Proteins essential for expression of the Hms+ phenotype of Yersinia pestis

Development of real-time PCR assays for specific detection of hmsH, hmsF, hmsR, and irp2 located within the 102-kb pgm locus of Yersinia pestis

Virulent isolates of three pathogenic Yersinia species (Yersinia pestis, Yersinia pseudotuberculosis, and Yersinia enterocolitica) harbor a 102-kb chromosomal region which encodes elements critical for virulence. A 35-kb high pathogenicity island is contained in this region, is a known virulence determinant, contains irp1 and irp2 iron-regulating genes. An additional segment, the 68-kb high pathogenicity island, contains genetic elements responsible for conferring the Y. pestis pigmentation phenotype on Congo red agar at 28 °C. Collectively, these contiguous segments are referred to as the pigmentation (pgm) locus, the absence of which results in strain attenuation and exemption from CDC Select Agent status. In this study, we developed a set of four real-time PCR assays to detect the presence or absence of multiple virulence genes located within this region. Specifically, we designed TaqMan(®) PCR assays to individually detect three hemin storage genes (hmsH, hmsF, and hmsR) which are genetic elements that confer the pigmentation phenotype, as well as the iron-regulating status of 25 Y. pestis isolates (representing 23 different strains), thus establishing a molecular based assay capable of determining the pgm status of candidate Y. pestis isolates. Included in the validation process, was a comparison of these real-time PCR assays and newly developed conventional PCR assays targeting much larger areas of the 102-kb region (including one assay spanning hmsR and hmsF, one spanning hmsH and hsmF, one targeting hmsF, and one targeting irp2). There was high concordance between the conventional and real-time PCR assays for all Y. pestis strains tested. The results from the comparative analysis document the specificity and sensitivity of the real-time PCR assays and further solidify the ostensible benefits of real-time PCR over conventional PCR.

Induction of the Yersinia pestis PhoP-PhoQ regulatory system in the flea and its role in producing a transmissible infection

Transmission of Yersinia pestis is greatly enhanced after it forms a bacterial biofilm in the foregut of the flea vector that interferes with normal blood feeding. Here we report that the ability to produce a normal foregut-blocking infection depends on induction of the Y. pestis PhoP-PhoQ two-component regulatory system in the flea. Y. pestis phoP-negative mutants achieved normal infection rates and bacterial loads in the flea midgut but produced a less cohesive biofilm both in vitro and in the flea and had a greatly reduced ability to localize to and block the flea foregut. Thus, not only is the PhoP-PhoQ system induced in the flea gut environment, but also this induction is required to produce a normal transmissible infection. The altered biofilm phenotype in the flea was not due to lack of PhoPQ-dependent or PmrAB-dependent addition of aminoarabinose to the Y. pestis lipid A, because an aminoarabinose-deficient mutant that is highly sensitive to cationic antimicrobial peptides had a normal phenotype in the flea digestive tract. In addition to enhancing transmissibility, induction of the PhoP-PhoQ system in the arthropod vector prior to transmission may preadapt Y. pestis to resist the initial encounter with the mammalian innate immune response.

The yersiniabactin transport system is critical for the pathogenesis of bubonic and pneumonic plague

Iron acquisition from the host is an important step in the pathogenic process. While Yersinia pestis has multiple iron transporters, the yersiniabactin (Ybt) siderophore-dependent system plays a major role in iron acquisition in vitro and in vivo. In this study, we determined that the Ybt system is required for the use of iron bound by transferrin and lactoferrin and examined the importance of the Ybt system for virulence in mouse models of bubonic and pneumonic plague. Y. pestis mutants unable to either transport Ybt or synthesize the siderophore were both essentially avirulent via subcutaneous injection (bubonic plague model). Surprisingly, via intranasal instillation (pneumonic plague model), we saw a difference in the virulence of Ybt biosynthetic and transport mutants. Ybt biosynthetic mutants displayed an approximately 24-fold-higher 50% lethal dose (LD(50)) than transport mutants. In contrast, under iron-restricted conditions in vitro, a Ybt transport mutant had a more severe growth defect than the Ybt biosynthetic mutant. Finally, a Delta pgm mutant had a greater loss of virulence than the Ybt biosynthetic mutant, indicating that the 102-kb pgm locus encodes a virulence factor, in addition to Ybt, that plays a role in the pathogenesis of pneumonic plague.

