Stable shuttle vectors for Neisseria gonorrhoeae, Haemophilus spp. and other bacteria based on a single origin of replication

There are three major Neisseria gonorrhoeae β-lactamase plasmid variants which are associated with specific lineages and carry distinct TEM alleles

Neisseria gonorrhoeae is a significant threat to global health with an estimated incidence of over 80 million cases each year and high levels of antimicrobial resistance. The gonococcal β-lactamase plasmid, pbla, carries the TEM β-lactamase, which requires only one or two amino acid changes to become an extended-spectrum β-lactamase (ESBL); this would render last resort treatments for gonorrhoea ineffective. Although pbla is not mobile, it can be transferred by the conjugative plasmid, pConj, found in N. gonorrhoeae. Seven variants of pbla have been described previously, but little is known about their frequency or distribution in the gonococcal population. We characterised sequences of pbla variants and devised a typing scheme, Ng_pblaST that allows their identification from whole genome short-read sequences. We implemented Ng_pblaST to assess the distribution of pbla variants in 15 532 gonococcal isolates. This demonstrated that only three pbla variants commonly circulate in gonococci, which together account for >99 % of sequences. The pbla variants carry different TEM alleles and are prevalent in distinct gonococcal lineages. Analysis of 2758 pbla-containing isolates revealed the co-occurrence of pbla with certain pConj types, indicating co-operativity between pbla and pConj variants in the spread of plasmid-mediated AMR in N. gonorrhoeae. Understanding the variation and distribution of pbla is essential for monitoring and predicting the spread of plasmid-mediated β-lactam resistance in N. gonorrhoeae.

Molecular Mechanisms of Drug Resistance and Epidemiology of Multidrug-Resistant Variants of Neisseria gonorrhoeae

The paper presents various issues related to the increasing drug resistance of Neisseria gonorrhoeae and the occurrence and spread of multidrug-resistant clones. One of the most important is the incidence and evolution of resistance mechanisms of N. gonorrhoeae to beta-lactam antibiotics. Chromosomal resistance to penicillins and oxyimino-cephalosporins and plasmid resistance to penicillins are discussed. Chromosomal resistance is associated with the presence of mutations in the PBP2 protein, containing mosaic variants and nonmosaic amino acid substitutions in the transpeptidase domain, and their correlation with mutations in the mtrR gene and its promoter regions (the MtrCDE membrane pump repressor) and in several other genes, which together determine reduced sensitivity or resistance to ceftriaxone and cefixime. Plasmid resistance to penicillins results from the production of beta-lactamases. There are different types of beta-lactamases as well as penicillinase plasmids. In addition to resistance to beta-lactam antibiotics, the paper covers the mechanisms and occurrence of resistance to macrolides (azithromycin), fluoroquinolones and some other antibiotics. Moreover, the most important epidemiological types of multidrug-resistant N. gonorrhoeae, prevalent in specific years and regions, are discussed. Epidemiological types are defined as sequence types, clonal complexes and genogroups obtained by various typing systems such as NG-STAR, NG-MAST and MLST. New perspectives on the treatment of N. gonorrhoeae infections are also presented, including new drugs active against multidrug-resistant strains.

Direct visualization of sequence-specific DNA binding by gonococcal type IV pili

Neisseria gonorrhoeae, the causative agent of gonorrhoea, is a major burden on global healthcare systems, with an estimated ~80-90 million new global cases annually. This burden is exacerbated by increasing levels of antimicrobial resistance, which has greatly limited viable antimicrobial therapies. Decreasing gonococcal drug susceptibility has been driven largely by accumulation of chromosomal resistance determinants, which can be acquired through natural transformation, whereby DNA in the extracellular milieu is imported into cells and incorporated into the genome by homologous recombination. N. gonorrhoeae possesses a specialized system for DNA uptake, which strongly biases transformation in favour of DNA from closely related bacteria by recognizing a 10-12 bp DNA uptake sequence (DUS) motif, which is highly overrepresented in their chromosomal DNA. This process relies on numerous proteins, including the DUS-specific receptor ComP, which assemble retractile protein filaments termed type IV pili (T4P) extending from the cell surface, and one model for neisserial DNA uptake proposes that these filaments bind DNA in a DUS-dependent manner before retracting to transport DNA into the periplasm. However, conflicting evidence indicates that elongated pilus filaments may not have such a direct role in DNA binding uptake as this model suggests. Here, we quantitatively measured DNA binding to gonococcal T4P fibres by directly visualizing binding complexes with confocal fluorescence microscopy in order to confirm the sequence-specific, comP-dependent DNA binding capacity of elongated T4P fibres. This supports the idea that pilus filaments could be responsible for initially capturing DNA in the first step of sequence-specific DNA uptake.

