Teses / dissertações: "Cyanobacteria"

1

Du, Plooy Schalk Jacobus. "Ecophysiology and nutrient uptake mechanisms facilitating the prolonged bloom persistence by Cyanothece sp. in Lake St Lucia, South Africa." Thesis, Nelson Mandela Metropolitan University, 2017. http://hdl.handle.net/10948/7344.

Texto completo da fonte

Resumo:

Cyanobacterial blooms are becoming more frequent worldwide, with possible negative effects on human health. The effects of climate change and eutrophication have been associated with persistent cyanobacterial blooms becoming more frequent. Altered water characteristics, salinity in particular, influence ecosystem dynamics that may lead to conditions conducive to cyanobacterial blooms. The occurrence of an 18-month long Cyanothece sp. bloom (the longest for any cyanobacterium recorded so far worldwide and the first of the genus) from June 2009 to December 2010 in Africa’s largest estuarine lake, St Lucia, highlighted the susceptibility of ecosystems to anthropogenic alterations. This study investigated the long-term survival and physiological adaptations of Cyanothece sp. to various and dynamic environmental conditions that contributed towards its bloom persistence. The main findings are the high salinities at which Cyanothece sp. could perform important physiological processes such as N uptake, N2 fixation and photosynthesis. Nutrient uptake (both nitrogen and phosphorus) was observed over the full experimental salinity range (0-300) while N2 fixation was only observed up to a salinity of 120. Nutrient uptake rates significantly decreased at this threshold salinity of 120. Interestingly, photosystem II activity was not observed in Cyanothece sp. during this study, but photosystem I activity was robust. Salinity had a minor influence on electron transport rates by photosystem I, high temperature (> 30°C) did however increase electron transport rates. Rapid responses to hypo-osmotic shock (i.e. osmotic downshift during freshening events) by Cyanothece sp. cells also helped minimize cell rupture due to high turgor pressure. Zooplankton abundance within the St Lucia system was negatively correlated with salinity, while grazing experiments indicated that the typical estuarine zooplankton species are able to graze on Cyanothece sp. cells. Therefore, the disappearance of zooplankton at salinities above 60 must have been an important factor in the bloom persistence. Apart from the ecological factors that were at play in St Lucia during the bloom period, the persistence of the Cyanothece sp. bloom can be attributed to the robust nature of their nutrient uptake, nitrogen fixation and photosynthetic systems to maintain activity despite extreme hypersalinity levels.

Estilos ABNT, Harvard, Vancouver, APA, etc.

2

Froscio, Suzanne M. "Investigation of the mechanisms involved in cylindrospermopsin toxicity : hepatocyte culture and reticulocyte lysate studies." Title page, contents and abstract only, 2002. http://web4.library.adelaide.edu.au/theses/09PH/09phf938.pdf.

Texto completo da fonte

Resumo:

Bibliography: leaves 121-139. The aim of this study was to determine the extent to which protein synthesis inhibition, lowered glutathione (GSH) levels and toxin metabolism contribute to the toxicity of cyclindrospermopsin. Both hepatocyte cultures and reticulocyte lysates were utilized as in vitro tools of investigation. The findings imply that the inhibition of protein synthesis by direct action of the toxin cannot be considered a primary cause of hepatocyte cell death over an acute time frame. Cytochrome P450-derived metabolites may play a crucial role in cytotoxicity, and the toxicity process does not appear to involve oxidative damage.

Estilos ABNT, Harvard, Vancouver, APA, etc.

3

Stewart, Ian. "Recreational exposure to freshwater cyanobacteria : epidemiology, dermal toxicity and biological activity of cyanobacterial lipopolysaccharides /." [St. Lucia, Qld.], 2004. http://www.library.uq.edu.au/pdfserve.php?image=thesisabs/absthe.pdf.

Texto completo da fonte

Estilos ABNT, Harvard, Vancouver, APA, etc.

