Pasteurella pestis: Role of Pesticin I and Iron in Experimental Plague

Loss of the genetic determinant for pesticin I in Pasteurella pestis results in concomitant loss of the plague coagulase and fibrinolytic factor. The median lethal dose for mice of an isolate lacking only these activities is increased by factors of about 10(1), 10(4), and 10(7) cells when administered by the intravenous, intraperitoneal, and subcutaneous routes, respectively. Virulence of the aforesaid strain can be enhanced in mice treated with 40 microg of ferrous iron. This response resembles that of Pasteurella pseudotuberculosis, a closely related species that normally lacks pesticin I.

Interconversion of Purine Mononucleotides in Pasteurella pestis

Included among the five established determinants of virulence in Pasteurella pestis are the abilities of cells to accomplish the de novo biosynthesis of purines and to grow as dark pigmented (P(+)) colonies on a solid synthetic medium containing hemin. P(+) isolates of P. pestis strain KIM-10 (mouse intraperitoneal ld(50) < 10 cells) failed to convert exogenous guanine-8-(14)C to adenine residues of ribonucleic acid (RNA) when cultivated in a minimal medium which favored the pigmentation reaction. This conversion occurred in P(+) cells grown in an enriched medium which did not support the pigmentation reaction and was observed in P(-) mutants cultivated in both types of media. Both P(+) and P(-) isolates converted exogenous adenine-8-(14)C but not adenine-2-(14)C at a significant rate to guanosine residues of RNA when grown under a variety of conditions. This difference appeared to reflect a deficiency of adenine deaminase. The mouse intraperitoneal ld(50) of purine-auxotrophs was about 10(2) cells when the metabolic block occurred prior to the de novo formation of inosine monophosphate (IMP). In contrast, the corresponding value for a mutant blocked between IMP and guanine monophosphate was > 10(7) cells in mice and > 10(8) cells in guinea pigs.

Effect of ca on the synthesis of deoxyribonucleic Acid in virulent and avirulent yersinia

Virulent and potentially virulent cells of Yersinia (Pasteurella) pestis produce virulence or V and W antigens (VW(+)) but remain static at 37 C during aeration in enriched Ca(2+)-deficient media containing 0.02 m Mg(2+). In this environment, which simulates mammalian intracellular fluid, VW(+) cells possessed a functional cytoplasmic membrane as judged by concentration of (14)C-isoleucine, release of (32)P, and consumption of oxygen at rates comparable to those of dividing cells cultivated with Ca(2+). Furthermore, rates of protein and ribonucleic acid synthesis were essentially identical in dividing and static VW(+) cells and in mutant VW(-) organisms. However, the rate of deoxyribonucleic acid (DNA) synthesis in static cells was about 10% of that observed in dividing organisms. Accordingly, bacteriostasis of VW(+) cells in the simulated intracellular environment is evidently caused by reactions directly associated with cessation of DNA synthesis rather than by alterations in the regulatory capacity of the cytoplasmic membrane.

Insights into the evolution of Yersinia pestis through whole-genome comparison with Yersinia pseudotuberculosis

Yersinia pestis, the causative agent of plague, is a highly uniform clone that diverged recently from the enteric pathogen Yersinia pseudotuberculosis. Despite their close genetic relationship, they differ radically in their pathogenicity and transmission. Here, we report the complete genomic sequence of Y. pseudotuberculosis IP32953 and its use for detailed genome comparisons with available Y. pestis sequences. Analyses of identified differences across a panel of Yersinia isolates from around the world reveal 32 Y. pestis chromosomal genes that, together with the two Y. pestis-specific plasmids, to our knowledge, represent the only new genetic material in Y. pestis acquired since the the divergence from Y. pseudotuberculosis. In contrast, 149 other pseudogenes (doubling the previous estimate) and 317 genes absent from Y. pestis were detected, indicating that as many as 13% of Y. pseudotuberculosis genes no longer function in Y. pestis. Extensive insertion sequence-mediated genome rearrangements and reductive evolution through massive gene loss, resulting in elimination and modification of preexisting gene expression pathways, appear to be more important than acquisition of genes in the evolution of Y. pestis. These results provide a sobering example of how a highly virulent epidemic clone can suddenly emerge from a less virulent, closely related progenitor.

The recent emergence of plague: a process of felonious evolution

Yersinia pestis, the causative agent of bubonic plague, evolved from closely related Yersinia pseudotuberculosis within the past 20,000 years, an event that corresponds to the end of the last ice age and distribution of Homo sapiens throughout the world. Y. pseudotuberculosis causes chronic but generally mild enteropathogenic infections whereas plague is the most devastating acute disease experienced by mankind. The very recent evolution of plague from its progenitor assures close genomic homogeneity between the two species and thus high probability that disparities in DNA sequence mediate dramatic differences in symptoms of infection. The purpose of this minireview is to define salient distinctions between the genomes of Y. pestis and Y. pseudotuberculosis and to equate unique functions to respective acute and chronic mechanisms of virulence. The significance of these processes is then related to the procedures the organisms use to survive when between hosts (i.e., the flea vector colonized by Y. pestis and natural environments including soil and water in the case of Y. pseudotuberculosis). Next, an attempt is made to order the various mutational events that caused the recent emergence of Y. pestis as a distinct species. Finally, selective pressures such as predatory soil nematodes are considered that possibly influenced the early evolution of those yersiniae now pathogenic to humans.

Detection of Yersinia pestis by pesticin fluorogenic probe-coupled PCR

The <<Taq Man>> assay (PE Applied Biosystems) combines PCR with concomitant release of fluorogenic nucleotides for immediate product detection by fluorometry. Yersinia pestis, the etiological agent of bubonic plague, expresses species-specific genes known to be located on two unique plasmids (9.6-kb pPCP and 100.9-kb pMT). Pesticin (pst) is a unique gene located on pPCP which encodes for a bacteriocin. Using fluorogenic probe coupled PCR as few as three copies of pst targets were detected from total Y. pestis genomic DNA. The pst probe used in this report was positive only for pesticinogenic isolates and did not show complementarity with Yersiniae nor with other bacteria targeted in this study suggesting, that the pst probe is very specific for Y. pestis. Under optimal conditions of Mg(2+)concentration and thermal cycle number, addition of extraneous DNA to respective assay mixtures had no effect on detection.

Detection of Yersinia pestis using branched DNA

In contrast to target amplification methods, e.g. polymerase chain reaction, the branched DNA (bDNA) signal amplification method quantitates target nucleic acid at physiological levels, involving a series of hybridization reactions without thermal cycling. In this report, we describe a modification of the bDNA assay in which a <<concatenated>> preamplifier oligonucleotide (206 mer) is used in concert with ELISA and light addressable potentiometric sensor (LAPS) formats to detect the plasminogen activator (pla) gene of Yersinia pestis, the etiological agent of plague. Pla is encoded by a 9.6-kb plasmid pPCP, which is essential for virulence. The detection limit of the bDNA-ELISA and LAPS assays is less than 10 000 and 1000 molecules of Y. pestis plasmid DNA, respectively.

