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  • 1
    Electronic Resource
    Electronic Resource
    Genome plasticity in Neisseria gonorrhoeae (1996)
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology letters 145 (1996), S. 0 
    Details
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract The pathogenic Neisseria have exploited the processes of horizontal DNA transfer and genetic recombination as mechanisms for the generation of extensive protein variation and modulation of gene expression. Localized recombinations have been well documented in members of multigene families as have alterations in short repetitive sequences. Here we report an analysis of the chromosomal structure of a defined lineage of Neisseria gonorrhoeae strain MS 11 pilin variants. This study reveals the occurrence of large rearrangements, including the amplification of a 26 kb region and an inversion involving more than a third of the chromosome. Additionally, a restriction site polymorphism that correlates with pilin expression has been observed. These findings highlight the flexibility of the gonococcal genome.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1574-6968.1996.tb08574.x
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  • 2
    Electronic Resource
    Electronic Resource
    Sequential action of factors involved in natural competence for transformation of Neisseria gonorrhoeae (1996)
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology letters 137 (1996), S. 0 
    Details
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract We previously identified and genetically characterized several factors essential for the natural competence of transformation in Neisseria gonorrhoeae. Here we analyse the sequential action of these factors and dissect the overall transformation process into three distinct steps, (i) the sequence-specific uptake of transforming DNA into a DNase-resistant state, (ii) the transfer of DNA to the cytosol and (iii) the processing and recombination of the incoming with the resident DNA. While two pilus-associated factors, PilE and PilC, were previously implicated in the early DNA uptake event, we show here that three competence factors unrelated to pilus biogenesis, ComA, ComL and Tpc, are not essential for DNA uptake and rather act in a subsequent step. The respective mutants, however, lack the characteristic nucleolytic processing observed with the incoming DNA in both wild-type and non-transformable RecA-deficient N. gonorrhoeae, indicating that they are blocked in the processing and/or the delivery of DNA to the cytoplasm. A hypothetical model proposing a sequential action of the known gonococcal competence factors is presented.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1574-6968.1996.tb08099.x
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  • 3
    Electronic Resource
    Electronic Resource
    C-terminal glycine-histidine tagging of the outer membrane protein Iga β of Neisseria gonorrhoeae (1995)
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology letters 127 (1995), S. 0 
    Details
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract A glycine-histidine tag (Gly3His6) was added to the C-terminus of a fusion protein consisting of the cholera toxin B-subunit (CtxB) and the IgA protease β-domain (Iga β). The aim was to facilitate single-step purification and to create a suitable tool for kinetic and structural studies on Iga β-driven protein translocation across the outer membrane of Gram-negative bacteria. We demonstrate that the glycine-histidine tag does not interfere with the assembly of Iga β in the outer membrane and that the translocator function of the modified Iga β is maintained. The applicability of the new construct for the dissection of the Iga β mediated translocation process and general aspects of C-terminal histidine tagging of outer membrane proteins are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1574-6968.1995.tb07481.x
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  • 4
    Electronic Resource
    Electronic Resource
    Transformation-mediated exchange of virulence determinants by co-cultivation of pathogenic Neisseriae (1992)
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology letters 100 (1992), S. 0 
    Details
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract The horizontal flow of genetic material between microbes utilizes three principal routes: conjugation, transduction and transformation. While the significance in nature of the first two pathways is generally accepted, the in vivo role of transformation remains uncertain, despite the early observations by Griffith in 1928 on the transformation of streptococci from an avirulent to a virulent state [1]. Recently, circumstantial evidence was collected suggesting a role for transformation-mediated horizontal exchange in the modulation of virulence determinants of pathogenic Neisseriae and the variation of surface structures. In order to further assess the significance of transformation-mediated exchange we performed simple co-cultivation experiments of different Neisseria strains. We observed an efficient intra- and interspecies transfer of essential virulence determinants; the process was sensitive to the presence of DNaseI in the culture and was blocked in transformation-deficient recipients.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1574-6968.1992.tb14062.x
