1,720,961 research outputs found
Genetic and phenotypic analysis of Chlamydomonas pale green mutants
Full text linkIn this thesis it was performed the characterization of different Chlamydomonas reinhardtii pale green mutants, both to investigate some important photosynthetic mechanisms and to identify mutations which result in enhanced productivity, to be exploitable for industrial applications. The Chlamydomonas pale mutant as2.1 is characterized by an increased high light resistance and a faster growth in photoautotrophic conditions, compared to the WT. Sequencing data from this strain revealed a large deletion/insertion rearrangement including the gene CpFTSY, a soluble receptor belonging to the CpSRP pathway. Through a targeted mutagenesis by CRISPR-Cas9 genome editing approach, we aimed to understand if the growth advantage was related to the lack of CpFTSY . Unexpectedly, the CpFTSY-knock out (KO) mutants were unable to grow photoautotrophycally and showed a diminished abundance of LHCs and supercomplexes content than the control genotype; moreover, in mutant lines carotenoids biosynthesis was up-regulated, thus suggesting a higher susceptibility to excess light stress. To clarify these differences between as2.1 and the genome edited strains, all these mutants were complemented by the CDS of CpFTSY, demonstrating that this gene is responsible for the high-growth phenotype of as2.1; however, characterization of complemented lines revealed CpFTSY was not the only actor involved in growth phenotype, rather a side mutation likely contributes to this feature. The characterization of the first two cpftsy KO strains we obtained by genome editing revealed differences in LHC composition and in the relative abundance of monomeric vs. trimeric antennae, therefore additional KO lines were produced targeting this locus by a different sgRNA. The screening of several independent lines revealed a huge variation in the composition of the photosynthetic apparatus, that could tentatively be ascribed to an additional pathway or gene affecting the biogenesis of antenna systems, that might possibly compensate the missing CPFTSY during the strain propagation. cpftsy genome edited strains were also analyzed in comparison with Chlamydomonas cao mutants, to compare the effects of an impairment in LHCs insertion systems vs. chlorophyll biosynthesis, on the assembly of peripheral antenna system. Moreover, to understand which system is more important for light harvesting capacity, it was also produced a double mutant cpftsy-cao and the effects of the combined mutations were compared with those of the single ones. cao single mutants, despite a strong reduction in PSII functional antenna size and LHCII content, showed a remarkable resistance to excess light conditions, and a faster growth in photoautotrophic conditions compared to the wild type under saturating irradiances. Chlorophyll b biosynthetic pathway therefore appears crucial in the supramolecular organization of the photosystems, in the regulation of LHCII and LHCI relative abundance and in the structural stability of the LHCs, while its depletion does not significantly affect the core functionality. Instead, cpftsy single mutants were less affected in LHCII composition and in PSII functional antenna size than cao lines, however their photoautotrophic growth was impaired. Unexpectedly CpFTSY gene plays a minor role in regulating LHC system biogenesis, while the lower PsaA (PSI core-complex subunit) and CP47 (PSII core-complex subunit) contents suggested an involvement in the insertion of core proteins. The phenotype of cpftsy-cao double mutant is a cumulative result of the phenotypes of single mutants, thus it confirmed that CAO and CpFTSY regulate different steps of photosynthetic machinery biogenesis, and differently contributes to light-harvesting function. To obtain an efficient CRISPR-Cas9 procedure to be applied to Chlamydomonas, a long work of optimization of the available protocols was carried out. In the second part of the thesis, all the steps are illustrated
Potential and Challenges of Improving Photosynthesis in Algae