Molecular characterization of KatY (antigen 5), a thermoregulated chromosomally encoded catalase-peroxidase of Yersinia pestis

The first temperature-dependent proteins (expressed at 37 degrees C, but not 26 degrees C) to be identified in Yersinia pestis were antigens 3 (fraction 1), 4 (pH 6 antigen), and 5 (hereafter termed KatY). Antigens 3 and 4 are now established virulence factors, whereas little is known about KatY, except that it is encoded chromosomally, produced in abundance, possesses modest catalase activity, and is shared by Yersinia pseudotuberculosis, but not Yersinia enterocolitica. We report here an improved chromatographic method (DEAE-cellulose, calcium hydroxylapatite, and Sephadex G-150) that yields enzymatically active KatY (2,423 U/mg of protein). Corresponding mouse monoclonal antibody 1B70.1 detected plasminogen activator-mediated hydrolysis of KatY, and a polyclonal rabbit antiserum raised against outer membranes of Y. pestis was enriched for anti-KatY. A sequenced approximately 16-kb Y. pestis DNA insert of a positive pLG338 clone indicated that katY encodes an 81.4-kDa protein (pI 6.98) containing a leader sequence of 2.6 kDa; the deduced molecular mass and pI of processed KatY were 78.8 kDa and 6. 43, respectively. A minor truncated variant (predicted molecular mass of 53.6 kDa) was also expressed. KatY is similar (39 to 59% identity) to vegetative bacterial catalase-peroxidases (KatG in Escherichia coli) and is closely related to plasmid-encoded KatP of enterohemorrhagic E. coli O157:H7 (75% identity). katY encoded a putative Ca2+-binding site, and its promoter contained three homologues to the consensus recognition sequence of the pCD-encoded transcriptional activator LcrF. rbsA was located upstream of katY, and cybB, cybC, dmsABC, and araD were mapped downstream. These genes are not linked to katG or katP in E. coli.

Expression of the plague plasminogen activator in Yersinia pseudotuberculosis and Escherichia coli

Enteropathogenic yersiniae (Yersinia pseudotuberculosis and Yersinia enterocolitica) typically cause chronic disease as opposed to the closely related Yersinia pestis, the causative agent of bubonic plague. It is established that this difference reflects, in part, carriage by Y. pestis of a unique 9.6-kb pesticin or Pst plasmid (pPCP) encoding plasminogen activator (Pla) rather than distinctions between shared approximately 70-kb low-calcium-response, or Lcr, plasmids (pCD in Y. pestis and pYV in enteropathogenic yersiniae) encoding cytotoxic Yops and anti-inflammatory V antigen. Pla is known to exist as a combination of 32.6-kDa (alpha-Pla) and slightly smaller (beta-Pla) outer membrane proteins, of which at least one promotes bacterial dissemination in vivo and degradation of Yops in vitro. We show here that only alpha-Pla accumulates in Escherichia coli LE392/pPCP1 cultivated in enriched medium and that either autolysis or extraction of this isolate with 1.0 M NaCl results in release of soluble alpha and beta forms possessing biological activity. This process also converted cell-bound alpha-Pla to beta-Pla and smaller forms in Y. pestis KIM/pPCP1 and Y. pseudotuberculosis PB1/+/pPCP1 but did not promote solubilization. Pla-mediated posttranslational hydrolysis of pulse-labeled Yops in Y. pseudotuberculosis PB1/+/pPCP1 occurred more slowly than that in Y. pestis but was otherwise similar except for accumulation of stable degradation products of YadA, a pYV-mediated fibrillar adhesin not encoded in frame by pCD. Carriage of pPCP by Y. pseudotuberculosis did not significantly influence virulence in mice.

Structural organization of virulence-associated plasmids of Yersinia pestis

The complete nucleotide sequence and gene organization of the three virulence plasmids from Yersinia pestis KIM5 were determined. Plasmid pPCP1 (9,610 bp) has a GC content of 45.3% and encodes two previously known virulence factors, an associated protein, and a single copy of IS100. Plasmid pCD1 (70,504 bp) has a GC content of 44.8%. It is known to encode a number of essential virulence determinants, regulatory functions, and a multiprotein secretory system comprising the low-calcium response stimulation that is shared with the other two Yersinia species pathogenic for humans (Y. pseudotuberculosis and Y. enterocolitica). A new pseudogene, which occurs as an intact gene in the Y. enterocolitica and Y. pseudotuberculosis-derived analogues, was found in pCD1. It corresponds to that encoding the lipoprotein YlpA. Several intact and partial insertion sequences and/or transposons were also found in pCD1, as well as six putative structural genes with high homology to proteins of unknown function in other yersiniae. The sequences of the genes involved in the replication of pCD1 are highly homologous to those of the cognate plasmids in Y. pseudotuberculosis and Y. enterocolitica, but their localization within the plasmid differs markedly from those of the latter. Plasmid pMT1 (100,984 bp) has a GC content of 50.2%. It possesses two copies of IS100, which are located 25 kb apart and in opposite orientations. Adjacent to one of these IS100 inserts is a partial copy of IS285. A single copy of an IS200-like element (recently named IS1541) was also located in pMT1. In addition to 5 previously described genes, such as murine toxin, capsule antigen, capsule anchoring protein, etc., 30 homologues to genes of several bacterial species were found in this plasmid, and another 44 open reading frames without homology to any known or hypothetical protein in the databases were predicted.

Suppression of mouse skin allograft rejection by protein A-Yersiniae V antigen fusion peptide

V antigen is an established virulence factor of Yersinia pestis, the causative agent of bubonic plague. Injection of homogenous staphylococcal protein A-V antigen fusion peptide into mice was previously found to suppress tumor necrosis factor-alpha and interferon-gamma necessary for generation of protective granulomas. Here, we show that BALB/c mice receiving daily intraperitoneal injections of 100 microg of control protein A initiated rejection of C57BL/6 mouse tail skin grafts after 6.2+/-1.1 days. This time doubled to 12.2+/-1.4 days upon similar administration of protein A-V antigen fusion peptide (P<0.001); times of total allograft retention remained constant. This finding indicates that V antigen can postpone inflammation known to be associated with recognition and destruction of foreign tissue by T lymphocytes.

Resistance to lipopolysaccharide mediated by the Yersinia pestis V antigen-polyhistidine fusion peptide: amplification of interleukin-10

We previously showed that injection of homogenous staphylococcal protein A-V antigen fusion peptide into mice delayed allograft rejection and suppressed the major proinflammatory cytokines tumor necrosis factor alpha (TNF-alpha) and gamma interferon (IFN-gamma) associated with generation of protective granulomas. This study was undertaken to determine if V antigen could prevent endotoxic shock, known to be mediated by excessive production of certain proinflammatory cytokines. After treatment with 50 microg of homogeneous V antigen-polyhistidine fusion peptide (Vh), the 50% lethal dose of purified lipopolysaccharide (LPS) in BALB/c mice immediately rose from 63 microg (normal controls) to 318 microg, fell to near baseline (71 microg) in 6 h, and then slowly rose to a maximum of 566 microg at 48 h before again returning to normal. Injected Vh alone (50 microg) promptly induced the anti-inflammatory cytokine interleukin-10 (IL-10) as well as modest levels of TNF-alpha (an inducer of IL-10) in spleen. Concomitant injection of Vh and an otherwise lethal dose of LPS (200 microg) dramatically decreased levels of TNF-alpha and IFN-gamma in the spleen and peritoneal lavage fluid as compared to values determined for LPS alone. These results would be expected if V antigen directly up-regulated IL-10 that is reported to generally down-regulate proinflammatory cytokines. Mice receiving 200 microg of LPS 48 h after injection of Vh exhibited patterns of cytokine synthesis similar to those observed in endotoxin-tolerant mice, a condition also reported to be mediated by IL-10. These findings suggest that V antigen serves as a virulence factor by amplifying IL-10, thereby repressing proinflammatory cytokines required for expression of cell-mediated immunity.

