Illuminating the evolutionary history of chlamydiae     

Horn M  Collingro A  Schmitz-Esser S  Beier CL  Purkhold U  Fartmann B  Brandt P  Nyakatura GJ  Droege M  Frishman D  Rattei T  Mewes HW  Wagner M 《Science (New York, N.Y.)》2004,304(5671):728-730

Chlamydiae are the major cause of preventable blindness and sexually transmitted disease. Genome analysis of a chlamydia-related symbiont of free-living amoebae revealed that it is twice as large as any of the pathogenic chlamydiae and had few signs of recent lateral gene acquisition. We showed that about 700 million years ago the last common ancestor of pathogenic and symbiotic chlamydiae was already adapted to intracellular survival in early eukaryotes and contained many virulence factors found in modern pathogenic chlamydiae, including a type III secretion system. Ancient chlamydiae appear to be the originators of mechanisms for the exploitation of eukaryotic cells.  相似文献   

The veterinary antibiotic journey: comparing the behaviour of sulfadiazine,sulfamethazine, sulfamethoxazole and tetracycline in cow excrement and two soils     

Caroline Bailey  Astrid Spielmeyer  Gerd Hamscher  Holger Schüttrumpf  Roy M. Frings 《Journal of Soils and Sediments》2016,16(6):1690-1704

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Microbial colonisation of roots as a function of plant species     

Astrid Appuhn 《Soil biology & biochemistry》2006,38(5):1040-1051

Fifteen plants species were grown in the greenhouse on the same soil and sampled at flowering to obtain rhizosphere soil and root material. In both fractions, the data on fungal and bacterial tissue obtained by amino sugar analysis were compared with the total microbial biomass based on fumigation-extraction and ergosterol data. The available literature on glucosamine concentrations in fungi and on muramic acid concentrations in bacteria was reviewed to prove the possibility of generating conversion values for general use in root material. All microbial properties analysed revealed strong species-specific differences in microbial colonisation of plant roots. The root material contained considerable amounts of microbial biomass C and biomass N, reaching mean levels of 10.9 and 1.4 mg g⁻¹ dry weight, respectively. However, the majority of CHCl₃ labile C and N, i.e. 89 and 55% was root derived. The average amount of ergosterol was 13 μg g⁻¹ dry weight and varied between 0.0 for Phacelia roots and 45.5 μg g⁻¹ dry weight for Vicia roots. The ergosterol content in root material of mycorrhizal and non-mycorrhizal plant species did not differ significantly. Fungal glucosamine was converted to fungal C by multiplication by 9 giving a range of 7.1-25.9 mg g⁻¹ dry weight in the root material. Fungal C and ergosterol were significantly correlated. Bacterial C was calculated by multiplying muramic acid by 45 giving a range from 1.7 to 21.6 mg g⁻¹ dry weight in the root material. In the root material of the 15 plant species, the ratio of fungal C-to-bacterial C ranged from 1.0 in mycorrhizal Trifolium roots to 9.5 in non-mycorrhizal Lupinus roots and it was on average 3.1. These figures mean that the microbial tissue in the root material consists on average of 76% fungal C and 24% bacterial C. The differences in microbial colonisation of the roots were reflected by differences in microbial indices found in the rhizosphere soil, most strongly for microbial biomass C and ergosterol, but to some extent also for glucosamine and muramic acid.  相似文献   

Responses of oribatid mite communities to summer drought: The influence of litter type and quality     

Astrid Rita Taylor  Volkmar Wolters 《Soil biology & biochemistry》2005,37(11):2117-2130

A litterbag experiment was used to study the impact of extended periods of summer drought on the structure of oribatid mite communities (Acari, Oribatida) developing in two litter types (beech, spruce) of two qualities (fresh, pre-incubated). Within each litter type, litter quality determined species composition and densities and, in turn, this determined the impact of drought upon the oribatid mite communities. In both litter types, drought had a greater impact on community development in the pre-incubated compared to the fresh litter. In the short-term perspective of the present study, oribatid mite communities in beech litter were less sensitive to summer drought than those in spruce litter. This was partly due to the presence of site-specific, drought-tolerant species but seemed also strongly related to differences in the decomposition patterns between the litter types. Marked changes in densities and composition of oribatid communities after only one period of summer-drought suggest that there is a potential for a significant alteration of oribatid community structure in both litter types if climatic changes persist.  相似文献   

