron-repressible outer membrane proteins, and grow at 37 degrees C in iron-deficient media. These traits are lost upon spontaneous deletion of a chromosomal 102-kb pgm locus (Pgm-). Here we demonstrate that an Hms+ but pesticin-resistant (Pst(r)) mutant acquired a 5-bp deletion in the pesticin receptor gene (psn) encoding IrpB to IrpD. Growth and assimilation of iron by Pgm- and Hms+ Pst(r) mutants were markedly inhibited by ferrous chelators at 37 degrees C; inhibition by ferric and ferrous chelators was less effective at 26 degrees C. Iron-deficient growth at 26 degrees C induced iron-regulated outer membrane proteins of 34, 28.5, and 22.5 kDa and periplasmic polypeptides of 33.5 and 30 kDa. These findings provide a basis for understanding the psn-driven system of iron uptake, indicate the existence of at least one additional 26 degrees C-dependent iron assimilation system, and define over 30 iron-repressible proteins in Y. pestis.

HmbR outer membrane receptors of pathogenic Neisseria spp.: iron-regulated, hemoglobin-binding proteins with a high level of primary structure conservation

We have recently cloned and characterized the hemoglobin receptor gene from Neisseria meningitidis serogroup C. N. meningitidis cells expressing HmbR protein were able to bind biotinylated hemoglobin, and the binding was specifically inhibited by unlabeled hemoglobin and not heme. The HmbR-mediated hemoglobin binding activity of N. meningitidis cells was shown to be iron regulated. The presence of hemoglobin but not heme in the growth medium stimulated HmbR-mediated hemoglobin binding activity. The efficiency of utilization of different hemoglobins by the HmbR-expressing N. meningitidis cells was shown to be species specific; human hemoglobin was the best source of iron, followed by horse, rat, turkey, dog, mouse, and sheep hemoglobins, The phenotypic characterization of HmbR mutants of some clinical strains of N. meningitidis suggested the existence of two unrelated hemoglobin receptors. The HmbR-unrelated hemoglobin receptor was shown to be identical to Hpu, the hemoglobin-haptoglobin receptor of N. meningitidis. The Hpu-dependent hemoglobin utilization system was not able to distinguish between different sources of hemoglobin; all animal hemoglobins were utilized equally well. HmbR-like genes are also present in N. meningitidis serogroups A and B, Neisseria gonorrhoeae MS11 and FA19, Neisseria perflava, and Neisseria polysaccharea. The hemoglobin receptor genes from N. meningitidis serogroups A and B and N. gonorrhoeae MS11 were cloned, and their nucleotide sequences were determined. The nucleotide sequence identity ranged between 86.5% (for N. meningitidis serogroup B hmbR and MS11 hmbR) and 93.4% (for N. meningitidis serogroup B hmbR and N. meningitidis serogroup C hmbR). The deduced amino acid sequences of these neisserial hemoglobin receptors were also highly related, with overall 84.7% conserved amino acid residues. A stop codon was found in the hmbR gene of N. gonorrhoeae MS11. This strain was still able to use hemoglobin and hemoglobin-haptoglobin complexes as iron sources, indicating that some gonococci may express only the HmbR-independent hemoglobin utilization system.