V antigen-polyhistidine fusion peptide: binding to LcrH and active immunity against plague

The structural gene for V antigen (lcrV) is known to be encoded within the lcrGVH-yopBD operon of the approximately 70-kb low-calcium-response or Lcr plasmid of Yersinia pestis. This 37-kDa monomeric peptide was reported to provide active immunity in mice, suppress inflammatory cytokines, and regulate expression of the low calcium response (Lcr+). Here we describe pVHB62, encoding a polyhistidine-V antigen fusion peptide (Vh) and linked LcrH. Vh underwent degradation from both the C terminus and N terminus during classical chromatographic fractionation but remained intact within two compartments during Ni2+ affinity chromatography. The first was homogeneous, capable of active immunization (mouse intravenous 50% lethal dose, > 10(7) bacteria), and stable at 4 degrees C. The second remained bound to the affinity column but could be eluted as a mixture of Vh, LcrH, and low-molecular-weight material by application of 6 M guanidine HCl. This mixture was dialyzed, denatured in 8 M urea, and again applied to the affinity column, which then hound Vh but not LcrH. The latter was recovered and renatured, and low-molecular-weight material was removed by biochemical fractionation. The resulting homogeneous LcrH bound protein AN antigen fusion peptide but not protein A in a sandwich enzyme-linked immunosorbent assay, and this reaction was inhibited by Vh. These observations indicate that LcrH normally binds V antigen in bacterial cytoplasm and suggest that only free LcrH down-regulates expression of the low calcium response.

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.

Suppression of cytokines in mice by protein A-V antigen fusion peptide and restoration of synthesis by active immunization

It is established that an approximately 70-kb Lcr plasmid enables Yersinia pestis, the causative agent of bubonic plague, to multiply in focal necrotic lesions within visceral organs of mice by preventing net synthesis of the cytokines tumor necrosis factor alpha (TNF-alpha) and gamma interferon (IFN-gamma), thereby minimizing inflammation (Lcr+). Rabbit antiserum raised against cloned staphylococcal protein A-V antigen fusion peptide (PAV) is known to passively immunize mice against 10 minimum lethal doses of intravenously injected Lcr+ cells of Y. pestis. In this study, injected PAV suppressed TNF-alpha and IFN-gamma in mice challenged with avirulent V antigen-deficient Y. pestis (lcrV or Lcr-) and promoted survival in vivo of these isolates as well as salmonellae and Listeria monocytogenes (with which the outcome was lethal). Active immunization of mice with PAV protected against 1,000 minimum lethal doses of intravenously injected Lcr+ cells of Y. pestis and Yersinia pseudotuberculosis but not Yersinia enterocolitica. The progressive necrosis provoked by Lcr+ cells of Y. pestis in visceral organs of nonimmunized mice was replaced after active immunization with PAV by massive infiltration of neutrophils and mononuclear cells (which generated protective granulomas indistinguishable from those formed against avirulent Lcr- mutants in nonimmunized mice). Distinct multiple abscesses typical of Lcr+ cells of Y. pseudotuberculosis were prevented by similar immunization. Significant synthesis of TNF-alpha and IFN-gamma occurred in spleens of mice actively immunized with PAV after challenge with Lcr+ cells of Y. pestis. These findings suggest that V antigen contributes to disease by suppressing the normal inflammatory response.

Physiological basis of the low calcium response in Yersinia pestis

It is established that duplication in vitro of that amount of Ca2+ (2.5 mM) and Mg2+ (1.5 mM) present in blood permits vegetative growth of Yersinia pestis with repression of virulence factors encoded by the Lcr plasmid (Lcr+); similar simulation of intracellular fluid (no Ca2+ and 20 mM Mg2+) promotes bacteriostasis with induction of these virulence determinants. However, proliferation of yersiniae in mice occurs primarily within necrotic focal lesions (supplied by Ca(2+)-deficient host cell cytoplasm) within visceral organs rather than in Ca(2+)-sufficient blood. The present study addressed this enigma by defining conditions necessary for achieving vegetative growth of Lcr+ yersiniae at 37 degrees C in simulated intracellular fluid. Maximum optical densities were increased by substitution of K+ for Na+ and elimination of Cl-; the combination of Na+ plus L-glutamate was selectively toxic to Lcr+ cells. This phenomenon was attributed in part to the absence of aspartase in Y. pestis (a lesion known to facilitate massive accumulation of L-aspartate via transamination of the oxalacetate pool by L-glutamate). Replacement of L-glutamate by exogenous L-aspartate or alpha-ketoglutarate reversed this toxicity by favoring retention of oxalacetate. Proliferation of Lcr+ cells in a medium containing K+ and L-aspartate but lacking added Ca2+ and Na+ was markedly enhanced by increasing the concentration of fermentable carbohydrate. Accordingly, in the worst-case scenario (i.e., added Na+, Cl-, and L-glutamate), Lcr+ yersiniae underwent restriction of growth after one doubling, and in the best-case scenario (i.e., added K+ and L-aspartate), the organisms completed more than five doublings, thereby achieving full-scale growth. Both of these Ca(2+)-deficient media promoted maximum induction of Mg(2+)-induced V antigen, a virulence factor encoded by the Lcr plasmid.

Passive immunity to yersiniae mediated by anti-recombinant V antigen and protein A-V antigen fusion peptide

LcrV (V antigen), a known unstable 37.3-kDa monomeric peptide encoded on the ca. 70-kb Lcr plasmid of Yersinia pestis, Yersinia pseudotuberculosis, and Yersinia enterocolitica, has been implicated as a regulator of the low-calcium response, virulence factor, and protective antigen. In this study, lcrV of Y. pestis was cloned into protease-deficient Escherichia coli BL21. The resulting recombinant V antigen underwent marked degradation from the C-terminal end during purification, yielding major peptides of 36, 35, 34, and 32 to 29 kDa. Rabbit gamma globulin raised against this mixture of cleavage products provided significant protection against 10 minimum lethal doses of Y. pestis (P < 0.01) and Y. pseudotuberculosis (P < 0.02). To both stabilize V antigen and facilitate its purification, plasmid pPAV13 was constructed so as to encode a fusion of lcrV and the structural gene for protein A (i.e., all but the first 67 N-terminal amino acids of V antigen plus the signal sequence and immunoglobulin G-binding domains but not the cell wall-associated region of protein A). The resulting fusion peptide, termed PAV, could be purified to homogeneity in one step by immunoglobulin G affinity chromatography and was stable thereafter. Rabbit polyclonal gamma globulin directed against PAV provided excellent passive immunity against 10 minimum lethal doses of Y. pestis (P < 0.005) and Y. pseudotuberculosis (P < 0.005) but was ineffective against Y. enterocolitica. Protection failed after absorption with excess PAV, cloned whole V antigen, or a large (31.5-kDa) truncated derivative of the latter but was retained (P < 0.005) upon similar absorption with a smaller (19.3-kDa) truncated variant, indicating that at least one protective epitope resides internally between amino acids 168 and 275.

Storage reservoirs of hemin and inorganic iron in Yersinia pestis

It is established that a high-frequency chromosomal deletion of ca. 100 kb accounts for the loss of properties making up the pigmented phenotype (Pgm+) of wild-type Yersinia pestis. These determinants are known to include virulence by peripheral routes of injection, sensitivity to the bacteriocin pesticin, adsorption of exogenous hemin or Congo red at 26 degrees C, and growth in iron-sequestered medium at 37 degrees C. We have now identified the outer membrane as the primary site of exogenous hemin storage in Pgm+ cells grown at 26 degrees C. Significant outer membrane storage of hemin did not occur in Pgm- mutants or in Pgm+ cells cultivated at 37 degrees C. However, both Pgm+ and Pgm- organisms grown at 37 degrees C contained a periplasmic reservoir of hemin, which may be associated with a temperature-dependent ca. 70-kDa peptide recently equated with antigen 5. At 37 degrees C, Pgm+ and Pgm- yersiniae also utilized a cytoplasmic ca. 19-kDa bacterioferritin-like peptide for deposition of inorganic iron. Incorporation of [55Fe]hemin into pools at 37 degrees C was not significantly inhibited by competition with excess unlabeled Fe3+. However, excess unlabeled hemin modestly competed with incorporation of label from 55FeCl3. This relative independence of storage pools observed at 37 degrees C is consistent with physiological linkage to in vivo acquisition and transport of Fe3+ from ferritin and of hemin from hemoglobin, myoglobin, or hemopexin.