Human IgG1, IgG3, and IgG3 Hinge-Truncated Mutants Show Different Protection Capabilities against Meningococci Depending on the Target Antigen and Epitope Specificity

We compared the bactericidal activity of recombinant sets of chimeric IgG monoclonal antibodies against two important outer membrane meningococcal vaccine antigens: PorA and factor H binding protein (FHbp). The sets contained human Fc portions from IgG1, IgG3, and two IgG3 mutants (IgG3m15 and IgGm17) with hinge regions of 15 and 17 amino acids encoded by hinge exons h2 and h1, respectively (human IgG3 has a hinge region of 62 amino acids encoded by hinge exons h1, h2, h3, and h4, while human IgG1 has a hinge region of only 15 amino acids encoded by one hinge exon) and mouse V regions. IgG1 showed higher bactericidal activity than IgG3 when directed against PorA (an abundant antigen), while IgG3 was more bactericidal than IgG1 when directed against FHbp (a sparsely and variably distributed antigen). On the other hand, the IgG3 hinge-truncated antibodies IgG3m15 and IgGm17 showed higher bactericidal activity than both IgG1 and IgG3 regardless of the target antigen. Thus, the Fc region of IgG3 antibodies appears to have an enhanced complement-activating function, independent of their long hinge region, compared to IgG1 antibodies. The greater activity of the truncated IgG3 hinge mutants indicates that the long hinge of IgG3 seems to downregulate through an unknown mechanism the inherent increased complement-activating capability of IgG3 Fc when the antibody binds to a sparse antigen.

Experimental Methods for Studying the BAM Complex in Neisseria meningitidis

Neisseria meningitidis is a human pathogen. It is intensively studied for host-pathogen interactions and vaccine development. However, its favorable growth properties, genetic accessibility, and small genome size also make it an excellent model organism for studying fundamental biological processes, such as outer membrane biogenesis. Indeed, the first component of the assembly machinery for outer-membrane proteins, the BAM complex, was identified in N. meningitidis. Here, we describe protocols to inactivate chromosomal genes and to express genes from a well-controlled promoter on a plasmid in N. meningitidis. Together, these protocols can be used, for example, to deplete cells from essential components of the BAM complex. We also describe a simple, gel-based assay to assess the proper functioning of the BAM complex in vivo.

The genetics of Neisseria species

Neisseria gonorrhoeae and Neisseria meningitidis are closely related organisms that cause the sexually transmitted infection gonorrhea and serious bacterial meningitis and septicemia, respectively. Both species possess multiple mechanisms to alter the expression of surface-exposed proteins through the processes of phase and antigenic variation. This potential for wide variability in surface-exposed structures allows the organisms to always have subpopulations of divergent antigenic types to avoid immune surveillance and to contribute to functional variation. Additionally, the Neisseria are naturally competent for DNA transformation, which is their main means of genetic exchange. Although bacteriophages and plasmids are present in this genus, they are not as effective as DNA transformation for horizontal genetic exchange. There are barriers to genetic transfer, such as restriction-modification systems and CRISPR loci, that limit particular types of exchange. These host-restricted pathogens illustrate the rich complexity of genetics that can help define the similarities and differences of closely related organisms.

Substrate specificity and kinetic characterization of peptidoglycan O-acetyltransferase B from Neisseria gonorrhoeae

The O-acetylation of the essential cell wall polymer peptidoglycan is a major virulence factor identified in many bacteria, both Gram-positive and Gram-negative, including Staphylococcus aureus, Bacillus anthracis, Neisseria gonorrhoeae, and Neisseria meningitidis. With Gram-negative bacteria, the translocation of acetyl groups from the cytoplasm is performed by an integral membrane protein, PatA, for its transfer to peptidoglycan by O-acetyltransferase PatB, whereas a single bimodal membrane protein, OatA, appears to catalyze both reactions of the process in Gram-positive bacteria. Only phenotypic evidence existed in support of these pathways because no in vitro biochemical assay was available for their analysis, which reflected the complexities of investigating integral membrane proteins that act on a totally insoluble and heterogeneous substrate, such as peptidoglycan. In this study, we present the first biochemical and kinetic analysis of a peptidoglycan O-acetyltransferase using PatB from N. gonorrhoeae as the model system. The enzyme has specificity for muropeptides that possess tri- and tetrapeptide stems on muramyl residues. With chitooligosaccharides as substrates, rates of reaction increase with increasing degrees of polymerization to 5/6. This information will be valuable for the identification and development of peptidoglycan O-acetyltransferase inhibitors that could represent potential leads to novel classes of antibiotics.

