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  • 1
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Science Ltd
    European journal of soil science 50 (1999), S. 0 
    ISSN: 1365-2389
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Standard procedure for dispersing natural soils for particle size fractionation can be too aggressive for soil containing coal and other organic particles from coal industries. We have investigated ultrasonic dispersion for the latter in four soils differing in pedogenesis (Phaeozem, Podzol, reclaimed mine soils), carbon content (27.5–138.6 g kg–1), clay content (80–153 g kg–1) and sources of particles (airborne coal dust, combustion residues, lignite particles). As we found previously for natural soils, the ultrasonic energy needed for complete dispersion varies between 450 and 500 J ml–1, but the resulting particle size distributions differ from those obtained by standard textural analysis. This is probably related to the different properties of native soil organic matter and coal and combusted particles. Coal and soot particles may partly resist oxidation with hydrogen peroxide, depending on material and particle size. The diameter of lignite particles, remaining after oxidation, is overestimated in sedimentation analysis by a factor of 1.66. Sand-sized lignite particles can be disrupted by ultrasonication and redistributed to finer particle size fractions. The ultrasonic dispersion and particle size fractionation procedure can be applied to soils containing coal and combusted particles, but caution is needed in interpreting the results if they contain large proportions of coal particles.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Science Ltd
    European journal of soil science 50 (1999), S. 0 
    ISSN: 1365-2389
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Soil organic matter can be intimately associated with mineral particles of various sizes. For structural studies, soil organic matter can be isolated in particle size fractions after complete dispersion of the aggregates by ultrasonication. The ultrasonic dispersion energy necessary for complete dispersion was investigated in three A and two B horizons originating from four soils differing in pedogenesis (Gleysol, Phaeozem, Podzol, Alisol), organic C (4.2–34.5 g kg–1) and clay content (24–294 g kg–1). Calorimetric calibration of five probe-type ultrasonifiers revealed that the actual energy output from an instrument can depart widely from its nominal output, and that this discrepancy varies from instrument to instrument. Calorimetric calibration is therefore essential for consistency and comparisons between laboratories. Between 450 and 500 J ml–1 of ultrasonic dispersion energy was enough to disperse completely all samples investigated. The particle size distributions obtained were close to those from standard analysis, except for smaller yields (–20 to –80 g kg–1) of sand size fractions, which suggests that dispersion by ultrasound is more effective. Based on total C, C:N ratio and distribution of dissolved C, no detachment of soil organic matter from primary organomineral complexes and no redistribution between particle size fractions could be detected in the range 30–590 J ml–1 of dispersion energy.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Science Ltd
    European journal of soil science 50 (1999), S. 0 
    ISSN: 1365-2389
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Burning vegetation produces partly charred plant material which subsequently could contribute to the highly refractory proportion of soil organic matter. The presence of charred organic carbon (COC) was investigated in 17 horizons originating from nine soils from Germany and the Netherlands using a suite of complementary methods (high-energy ultraviolet photo-oxidation, scanning electron microscopy, solid-state 13C nuclear magnetic resonance, lignin analysis by CuO oxidation). Charred organic carbon could not be detected in the A horizons of an Alisol and a Gleysol, but it contributed up to 45% of the organic carbon and up to about 8 g kg–1 of the soil in a range of grey to black soils (Cambisol, Luvisol, Phaeozem, Chernozem and Greyzem). All these soils have chernozemic soil properties (dark colour, A–C profile, high base saturation, bioturbation). A 10-km colour sequence of four chernozemic soils, which were very similar in chemical and physical properties, showed a strong relation between colour and the content of COC. This suggests that the COC affects mainly soil colour in the sequence studied. Finely divided COC seems to be a major constituent of many chernozemic soils in Germany. These results suggest that besides climate, vegetation and bioturbation, fire has played an important role in the pedogenesis of chernozemic soils.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Oxford BSL : Blackwell Science Ltd
    Molecular microbiology 31 (1999), S. 0 
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Diffusely adhering Escherichia coli (DAEC) strains have been implicated in epidemiological studies as a cause of diarrhoea in children. However, the molecular interactions of these pathogens with target cells have remained largely obscure. We found that some DAEC strains contain homologues of the locus of enterocyte effacement (LEE) pathogenicity island and secrete EspA, EspB and EspD proteins necessary for the formation of the attaching and effacing (A/E) lesions. To characterize the function of the EspD protein further, we cloned and sequenced the espD genes of two DA-EPEC strains and compared their deduced amino-acid sequences with known EspD sequences. A pattern of two conserved transmembrane regions and one conserved coiled-coil region is predicted in EspD and also in the type III system secreted proteins YopB, PopB, IpaB and SipB of Yersinia, Pseudomonas, Shigella and Salmonella respectively. The EspD protein is inserted into a trypsin-sensitive location in the HeLa cell membrane at sites of bacterial contact, but is not translocated into the cytoplasm. Secretion of EspD increases upon contact with host cells. We propose that the membrane-located EspD protein is part of the translocation apparatus for Esp proteins into the target host cell performing functions similar to YopB in Yersinia.
    Type of Medium: Electronic Resource
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