4

Wang, Kai. "INTERACTIONS OF CYANOBACTERIA AND CO-OCCURRING MICROORGANISMS DURING CYANOBACTERIAL HARMFUL ALGAL BLOOMS." Kent State University / OhioLINK, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=kent1619622253977384.

Texto completo da fonte

Estilos ABNT, Harvard, Vancouver, APA, etc.

5

Menke, Sharon M. "NifD: Its Evolution and Phylogenetic Use in Cyanobacteria." Miami University / OhioLINK, 2007. http://rave.ohiolink.edu/etdc/view?acc_num=miami1176983927.

Texto completo da fonte

Estilos ABNT, Harvard, Vancouver, APA, etc.

6

Lindberg, Pia. "Cyanobacterial Hydrogen Metabolism - Uptake Hydrogenase and Hydrogen Production by Nitrogenase in Filamentous Cyanobacteria." Doctoral thesis, Uppsala University, Physiological Botany, 2003. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-3541.

Texto completo da fonte

Resumo:

Molecular hydrogen is a potential energy carrier for the future. Nitrogen-fixing cyanobacteria are a group of photosynthetic microorganisms with the inherent ability to produce molecular hydrogen via the enzyme complex nitrogenase. This hydrogen is not released, however, but is recaptured by the bacteria using an uptake hydrogenase. In this thesis, genes involved in cyanobacterial hydrogen metabolism were examined, and the possibility of employing genetically modified cyanobacteria for hydrogen production was investigated.Nostoc punctiforme PCC 73102 (ATCC 29133) is a nitrogen-fixing filamentous cyanobacterium containing an uptake hydrogenase encoded by hupSL. The transcription of hupSL was characterised, and putative regulatory elements in the region upstream of the transcription start site were identified. One of these, a binding motif for the global nitrogen regulator NtcA, was further investigated by mobility shift assays, and it was found that the motif is functional in binding NtcA. Also, a set of genes involved in maturation of hydrogenases was identified in N. punctiforme, the hypFCDEAB operon. These genes were found to be situated upstream of hupSL in the opposite direction, and they were preceded by a previously unknown open reading frame, that was found to be transcribed as part of the same operon.The potential for hydrogen production by filamentous cyanobacteria was investigated by studying mutant strains lacking an uptake hydrogenase. A mutant strain of N. punctiforme was constructed, where hupL was inactivated. It was found that cultures of this strain evolve hydrogen during nitrogen fixation. Gas exchange in the hupL- mutant and in wild type N. punctiforme was measured using a mass spectrometer, and conditions under which hydrogen production from the nitrogenase could be increased at the expense of nitrogen fixation were identified. Growth and hydrogen production in continuous cultures of a Hup- mutant of the related strain Nostoc PCC 7120 were also studied. This thesis advances the knowledge about cyanobacterial hydrogen metabolism and opens possibilities for further development of a process for hydrogen production using filamentous cyanobacteria.

Estilos ABNT, Harvard, Vancouver, APA, etc.

7

Berry, Gerald A. "Mosquito Larvicides from Cyanobacteria." FIU Digital Commons, 2014. http://digitalcommons.fiu.edu/etd/1449.

Texto completo da fonte

Resumo:

Cyanobacteria (blue-green algae) produce a diverse array of toxic or otherwise bioactive metabolites. These allelochemicals may also play a role in defense against potential predators and grazers, particularly aquatic invertebrates and their larvae, including mosquitoes. Compounds derived from cyanobacteria collected from the Florida Everglades and other Florida waterways were investigated as insecticides against the mosquito Aedes aegypti, a vector of dengue and yellow fever. Screening of cyanobacterial biomass revealed several strains that exhibited mosquito larvicidal activity. Guided via bioassay guided fractionation, a non-polar compound from Leptolyngbya sp. 21-9-3 was found to be the most active component. Characterization revealed the prospective compound to be a monounsaturated fatty acid with the molecular formula C16H30O2. This is the first evidence of mosquito larvicidal activity for this particular fatty acid. With larvicidal becoming more prevalent, fatty acids should be explored for future mosquito control strategies.

