1,721,680 research outputs found
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Variations on the Author
Full text link“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
Full text linkWe 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
Molecular basis for differential host response of sorghum against different formae speciales of Sporisorium reilianum
No full textThe biotrophic pathogenic smut fungus Sporisorium reilianum causes head smut in maize and sorghum and threatens the worldwide cultivation of infected plants. The fungus exists in two formae speciales, S. reilianum f. sp. zeae (SRZ) and S. reilianum f. sp. reilianum (SRS), that can infect maize and sorghum, respectively. Prior to plant infection, compatible haploid sporidia mate, forming infectious dikaryotic filaments. Hundreds of effector proteins are predicted to be secreted during S. reilianum infection that may help the fungus to colonize the host or lead to recognition by non-host plants, triggering defense response. When infecting its preferred host, S. reilianum does not induce visual signs of defense response on leaves other than weak chlorosis and minor cell death. Differently, sorghum infection with SRZ is challenged by several plant defense responses that prevent pathogen systemic spread. The strongest visual defense response of sorghum against SRZ is the production of phytoalexins that lead to a red coloration of infected leaf tissues. To better understand the molecular events that take place during SRZ infection of sorghum, we followed several experimental approaches. In approach one, we used fractionated cellular components of SRZ and infiltrated sorghum leaves to test whether cell wall components play a role in phytoalexin induction. Commercial compounds known to induce phytoalexins in other systems were also tested. However, no clear indication of the involvement of cell wall components in the induction of phytoalexins could be proved. In approach two, we tested whether SRZ-specific secreted effectors are responsible for phytoalexin induction. Candidate effectors were tested for their ability to induce phytoalexin formation by particle bombardment of sorghum leaves. None of the tested effectors could consistently induce phytoalexins in the targeted or neighboring cells. In approach three, the most highly differentially expressed selected candidate effectors were individually deleted in SRZ. Deletion of one candidate, sr14274, led to highly reduced phytoalexin induction as a result of greatly impaired virulence. In approach four, we aimed to test the effect of individual proteins of SRZ on the induction of phytoalexins or cell death in sorghum. To this end, 46 selected candidates were cloned for heterologous protein production in E. coli, using the pTSGATE1 plasmid. Due to time constraints, protein expression and leaf infiltration were not tested. Finally, in approach five, we tested selected effector candidates for their ability to suppress hypersensitive cell death triggered by the elicitin INF1 of Phytophthora infestans by agroinfiltration in Nicotiana benthamiana. A predicted cytoplasmic effector, sr16441ΔSP, was able to reliably suppress INF1-induced cell death. This study revealed a putative function for a new effector candidate that may help us to understand the molecular processes happening upon sorghum infection with SRZ
Upcycling of plastic monomers by mixed microbial cultures
No full textDue to their robustness, versatile properties, and low price, plastics are used for such different applications as bone screws in medical applications and packaging in the food sector at ever-increasing amounts. The environmental problem caused by mismanaged plastic waste is prominent in many parts of this world, causing contaminations of the soil and marine ecosystems. To tackle this challenge, the end-of-life use of plastic must be considered in the value chain, including the fate of the polymers. A not yet industrially implemented possibility is to use waste plastic as a carbon source for microbes and produce value-added products. Ideally, the generated products have a higher value than the original plastic product and hence would not be just recycled but upcycled, a theme of the presented thesis. Polyurethanes (PU) and polyethylene terephthalate (PET) are in the top 10 plastics produced and can either partially or fully be degraded using enzymes. These enzymes found in nature can hydrolyze these polymers, thereby releasing monomers like adipic acid, 1,4- butanediol, ethylene glycol, 2,4-toluenediamine, and terephthalic acid. The plastic monomers can be utilized as a carbon source by microorganisms like the biotechnological workhorse Pseudomonas putida KT2440 or new species like Pseudomonas capeferrum TDA1 to produce high-value products, like rhamnolipids, phenazine, and polyhydroxyalkanoates, presented in this thesis. More specifically, this thesis presents a defined mixed culture utilizing the mock of a PU hydrolysate as a sole carbon source for growth and mono-rhamnolipid synthesis. The isocyanate derivative, 2,4-toluenediamine (TDA), exhibited strong inhibitory effects and hence was extracted prior to carbon use with 5 wt% di-(2-ethylhexyl) phosphoric acid (D2EHPA) in paraffin oil. The extraction of TDA was necessary, despite a member of the consortium could degrade this plastic monomer, indicating that the biochemical potential and the rates of thedifferent members have to be taken into consideration in the design of mixed cultures.P. capeferrum TDA1 can natively utilize adipic acid, 1,4-butanediol, and 2,4-toluenediamine, but not ethylene glycol and terephthalic acid. As an alternative approach, a consolidated mutant based on P. capeferrum TDA1 was established to utilize all monomers from PU and PET and to produce mono-rhamnolipids. Adaptive laboratory evolution was conducted to enable growth on ethylene glycol, while the tph operon from P. umsongensis GO16 was transformed to enable growth on terephthalic acid. The results are discussed in the context of the bow-tie structure of metabolism and plastic waste as a carbon source in a circular (bio)economy
Optimization of itaconic acid production by U. maydis through metabolic engineering & adaptive laboratory evolution
