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Molecular ecology of Frankia and other soil bacteria under natural and chlorobenzoate-stressed conditions
No full textMicrobial Ecology studies aim to describe and assess the behavior and activity of microorganisms in their natural environments (Brock 1966). Nowadays it is clear that the large number of existing microorganisms has surpassed our capabilities to rapidly characterise them by traditional culturing methods. This has resulted in a poor understanding of the structure and composition of microbial communities. As an alternative, microbial communities can be described on the basis of 16S rRNA sequence diversity, without the bias-introducing step of cultivation.In the present thesis a molecular analysis is given of two ecosystems that harbour several uncultured bacteria. The first part of the thesis is focused on the detection and characterisation of Frankia in actinorhizal nodules and soil. Elucidation of the actual diversity within the family Frankiaceae was hampered by the inability to obtain isolates from all known actinorhizal plants. So far, the Nod <sup>+</SUP>/Fix <sup>+</SUP>Frankia symbionts in root nodules of plants from the families Coriariaceae, Datiscaceae, Rosaceae and Rhamnaceae (with exceptions reported by Carú 1993, Carú et al . 1990, and Carrasco et al . 1995) have resisted isolation. Best opportunities to characterise those uncultured endophytes require molecular methods that relay heavily on an easy and efficient technique to extract DNA from the respective actinorhizal nodules. Chapter 2 describes the techniques to isolate DNA from root nodules of different actinorhizal plants such as Casuarina sp, Alnus sp and Ceanothus sp. The procedure has also been successfully applied by Wolters et al . (1997b) in the minuscule ineffective nodules on Alnus glutinosa .Several attempts to characterise the uncultured endophytes from Coriaria sp. and Datisca sp. plants pointed on the one hand, to the presence in those actinorhizae of Frankia -related actinomycetes. This assumption was based mainly on the repeated isolation from those nodules of Nod <sup>-</SUP>/Fix <sup>-</SUP>Frankia -like strains (Hafeez 1983, Mirza et. al . 1994b, c). On the other hand, the effective (Fix <sup>+</SUP>), non-isolated symbionts showed to be phylogenetically closely related (Mirza et al. 1994a), forming a separate lineage within the genus, in spite of the distant geographical distribution of the plants (Nick et al. 1992).The work described in Chapter 3 is focussed on the localisation and phylogenetic position of the nitrogen-fixing Frankia and Nod <sup>-</SUP>/Fix <sup>-</SUP>actinomycetes, both present in root nodules of the Mexican actinorhizal plant Ceanothus caeruleus . Application of the TGGE technique allowed localising the Nod <sup>-</SUP>/Fix <sup>-</SUP>actinomycete in the outer layers of the C. caeruleus nodules. Similar bacteria were also detected in Hippophaë rhamnoides nodules induced with soil inoculum that was collected in the vicinity of the former plant. The fact that a second nodule inhabitant was commonly present in these nodules containing recalcitrant endophytes may allow some speculations about their possible role in the symbiosis. However, it seems worthwhile to apply the same TGGE methodology to other actinorhizal nodules, even to those containing Frankia strains that are easy-to-isolate (i.e. Elaeagnus,Casuarina, Alnus spp.), since the detection of Frankia -related actinomycetes, in addition to the Fix <sup>+</SUP>endophyte, would provide further evidence about the need for their presence. Coincidentally, the Nod <sup>-</SUP>/Fix <sup>-</SUP>isolates from Coriaria, Datisca and Ceanothus are phylogenetically related, pointing again to a certain specificity for their presence in the nodules. This relatedness has also been supported by analysis of low molecular weight RNA (i.e. 5S rRNA and tRNA's) using staircase electrophoresis (Velázquez et al. 1998).The 16S rDNA sequence from the non-isolated Fix <sup>+</SUP>endophyte in C. caeruleus root nodules (Chapter 3), was the first full sequence obtained from a field-collected Ceanothus symbiont. Parsimony and phylogenetic distance analyses grouped it within the Dryas cluster that originally contained only the uncultured endophytes from Dryas , Coriaria and Datisca as proposed by Normand et al. (1996). Benson et al . (1996) redefined this cluster by adding other uncultured endophytes present in Ceanothus griseus (Rhamnaceae), Purshia tridentata and Dryas drummondii (Rosaceae) root nodules. Since the determined partial 16S rDNA sequences were almost identical, they suggested that the Frankia diversity from these actinorhizal plant families might be low. However, Clawson et al. (1998) demonstrated that Frankia isolates obtained from several genera within the Rhamnaceae (i.e. Talguenea , Colletia , Discaria, Retanilla and Trevoa ) were phylogenetically different than those in Ceanothus, grouping in the Elaeagnus cluster. These findings were consistent with morphological differences of the endophytes in planta , since the vesicles found in the Ceanothus symbionts resemble more to those in the Rosaceae, while all the latter host plants in the Rhamnaceae family have endophytes like those in Elaeagnus .The results reported in the first part of the thesis have demonstrated that TGGE and sequence analysis of 16S rDNA provide an accurate picture for the identification of recalcitrant endophytes in root nodules of actinorhizal plants. It has also been demonstrated that besides the N <sub>2</sub> -fixing endophyte, root nodules of C. caeruleus also harbour Frankia -related actinomycetes. Since these have also been observed in other actinorhizae, a further study is needed to understand the possible function of these co-symbionts.The work described in the second part of the thesis was addressing the changes occurring under chlorobenzoate stress in the soil bacterial community and other selected groups of bacteria present in peat soil collected from a natural Alnus glutinosa stand. A combination of culturing and non-culture based approaches was used for the assessment. Among the latter approaches, the possibilities offered by TGGE were exploited in several ways. Profiling of complex communities and subsequent analysis of specific bacterial groups has been one of the major applications of TGGE (Felske et al . 