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Aislamiento y caracterización de bacterias antárticas capaces de metabolizar fenantreno en presencia de metales pesados
Get PDFLa Antártica es el continente más austral de la tierra, contiene cerca del 80% de las reservas de agua dulce del planeta y presenta una serie de condiciones extremas, como bajas temperaturas y alta radiación ultravioleta. A pesar de esto, el hombre ha sido capaz de sobrevivir en la región y realizar actividades científicas y de explotación durante más de 80 años. Como consecuencia, las distintas zonas habitadas han sufrido contaminación, principalmente asociada a diesel. Este compuesto es nocivo, ya que presenta una gran cantidad de moléculas orgánicas como hidrocarburos aromáticos policíclicos (HAPs) y compuestos inorgánicos como metales pesados (Cd, Cr y Pb). La descontaminación de HAPs se puede llevar a cabo mediante procesos físicos, químicos y biológicos. Los procesos biológicos representan una opción ecológica, económica y segura, que involucra una menor alteración de los suelos y en consecuencia constituye una excelente alternativa para la descontaminación del territorio Antártico. A la fecha, se ha reportado un gran número de bacterias capaces de degradar HAPs. Sin embargo, debido al Tratado Antártico no está permitido ingresar microorganismos o ADN foráneo al continente, por lo que se hace vital encontrar bacterias nativas que puedan ser usadas en la biorremediación de diesel en Antártica. Debido a su mayor solubilidad en agua, menor toxicidad para el humano y similitud estructural con otros HAPs, el compuesto que se utiliza como modelo para aislar y estudiar microorganismos degradadores de HAPs es el fenantreno.
En base a lo expuesto, se planteó la hipótesis: “La presencia de hidrocarburos aromáticos policíclicos y metales pesados en suelos antárticos ha favorecido el desarrollo de bacterias degradadoras de fenantreno resistentes a metales”. El objetivo general de este trabajo fue aislar y caracterizar bacterias antárticas resistentes a metales pesados (Cd, Cr y Pb) y evaluar su capacidad de metabolizar fenantreno. Para esto se utilizó muestras de suelo antártico obtenido de distintas zonas expuestas y no expuestas a diesel, las cuales fueron caracterizadas química y biológicamente. Además, se aisló y caracterizó bacterias degradadoras de fenantreno resistentes a metales y se estudiaron los procesos asociados a la degradación de fenantreno.
Durante este trabajo de tesis se utilizó muestras de suelo obtenidas de la 49° Expedición Científica Antártico (ECA 49°): 4 muestras de suelos no expuestos a diesel (A0, B4, C3 y C8) y 4 muestras de suelos expuestos a diesel (D3, D4, E2 y E4). El análisis del suelo determinó la presencia de HAPs en los suelos expuestos a diesel, en promedio 1000 veces más concentrado que en los suelos sin exposición. Además, en los suelos D3 y D4 (suelos expuestos a diesel) se observó una mayor concentración de cadmio y plomo total en comparación a todas las muestras, sobre los 30 y 600 mg Kg-1, respectivamente. Respecto a la caracterización biológica, el suelo expuesto a diesel D4 presentó mayor actividad biológica y número de heterótrofos, relacionado directamente al contenido de HAP (el suelo D4 presentó la mayor concentración del hidrocarburo, ̴ 30 mg Kg-1).
De los 8 suelos se aisló 350 microorganismos, de los cuales 53 fueron capaces de degradar fenantreno. Mediante un screening desarrollado durante esta tesis basado en espectroscopía de fluorescencia total asociada a calibración multivariada, se seleccionó 3 aislados por su alto nivel de degradación. Estos microorganismos se caracterizaron, en particular la cepa D43FB (identificada como Pseudomonas flavescens) resiste 25 mg L-1 de Cd+2 y 5 mg L-1 de Cr+6. Además, tras 7 de incubación es capaz de degradar hasta un 80% de fenantreno en medio M9 con el hidrocarburo como única fuente de carbono. Al agregar 0.025, 0.05 y 0.5 mg L-1 de Cd+2 el porcentaje de degradación es 60, 26 y 25 mg L-1, respectivamente. Además, en un proceso de bioaumetación de suelos degrada aproximadamente un 75% de los hidrocarburos presentes en el terrario. Por otro lado, a este aislado se asoció su capacidad de degradar fenantreno a la facultad de formar biopelículas y adherirse a cristales de este compuesto, junto con descartar la liberación de biosurfactante o la quimiotaxis. Siendo una excelente alternativa para más ensayos de biorremediación de suelos.