Phosphorus fractions and dynamics in surface earthworm casts under native and improved grasslands in a Colombian savanna Oxisol     

Juan J Jiménez  Alex CepedaThibaud Decaëns  Astrid ObersonDennis K Friesen 《Soil biology & biochemistry》2003,35(5):715-727

The objective of this study was to assess the effect of a native anecic species on phosphorus availability in an Oxisol characterised by a low chemical fertility. Experiments were carried out at Carimagua research station in a representative site of the isohyperthermic savannas on the Colombian Orinoco basin. One field study and two laboratory/incubation studies were performed in a natural herbaceous savanna and a Brachiaria decumbens and Pueraria phaseoloides pasture. In the laboratory, experiment pots were prepared containing soil collected from the respective field paddock's topsoil. Total P content was higher in earthworm casts than in the surrounding soil in field samples, 50% in native savanna soil and more than 100% in pasture soil. In casts produced under laboratory conditions this increase was relatively low (10-20%). Under field conditions, almost without exception, all P fractions were increased in casts relative to the original soil (corresponding to the increase in total P content), being relatively greater in the labile inorganic P fractions. In addition, samples from the natural savanna showed that pH of casts was higher (5.2) than that of soil (4.6) in both field and laboratory samples. Except in the native savanna under field conditions, the phosphatase activity was reduced in casts by 16.7 to 44%. From our results we conclude that earthworms in the field incorporate P from litter or other organic sources (i.e. undecomposed plant and root material, earthworm faeces) which is not normally measured in the analysis of bulk soil.  相似文献   

The desorption of silver and thallium from soils in the presence of a chelating resin with thiol functional groups     

Astrid R. Jacobson  Sondra Klitzke  Murray B McBride  Philippe Baveye  Tammo S. Steenhuis 《Water, air, and soil pollution》2005,160(1-4):41-54

Silver (Ag) and thallium (Tl) are non-essential elements that are toxic to many biota at trace levels, but are rarely studied in soil environments. Ag sorbs strongly to soils, especially those rich in organic matter whereas Tl sorption is influenced by clay content. However, the mobility and bioavailability of Tl and Ag are ultimately affected less by the soil sorptive capacity than by the ease with which these elements desorb from soils. In that context, the strength of Ag and Tl sorption to illite-rich mineral soils with differing textures and an organic peaty-muck soil, from New York State, was investigated by studying their desorption using, as a sink for the metals, a resin (Duolite G-73) containing a thiol functional group. Desorption was monitored over time (1 h, 4 weeks) from soils previously equilibrated with Tl⁺ or Ag⁺ for 24 h (steady-state) or for up to 1 year. Within 24 h, 60% of the sorbed Tl was recovered by the resin. Within 2 weeks, 80–100% of the Tl desorbed from all four soils equilibrated for both 24 h and 1 year periods. Ag was not effectively recovered from the resin. However, qualitative review indicates that more Ag was desorbed after the 24 h sorption period than after the 1 year period. More Ag desorbed from the sandy soil than from the peaty-muck soil or the mineral soils with higher clay contents. However, within two weeks silver was mobilized from the peaty-muck soil. The observed release of Ag and Tl from soils, coupled with their toxicity at trace levels to a broad range of soil organisms, suggests that they may pose an environmental concern when present in soils at elevated concentrations.  相似文献   

The automated determination of glucosamine,galactosamine, muramic acid,and mannosamine in soil and root hydrolysates by HPLC   总被引：2，自引：0，他引：2  

Astrid Appuhn  Rainer Georg Joergensen  Markus Raubuch  Edwin Scheller  Brigitte Wilke 《植物养料与土壤学杂志》2004,167(1):17-21