Meningococcal omp85 in detergent-extracted outer membrane vesicle vaccines induces high levels of non-functional antibodies in mice

The vaccine potential of meningococcal Omp85 was studied by comparing the immune responses of genetically modified deoxycholate-extracted outer membrane vesicles, expressing five-fold higher levels of Omp85, with wild-type vesicles. Groups (n = 6-12) of inbred and outbred mouse strains (Balb/c, C57BL/6, OFI and NMRI) were immunized with the two vaccines, and the induced antibody levels and bactericidal and opsonic activities measured. Except for Balb/c mice, which were low responders, the genetically modified vaccine raised high Omp85 antibody levels in all mouse strains. In comparison, the wild-type vaccine gave lower antibody levels, but NMRI mice responded to this vaccine with the same high levels as the modified vaccine in the other strains. Although the vaccines induced strain-dependent Omp85 antibody responses, the mouse strains showed high and similar serum bactericidal titres. Titres were negligible with heterologous or PorA-negative meningococcal target strains, demonstrating the presence of the dominant bactericidal PorA antibodies. The two vaccines induced the same opsonic titres. Thus, the genetically modified vaccine with high Omp85 antibody levels and the wild-type vaccine induced the same levels of functional activities related to protection against meningococcal disease, suggesting that meningococcal Omp85 is a less attractive vaccine antigen.

Mechanism of action of Neisseria gonorrhoeae O-acetylpeptidoglycan esterase, an SGNH serine esterase

O-Acetylpeptidoglycan esterase from Neisseria gonorrhoeae functions to release O-acetyl groups from the C-6 position of muramoyl residues in O-acetylated peptidoglycan, thereby permitting the continued metabolism of this essential cell wall heteropolymer. It has been demonstrated to be a serine esterase with sequence similarity to the family CE-3 carbohydrate esterases of the CAZy classification system. In the absence of a three-dimensional structure for any Ape, further knowledge of its structure and function relationship is dependent on modeling and kinetic studies. In this study, we predicted Neisseria gonorrhoeae Ape1a to be an SGNH hydrolase with an adopted α/β-hydrolase fold containing a central twisted four-stranded parallel β-sheet flanked by six α-helices with the putative catalytic triad, Asp-366, His-369, and Ser-80 appropriately aligned within a pocket. The role of eight invariant and highly conserved residues localized to the active site was investigated by site-directed replacements coupled with kinetic characterization and binding studies of the resultant engineered enzymes. Based on these data and theoretical considerations, Gly-236 and Asn-268 were identified as participating at the oxyanion hole to stabilize the tetrahedral species in the reaction mechanism, whereas Gly-78, Asp-79, His-81, Asn-235, Thr-267, and Val-368 are proposed to position appropriately the catalytic residues and participate in substrate binding.

Generating knock-out and complementation strains of Neisseria meningitidis

The human-restricted pathogens Neisseria meningitidis and Neisseria gonorrhoeae are naturally competent for DNA uptake. This trait has been exploited extensively for genetic manipulation of these bacteria in the laboratory. Most transformation protocols were developed for N. gonorrhoeae, but appear to work also for N. meningitidis. In this chapter, we describe a number of protocols for genetic manipulation of N. meningitidis. Specifically, we describe how to (1) obtain knock-out mutants containing antibiotic-resistance markers, (2) generate markerless knock-out mutants, and (3) construct complementation strains. The generation of such mutants provides a valuable resource for studies of bacterial pathogenesis and vaccine development.