A Legionella pneumophila gene that promotes hemin binding

The ability to bind and utilize hemin is a trait common to many human pathogens. Nevertheless, the relationship between Legionella pneumophila, the agent of Legionnaires' disease, and hemin has received little attention. Thus, we explored the capacity of a virulent, serogroup 1 strain of L. pneumophila to bind hemin and use it as an iron source. Hemin, but not protoporphyrin IX, restored bacterial growth in iron-limiting media, indicating that it can serve as an iron source for L. pneumophila. In support of this idea, we observed that wildtype legionellae were able to bind 50 to 60% of added hemin, a binding capacity that was comparable to those of other pathogens. To begin to identify proteins involved in hemin acquisition, we identified a Legionella locus that conferred hemin binding upon Escherichia coli. Subcloning and nucleotide sequence analysis determined that a single open reading frame, which was designated hbp for hemin-binding promotion, was responsible for this binding activity. The hbp gene was predicted to encode a secreted, 15.5-kDa protein. To ascertain the importance of this gene in L. pneumophila biology, we used allelic exchange to construct an hbp mutant. Importantly, the mutant displayed a 42% reduction in hemin binding, confirming that hbp potentiates hemin acquisition by L. pneumophila. However, the strain was unaltered in its ability to grow within macrophage-like cells and freshwater amoebae, indicating that hbp is not required for intracellular infection. Despite this, Southern hybridization analysis and database searches demonstrated that hbp is nearly exclusive to the L. pneumophila species.

Binding and accumulation of hemin in Neisseria gonorrhoeae

The ability to utilize hemin and hemin-containing compounds for nutritional iron (Fe) uptake has been documented for several pathogenic bacteria. Neisseria gonorrhoeae can utilize free hemin as a source of Fe for growth; however, little is known concerning the mechanisms involved in hemin transport. In this study we have characterized the binding and accumulation of hemin by N. gonorrhoeae and defined the specificity of the gonococcal hemin receptor. N. gonorrhoeae F62 was grown in a chemically defined medium containing the iron chelator Desferal, and hemin transport was initiated by the addition of [59Fe]hemin (4.0 or 8.0 microM; specific activity, 7.0 Ci/mol). 59Fe uptake from radiolabeled hemin by N. gonorrhoeae was energy dependent, and 59Fe was shown to accumulate in the cell at a constant rate during logarithmic growth. However, we observed a decrease in the uptake of 59Fe from radiolabeled hemin when inorganic iron was present in the growth medium. Binding of 59Fe from radiolabeled hemin was inhibited by the addition of either cold hemin, hematoporphyrin, or hemoglobin, but not by ferric citrate. Although [14C]hemin was found to support the growth of N. gonorrhoeae, we did not detect the uptake of 14C from radiolabeled hemin. Extraction of the gonococcal periplasmic ferric binding protein (Fbp) from cultures grown with [59Fe]hemin indicated that a majority of the 59Fe was associated with the Fbp. Taken together, the results presented here indicate that hemin binds to a gonococcal outer membrane receptor through the protoporphyrin portion of the molecule and that following binding, iron is removed and transported into the cell, where it is associated with the gonococcal periplasmic ferric binding protein, Fbp.

Iron-repressible outer membrane proteins of Helicobacter pylori involved in heme uptake

Helicobacter pylori is known to be a causative agent of gastritis and peptic ulcer disease in humans. The acquisition of iron from the human host may contribute greatly to the virulence of this organism. To study this, H. pylori was cultured under iron-restrictive conditions to induce synthesis of possible iron-regulated outer membrane proteins. This was achieved by the addition of 20% (vol/vol) heat-inactivated newborn calf serum, which contains iron-binding proteins like transferrin and albumin, and no free iron. The newborn calf serum was able to bind free ionic iron in brucella broth culture medium. Electrophoretic analysis of outer membrane preparations from H. pylori cultured under conditions of iron restriction showed several proteins to be present at elevated levels. These appeared to be iron-repressible outer membrane proteins (IROMPs). In addition, IROMPs with molecular sizes of 77, 50, and 48 kDa were isolated by use of hemin-agarose affinity chromatography. These three heme-binding IROMPs might be involved in the uptake of heme from the host and might therefore be important virulence factors of H. pylori.

Environmental modulation of gene expression and pathogenesis in Yersinia

The yersiniae are a useful model for understanding how environmental modulation of gene expression allows pathogens to inhabit a wide range of niches. This review follows the enteropathogenic yersiniae, Yersinia enterocolitica and Yersinia pseudotuberculosis, and the agent of plague, Yersinia pestis, through their life cycles, describing how adaptive gene expression may promote successful pathogenesis.

