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  • 1
    Electronic Resource
    Electronic Resource
    Femtosecond relaxation of minority electrons in heavily carbon-doped GaAs (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 2255-2259 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Relaxation of minority electrons in carbon-doped GaAs with hole concentrations as high as 6×1019 cm−3 is measured with femtosecond optical techniques. The relaxation of photoexcited electrons depends strongly on the doping level above 1019 cm−3. The dependence of the transient absorption and reflectivity on the hole concentration indicates that electrons relax rapidly by electron-hole scattering into low-energy states which are available as a result of band-gap renormalization and band tailing.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.357644
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  • 2
    Electronic Resource
    Electronic Resource
    Hydrogen as a Modifier of the Structure and Electronic Properties of Platinum in Acidic Zeolite LTL: A Combined Infrared and X-ray Absorption Spectroscopy Study (1995)
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 99 (1995), S. 16067-16075 
    Details
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/j100043a055
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  • 3
    Electronic Resource
    Electronic Resource
    Identification and characterization of BipA, a Bordetella Bvg-intermediate phase protein (2001)
    Oxford, UK : Blackwell Science, Ltd
    Molecular microbiology 39 (2001), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The Bordetella BvgAS sensory transduction system has traditionally been viewed as controlling a transition between two distinct phenotypic phases: the Bvg+ or virulent phase and the Bvg− or avirulent phase. Recently, we identified a phenotypic phase of Bordetella bronchiseptica that displays reduced virulence in a rat model of respiratory infection concomitant with increased ability to survive nutrient deprivation. Characterization of this phase, designated Bvg-intermediate (Bvgi), indicated the presence of antigens that are maximally, if not exclusively, expressed in this phase and therefore suggested the existence of a previously unidentified class of Bvg-regulated genes. We now report the identification and characterization of a Bvgi phase protein, BipA (Bvg-intermediate phase protein A), and its structural gene, bipA. Reverse transcriptase–polymerase chain reaction (RT–PCR) analysis indicates that bipA is expressed maximally under Bvgi phase conditions and thus represents the first identified Bvgi phase gene. bipA encodes a 1578-amino-acid protein that shares amino acid sequence similarity at its N-terminus with the proposed outer membrane localization domains of intimin (Int) of enteropathogenic and enterohaemorrhagic Escherichia coli and invasin (Inv) of Yersinia spp. Although not apparent at the amino acid level, BipA is also similar to Int and Inv in that the proposed membrane-spanning domain is followed by several 90-amino-acid repeats and a distinct C-terminal domain. Localization studies using an antibody directed against the C-terminus of BipA indicated that its C-terminus is exposed on the bacterial cell surface. Western blot analysis with this same antibody indicated that BipA homologues are expressed in Bvgi phase Bordetella pertussis and Bordetella parapertussis. Comparison of a ΔbipA strain with wild-type B. bronchiseptica indicated that BipA is not required for Bvgi phase-specific aggregative adherence to rat lung epithelial cells in vitro or for persistent colonization of the rabbit respiratory tract in vivo. However, our data are consistent with the hypothesis that BipA, and the Bvgi phase in general, play an important role in the Bordetella infectious cycle, perhaps by contributing to aerosol transmission.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2958.2001.02191.x
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  • 4
    Electronic Resource
    Electronic Resource
    Modulation of host immune responses, induction of apoptosis and inhibition of NF-κB activation by the Bordetella type III secretion system (2000)
    Oxford, UK : Blackwell Science Ltd
    Molecular microbiology 35 (2000), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Bordetella bronchiseptica establishes respiratory tract infections in laboratory animals with high efficiency. Colonization persists for the life of the animal and infection is usually asymptomatic in immunocompetent hosts. We hypothesize that this reflects a balance between immunostimulatory events associated with infection and immunomodulatory events mediated by the bacteria. We have identified 15 loci that are part of a type III secretion apparatus in B. bronchiseptica and three secreted proteins. The functions of the type III secretion system were investigated by comparing the phenotypes of wild-type bacteria with two strains that are defective in type III secretion using in vivo and in vitro infection models. Type III secretion mutants were defective in long-term colonization of the trachea in immunocompetent mice. The mutants also elicited higher titres of anti-Bordetella antibodies upon infection compared with wild-type bacteria. Type III secretion mutants also showed increased lethal virulence in immunodeficient SCID-beige mice. These observations suggest that type III-secreted products of B. bronchiseptica interact with components of both innate and adaptive immune systems of the host. B. bronchiseptica induced apoptosis in macrophages in vitro and inflammatory cells in vivo and type III secretion was required for this process. Infection of an epithelial cell line with high numbers of wild type, but not type III deficient B. bronchiseptica resulted in rapid aggregation of NF-κB into large complexes in the cytoplasm. NF-κB aggregation was dependent on type III secretion and aggregated NF-κB did not respond to TNFα activation, suggesting B. bronchiseptica may modulate host immunity by inactivating NF-κB. Based on these in vivo and in vitro results, we hypothesize that the Bordetella type III secretion system functions to modulate host immune responses during infection.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2958.2000.01785.x
