1,720,958 research outputs found
Role of glycerol transport system and Hog1 in yeast cell survival during anhydrobiosis
No full textŠī darba mērķis bija izpētīt glicerīna transportsistēmu un Hog1p iespējamo lomu raugu šūnu dzīvotspējas saglabāšanā anhidrobiozes stāvoklī. Lai sasniegtu šo mērķi, izmantoja raugu Saccharomyces cerevisiae BY4741 un tā izogēnos celmus, kuriem trūka viens vai vairāki gēni, kuri ir atbildīgi par glicerīna transportiera Stl1p, glicerīna eksporta kanāla Fps1p un regulatorās Hog1p MAP kināzes ekspresiju raugu šūnās.
Darbam bija izvirzīti sekojošie uzdevumi: izpētīt S. cerevisiae BY4741 spējas pāriet anhidrobiozes stāvoklī; novērtēt glicerīna transportsistēmu Stl1p un Fps1p, ka arī Hog1p ietekmi uz raugu šūnu rezistenci pret dehidratāciju; izpētīt raugu spējas pārdzīvot osmotisko stresu un šīs iedarbības ietekmi uz šūnu spējām pārdzīvot dehidratācijas stresu.
Visus raugu celmus varēja izmantot anhidrobiozes pētījumiem; tiem nekonstatēja izmaiņas šūnu morfoloģijā, sasniedzot stacionāro augšanas fāzi ar 98 - 100% dzīvotspēju. Izejas celms S. cerevisiae BY4741 var saglabāt 45% dzīvotspēju pēc dehidratācijas, ja mitrums ir 10 - 11%. Pirmo reizi atklāja, ka glicerīna transportierim Stl1p ir nozīmīga loma raugu šūnu dzīvotspējas saglabāšanā anhidrobiozes stāvoklī. Hog1p kināzes trūkums raugu šūnās būtiski samazina to izturību pret dehidratācijas iedarbību. Bet rauga celms ar glicerīna eksporta kanāla Fps1p delēciju pēc dehidratācijas saglabāja šūnu dzīvotspēju līdzīgu izejas celmam. Rauga mutants hog1Δstl1Δfps1Δ nav spējīgs pārdzīvot dehidratāciju. Meklējot iespējamo skaidrojumu iegūtajiem datiem, novēroja, ka raugu mutantu zemā dzīvotspēja pēc dehidratācijas korelēja ar zemo trehalozes daudzumu šūnās pirms dehidratācijas. Papildus konstatēja, ka šūnu reaktivācija no anhidrobiozes stāvokļa, izmantojot lēno rehidratāciju, būtiski paaugstina šūnu dzīvotspēju. Atklāja, ka aizvietojot glikozi kā oglekļa avotu ar glicerīnu, visu raugu celmu rezistence pret dehidratāciju nozīmīgi paaugstinājās. Visi raugu celmi bija spējīgi pārdzīvot osmotisko stresu, kas saistīts ar biomasas inkubāciju šķīdumos ar 1 M NaCl, KCl, glicerīnu un 2 M sorbitolu. Pēc šūnu pakļaušanas šādai iedarbībai, visiem raugu celmiem paaugstinājās šūnu dzīvotspēja pēc dehidratācijas, it īpaši paraugiem, inkubētiem glicerīna un sorbitola šķīdumos.
Maģistra darbā ir 64 lappuses, 19 attēli, 13 tabulas un 97 informācijas avoti.The aim of this research was to study the possible role of glycerol transport systems and Hog1p in the maintenance of yeast cell survival in the state of anhydrobiosis. To achieve the goal of this work the yeast Saccharomyces cerevisiae BY4741 and it’s isogenic strains lacking one or more genes encoding the Stl1p glycerol importer, the Fps1p glycerol exporter and regulatory Hog1 MAP kinase were used.