No full textSunlight energy largely exceeds the energy required by anthropic activities, and therefore its exploitation represents a major target in the field of renewable energies. The interest in the mass cultivation of green microalgae has grown in the last decades, as algal biomass could be employed to cover a significant portion of global energy demand. Advantages of microalgal vs. plant biomass production include higher light-use efficiency, efficient carbon capture and the valorization of marginal lands and wastewaters. Realization of this potential requires a decrease of the current production costs, which can be obtained by increasing the productivity of the most common industrial strains, by the identification of factors limiting biomass yield, and by removing bottlenecks, namely through domestication strategies aimed to fill the gap between the theoretical and real productivity of algal cultures. In particular, the light-to-biomass conversion efficiency represents one of the major constraints for achieving a significant improvement of algal cell lines. This review outlines the molecular events of photosynthesis, which regulate the conversion of light into biomass, and discusses how these can be targeted to enhance productivity through mutagenesis, strain selection or genetic engineering. This review highlights the most recent results in the manipulation of the fundamental mechanisms of algal photosynthesis, which revealed that a significant yield enhancement is feasible. Moreover, metabolic engineering of microalgae, focused upon the development of renewable fuel biorefineries, has also drawn attention and resulted in efforts for enhancing productivity of oil or isoprenoids
Biomass from microalgae: the potential of domestication towards sustainable biofactories
No full textAbstract Interest in bulk biomass from microalgae, for the extraction of high-value nutraceuticals, bio-products, animal feed and as a source of renewable fuels, is high. Advantages of microalgal vs. plant biomass production include higher yield, use of non-arable land, recovery of nutrients from wastewater, efficient carbon capture and faster development of new domesticated strains. Moreover, adaptation to a wide range of environmental conditions evolved a great genetic diversity within this polyphyletic group, making microalgae a rich source of interesting and useful metabolites. Microalgae have the potential to satisfy many global demands; however, realization of this potential requires a decrease of the current production costs. Average productivity of the most common industrial strains is far lower than maximal theoretical estimations, suggesting that identification of factors limiting biomass yield and removing bottlenecks are pivotal in domestication strategies aimed to make algal-derived bio-products profitable on the industrial scale. In particular, the light-to-biomass conversion efficiency represents a major constraint to finally fill the gap between theoretical and industrial productivity. In this respect, recent results suggest that significant yield enhancement is feasible. Full realization of this potential requires further advances in cultivation techniques, together with genetic manipulation of both algal physiology and metabolic networks, to maximize the efficiency with which solar energy is converted into biomass and bio-products. In this review, we draft the molecular events of photosynthesis which regulate the conversion of light into biomass, and discuss how these can be targeted to enhance productivity through mutagenesis, strain selection or genetic engineering. We outline major successes reached, and promising strategies to achieving significant contributions to future microalgae-based biotechnology
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
Design of a highly thermostable hemicellulose-degrading blend from Thermotoga neapolitana for the treatment of lignocellulosic biomass
No full textThe biological conversion of lignocellulose into fermentable sugars is a key process for the sustainable production of biofuels from plant biomass. Polysaccharides in plant feedstock can be valorized using thermostable mixtures of enzymes that degrade the cell walls, thus avoiding harmful and expensive pre-treatments. (Hyper) thermophilic bacteria of the phylum Thermotogae provide a rich source of enzymes for such industrial applications. Here we selected T. neapolitana as a source of hyperthermophilic hemicellulases for the degradation of lignocellulosic biomass. Two genes encoding putative hemicellulases were cloned from T. neapolitana genomic DNA and expressed in Escherichia coli. Further characterization revealed that the genes encoded an endo-1,4-ss galactanase and an a-L-arabinofuranosidase with optimal temperatures of (similar to)90 degrees C and high turnover numbers during catalysis (kcat values of (similar to)177 and (similar to)133 s(-1), respectively, on soluble substrates). These enzymes were combined with three additional T. neapolitana hyperthermophilic hemicellulases -endo-1,4-beta-xylanase (XynA), endo-1,4-beta-mannanase (ManB/Man5A) and beta-glucosidase (GghA) -to form a highly thermostable hemicellulolytic blend. The treatment of barley straw and corn bran with this enzymatic cocktail resulted in the solubilization of multiple hemicelluloses and boosted the yield of fermentable sugars by up to 65% when the complex substrates were further degraded by cellulases
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
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