Analysis of HmsH and its role in plague biofilm formation

The Yersinia pestis Hms(+) phenotype is a manifestation of biofilm formation that causes adsorption of Congo red and haemin at 26 degrees C but not at 37 degrees C. This phenotype is required for blockage of the proventricular valve of the oriental rat flea and plays a role in transmission of bubonic plague from fleas to mammals. Genes responsible for this phenotype are located in three separate operons, hmsHFRS, hmsT and hmsP. HmsH and HmsF are outer membrane (OM) proteins, while the other four Hms proteins are located in the inner membrane. According to the Hidden Markov Method-based predictor, HmsH has a large N terminus in the periplasm, a beta-barrel structure with 16 beta-strands that traverse the OM, eight surface-exposed loops, and seven short turns connecting the beta-strands on the periplasmic side. Here, we demonstrate that HmsH is a heat-modifiable protein, a characteristic of other beta-barrel proteins, thereby supporting the bioinformatics analysis. Alanine scanning mutagenesis was used to identify conserved amino acids in the HmsH-like family that are critical for the function of HmsH in biofilm formation. Of 23 conserved amino acids mutated, four residues affected HmsH function and three likely caused protein instability. We used formaldehyde cross-linking to demonstrate that HmsH interacts with HmsF but not with HmsR, HmsS, HmsT or HmsP. Loss-of-function HmsH variants with single alanine substitutions retained their beta-structure and interaction with HmsF. Finally, using a polar hmsH : : mini-kan mutant, we demonstrated that biofilm development is not important for the pathogenesis of bubonic or pneumonic plague in mice.

Ser/Thr/Tyr phosphoproteome analysis of pathogenic and non-pathogenic Pseudomonas species

Protein phosphorylation on serine, threonine, and tyrosine is well established as a crucial regulatory posttranslational modification in eukaryotes. With the recent whole-genome sequencing projects reporting the presence of serine/threonine kinases and two-component proteins both in prokaryotes and eukaryotes, the importance of protein phosphorylation in archaea and bacteria is gaining acceptance. While conventional biochemical methods failed to obtain a snapshot of the bacterial phosphoproteomes, advances in MS methods have paved the way for in-depth mapping of phosphorylation sites. Here, we present phosphoproteomes of two ecologically diverse non-enteric Gram-negative bacteria captured by a nanoLC-MS-based approach combined with a novel phosphoenrichment method. While the phosphoproteome data from the two species are not very similar, the results reflect high similarity to the previously published dataset in terms of the pathways the phosphoproteins belong to. This study additionally provides evidence to prior observations that protein phosphorylation is common in bacteria. Notably, phosphoproteins identified in Pseudomonas aeruginosa belong to motility, transport, and pathogenicity pathways that are critical for survival and virulence. We report, for the first time, that motility regulator A, probably acting via the novel secondary messenger cyclic diguanylate monophosphate, significantly affects protein phosphorylation in Pseudomonas putida.

Yersinia pestis biofilm in the flea vector and its role in the transmission of plague

Transmission by fleabite is a relatively recent evolutionary adaptation of Yersinia pestis, the bacterial agent of bubonic plague. To produce a transmissible infection, Y. pestis grows as an attached biofilm in the foregut of the flea vector. Biofilm formation both in the flea foregut and in vitro is dependent on an extracellular matrix (ECM) synthesized by the Yersinia hms gene products. The hms genes are similar to the pga and ica genes of Escherichia coli and Staphylococcus epidermidis, respectively, that act to synthesize a poly-beta-1,6-N-acetyl-d-glucosamine ECM required for biofilm formation. As with extracellular polysaccharide production in many other bacteria, synthesis of the Hms-dependent ECM is controlled by intracellular levels of cyclic-di-GMP. Yersinia pseudotuberculosis, the food- and water-borne enteric pathogen from which Y. pestis evolved recently, possesses identical hms genes and can form biofilm in vitro but not in the flea. The genetic changes in Y. pestis that resulted in adapting biofilm-forming capability to the flea gut environment, a critical step in the evolution of vector-borne transmission, have yet to be identified. During a flea bite, Y. pestis is regurgitated into the dermis in a unique biofilm phenotype, and this has implications for the initial interaction with the mammalian innate immune response.

Analysis of Yersinia pestis gene expression in the flea vector

Yersinia pestis is the causative agent of plague. Unlike the other pathogenic Yersinia species, Y. pestis has evolved an arthropod-borne route of transmission, alternately infecting flea and mammalian hosts. Distinct subsets of genes are hypothesized to be differentially expressed during infection of the arthropod vector and mammalian host. Genes crucial for mammalian infection are referred to as virulence factors whilst genes playing a role in the flea vector are termed transmission factors. This article serves as a review of known factors involved in flea-borne transmission and introduces an 'in vivo' microarray approach to elucidating the genetic basis of Y. pestis infection of- and transmission by the flea.