The following tasks were set up: to investigate the ability of S. cerevisiae BY4741 to be transferred into the state of anhydrobiosis; to evaluate the influence of Stl1p and Fps1p glycerol transport systems and Hog1p on the yeast cell resistance to dehydration; to study the abilities of yeasts to survive under the osmotic stress and the influence of this treatment on the cells resistance to dehydration.
All yeast strains were used for the investigations of anhydrobiosis; the changes in the morphology of cells were not obtained during the stationary phase of growth and viability of all strains was about 98 - 100%. Wild strain S. cerevisiae BY4741 maintains 45% of viable cells after dehydration if humidity of cells is 10 - 11%. For the first time it was shown that Stl1p glycerol transporter has a crucial role in the maintenance of cells viability during the state of anhydrobiosis. The deletion of Hog1p kinase significantly decreases cells resistance to dehydration. But the yeast mutant with deletion of Fps1p glycerol exporter had the same viability of cells after dehydration as the wild type. Yeast mutant hog1Δstl1Δfps1Δ is not able to survive during dehydration. To find out the possible interpretation of acquired results, it was obtained, that the low viability of yeast mutants during dehydration correlated with the low content of trehalose in the intact cells before dehydration treatment. In addition it was established that reactivation of cells from the state of anhydrobiosis using the slow rehydration significantly increases the viability of cells. It was shown, that replacement of glucose with glycerol in the growth medium can improve the resistance of cells to dehydration. All yeast strains survived during the osmotic stress connected with the incubation of biomass in solutions with 1 M NaCl, KCl, glycerol and 2 M sorbitol. After treatment with osmotic stress viability of cells after dehydration increased, especially it was obtained in samples treated with glycerol and sorbitol.
The research work contains 64 pages, 19 figures, 13 tables and 97 literature sources
The characterization of yeast maltose transport systems in the influence of dehydration
No full textŠī darba pētījuma mērķis bija izpētīt raugu šūnu citoplazmatiskās membrānas maltozes transportsistēmu funkcionalās izmaiņas dehidratācijas un sekojošās rehidratācijas ietekmē divos raugu celmos Saccharomyces cerevisiae 14 un Saccharomyces cerevisiae L-73. Ir zināms, ka maltoze raugu šūnās tiek transportēta ar specifisko proteīnu palīdzību un transportieru ekspresija un darbība ir saistīta ar maltozes klātbūtni apkārtējā vidē. Izvirzītā mērķa sasniegšanai izmantoja divas metodes: maltozes transportsistēmu izmaiņas novērtēja pēc maltozei līdzīga substrāta p-nitrofenil-α-D-glikopiranozīda (pNPαG) transporta un pēc maltozes patēriņa ar 3,5-Dinitrosalicilskābes palīdzību.The aim of this research was to study the functional changes of maltose transportsystems in the influence of dehydration and following rehydration in two yeast strains Saccharomyces cerevisiae 14 and Saccharomyces cerevisiae L-73. The maltose transporters were chosen for investigation because their expression and functioning in yeasts depend on maltose presence in the medium.To achieve the goal of this work two methods were used: to study the transport of p-nitrophenyl-α-D-glucopyranoside (pNPαG) as analogous substrate to maltose and to study the consumption of maltose measured by 3,5-Dinitrosalicylic acid
Effects of selenium on yeast resistance to some stressors
