1,720,996 research outputs found
Candida freyschussii: an oleaginous yeast producing lipids from glycerol
No full textA surplus of glycerol is obtained from biodiesel manufacturing and represents a waste product whose applications are lacking. Thus, the use of glycerol as substrate for fermentation processes yielding valuable products is very attractive. In this study, the utilization of glycerol as a growth substrate for the cultivation of oleaginous yeasts was explored with the aim to produce microbial oils. Forty strains of environmental non-conventional yeasts belonging to 19 different species were screened for the ability to grow on glycerol and produce intracellular lipids in a medium containing an excess of this carbon source (C:N = 48:1). Three strains, belonging to the species Candida freyschussii, Pichia farinosa, and Saccharomyces spencerorum, depleted 40 g/L glycerol within 120 h and produced intracellular lipids. C. freyschussii yielded the highest amounts, lipids accounting for the 33 % of biomass on dry basis. 1H-NMR analysis revealed that the lipid extract did not contain detectable free fatty acids and was composed mostly of triacylglycerols. Lipid composition, determined by GC-MS analysis, was similar to plant oils, and may be optimal feedstock for biodiesel production, being dominated by monounsaturated C16 and C18. As in other oleaginous yeasts, lipid production by C. freyschussii sp. increased with the increase of the C:N ratio of the medium, but growth was inhibited at glycerol concentrations higher than 40 g/L. As a result, lipid production was the highest with 40 g/L glycerol, yielding 4.7 g/L lipids, with a mean volumetric productivity of 0.15 g/L/h. In order to prevent growth inhibition over 40 g/L glycerol and extend the lipogenic phase, different fed-batch strategies were tried. The best performing processes took advantage from the feeding with concentrated media exhibiting the same C:N ratio of the basal medium, leading to very productive high cell density cultures. With the continuous feeding of 20X-concentrated medium, 29 g/L lipids (i.e. the 32 % of biomass) were obtained in 100 h of cultivation, with a mean volumetric productivity of 0.30 g/L/h. The values herein reported are among the highest yield and productivity values ever obtained for fermentative processes exploiting oleaginous fungi to produce lipids from glycerol. Therefore, C. freyschussii could be considered as an interesting microorganism to convert glycerol into microbial oils for biofuel industr
1H NMR of native and azide-inhibited laccase from Rhus vernicifera
No full textThe H NMR spectra of the fully oxidized Rhus vernicifera laccase and of its 1:1 and 2:1 azide adducts are reported for the first time.These spectra, which are the first so far reported for a multi copper oxidase, contain a number of broad hyperfine-shifted resonances in thehigh frequency region of the spectrum, which are attributed to the metal binding residues of the mononuclear T1 center. The differencesbetween the patterns of the hyperfine resonances of the free enzyme and its azide derivatives suggest that the alterations in the structuralproperties of the T3 site induced by the binding of the first azide molecule induce a limited alteration of the spin density distribution over1 the T1 copper ligands. Overall, these data demonstrate that H NMR can be fruitfully applied to characterize the electronic properties ofthe metal sites of blue oxidases at room temperature
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
Dietary Isoflavones and Intestinal Microbiota: Metabolism and Transformation into Bioactive Compounds
Full text linkEdible plants provide the human with hundreds of non-nutritional phytochemicals which are recognized as beneficial, such as isoflavones. Likewise other polyphenols, isoflavones may undergo extensive transformations during passage through human digestive tract, especially in the colon, where members of the complex commensal microbiota are capable to carry out synergistically a broad range of metabolic transformations affecting the fate and the biological activity of phytochemicals. Diverse bacterial species occurring in the large intestine hydrolyze the glucose conjugated forms of isoflavones, releasing the corresponding aglycones, which may undergo further microbial conversions (especially reductions) giving rise to a wide spectrum of isoflavone-derived compounds. The end-products of microbial transformations are subjected to substantial person-to-person variation, reflecting the impact of the colonic microbiota, since intestinal bacteria may greatly increase or compromise the biological activity of dietary isoflavones. In fact, certain reduction products (e.g. S-equol) possess superior antioxidant and estrogen-like activities, while others are precursors for C-ring cleavage and lead to isoflavone degradation. Extensive research has been performed to characterize the intestinal bacteria which are responsible for isoflavones transformations. In particular, many efforts are being carried out to identify single bacteria that convert the major soy isoflavone daidzein into S-equol, in the perspective to enrich soy products with such a valuable isoflavone-derived metabolite. Besides, diverse bacteria which are capable of deglycosylation, demethylation, and various reduction reactions are increasingly being identified. Nonetheless, only bifidobacteria and lactobacilli, which produce β-glucosidase that hydrolyze isoflavone glycosides into the corresponding aglycones, are currently exploited to improve the biological activity of soymilk
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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