The rise of the rhizosolenid diatoms     

Damsté JS  Muyzer G  Abbas B  Rampen SW  Massé G  Allard WG  Belt ST  Robert JM  Rowland SJ  Moldowan JM  Barbanti SM  Fago FJ  Denisevich P  Dahl J  Trindade LA  Schouten S 《Science (New York, N.Y.)》2004,304(5670):584-587

The 18S ribosomal DNA molecular phylogeny and lipid composition of over 120 marine diatoms showed that the capability to biosynthesize highly branched isoprenoid (HBI) alkenes is restricted to two specific phylogenetic clusters, which independently evolved in centric and pennate diatoms. The molecular record of C25 HBI chemical fossils in a large suite of well-dated marine sediments and petroleum revealed that the older cluster, composed of rhizosolenid diatoms, evolved 91.5 +/- 1.5 million years ago (Upper Turonian), enabling an accurate dating of the pace of diatom evolution that is unprecedented. The rapid rise of the rhizosolenid diatoms probably resulted from a major reorganization of the nutrient budget in the mid-Cretaceous oceans, triggered by plate tectonics.  相似文献   

Independent codes for spatial and episodic memory in hippocampal neuronal ensembles     

Leutgeb S  Leutgeb JK  Barnes CA  Moser EI  McNaughton BL  Moser MB 《Science (New York, N.Y.)》2005,309(5734):619-623

Hippocampal neurons were recorded under conditions in which the recording chamber was varied but its location remained unchanged versus conditions in which an identical chamber was encountered in different places. Two forms of neuronal pattern separation occurred. In the variable cue-constant place condition, the firing rates of active cells varied, often over more than an order of magnitude, whereas the location of firing remained constant. In the variable place-constant cue condition, both location and rates changed, so that population vectors for a given location in the chamber were statistically independent. These independent encoding schemes may enable simultaneous representation of spatial and episodic memory information.  相似文献   

Genome-wide RNAi analysis of growth and viability in Drosophila cells     

Boutros M  Kiger AA  Armknecht S  Kerr K  Hild M  Koch B  Haas SA  Paro R  Perrimon N;Heidelberg Fly Array Consortium 《Science (New York, N.Y.)》2004,303(5659):832-835

A crucial aim upon completion of whole genome sequences is the functional analysis of all predicted genes. We have applied a high-throughput RNA-interference (RNAi) screen of 19,470 double-stranded (ds) RNAs in cultured cells to characterize the function of nearly all (91%) predicted Drosophila genes in cell growth and viability. We found 438 dsRNAs that identified essential genes, among which 80% lacked mutant alleles. A quantitative assay of cell number was applied to identify genes of known and uncharacterized functions. In particular, we demonstrate a role for the homolog of a mammalian acute myeloid leukemia gene (AML1) in cell survival. Such a systematic screen for cell phenotypes, such as cell viability, can thus be effective in characterizing functionally related genes on a genome-wide scale.  相似文献   

The Consumption of <Emphasis Type="Italic">Hibiscus sabdariffa</Emphasis> Dried Calyx Ethanolic Extract Reduced Lipid Profile in Rats     

Carvajal-Zarrabal O  Waliszewski SM  Barradas-Dermitz DM  Orta-Flores Z  Hayward-Jones PM  Nolasco-Hipólito C  Angulo-Guerrero O  Sánchez-Ricaño R  Infanzón RM  Trujillo PR 《Plant foods for human nutrition (Dordrecht, Netherlands)》2005,60(4):153-159

The scientific basis for the statement that plants and their active constituents play an important role in the prevention of chronic and degenerative diseases is continously advancing. The object of the present study was to evaluate the effect of Hibiscus sabdariffa L. dried calyx ethanolic extract on the serum lipid profile of Sprague-Dawley rats. The rats were fed during 4 weeks with either a basal diet, containing high cholesterol (1%), cholic acid (0.25%), lard oil (10%), or a supplemental diet with H. sabdariffa extract at 5%, 10%, and 15% levels (SD₅, SD₁₀, SD₁₅). Weight gain and faeces dry weight were both very significantly less (p ≤ 0.01) in SD₁₀ and SD₁₅ groups as compared to the control group, as was food efficiency in SD₁₅. In the case of SD₁₀, food efficiency was only significantly lower (p ≤ 0.05). Faeces dry weight in SD₅ however, was the only one found to be significantly higher (p ≤ 0.05). Triacylglycerols and LDL levels were both significantly less (p ≤ 0.05) in all groups (SD₅, SD₁₀, and SD₁₅) as compared to the control. For total lipids, SD₁₀ and SD₁₅ showed significantly lower levels (p ≤ 0.05), whereas very significant differences (p ≤ 0.01) were observed in the case of SD₅. All groups had lower cholesterol levels compared to controls; however, only the SD₅ group was statistically significant (p ≤ 0.05). No significant results were found in any group in the cases of either phospholipid or HDL levels. A hypothesis of hibiscus acid racemization, (+)-HCA to (−)-HCA, mediated by intestinal flora enzymes possibly explains the significant triacylglycerol decrease in all experimental groups. VLDL, the precursor of LDL, is composed predominantly of triacylglycerols, suggesting that the significant decrease in LDL is related to observed triacylglycerol synthesis inhibition. Five percent H. sabdariffa extract addition showed the best results in the reduction of serum lipids under study conditions.  相似文献   

