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  • 1
    Electronic Resource
    Electronic Resource
    The dynamic characteristics and migration of a pyramid dune (2005)
    Oxford, UK : Blackwell Science Ltd
    Sedimentology 52 (2005), S. 0 
    Details
    ISSN: 1365-3091
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: The results of wind tunnel experiments and field observations show that when the intersection angle between airflow direction and dune crest (ridge) line is 〉 30°, a reverse vortex is formed. Because of the convergence of sand streams from the windward and lee slopes at the crest, sand accumulates in the crestal region, causing vertical growth. Nevertheless, studies also show that the common asymmetry of the two slopes of a dune may significantly influence the evolution of arms of a pyramid dune. The migration rates of pyramid dunes are mediated by the interplay of their arms moving transversely and the vertical growth in response to the variations in wind regimes. Comparing the effects of airflow transverse to a given arm with longitudinal airflow, it is indicated that the transverse airflow is more significant in controlling the arms of pyramid dunes. The whole body of the studied pyramid dune, particularly the upper quarter section, migrated SE direction during the monitoring period. The patterns of wind erosion and deposition change alternately with seasonal variations in wind directions. The W, NE and SE sides undergo constant erosion, deposition and both erosion and deposition, respectively. The results of long-term monitoring of a pyramid dune show that southerly winds, resulting from a local circulation, markedly affect the transverse migration of the whole pyramid dune.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-3091.2005.00696.x
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  • 2
    Electronic Resource
    Electronic Resource
    Antibiotics that inhibit cell wall biosynthesis induce expression of the Bacillus subtilisσW and σM regulons (2002)
    Oxford, UK : Blackwell Science Ltd
    Molecular microbiology 45 (2002), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Bacillus subtilis encodes seven extracytoplasmic function (ECF) sigma factors. The σ W regulon includes functions involved in detoxification and protection against antimicrobials, whereas σ M is essential for growth at high salt concentrations. We now report that antibiotics that inhibit cell wall biosynthesis induce both σ W and σ M regulons as monitored using DNA microarrays. Induction of selected σ W -dependent genes was confirmed using lacZ reporter fusions and Northern blot analysis. The ability of vancomycin to induce the σ W regulon is dependent on both σ W and the cognate anti- σ , RsiW, but is independent of the transition state regulator AbrB. These results suggest that the membrane-localized RsiW anti- σ W factor mediates the transcriptional response to cell wall stress. Our findings are consistent with the idea that one function of ECF σ factors is to coordinate antibiosis stress responses and cell envelope homeostasis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2958.2002.03050.x
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  • 3
    Electronic Resource
    Electronic Resource
    Global analysis of the Bacillus subtilis Fur regulon and the iron starvation stimulon (2002)
    Oxford, UK : Blackwell Science Ltd
    Molecular microbiology 45 (2002), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The Bacillus subtilis ferric uptake repressor (Fur) protein coordinates a global transcriptional response to iron starvation. We have used DNA microarrays to define the Fur regulon and the iron starvation stimulon. We identify 20 operons (containing 39 genes) that are derepressed both by mutation of fur and by treatment of cells with the iron chelator 2,2′-dipyridyl. These operons are direct targets of Fur regulation as judged by DNase I footprinting. Analyses of lacZ reporter fusions to six Fur-regulated promoter regions reveal that repression is highly selective for iron. In addition to the Fur regulon, iron starvation induces members of the PerR regulon and leads to reduced expression of cytochromes. However, we did not find any evidence for genes that are directly activated by Fur or repressed by Fur under iron-limiting conditions. Although genome searches using the 19 bp Fur box consensus are useful in identifying candidate Fur-regulated genes, some genes associated with Fur boxes are not demonstrably regulated by Fur, whereas other genes are regulated from sites with little apparent similarity to the conventional Fur consensus.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2958.2002.03113.x
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  • 4
    Electronic Resource
    Electronic Resource
    The global transcriptional response of Bacillus subtilis to manganese involves the MntR, Fur, TnrA and σB regulons (2003)
    Oxford, UK : Blackwell Science Ltd
    Molecular microbiology 49 (2003), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: We have used DNA microarrays to monitor the global transcriptional response of Bacillus subtilis to changes in manganese availability. Mn(II) leads to the MntR-dependent repression of both the mntH and mntABCD operons encoding Mn(II) uptake systems. Mn(II) also represses the Fur regulon. This repression is unlikely to be a direct effect of Mn(II) on Fur as repression is sensitive to 2,2′-dipyridyl, an iron-selective chelator. We suggest that elevated Mn(II) displaces iron from cellular-binding sites and the resulting rise in free iron levels leads to repression of the Fur regulon. Many of the genes induced by Mn(II) are activated by σB or TnrA. Both of these regulators are controlled by Mn(II)-dependent enzymes. Induction of the σB-dependent general stress response by Mn(II) is largely dependent on RsbU, a Mn(II)-dependent phosphatase that dephosphorylates RsbV, ultimately leading to release of active σB from its antisigma, RsbW. The activity of TnrA is inhibited when it forms an inactive complex with feedback-inhibited glutamine synthetase. Elevated Mn(II) reduces the sensitivity of glutamine synthetase to feedback inhibitors, and we suggest that this leads to the observed increase in TnrA activity. In sum, three distinct mechanisms can account for most of the transcriptional effects elicited by manganese: (i) direct binding of Mn(II) to metalloregulators such as MntR, (ii) perturbation of cellular iron pools leading to increased Fur activity and (iii) altered activity of Mn(II)-dependent enzymes that regulate the activity of σB and TnrA.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2958.2003.03648.x
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  • 5
    Electronic Resource
    Electronic Resource
    Cell wall stress responses in Bacillus subtilis: the regulatory network of the bacitracin stimulon (2003)
    Oxford, UK : Blackwell Science Ltd
    Molecular microbiology 50 (2003), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: In response to sublethal concentrations of antibiotics, bacteria often induce an adaptive response that can contribute to antibiotic resistance. We report the response of Bacillus subtilis to bacitracin, an inhibitor of cell wall biosynthesis found in its natural environment. Analysis of the global transcriptional profile of bacitracin-treated cells reveals a response orchestrated by two alternative σ factors (σB and σM) and three two-component systems (YvqEC, YvcPQ and BceRS). All three two-component systems are located next to target genes that are strongly induced by bacitracin, and the corresponding histidine kinases share an unusual topology: they lack about 100 amino acids in their extracellular sensing domain, which is almost entirely buried in the cytoplasmic membrane. Sequence analysis indicates that this novel N-terminal sensing domain is a characteristic feature of a subfamily of histidine kinases, found almost entirely in Gram-positive bacteria and frequently linked to ABC transporters. A systematic mutational analysis of bacitracin-induced genes led to the identification of a new bacitracin-resistance determinant, bceAB, encoding a putative ABC transporter. The bcrC bacitracin resistance gene, which is under the dual control of σX and σM, was also induced by bacitracin. By comparing the bacitracin and the vancomycin stimulons, we can differentiate between loci induced specifically by bacitracin and those that are induced by multiple cell wall-active antibiotics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2958.2003.03786.x
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