Combined roles of human IgG subclass, alternative complement pathway activation, and epitope density in the bactericidal activity of antibodies to meningococcal factor h binding protein

Meningococcal vaccines containing factor H binding protein (fHbp) are in clinical development. fHbp binds human fH, which enables the meningococcus to resist complement-mediated bacteriolysis. Previously, we found that chimeric human IgG1 mouse anti-fHbp monoclonal antibodies (MAbs) had human complement-mediated bactericidal activity only if the MAb inhibited fH binding. Since IgG subclasses differ in their ability to activate complement, we investigated the role of human IgG subclasses on antibody functional activity. We constructed chimeric MAbs in which three different murine fHbp-specific binding domains were each paired with human IgG1, IgG2, or IgG3. Against a wild-type group B isolate, all three IgG3 MAbs, irrespective of their ability to inhibit fH binding, had bactericidal activity that was >5-fold higher than the respective IgG1 MAbs, while the IgG2 MAbs had the least activity. Against a mutant with increased fHbp expression, the anti-fHbp MAbs elicited greater C4b deposition (classical pathway) and greater bactericidal activity than against the wild-type strain, and the IgG1 MAbs had similar or greater activity than the respective IgG3 MAbs. The bactericidal activity against both wild-type and mutant strains also was dependent, in part, on activation of the alternative complement pathway. Thus, at lower epitope density in the wild-type strain, the IgG3 anti-fHbp MAbs had the greatest bactericidal activity. At a higher epitope density in the mutant, the IgG1 MAbs had similar or greater bactericidal activity than the IgG3 MAbs, and the activity was less dependent on the inhibition of fH binding than at a lower epitope density.

Genetic Manipulation of Neisseria gonorrhoeae

The sexually transmitted pathogen, Neisseria gonorrhoeae, undergoes natural transformation at high frequency. This property has led to the rapid dissemination of antibiotic resistance markers and to the panmictic structure of the gonococcal population. However, high-frequency transformation also makes N. gonorrhoeae one of the easiest bacterial species to manipulate genetically in the laboratory. Techniques have been developed that result in transformation frequencies >50%, allowing the identification of mutants by screening and without selection. Constructs have been created to take advantage of this high-frequency transformation, facilitating genetic mutation, complementation, and heterologous gene expression. Techniques are described for genetic manipulation of N. gonorrhoeae, as well as for growth of this fastidious organism.

O-acetylation of peptidoglycan in gram-negative bacteria: identification and characterization of peptidoglycan O-acetyltransferase in Neisseria gonorrhoeae

The ape2 gene encoding a hypothetical O-acetylpeptidoglycan esterase was amplified from genomic DNA of Neisseria gonorrhoeae FA1090 and cloned to encode either the full-length protein or a truncated version lacking its hypothetical signal sequence. Expression trials revealed that production of the full-length version possessing either an N-terminal or C-terminal His(6) tag was toxic to Escherichia coli transformants and that the host rapidly degraded the small amount of protein that was produced. An N-terminally truncated protein could be produced in sufficient yields for purification only if it possessed an N-terminal His(6) tag. This form of the protein was isolated and purified to apparent homogeneity, and its enzymatic properties were characterized. Whereas the protein could bind to insoluble peptidoglycan, it did not function as an esterase. Phenotypic characterization of E. coli transformants producing various forms of the protein revealed that it functions instead to O-acetylate peptidoglycan within the periplasm, and it was thus renamed peptidoglycan O-acetyltransferase B. This activity was found to be dependent upon a second protein, which functions to translocate acetate from the cytoplasm to the periplasm, demonstrating that the O-acetylation of peptidoglycan in N. gonorrhoeae, and other gram-negative bacteria, requires a two component system.

Meningococcal outer membrane vesicle vaccines derived from mutant strains engineered to express factor H binding proteins from antigenic variant groups 1 and 2

Meningococcal outer membrane vesicle (OMV) vaccines, which are treated with detergents to decrease endotoxin activity, are safe and effective in humans. However, the vaccines elicit serum bactericidal antibody responses largely directed against PorA, which is antigenically variable. We previously prepared a native (non-detergent-treated) OMV vaccine from a mutant of group B strain H44/76 in which the lpxL1 gene was inactivated, which resulted in penta-acylated lipid A with attenuated endotoxin activity. To enhance protection, we overexpressed factor H binding protein (fHbp) from the antigenic variant 1 group. The vaccine elicited broad serum bactericidal antibody responses in mice against strains with fHbp variant 1 (approximately 70% of group B isolates) but not against strains with variant 2 or 3. In the present study, we constructed a mutant of group B strain NZ98/254 with attenuated endotoxin that expressed both endogenous variant 1 and heterologous fHbp variant 2. A mixture of the two native OMV vaccines from the H44/76 and NZ98/254 mutants stimulated proinflammatory cytokine responses by human peripheral blood mononuclear cells similar to those stimulated by control, detergent-treated OMV vaccines from the wild-type strains. In mice, the mixture of the two native OMV vaccines elicited broad serum bactericidal antibody responses against strains with heterologous PorA and fHbp in the variant 1, 2, or 3 group. By adsorption studies, the principal bactericidal antibody target was determined to be fHbp. Thus, native OMV vaccines from mutants expressing fHbp variants have the potential to be safe for humans and to confer broad protection against meningococcal disease from strains expressing fHbp from each of the antigenic variant groups.