Association between virulence of Yersinia pestis and suppression of gamma interferon and tumor necrosis factor alpha

It is established that Yersinia pestis, the causative agent of bubonic plague, and enteropathogenic Yersinia pseudotuberculosis and Yersinia enterocolitica share a ca. 70-kb low-calcium response or Lcr plasmid (Lcr+). The latter is known to encode regulatory functions that restrict growth at 37 degrees C in Ca(2+)-deficient medium and virulence factors that are expressed only in vitro within this environment (e.g., certain Yops and V antigen). In this study, gamma interferon (IFN-gamma) was never detected in mice infected with 10 minimum lethal doses (MLD) of Lcr+ cells of Y. pestis, and significant levels of tumor necrosis factor alpha (TNF-alpha) arose only prior to death. Prompt and marked synthesis of these cytokines was observed upon infection with avirulent Lcr- mutants. Treatment of mice with exogenous IFN-gamma plus TNF-alpha inhibited multiplication of Lcr+ yersiniae in vivo, thereby providing protection against challenge with 10 MLD. Administration of both cytokines was required for absolute survival, suggesting a synergistic rather than cumulative interaction. This protective effect entailed cytokine priming as judged by subsequent detection of substantial levels of endogenous IFN-gamma and TNF-alpha. Monospecific anti-V-antigen, known to provide passive immunity against 10 MLD of Lcr+ Y. pestis, permitted significant synthesis of endogenous IFN-gamma and TNF-alpha. These findings demonstrate that Lcr+ yersiniae suppress synthesis of cytokines and suggest that this effect is mediated by one or more Lcr plasmid-encoded virulence factors.

Determination of genome size, macrorestriction pattern polymorphism, and nonpigmentation-specific deletion in Yersinia pestis by pulsed-field gel electrophoresis

Of 16 restriction endonucleases known to hydrolyze rare 6- or 8-base recognition sequences that were tested, only SpeI, NotI, AscI, and SfiI generated fragments of chromosomal DNA from Yersinia pestis, the causative agent of bubonic plague, of sufficient length to permit physical analysis by pulsed-field gel electrophoresis (PFGE). Of the individual bands detected after single-dimensional PFGE of these digests, the largest sum was obtained with SpeI (3,575.6 +/- 114.6 kb). Of these 41 bands, 3 were found to contain comigrating fragments, as judged by the results of two-dimensional SpeI-ApaI PFGE; addition of these fragments and the three plasmids of the species yielded a refined estimate of 4,397.9 +/- 134.6 kb for the genome. This size was similar for eight strains of diverse geographical origin that exhibited distinct DNA macrorestriction patterns closely related to their biotypes. The high-frequency chromosomal deletion known to exist in nonpigmented mutants (unable to assimilate Fe3+ at 37 degrees C or store hemin at 26 degrees C) was shown by two-dimensional PFGE analysis with SpeI and ApaI or with SfiI and SpeI to be 92.5 and 106 kb in size, respectively. The endpoints of this deletion were precise, and its size was more than sufficient to encode the eight known peptides reported to be absent in nonpigmented mutants. This deletion had not occurred (but was able to do so) in a rare mutant capable of hemin storage but not iron transport.

Factors promoting acute and chronic diseases caused by yersiniae

The experimental system constructed with the medically significant yersiniae provides a powerful basic model for comparative study of factors required for expression of acute versus chronic disease. The system exploits the close genetic similarity between Yersinia pestis, the etiological agent of bubonic plague, and enteropathogenic Yersinia pseudotuberculosis and Yersinia enterocolitica. Y. pestis possesses three plasmids, of which one, shared by the enteropathogenic species, mediates a number of virulence factors that directly or indirectly promote survival within macrophages and immunosuppression. The two remaining plasmids are unique and encode functions that promote acute disease by enhancing bacterial dissemination in tissues and resistance to phagocytosis by neutrophils and monocytes. These properties are replaced in the enteropathogenic yersiniae by host cell invasins and an adhesin which promote chronic disease; the latter are cryptic in Y. pestis. Additional distinctions include specific mutational losses in Y. pestis which result in loss of fitness in natural environments plus gain of properties that facilitate transmission and infection via fleabite.

Expression of the low calcium response in Yersinia pestis

Pathogenic yersiniae undergo an established low calcium response (LCR) at 37 degrees C in Ca2+-deficient media characterized by restricted growth with synthesis of Lcr plasmid-encoded virulence functions. The latter include outer membrane peptides (Yops) known to undergo Pst plasmid-mediated post-translational degradation in Yersinia pestis but not in enteropathogenic yersiniae lacking this plasmid. Salient Yops of Y. pestis are shown here to be either maintained in the steady state or to exist as a stable degradation product (p24 of Yop E). Processing of plague plasminogen activator (p36 to p33), responsible for hydrolysis of Yops, required 2 h. Avirulence of mutants with inserted Mu dl1 (Apr lac) in yopE was verified and shown to occur independently of introduced fusion-dependent peptides. However, avirulence of such yopE mutants but not that of isolates lacking the Lcr plasmid was phenotypically suppressed in mice injected with iron. Appearance of 20,500 and 40,500 Da heat-shock peptides preceded onset of the LCR. Lcr plasmid mediated V antigen (p38) and p20, Pst plasmid-encoded p36, and chromosomally promoted p56 and p70 were synthesized throughout the LCR. Classical antigen 5 was equated with p70 which was shared by Yersinia pseudotuberculosis but not Yersinia enterocolitica.

Outer membrane peptides of Yersinia pestis mediating siderophore-independent assimilation of iron

It is established that wild-type cells of Yersinia pestis absorb exogenous hemin or Congo red and thus grow as pigmented colonies at 26 degrees C on media containing these chromatophores (Pgm+). Pgm+ isolated are known to possess a siderophore-independent mechanism of iron-transport (required for growth in iron-deficient medium) which is absent in avirulent Pgm- mutants. Production of the bacteriocin pesticin and linked invasins (Pst+) is an additional defined virulence factor of yersiniae; mutation of Pgm+,Pst- organisms to pesticin-resistance (Pstr) results in concomitant conversion to Pgm-. In this study, autoradiograms of two-dimensional gels of [35S]methionine-labeled outer membranes from Pgm- mutants were compared to those of the Pgm+,Pst+ or Pgm+,Pst- parent. An apparently single predominant peptide present in these preparations (greater than 10% of total membrane protein) existed as a family of iron-modifiable 17.9-kDa molecules focusing down to isoelectric points of about 4.6 and up to 5.89. Expression of eight detectable Pst(+)-specific peptides was not significantly influenced by exogenous iron. Pgm+ yersiniae constitutively produced pigmentation-specific peptide F and five iron-repressible peptides termed IrpA to IrpE. Typical spontaneous mutation to Pgm- resulted in loss of peptide F and IrpB-E. A rare Pgm+,Pstr mutant, selected on Congo red agar containing pesticin, also lost IrpB-E but retained peptide F. This isolate, like Pgm- mutants, failed to grow in iron-deficient medium. Regardless of phenotype, all yersiniae utilized hemin, hemopexin, myoglobin, hemoglobin, and ferritin, but not transferrin or lactoferrin, as sole sources of iron.