Evidence for two evolutionary lineages of highly pathogenic Yersinia species

Sensitivity to Yersinia pestis bacteriocin pesticin correlates with the existence of two groups of human pathogenic yersiniae, mouse lethal and mouse nonlethal. The presence of the outer membrane pesticin receptor (FyuA) in mouse-lethal yersiniae is a prerequisite for pesticin sensitivity. Genes that code for FyuA (fyuA) were identified and sequenced from pesticin-sensitive bacteria, including Y. enterocolitica biotype 1B (serotypes O8; O13, O20, and O21), Y. pseudotuberculosis serotype O1, Y. pestis, two known pesticin-sensitive Escherichia coli isolates (E. coli Phi and E. coli CA42), and two newly discovered pesticin-sensitive isolates, E. coli K49 and K235. A 2,318-bp fyuA sequence was shown to be highly conserved in all pesticin-sensitive bacteria, including E. coli strains (DNA sequence homology was 98.5 to 99.9%). The same degree of DNA homology (97.8 to 100%) was established for the sequenced 276-bp fragment of the irp2 gene that encodes high-molecular-weight protein 2, which is also thought to be involved in the expression of virulence by Yersinia species. Highly conserved irp2 was also found in all pesticin-sensitive E. coli strains. On the basis of the fyuA and irp2 sequence homologies, two evolutionary groups of highly pathogenic Yersinia species can be established. One group includes Y. enterocolitica biotype 1B strains, while the second includes Y. pestis, Y. pseudotuberculosis serotype O1, and irp2-positive Y. pseudotuberculosis serotype O3 strains. E. coli Phi, CA42, K49, and K235 belong to the second group. The possible proximity of these two iron-regulated genes (fyuA and irp2), as well as their high levels of sequence conservation and similar G+C contents (56.2 and 59.8 mol%), leads to the assumption that these two genes may represent part of an unstable pathogenicity island that has been acquired by pesticin-sensitive bacteria as a result of a horizontal transfer.

Analysis of the pesticin receptor from Yersinia pestis: role in iron-deficient growth and possible regulation by its siderophore

We have sequenced a region from the pgm locus of Yersinia pestis KIM6+ that confers sensitivity to the bacteriocin pesticin to certain strains of Escherichia coli and Y. pestis. The Y. pestis sequence is 98% identical to the pesticin receptor from Yersinia enterocolitica and is homologous to other TonB-dependent outer membrane proteins. Y. pestis strains with an in-frame deletion in the pesticin receptor gene (psn) were pesticin resistant and no longer expressed a group of iron-regulated outer membrane proteins, IrpB to IrpD. In addition, this strain as well as a Y. pestis strain with a mutation constructed in the gene (irp2) encoding the 190-kDa iron-regulated protein HMWP2 could not grow at 37 degrees C in a defined, iron-deficient medium. However, the irp2 mutant but not the psn mutant could be cross-fed by supernatants from various Yersinia cultures grown under iron-deficient conditions. An analysis of the proteins synthesized by the irp2 mutant suggests that HMWP2 may be indirectly required for maximal expression of the pesticin receptor. HMWP2 likely participates in synthesis of a siderophore which may induce expression of the receptor for pesticin and the siderophore.

Pleiotropic effects of a Yersinia pestis fur mutation

A Yersinia pestis fur mutation was constructed by insertionally disrupting the fur open reading frame. Analysis of a Fur-regulated beta-galactosidase reporter gene revealed a loss of iron regulation as a result of the fur mutation. trans complementation with the cloned Y. pestis fur gene restored iron regulation. The expression of most iron-regulated proteins was also deregulated by this mutation; however, a number of iron-repressible and two iron-inducible polypeptides retained normal regulation. Mutations in fur or hmsH, a gene encoding an 86-kDa surface protein required for hemin storage, increased the sensitivity of Y. pestis cells to the bacteriocin pesticin. Interestingly, the Y. pestis fur mutant lost temperature control of hemin storage; however, expression of the HmsH polypeptide was not deregulated. When grown with excess iron, a Y. pestis fur mutant possessing the 102-kb pigmentation locus exhibited severe growth inhibition and a dramatic increase in the number of spontaneous nonpigmented chromosomal deletion mutants present at late log phase. These results suggest that the Fur protein of Y. pestis is an important global regulator and that a separate Fur-independent iron regulatory system may exist.