Genetic manipulation of Neisseria gonorrhoeae

The sexually-transmitted pathogen, Neisseria gonorrhoeae, undergoes natural transformation at high frequency. This property has led to the rapid dissemination of antibiotic resistance markers and to the panmictic structure of the gonococcal population. However, high frequency transformation also makes N. gonorrhoeae one of the easiest bacterial species to manipulate genetically in the laboratory. Techniques have been developed that result in transformation frequencies >50%, allowing the identification of mutants by screening and without selection. Constructs have been created to take advantage of this high frequency transformation, facilitating genetic mutation, complementation, and heterologous gene expression. Techniques are described for genetic manipulation of N. gonorrhoeae, as well as for growth of this fastidious organism.

A role for Haemophilus ducreyi Cu,ZnSOD in resistance to heme toxicity

The Cu,Zn superoxide dismutase (Cu,ZnSOD) from Haemophilus ducreyi is the only enzyme of this class which binds a heme molecule at its dimer interface. To explore the role of the enzyme in this heme-obligate bacterium, a sodC mutant was created by insertional inactivation. No difference in growth rate was observed during heme limitation. In contrast, under heme rich conditions growth of the sodC mutant was impaired compared to the wild type strain. This growth defect was abolished by supplementation of exogenous catalase. Genetic complementation of the sodC mutant in trans demonstrated that the enzymatic property or the heme-binding activity of the protein could repair the growth defect of the sodC mutant. These results indicate that Cu,ZnSOD protects Haemophilus ducreyi from heme toxicity.

Neisseria gonorrheae O-Acetylpeptidoglycan Esterase, a Serine Esterase with a Ser-His-Asp Catalytic Triad

O-Acetylpeptidoglycan esterase from Neisseria gonorrheae FA1090 is similar in sequence to family CE-3 carbohydrate esterases of the CAZy classification system, and it functions to release O-linked acetyl groups from the C-6 position of muramoyl residues in O-acetylated peptidoglycan. Here, we characterize the peptidoglycan of N. gonorrheae FA1090 as being O-acetylated and find that it serves as a substrate for the esterase. The influence of pH on the activity of O-acetylpeptidoglycan esterase was determined, and pKa values of 6.38 and 6.78 for the enzyme-substrate complex (VEt-1) and free enzyme (VEt-1KM-1), respectively, were calculated. The enzyme was inactivated by sulfonyl fluorides but not by EDTA. Multiple-sequence alignment of the O-acetylpeptidoglycan esterase family 1 enzymes with members of the CE-3 enzymes and protein modeling studies identified Ser80, Asp366, and His369 as three invariant amino acid residues that could potentially serve as a catalytic triad. Replacement of each with alanine was accomplished by site-directed mutagenesis, and the resulting mutant proteins were purified to apparent homogeneity. The specific activity of each of the three esterase derivatives was greatly reduced on O-acetylpeptidoglycan. Using the artificial substrate p-nitrophenyl acetate, a kinetic analysis revealed that the turnover number (VEt-1) but not KM was affected by the replacements. These data thus indicate that N. gonorrheae O-acetylpeptidoglycan esterase, and by analogy the CE-3 family of enzymes, function as serine esterases involving a Ser-His-Asp catalytic triad.