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  • 5
    Electronic Resource
    Electronic Resource
    Neisseria gonorrhoeae reverse transcriptase activity does not mediate pilin gene conversion (1997)
    Oxford BSL : Blackwell Publishing Ltd
    Molecular microbiology 24 (1997), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2958.1997.3681707.x
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  • 6
    Electronic Resource
    Electronic Resource
    Aflagellated mutants of Helicobacter pylori generated by genetic transformation of naturally competent strains using transposon shuttle mutagenesis (1993)
    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 8 (1993), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Three out of 10 Helicobacter pylori clinical isolates were found to be naturally competent for genetic transformation to streptomycin resistance by chromosomal DNA extracted from a spontaneous streptomycin-resistant H. pylori mutant. The frequency of transformation varied between 5 × 10−4 and 4 × 10−6, depending on the H. pylori isolate used. Transposon shuttle mutagenesis based on this natural competence was established using the flagellin gene flaA as the target. The cloned flaA gene was interrupted by insertion of TnMax1, a mini-Tn1721 transposon carrying a modified chloramphenicol-acetyltransferase gene, the catGC cassette. Natural transformation of competent H. pylori strains with plasmid constructs harbouring a catGC-inactivated flaA gene resulted in chloramphenicol-resistant transformants at an average frequency of 4 × 10−5. Southern hybridization experiments confirmed the replacement of the chromosomal H. pylori flaA gene by the cat-inactivated cloned gene copy via homologous recombination resulting in allelic exchange. Phenotypic characterization of the mutants demonstrated the absence of flagella under the electron microscope and the loss of bacterial motility. Immunoblots of cell lysates of the H. pylori mutants with an antiserum raised against the C-terminal portion of recombinant H. pylori major flagellin (FlaA) confirmed the absence of the 54kDa FlaA protein. This efficient transposon shuttle mutagenesis procedure for H. pylori based on natural competence opens up new possibilities for the genetic assessment of putative H. pylori virulence determinants.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2958.1993.tb01618.x
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  • 7
    Electronic Resource
    Electronic Resource
    Interaction of two variable proteins (PilE and PilC) required for pilus-mediated adherence of Neisseria gonorrhoeae to human epithelial cells (1992)
    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 6 (1992), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Pili confer the initial ability of Neisseria gonorrhoeae to bind to epithelial cells. Pilin (PilE), the major pilus subunit, and a minor protein termed PilC, reportedly essential for pilus biogenesis, undergo intra-strain phase and structural variation. We demonstrate here that at least two different adherence properties are associated with the gonococcal pili: one is specific for erythrocytes, which is virtually unaffected by PilE variation, and another is specific for epithelial cells, and is modulated in response to the variation of PilE. Based on this finding, mutants of a recA - strain were selected that had lost the ability to bind to human cornea epithelial cells (A-) but retained the ability to form pili (P+) and to agglutinate human erythrocytes (H+). The adherence-negative mutants failed to produce detectable levels of PMC1 or PilC2 proteins, representing pilC phase variants generated in the absence of RecA. The A-pilC phase variants were indistinguishable from their A+parents and spontaneous A+ revertants with regard to the amount of PilE produced and its electrophoretic mobility, the degrees of piliation and haemagglutination, and the pilE nucleotide sequence. These data demonstrate a central role for PilC in pilus-mediated adherence of N. gonorrhoeae to human epithelial cells and further indicate that neither PNC1 nor PilC2 is obligatory for the assembly of gonococcal pili.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2958.1992.tb02211.x
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  • 8
    Electronic Resource
    Electronic Resource
    Novel determinant (comA) essential for natural transformation competence in Neisseria gonorrhoeae and the effect of a comA defect on pilin variation (1993)