Analysis and occurrence of 14 sulfonamide antibacterials and chloramphenicol in honey by solid-phase extraction followed by LC/MS/MS analysis     

Sheridan R  Policastro B  Thomas S  Rice D 《Journal of agricultural and food chemistry》2008,56(10):3509-3516

A method was developed for the analysis of 14 sulfonamide antibiotics and chloramphenicol in honey. These antibiotics have been banned for use in food-producing animals; yet, their residues were found in many samples, illustrating the need for a multiresidue analysis for these antibiotics in honey. The method described here uses an acid hydrolysis step to liberate the sugar-bound sulfonamides followed by a solid-phase extraction to remove potential interferences. Analysis was by liquid chromatography--electrospray ionization--tandem mass spectrometry in negative mode for all 15 analytes. This MRM method generated two structurally significant transitions per compound, and it was designed to conform to U.S. Food and Drug Administration MS confirmation guidelines. It also provides 4-EU identification points. One hundred sixteen samples from 25 countries were analyzed, and 38% were found to contain at least one target antimicrobial. Five different target compounds were found in honey from 13 different countries.  相似文献   

The Collembola community of pure and mixed stands of beech (Fagus sylvatica) and spruce (Picea abies) of different age     

Jrg-Alfred Salamon  Stefan Scheu  Matthias Schaefer 《Pedobiologia》2008,51(5-6):385-396

The idea of establishing mixed forests that are better adapted to site conditions than spruce monocultures has attracted increasing attention of forest owners and governmental institutions over the last decades. Currently, beech is being replanted and an increasing proportion of German forests are mixed stands. Focusing on the reaction of the soil fauna to forest conversion, this study investigates the response of the Collembola community to replacement of beech by spruce or by mixed stands of beech and spruce. Stands of different age were investigated in a factorial design with the factors stand type (beech, spruce and mixed stands) and stand age (30 and 120 years). Collembola communities did not differ strongly between stand types and stand age and were dominated by Folsomia quadrioculata and Mesaphorura species (e.g. Mesaphorura macrochaeta). Moreover, neither total abundance of Collembola nor densities of the fungal feeding euedaphic Onychiurinae and Tullbergiinae significantly responded to stand type and stand age. The density of the epedaphic and partly herbivorous groups Symphypleona/Neelipleona and Entomobryidae in the 120-year-old stands significantly exceeded that in the 30-year-old stands; presumably, this was due to the well developed herb layer in the 120-year-old stands with more open canopies. Canonical correspondence analysis (CCA) of the Collembola community of the L/F horizon also indicated that most of the epigeic species were associated with the 120-year-old stands. Moreover, the diversity of Collembola significantly increased with forest age which likely reflects increased amount and diversity of food resources in the 120-year-old stands. The density of the hygrophilous species Fo. quadrioculata was significantly higher in the spruce than in the beech stands; probably this was due to the higher water content in litter of the spruce stands. Moreover, the results of the CCAs indicated that soil pH is an important structuring force for the Collembola communities. Overall, the results suggest that stand type and forest age impact Collembola communities, presumably via changes in the amount and quality of food resources, such as living plant and herb litter materials. The pronounced changes which occurred with forest age likely were related to the development of more dense and diverse herb layer in mature forests which provides additional food resources in particular for epedaphic species. On the other hand, dominant species/functional groups of Collembola, such as hemiedaphic species, appear to depend predominantly on abiotic factors, most importantly soil pH and soil water content.  相似文献   

Combined effects of zinc and earthworm density on soil ecosystem functioning     

Joost Lahr  Stefan A.E. Kools  Annemariet van der Hout  Jack H. Faber 《Soil biology & biochemistry》2008,40(2):334-341

