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Expression level and genomic organization of the sulphite efflux gene SSU1 in two enological strains of Saccharomyces cerevisiae
No full textA sulphite-inducible form of the sulphite efflux gene SSU1 in a Saccharomyces cerevisiae wine yeast
No full textSulphite is widely used as a preservative in foods and beverages for its antimicrobial and antioxidant activities, particularly in winemaking where SO(2) is frequently added. Thus, sulphite resistance mechanisms have been extensively studied in the fermenting yeast Saccharomyces cerevisiae. Sulphite detoxification, involving a plasma membrane protein encoded by the SSU1 gene, is the most efficient resistance mechanism in S. cerevisiae. In this study, we characterized the unusual expression pattern of SSU1 in the wine strain 71B. We provide, for the first time, evidence of SSU1 induction by sulphite. The study of SSU1 expression during fermentation and in different growth conditions showed that sulphite is the main regulator of SSU1 expression, explaining its specific pattern. Combining analyses of gene expression and growth behaviour in response to sulphite, we found that 71B displayed unique behavioural patterns in response to sulphite pre-adaptation that may be explained by changes in SSU1 expression. Examination of the genomic organization of the SSU1 locus and sequencing of the region revealed three different alleles in 71B, two of which corresponded to translocated VIII-XVI forms. The lack of differences between promoter regions suggests that this inducible SSU1 expression pattern is due to modification of regulatory/signalling pathways
Comparison of wine yeasts transcriptome during alcoholic fermentation shows differences in sulphur metabolism
No full textWine yeasts are subjected to stress conditions that change continuously during a dynamic process such
as alcoholic fermentation. Due to utility of DNA chips to investigate how gene expression changes within
biological processes, several attempts have been made on wine yeasts (Perez-Ortin et al., 2002). In this
work microarray technology has been used to investigate metabolic shifts at transcriptional level of yeast
strains differing for fermentation performances and production of secondary compounds.
In particular, a genome-wide expression analysis was performed comparing two commercial yeasts
(Lalvin EC1118 and 71B) under oenological conditions (50 mg/L of sulphites added at the beginning of
vinification). As expected, most of the upregulated genes are stress responsive elements, chaperonins or
heat shock proteins (data not shown). The most interesting finding from microarray data regards the
different gene expression of sulphur metabolism pathway and sulphite resistance. In particular, sulphur
amino acids biosynthesis was up-regulated in 71B; sulphite uptake/reduction pathway seemed also to be
induced. The sulphite efflux permease Ssu1, involved in sulphite resistance (Park & Bakalinsky, 2000)
was also highly expressed. This is consistent with the evidence that yeast can cope with sulphite stress
by several mechanisms, such as acetaldehyde production, up-regulation of sulphite uptake and reduction
and sulphite efflux from the cell by the membrane pump Ssu1 (Casalone et al., 1992). Since sulphites are
widely used preservatives in foods and beverages, these metabolic pathways have been studied for many
years because of their technological interest: their crosslink has been demonstrated and protein involved
have been identified; this notwithstanding, their regulation is still unclear (Aranda et al., 2006) especially
during alcoholic fermentation. For these reasons a further investigation on microarray data concerning
sulphur metabolism was carried out. Time course Real-time PCR experiments were performed for
confirming previous evidences: expression level of SSU1 was tested, together with its transcriptional
regulator FZF1 and two genes belonging to sulphured amino acids biosynthesis pathway (MET10 and
MET17).
These expression data pointed out that in 71B strain SSU1 is activated during stationary phase, whereas
previous works demonstrated its constitutive expression. This is the first report of a regulated SSU1 gene
expression in Saccharomyces cerevisiae. Therefore its activation mechanism was further investigated by
Real-Time PCR gene expression analysis for determining whether the induction is FZF1 dependent in the
two strains. Moreover, sulphite resistance assays were carried out in synthetic must to evaluate
physiological effects of the different activation mechanisms. Furthermore, PCR primers were designed to
explore the organization SSU1 locus and its position in the genome, since this gene has been previously
described as a marker of genome polymorphism and genetic evolution of wine yeasts (Aa et al., 2006).
At the moment, SSU1 alleles distribution is under investigation by genetic comparison of the same locus
in other wine strains; this work is part of a wider project of genetic characterization of autochthonous
yeasts strain that will lead to the complete sequencing of four wine yeast genomes
The keystone role of FLO5 gene in triggering flocculation of a Saccharomyces cerevisiae wine strain
No full textGoing Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Get PDFWe 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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