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  • 5
    Electronic Resource
    Electronic Resource
    Diversity in the Bordetella virulence regulon: transcriptional control of a Bvg-intermediate phase gene (2001)
    Oxford, UK : Blackwell Science Ltd
    Molecular microbiology 40 (2001), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The BvgAS signal transduction system controls the expression of at least three distinct phenotypic phases that lie along a continuum of gene expression states. The Bvg+ phase is characterized by the expression of adhesins and toxins, whereas the Bvg− phase is characterized by motility in Bordetella bronchiseptica and the expression of vrg loci in Bordetella pertussis. The Bvg-intermediate (Bvgi) phase is characterized by the absence of Bvg-repressed phenotypes, the expression of some, but not all, Bvg-activated virulence factors and the presence of a recently discovered set of antigens and phenotypes that are unique to this phase. We report here the transcriptional regulation of bipA, the first-identified Bvgi phase gene. We have mapped the bipA promoter and identified numerous BvgA binding sites in the transcriptional control region. Based on these data, we present a model in which phase-dependent expression of bipA results from the spatial distribution and relative affinities of multiple BvgA binding sites relative to the start site of transcription.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2958.2001.02415.x
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  • 6
    Electronic Resource
    Electronic Resource
    The BvgAS virulence control system regulates type III secretion in Bordetella bronchiseptica (1998)
    Oxford BSL : Blackwell Publishing Ltd
    Molecular microbiology 28 (1998), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The BvgAS signal transduction system in Bordetella spp. mediates a transition between infectious (Bvg+) and non-infectious (Bvg−) phases by sensing environmental conditions and regulating gene expression. Using differential display, arbitrary-primed polymerase chain reaction (PCR), we identified a gene expressed in the Bvg+ phase of Bordetella bronchiseptica that shows a high degree of sequence similarity to a locus involved in providing energy for type III secretion in pathogenic Gram-negative bacteria (yscN in Yersinia spp.). We determined that the expression of this homologue in B. bronchiseptica (designated bscN ) is regulated by bvg. Several open reading frames surrounding the bscN locus also show sequence similarity to loci encoding type III secretion apparatus components in other bacteria. An in-frame deletion of bscN in B. bronchiseptica leads to decreased secretion of several proteins, decreased cytotoxicity towards cultured cell lines and a defect in causing tyrosine dephosphorylation of specific proteins in infected cells in vitro. The deletion strain also revealed that bscN-mediated secretion is required for persistent colonization of the trachea in a rat infection model. Loci encoding type III secretion homologues were identified in four strains of B. pertussis and two strains of B. parapertussis. B. pertussis strain 18323 and an ovine isolate of B. parapertussis show significant transcription of the genes in vitro.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2958.1998.00850.x
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  • 7
    Electronic Resource
    Electronic Resource
    A mutation in the Bordetella bronchiseptica bvgS gene results in reduced virulence and increased resistance to starvation, and identifies a new class of Bvg-regulated antigens (1997)
    Oxford UK : Blackwell Science Ltd
    Molecular microbiology 24 (1997), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The Bordetella BvgAS signal-transduction system has traditionally been viewed as mediating a transition between two distinct phenotypic phases: the Bvg+ phase, characterized by the expression of adhesins and toxins, and the Bvg− phase, characterized by motility in Bordetella bronchiseptica and by the expression of vrg loci in Bordetella pertussis. In B. bronchiseptica, the Bvg+ phase is necessary and sufficient for respiratory tract colonization whereas the Bvg− phase is required for growth under nutrient-limiting conditions. This report describes the characterization of a mutant that is locked in a Bvg-intermediate (Bvgi) phase. The mutation conferring this phenotype, designated bvgS-I1, results in a threonine-to-methionine substitution near the primary site of phosphorylation in BvgS. Compared to its Bvg+-phase-locked parent, the Bvgi mutant displays increased resistance to nutrient limitation and reduced virulence. Molecular analyses indicate that the mutant has lost the ability to express a subset of Bvg+-phase factors and has gained the ability to express factors unique to the Bvgi phase. Although identified by mutation, this work indicates that the Bvgi phase is expressed by wild-type B. bronchiseptica in response to certain (semi-modulating) environmental conditions. The identification of Bvgi-specific antigens suggests the existence of a new class of Bvg-regulated genes. We hypothesize that BvgAS is capable of mediating the expression of a spectrum of phenotypic phases in response to the various environments encountered as Bordetella travels within and between mammalian hosts.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2958.1997.3821741.x