Amino sugars make a significant contribution to soil organic N and are mainly of microbial origin. The most important amino sugars in soil are glucosamine, galactosamine, muramic acid, and mannosamine. A method was developed for the simultaneous determination of these four amino sugars by high‐performance reverse‐phase liquid chromatography in standard solutions, soil and root hydrolysates. Pre‐column derivatization with o‐phthaldialdehyde (OPA) was used in an automated sample injector with thermostatic regulation of the reagent at 4 °C. The separation of the four amino sugars was fully satisfactory and was not disturbed by other fluorescent components in the soil and root hydrolysates.  相似文献   

Sea anemone genome reveals ancestral eumetazoan gene repertoire and genomic organization     

Putnam NH  Srivastava M  Hellsten U  Dirks B  Chapman J  Salamov A  Terry A  Shapiro H  Lindquist E  Kapitonov VV  Jurka J  Genikhovich G  Grigoriev IV  Lucas SM  Steele RE  Finnerty JR  Technau U  Martindale MQ  Rokhsar DS 《Science (New York, N.Y.)》2007,317(5834):86-94

Sea anemones are seemingly primitive animals that, along with corals, jellyfish, and hydras, constitute the oldest eumetazoan phylum, the Cnidaria. Here, we report a comparative analysis of the draft genome of an emerging cnidarian model, the starlet sea anemone Nematostella vectensis. The sea anemone genome is complex, with a gene repertoire, exon-intron structure, and large-scale gene linkage more similar to vertebrates than to flies or nematodes, implying that the genome of the eumetazoan ancestor was similarly complex. Nearly one-fifth of the inferred genes of the ancestor are eumetazoan novelties, which are enriched for animal functions like cell signaling, adhesion, and synaptic transmission. Analysis of diverse pathways suggests that these gene "inventions" along the lineage leading to animals were likely already well integrated with preexisting eukaryotic genes in the eumetazoan progenitor.  相似文献   

The radical site in chlamydial ribonucleotide reductase defines a new R2 subclass     

Högbom M  Stenmark P  Voevodskaya N  McClarty G  Gräslund A  Nordlund P 《Science (New York, N.Y.)》2004,305(5681):245-248

Ribonucleotide reductase (RNR) synthesizes the deoxyribonucleotides for DNA synthesis. The R2 protein of normal class I ribonucleotide reductases contains a diiron site that produces a stable tyrosyl free radical, essential for enzymatic activity. Structural and electron paramagnetic resonance studies of R2 from Chlamydia trachomatis reveal a protein lacking a tyrosyl radical site. Instead, the protein yields an iron-coupled radical upon reconstitution. The coordinating structure of the diiron site is similar to that of diiron oxidases/monoxygenases and supports a role for this radical in the RNR mechanism. The specific ligand pattern in the C. trachomatis R2 metal site characterizes a new group of R2 proteins that so far has been found in eight organisms, three of which are human pathogens.  相似文献   

ICT and Sustainable Mobility: From Impacts to Policy     

Bart W. Wiegmans  Nanou Beekman  Astrid Boschker  Wim Van Dam  Norbert Nijhof 《Growth and change》2003,34(4):473-489

ABSTRACT The question “Will using Information and Communication Technology (ICT) systems enable a more sustainable mobility?” is answered through analyzing current ICT policy in the EU and the United States of America (USA), through developing a conceptual model to structure the expected direct and indirect effects of ICT systems on mobility, and through building models for three selected ICT systems to estimate their quantitative effects on mobility. Based on the models, ICT systems seem to have limited mobility reduction potential (in terms of CO₂ emissions and kilometer savings). On the short term, because of efficiency gains, ICT systems have a positive impact. In the long term, better quality of mobility will attract new demand and this will again result in an increase of travel. For policymakers this implies that ICT systems in the short run can make mobility more efficient. In the long run, to prevent the more efficient mobility from attracting new traffic, the implementation of any ICT system should be accompanied by a stronger pricing policy.  相似文献