El trabajo planteado tiene profundas implicaciones para estudios en biorremediación y potencialmente podría representar una alternativa de descontaminación de ecosistemas antárticos aprovechando los bio recursos propios de la Antártica. La proyección de este trabajo está asociada a dilucidar completamente los procesos asociados a la degradación de Pseudomonas flavescens D43FB y continuar ensayos de biorremediación en terrarios, y así eventualmente terminar la investigación en un proceso in situ en AntárticaAntarctica is the southernmost continent on earth, contains ~80% of the planet's fresh water and presents a series of extreme conditions such as low temperatures and high ultraviolet radiation. Despite this, the man has been able to survive in the region doing scientific and operational activities for over 80 years. Consequently, various inhabited areas have been contaminated mainly with diesel. This compound is harmful, because it is composed by organic molecules such as polycyclic aromatic hydrocarbons (PAHs) and heavy metals (Cd, Cr and Pb). Decontamination of PAHs can be accomplished by physical, chemical and biological processes. Biological processes represent an ecological, economical and safe option that involves a minor alteration of the soil and thus is an excellent alternative for the decontamination of the Antarctic territory. To date, a large number of bacteria capable of degrading PAHs has been reported, however due to the Antarctic treaty is prohibited to enter foreign DNA and microorganisms to the mainland, so it is vital to find native bacteria that can be used in diesel bioremediation. Due to its higher solubility in water, lower toxicity to humans and structural similarities to other PAHs, the compound used as a model to isolate and study PAH degraders is phenanthrene. Based on the above, in this thesis the following hypothesis was proposed: "The presence of polycyclic aromatic hydrocarbons and heavy metals in Antarctic soils has favored the development of phenanthrene degrading bacteria resistant to heavy metals". The overall objective of this work was to isolate and characterize Antarctic bacteria resistant to heavy metals (Cd, Cr and Pb) and assess their ability to metabolize phenanthrene. To accomplish this, Antarctic soils obtained from different areas exposed to diesel were characterized chemically and biologically. Also, phenanthrene degrading bacteria resistant to heavy metals were isolated and characterized, and the degradation mechanisms involved were studied.
Soil samples were obtained during the 49th expedition to the Antarctic continent (ECA 49), 4 soils none exposed to diesel (A0, B4, C3 and C8) and 4 soils exposed to diesel (D3, D4, E2 and E4). Soil analysis determined the presence of tri-aromatic polycyclic hydrocarbons in soil exposed to diesel, on average 1000 times more concentrated than in soils with no exposure. Moreover, D3 and D4 soils (exposed to diesel) display a greater cadmium concentration and total lead when compared to all samples, ~30 and 600 mg Kg-1, respectively. Regarding the biological characterization, soil exposed to diesel D4, display greater biological activity and heterotrophes, a result that was directly related to PAH content (D4 soil display the highest concentration of hydrocarbons, ~30 mg Kg-1). This relationship was confirmed by a soil enrichment test with phenanthrene, where it was observed that phenanthrene acts as a supplement in soils exposed to diesel.