In traditional environmental risk assessment for soils, interactions between biota, contaminants and soil functioning are seldom taken into account. Also, single species toxicity tests are conducted with a fixed number of test animals. The objective of this study was to investigate effects of zinc (0–620 mg Zn kg^?1 dry soil) on soil ecosystem processes at different densities of the earthworm Lumbricus rubellus. Experiments were conducted using 1-liter microcosms equipped with respirometers. The presence of L. rubellus stimulated relevant soil processes and parameters: litter fragmentation, leaf litter mass loss from the soil surface, soil organic matter (SOM) content and soil respiration. Zinc was not lethal to L. rubellus, but negatively impacted soil respiration at the highest concentrations. Litter mass loss from the soil surface was also decreased by zinc and there was a significant interaction with worm density. The results of the study demonstrate that the impact of zinc on soil processes depends on the presence and densities of key soil organisms such as earthworms that influence decomposition and SOM content. The outcome of this research can be used to make existing models for site-specific risk assessment more ecologically relevant, linking effects of contaminants on soil fauna populations with effects on ecosystem functioning.  相似文献   

Determination of alcohol and extract concentration in beer samples using a combined method of near-infrared (NIR) spectroscopy and refractometry     

Castritius S  Kron A  Schäfer T  Rädle M  Harms D 《Journal of agricultural and food chemistry》2010,58(24):12634-12641

A new approach of combination of near-infrared (NIR) spectroscopy and refractometry was developed in this work to determine the concentration of alcohol and real extract in various beer samples. A partial least-squares (PLS) regression, as multivariate calibration method, was used to evaluate the correlation between the data of spectroscopy/refractometry and alcohol/extract concentration. This multivariate combination of spectroscopy and refractometry enhanced the precision in the determination of alcohol, compared to single spectroscopy measurements, due to the effect of high extract concentration on the spectral data, especially of nonalcoholic beer samples. For NIR calibration, two mathematical pretreatments (first-order derivation and linear baseline correction) were applied to eliminate light scattering effects. A sample grouping of the refractometry data was also applied to increase the accuracy of the determined concentration. The root mean squared errors of validation (RMSEV) of the validation process concerning alcohol and extract concentration were 0.23 Mas% (method A), 0.12 Mas% (method B), and 0.19 Mas% (method C) and 0.11 Mas% (method A), 0.11 Mas% (method B), and 0.11 Mas% (method C), respectively.  相似文献   

Natural and experimental evidence of melt lubrication of faults during earthquakes     

Di Toro G  Hirose T  Nielsen S  Pennacchioni G  Shimamoto T 《Science (New York, N.Y.)》2006,311(5761):647-649

Melt produced by friction during earthquakes may act either as a coseismic fault lubricant or as a viscous brake. Here we estimate the dynamic shear resistance (tau(f)) in the presence of friction-induced melts from both exhumed faults and high-velocity (1.28 meters per second) frictional experiments. Exhumed faults within granitoids (tonalites) indicate low tau(f) at 10 kilometers in depth. Friction experiments on tonalite samples show that tau(f) depends weakly on normal stress. Extrapolation of experimental data yields tau(f) values consistent with the field estimates and well below the Byerlee strength. We conclude that friction-induced melts can lubricate faults at intermediate crustal depths.  相似文献   

Authentication of the botanical and geographical origin of honey by mid-infrared spectroscopy   总被引：1，自引：0，他引：1  

Ruoff K  Luginbühl W  Künzli R  Iglesias MT  Bogdanov S  Bosset JO  von der Ohe K  von der Ohe W  Amado R 《Journal of agricultural and food chemistry》2006,54(18):6873-6880

The potential of Fourier transform mid-infrared spectroscopy (FT-MIR) using an attenuated total reflectance (ATR) cell was evaluated for the authentication of 11 unifloral (acacia, alpine rose, chestnut, dandelion, heather, lime, rape, fir honeydew, metcalfa honeydew, oak honeydew) and polyfloral honey types (n = 411 samples) previously classified with traditional methods such as chemical, pollen, and sensory analysis. Chemometric evaluation of the spectra was carried out by applying principal component analysis and linear discriminant analysis, the error rates of the discriminant models being calculated by using Bayes' theorem. The error rates ranged from <0.1% (polyfloral and heather honeys as well as honeydew honeys from metcalfa, oak, and fir) to 8.3% (alpine rose honey) in both jackknife classification and validation, depending on the honey type considered. This study indicates that ATR-MIR spectroscopy is a valuable tool for the authentication of the botanical origin and quality control and may also be useful for the determination of the geographical origin of honey.  相似文献