Evaluation of different iron sources and their influence in biofilm formation by the dental pathogen Actinobacillus actinomycetemcomitans

Actinobacillus actinomycetemcomitans, a pathogen associated with oral and extra-oral infections, requires iron to grow under limiting conditions. Although incapable of producing siderophores, this pathogen could acquire iron by direct interaction with compounds such as haemin, haemoglobin, lactoferrin and transferrin. In this work the ability of different A. actinomycetemcomitans strains to bind and use different iron sources was tested. None of the strains tested used haemoglobin, lactoferrin or transferrin as sole sources of iron. However, all of them used FeCl(3) and haemin as iron sources under chelated conditions. Dot-blot binding assays showed that all strains bind lactoferrin, haemoglobin and haemin, but not transferrin. Insertion inactivation of hmsF, which encodes a predicted cell-envelope protein related to haemin-storage proteins produced by other pathogens, reduced haemin and Congo red binding drastically without affecting haemin utilization as an iron source under chelated conditions. Biofilm assays showed that all strains tested attached to and formed biofilms on plastic under iron-rich and iron-chelated conditions. However, scanning electron microscopy showed that smooth strains formed simpler biofilms than rough isolates. Furthermore, the incubation of rough cells in the presence of FeCl(3) or haemin resulted in the formation of more aggregates and microcolonies compared with the fewer cell aggregates formed when cells were grown in the presence of the synthetic iron chelator dipyridyl. These cell responses to changes in extracellular iron concentrations may reflect those that this pathogen expresses under the conditions it encounters in the human oral cavity.

Identification of critical amino acid residues in the plague biofilm Hms proteins

Yersinia pestis biofilm formation causes massive adsorption of haemin or Congo red in vitro as well as colonization and eventual blockage of the flea proventriculus in vivo. This blockage allows effective transmission of plague from some fleas, like the oriental rat flea, to mammals. Four Hms proteins, HmsH, HmsF, HmsR and HmsS, are essential for biofilm formation, with HmsT and HmsP acting as positive and negative regulators, respectively. HmsH has a beta-barrel structure with a large periplasmic domain while HmsF possesses polysaccharide deacetylase and COG1649 domains. HmsR is a putative glycosyltransferase while HmsS has no recognized domains. In this study, specific amino acids within conserved domains or within regions of high similarity in HmsH, HmsF, HmsR and HmsS proteins were selected for site-directed mutagenesis. Some but not all of the substitutions in HmsS and within the periplasmic domain of HmsH were critical for protein function. Substitutions within the glycosyltransferase domain of HmsR and the deacetylase domain of HmsF abolished biofilm formation in Y. pestis. Surprisingly, substitution of highly conserved residues within COG1649 did not affect HmsF function.

Polyamines are essential for the formation of plague biofilm

We provide the first evidence for a link between polyamines and biofilm levels in Yersinia pestis, the causative agent of plague. Polyamine-deficient mutants of Y. pestis were generated with a single deletion in speA or speC and a double deletion mutant. The genes speA and speC code for the biosynthetic enzymes arginine decarboxylase and ornithine decarboxylase, respectively. The level of the polyamine putrescine compared to the parental speA+ speC+ strain (KIM6+) was depleted progressively, with the highest levels found in the Y. pestis DeltaspeC mutant (55% reduction), followed by the DeltaspeA mutant (95% reduction) and the DeltaspeA DeltaspeC mutant (>99% reduction). Spermidine, on the other hand, remained constant in the single mutants but was undetected in the double mutant. The growth rates of mutants with single deletions were not altered, while the DeltaspeA DeltaspeC mutant grew at 65% of the exponential growth rate of the speA+ speC+ strain. Biofilm levels were assayed by three independent measures: Congo red binding, crystal violet staining, and confocal laser scanning microscopy. The level of biofilm correlated to the level of putrescine as measured by high-performance liquid chromatography-mass spectrometry and as observed in a chemical complementation curve. Complementation of the DeltaspeA DeltaspeC mutant with speA showed nearly full recovery of biofilm to levels observed in the speA+ speC+ strain. Chemical complementation of the double mutant and recovery of the biofilm defect were only observed with the polyamine putrescine.