Estilos ABNT, Harvard, Vancouver, APA, etc.

8

Bibby, T. S. "Photosynthetic complexes of cyanobacteria." Thesis, Imperial College London, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.595520.

Texto completo da fonte

Estilos ABNT, Harvard, Vancouver, APA, etc.

9

Lee, Elvina. "Molecular systematics of cyanobacteria." Thesis, Lee, Elvina (2016) Molecular systematics of cyanobacteria. PhD thesis, Murdoch University, 2016. https://researchrepository.murdoch.edu.au/id/eprint/34883/.

Texto completo da fonte

Resumo:

Cyanobacteria constitute a phylum of ubiquitous cosmopolitan bacteria with the ability to perform oxygenic photosynthesis. Their ancient origins, ecological and economic potential, biotechnological applications and impact on water systems have attracted much interest from the academia, industry, health authorities and regulators. Despite this, cyanobacteria classification and nomenclature still remains difficult. One of the aims of this project was to further our understanding of cyanobacteria systematics by (1) testing polyphasic characterization methods and (2) examining the effect of various phylogenetic reconstruction strategies. Additionally, (3) Next Generation Sequencing (NGS) assays using novel cyanobacteria 16S rDNA targeted primers were implemented to provide better taxa resolution than that offered by “universal” 16S rDNA primers. Cyanobacteria strains from various water sources in Australia were isolated, characterised at four loci commonly used for cyanobacteria molecular classification, and tested for the presence of genes implicated in toxin and terpene (odour) production. A total of 55 novel cyanobacterial strains were isolated and maintained in culture, forming the first known collection of cyanobacteria isolates from Western Australia. Comparison of molecular– and morphology– based identifications not only showed the limitations of the current methods (only 45% of the isolates showed agreement) but also provided the opportunity to suggest guidelines and conceive a way forward towards more effective identification approaches. Examination of alternative phylogenetic markers, workflows and stringencies showed that between alignment algorithms, alignment curations and tree building methods, the latter had the greatest effect on tree topology. This result was consistent regardless of locus, alignment and curation strategy employed. Finally, two sets of novel cyanobacteria-targeted primers were designed for use with NGS technologies. As compared to the universal 16S rRNA primers, these primers showed higher specificity and preferential amplification of cyanobacteria and proteobacteria DNA. Of the sequences obtained using these two new primer pairs, cyanobacteria sequences comprised 50.5% and 54.4%, while proteobacteria sequences comprised 44.5% and 40.3% respectively. In comparison, with the universal 16S rRNA primers, cyanobacteria and proteobacteria comprised 15.3% and 33.4% respectively of the sequences analysed. Using morphological and molecular methods, this project provides a snapshot of the as yet unstudied freshwater cyanobacterial diversity found in Western Australia using polyphasic methods. The limitations of the current identification approaches, uncovered during the first phase of the project, were harnessed to develop a method to assess the variability of phylogenetic reconstructions. Finally, novel cyanobacteria specific NGS primers demonstrated how adopting the latest NGS technology represents a promising advance in the molecular investigation of cyanobacteria.

Estilos ABNT, Harvard, Vancouver, APA, etc.

10

Williams, Philip. "Chemical investigations of marine cyanobacteria : the search for new anticancer agents from the sea /." Thesis, University of Hawaii at Manoa, 2003. http://hdl.handle.net/10125/6878.

Texto completo da fonte

Estilos ABNT, Harvard, Vancouver, APA, etc.

11

Page, T. S. "Molybdenum independent nitrogenases in cyanobacteria." Thesis, Swansea University, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.638392.