Plasminogen activator/coagulase gene of Yersinia pestis is responsible for degradation of plasmid-encoded outer membrane proteins

The related family of virulence plasmids found in the three major pathogens of the genus Yersinia all have the ability to encode a set of outer membrane proteins. In Y. enterocolitica and Y. pseudotuberculosis, these proteins are major constituents of the outer membrane when their synthesis is fully induced. In contrast, they have been difficult to detect in Y. pestis. It has recently been established that Y. pestis does synthesize these proteins, but that they are rapidly degraded due to some activity determined by the 9.5-kilobase plasmid commonly found in Y. pestis strains. We show that mutations in the pla gene of this plasmid, which encodes both the plasminogen activator and coagulase activities, blocked this degradation. A cloned 1.4-kilobase DNA fragment carrying pla was also sufficient to cause degradation in the absence of the 9.5-kilobase plasmid.

Transport of Ca2+ by Yersinia pestis

Low-calcium-response, or Lcr, plasmids of yersiniae are known to promote an in vitro nutritional requirement for 2.5 mM Ca2+ at 37 degrees C which, if not fulfilled, results in cessation of growth with induction of virulence functions (Lcr+). The mechanism whereby Ca2+ regulates this metabolic shift is unknown. Radioactive Ca2+ was not actively accumulated by yersiniae but was excluded by an exit reaction analogous to those described for other bacteria. Nevertheless, cultivation at 37 degrees C with 0.1 mM Ca2+, a level insufficient to prevent restriction of cell division, promoted significantly more binding of the cation by Lcr+ organisms than by plasmid-deficient Lcr- mutants. According, Lcr+ yersiniae may possess unique ligands capable of recognizing Ca2+.

Post-translational regulation of Lcr plasmid-mediated peptides in pesticinogenic Yersinia pestis

The low calcium response of wild type Yersinia pestis, the causative agent of bubonic plague, and of enteropathogenic Yersinia pseudotuberculosis and Yersinia enterocolitica is known to be mediated by a shared Lcr plasmid of about 70 kb. At 37 degrees C in Ca2+-deficient medium, this element promotes restriction of growth with concomitant production of virulence functions including the common V antigen and a set of yersiniae outer membrane peptides termed YOPs (Lcr+). The latter are expressed by the enteropathogenic species but not by wild type Y. pestis which possesses a unique 10 kb Pst plasmid associated with pesticinogeny (Pst+). We show in this report that, after pulse with 35S-methionine, peptides with molecular weights corresponding to YOPs of 78, 47, 45, 44, 36, and 26 kDa are synthesized during the low calcium response by both Lcr+, Pst+ and Lcr+, Pst- cells of Y. pestis. Although stable in the latter, radioactivity in YOPs of wild type was rapidly chased into lower molecular weight degradation products. At least four soluble peptides, including V, were also labeled during starvation for Ca2+; these structures were stable in both Lcr+, Pst+ and Lcr+, Pst- yersiniae. These findings suggest that a product encoded by the Pst plasmid of Y. pestis is required for post-translational regulation of outer membrane but not soluble peptides mediated by a second unrelated Lcr plasmid.

Modulation of the low-calcium response in Yersinia pestis via plasmid-plasmid interaction

Virulent cells of Yersinia pestis, Yersinia pseudotuberculosis, and Yersinia enterocolitica are known to exhibit a low-calcium response in vitro characterized by restriction of growth and induction of V antigen at 37 degrees C in Ca2+-deficient media (Lcr+). A shared Lcr plasmid mediates these properties and encodes yersiniae outer membrane peptides (Yops) that are expressed in Lcr+ Y. pseudotuberculosis and Y. enterocolitica but not Y. pestis. We present direct evidence here verifying that synthesis of major Yops in the former two species is, like V, repressed by Ca2+ and that these structures are located primarily in the outer membrane. We also verified that rabbits infected with live Lcr+ Y. pestis can raise antibodies against V and Yops. Similar antisera, however, were recovered after immunization with sterile extracts of Ca2+-starved Lcr+ cells of Y. pestis. Results of immunoblots obtained with these antisera showed that restricted Y. pestis produced Yops of about 46 kDa (YopB) and 44 kDa (YopC) after shiftup by addition of Ca2+ at 37 degrees C or reduction of temperature to 26 degrees C. It is established that virulent cells of Y. pestis also possess a unique plasmid known to mediate pesticinogeny (Pst+). Restricted Lcr+, Pst- Y. pestis expressed YopB and YopC plus additional 76 kDa (YopF), 48 kDa (YopH), 36 kDa (YopD), 32.5 kDa (YopJ), and 27 kDa (YopE) outer membrane structures at concentrations comparable to those in Ca2+-starved Y. pseudotuberculosis and Y. enterocolitica. These findings indicate that carriage of the Pst plasmid prevents expression of the Lcr plasmid-mediated Yops in wild type Y. pestis.

Resistance to pesticin, storage of iron, and invasion of HeLa cells by Yersiniae

The independent abilities of Yersinia pestis to absorb exogenous pigments including hemin and Congo red (Pgm+) and to produce the bacteriocin pesticin with genetically linked invasive enzymes (Pst+) are established virulence factors of the species. Pst- Pgm+ strains of Y. pestis are sensitive to pesticin (Psts), and mutation of these isolates to pesticin resistance (Pstr) is known to result in concomitant conversion to Pgm-. Wild-type cells of Yersinia pseudotuberculosis and Yersinia enterocolitica are Pgm- but may be Psts; mutation of the latter to Pstr also results in avirulence. In this study, typical Pgm- mutants of Y. pestis exhibited a dramatic nutritional requirement at 37 degrees C but not 26 degrees C for iron which could be fulfilled by either Fe3+ or hemin. Iron privation of Pgm- yersiniae resulted in formation of osmotically stable spheroplasts similar to those previously observed after exposure of Psts bacteria to pesticin. At 37 degrees C, Pgm+ organisms rapidly overgrew initially predominant Pgm- populations in iron-deficient medium. However, Pgm-isolates could undergo a second mutation that permitted successful competition with Pgm+ cells in this environment. The mutation to Pstr in Y. pseudotuberculosis and Y. enterocolitica did not promote a similar requirement for iron but rather prevented these organisms from penetrating HeLa cells. The ability to invade these nonprofessional phagocytes was not shared by Pgm+ or Pgm- cells of Y. pestis.

Proteolysis of V antigen from Yersinia pestis

Lcr-plasmids of yersiniae are known to mediate a unique low calcium response characterised by restriction of growth in vitro with induction of putative virulence factors including yersiniae outer membrane-peptides (YOPs) and V antigen (Lcr+). A medium was developed that permitted expression of high yields of V by Yersinia pestis KIM in large fermenter vessels. Immunoblots of specific precipitates prepared by prior molecular sieving showed that native unaggregated V exists as a monomeric 37,000 dalton peptide. Fractionation by precipitation with (NH4)2SO4 and chromatography on phenyl-Sepharose, DEAE cellulose, Sephacryl S200, calcium hydroxyapatite, and Sephadex G200 yielded highly purified antigen as judged by sodium dodecyl sulfate-polyacrylamide gel electrophoresis of parallel preparations from Lcr+ and Lcr- yersiniae. However, yields of V obtained by this process were unexpectedly low. As determined from immunoblots with monospecific polyclonal and monoclonal anti-V, this loss of activity occurred as a function of evident degradation at every step of purification yielding antigenic fragments of about 36,000, 34,000, 31,000, 30,000, and 28,000 daltons. Neutral or acidic pH favored hydrolysis; insignificant cleavage occurred in viable Lcr+ cells of Y. pestis or in culture supernatant fluids. V in neutral cytoplasm from Yersinia pseudotuberculosis or Yersinia enterocolitica did not undergo comparable degradation.