Shielding of immunogenic domains in Neisseria meningitidis FrpB (FetA) by the major variable region

The meningococcal iron-limitation-inducible outer membrane protein FrpB (FetA) has been shown to induce bactericidal antibodies, and is, therefore, considered a vaccine candidate. However, these antibodies are strain specific and, consistently, epitope mapping showed that they are directed against a region, located in a surface-exposed loop, L5, that displays considerable sequence variability between strains. Here, we attempted to redirect the immune response to more conserved domains of the protein by deleting L5. Immunization with an FrpB protein lacking L5 resulted in a bactericidal antibody response, and epitope mapping showed that these antibodies were directed against loop L3, which also displays considerable sequence variability. To re-direct the immune response further, immunizations were performed with an FrpB protein lacking both L5 and L3. The antibodies obtained were not bactericidal. Furthermore, the bactericidal antibodies against L3 were only bactericidal in the absence of L5, and immunofluorescence microscopy experiments showed that L5 efficiently shields other immunogenic cell surface-exposed epitopes outside of this region on living cells. Whereas the ability of micro-organisms to vary surface-exposed domains that are targets for protective immunity has long been established, the current work shows that such domains can be remarkably efficient in shielding other, more conserved epitopes.

The meningococcal vaccine candidate GNA1870 binds the complement regulatory protein factor H and enhances serum resistance

Neisseria meningitidis binds factor H (fH), a key regulator of the alternative complement pathway. A approximately 29 kD fH-binding protein expressed in the meningococcal outer membrane was identified by mass spectrometry as GNA1870, a lipoprotein currently under evaluation as a broad-spectrum meningococcal vaccine candidate. GNA1870 was confirmed as the fH ligand on intact bacteria by 1) abrogation of fH binding upon deleting GNA1870, and 2) blocking fH binding by anti-GNA1870 mAbs. fH bound to whole bacteria and purified rGNA1870 representing each of the three variant GNA1870 families. We showed that the amount of fH binding correlated with the level of bacterial GNA1870 expression. High levels of variant 1 GNA1870 expression (either by allelic replacement of gna1870 or by plasmid-driven high-level expression) in strains that otherwise were low-level GNA1870 expressers (and bound low amounts of fH by flow cytometry) restored high levels of fH binding. Diminished fH binding to the GNA1870 deletion mutants was accompanied by enhanced C3 binding and increased killing of the mutants. Conversely, high levels of GNA1870 expression and fH binding enhanced serum resistance. Our findings support the hypothesis that inhibiting the binding of a complement down-regulator protein to the neisserial surface by specific Ab may enhance intrinsic bactericidal activity of the Ab, resulting in two distinct mechanisms of Ab-mediated vaccine efficacy. These data provide further support for inclusion of this molecule in a meningococcal vaccine. To reflect the critical function of this molecule, we suggest calling it fH-binding protein.

Identification and Characterization of O-Acetylpeptidoglycan Esterase: A Novel Enzyme Discovered in Neisseria gonorrhoeae

Modification of the bacterial cell wall heteropolymer peptidoglycan by addition of an acetyl group to the C-6 hydroxyl group of N-acetylmuramoyl residues is known to inhibit the activity of muramidases (lysozymes) of innate immune systems. The O-acetylation of peptidoglycan also precludes the action of intrinsic lytic transglycosylases, enzymes that require a free C-6 hydroxyl group to generate their 1,6-anhydromuropeptide products. This class of autolysins is ubiquitous in peptidoglycan-synthesizing bacteria as they are responsible for insertion of pores and flagella, spore formation, and the general metabolism of peptidoglycan. We recently discovered a cluster of genes in the Neisseria gonorrhoeae chromosome that are proposed to participate in peptidoglycan O-acetylation (Weadge, J. T., Pfeffer, J. M., and Clarke, A. J. (2005) BMC Microb. 5, 49). In the current study, we demonstrate that one of these genes, ape1 functions as an O-acetylpeptidoglycan esterase. The ape1 gene was cloned and overexpressed in Escherichia coli as a fusion protein with a hexa-histidine tag. The expressed protein was purified to apparent homogeneity and assayed for activity as an esterase using three different assays involving high-performance liquid chromatography and chromogenic detection methods which measured the release of ester-linked acetate from a variety of polymer and soluble substrates. These assays demonstrated that Ape1 has a higher specific activity on O-acetylated peptidoglycan compared to O-acetylated xylan. Consequently, Ape1 represents the first enzyme characterized as an O-acetylpeptidoglycan esterase. The physicochemical and kinetic parameters of Ape1 were determined using soluble chromogenic substrates for convenience. Thus, its pH optima for stability and activity were observed to be 6.0 and 6.2, respectively, while its optimum temperature for activity was 55 degrees C. Two forms of truncated Ape1 are generated in E. coli, one lacked the complete predicted N-terminal signal sequence, while the second involved a proteolytic cleavage within this signal sequence. The smaller truncated form was localized predominantly to the periplasm, whereas the larger form was mainly associated with the outer membrane, and to a lesser extent, the cytoplasmic membrane, sites expected for the maintenance of peptidoglycan.

