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Digitale Medien

Improved automated extraction and separation procedure for soil lipid analyses (2004)

Wiesenberg, G. L. B. ; Schwark, L. ; Schmidt, M. W. I.

Oxford, UK; Malden, USA : Blackwell Science Ltd

European journal of soil science 55 (2004), S. 0

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ISSN: 1365-2389

Quelle: Blackwell Publishing Journal Backfiles 1879-2005

Thema: Geologie und Paläontologie , Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft

Notizen: Analysis of soil lipids may contribute to an improved understanding of atmosphere to soil carbon fluxes, soil organic matter source differentiation and pollutant accumulation. Soil lipids, mostly originating from plants and microorganisms, have traditionally been analysed by non-automated extraction and separation methods, which produce several lipid fractions, operationally defined by polarity. Here we present a combination of fast, automated and reproducible techniques, adopted from organic geochemical studies, for preparative separation of individual soil lipid fractions with increasing polarity. These techniques involve commercially available instruments, including accelerated solvent extraction and a two-step automated medium-pressure liquid chromatography procedure. The method yields eight lipid fractions consisting of five fractions fully amenable to gas chromatography/mass spectrometry (GC/MS) (aliphatic hydrocarbons, aromatic hydrocarbons, ketones, alcohols, carboxylic acids), and three fractions of highly polar or high molecular weight compounds (bases, very long-chain wax esters (C40+), high polarity compounds) that were not measurable with GC/MS under standard conditions. We tested the method on five agricultural soils. Results show that (i) mass recoveries for the individual fractions are reproducible, (ii) within individual fractions compound distribution patterns are reproducible, as demonstrated for alkanes and carboxylic acids, and (iii) individual fractions represent distinct and clean compound classes, free of interfering substances detectable by GC/MS. Thus, automated separation can be a fast, effective and reproducible procedure for fractionation of complex mixtures of soil lipids into clean compound classes, directly suitable for a variety of molecular (e.g. GC/MS) and isotopic characterizations (e.g. gas chromatography coupled with isotope ratio monitoring mass spectrometry or accelerator mass spectrometry).

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1111/j.1351-0754.2004.00601.x

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Digitale Medien

Organic matter in particle-size fractions from A and B horizons of a Haplic Alisol (2002)

Schmidt, M. W. I. ; Kögel- Knabner, I.

Oxford, UK : Blackwell Science Ltd

European journal of soil science 53 (2002), S. 0

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ISSN: 1365-2389

Quelle: Blackwell Publishing Journal Backfiles 1879-2005

Thema: Geologie und Paläontologie , Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft

Notizen: The organic matter in soils may be stabilized by its interactions with minerals. We have studied such interactions in a Haplic Alisol under forest in which clay and organic matter have migrated from an eluvial A horizon to accumulate in an illuvial B horizon. We have tried to trace the fate of organic matter in these horizons (Ah and Bvt) by determining clay mineralogy, carbon and nitrogen content, hydrolysable amino acids, lignin signature by alkaline CuO oxidation and carbon species by 13C CPMAS NMR of bulk soils and particle-size fractions. In both horizons, most of the organic matter was present in O–alkyl and methylene structures, each contributing one-third to the bulk organic matter. In the Ah horizon the ratios of carbon-to-nitrogen, and yields for lignin and hydrolysable amino acids decreased as the particle-size class decreased, but side-chain oxidation of lignin compounds increased with decreasing particle size. In contrast to previous observations, the proportions of O–alkyl carbon increased as particle size decreased, constituting a major proportion of the organic carbon in the clay-size fractions from both the Ah and Bvt horizons (≥ 38%), while proportions of methylene carbon decreased. Illite was the dominant mineral in the fraction ≤ 6 μm, whereas the mobile fine clay fraction (〈0.2 μm) was rich in smectites – minerals with large surface areas. Our results support the hypothesis that potentially labile organic matter, such as O–alkyl carbon typically present in polysaccharides, may be stabilized against further degradation in organomineral complexes.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1046/j.1365-2389.2002.00460.x

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3

Digitale Medien

Never say never again: protein glycosylation in pathogenic bacteria (2002)

Benz, Inga ; Schmidt, M. Alexander

Oxford, UK : Blackwell Science Ltd

Molecular microbiology 45 (2002), S. 0

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ISSN: 1365-2958

Quelle: Blackwell Publishing Journal Backfiles 1879-2005

Thema: Biologie , Medizin

Notizen: In recent years, accumulating evidence for glycosylated bacterial proteins has overthrown an almost dogmatic belief that prokaryotes are not able to synthesize glycoproteins. Now it is widely accepted that eubacteria express glycoproteins. Although, at present, detailed information about glycosylation and structure–function relationships is available for only few eubacterial proteins, the variety of different components and structures observed already indicates that the variations in bacterial glycoproteins seem to exceed the rather limited display found in eukaryotes. Numerous virulence factors of bacterial pathogens have been found to be covalently modified with carbohydrate residues, thereby identifying these factors as true glycoproteins. In several bacterial species, gene clusters suggested to represent a general pro-tein glycosylation system have been identified. In other cases, genes encoding highly specific glycosyltransferases have been found to be directly linked with virulence genes. These findings raise interesting questions concerning a potential role of glycosylation in pathogenesis. In this review, we will therefore focus on protein glycosylation in Gram-negative bacterial pathogens.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1046/j.1365-2958.2002.03030.x

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