Serotype differences and lack of biofilm formation characterize Yersinia pseudotuberculosis infection of the Xenopsylla cheopis flea vector of Yersinia pestis

Yersinia pestis, the agent of plague, is usually transmitted by fleas. To produce a transmissible infection, Y. pestis colonizes the flea midgut and forms a biofilm in the proventricular valve, which blocks normal blood feeding. The enteropathogen Yersinia pseudotuberculosis, from which Y. pestis recently evolved, is not transmitted by fleas. However, both Y. pestis and Y. pseudotuberculosis form biofilms that adhere to the external mouthparts and block feeding of Caenorhabditis elegans nematodes, which has been proposed as a model of Y. pestis-flea interactions. We compared the ability of Y. pestis and Y. pseudotuberculosis to infect the rat flea Xenopsylla cheopis and to produce biofilms in the flea and in vitro. Five of 18 Y. pseudotuberculosis strains, encompassing seven serotypes, including all three serotype O3 strains tested, were unable to stably colonize the flea midgut. The other strains persisted in the flea midgut for 4 weeks but did not increase in numbers, and none of the 18 strains colonized the proventriculus or produced a biofilm in the flea. Y. pseudotuberculosis strains also varied greatly in their ability to produce biofilms in vitro, but there was no correlation between biofilm phenotype in vitro or on the surface of C. elegans and the ability to colonize or block fleas. Our results support a model in which a genetic change in the Y. pseudotuberculosis progenitor of Y. pestis extended its pre-existing ex vivo biofilm-forming ability to the flea gut environment, thus enabling proventricular blockage and efficient flea-borne transmission.

Molecular and physiological insights into plague transmission, virulence and etiology

Plague is caused by Yersinia pestis, which evolved from the enteric pathogen Y. pseudotuberculosis, which normally causes a chronic and relatively mild disease. Y. pestis is not only able to parasitize the flea but also highly virulent to rodents and humans, causing epidemics of a systemic and often fatal disease. Y. pestis could be used as a bio-weapon and for bio-terrorism. It uses a number of strategies that allow the pathogen to change its lifestyle rapidly to survive in fleas and to grow in the mammalian hosts. Extensive studies reviewed here give an overall picture of the determinants responsible for plague pathogenesis in mammalians and the transmission by fleas. The availability of multiple genomic sequences and more extensive use of genomics and proteomics technologies should allow a comprehensive dissection of the complex of host-adaptation and virulence in Y. pestis.

The phosphodiesterase activity of the HmsP EAL domain is required for negative regulation of biofilm formation in Yersinia pestis

In Yersinia pestis, biofilm formation is stimulated by HmsT, a GGDEF-domain containing protein that synthesizes cyclic-di-GMP (c-di-GMP), and inhibited by HmsP, an EAL-domain protein. Only the EAL-domain portion of HmsP is required to inhibit biofilm formation. The EAL domain of HmsP was purified as a 6XHis-tag fusion protein and demonstrated to have phosphodiesterase activity using bis(p-nitrophenyl) phosphate (bis-pNPP) as a substrate. This enzymatic activity was strictly manganese dependent. A critical residue (E506) of HmsP within the EAL domain, that is required for inhibition of biofilm formation, is also essential for this phosphodiesterase activity. While the proposed function of EAL-domain proteins is to linearize c-di-GMP, this is a direct demonstration of the required phosphodiesterase activity of a purified EAL-domain protein.

Phenotypic convergence mediated by GGDEF-domain-containing proteins

GGDEF domain-containing proteins have been implicated in bacterial signal transduction and synthesis of the second messenger molecule cyclic-di-GMP. A number of GGDEF proteins are involved in controlling the formation of extracellular matrices. AdrA (Salmonella enterica serovar Typhimurium) and HmsT (Yersinia pestis) contain GGDEF domains and are required for extracellular cellulose production and biofilm formation, respectively. Here we show that hmsT is able to restore cellulose synthesis to a Salmonella serovar Typhimurium adrA mutant and that adrA can replace hmsT in Y. pestis Hms-dependent biofilm formation. Like Y. pestis HmsT overproducers, Y. pestis cells carrying adrA under the control of an arabinose-inducible promoter produced substantial biofilms in the presence of arabinose. Finally, we demonstrate that HmsT is involved in the synthesis of cyclic di-GMP.