The pigmentation locus of Yersinia pestis KIM6+ is flanked by an insertion sequence and includes the structural genes for pesticin sensitivity and HMWP2

The pigmentation (Pgm+) phenotype of Yersinia pestis includes a number of different characteristics which appear to be associated with a 102 kb segment of chromosomal DNA known as the pgm locus. In Y. pestis KIM6+, the pgm locus is flanked by direct copies of a repeated element that probably plays a role in the spontaneous deletion of this region. We have sequenced the ends of these elements and shown that they have features in common with bacterial insertion sequences. In addition we show that a clone, pSDR498, from the pgm locus of KIM6+ restores pesticin sensitivity and the iron-regulated expression of three polypeptides, 240 kDa, 190 kDa, and 68 kDa in size, to Pgm- cells. In vitro transcription/translation assays and Escherichia coli minicells were used to analyse the products encoded by various subclones of pSDR498. Pesticin sensitivity mapped to a 5.9 kb fragment that encodes a 68 kDa protein derived from a 72 kDa precursor. Synthesis of the 190 kDa protein was restored by a 19.2 kb clone, indicating that the structural gene for this protein also resides within the pgm locus of Y. pestis KIM6+. Finally, a survey of our Pgm- strains indicates that 97% have also deleted the sequences encoding the 190 kDa protein and pesticin sensitivity.

The pesticin receptor of Yersinia enterocolitica: a novel virulence factor with dual function

The iron-repressible outer membrane protein FyuA of Yersinia enterocolitica operates as a receptor with dual function: (i) as a receptor for the Y. pestis bacteriocin pesticin, and (ii) as a receptor for yersiniabactin, a siderophore that is produced by mouse-virulent Y. enterocolitica strains of biogroup IB. Cloning of the FyuA-encoding gene was achieved by mobilization of a genomic cosmid library of the pesticin-sensitive and mouse-virulent Y. enterocolitica O:8 strain WA into the pesticin-resistant WA fyuA mutant and subsequent in vivo selection of transconjugants for the ability to survive and multiply in mice (phenotype mouse virulence). The reisolated transconjugants which survived in mice for 3 d harboured a unique cosmid and phenotypically were pesticin sensitive. From this cosmid a 2650 bp SalI-PstI fragment conferring pesticin sensitivity was subcloned. Sequencing of this DNA fragment revealed a single open reading frame of 2022 bp, which encodes a deduced polypeptide of 673 amino acids with a predicted molecular mass of 73,677 Da. Cleavage of a putative signal sequence composed of 22 amino acids should lead to a mature protein of 651 amino acids with a molecular mass of 71,368 Da. The open reading frame is preceded by a sequence which shares homology with the postulated consensus Fur iron-repressor protein-binding site. FyuA shows homology to other iron-regulated TonB-dependent outer membrane proteins with receptor functions (e.g. BtuB, CirA, FepA, IutA, FhuA, FoxA, FcuA). On the basis of multiple alignment of amino acid sequences of FyuA and other TonB-dependent receptors, a phylogenetic tree was constructed, demonstrating that FyuA probably belongs to the citrate subfamily or represents a new subfamily of TonB-dependent receptors. Moreover, by complementation of the WA fyuA mutant by the cloned fyuA gene, yersiniabactin uptake and mouse virulence were restored. These studies demonstrate that the cloned pesticin/yersiniabactin receptor FyuA of Y. enterocolitica has the typical features of iron-regulated TonB-dependent outer membrane receptors for siderophores and bacteriocins and is required for mouse virulence.