1,720,964 research outputs found
Morphological traits in nitrogen fixing heterocytous cyanobacteria: possible links between morphology and eco-physiology
Get PDFHeterocytous cyanobacteria are able to fix nitrogen (in heterocytes) and to produce dormant cells (akinetes). Heterocyte and akinete shape, size, and relative position have taxonomical relevance and possibly ecological value too. We collected—from literature and nature—and compared morphological data on vegetative cells, heterocytes, and akinetes across four genera taxonomically separated from Anabaena. In average, heterocyte size doubled that of vegetative cells—probably because of extra cell wall deposition. Heterocyte morphology was remarkably similar across genera, both in size and shape (spherical). The latter may decrease oxygen diffusion from adjoining vegetative cells. Akinetes were huge (one order of magnitude bigger) compared to vegetative cells, probably because of its massive genome replication, extra deposition of wall layers, allocation of storage and number of vegetative cells fused during akinete differentiation. Akinete shape was mostly cylindrical, or oval, but rarely spherical. In line with molecular data, we found morphological differences between Anabaena (non-aerotopated, soil or benthic) and Dolichospermum (aerotopated, planktonic), including vegetative cell size, and akinete size, shape, and relative position to the heterocyte. Differences may relate to adaptations to their contrasting environments (benthic versus planktic). Further research is needed to generalize our results to other heterocytous genera.Fil: de Tezanos Pinto, Paula. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Ecología, Genética y Evolución de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Ecología, Genética y Evolución de Buenos Aires; ArgentinaFil: Kust, Andreja. University of South Bohemia; República ChecaFil: Devercelli, Melina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto Nacional de Limnología. Universidad Nacional del Litoral. Instituto Nacional de Limnología; ArgentinaFil: Kozlíková Zapomělová, Eliška. University of South Bohemia; República Chec
Polyphasic analysis and secondary metabolite patterns in nostocacean cyanobacteria with different life strategies
No full textUnbranched heterocytous cyanobacteria exhibit complex filament and colony architectures and variable life strategies from symbionts to free living planktic and non-planktic species. They are counted among microbial groups showing an extensive production of secondary metabolites, resulting in both pharmaceutically important and toxic compounds. The main focus of this thesis is to broaden our knowledge on bioactive secondary metabolite potential in this widespread group of cyanobacteria. An effective combination of methods including whole genome sequencing, bioinformatic analysis, and analytical chemistry techniques are applied to accomplish this task. The discrepancies in distribution of various classes of compounds among ecological groups defined by different life strategies are discussed. Additionally, the thesis endeavours to test multidisciplinary approaches to tackle taxonomic assignments of unresolved unbranched heterocytous cyanobacteria using morphological, phylogenetic and ecophysiological methods, including a meta-analysis of morphological traits
Cyanochelins, an Overlooked Class of Widely Distributed Cyanobacterial Siderophores, Discovered by Silent Gene Cluster Awakening
No full textCyanobacteria require iron for growth and often inhabit iron-limited habitats, yet only a few siderophores are known to be produced by them. We report that cyanobacterial genomes frequently encode polyketide synthase (PKS)/nonribosomal peptide synthetase (NRPS) biosynthetic pathways for synthesis of lipopeptides featuring b-hydroxyaspartate (b-OH-Asp), a residue known to be involved in iron chelation. Iron starvation triggered the synthesis of b-OH-Asp lipopeptides in the cyanobacteria Rivularia sp. strain PCC 7116, Leptolyngbya sp. strain NIES-3755, and Rubidibacter lacunae strain KORDI 51-2. The induced compounds were confirmed to bind iron by mass spectrometry (MS) and were capable of Fe31 to Fe21 photoreduction, accompanied by their cleavage, when exposed to sunlight. The siderophore from Rivularia, named cyanochelin A, was structurally characterized by MS and nuclear magnetic resonance (NMR) and found to contain a hydrophobic tail