No full textŠī darba mērķis bija novērtēt selēna ietekmi uz rauga Saccharomyces cerevisiae izturību pret dažādiem stresa faktoriem. Darbam bija izvirzīti sekojošie uzdevumi: noteikt vai selēna izvēlētās koncentrācijas ietekmē S. cerevisiae 14 un S. cerevisiae 77 rauga celmu šūnu augšanu; salīdzināt divu raugu celmu S. cerevisae 14 un S. cerevisiae 77 izturību pret dehidratācijas/rehidratācijas stresu; izpētīt kā kultivēšana barotnēs ar dažādām selēna koncentrācijām ietekmē S. cerevisiae 14 un S. cerevisiae 77 spējas pāriet anhidrobiozes stāvoklī un reaktivāciju no tā; noskaidrot vai ar selēnu bagātinātās barotnēs kultivētām rauga šūnām ir augstāka izturība pret oksidatīvo hiperosmotisko stresu un siltumšoku. Tika konstatēts, ka selēna izvēlētās koncentrācijas neietekmēja S. cerevisiae 14 un S. cerevisiae 77 celmu augšanu. Dehidratēto šūnu dzīvotspēja bez papildus pievienota selēna S. cerevisiae 14 bija 37,7 ± 5,7 % un S. cerevisiae 77 50,4 ± 5,0 %. Ja rauga celms ir semi-rezistents (S. cerevisiae 14), tad salīdzinot ar kontroli 5 µg/ml un 10 µg/ml koncentrācijām, nebija būtiskas atšķirības, toties būtiska dzīvotspējas atšķirību novēroja pie 0,5 µg/ml, 1 µg/ml selēna koncentrācijām. Savukārt, ja celms ir izturīgs pret dehidratācijas stresu (S. cerevisiae 77), tad selēns koncentrācijās 0,5 – 5 µg/ml neuzlaboja/neietekmēja šūnu izturību pret dehidratāciju. Savukārt visaugstākā selēna koncentrācija samazināja šūnu spēju izturēt dehidratācijas stresu. Tātad ja, celms ir jutīgāks pret dehidratācijas stresu, tad neliels daudzums selēna, kas ir uzņemts šūnās dod papildus priekšrocības šo stresu izturēt. Savukārt, jo vairāk selēns ir uzkrājies rauga šūnās, tas dod pretēju efektu. Pārbaudot plazmatiskās membrānas caurlaidību pēc ātrās rehidratācijas būtiskas izmaiņas netika novērotas nevienam no S. cerevisiae celmiem, toties pēc lēnās rehidratācijas S. cerevisiae 14 ar selēna koncentrāciju 5 µg/ml un 10 µg/ml membrānas caurlaidība būtiski paaugstinājās. Izmantotās selēna koncentrācijas S. cerevisiae 77 celma plazmatiskās membrānas caurlaidību pēc rehidratācijas neietekmēja. Rezultāti parādīja, ka selēns nepalīdz vai nepasliktina apstākļus šūnām atsevišķu stresu ietekmē, bet tam ir nozīme, kad uz šūnām iedarbojas ar daudzfaktoriālu stresu, kā dehidratācija.The aim of this research was to evaluate the effect of selenium on the resistance of the yeast Saccharomyces cerevisiae to various stress factors. The following tasks were set for this research: to determine whether the selected concentrations of selenium affect the growth of cells of S. cerevisiae 14 and S. cerevisiae 77 yeast strains; to compare the resistance of two yeast strains S. cerevisae 14 and S. cerevisiae 77 to dehydration/rehydration stress; to investigate how cultivation in media with different concentrations of selenium affects the ability of S. cerevisiae 14 and S. cerevisiae 77 to go into anhydrobiosis state and reactivation from this state; to find out whether yeast cells cultured in selenium-enriched media have a higher resistance to oxidative hyperosmotic stress and heat shock. It was found that the selected concentrations of selenium did not affect the growth of S. cerevisiae 14 and S. cerevisiae 77 strains. The viability of dehydrated cells without additional selenium in S. cerevisiae 14 was 37.7 ± 5.7 % and in S. cerevisiae 77 50.4 ± 5.0 %. If the yeast strain is semi-resistant (S. cerevisiae 14), there was no significant difference compared to the control and 5 µg/ml and 10 µg/ml concentrations of selenium, but a significant difference in viability was observed between 0.5 µg /ml and 1 µg/ml concentrations. On the other hand, if the strain is resistant to dehydration stress (S. cerevisiae 77), then selenium in concentrations of 0.5 - 5 µg/ml did not improve/didn`t affect the resistance of cells to dehydration. However, the highest concentration of selenium reduced the ability of cells to withstand dehydration stress. So if the strain is more sensitive to dehydration stress, then a small amount of selenium that has been accumulated in the cells gives an additional advantage to withstand this stress. On the other hand, if too much selenium has accumulated in the yeast cells, then it gives the opposite effect. When examining the permeability of the cell membrane after rapid rehydration, no significant changes were observed for any of the S. cerevisiae strains, however, after slow rehydration, S. cerevisiae 14 with selenium concentrations of 5 µg/ml and 10 µg/ml significantly increased membrane permeability. The applied selenium concentrations did not affect the permeability of the plasma membrane of S. cerevisiae 77 strain after rehydration. The results showed that selenium does not help or worsen the conditions of the cells under the influence of a single factor stress, but it plays a role when the cells are affected by a multifactorial stress, such as dehydration
