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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Theoretical feedbacks between Neoproterozoic glaciations and Eukaryotic evolution

Boyle, Richard A. January 2008 (has links)
Physiological consequences of transitions in the level of selection explain the existence of Neoproterozoic lichen symbioses. Between-individual differentiation within groups causes physiological buffering, giving altruists higher fitness than cheaters in variable environments. Altruists increase from rarity. Reciprocal feedback between a genotype frequency and an abiotic state may be equivalent to kin selection. At contemporary degassing rate, biotic silicate weathering enhancement 10 – 20 times greater than present would have been required for a biologically-triggered snowball Earth. However, biotic enhancement could have compensated by declining abiotic silicate weathering rate at low temperatures – sufficiently to accentuate a tectonically-driven glaciation. Marine carbonate speciation causes a slushball ocean to become a net CO2 source at large reservoir sizes, making glacial duration shorter than a hard snowball by a factor of the atmospheric CO2­ degassing fraction. Equilibrated oceans require a carbonate weathering:burial ratio Wcarb : Bcarb > 1 for deglaciation by CO2(g) increase. If adequate biotic silicate weathering enhancement rapidly occurs after deglaciation, subsequent reglaciation will occur within 3 – 5Myrs. The contrast with the ~50Ma separating Neoproterozoic events invokes the elapse of a coevolutionary “succession time”, before which biotically-triggered reglaciation is improbable. Low post-glacial silicate weathering is consistent with Si-depleted cap carbonates. Phanerozoic reduction in glacial susceptibility resulted from physiological evolution of biotic weathering and/or calcification. Emergence of terminal cellular differentiation in Ediacara/Metazoa required an environmental context E, provided by Neoproterozoic glaciations, in which the high fitness cost was adaptive. Restriction of the biosphere to refugia experiencing extreme, repeated founder effects raised kin selection for altruism. Between-group isolation limited cheat migration, accentuating group viability selection for altruism. Both processes occurred globally, over multi-million year timescales; explaining subsequent proliferation of Ediacaran macrobiota.
2

A study of amylolytic streptococci from the rumen of the sheep

Walker, M. J. D. January 1954 (has links)
No description available.
3

The role of Ku in retrotransposition in Saccharomyces cerevisiae

Downs, J. January 1999 (has links)
In order to determine whether the mobility of transposable elements is affected by Ku, a genetic system using the Tyl retrotransposon in <I>Saccharomyces cerevisiae</I> was used. Phenotypic analysis of yeast strains containing a null mutation of either subunit of Ku showed that Tyl retrotransposition rates were markedly reduced compared to wild-type cells. This phenotype appears to be specific to mutations in Ku, as strains with mutations in other DNA repair proteins were analysed and no significant effect on retrotransposition was observed. Biochemical techniques were employed to determine the stage of the retrotransposon life-cycle at which Ku was acting to facilitate the process. It has been determined that transcription, translation, and reverse transcription of the retroelement and element-encoded proteins are unaffected by the absence of Ku. Furthermore, there is no defect in proteolytic processing of a precursor fusion protein, retrotransposon virus-like particle assembly, or reverse transcriptase activity in the absence of Ku. Examination of another retrotransposon shows that same phenotype in the absence of Ku, suggesting that the mechanism by which Ku is facilitating retrotransposition is a general one, and not likely to be via targeting the integration machinery to specific regions of the genome. Ku was demonstrated to co-fractionate with the virus-like particles during purification, and immunoprecipitation experiments using antibodies directed at one of the Ku subunits demonstrate an interaction with the retrotransposon cDNA and integrase, but not the reverse transcriptase. Ku has previously been shown to bind to DNA double-strand ends <I>in vitro</I>, so one model by which Ku could facilitate retrotransposition is by binding to the cDNA ends and protecting them from nuclease-mediated degradation. However, examination of purified cDNA from wild-type and <I>yku70</I> mutant strains shows no difference in the amount or integrity of DNA.
4

Comparative genomic analysis of three Leishmania species that cause diverse disease pathologies