HmsP, a putative phosphodiesterase, and HmsT, a putative diguanylate cyclase, control Hms-dependent biofilm formation in Yersinia pestis

The Hms(+) phenotype of Yersinia pestis promotes the binding of haemin or Congo red (CR) to the cell surface at temperatures below 34 degrees C. We previously demonstrated that temperature regulation of the Hms(+) phenotype is not controlled at the level of transcription. Instead, HmsH, HmsR and HmsT are degraded upon a temperature shift from 26 degrees C to 37 degrees C. We used random transposon mutagenesis to identify new genes involved in the temperature-regulated expression of the Hms phenotype. One of these genes, which we designated hmsP, encodes a putative phosphodiesterase with a conserved EAL motif. Mutations in hmsP caused formation of red colonies on CR plates at 26 degrees C and 37 degrees C. Strains complemented with hmsP(+) on a plasmid form white colonies at both temperatures. We used a crystal violet assay and confocal laser scanning microscopy to demonstrate Hms-dependent biofilm formation by Y. pestis cells. Y. pestis Hms(+) strains grown at 26 degrees C but not at 37 degrees C form a biofilm on borosilicate glass surfaces. Strains that either overexpress HmsT (a GGDEF domain protein) or have a mutation in hmsP produced an extremely thick biofilm. Alanine substitutions for each of the GGEE residues (amino acids 296-299) of HmsT as well as the E506 and L508 residues of HmsP caused a loss of function. We propose that HmsT and HmsP together control the amount of biofilm produced in Y. pestis. Degradation of HmsT at 37 degrees C may be a critical factor in controlling the temperature-dependent expression of the Hms biofilm.

Temperature regulation of the hemin storage (Hms+) phenotype of Yersinia pestis is posttranscriptional

In Yersinia pestis, the Congo red (and hemin) binding that is characteristic of the Hms+ phenotype occurs at temperatures up to 34 degrees C but not at higher temperatures. Manifestation of the Hms+ phenotype requires at least five proteins (HmsH, -F, -R, -S, and -T) that are organized into two separate operons: hmsHFRS and hmsT. HmsH and HmsF are outer membrane proteins, while HmsR, HmsS, and HmsT are predicted to be inner membrane proteins. We have used transcriptional reporter constructs, RNA dot blots, and Western blots to examine the expression of hms operons and proteins. Our studies indicate that transcription from the hmsHFRS and hmsT promoters is not regulated by the iron status of the cells, growth temperature, or any of the Hms proteins. In addition, the level of mRNA for both operons is not significantly affected by growth temperature. However, protein levels of HmsH, HmsR, and HmsT in cells grown at 37 degrees C are very low compared to those in cells grown at 26 degrees C, while the amounts of HmsF and HmsS show only a moderate reduction at the higher growth temperature. Neither the Pla protease nor a putative endopeptidase (Y2360) encoded upstream of hmsH is essential for temperature regulation of the Hms+ phenotype. However, HmsT at 37 degrees C is sensitive to degradation by Lon and/or ClpPX. Thus, the stability of HmsH, HmsR, and HmsT proteins likely plays a role in temperature regulation of the Hms+ phenotype of Y. pestis.

The haem pigment of the oral anaerobes Prevotella nigrescens and Prevotella intermedia is composed of iron(III) protoporphyrin IX in the monomeric form

The haem pigment of Porphyromonas gingivalis is composed of micro -oxo bishaem, [Fe(III)PPIX](2)O, but the nature of that generated by Prevotella species has not been established. Mössbauer, Raman and UV-visible spectrophotometry were used to characterize the haem pigment of Prevotella intermedia and Prevotella nigrescens. Mössbauer and Raman spectroscopy revealed the major haem species to be monomeric iron protoporphyrin IX, Fe(III)PPIX.OH (haematin). The terminal growth pH of both species on blood agar was between 5.8 and 6.0, which favours the formation and maintenance of monomeric Fe(III)PPIX.OH. Incubation of Pr. nigrescens and Pr. intermedia with oxyhaemoglobin at pH 6.5 resulted in formation of aquomethaemoglobin which was degraded to generate Fe(III)PPIX.OH which in turn became cell-associated, whilst incubation at pH 7.5 resulted in formation of [Fe(III)PPIX](2)O. It is concluded that both Prevotella species degrade oxyhaemoglobin to form [Fe(III)PPIX](2)O as an intermediate, which is converted to Fe(III)PPIX.OH through a depression in pH. The low pH encourages cell-surface deposition of insoluble Fe(III)PPIX.OH which would act as a barrier against oxygen and reactive oxygen species, and also protect against H(2)O(2) through its inherent catalase activity.