1996). With this approach, major population shifts induced by either 3CBA or 2,5DCB were detected in the uncultured bacterial community (Chapter 4). Although only the former compound was readily metabolised in soil, both xenobiotics promoted similar changes. Several bacterial populations were reduced or suppressed, while few others were enriched in time, as assessed by shifts in the TGGE banding patterns of the total bacterial community.To characterise the soil-enriched bacterial populations, 3CBA-degrading enrichment cultures were obtained and their composition was addressed by TGGE. Further isolation attempts were directed by this means to prove that the isolated strains were indeed the same enriched organisms as detected in soil. One of the enrichment cultures contained two of the soil-enriched bacteria as predominant components. Although isolation was not achieved, both bacteria were identified as belonging to the genus Burkholderia . The bacterial group detected as predominantly enriched in both spiked soils was not present in any of the enrichment cultures, suggesting that the microorganisms belonging to this groups are either unable to degrade 3CBA or not growing under the used culturing conditions. In any case their fitness to the soil conditions imposed by the addition of chlorobenzoates was high, but the mechanisms involved were not elucidated. These bacteria were also identified as Burkholderia by partial 16S rDNA sequence analysis (Chapter 4).The diversity (H) and the equitability (J) indices are important parameters used by ecologists to assess the species richness and the species evenness, respectively, within a community. As the estimation of such indices relies heavily on species definition and individuals enumeration, their application in microbial ecology studies is seldomly possible. Furthermore, assessment of H and J in uncultured bacterial communities must rely on the interpretation of community fingerprints, which should provide means to distinguish between species or operational taxonomic units (OTU), and to estimate their abundance. TGGE community profiling offers both possibilities, and the community changes occurring in the model soil system were evaluated with this original approach (Chapter 5).In addition, H and J indices were also estimated for the fluorescent pseudomonads group, a selected culturable fraction of the bacterial community. OTU recognition was addressed by using TGGE as a ribotype-fingerprinting technique for the isolated fluorescent pseudomonads. Estimation of H and J at the community level without culturing by TGGE profiling, and at the group level by a combination of culturing and TGGE ribotyping should allow to address and compare the population changes occurring, since the target molecule used in both TGGE was the same. Such comparison was only partially possible since most of the bands corresponding to the fluorescent pseudomonads could not be assessed in the community profiles. However, estimation of H and J indices indicated a clear reduction of species richness and individuals abundance in the uncultured community, which was related to the presence of chlorobenzoates in soil. Evaluation of population shifts by indexed values as H and J proved to be a useful means for analysing the community structure in time, and may be used to assess short and long-term responses of a bacterial community to environmental perturbations.Chapter 6 describes the changes in the total frankiae in soil and in the fraction of the population that is able to produce root nodules in Alnus glutinosa seedlings . Culture-independent approaches based on the most probable number concept were used, one in combination with a Frankia -specific PCR detection and another in combination with a plant-nodulation bioassay. After 15 days of incubation in the presence of chlorobenzoates both fractions of the soil Frankia populations were reduced in more than one order of magnitude, while the populations in the unspiked control soil were not affected. The results indicated that 3CBA and 2,5DCB both had a negative effect on the size of the native Frankia population from the used peat forest soil. This negative effect was also evident during in vitro experiments using Frankia strains isolated from Alnus sp. The presence of 1 mM 3CBA in the culture medium, in addition to the normal carbon source, resulted in reduction or suppression of biomass yield.The influence of Alnus glutinosa on the dechlorination of 3CBA by Pseudomonas sp. strain B13 was assessed in hydroponic cultures. It was expected that root exudates could enhance the dechlorination activity of Pseudomonas B13. When the bacteria were incubated in the presence of an alder plant, only a slight increase in the dechlorination rate of 3CBA was registered in comparison to the control without plant. The main observed effect in the alder plants appears to be a protection against 3CBA toxicity, as the alders inoculated with Pseudomonas B13 showed a better survival rate and grew more vigorously than the non-inoculated plants.The toolbox for microbial ecology studies is increasing constantly by means of developing new techniques or by adapting foreign tools into the field, such as indices to evaluate species diversity and eveness. Although the information provided by these community parameters facilitates comparisons and assessment of changes, their suitability to evaluate bacterial communities is still uncomplete. Estimation of diversity indices requires the recognition of bacterial species as discrete units, and this condition is far from real in natural environments. Species-independent approaches to evaluate diversity must be developed, that consider the bacterial diversity as a continuous range of phylogenetically related taxonomic units.In conclusion, the work described in the first part of the thesis strengthen the current phylogenetic division of the Frankiaceae, by adding new evidence supporting two of the already described clusters ( Dryas cluster, Nod <sup>-</SUP>/Fix <sup>-</SUP>cluster). Although the current taxonomic status of the latter cluster must be better evaluated in order to assess its pertinence to the genus Frankia . In addition, the common occurrence of Nod <sup>-</SUP>/Fix <sup>-</SUP>Frankia -like actinomycetes in nodules containing recalcitrant endophytes, mainly from the Dryas cluster, was also demonstrated for Ceanothus actinorhiza. In the second part, the suitability and versatility of molecular tools such as TGGE were demonstrated by their application in community profiling and estimation of bacterial diversity. Community changes occurring in stressed and unstressed soil systems were easily detected and assessed by this means.In addition, specific populations such as the Burkholderia -like bacteria that strongly reacted to the addition of chlorobenzoates to soil were further characterised. Moreover, TGGE was shown to be a fast ribotyping technique that may enable its use in combination with the community profiles to address shifts of specific groups within bacterial communities. It is tempting to suggest that this general approach will be of importance to direct the isolation of hitherto uncultured bacteria from soil
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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