350 environmental microorganisms were isolated from the 8 Antarctic soils, 53 of them were able to degrade phenanthrene. Three of them were selected for their high capacity to degrade the hydrocarbon. These isolates were selected through a screening developed during this thesis, based on total fluorescence spectroscopy associated to second order multivariate calibration. Selected isolates were characterized and the resistance to heavy metals was determined. In particular, strain D43FB (corresponding to Pseudomonas flavescens) resists 25 mg L-1 of Cd+2 and 5 mg L-1 of Cr+6. After 7 days, this bacterium was able to degrade ~80% of phenanthrene in M9 medium with the hydrocarbon as a sole carbon source. By adding 0.025, 0.05 and 0.5 mg L-1 of Cd+2 this value decreases to 60, 26 and 25 mg L-1, respectively. Moreover, in a bioaugmentation assay of soil the isolate is capable of degrading ̴75 % of PAH present in the terrarium. In the other hand, the capacity of this microorganism to degrade phenanthrene was associated with their ability to form biofilm and adhere to phenanthrene crystals.
The proposed work has profound implications for bioremediation studies and potentially could represent an alternative for the decontamination of Antarctic ecosystems. The projection of this work is linked to fully elucidate the mechanism of degradation of Pseudomonas flavescens D43FB and continue testing bioremediation in terrariums, and so eventually complete the investigation with an in situ process in AntarcticaFondecyt, INACH T_19-11 e INACH MT-05_13Versión original del auto
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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
Author Under Sail The Imagination of Jack London, 1893-1902
No full textIn Author Under Sail, Jay Williams offers the first complete literary biography of Jack London as a professional writer engaged in the labor of writing. It examines the authorial imagination in London's work, the use of imagination in both his fiction and nonfiction, and the ways he defined imagination in the creative process in his business dealings with his publishers, editors, and agents. In this first volume of a two-volume biography, Williams traverses the years 1893 to 1902, from London's "Story of a Typhoon" to The People of the Abyss. The Jack London who emerges in the pages of Author Under Sail is a writer whose partnership with publishers, most notably his productive alliance with George Brett of Macmillan, was one of the most formative in American literary history. London pioneered many author models during the heyday of realism and naturalism, blurring the boundaries of these popular genres by focusing on absorption and theatricality and the representation of the seen and unseen. London created an impassioned, sincere, and extremely personal realism unlike that of other American writers of the time. Author Under Sail is a literary tour de force that reveals the full range of London as writer, creative citizen, and entrepreneur at the same time it sheds light on the maverick side of machine-age literature.Intro -- Title Page -- Copyright Page -- Dedication -- Contents -- Acknowledgments -- Introduction -- 1. Spirit Truth -- 2. From Absorption to Theatricality and Back Again -- 3. "I Will Build a New Present" -- 4. Sons as Authors -- 5. Fathers as Publishers -- 6. The Daughter as Author -- 7. Lovers as Authors -- 8. At Sea with the Family -- 9. Yellow News, Yellow Stories -- 10. The Return Home -- Notes -- Bibliography -- Index -- About Jay WilliamsIn Author Under Sail, Jay Williams offers the first complete literary biography of Jack London as a professional writer engaged in the labor of writing. It examines the authorial imagination in London's work, the use of imagination in both his fiction and nonfiction, and the ways he defined imagination in the creative process in his business dealings with his publishers, editors, and agents. In this first volume of a two-volume biography, Williams traverses the years 1893 to 1902, from London's "Story of a Typhoon" to The People of the Abyss. The Jack London who emerges in the pages of Author Under Sail is a writer whose partnership with publishers, most notably his productive alliance with George Brett of Macmillan, was one of the most formative in American literary history. London pioneered many author models during the heyday of realism and naturalism, blurring the boundaries of these popular genres by focusing on absorption and theatricality and the representation of the seen and unseen. London created an impassioned, sincere, and extremely personal realism unlike that of other American writers of the time. Author Under Sail is a literary tour de force that reveals the full range of London as writer, creative citizen, and entrepreneur at the same time it sheds light on the maverick side of machine-age literature.Description based on publisher supplied metadata and other sources.Electronic reproduction. Ann Arbor, Michigan : ProQuest Ebook Central, YYYY. Available via World Wide Web. Access may be limited to ProQuest Ebook Central affiliated libraries
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