Texto completo da fonte

Resumo:

Anabaena variabilis ATCC 29413, Anabaena cylindrica CCAP 1403/2A, Anabaena sp. PCC 7120, Anabaena sp. UCSB26, Microcoleus chthonoplastes and Calothrix sp. PCC 7601 appear to possess Mo-independent nitrogenases. All of these cyanobacteria grew diazotrophically in the presence of 1 mM tungstate, as well as in medium from which Mo had been carefully removed, whether or not V had been added. In growth media lacking Mo they reduced C2H2 to C2H6 as well as C2H4. Nevertheless, growth and C2H2 reduction were greatest in medium containing Mo. Nostoc sp. UCSB7, Nostoc gun UCSB31, Mastigocladus laminosus CCAP 1447/1 and Scytonema javanicum CCAP 1473/1 grew and fixed N2 in the presence of 1 mM tungstate, but did not reduce C2H2 to C2H6 in medium from which Mo had been removed. These strains are good scavengers of small traces of Mo. In cultures of Anabaena variabilis ATCC 29413, Anabaena cylindrica CCAP 1403/2A and Anabaena sp. PCC 7120, C2H2 activity recovered at a faster rate in V-medium than in Mo-medium, following incubation at low temperatures (5°C - 20°C). No evidence was provided to suggest that any of the cynobacteria studied possess a Mo-independent nitrate reductase. Anabaena variabilis ATCC 29413 and Anabaena sp. PCC 7120 grew in NO3- containing medium supplemented with V, but only at the expense of N2-fixation: C2H2 reduced to C2H6 under these conditions. Anabaena variabilis ATCC 29413, Anabaena cylindrica CCAP 1403/2A, Anabaena sp. PCC 7120 and Nostoc sp. UCSB7 grew in medium containing NO2- or NH4+ when supplemented with Mo, V or W. No C2H2 reduction was observed under any of these conditions. Growth rates were significantly slower in the presence of NH4+ than on N2, NO3- or NO2-. Isolation of the V-nitrogenase from Clostridium pasteurianum was performed using an S-200 gel filtration column. EPR studies have shown that the component 1 protein of this enzyme possesses both FeMoco and FeVaco. The C2H2 reduction pattern is indicative of a Mo-independent system.

Estilos ABNT, Harvard, Vancouver, APA, etc.

12

Deng, Li. "Cyanophages of bloom-forming cyanobacteria." Thesis, University of Bristol, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.492570.

Texto completo da fonte

Resumo:

Cyanobacteria are an important and a diverse group of photo synthetic prokaryotes found in marine, freshwater and terrestrial environments. Over the past two decades, research has shown that cyanobacterial community structures are influenced through infection by cyanobacterial viruses (cyanophages). In marine systems cyanophages have been shown to play roles in the mortality of their hosts, as well as in driving the succession and evolution of phenotypes.

Estilos ABNT, Harvard, Vancouver, APA, etc.

13

Vijayan, Vikram. "Circadian Gene Expression in Cyanobacteria." Thesis, Harvard University, 2012. http://dissertations.umi.com/gsas.harvard:10665.

Texto completo da fonte

Resumo:

Cyanobacteria are photosynthetic prokaryotes that live in aquatic environments. The cyanobacterium Synechococcus elongatus PCC 7942, (hereafter S. elongatus) coordinates its day and night behaviors via a circadian clock. The clock is entrained by light/dark cycles but continues to run in constant light conditions. The core circadian clock in S. elongatus is encoded by post-translational modifications of three Kai proteins, but the extent and mechanism of circadian gene expression are unknown. We provide the first unbiased characterization of circadian gene expression in S. elongatus, demonstrating that \(\sim 65\%\) of genes display oscillation in continuous light conditions, with some genes peaking in expression at subjective dawn and others at subjective dusk. We next sought to identify the mechanism by which such a large fraction of the genome could be rhythmically controlled. Through bioinformatic, correlative, and perturbation experiments, we find that circadian changes in chromosome topology/supercoiling are sufficient to drive rhythmic expression (Chapter 2). To further investigate how chromosome topology can control gene expression we performed a high resolution characterization of transcripts and RNA polymerase across the S. elongatus genome (Chapter 3). Bioinformatic analysis of transcription start sites suggests that the AT/GC content a particular region of the promoter is informative in defining the phase at which a transcript is maximally expressed. We find that these sequences are sufficient to drive circadian gene expression at a particular phase and that mutation of single nucleotides in this region can reverse the expression phase of a transcript (Chapter 4). To understand the role of chromosome dynamics in circadian gene expression and cyanobacterial physiology, we tagged and followed chromosomes over multiple cell divisions. We find that S. elongatus cells harbor multiple ordered copies of a single chromosome, and the organization of chromosomes in the cytoplasm facilitates equal segregation of chromosomes to daughter cells (Chapter 5).