Identification of Actinobacillus suis genes essential for the colonization of the upper respiratory tract of swine

Actinobacillus suis has emerged as an important opportunistic pathogen of high-health-status swine. A colonization challenge method was developed, and using PCR-based signature-tagged transposon mutagenesis, 13 genes belonging to 9 different functional classes were identified that were necessary for A. suis colonization of the upper respiratory tract of swine.

A novel neisserial shuttle plasmid: A useful new tool for meningococcal research

We report the identification and nucleotide sequence analysis of a cryptic plasmid pMIDG2830 from the Gram-negative bacterium Neisseria flavescens. The largest open reading frame encodes a protein similar to the replication protein, RepA, found in pAB49 from Acinetobacter baumannii and pNI10 from Pseudomonas. Modified by the incorporation of a kanamycin resistance cassette, the plasmid can be stably maintained in Escherichia coli and Neisseria meningitidis, and can be used as a shuttle plasmid in meningococcal research.

Protective antibody responses elicited by a meningococcal outer membrane vesicle vaccine with overexpressed genome-derived neisserial antigen 1870

Background. Meningococcal outer membrane vesicle (OMV) vaccines are efficacious in humans but have serosubtype-specific serum bactericidal antibody responses directed at the porin protein PorA and the potential for immune selection of PorA-escape mutants.Methods. We prepared an OMV vaccine from a Neisseria meningitidis strain engineered to overexpress genome-derived neisserial antigen (GNA) 1870, a lipoprotein discovered by genome mining that is being investigated for use in a vaccine.Results. Mice immunized with the modified GNA1870-OMV vaccine developed broader serum bactericidal antibody responses than control mice immunized with a recombinant GNA1870 protein vaccine or an OMV vaccine prepared from wild-type N. meningitidis or a combination of vaccines prepared from wild-type N. meningitidis and recombinant protein. Antiserum from mice immunized with the modified GNA1870-OMV vaccine also elicited greater deposition of human C3 complement on the surface of live N. meningitidis bacteria and greater passive protective activity against meningococcal bacteremia in infant rats. A N. meningitidis mutant with decreased expression of PorA was more susceptible to bactericidal activity of anti-GNA1870 antibodies.Conclusions. The modified GNA1870-OMV vaccine elicits broader protection against meningococcal disease than recombinant GNA1870 protein or conventional OMV vaccines and also has less risk of selection of PorA-escape mutants than a conventional OMV vaccine.

The N terminus of MinD contains determinants which affect its dynamic localization and enzymatic activity

MinD is involved in regulating the proper placement of the cytokinetic machinery in some bacteria, including Neisseria gonorrhoeae and Escherichia coli. Stimulation of the ATPase activity of MinD by MinE has been proposed to induce dynamic, pole-to-pole oscillations of MinD in E. coli. Here, we investigated the effects of deleting or mutating conserved residues within the N terminus of N. gonorrhoeae MinD (MinD(Ng)) on protein dynamism, localization, and interactions with MinD(Ng) and with MinE(Ng). Deletions or mutations were generated in the first five residues of MinD(Ng), and mutant proteins were evaluated by several functional assays. Truncation or mutation of N-terminal residues disrupted MinD(Ng) interactions with itself and with MinE. Although the majority of green fluorescent protein (GFP)-MinD(Ng) mutants could still oscillate from pole to pole in E. coli, the GFP-MinD(Ng) oscillation cycles were significantly faster and were accompanied by increased cytoplasmic localization. Interestingly, in vitro ATPase assays indicated that MinD(Ng) proteins lacking the first three residues or with an I5E substitution possessed higher MinE(Ng)-independent ATPase activities than the wild-type protein. These results indicate that determinants found within the extreme N terminus of MinD(Ng) are implicated in regulating the enzymatic activity and dynamic localization of the protein.

