1,720,968 research outputs found
Ecotoxicological effects of Graphene-Based Materials
No full textIn the recent years, the rapid advancement in the field of nanomaterials has increased their development and consequently their production and commercialization. Among nanomaterials, the carbon-based ones are the most widely researched because of their potential on the most diverse fields, with a predominant role occupied by Graphene-Based Materials (GBMs).
Graphene is a two-dimensional, single layer sheet of carbon atoms organized in a honeycombed network with six-membered rings. Since its discovery, the attention of researchers was focused on its unique and exceptional properties, such as mechanical stiffness, strength, elasticity, very high electrical and thermal conductivity, which led to the development of numerous applications. The huge investments brought to an incredible advancement in the industrial field, unfortunately accompanied by a slower progress in the understanding of the impact on human health and the environment.
So far, the effects of GBMs have been evaluated mostly on animal and bacterial model organisms, suggesting that GBMs toxicity is dependent on various physiochemical properties such as shape, size, oxidative state and presence of functional groups.
The aim of this PhD project was to assess the ecotoxicological effects of two GBMs, few-layers graphene (FLG) and graphene oxide (GO), on aeroterrestrial green microalgae. These GBMs were selected as reference material by the Working Package 4, Health and Environment, in the framework of the European Project Graphene-Flagship.
Short-term exposure (30 and 60 minutes) effects were evaluated on the algal species Coccomyxa subellipsoidea and Trebouxia gelatinosa in terms of membrane permeability with the quantification of potassium leakage by inductively coupled plasma-atomic emission spectrometry.
Long-term exposure (4 weeks) effects were evaluated on Apatococcus lobatus, Chlorella vulgaris, C. subellipsoidea and T. gelatinosa through chlorophyll a fluorescence measurements (Fv/Fm parameter) and quantifications of the total photosynthetic pigments content.
After a short-term exposure of GBMs on the alga T. gelatinosa, internalization was investigated with confocal laser scan microscopy. Potential oxidative effects of GBMs were then studied analyzing the efficiency of the photosystems through measurements of chlorophyll a fluorescence emission (Fv/Fm parameter), changes of gene expression of eight genes of interest through quantitative Real-Time PCR, and quantification of HSP70 protein through western blot.
According to the final results obtained, no negative effects were observed for either FLG or GO, in both short- and long-term exposures. Internalization was not clearly observed, even though the FLG exposure after 30 minutes induced the downregulation of the gene coding for HSP70 protein. These results supported the hypothesis that a harmless interaction occurred between GBMs and algae at cell wall – plasma membrane level, involving potentially a yet unknown signaling pathway
Lichens and the omics
No full textThe massive development of tools, such as the omics technologies, which allow scientists to look at biological processes on large scales, is a fundamental component of the so-called Systems Biology. This subject studies biological systems in order to achieve a comprehensive and integrated view of their biology (Ideker et al., 2001). For these aims, the complementation of different disciplines such as molecular biology, biochemistry, and
bioinformatics is of key importance (Graves & Haystead, 2002). The main purpose of omics is the quantification and characterization of the
complete set of the biological molecules which shape structures, functions and dynamics of cells and organisms (Simò et al., 2014). The -ome suffix refers to the whole composition of groups of molecules like nucleic acids, proteins and metabolites at a given time or place: genomics is the study of the genome, transcriptomics is the study of the total RNA, proteomics is the study of the entire set of proteins and metabolomics is the study of the set of low molecular weight metabolites (Smith et al., 2005).
When the analysis is referred to genes, transcripts, proteins or metabolites recovered from environmental samples, which may contain many different
organisms, the recently introduced term meta-omics is used (Valles-Colomer et al., 2016). For instance, metagenomics is defined as the analysis of all the genomes contained in an environmental sample (Thomas et al., 2012). Here we offer an overview of these up-to date tools and present what has
already been done in the study of the lichen symbiosis
The desiccation-related proteins in Trebouxia: a family to discover
No full textThe transcriptome of Trebouxia gelatinosa, belonging to one of the most common genus of lichen photobionts, gave an interesting overview of the mechanisms that underlay the desiccation tolerance in this species, regarding structure, physiology and biochemistry. The analysis of the annotated transcripts of both the dehydrated and rehydrated cultured alga revealed interesting and peculiar features of this poikilohydric organism. In particular the presence of a large number of desiccation-related proteins (DRPs) was highlighted, most of them affected by at least one of the two treatments. The DRP family has been first described in the resurrection plants, then also in other plants and in green algae. In T. gelatinosa 13 sequences are classified as desiccation-related proteins. These identified sequences, clearly pertaining to the same multigenic family, are usually characterized by a c.170 a long ferritinlike domain (PF13668), followed by a C-terminal region of variable length without known annotated domains. Nine out of the 13 annotated transcripts were significantly responsive to dehydration and/or rehydration by either being up- or down-regulated. Because the number of DRP genes predicted in the analysed genomes of vascular plants is generally low - ranging from 0 to 5 - this gene family seems to have undergone an expansion in T. gelatinosa. Although the exact role of DRPs in the dehydration/rehydration processes is still unclear, their massive response, both in terms of gene number and fold change, to the hydric status of T. gelatinosa points out that they are prominent players in drought tolerance not only in resurrection plants but also in lichen photobionts. Our study aims at expanding the knowledge of the DRP family in rebouxia, in order to understand the role of these proteins and their expansion in desiccation tolerance and in relation to lichen symbiosis
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
Potential horizontal gene transfer (HGT) of Desiccation Related Proteins in the lichen photobiont Trebouxia gelatinosa
No full textDesiccation Related Proteins (DRPs), firstly described in desiccation tolerant plants, are present also in several unrelated bacterial and algal groups. Although their role is still unknown, their presence seems
to confer an increased desiccation tolerance in some extremophile bacteria, including the Deinococcus/Thermus phylum. In this study we describe our findings on the DRPs present in the transcriptome of
Trebouxia gelatinosa, a member of the most common lichen-forming genus of green algae. Thirteen sequences were classified as DRPs: they are characterized by a c.170 aa long ferritin-like domain (PF13668), followed by one or two domains of unknown function. This gene family has undergone relevant expansion in T. gelatinosa: in the majority of green algae DRPs are present in few copies or they are completely absent. Further, their diversification finds no parallelism in other desiccation tolerant organisms investigated so far. Bayesian phylogenetic inference pointed out that DRPs of green algae are unlikely to be orthologous to those found in Embryophyta. Conversely, they share an unexpected sequence similarity to DRPs found in bacteria. This result led us to consider a bacterial origin for Trebouxia DRP genes, which may have ancestrally been acquired by horizontal gene transfer (HGT) from lichen-associated bacteria
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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