Processing of heme and heme-containing proteins by bacteria

An extensive amount of new knowledge on bacterial systems involved in heme processing has been accumulated in the last 10 years. We discuss common themes in heme transport across bacterial outer and inner membranes, emphasizing proteins and mechanisms involved. The processing of heme in the bacterial cytoplasm is extensively covered, and a new hypothesis about the fate of heme in the bacterial cell is presented. Auxiliary genes involved in heme utilization, i.e., TonB, proteases, proteins involved in heme storage and pigmentation, as well as genes involved in regulation of heme assimilation are reviewed.

Detection of heme-binding proteins in epidemic strains of Burkholderia cepacia

A panel of 30 previously characterized strains representing five genomovars from the Burkholderia cepacia complex (E. Mahenthiralingam, T. Coenye, J. W. Chung, D. P. Speert, J. R. W. Govan, P. Taylor, and P. Vandamme, J. Clin. Microbiol. 38:910--913, 2000) were examined for their iron protoporphyrin IX-binding ability. These included B. cepacia genomovars I and III and B. stabilis (formerly B. cepacia genomovar IV), B. multivorans (formerly B. cepacia genomovar II), and B. vietnamiensis (formerly B. cepacia genomovar V). Cells were exposed to micro-oxo bisheme of iron protoporphyrin IX (micro-oxo dimers) and examined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis under nonreducing, nondenaturing conditions for the presence of heme-binding proteins using tetramethylbenzidine-H(2)O(2) staining. Seven of the 30 strains, each belonging to B. cepacia genomovar III and designated epidemic (in possessing the B. cepacia epidemic strain marker), expressed a 96- to 100-kDa heme-binding protein which was located in the outer membrane. The heme-binding protein of B. cepacia genomovar III epidemic strain C5424 bound iron(III) protoporphyrin IX in both the monomeric and micro-oxo bisheme forms. Cells of all strains grown on Columbia agar bound iron protoporphyrin IX in the micro-oxo bisheme (dimeric) form. There were no statistical differences between the five genomovars, or those possessing the heme-binding protein, in their micro-oxo bisheme-binding ability. Possession of the outer membrane heme-binding protein may be a pathogenicity trait in enabling the bacterium to withstand oxidative stresses in inflammatory exudates in the lung and may aid identification of invasive epidemic strains of B. cepacia.

High-pathogenicity island of Yersinia spp. in Escherichia coli strains isolated from diarrhea patients in China

The high-pathogenicity island (HPI) of Yersinia has been observed in 93% of 60 enteroadhesive Escherichia coli strains and 80% of E. coli strains isolated from blood samples. In the present study we investigated 671 fecal samples from patients with diarrhea in Shandong Province, China, and isolated HPI-harboring E. coli from 6. 26% of the samples. The isolation rates for patients with diarrhea in three age groups, 10 to 20, 30 to 40, and 50 to 60 years, were 6. 70, 12.35, and 10.81%, respectively. Therefore, HPI-harboring E. coli is the third most frequently isolated enteric pathogen from patients with diarrhea. Vomiting and abdominal pain were recorded for 33.33 and 66.67% of the patients, respectively. Stools with blood were observed for 9.52% of the patients. Twenty-four of 42 (57%) patients experienced a temperature over 37.4 degrees C. These observations indicate that HPI-harboring E. coli is one of the major causes of diarrheal disease in China and that the clinical symptoms caused by HPI-harboring E. coli differ from those caused by enteroadhesive E. coli.

Temperature-regulated expression of bacterial virulence genes

Virulence gene expression in most bacteria is a highly regulated phenomenon, affected by a variety of parameters including osmolarity, pH, ion concentration, iron levels, growth phase, and population density. Virulence genes are also regulated by temperature, which acts as an 'on-off' switch in a manner distinct from the more general heat-shock response. Here, we review temperature-responsive expression of virulence genes in four diverse pathogens.