No full textThe incessant growth of the world population leads to an already gigantic and still increasing demand for food, energy, fuels, and chemicals. With the finiteness of fossil resources as main feedstocks, a change from petroleum-derived to sustainable, economically bio-based production processes is indispensable to accomplish the global needs. One of these processes is the production of itaconic acid ranked as one of the top 12 value added chemicals from biomass by the DoE. Nowadays, industrial biotechnological production is performed by using the filamentous fungus Aspergillus terreus. To circumvent the challenges going along with such a filamentous production host, alternatives are searched. In this context, the Ustilaginaceae family including Ustilago maydis attracted special attention. To establish an industrial itaconate production host competitive to A. terreus and to significantly improve the itaconate production performance of U. maydis, two strategies were chased in this thesis: metabolic engineering and adaptive laboratory evolution. By the reduction of the diverse by-product spectrum of U. maydis MB215 by the deletion of 2-hydroxy paraconate, mannosyl-erythritol lipid, ustilagic acid and triacylglycerol biosynthesis in combination with the upregulation of ria1, the itaconate biosynthesis gene cluster regulator, the flow of substrate could be extensively pushed towards itaconate biosynthesis. This lead to an itaconate titer increased by 10.2-fold compared to the wildtype. Due to the upregulation of the cis-aconitate/malate antiporter mtt1 as consequence of ria1↑, the production of malate, another by-product, could simultaneously be decreased by 84 %.In this by-product reduced U. maydis strain, further metabolic engineering steps were performed: filamentous growth prevention by fuz7 deletion and overexpression of mttA encoding for the A. terreus mitochondrial tricarboxylate transporter. By ∆fuz7, the designed strain was able to produce itaconate with improved production parameters, especially with an 25% increased yield from glucose. This could even be outplayed by additional PetefmttA insertion. A clone with three PetefmttA copies reached an itaconate titer of 54 g L-1 and a maximal yield of 0.64 gITA gglu-1, which corresponds to 89 % of the theoretical value. The great itaconate production improvements imply a higher metabolic and osmotic stress level for the cells. Adaptive laboratory evolution was therefore used to generate a strain with increased low pH and product resistance to itaconate. The fitness of U. maydis could be significantly improved represented by strains able to grow at pH 4 and in the presents of 40 g L-1 itaconate. The consolidation of all major modifications identified in this thesis in one strain, though, resulted in a loss of this tolerance. Especially the deletion of triacylglycerol production, the cells rely on as main energy reserves, seems to destabilize the cells in the long term. However, the results clearly illustrate that the final engineered strains feature great, far optimized itaconate production parameters close to the theoretical maximum making U. maydis - besides A. terreus - an industrial relevant production host for itaconic acid
Itaconic acid production by ustilago maydis
No full textThe overall goal of this thesis was to establish Ustilago maydis as an alternative whole cell biocatalyst for the biosynthesis of itaconate from renewable substrates, such as cellulose or hemicellulose. Since the production of valuable and biotechnologically relevant chemicals by microorganisms is strongly influenced by the composition of the medium, its optimization is an integral part of biotechnological process development. Therefore, a new medium composition (modified Tabuchi medium) for itaconate production by Ustilaginaceae was developed. This modified Tabuchi medium consists of 50 g L-1 glucose, 0.8 g L-1 NH4Cl, 0.2 g L-1 MgSO4•7H2O, 0.01 g L-1 FeSO4•7H2O, 0.5 g L-1 KH2PO4, 1 mL L-1 vitamin solution, 10 mL L 1 trace element solution and as buffer 19.5 g L-1 2-(N-morpholino)ethanesulfonic acid (MES). The modified medium circumvents the disadvantages of the standard Tabuchi medium, such as low reproducibility and complex/insoluble medium components, and therefore allows reliable physiological experiments as well as high throughput screenings (HTS).To identify potential novel natural biocatalysts for possible platform chemicals, such as itaconate, malate, or succinate, the biodiversity of the fungal family Ustilaginaceae (68 Ustilaginaceae of 13 species) was prospected in this medium via HTS, showing the production of a versatile range of value-added chemicals. Additionally, the influence of buffer concentration (pH) on acid production was investigated. Based on this screening, the most suitable itaconate producer, U. maydis MB215, was selected and characterized in more detail in bioreactor experiments obtaining total acid concentrations (itaconate, malate, and succinate) of up to 35 ± 4 g L-1.In order to combine the utilization of raw biomass components such as cellulose and hemicellulose with the production of valuable platform chemicals such as itaconate, the xylan degradation ability of this strain was investigated. Thereby, the endo-1,4-beta xylanase UmXyn11A (um06350.1) of U. maydis responsible for xylan degradation was identified, characterized, and expressed heterologously.Furthermore, the clustered genes, um05074 (cyp3), um05076 (tad1), um11777 (itp1), um11778 (adi1), um05079 (mtt1), and um05080 (ria1), encoding the proteins responsible for itaconate production and possibly its degradation in U. maydis MB215 were identified. Based on this information a novel biosynthesis pathway for itaconate was established. This knowledge was used to enhance U. maydis’ itaconate production twofold by overexpressing the transcription factor which regulates the gene expression of the itaconate cluster. With the identification of the itaconate biosynthesis pathway, this thesis lays the foundation for further optimization of this pathway and is therefore a first step towards industrial application of U. maydis as a member of the highly interesting group of Ustilaginaceae
Metabolic engineering of Pseudomonas putida for the production of aromatics from glucose
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