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  • 1
    Electronic Resource
    Electronic Resource
    The kinetic and internal energy of NO from the photodissociation of nitrobenzene (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 100 (1994), S. 1946-1952 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Laser induced fluorescence probing of the nitric oxide fragment determines the distribution of rotational and vibrational energies of NO produced in the 226 and 280 nm photolysis of nitrobenzene. Combining these results with kinetic energy measurements using vacuum ultraviolet photoionization to detect the fragment gives a detailed view of the energy release in the photolysis. Boltzmann distributions describe the rotational state populations at both photolysis wavelengths. The rotational temperature of NO from the 226 nm photolysis is (3700±350) K, corresponding to an average rotational energy of (0.32±0.03) eV, and that of NO from the 280 nm photolysis is (2400±200) K, corresponding to an average rotational energy of (0.20±0.03) eV. We observe no vibrationally excited NO and place an upper limit of 10% on the fraction of nitric oxide produced in any one vibrationally excited state. Two different limiting models, impulsive energy release and statistical energy redistribution, both correctly predict much more rotational than vibrational excitation, but neither completely describes the observed internal and kinetic energies. The impulsive model finds more NO rotational and translational energy, but much less phenoxy fragment internal energy than we observe. The statistical model does better for the NO rotation and phenoxy fragment internal energy, but underestimates the translational energy substantially. A combination of these two types of behavior provides a physical picture that qualitatively explains our observations. It is likely that statistical energy redistribution occurs during the approach to the transition state for isomerization of nitrobenzene to phenyl nitrite and impulsive energy release dominates during the subsequent rupture of the CO–NO bond.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.466547
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  • 2
    Electronic Resource
    Electronic Resource
    PHOTOCHEMISTRY AND REDOX ACTIVITY OF SOME METALLOPORPHYRIN COMPLEXES (1973)
    Oxford, UK : Blackwell Publishing Ltd
    Annals of the New York Academy of Sciences 206 (1973), S. 0 
    Details
    ISSN: 1749-6632
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Natural Sciences in General
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1749-6632.1973.tb43234.x
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  • 3
    Electronic Resource
    Electronic Resource
    Synthetic oligodeoxyribonucleotide probes to detect verocytotoxin-producing Escherichia coli in diseased pigs (1989)
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology letters 57 (1989), S. 0 
    Details
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract Oligonucleotide probes constructed from the sequences published for Shiga-like toxin I (SLT-I) and Shiga-like toxin II (SLT-II) genes and antibody against the purified toxins were used to study the SLT (SLT-IIp) produced by porcine E. coli O138 and O139 strains. By DNA hybridization assays no homology was observed between SLT-I and SLT-IIp. By contrast the oligonucleotide probe derived from the slt-II A gene detected porcine strains of E. coli producing SLT-IIp and E. coli strains associated with human disease producing SLT-II. Homology of nucleotide sequences between SLT-IIp and SLT-II is reflected by serological cross-reactivity as demonstrated by a dot blot ELISA and neutralization of SLT-IIp with anti-SLT-II. The toxins were distinguishable in their ability to kill HeLa S-3 cells. The oligonucleotide probe and anti-SLT-II can facilitate identification of SLT-IIp producing E. coli to further clarify their role in diseased pigs.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1574-6968.1989.tb03308.x
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  • 4
    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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  • 5
    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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  • 6
    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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  • 7
    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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  • 8
    Electronic Resource
    Electronic Resource
    Generalized transposon shuttle mutagenesis in Neisseria gonorrhoeae: a method for isolating epithelial cell invasion-defective mutants (1994)
    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 12 (1994), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: One requirement for the invasion of, and tight adherence to, human epitheiial cells by Neisseria gonorrhoeae is the synthesis of distinct opacity (Opa) outer membrane proteins, encoded by a family of phase-variable chromosomal genes. However, cloning and surface expression of invasion-promoting Opas in Escherichia coli is not sufficient for the efficient invasion of epithelial cells: additional factors besides Opa may be involved in this process. Using the phoA mini-transposon TnMax4, a library of gonococcal mutants affected in the expression of genes encoding exported proteins was generated through shuttle mutagenesis. Of a total of 608 PhoA+ plasmid clones identified in E. coli E145 approximately 40% were used successfully in transforming N. gonorrhoeae and in activating the corresponding chromosomal genes. Gonococci producing the invasion-promoting Opa50 served as the genetic background to identify 51 mutants unable to enter Chang human epithelial cells. We expect some of these mutations affect the interaction of N. gonorrhoeae with epithelial cells directly, while other mutants may carry defects in general house-keeping, secretory and/or regulatory determinants. In some mutants the loss of invasiveness appears to be due to a negative dominant effect of the PhoA+ fusions produced in these mutants. Some of the identified genes display a phase-variation phenomenon in E. coli and several genes are found in multiple copies in N. gonorrhoeae and/or present only in pathogenic Neisseria species.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2958.1994.tb01068.x
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  • 9
    Electronic Resource
    Electronic Resource
    Genes coding for Shiga-like toxin and heat-stabile enterotoxin in porcine strains of Escherichia coli (1989)
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology letters 58 (1989), S. 0 
    Details
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract Besides diarrheagenic enterotoxigenic Escherichia coli (ETEC) that produce classical heat stable and/or heat labile enterotoxins (STs, LTs) and the class of Shiga-like toxin-producing enterohemorrhagic E. coli (EHEC), a new category of E. coli is defined sharing similarities with ETEC and EHEC. DNA hybridization studies indicate that some E. coli serovars from porcine origin harbor genes encoding cytotonic ST and cytotoxic Shiga-like toxin. The presence of two potent toxins might contribute to the virulence of such strains and should be taken into consideration when bioassays are performed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1574-6968.1989.tb03029.x
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  • 10
    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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