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  • 8
    Electronic Resource
    Electronic Resource
    Roles for motility in bacterial–host interactions (1997)
    Oxford UK : Blackwell Science Ltd
    Molecular microbiology 24 (1997), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The ability to move in a directed manner may confer distinct advantages upon host-adapted prokaryotes. Potential benefits of motility include increased efficiency of nutrient acquisition, avoidance of toxic substances, the ability to translocate to preferred hosts and access optimal colonization sites within them, and dispersal in the environment during the course of transmission. The costs of motility also may be significant. These include the metabolic burden of synthesizing flagellar components, the energetic expense of fuelling flagellar motors and the presentation of polymeric and highly antigenic targets to the immune system. It is therefore not surprising that synthesis of the motility apparatus is usually subject to strict control. Studies of a variety of bacterial–host interactions demonstrate roles for motility, and its regulation, at points throughout the infectious cycle.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2958.1997.4281787.x
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  • 9
    Electronic Resource
    Electronic Resource
    Comparative analysis of the virulence control systems of Bordetella pertussis and Bordetella bronchiseptica (1996)
    Oxford BSL : Blackwell Science Ltd
    Molecular microbiology 22 (1996), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Bordetella pertussis and Bordetella bronchiseptica contain nearly identical BvgAS signal-transduction systems that mediate a biphasic transition between virulent (Bvg+) and avirulent (Bvg–) phases. In the Bvg+ phase, the two species express a similar set of adhesins and toxins, and in both organisms the transition to the Bvg– phase occurs in response to the same environmental signals (low temperature or the presence of nicotinic acid or sulphate anion). These two species differ, however, with regard to Bvg–-phase phenotypes, host specificity, the severity and course of the diseases they cause, and also potentially in their routes of transmission. To investigate the contribution of the virulence-control system to these phenotypic differences, we constructed a chimeric B. bronchiseptica strain containing bvgAS from B. pertussis and compared it with wild-type B. bronchisepticain vitro and in vivo. The chimeric strain was indistinguishable from the wild type in its ability to express Bvg+- and Bvg–-phase-specific factors. However, although the chimeric strain responded to the same signals as the wild type, it differed dramatically in sensitivity to these signals; significantly more nicotinic acid or MgSO4 was required to modulate the chimeric strain compared with the wild-type strain. Despite this difference in signal sensitivity, the chimeric strain was indistinguishable from the wild type in its ability to cause respiratory-tract infections in rats, indicating that the bvgAS loci of B. pertussis and B. bronchiseptica are functionally interchangeable in vivo. By exchanging discrete fragments of bvgAS, we found that the periplasmic region of BvgS determines signal sensitivity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2958.1996.01538.x
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  • 10
    Electronic Resource
    Electronic Resource
    A genome-wide screen identifies a Bordetella type III secretion effector and candidate effectors in other species (2005)
    Oxford, UK : Blackwell Science Ltd
    Molecular microbiology 58 (2005), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Bordetella bronchiseptica utilizes a type III secretion system (TTSS) for induction of non-apoptotic cytotoxicity in host cells and modulation of host immunity. The identity of Bordetella TTSS effectors, however, has remained elusive. Here we report a genome-wide screen for TTSS effectors based on shared biophysical and functional characteristics of class I chaperones and their frequent colocalization with TTSS effectors. When applied to B. bronchiseptica, the screen identified the first TTSS chaperone-effector locus, btcA-bteA, and we experimentally confirmed its function. Expression of bteA is co-ordinated with expression of TTSS apparatus genes, BteA is secreted through the TTSS of B. bronchiseptica, it is required for cytotoxicity towards mammalian cells, and it is highly conserved in the human-adapted subspecies B. pertussis and B. parapertussis. Transfection of bteA into epithlieal cells results in rapid cell death, indicating that BteA alone is sufficient to induce potent cytotoxicity. Finally, an in vitro interaction between BteA and BtcA was demonstrated. The search for TTSS chaperones and effectors was then expanded to other bacterial genomes, including mammalian and insect pathogens, where we identified a large number of novel candidate chaperones and effectors. Although the majority of putative effectors are proteins of unknown function, several have similarities to eukaryotic protein domains or previously identified effectors from other species.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2958.2005.04823.x
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