| 1. |
- Milton, M. J. T, et al.
(författare)
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Raman-shifted laser sources suitable for differential-absorption lidar measurements of ozone in the troposphere
- 1998
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Ingår i: Applied Physics B. - : Springer Science and Business Media LLC. - 0946-2171. ; 66:1, s. 105-113
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Tidskriftsartikel (refereegranskat)abstract
- Measurements have been performed at eight laboratories on Raman-shifted radiation from frequency-quadrupled Nd:YAG and KrF lasers. Each of these sources is a possible candidate for making differential-absorption lidar measurements of ozone in the free troposphere. The spectral purity, efficiency and divergence of the different sources are compared and explained using a simplified model of the Raman interaction. Particular attention has been given to the use of buffer gases to optimize the Raman gain and divergence. The experimental results show that the operating conditions required to optimize the output energy of each of these types of laser source can be quite different. In the case of the KrF laser, it has been shown that high energies can be generated at low active gas pressures, and that increasing the pressure increases the beam quality, but decreases the energy.
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| 2. |
- Milton, Debra L., et al.
(författare)
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Quorum sensing in Vibrio anguillarum : characterization of the vanI/vanR locus and identification of the autoinducer N-(3-oxodecanoyl)-L-homoserine lactone
- 1997
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Ingår i: Journal of Bacteriology. - 0021-9193 .- 1098-5530. ; 179:9, s. 3004-3012
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Tidskriftsartikel (refereegranskat)abstract
- Certain gram-negative pathogens are known to control virulence gene expression through cell-cell communication via small diffusible signal molecules termed autoinducers. This intercellular signal transduction mechanism termed quorum sensing depends on the interaction of an N-acylhomoserine lactone (AHL) auto-inducer molecule with a receptor protein belonging to the LuxR family of positive transcriptional activators. Vibrio anguillarum is a gram-negative pathogen capable of causing a terminal hemorrhagic septicemia known as vibriosis in fish such as rainbow trout. In this study, we sought to determine whether V. anguillarum employs AHLs to regulate virulence gene expression. Spent V. anguillarum culture supernatants stimulated bioluminescence in a recombinant lux-based Escherichia coli AHL biosensor strain, whereas they both stimulated and inhibited AHL-mediated violacein pigment production in Chromobacterium violaceum. This finding suggested that V. anguillarum may produce multiple AHL signal molecules. Using high-performance liquid chromatography and high-resolution tandem mass spectrometry, we identified the major V. anguillarum AHL as N-(3-oxodecanoyl)-L-homoserine lactone (ODHL), a structure which was unequivocally confirmed by chemical synthesis. The gene (vanI) responsible for ODHL synthesis was cloned and sequenced and shown to belong to the LuxI family of putative AHL synthases. Further sequencing downstream of vanI revealed a second gene (vanR) related to the LuxR family of transcriptional activators. Although deletion of vanI abolished ODHL synthesis, no reduction of either metalloprotease production or virulence in a fish infection model was observed. However, the vanI mutant remained capable of weakly activating both bioluminescence and violacein in the E. coli and C. violaceum biosensors, respectively, indicating the existence of additional layers of AHL-mediated regulatory complexity.
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| 3. |
- Wu, Z., et al.
(författare)
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Vibrio cholerae hemagglutinin/protease (HA/protease) causes morphological changes in cultured epithelial cells and perturbs their paracellular barrier function
- 1996
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Ingår i: Microbial Pathogenesis. - : Elsevier BV. - 0882-4010 .- 1096-1208. ; 21:2, s. 111-123
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Tidskriftsartikel (refereegranskat)abstract
- In this report, we describe the cytotoxic activity of the cholera hemagglutinin/protease (HA/protease). A concentrated protein sample from the 37 degrees C overnight culture supernatant of CVD110, a delta ctxA, delta zot, delta Ace and hlyA::(ctxB mer) mutant of El Tor biotype Ogawa serotype strain E7946 caused morphological changes in cultured MDCK-I epithelial cells and altered their arrangement of filamentous actin (F-actin) and Zonula occludens-associated protein ZO-1. The drastic morphological changes can be inhibited by Zincov, a specific bacterial metalloprotease inhibitor. The cytotoxic fractions of the sample after FPLC gelfiltration fractionation showed two visible protein bands with molecular weights of approximately 34- and 32 kDa. Microsequencing of these two proteins revealed that they were the cholera HA/protease.
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