1,721,122 research outputs found
Genetic engineering of lipid biosynthesis in Nannochloropsis gaditana for food oil production
No full textÈ ormai riconosciuto che le attività dell’uomo sono responsabili del cambiamento climatico. Fra queste attività l’agricoltura è responsabile dell’emissione di circa un quinto dei gas serra e determina una serie di effetti negativi sull’ambiente come l’erosione del suolo e la perdita di biodiversità. Per soddisfare le richieste della crescente popolazione, la domanda di terreni da destinare all’agricoltura è in continua crescita, ma sarà necessario prevenire l’inasprimento delle questioni ambientali cercando delle soluzioni più sostenibili. In questa prospettiva le microalghe sono state proposte come una fonte sostenibile di proteine, oli e pigmenti. Per la produzione sostenibile di oli alimentari, Nannochloropsis gaditana è stata proposta come un’ottima fonte per via della sua capacità di accumulare lipidi fino al 60% della sua biomassa e di sintetizzare omega-3 con riconosciute proprietà antinfiammatorie. È stato suggerito che questa capacità di accumulo di lipidi sia dovuta all’abbondanza di geni coinvolti nella biosintesi, che ne complica la diretta estrapolazione di informazioni a partire da organismi modello come Arabidopsis thaliana e Chlamydomonas reinhardtii. Tuttavia, l’utilizzo nel settore alimentare di N. gaditana e di altre microalghe oleaginose è ancora limitato, per via della diversa composizione rispetto agli oli vegetali attuali, determinando quindi diverse proprietà chimico fisiche.
Dato che il profilo lipidico è strettamente correlato ai geni coinvolti nella pathway di biosintesi, l’ingegneria genetica è stata proposta come strategia efficace per produrre oli di interesse nel settore alimentare. Lo scopo di questa tesi è stato perciò un’approfondita analisi della via di biosintesi dei lipidi di N. gaditana, per elucidarne le caratteristiche e identificare geni per le modiche.
Per modificare la qualità degli oli, abbiamo indagato la via di biosintesi degli acidi grassi, analizzando il ruolo di una desaturasi e una tioesterasi, rispettivamente responsabili del grado di saturazione e della lunghezza delle catene aciliche. Abbiamo prodotto dei ceppi con un profilo di acidi grassi alterato e siamo riusciti a caratterizzare alcuni nodi della biosintesi, che sono risultati più complessi rispetto ad altri organismi modello. Abbiamo poi esaminato gli ultimi step della biosintesi dei lipidi, per generare ceppi con una maggiore capacità di accumulo e quindi una possibile applicazione industriale. N. gaditana si è rivelata un organismo interessante per lo studio della biosintesi dei lipidi, capace di offrire un’ampia possibilità di modiche genetiche, sia per comprendere meglio la pathway ma anche per produrre ceppi di interesse industriale. Dato il rilievo dell’ingegneria genetica, abbiamo approfondito lo sviluppo e l’applicazione di nuovi tools, per offrire una più ampia gamma di strategie. Infine, per l’interesse industriale che N. gaditana potrà avere, abbiamo valutato gli effetti di una luce, caratterizzata da intensità variabile, per offrire una prospettiva della crescita su larga scala.It is now well recognized that human activities are responsible of climate change. Among these activities, agriculture is responsible of about one fifth of greenhouse gas emission, and determines a series of negative environmental impacts, like soil deterioration and the loss of biodiversity. While the demand for agricultural land is constantly increasing to meet the needs of the rising population, it will be imperative to prevent the exacerbation of environmental issues by seeking more sustainable solutions. In this perspective microalgae were proposed as a sustainable source of proteins, oils and pigments and so on. For the sustainable production of food oils, Nannochloropsis gaditana was proposed as an optimal source due to its outstanding capacity of accumulating lipids, up to the 60% of its biomass and furthermore it synthetises omega-3 with recognized anti-inflammatory properties. It has been proposed that this outstanding capacity of accumulating lipids is due to the abundance of lipid-related genes in the genome, which complicate the direct extrapolation of information about the pathway from model organisms like Arabidopsis thaliana and Chlamydomonas reinhardtii. However, the use of N. gaditana and other oleaginous microalgae in the food industry is still limited, due to the different composition compared to crop-derived oils, leading to diverse chemical-physical properties.
Since the lipid profile is strictly linked to the genes involved in the biosynthetic pathway, genetic engineering has been proposed as an effective strategy to produce industrial relevant oil for food application. The aim of this thesis was therefore a deep investigation of the lipid biosynthetic pathway of N. gaditana, to elucidate its peculiar characteristics and identify interesting target genes for modification.
To modify the quality of oils, we investigated the fatty acid biosynthetic pathway, by analysing the role of a desaturase and a thioesterase, responsible for the degree of saturation and the length of the acyl chains respectively. We were able to produce strains with an altered fatty acid profile and to partially elucidate the pathway, that in N. gaditana proved to be more complex with respect to model organisms. We then examined the last steps of lipid biosynthesis, to generate strains with an increased lipid content and possible applications at industrial level. N. gaditana turned out to be an interesting organism for the investigation of lipid biosynthesis, offering a wide possibility of genome modification, to both comprehend the pathway and the produce industrial relevant strains. Due to the relevance of genetic engineering, we explored the development and application of new tools, to offer then a broader variety of strategies. Finally, due to the industrial relevance that N. gaditana may have, we evaluated the effects the variable light conditions on cultures, to provide a perspective for large scale cultivation
Photosynthesis regulation in response to fluctuating light in the secondary endosymbiont alga Nannochloropsis gaditana
Full text linkIn nature, photosynthetic organisms are exposed to highly dynamic environmental conditions where the excitation energy and electron flow in the photosynthetic apparatus need to be continuously modulated. Fluctuations in incident light are particularly challenging since they drive oversaturation of photosynthesis, with consequent oxidative stress and photoinhibition. Plants and algae have evolved several mechanisms to modulate their photosynthetic machinery to cope with light dynamics, such as thermal dissipation of excited chlorophyll states (Non-Photochemical Quenching, NPQ) and regulation of electron transport. The regulatory mechanisms involved in the response to light dynamics have adapted during evolution and exploring biodiversity is a valuable strategy for expanding our understanding of their biological roles. In this work, we investigated the response to fluctuating light in Nannochloropsis gaditana, a eukaryotic microalga of the phylum Heterokonta originating from a secondary endosymbiotic event. N. gaditana is negatively affected by light fluctuations, leading to large reductions in growth and photosynthetic electron transport. Exposure to light fluctuations specifically damages photosystem I, likely because of ineffective regulation of electron transport in this species. The role of Non-Photochemical Quenching, also assessed using a mutant strain specifically depleted of this response, was instead found to be minor, especially in responding to the fastest light fluctuations
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
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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