Depledge, Daniel Pearce January 2008 (has links)
In 1940, Virginia Woolf called for a more inclusive form of biography, which would include ‘the failures as well as the successes, the humble as well as the illustrious’. She did so partly as a reaction against Victorian biography, deemed to have been overly preoccupied with the great and the heroic. Yet a significant number of Victorian biographers did in fact write biographies that went against the trend of hero-worshipping ‘Great Lives’ and focused instead on the humble, the marginal, or the neglected. Though many are simplistic, pious productions, others sought to engage in contemporary debates surrounding the role and place of the individual in society in a sophisticated and complex manner. The thesis begins with an overview of the period’s biographical writings. The second and third chapters explore the representation of marginality and powerlessness through biographies of female and working-class subjects. The fourth and fifth chapters are concerned with issues of canonisation: the championing of neglected artists, and the Dictionary o f National Biography are discussed. A final, brief, chapter on Virginia W oolfs conception of ‘obscure lives’ seeks to broaden our understanding of her literary influences. The ‘obscure’ biographical subject emerges as a paradoxical figure used as a safe means of exploring the boundary between the private and the public. Above all, and in contrast with the trend instigated by Woolf, biographers were not concerned with securing immortality for their subjects, but with prompting within their readers feelings of empathy and gratitude. The thesis attempts to balance a survey of this trend with close analysis of works that manipulated the biographical genre in interesting ways. It is also a study of how Thomas Carlyle’s and George Eliot’s influence was disseminated within an under-studied literary genre. The thesis includes, as an appendix, a descriptive catalogue of over two hundred Victorian biographies.
5

Biochemical and cellular studies of the Bacillus Subtilis JmjC protein YxbC

Cromwell, Tamsyn L. C. January 2009 (has links)
A Wicked Countenance: The Vengeance Seeking Woman in Japanese Cinema argues the female onryo, or vengeance seeking spirit, belies Japan's often conflicted relationships to the various socio/political contexts of the last 100 years. The onryo is an archetype, appearing throughout Japanese film, theatre and folkloric cultures, and yet the specificities of that archetype change greatly through time. Japanese modem history has been conditioned by its various interactions in geo-politics and this thesis argues that the various permutations of the onryo have been correspondingly impacted by the nation's political actions. Viewing history, not as a teleological series of cause/effect relations but rather as a product of a system of competing discourses, the thesis argues that those discourses shape the onryo in differing manners dependent on the competing ideological positions of the era. Film cannot escape its context and is imbued with the ideologies of the society from which it is produced. Ideology is itself a product of the interaction between a society and its media, both being shaped and reinforced through that interaction. While capitalism, as proposed by Eric Cazdyn in his The Flash of Capital, has been the dominant contributing discourse in the shaping of ideology, my own work, stemming from Cazdyn's project, considers discourses as varied as feminism, cultural nationalism and nationhood. These are discourses which, though marked by capitalism, comprise inherent particularities which direct ideology in ways independent of capitalism. In this work, Japanese film history is divided into three different temporallideological contexts. The first half of the 20th century in Japan was mar(rlk)ed by the introduction of the west to Japan. The earliest films struggle to create a Japanese cinematic language and while ideology struggled to better articulate what constituted appropriate womanly behavior, women often became representations of 'womanliness'. The postwar period, conversely was a time of questioning. With the end of the occupation, Japan re-discovered political and cultural autonomy. Japanese film culture began to actively explore its relations to the past, and to question what it is to be a Japanese individual with autonomy and how to participate in the democratic environment of free will and personal subjectivity. The films then become an exploration of the attempts to negotiate the self as Japanese within the context of political autonomy and the onryo becomes indicative of that quest to articulate 'japaneseness.' Finally, the contemporary period is an era marked by globalization. Empire, as defined by Antonio Negri and Michael Hardt in their book of the same name, is different from Imperialism. Empire posits that the new world order of interdependency and corporate economic expansion has resulted in the exploitation of offshore labour forces for personal economic gain and that all people who participate in contemporary capitalism are culpable in Empire's exploitations. The films, cognizant of the culpability of the individual within Empire's exploitations, manifest those fears in the onryo. The onryo, devastating in its usage of the media's vehicles of transmission (television, cell phones, the internet), becomes metaphorical of capitalism's destructiveness. While the thesis examines Japanese film culture of the last 100 years, the onryo films themselves are not restricted to those past historical contexts. As long as film continues to be produced by Japan, they will continue to reflect the ideological idiosyncrasies germane to the Japanese identity.
6

The development of a transparent soil and its application in imaging root trajectories and root bacteria interactions