    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 10 (1993), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: A novel genetic determinant (comA) has been identified and found to be required for the transformation of piliated Neisseria gonorrhoeae. Mutants in comA of strain MS11 grow normally and are DNA-uptake proficient but blocked in the translocation of DNA into the cytoplasm. Here we show by site-specific mutagenesis and genetic complementation that only one of two open reading frames identified in comA is essential for competence: it encodes a protein (ComA) with a predicted size of 74kDa. The comAgene maps upstream of the iga locus and is transcribed in the opposite orientation, probably under the control of a putative σ;54 type promoter. While DNA probes specific for the N. gonorrhoeae iga locus reveal only a little cross-reactivity with commensal Neisseria species, the neighbouring comA gene appears to be present in most of them. ComA fusion proteins were obtained by in vitro translation. The synthesized gene products migrated atypically in SDS gels indicating its strong hydrophobicity. Several transmembrane α-helices were predicted from the amino acid sequence of ComA which, in the context of an observed sequence similarity with other inner membrane proteins, suggests a location for the protein in the inner membrane. Using piliated and non-piliated comA mutants the consequences of transformation deficiency on pilin phase variation were assessed. We show that the comA defect affects some but not all types of DNA rearrangements associated with pilE variation. The results are in agreement with previous observations supporting the notion that multiple recombination pathways contribute to the variability of pilE.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2958.1993.tb00942.x
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  • 9
    Electronic Resource
    Electronic Resource
    Tetrapac (tpc), a novel genotype of Neisseria gonorrhoeae affecting epithelial cell invasion, natural transformation competence and cell separation (1996)
    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 19 (1996), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: We characterized a novel mutant phenotype (tetrapac, tpc) of Neisseria gonorrhoeae (Ngo) associated with a distinctive rough-colony morphology and bacterial growth in clusters of four. This phenotype, suggesting a defect in cell division, was isolated from a mutant library of Ngo MS11 generated with the phoA minitransposon TnMax4. The tpc mutant shows a 30% reduction in the overall murein hydrolase activity using Escherichia coli murein as substrate. Tetrapacs can be resolved by co-cultivation with wild-type Ngo, indicating that Tpc is a diffusible protein. Interestingly, Tpc is absolutely required for the natural transformation competence of piliated Ngo. Mutants in tpc grow normally, but show a ∼ 10-fold reduction in their ability to invade human epithelial cells. The tpc sequence reveals an open reading frame of ∼1 kb encoding a protein (Tpc) of 37kDa. The primary gene product exhibits an N-terminal leader sequence typical of lipoproteins, but palmitoylation of Tpc could not be demonstrated. The ribosomal binding site of tpc is immediately downstream of the translational stop codon of the folC gene coding for an enzyme involved in folic acid biosynthesis and one-carbon metabolism. The tpc gene is probably co-transcribed from the folC promoter and a promoter located within the folC gene. The latter promoter sequence shares significant homology with E. coli gearbox consensus promoters. All three mutant phenotypes, i.e. the cell separation defect, the transformation deficiency and the defect in cell invasion can be restored by complementation of the mutant with an intact tpc gene. To some extent the tcp phenotype is reminiscent of iap in Listeria, lytA in Streptococcus pneumoniae and lyt in Bacillus subtilis, all of which are considered to represent murein hydrolase defects.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2958.1996.tb02479.x
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  • 10
    Electronic Resource
    Electronic Resource
    Immunogenicity and evolutionary variability of epitopes within IgA1 protease from serogroup A Neisseria meningitidis (1994)
    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 11 (1994), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Five murine epitopes were defined and mapped within IgA1 protease produced by Neisseria meningitidis. Epitopes 1 and 2 were present in IgA1 protease from all strains, and from Neisseria gonorrhoeae. Epitopes 3 through to 5 varied between subgroups of serogroup A meningococci. but have remained constant over decades within the subgroups, except for epitope 4, which changed between 1983 and 1987 during the spread of subgroup III meningococci from Asia to Africa. Binding of monoclonal antibodies to epitopes 1, 4 and 5 neutralized enzymatic function. Human sera containing antibodies to lgA1 protease as a result of natural infection inhibited binding of monoclonal antibodies to epitope 4 but not to the other epitopes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2958.1994.tb00299.x
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