bound to phenolate and oxazole moieties followed by five amino acids, including two modified aspartate residues for iron chelation. Phylogenomic analysis revealed 26 additional cyanochelin-like gene clusters across a broad range of cyanobacterial lineages. Our data suggest that cyanochelins and related compounds are widespread b-OH-Asp-featuring cyanobacterial siderophores produced by phylogenetically distant species upon iron starvation. Production of photolabile siderophores by phototrophic cyanobacteria raises questions about whether the compounds facilitate iron monopolization by the producer or, rather, provide Fe21 for the whole microbial community via photoreduction. IMPORTANCE All living organisms depend on iron as an essential cofactor for indispensable enzymes. However, the sources of bioavailable iron are often limited. To face this problem, microorganisms synthesize low-molecular-weight metabolites capable of iron scavenging, i.e., the siderophores. Although cyanobacteria inhabit the majority of the Earth’s ecosystems, their repertoire of known siderophores is remarkably poor. Their genomes are known to harbor a rich variety of gene clusters with unknown function. Here, we report the awakening of a widely distributed class of silent gene clusters by iron starvation to yield cyanochelins, b-hydroxy aspartate lipopeptides involved in iron acquisition. Our results expand the limited arsenal of known cyanobacterial siderophores and propose products with ecological function for a number of previously orphan gene clusters
POLYPHASIC CHARACTERIZATION OF Anabaena spp. (CYANOBACTERIA)FROM SOKOLOC AREA, CZECH REPUBLIC
No full textCilj ovog rada je polifaznim pristupom, tj. kombinacijom morfološkog i molekularnog pristupa načiniti karakterizaciju 16 sojeva bentonskih iperifitonskih vrsta Anabaena spp. sakupljenih tijekom 2010. i 2011. godine na osam različitihlokaliteta iz areala Sokolov (u sjevernom djelu Češke Republike). Na temelju dobivenih rezultata morfoloških svojstava (dimenzija vegetativnih stanica, heterocita i akineta) sojevi su podijeljeni u pet morfoloških skupina (morfoloških tipova). Odabrani sojevi koji predstavljaju odvojene filogenetske klastere bazirane na 16S rRNA genu, podvrgnuti su eksperimentu s različitim vrijednostima temperature i intenziteta svjetlosti gdje nisu pokazali značajne promjene u dimenzijama vegetativnih stanica, heterocita i akineta. Za iste sojeve eksperimentalno je određen optimalan rast, koji je za tri soja (04VR10L1, 11VR10JH,01DRMII10) bio sličan, dok se za soj 12SO10CI bitno razlikovao. Za većinu sojeva,grupiranje sojeva prema 16S rRNA genu odgovaralo je grupiranju prema morfološkim svojstvima. Prema dobivenim rezultatima, možemo zaključiti da je bentonski i perifitonski rod Anabaena filogenetički heterogen. Potrebna su daljnja istraživanja s većim brojem sojeva za bolje razumijevanje bioraznolikosti Anabaena spp.Main aim of this thesis is polyphasic characterization of 16 benthic andperiphytic Anabaena strain collected from eight localities in the north part of the Czech Republic in 2010-2011 near the town Sokolov. They were studied using a polyphasic approach, a combination of morphological and molecular approaches. According to the morphological comparison, there are five morphological groups (morphological types) we can find within the group of the studied strains. Morphological characteristics of the four studied Anabaena strains were measured under various temperature and light intensity. The effect of temperature and light on the dimensions of vegetative cells, heterocytes and akinetes was weak. Four strains exposed to growth optima experiments represented distant phylogeneticclusters based on the 16S rRNA gene, three of them (04VR10L1, 11VR10JH, 01DRMII10)had really similar temperature and light optima. Only the growth optima of the fourth strain,12SO10CI , were significantly different from them. According to the results, we can conclude benthic and periphytic Anabaena genus is phylogenetically heterogeneous. Clustering of the strains based on the 16S rRNA gene corresponds to morphological differences in most cases among 16 studied strains. More extended study on a higher number of strains is necessary fora deeper understanding the biodiversity of Anabaena spp
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
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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