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PLoS ONE
Get PDFNatural products (NPs) are an attractive source of chemical diversity for small-molecule drug discovery. Several challenges nevertheless persist with respect to NP discovery, including the time and effort required for bioassay-guided isolation of bioactive NPs, and the limited biomedical relevance to date of in vitro bioassays used in this context. With regard to bioassays, zebrafish have recently emerged as an effective model system for chemical biology, allowing in vivo high-content screens that are compatible with microgram amounts of compound. For the deconvolution of the complex extracts into their individual constituents, recent progress has been achieved on several fronts as analytical techniques now enable the rapid microfractionation of extracts, and microflow NMR methods have developed to the point of allowing the identification of microgram amounts of NPs. Here we combine advanced analytical methods with high-content screening in zebrafish to create an integrated platform for microgram-scale, in vivo NP discovery. We use this platform for the bioassay-guided fractionation of an East African medicinal plant, Rhynchosia viscosa, resulting in the identification of both known and novel isoflavone derivatives with anti-angiogenic and anti-inflammatory activity. Quantitative microflow NMR is used both to determine the structure of bioactive compounds and to quantify them for direct dose-response experiments at the microgram scale. The key advantages of this approach are (1) the microgram scale at which both biological and analytical experiments can be performed, (2) the speed and the rationality of the bioassay-guided fractionation – generic for NP extracts of diverse origin – that requires only limited sample-specific optimization and (3) the use of microflow NMR for quantification, enabling the identification and dose-response experiments with only tens of micrograms of each compound. This study demonstrates that a complete in vivo bioassay-guided fractionation can be performed with only 20 mg of NP extract within a few days.volumen 8; número
The Ecology of Microbial Communities Associated with Macrocystis pyrifera.
Get PDFKelp forests are characterized by high biodiversity and productivity, and the cycling of kelp-produced carbon is a vital process in this ecosystem. Although bacteria are assumed to play a major role in kelp forest carbon cycling, knowledge of the composition and diversity of these bacterial communities is lacking. Bacterial communities on the surface of Macrocystis pyrifera and adjacent seawater were sampled at the Hopkins Marine Station in Monterey Bay, CA, and further studied using 454-tag pyrosequencing of 16S RNA genes. Our results suggest that M. pyrifera-dominated kelp forests harbor distinct microbial communities that vary temporally. The distribution of sequence tags assigned to Gammaproteobacteria, Alphaproteobacteria and Bacteriodetes differed between the surface of the kelp and the surrounding water. Several abundant Rhodobacteraceae, uncultivated Gammaproteobacteria and Bacteriodetes-associated tags displayed considerable temporal variation, often with similar trends in the seawater and the surface of the kelp. Bacterial community structure and membership correlated with the kelp surface serving as host, and varied over time. Several kelp-specific taxa were highly similar to other bacteria known to either prevent the colonization of eukaryotic larvae or exhibit antibacterial activities. Some of these kelp-specific bacterial associations might play an important role for M. pyrifera. This study provides the first assessment of the diversity and phylogenetic profile of the bacterial communities associated with M. pyrifera
A Metabolic Probe-Enabled Strategy Reveals Uptake and Protein Targets of Polyunsaturated Aldehydes in the Diatom Phaeodactylum tricornutum.
Get PDFDiatoms are unicellular algae of crucial importance as they belong to the main primary producers in aquatic ecosystems. Several diatom species produce polyunsaturated aldehydes (PUAs) that have been made responsible for chemically mediated interactions in the plankton. PUA-effects include chemical defense by reducing the reproductive success of grazing copepods, allelochemical activity by interfering with the growth of competing phytoplankton and cell to cell signaling. We applied a PUA-derived molecular probe, based on the biologically highly active 2,4-decadienal, with the aim to reveal protein targets of PUAs and affected metabolic pathways. By using fluorescence microscopy, we observed a substantial uptake of the PUA probe into cells of the diatom Phaeodactylum tricornutum in comparison to the uptake of a structurally closely related control probe based on a saturated aldehyde. The specific uptake motivated a chemoproteomic approach to generate a qualitative inventory of proteins covalently targeted by the α,β,γ,δ-unsaturated aldehyde structure element. Activity-based protein profiling revealed selective covalent modification of target proteins by the PUA probe. Analysis of the labeled proteins gave insights into putative affected molecular functions and biological processes such as photosynthesis including ATP generation and catalytic activity in the Calvin cycle or the pentose phosphate pathway. The mechanism of action of PUAs involves covalent reactions with proteins that may result in protein dysfunction and interference of involved pathways
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Charakterisierung des Alterungsverhaltens automobiler Klebstoffe mit Hilfe der Differential Scanning Calorimetry
