1,720,963 research outputs found
Heterologous expression of cyanobacterial Orange Carotenoid Protein (OCP2) as a soluble carrier of ketocarotenoids in Chlamydomonas reinhardtii
Full text linkPhotosynthetic organisms evolved different mechanisms to protect themselves from high irradiances and photodamage. In cyanobacteria, the photoactive Orange Carotenoid-binding Protein (OCP) acts both as a light sensor and quencher of excitation energy. It binds keto-carotenoids and, when photoactivated, interacts with phycobilisomes, thermally dissipating the excitation energy absorbed by the latter, and acting as efficient singlet oxygen quencher. Here, we report the heterologous expression of an OCP2 protein from the thermophilic cyanobacterium Fischerella thermalis (FtOCP2) in the model organism for green algae, Chlamydomonas reinhardtii. Robust expression of FtOCP2 was obtained through a synthetic redesigning strategy for optimized expression of the transgene. FtOCP2 expression was achieved both in UV-mediated mutant 4 strain, previously selected for efficient transgene expression, and in a background strain previously engineered for constitutive expression of an endogenous β-carotene ketolase, normally poorly expressed in this species, resulting into astaxanthin and other ketocarotenoids accumulation. Recombinant FtOCP2 was successfully localized into the chloroplast. Upon purification it was possible to demonstrate the formation of holoproteins with different xanthophylls and ketocarotenoids bound, including astaxanthin. Moreover, isolated ketocarotenoid-binding FtOCP2 holoproteins conserved their photoconversion properties. Carotenoids bound to FtOCP2 were thus maintained in solution even in absence of organic solvent. The synthetic biology approach herein reported could thus be considered as a novel tool for improving the solubility of ketocarotenoids produced in green algae, by binding to water-soluble carotenoids binding proteins
Heterologous expression of the cyanobacterial fructose-1,6−/sedoheptulose-1,7-bisphosphatase in Chlamydomonas reinhardtii causes increased cell size and biomass productivity in mixotrophic conditions
No full textThe Calvin-Benson-Bassham (CBB) cycle is the metabolic pathway responsible for COQ assimilation in oxygenic photosynthetic organisms. Two key rate-limiting steps in this cycle are catalyzed by the enzymes fructose-1,6bisphosphatase (FBPase) and sedoheptulose-1,7-bisphosphatase (SBPase), making them promising targets for genetic enhancement to improve carbon fixation. A potential strategy involves overexpressing a cyanobacterial dual-function FBP/SBPase, which catalyzes both reactions. Overexpression of this enzyme in tobacco plants or in other plants led to an increase in growth rate and biomass accumulation. Here, the overexpression of the same enzyme was achieved in Chlamydomonas reinhardtii. The recombinant cyanobacterial FBP/SBPase isolated from C. reinhardtii exhibited the expected catalytic activity, being Mg2+ dependent and strongly activated in the presence of a reducing agent. The FBP/SBPase expressing lines exhibited an increased photosynthetic activity at the cell level and decreased production of singlet oxygen upon exposure to high irradiances, suggesting improved capacity to manage high excitation pressure of the photosynthetic apparatus. Increased cell volume was measured in FBP/SBPase-expressing lines under different growth conditions. However, increased biomass productivity was observed only in mixotrophy when light and CO2 were limiting, leading to increased starch, protein, and lipid content on a cellular basis. The observed phenotype caused an increased sedimentation rate in the transformant lines: the expression of FBP/SBPase enzyme could thus be considered as a strategy to improve the cell harvesting process. These findings provide new insights into carbon metabolism in microalgae and could, in the future, support improved biomass accumulation, paving the way for effective domestication and industrial use
Abiotic Stress-Induced Chloroplast and Cytosolic Ca2+ Dynamics in the Green Alga Chlamydomonas reinhardtii
Full text linkCalcium (Ca2+)-dependent signalling plays a well-characterised role in the perception and response mechanisms to environmental stimuli in plant cells. In the context of a constantly changing environment, it is fundamental to understand how crop yield and microalgal biomass productivity are affected by external factors. Ca2+ signalling is known to be important in different physiological processes in microalgae but many of these signal transduction pathways still need to be characterised. Here, compartment-specific Ca2+ dynamics were monitored in Chlamydomonas reinhardtii cells in response to environmental stressors, such as nutrient availability, osmotic stress, temperature fluctuations and carbon sensing. An in vivo single-cell imaging approach was adopted to directly visualise changes of Ca2+ concentrations at the level of specific subcellular compartments, using C. reinhardtii lines expressing a genetically encoded ratiometric Ca2+ indicator. Hyper-osmotic shock caused cytosolic and chloroplast Ca2+ elevations, whereas high temperature and inorganic carbon availability primarily induced Ca2+ transients in the chloroplast. In contrast, hypo-osmotic stress only induced Ca2+ elevations in the cytosol. The results herein reported show that in Chlamydomonas cells compartment-specific Ca2+ transients are closely related to specific external environmental stimuli, providing useful guidance for studying signal transduction mechanisms exploited by microalgae to respond to specific natural conditions
Photoautotrophic cultivation of a Chlamydomonas reinhardtii mutant with zeaxanthin as the sole xanthophyll
No full textBackground Photosynthetic microalgae are known for their sustainable and eco-friendly potential to convert carbon dioxide into valuable products. Nevertheless, the challenge of self-shading due to high cell density has been identified as a drawback, hampering productivity in sustainable photoautotrophic mass cultivation. To address this issue, mutants with altered pigment composition have been proposed to allow a more efficient light diffusion but further study on the role of the different pigments is still needed to correctly engineer this process. Results We here investigated the Chlamydomonas reinhardtii Delta zl mutant with zeaxanthin as the sole xanthophyll. The Delta zl mutant displayed altered pigment composition, characterized by lower chlorophyll content, higher chlorophyll a/b ratio, and lower chlorophyll/carotenoid ratio compared to the wild type (Wt). The Delta zl mutant also exhibited a significant decrease in the light-harvesting complex II/Photosystem II ratio (LHCII/PSII) and the absence of trimeric LHCIIs. This significantly affects the organization and stability of PSII supercomplexes. Consequently, the estimated functional antenna size of PSII in the Delta zl mutant was approximately 60% smaller compared to that of Wt, and reduced PSII activity was evident in this mutant. Notably, the Delta zl mutant showed impaired non-photochemical quenching. However, the Delta zl mutant compensated by exhibiting enhanced cyclic electron flow compared to Wt, seemingly offsetting the impaired PSII functionality. Consequently, the Delta zl mutant achieved significantly higher cell densities than Wt under high-light conditions. Conclusions Our findings highlight significant changes in pigment content and pigment-protein complexes in the Delta zl mutant compared to Wt, resulting in an advantage for high-density photoautotrophic cultivation. This advantage is attributed to the decreased chlorophyll content of the Delta zl mutant, allowing better light penetration. In addition, the accumulated zeaxanthin in the mutant could serve as an antioxidant, offering protection against reactive oxygen species generated by chlorophylls
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
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