The 102-kilobase unstable region of Yersinia pestis comprises a high-pathogenicity island linked to a pigmentation segment which undergoes internal rearrangement

Several pathogenicity islands have recently been identified in different bacterial species, including a high-pathogenicity island (HPI) in Yersinia enterocolitica 1B. In Y. pestis, a 102-kb chromosomal fragment (pgm locus) that carries genes involved in iron acquisition and colony pigmentation can be deleted en bloc. In this study, characterization and mapping of the 102-kb region of Y. pestis 6/69 were performed to determine if this unstable region is a pathogenicity island. We found that the 102-kb region of Y. pestis is composed of two clearly distinct regions: an approximately 35-kb iron acquisition segment, which is an HPI per se, linked to an approximately 68-kb pigmentation segment. This linkage was preserved in all of the Y. pestis strains studied. However, several nonpigmented Y. pestis strains harboring an irp2 gene have been previously identified, suggesting that the pigmentation segment is independently mobile. Comparison of the physical map of the 102-kb region of these strains with that of strain 6/69 and complementation experiments were carried out to determine the genetic basis of this phenomenon. We demonstrate that several different mechanisms involving mutations and various-size deletions are responsible for the nonpigmented phenotype in the nine strains studied. However, no deletion corresponded exactly to the pigmentation segment. The 102-kb region of Y. pestis is an evolutionarily stable linkage of an HPI with a pigmentation segment in a region of the chromosome prone to rearrangement in vitro.

Prevalence of the "high-pathogenicity island" of Yersinia species among Escherichia coli strains that are pathogenic to humans

The fyuA-irp gene cluster contributes to the virulence of highly pathogenic Yersinia (Yersinia pestis, Yersinia pseudotuberculosis, and Yersinia enterocolitica 1B). The cluster encodes an iron uptake system mediated by the siderophore yersiniabactin and reveals features of a pathogenicity island. Two evolutionary lineages of this "high pathogenicity island" (HPI) can be distinguished on the basis of DNA sequence comparison: a Y. pestis group and a Y. enterocolitica group. In this study we demonstrate that the HPI of the Y. pestis evolutionary group is disseminated among species of the family Enterobacteriaceae which are pathogenic to humans. It prevails in enteroaggregative Escherichia coli and in E. coli blood culture isolates (93 and 80%, respectively), but is rarely found in enteropathogenic E. coli, enteroinvasive E. coli, and enterotoxigenic E. coli isolates. In contrast, the HPI was absent from enterohemorrhagic E. coli, Shigella, and Salmonella enterica strains investigated. Polypeptides encoded by the fyuA, irp1, and irp2 genes located on the HPI could be detected in E. coli strains pathogenic to humans. However, these E. coli strains showed a reduced sensitivity to the bacteriocin pesticin, whose uptake is mediated by the FyuA receptor. Escherichia strains do not possess the hms gene locus thought to be a part of the HPI of Y. pestis. Deletions of the juA-irp gene cluster affecting solely the fyuA part of the HPI were identified in 3% of the E. coli strains tested. These results suggest horizontal transfer of the HPI between Y. pestis and some pathogenic E. coli strains.

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.

Molecular biology of S-layers

In this chapter we report on the molecular biology of crystalline surface layers of different bacterial groups. The limited information indicates that there are many variations on a common theme. Sequence variety, antigenic diversity, gene expression, rearrangements, influence of environmental factors and applied aspects are addressed. There is considerable variety in the S-layer composition, which was elucidated by sequence analysis of the corresponding genes. In Corynebacterium glutamicum one major cell wall protein is responsible for the formation of a highly ordered, hexagonal array. In contrast, two abundant surface proteins from the S-layer of Bacillus anthracis. Each protein possesses three S-layer homology motifs and one protein could be a virulence factor. The antigenic diversity and ABC transporters are important features, which have been studied in methanogenic archaea. The expression of the S-layer components is controlled by three genes in the case of Thermus thermophilus. One has repressor activity on the S-layer gene promoter, the second codes for the S-layer protein. The rearrangement by reciprocal recombination was investigated in Campylobacter fetus. 7-8 S-layer proteins with a high degree of homology at the 5' and 3' ends were found. Environmental changes influence the surface properties of Bacillus stearothermophilus. Depending on oxygen supply, this species produces different S-layer proteins. Finally, the molecular bases for some applications are discussed. Recombinant S-layer fusion proteins have been designed for biotechnology.

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.

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.

Role of the Yersinia pestis hemin storage (hms) locus in the transmission of plague by fleas

Yersinia pestis, the cause of bubonic plague, is transmitted by the bites of infected fleas. Biological transmission of plague depends on blockage of the foregut of the flea by a mass of plague bacilli. Blockage was found to be dependent on the hemin storage (hms) locus. Yersinia pestis hms mutants established long-term infection of the flea's midgut but failed to colonize the proventriculus, the site in the foregut where blockage normally develops. Thus, the hms locus markedly alters the course of Y. pestis infection in its insect vector, leading to a change in blood-feeding behavior and to efficient transmission of plague.