Mechanisms of bacterial virulence

In this review the nature of prokaryotic parasites was first discussed with emphasis on the evolution of virulence. Subsequently, nonspecific mechanisms of host defense were considered with emphasis on recent findings relating to bacterial killing by serum and professional phagocytes. Based on this background, the nature of virulence factors required for growth of pathogens in the nonimmune host was considered. Strategies used by extracellular and intracellular parasites were compared. It is evident from the resulting overview of experimental findings that knowledge concerning virulence of extracellular parasites outweighs that collected for both facultative and obligate intracellular parasites. Remaining problems regarding extracellular parasitism include precise resolution of the nature of serum resistance, pilus-independent adhesion, tissue invasiveness, and resistance to phagocytosis. Solutions to these questions will probably arise during the course of studies primarily emphasizing bacterial structure and function. Unresolved problems concerning intracellular parasites include definition of regulatory changes involved in adaptation for intra- and extracellular growth, the nature of reactions preventing phagosome-lysosome fusion, mechanisms of survival within phagolysosomes, and explanations for host-cell dependence. These topics provide real problems in cellular and molecular biology, and they will probably be resolved by those familiar with these disciplines. The ability of parasitic prokaryotes to shut off otherwise effective specific immune responses was shown to cross phenotypic lines. Resolution of these somewhat sinister mechanisms of virulence will require an understanding of fundamental immune processes. Further study of bacterial virulence factors will probably provide an understanding of basic cellular processes relevant to other biological disciplines. Indeed, information of this nature may not be obtainable by any other experimental approach.

Roles of V antigen in promoting virulence and immunity in yersiniae

It is established that yersiniae harboring an approximately 45-megadalton Vwa-plasmid can produce V and W antigens (Vwa+), and that sera containing anti-V provides passive protection to mice against Yersinia pestis. This observation was extended by the use of monospecific anti-V prepared by injecting rabbits with partially purified V, absorption of antisera with a Vwa- extract, and then separation of gamma-globulin by traditional processes of fractionation or by affinity chromatography. These preparations provided passive protection against 10 minimum lethal doses of virulent Y. pestis KIM, Yersinia pseudotuberculosis PB1, and Yersinia enterocolitica WA. Kinetics of elimination of these Vwa+ yersiniae from organs and blood of passively immunized mice closely resembled those of avirulent Vwa- mutants from normal mice. Injection into mice of sterile crude extracts of Y. pseudotuberculosis PB1 containing V promoted significant survival and retention of Vwa- mutants of Y. pestis, Y. pseudotuberculosis, and Y. enterocolitica. This effect was eliminated by the removal of V before injection by precipitation with monospecific antibody. These results indicate that V antigen per se is the major virulence factor mediated by Vwa-plasmids.

Roles of V antigen in promoting virulence and immunity in yersiniae

It is established that yersiniae harboring an approximately 45-megadalton Vwa-plasmid can produce V and W antigens (Vwa+), and that sera containing anti-V provides passive protection to mice against Yersinia pestis. This observation was extended by the use of monospecific anti-V prepared by injecting rabbits with partially purified V, absorption of antisera with a Vwa- extract, and then separation of gamma-globulin by traditional processes of fractionation or by affinity chromatography. These preparations provided passive protection against 10 minimum lethal doses of virulent Y. pestis KIM, Yersinia pseudotuberculosis PB1, and Yersinia enterocolitica WA. Kinetics of elimination of these Vwa+ yersiniae from organs and blood of passively immunized mice closely resembled those of avirulent Vwa- mutants from normal mice. Injection into mice of sterile crude extracts of Y. pseudotuberculosis PB1 containing V promoted significant survival and retention of Vwa- mutants of Y. pestis, Y. pseudotuberculosis, and Y. enterocolitica. This effect was eliminated by the removal of V before injection by precipitation with monospecific antibody. These results indicate that V antigen per se is the major virulence factor mediated by Vwa-plasmids.

In vivo comparison of avirulent Vwa- and Pgm- or Pstr phenotypes of yersiniae

The abilities of Yersinia pestis to undergo restriction in Ca2+-deficient medium with concomitant production of V and W antigens (Vwa+) and to absorb exogenous pigments (Pgm+) are established virulence factors. Mutation of Y. pestis to Pgm- is known to promote resistance to pesticin (Pstr) and reduced lethality by peripheral routes of injection. Vwa+ Pgm- isolates of Y. pestis were shown in this study to retain virulence in mice when injected intravenously. Although Pgm- in appearance, wild-type cells of Yersinia pseudotuberculosis and Yersinia enterocolitica may also be sensitive to pesticin. Pstr mutants of Vwa+ strains of these species were similarly of reduced virulence, especially by peripheral routes of injection. The consequences of mutation to Vwa- and Pgm- or Pstr on growth and persistence in vivo were determined. After intravenous injection, Vwa+ yersiniae of all species exhibited sustained growth in mouse spleen, liver, and lung and accumulated in blood. Septicemia was not observed after similar injection of Vwa- mutants which were unable to maintain comparable rates of net increase in tissues. Mutation to Pgm- or Pstr did not influence proliferation but resulted in enhanced clearance from organs. It is known that reticuloendothelial cells serve as favored sites of replication for all wild-type yersiniae. Our results are consistent with the hypothesis that the Vwa+ phenotype favors growth within macrophages and that the Pgm+ and pesticin-sensitive phenotypes permit long-term, probably extracellular, retention within organs. Virulence in standard animal models (mice, rats, and guinea pigs) was not correlated with resistance to the bactericidal action of serum.

The Vwa+ virulence factor of yersiniae: the molecular basis of the attendant nutritional requirement for Ca++

The plague V antigen is a cytoplasmic 90,000-dalton peptide, and the W antigen is a primarily extracellular 145,000-dalton lipoprotein of unknown origin. Wild-type yersiniae undergo restriction of cell division when producing these plasmid-mediated virulence antigens (Vwa+) during cultivation at 37 C in Ca++-deficient media. In Yersinia pestis both restriction and synthesis of V and W antigens are potentiated in this environment by elevated Mg++ and prevented by Ca++ or exogenous nucleoside triphosphates. Restriction occurs by mechanisms that also are involved in nutritional stepdown (shutoff of stable RNA synthesis with reduction of nucleotide pools). Attendant regulatory mechanisms remain undefined; they are independent of MS nucleotides but may involve V antigen. Restriction is similar in Vwa+ Yersinia pseudotuberculosis and Yersinia enterocolitica, which, unlike Y. pestis, produce ancillary outer membrane peptides. Synthesis of these activities is dependent on elevated temperature but may not be influenced by Ca++; their presence is associated with spontaneous autoagglutination in vitro.

Vwa+ phenotype of Yersinia enterocolitica

Expression of the Vwa+ phenotype of Yersinia pestis in vitro is known to reflect maximum induction of virulence (or V and W antigens) at 37 degrees C with concomitant restriction of cell division. Both phenomena are potentiated by 20 mM Mg2+ and prevented by cultivation at 26 or 37 degrees C with 2.5 mM Ca2+. We have now compared this classic plasmid-mediated phenotype with those of Vwa+ Yersinia pseudotuberculosis and Yersinia enterocolitica which, unlike Y. pestis, produce ancillary outer membrane peptides unrelated to the V and W antigens. All of 10 wild-type strains of Y. enterocolitica (serotypes O:3, O:4,32, O:8, O:9, O:15, and O:21) exhibited a nutritional requirement for Ca2+ at 37 degrees C and produced significant V antigen. Like Y. pseudotuberculosis, autoagglutination of Vwa+ Y. enterocolitica was dependent upon prior growth at 37 degrees C but was not influenced by Ca2+. Autoagglutination of Y. pestis was never observed. Resistance of Y. enterocolitica to 10% human serum was typically dependent upon prior growth at 37 degrees C, either with or without added Ca2+, and carriage of a Vwa plasmid. In contrast, serum resistance of Y. pseudotuberculosis was temperature but not plasmid dependent and that of Y. pestis was constitutive.

