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  • Earth Resources and Remote Sensing  (1)
  • Shigella flexneric  (1)
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    Electronic Resource
    Electronic Resource
    Differential regulation of the plasmid-encoded genes in the Shigella flexneri virulence regulon (1997)
    Springer
    Molecular genetics and genomics 256 (1997), S. 93-103 
    Details
    ISSN: 1617-4623
    Keywords: Key words Virulence genes ; Environmental regulation ; H-NS ; DNA Superceiling ; Shigella flexneric
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Expression of the Shigella flexneri virulence gene regulon is controlled by multiple environmental signals acting through a regulatory cascade. The primary regulator is VirF, which is a positive regulator of the secondary regulatory gene virB and the structural gene icsA. The product of the virB gene in turn activates transcription of the genes coding for the invasion proteins, and for the type III secretion system which promotes export of the invasion proteins to the bacterial cell surface. The genes making up the regulon were studied in their native locations on the 230-kb virulence plasmid. Transcriptional control was detected at each level of the regulatory cascade. A gearing effect was detected upon thermal induction of transcription in the regulon, with the virF gene being induced by about two fold, virB by 10-fold and the structural genes by 100-fold. In addition, each gene studied displayed individual characteristics in its response to stimuli such as growth medium osmolarity, pH, variations in DNA superhelicity and the presence or absence of H-NS. The primary regulatory gene virF, displayed loose regulation under standard laboratory growth conditions. Regulation was tighter at the secondary regulator virB, while control of structural gene expression was tighter still. It is proposed that this regulatory pattern ensures that energetically wasteful expression of the structural genes under inappropriate conditions is avoided while allowing the regulatory genes to be expressed sufficiently under non-permissive conditions to ensure a rapid response to inducing conditions when these arise. Once induced, fine tuning of the response can be achieved through the different sensitivities of the individual regulon members to external stimuli.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004380050550
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    Paper (German National Licenses)
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  • 2
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    In-Situ and GRACE-Based Groundwater Observations: Similarities, Discrepancies, and Evaluation in the High Plains Aquifer in Kansas (2018)
    In:  CASI
    Details
    Publication Date: 2019-09-28
    Description: Relating Gravity Recovery and Climate Experiment (GRACE)derived terrestrial water storage anomaly (aTWS) variations to in situ groundwater data is important to understanding GRACE data utility. Here GRACEderived annual changes in aTWS (TWS) from National Aeronautics and Space Administration's Jet Propulsion Laboratory and Goddard Space Flight Center are compared to annual changes in saturated groundwater volumes (GW) in the High Plains aquifer (HPA) and overlying alluvial aquifers in Kansas. Regression analysis suggests that trends in TWS are strongly related to trends in GWalluvial and weakly related to trends in GWHPA, although the magnitude of TWS is much larger than GWalluvial and is similar to GWHPA. Unlike alluvial aquifers, a thick vadose zone overlies the HPA. Estimates of changes in vadose zone water content (VZ) using GRACE products are similar in magnitude to annual variations in North American Land Data Assimilation soil moisture data, suggesting an unexpected dominance of VZ in TWS despite significant groundwater depletion. Results demonstrate that water storage changes in shallow alluvial aquifers, the root zone, the deep vadose zone, and the HPA itself are all significant in the HPA region of Kansas. Consequently, GRACE observations cannot, alone, be taken to reflect variations in saturated zone groundwater storage in the HPA, or other large, heavily used aquifers subject to substantial groundwater depletion, when deep unsaturated zones exist. GRACE can best provide guidance on regional aquifer storage changes where water storage changes in the vadose zone and perched or adjacent aquifers are well constrained.
    Keywords: Earth Resources and Remote Sensing
    Type: GSFC-E-DAA-TN60582 , Water Resources Research (ISSN 0043-1397) (e-ISSN 1944-7973); 54; 10; 8034-8044
    Format: application/pdf
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