Downie, Helen January 2013 (has links)
Biological processes that occur in the soil have important environmental implications. These processes include root growth and microbial interactions with roots and so il particles and they influence the efficiency of crop production and, in turn, global food security. The observation and imaging of these below-ground processes is difficult due to the opacity of soil and so this thesis presents a new artificial soil analogue that is transparent and therefore allows optical imaging. Transparent soil is a 3D matrix of chemically treated particles of the low refractive index fluoropolymer Nafion, water, plant nutrients and air and has water retention and ion exchange properties similar to natural soils. Before imaging, the transparent soil was saturated with a refractive index matched liquid for appropriate transparency. The substrate was used for 3D imaging of living root systems and high resolution imaging of living roots at a cellular level in relation to the fluorescent-labelled Nafion particles of the substrate. Soil physical conditions influence the growth rate and direction of roots. The substrate compaction and particle size range was varied in transparent soil to quantify the effect of these conditions on 3D root trajectories of lettuce plants. Root systems of plants grown in different substrate conditions were imaged and the root lengths were measured along with the curvature and verticality at sequential points along the roots. There was a greater range of root curvatures in substrates with larger particl e size s and deviation from vertical increased with distance along the root . In substrates with different compactions, there was no effect of compaction on the root curvature or verticality measurements, however the measurements were influenced by the distance along the root. Soil microbes were also studied using the transparent soil system. Pseudomonas fluorescens, a plant growth promoting rhizobacteria, associates closely with plant roots and can act as a biocontrol agent by conveying pathogen resistance to the plant. For this reason, the interaction between lettuce roots and GFP labelled P. fluorescens was studied with the aim of quantifying colonisation patterns along the root and the abundance of bacteria in the substrate surrounding the roots. Transparent soil with two different particle size categories was used to investigate if the substrate particle size affected the colonisation of the roots. Imaging of living roots and bacteria was carried out at 3D sample points along the root and adjacent to the root and it was found that there was a greater abundance of bacteria on the roots than in the substrate. There was a consistent base level of bacterial fluorescence in imaging points that did not include roots, regardless of whether or not there was a plant in the sample and the distance from the root. Substrate particle size had no effect on root colonisation.
7

Studies on the metabolism of bacterial lipid granules

Macrae, R. M. January 1959 (has links)
No description available.
8

Investigations into the measurement of nitrogen fixation in freshwater lake sediments

Sylvester Bradley, R. January 1976 (has links)
No description available.
9

Studies on methane-utilizing bacteria

Phillips, K. C. January 1971 (has links)
No description available.
10

The transducer-like proteins of Campylobacter jejuni

Sandhu, Randeep January 2011 (has links)
Campylobacter jejuni is the leading cause of gastrointestinal disease in the developed world. Chemotactic motility is a pre-requisite for intestinal colonisation by C. jejuni. In silico analysis of the C. jejuni NCTC 11168 genome identified homologues of 10 chemotaxis receptor and two aerotaxis genes. Six of the ten putative Transducer-like proteins (Tlp 1, 2, 3, 4, 7 and 10) resemble chemoreceptors of Escherichia coli. The aim of this project is to characterise the C. jejuni Tlp1-4 chemoreceptors. The genes encoding the Tlps were inactivated using an insertional inactivation strategy. Isogenic mutants were made in tlp1, tlp2 and tlp4; a final mutant in tlp3 could not be obtained. A tlp1 complement was also constructed in this work. The tlp1 mutant showed reduced chicken colonisation ability when tested by our collaborators. Chemotactic phenotypes of the tlp mutants were determined in the swarm assay; the tlp mutants appeared defective for chemotaxis when compared with the wild-type and non-motile flaAB mutant. The Capillary assay and Hard-Agar Plug (HAP) assay were developed as methods to ascertain the ligand specificities of the Tlp chemoreceptors under study. Unfortunately, the Capillary assay proved to be insufficiently reproducible for effective use with C. jejuni. The HAP procedure was optimised using a C. jejuni wild-type motile variant. Positive chemoattractant responses were observed in NCTC 11168 for the first time towards a range of chemicals. Data derived from the modified HAP assay indicated that Tlp1 may be the receptor for serine. Chemotactic responses could not be detected in the tlp2 and tlp4 mutants in the HAP assay. The signalling domain of Tlp1 was purified using a polyhistidine tag and used to produce a polyclonal antibody. The Tlp1 primary antibody and immunofluorescence labeling has shown for the first time that the Tlps cluster at the cell poles in C. jejuni.

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