Going 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
Volatilomic signatures of different strains of Helicobacter pylori
Get PDFBackground: Helicobacter pylori (H. pylori) infection is the most extensively studied risk factor for gastric cancer. As with any bacteria, H. pylori will release distinctive odors that result from an emission of volatile metabolic byproducts in unique combinations and proportions. Effectively capturing and identifying these volatiles can pave the way for the development of innovative and non-invasive diagnostic methods for determining infection. Here we characterize the H. pylori volatilomic signature, pinpoint potential biomarkers of its presence, and evaluate the variability of volatilomic signatures between different H. pylori isolates. Materials and Methods: Using needle trap extraction, volatiles in the headspace above H. pylori cultures were collected and, following thermal desorption at 290°C in a splitless mode, were analyzed using gas chromatography–mass spectrometry. The resulting volatilomic signatures of H. pylori cultures were compared to those obtained from an analysis of the volatiles in the headspace above the cultivating medium only. Results: Amongst the volatiles detected, 21 showed consistent differences between the bacteria cultures and the cultivation medium, with 11 compounds being elevated and 10 showing decreased levels in the culture's headspace. The 11 elevated volatiles are four ketones (2-pentanone, 5-methyl-3-heptanone, 2-heptanone, and 2-nonanone), three alcohols (2-methyl-1-propanol, 3-methyl-1-butanol, and 1 butanol), one aromatic (styrene), one aldehyde (2-ethyl-hexanal), one hydrocarbon (noctane), and one sulfur compound (dimethyl disulfide). The 10 volatiles with lower levels in the headspace of the cultures are four aldehydes (2-methylpropanal, benzaldehyde, 3-methylbutanal, and butanal), two heterocyclic compounds (2-ethylfuran and 2-pentylfuran), one ketone (2-butanone), one aromatic (benzene), one alcohol (2-butanol) and bromodichloromethane. Of the volatile species showing increased levels, the highest emissions are found to be for 3-methyl-1-butanol, 1-butanol and dimethyl disulfide. Qualitative variations in their emissions from the different isolates was observed. Conclusions: The volatiles emitted by H. pylori provide a characteristic volatilome signature that has the potential of being developed as a tool for monitoring infections caused by this pathogen. Furthermore, using the volatilome signature, we are able to differentiate different isolates of H. pylori. However, the volatiles also represent potential confounders for the recognition of gastric cancer volatile markers.Fil: Vangravs, Reinis. Universidad de Letonia; LetoniaFil: Mezmale, Linda. Universidad de Letonia; LetoniaFil: Slefarska Wolak, Daria. University of Innsbruck; AustriaFil: Dauss, Edgars. Universidad de Letonia; LetoniaFil: Ager, Clemens. Universidad de Letonia; LetoniaFil: Corvalan, Alejandro H.. Pontificia Universidad Católica de Chile; ChileFil: Fernandez, Elmer Andres. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba; Argentina. Fundación para el Progreso de la Medicina; ArgentinaFil: Mayhew, Chris A.. Universidad de Innsbruck; AustriaFil: Leja, Marcis. Universidad de Letonia; LetoniaFil: Mochalski, Pawel. Universidad de Innsbruck; Austri
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
- …