No full textAus logistischen Gründen werden Klebstoffe vor ihrer Verarbeitung gelagert. Während der Lagerung können die Klebstoffe altern und unbrauchbar werden. Zudem haben die Temperatur und die Luftfeuchtigkeit einen Einfluss auf den Verlauf der Alterung. In dieser Masterarbeit soll die Alterung verschiedener Klebstoffe mittels der DSC untersucht und Veränderungen erkannt werden. Um eine Aussage treffen zu können, ob ein Klebstoff verarbeitet werden kann oder entsorgt werden muss. Die untersuchen Klebstoffe teilen sich in drei feuchtigkeitshärtende Polyurethane, ein 1K heißhärtenden Kautschuk, ein 1K heißhärtendes Epoxidharz und ein 2K heißhärtendes Epoxidharz mit einem Polyacrylat Anteil auf. Am Anfang der Arbeit wurden für die Klebstoffe DSC-Methoden festgelegt und die Signale identifiziert. Anschließend wurden die Klebstoffe künstlich bei 60 °C gealtert und der Alterungsverlauf untersucht. Des Weiteren wurden die Klebstoffe bei 60 °C und 70 % Luftfeuchtigkeit gealtert. Zusätzlich zu den DSC-Messungen erfolgten rheologische Untersuchungen und Zugscherversuche. Die aus diesen Experimenten gewonnenen Erkenntnisse zeigen, dass bei den Epoxidharzen chemische Reaktionen zur Alterung führen. Die Alterung des Kautschuks ist dagegen rein physikalischer Natur. Die Alterungsursache bei den Polyurethanen konnte nicht eindeutig festgestellt werden. Außerdem konnte aus den Ergebnissen mögliche Reaktionsabläufe für die chemischen Reaktionen der beiden Epoxidharze postuliert werden. Zudem zeigen die Ergebnisse, dass die Aussagefähigkeit der DSC-Messung stark von Klebstoff abhängig ist
Strukturaufklärung und Quantifizierung von neuen Toxinen in marinen Mikroalgen durch NMR und Molekular Modelling basierten Techniken
No full textMarine biotoxins produced by dinoflagellates exhibit a remarkable structural diversity. During the course of this thesis, I present the elucidation of six novel compounds in total, two for each of the toxin groups of azaspiracids, gymnodimines, and spirolides. The LC-MS based quantification, as used in shellfish surveillance, of the novel azaspiracids was compared with NMR based quantification. Further, four cyclic imine toxins had their full relative stereochemistry elucidated. The simulated chemical shifts revealed a systematic effect between the chirality at C 4 and neighboring nuclei. Based on this systematic effect, reasonable doubts arise towards determination of R configuration at C-4 in 13,19-didesmethyl SPX C. The configuration of C-4 was assigned with simulated and measured NMR spectra, suggesting that all tested GYMs and SPXs have the S configuration at that position. This assignment supports the hypothesis of a common biosynthetic pathway for both compound groups
Untersuchung von Kieselalgen-Bakterien-Interaktionen mit dem Modellorganismus Thalassiosira rotula
No full textMarine microalgae are key primary producers responsible for more than 45% of global net primary production, fixing billions of tons of inorganic carbon each year. Diatoms constitute one of the most diverse and ecologically important group of microalgae. While diatom productivity and health are likely to be strongly governed by the structure and function of the diatom microbiome, we have little understanding which factors contribute to the microbiome assembly. In order to investigate the microbiome establishment on diatoms, an in vitro model system for reproducible laboratory studies was developed with the marine diatom Thalassiosira rotula. Thus, this thesis describes the isolation of diatoms and bacteria from the environment and the development of an in vitro model system for reproducible laboratory studies followed by the investigation of the microbiome assembling on the diatom T. rotula using co-culture experiments. In Chapter 2 diatoms and bacteria were co-isolated from a spring bloom in the German Bight of the North Sea. The isolation resulted in four different diatom species and 200 morphological different bacteria in culture. The marine diatom Thalassiosira rotula was selected as the model organism for the in vitro studies with diatoms and bacteria. Chapter 3 focused on the development of a co-culture to study mutualistic interactions between the diatom T. rotula and bacteria as well as the generation of an axenic (bacteria-free) culture of the diatom T. rotula. The experiments revealed that the diatom T. rotula is auxotroph for B-vitamins and that the bacterial community of T. rotula is able to maintain the growth of the vitamin-free diatom with the provision of vitamins. In Chapter 4 and 5 the microbiome assembling was investigated by exposing the vitamin-free and axenic diatom T. rotula to several bacterial source communities obtained from different diatom species. The co-culture experiments revealed that each of the newly established microbiomes on the T. rotula acceptor supports the growth of the diatom under vitamin absence, indicating that all microbiomes comprise bacteria capable for B-vitamin synthesis. To investigate the factors that contribute to the microbiome assembling, the bacterial community compositions of the different inoculated bacterial source communities and newly assembled acceptor microbiomes were analysed. The analysis revealed that the different inoculated bacterial source communities were highly different in their bacterial community composition and contained up to 4406 different operational taxonomic units (OTUs). On the contrary, the analysis of the newly established acceptor microbiomes revealed that all acceptor microbiomes were similar to each other in respect to their bacterial community composition and that they were more similar to the original T. rotula bacterial source community than to the donor cultures where the bacterial source communities were obtained from. The similarity of the acceptor microbiomes was most likely caused by 10 OTUs, which constituted for more than 80% of the total relative abundance of all acceptor microbiomes. Furthermore, these 10 OTUs were shown to be most responsible for the differences between acceptor microbiomes and bacterial source communities and were thus described as the core microbiome of the diatom T. rotula. Consequently, it was shown for the first time that the ecologically relevant diatom T. rotula establishes a robust and reproducible bacterial core microbiome of 10 OTUs if it is offered highly diverse and compositionally different bacterial source communities with up to 4406 OTUs. The results of the robust and reproducible microbiome composition on the diatom T. rotula suggest that host factors contribute more than the bacterial diversity in the environment to the shaping of the microbiome composition
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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