The hmu locus of Yersinia pestis is essential for utilization of free haemin and haem--protein complexes as iron sources

Yersinia pestis strains utilize haem and several haem-protein complexes as sole sources of iron. In this study, the haemin uptake locus (hmu) of Y. pestis KIM6+ was selected from a genomic library by transduction into an Escherichia coli siderophore synthesis (entC) mutant. Recombinant plasmids containing a common 16 kb BamHI insert were isolated that allowed E. coli entC to use haemin as an iron source. An 8.6 kb region of this insert was found to be essential for haemin utilization and encoded at least five proteins with molecular masses of 79/77, 44, 37, 35, and 30/27.5 kDa. A 10.9 kb Clal fragment containing the hmu locus showed varying degrees of homology to genomic DNA from Yersinia pseudotuberculosis, Yersinia enterocolitica, and other genera of Enterobacteriaceae. An E. coli hemA aroB strain harbouring cloned hmu genes used haemin as both an iron and porphyrin source but only on iron-poor medium, suggesting that haemin uptake is tightly iron regulated. Additionally, haemoglobin and myoglobin were used as iron sources by an E. coli entC (pHMU2.2) strain. Deletion of the hmu locus from Y. pestis KIM6+ chromosome generated a mutant that grew poorly on iron-depleted medium containing free haemin as well as mammalian haem-protein complexes including haemoglobin, haemoglobin-haptoglobin, myoglobin, haem-haemopexin, and haem-albumin unless it was complemented with cloned hmu genes.

Regulation of hemin and iron transport in Porphyromonas gingivalis

As with other pathogens, a requirement for the in vivo growth of Porphyromonas gingivalis is that the organism must be capable of obtaining iron from the host. The ability to utilize hemin and hemin-containing compounds for nutritional iron has been documented for several pathogenic bacteria, including P. gingivalis; however, the mechanisms involved in hemin uptake are poorly defined. I have determined that P. gingivalis transports the entire hemin moiety into the cell by an energy-dependent mechanism and that the binding and accumulation of hemin are induced by growth of cultures in the presence of hemin. A model of hemin transport in P. gingivalis consistent with these results is presented. I have also found that, in P. gingivalis, hemin regulates the expression of several putative virulence factors; this in turn results in the increased virulence potential of P. gingivalis as assessed in an animal model. Regulation of hemin-responsive genes in P. gingivalis may occur by a negative regulator, as has been described in other pathogenic organisms.

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.

Binding and accumulation of hemin in Porphyromonas gingivalis are induced by hemin

Although hemin is an essential nutrient for the black-pigmented oral bacterium Porphyromonas gingivalis, the mechanisms involved in hemin binding and uptake are poorly defined. In this study, we have examined the binding of hemin and Congo red (CR) to P. gingivalis whole cells and have defined the conditions for maximal binding. Additionally, the accumulation of hemin by P. gingivalis under growing conditions has been characterized. P. gingivalis A7436 was grown under hemin- or iron-deplete conditions (basal medium [BM] or Schaedler broth with dipyridyl [SBD]) or under hemin- or iron-replete conditions (BM with hemin [BMH] or Schaedler broth [SB]), and hemin and CR binding were assessed spectrophotometrically. Binding of hemin by P. gingivalis whole cells was rapid and was observed in samples obtained from cells grown under hemin- and iron-replete and hemin-deplete conditions but was not observed in cells grown under iron limitation. We also found that P. gingivalis whole cells bound more hemin when grown in BMH or SB than cells grown in BM or SBD. Binding of CR by P. gingivalis A7436 was also enhanced when cells were grown in the presence of hemin or when cells were incubated with hemin prior to CR binding. Hemin binding and accumulation were also assessed using [14C]hemin and [59Fe]hemin under growing conditions. Both [14C]hemin and [59Fe]hemin were accumulated by P. gingivalis, indicating that iron and the porphyrin ring were taken into the cell. Binding and accumulation of hemin under growing conditions were also induced by growth of P. gingivalis in hemin-replete media. Hemin accumulation was inhibited by the addition of KCN to P. gingivalis cultures, indicating that active transport was required for hemin uptake. [14C]hemin binding and accumulation were also inhibited by the addition of either cold hemin or protoporphyrin IX. Taken together, these results indicate that P. gingivalis transports the entire hemin moiety into the cell and that the binding and accumulation of hemin are induced by growth of cultures in the presence of hemin.