Effect of exogenous nucleotides on Ca2+ dependence and V antigen synthesis in Yersinia pestis

Cells of Yersinia pestis strain EV76 are known to cease growth after a shift from 26 to 37 degrees C in neutral Ca2+-deficient medium; this effect is potentiated by Mg2+. With 2.5 mM Mg2+ and no added Ca2+, restriction was relaxed at elevated pH at which maximum cell yields occurred in the presence of 20 mM exogenous ATP. This ATP-dependent growth was inhibited by Ca2+ or 20 mM Mg2+; the nucleotide was neither transported into the organism nor hydrolyzed extracellularly. With strain EV76, ATP could be replaced by GTP but not other nucleotides, nucleosides, free bases, or pyrophosphate. CTP and UTP also promoted growth of strain KIM, in which limited division also occurred with nucleoside di- and monophosphates. Intracellular V antigen was detected 1 h after temperature shift in Ca2+-deficient medium containing 20 mM Mg2+, a time corresponding to the earliest known events associated with restriction (shutoff of stable RNA synthesis and reduction of adenylate energy charge). Maximum yield of V was obtained 2 h later when cell division ceased; the titer of the antigen remained constant thereafter. The specific activity of V in cells grown with ATP was significantly reduced, especially at elevated pH. These results would be expected if exogenous nucleotides promote growth by sequestering sufficient Mg2+ to prevent restriction of cell division mediated by V antigen.

Localization in Yersinia pestis of peptides associated with virulence

An avirulent guanine auxotroph of wild-type Yersinia pestis was used to select isogenic mutants lacking invasive determinants of virulence including V and W antigens (Vwa-), genetically linked fibrinolysin, coagulase, and pesticin activities (Pst-), and the capacity to absorb exogenous pesticin and pigments including hemin (Pgm-). After growth in environments known to favor expression of these factors by the parent, cells were converted to spheroplasts and disrupted to obtain preparations of cytoplasm; particulate matter was separated into inner and outer membranes by sucrose gradient centrifugation. Peptides present in these fractions were then solubilized and compared by two-dimensional polyacrylamide gel electrophoresis. Components unique to Vwa+ cells, including V antigen, were restricted to the cytoplasmic fraction. In contrast, peptides possibly corresponding to fibrinolysin and coagulase were located primarily within the outer membrane of the Pst+ parent; pesticin was not identified. Similarly, a major outer membrane peptide, possibly representing the pesticin and pigment receptor, was peculiar to the Pgm+ parent. Accordingly, two of the virulence factors examined (Pst+ and Pgm+) can interact directly with host cells or fluids by virtue of their location on the bacterial surface. The remaining cytoplasmic Vwa+ determinant remains a candidate for a regulatory system whose role in pathogenicity is expression of functions required for intracellular survival.

RNA synthesis in Yersinia pestis during growth restriction in calcium-deficient medium

Yersinia pestis requires 2.5 mM Ca(2+) for growth at 37 degrees C but not at 26 degrees C. After a shift from 26 to 37 degrees C in a Ca(2+)-deficient medium, an ordered series of metabolic alterations occur which result in transition from a growing cell to a viable but non-proliferating cell. The earliest known alteration in normal metabolism associated with this transition is a termination of net RNA synthesis. Competitive RNA/DNA hybridizations with uniformly labeled RNA and stable RNA competitor indicated identical mRNA to stable RNA ratios in growing cells and non-proliferating Ca(2+)-deprived cells. Similar hybridizations with pulse-labeled RNA demonstrated that growing cells synthesized 57% mRNA, 37% rRNA, and 5% tRNA, whereas Ca(2+)-deprived cells synthesized 95% mRNA, 4.7% rRNA, and 0.7% tRNA. After addition of radioactive uracil and rifampin to growing and Ca(2+)-deprived cells, decay of approximately 40 and 90% of the newly synthesized RNA was found for growing and Ca(2+)-deprived cells, respectively. The half-life of the mRNA was found to be 1.5 min for growing cells and 4.5 min for Ca(2+)-deprived cells. Y. pestis elicited increases in the levels of guanosine tetraphosphate and guanosine pentaphosphate in response to amino acid deprivation and yielded transient increases in the levels of these phosphorylated nucleotides after a shift from 26 to 37 degrees C. These increases were independent of Ca(2+) availability and preceded the alteration in RNA synthesis by more than 1 h. The levels of these phosphorylated nucleotides then stabilized at about 80 and 40 pmol for Ca(2+)-deprived and Ca(2+)-supplemented cultures, respectively, and did not increase further in the Ca(2+)-deprived culture at the time corresponding to the reduction in stable RNA synthesis. These findings indicate that the early lesion in RNA synthesis associated with the growth restriction of Ca(2+)-deprived Y. pestis reflects a block in stable RNA synthesis and that this effect is not mediated by guanosine tetraphosphate or guanosine pentaphosphate.

Mutations to tolerance and resistance to pesticin and colicins in Escherichia coli phi

The universal colicin-indicator strain Escherichia coli phi, unlike E. coli strain K-12, is sensitive to pesticin, a bacteriocin produced by wild-type Yersinia pestis. Eleven distinct phenotypes of E. coli phi mutants were obtained by selection for insensitivity to pesticin, group B colicins, the group A colicin S4, or coliphage T5. Representative isolates from eight of these classes closely resembled resistant receptor mutants (Cir-, Fep-, and TonA-) or tolerant mutants (TonB-, ExbB-, ExbC-, Ivt-, and Cmt-) described in Escherichia coli K-12. The remainder were unique; of these, one resembled TonB- but was also tolerant to colicin S4 (TonB/S4-), and the others exhibited specific resistance to either colicin S4 (Sfr-) or to pesticin (Psr-). All receptor mutants except Psr- remained sensitive to pesticin, whereas TonB/S4, TonB-, ExbB-, and ExbC- isolates were highly tolerant to this bacteriocin.

Cytoplasmic and membrane proteins of yersiniae cultivated under conditions simulating mammalian intracellular environment

A procedure is described for fractionating Yersinia grown in small cultures into inner and outer membranes and soluble cytoplasmic proteins. The procedure was applied to the three recognized species of the genus grown under conditions simulating mammalian intracellular fluid with respect to Ca2+ and Mg2+. These conditions are known to elicit the production of the plague virulence antigen V. Isolates capable of making this antigen were compared with virulence-antigen-negative derivatives by two-dimensional electrophoresis. The V antigen was localized to the soluble protein fraction as a peptide that comigrates with the major component of a specific immunoprecipitate. This peptide had an apparent molecular weight of 38,000 and was not found in either apparent molecular weight of 38,000 and was not found in either membrane fraction. The comparison of virulence antigen-producers and nonproducers of Y. pseudotuberculosis and Y. enterocolitica revealed large qualitative and quantitative differences in outer membrane protein patterns, whereas the same comparison for Y. pestis showed only minor differences. The complexity of changes in the various protein fractions corroborate data in the literature indicating that extensive physiological changes occur in virulent organisms cultivated under simulated intracellular conditions.