A Neisserial autotransporter NalP modulating the processing of other autotransporters

Autotransporters constitute a relatively simple secretion system in Gram-negative bacteria, depending for their translocation across the outer membrane only on a C-terminal translocator domain. We have studied a novel autotransporter serine protease, designated NalP, from Neisseria meningitidis strain H44/76, featuring a lipoprotein motif at the signal sequence cleavage site. Indeed, lipidation of NalP could be demonstrated, but the secreted 70 kDa domain of NalP lacked the lipid-moiety as a result of additional N-terminal processing. A nalP mutant showed a drastically altered profile of secreted proteins. Mass-spectrometric analysis of tryptic fragments identified the autotransporters IgA protease and App, a homologue of the adhesin Hap of Haemophilus influenzae, as the major secreted proteins. Two forms of both of these proteins were found in the culture supernatant of the wild-type strain, whereas only the lower molecular-weight forms predominated in the culture supernatant of the nalP mutant. The serine-protease active site of NalP was required for the modulation of the processing of these autotransporters. We propose that, apart from the autoproteolytic processing, NalP can process App and IgA protease and hypothesize that this function of NalP could contribute to the virulence of the organism.

Gonococcal MinD affects cell division in Neisseria gonorrhoeae and Escherichia coli and exhibits a novel self-interaction

The Min proteins are involved in determining cell division sites in bacteria and have been studied extensively in rod-shaped bacteria. We have recently shown that the gram-negative coccus Neisseria gonorrhoeae contains a min operon, and the present study investigates the role of minD from this operon. A gonococcal minD insertional mutant, CJSD1, was constructed and exhibited both grossly abnormal cell division and morphology as well as altered cell viability. Western blot analysis verified the absence of MinD from N. gonorrhoeae (MinD(Ng)) in this mutant. Hence, MinD(Ng) is required for maintaining proper cell division and growth in N. gonorrhoeae. Immunoblotting of soluble and insoluble gonococcal cell fractions revealed that MinD(Ng) is both cytosolic and associated with the insoluble membrane fraction. The joint overexpression of MinC(Ng) and MinD(Ng) from a shuttle vector resulted in a significant enlargement of gonococcal cells, while cells transformed with plasmids encoding either MinC(Ng) or MinD(Ng) alone did not display noticeable morphological changes. These studies suggest that MinD(Ng) is involved in inhibiting gonococcal cell division, likely in conjunction with MinC(Ng). The alignment of MinD sequences from various bacteria showed that the proteins are highly conserved and share several regions of identity, including a conserved ATP-binding cassette. The overexpression of MinD(Ng) in wild-type Escherichia coli led to cell filamentation, while overexpression in an E. coli minD mutant restored a wild-type morphology to the majority of cells; therefore, gonococcal MinD is functional across species. Yeast two-hybrid studies and gel-filtration and sedimentation equilibrium analyses of purified His-tagged MinD(Ng) revealed a novel MinD(Ng) self-interaction. We have also shown by yeast two-hybrid analysis that MinD from E. coli interacts with itself and with MinD(Ng). These results indicate that MinD(Ng) is required for maintaining proper cell division and growth in N. gonorrhoeae and suggests that the self-interaction of MinD may be important for cell division site selection across species.

Multiple origins and replication proteins influence biological properties of beta-lactamase-producing plasmids from Neisseria gonorrhoeae

The beta-lactamase-producing Asia-type plasmid pJD4 of Neisseria gonorrhoeae is a 7.4-kb, broad-host-range plasmid. It is part of a family of plasmids which are structurally related yet vary in size, found in both N. gonorrhoeae and Haemophilus ducreyi. Branch-point analysis by electron microscopy indicates that pJD4 carries three clustered but distinguishable origins of replication, which we named ori1, ori2, and ori3. Although pJD4 belongs to incompatibility (Inc) group W, it also carries a silent IncFII determinant which is expressed when ori2 and ori3 are absent. The Africa-type plasmid pJD5, a naturally occurring deletion derivative of pJD4, carries only ori1, belongs to the IncFII group, and, in contrast to pJD4, requires DNA polymerase I (Pol I) for replication. Plasmids constructed from pJD4 which lack ori1 but carry ori2 and ori3 do not require Pol I and are incompatible with IncW plasmids, suggesting that the ori2 or ori3 region contains the IncW determinant. We have cloned a replication initiation protein (RepB) that is necessary for ori2 and ori3 to function. This Rep protein is distinct from RepA, which is necessary for ori1. Thus, pJD4 is unique because it is the smallest plasmid characterized containing three origins of replication and two unique Rep proteins.