1,720,970 research outputs found
The oxygen level determines the fermentation pattern in Kluyveromyces lactis
No full textYeasts belonging to the lineage that underwent whole-genome duplication (WGD) possess a good fermentative potential and can proliferate in the absence of oxygen. In this study, we analyzed the pre-WGD yeast Kluyveromyces lactis and its ability to grow under oxygen-limited conditions. Under these conditions, K. lactis starts to increase the glucose metabolism and accumulates ethanol and glycerol. However, under more limited conditions, the fermentative metabolism decreases, causing a slow growth rate. In contrast, Saccharomyces cerevisiae and Saccharomyces kluyveri in anaerobiosis exhibit almost the same growth rate as in aerobiosis. In this work, we showed that in K. lactis, under oxygen-limited conditions, a decreased expression of RAG1 occurred. The activity of glucose-6-phosphate dehydrogenase also decreased, likely causing a reduced flux in the pentose phosphate pathway. Comparison of related and characterized yeasts suggests that the behavior observed in K. lactis could reflect the lack of an efficient mechanism to maintain a high glycolytic flux and to balance the redox homeostasis under hypoxic conditions. This could be a consequence of a recent specialization of K. lactis toward living in a niche where the ethanol accumulation at high oxygen concentrations and the ability to survive at a low oxygen concentration do not represent an advantage
Fermentative lifestyle in yeasts belonging to the Saccharomyces complex
No full textThe yeast Saccharomyces cerevisiae is characterized by its ability to: (a) degrade glucose or fructose to ethanol, even in the presence of oxygen (Crabtree effect); (b) grow in the absence of oxygen; and (c) generate respiratory-deficient mitochondrial mutants, so-called petites. How unique are these properties among yeasts in the Saccharomyces clade, and what is their origin? Recent progress in genome sequencing has elucidated the phylogenetic relationships among yeasts in the Saccharomyces complex, providing a framework for the understanding of the evolutionary history of several modern traits. In this study, we analyzed over 40 yeasts that reflect over 150 million years of evolutionary history for their ability to ferment, grow in the absence of oxygen, and generate petites. A great majority of isolates exhibited good fermentation ability, suggesting that this trait could already be an intrinsic property of the progenitor yeast. We found that lineages that underwent the whole-genome duplication, in general, exhibit a fermentative lifestyle, the Crabtree effect, and the ability to grow without oxygen, and can generate stable petite mutants. Some of the pre-genome duplication lineages also exhibit some of these traits, but a majority of the tested species are petite-negative, and show a reduced Crabtree effect and a reduced ability to grow in the absence of oxygen. It could be that the ability to accumulate ethanol in the presence of oxygen, a gradual independence from oxygen and/or the ability to generate petites were developed later in several lineages. However, these traits have been combined and developed to perfection only in the lineage that underwent the whole-genome duplication and led to the modern Saccharomyces cerevisiae yeast
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
How did Saccharomyces evolve to become a good brewer?
No full textBrewing and wine production are among the oldest technologies and their products are almost indispensable in our lives. The central biological agents of beer and wine fermentation are yeasts belonging to the genus Saccharomyces, which can accumulate ethanol. Recent advances in comparative genomics and bioinformatics have made it possible to elucidate when and why yeasts produce ethanol in high concentrations, and how this remarkable trait originated and developed during their evolutionary history. Two research groups have shed light on the origin of the genes encoding alcohol dehydrogenase and the process of ethanol accumulation in Saccharomyces cerevisiae
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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