Plasmids in Yersinia pestis

Pesticinogenic and Ca2+-dependent strains of Yersinia pestis harbored plasmids of about 6 and 45 megadaltons, respectively. In addition, most isolates examined possessed a cryptic 65-megadalton plasmid.

Influence of chromosome integrity on Escherichia coli cell division

The antitumor agent cis-platinum(II)diamminodichloride (PDD) caused wild-type and recA+ deoxyribonucleic acid (DNA) repair-deficient mutant cells of Escherichia coli K-12 to grow as long, multinucleated filaments. At 5 micrograms/ml, the times required for reduction of viability to 37% for wild-type, polA, recB,C, uvrA, and recA organisms were > 200, 200, 120, 25, and 5 min, respectively. Only recA cells exhibited @reckless" degradation of DNA at this concentration of PDD. As shown by sedimentation in alkaline sucrose gradients, generation of single-strand breaks in DNA of the remaining organisms was a major consequence of growth in PDD. Upon incubation in fresh medium after removal of the compound and storage for 4 h at 4 degrees C, a respective lag of 3, 4, 6, and 9 h occurred before filaments of wild-type, polA, recB,C, and uvrA cells commenced cell division. Maintenance at 4 degrees C, which evidently delayed postshift initiation of chromosome replication, was only essential for fragmentation of uvrA filaments. In all cases, these periods of division delay corresponded to those required for restoration of normal chromosomal molecular weight as determined in alkaline sucrose gradients.

Plague virulence antigens from Yersinia enterocolitica

The virulence of Yersinia enterocolitica, biotype 2, serotype O:8, in mice is related to its ability to produce plague V and W antigens. V and W antigens in Y. enterocolitica are shown to be immunologically identical to the previously described V and W antigens of Yersinia pestis and Yersinia pseudotuberculosis.

Consequences of Ca2+ deficiency on macromolecular synthesis and adenylate energy charge in Yersinia pestis

A 37 but not 26 degrees C virulent Yersinia pestis is known to require at least 2.5 mM Ca2+ for growth; this requirement is potentiated by Mg2+. After shift of log-phase cells (doubling time of 2 h) from 26 to 37 degrees C in Ca2+-deficient medium, shutoff of net ribonucleic acid synthesis preceded that of protein and cell mass. With 2.5 mM Mg2+, about two doublings in cell mass and number occurred before restriction with synthesis of sufficient deoxyribonucleic acid to account for initiation and termination of two postshift rounds of chromosome replication. Temperature shift with 20 mMMg2+ resulted in a single doubling of cell mass and number with one round of chromosome replication. Subsequent to shutoff of ribonucleic acid accumulation, ribonucleoside but not deoxyribonucleoside triphosphate pools became reduced to about 50% of normal values and the adenylate energy change fell from about 0.8, typical of growing cells, to about 0.6. Excretion of significant concentrations of adenine nucleotides under both permissive and restrictive conditions was observed. Only trace levels (less than 0.01 microM ol/g [dry weight]) of guaninosine 5'-diphosphate 3'-diphosphate accumulated under restrictive or permissive conditions; guanosine 5'-triphosphate 3'-diphosphate was not detected. Return of fully restricted cells from 37 to 26 degrees C with Ca2+ resulted in prompt growth, whereas addition of Ca2+ at 37 degrees C was ineffective. This finding indicates that the observed temperature-sensitive lesion in ribonucleic acid synthesis that results in restriction can be prevented but not reversed by cultivation with Ca2+.

Mode of action of pesticin: N-acetylglucosaminidase activity

Homogeneous preparations of pesticin, a bacteriocin produced by Yersinia pestis, neither significantly inhibited net synthesis of deoxyribonucleic acid, ribonucleic acid, or protein in Escherichia coli phi nor caused detectable degradation of deoxyribonucleic acid in vivo. Accordingly, its mode of action does not resemble that of colicin E2 as suggested by others. However, incorporation of cell wall-specific label ([14C]diaminopimelic acid) into trichloroacetic acid-insoluble material of growing cells was inhibited by pesticin which also promoted release of such radioactivity from both resting cells and purified mureinlipoprotein. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of reaction mixtures containing appropriately labeled mureinlipoprotein showed that [3H]N-acetylglucosamine comigrated either with [14C]diaminopimelic acid in the murein peptide or with [14C]isoleucine of the Braun lipoprotein. As judged by these findings and pesticin-dependent release of reducing equivalents but not 4-hydroxy-2-acetamido sugars, the bacteriocin possesses N-acetylglucosaminidase activity. Hydrolysis of murein-lipoprotein occurred over a broad pH, with an optimum of 4.7. Mureinlipoproteins from a variety of pesticin-sensitive and -resistant organisms were hydrolyzed by the bacteriocin, indicating that its antibacterial specificity resides at the level of absorption.

Accumulation of iron by yersiniae

Escherichia coli, Bacillus megaterium, and three species of yersiniae grew rapidly without significant production of soluble siderophores in a defined iron-sufficient medium (20 microM Fe3+). In iron-deficient medium (0.1 to 0.3 microM Fe3+) all organisms showed reduced growth, and there was extensive production of siderophores by E. coli and B. megaterium. Release of soluble siderophores by Yersinia pestis, Y. pseudotuberculosis, or Y. enterocolitica in this medium was not detected. Citrate (1 mM) inhibited growth of yersiniae in iron-deficient medium, indicating that the organisms lack an inducible Fe3+-citrate transport mechanism. Uptake of 59Fe3+ by all yersiniae was an energy-dependent saturable process, showing increased accumulation after adaptation to iron-deficient medium. Growth of Y. pseudotuberculosis and Y. enterocolitica but not Y. pestis on iron-limited solid medium was enhanced to varying degrees by exogenous siderophores (desferal, schizokinen, aerobactin, and enterochelin). Only hemin (0.1 pmol) or a combination of inorganic iron plus protoporphyrin IX promoted growth of Y. pestis on agar rendered highly iron deficient with egg white conalbumin (10 microM). Growth of Y. pseudotuberculosis and Y. enterocolitica was stimulated on this medium by Fe3+ or hemin. These results indicate that hemin can serve as a sole source of iron for yersiniae and that the organisms possess an efficient cell-bound transport system for Fe3+.

Consequences of aspartase deficiency in Yersinia pestis

Growing cells of Yersinia pseudotuberculosis, but not those of closely related Yersinia pestis, rapidly destroyed exogenous L-aspartic and L-glutamic acids, thus prompting a comparative study of dicarboxylic amino acid catabolism. Rates of amino acid metabolism by resting cells of both species were determined at pH 5.5, 7.0, and 8.5. Regardless of pH, Y. pseudotuberculosis destroyed L-glutamic acid, L-glutamine, L-aspartic acid, and L-asparagine at rates greater than those observed for Y. pestis. Although rates of proline degardation were similar, its metabolism by Y. pestis at pH 8.5 resulted in excretion of glutamic and aspartic acids. Similarly, Y. pestis excreted aspartic acid when incubated with L-glutamic acid (pH 8.5) or L-asparagine (pH 5.5, 7.0, and 8.5). Aspartase activity was not detected in extracts of 10 strains of Y. pestis but was present in all 11 isolates of Y. pseudotuberculosis. The latter contained significantly more glutaminase, asparaginase, and L-glutamate-oxalacetate transminase activity than did extracts of Y. pestis; specific activities of L-glutamate dehydrogenase and alpha-ketoglutarate dehydrogenase were similar. The observed differences in dicarboxylic amino acid metabolism are traceable to asparatase deficiency in Y. pestis and may account for the slow doubling time of this organism relative to Y. pseudotuberculosis.