Estilos ABNT, Harvard, Vancouver, APA, etc.

14

Nürnberg, Dennis J. "Intercellular communication in filamentous cyanobacteria." Thesis, Queen Mary, University of London, 2015. http://qmro.qmul.ac.uk/xmlui/handle/123456789/8811.

Texto completo da fonte

Resumo:

Cyanobacteria represent one of the morphologically most diverse groups in the bacterial world, and one of the few where true multicellularity evolved. Their diversity ranges from single cells to branched filamentous forms. Some filamentous cyanobacteria are additionally able to undergo cell differentiation forming a two cell type system that represents the simplest model of multicellularity. Anabaena sp. PCC 7120 has been studied extensively in recent years as a model organism. Under nitrogen deprivation it differentiates photosynthetically-active vegetative cells into heterocysts, specialised cells for nitrogen fixation. Accordingly, true multicellularity of nitrogen-fixing cyanobacteria requires different forms of intercellular communication and mutual exchange of nutritional and regulatory compounds. Although several studies could show that molecules are exchanged between cells in Anabaena sp. PCC 7120, little is known about the properties and routes that allow molecules to diffuse between adjacent cells. In this work, the transfer of several physiologically-important molecules was investigated, including the fluorescent sucrose analogue esculin, the fluorescent glucose derivatives 2-NBDG (2-(N-(7-Nitrobenz-2-oxa-1,3-diazol-4-yl)amino)-2-deoxyglucose) and 6-NBDG (6-(N-(7-Nitrobenz-2-oxa-1,3-diazol-4-yl)amino)-6-deoxyglucose), and the artificial fluorescent tracer BCECF (2′,7′-Bis-(2-carboxyethyl)-5-(and-6-)carboxyfluorescein). Furthermore, the role of the septal proteins FraC, FraD and SepJ for the exchange of these molecules was examined in Anabaena sp. PCC 7120. Confocal microscopy and fluorescence recovery after photobleaching (FRAP) experiments reveal that cytoplasmic diffusion through channels between neighbouring cells is the primary route for molecular exchange. Loss of FraC, FraD and SepJ strongly reduced the movement of molecules between cells. Overexpression of sepJ altered the heterocyst spacing pattern in Anabaena sp. PCC 7120, suggesting a role of SepJ for the diffusion of regulators. Further, multicellularity in terms of intercellular communication was explored in Mastigocladus laminosus, a true branching cyanobacterium that is one of the morphologically most complex prokaryotes. FRAP analyses indicate the cytoplasmic continuity of the filament network and the dependency of molecular exchange on the morphology of the trichomes.

Estilos ABNT, Harvard, Vancouver, APA, etc.

15

Taylor, George. "Fatty acid metabolism in cyanobacteria." Thesis, University of Exeter, 2012. http://hdl.handle.net/10871/9363.

Texto completo da fonte

Resumo:

With crude oil demand rising and supplies being depleted, alternative energy, specifically biofuels, are of intense scientific interest. Current plant crop based biofuels suffer from several problems, most importantly the use of land needed for food. Cyanobacteria offer a solution to this problem as they do not compete with land for food and produce hydrocarbons that can be used as biofuels. Upon examination of metabolic pathways competing with hydrocarbon synthesis, it appeared that cyanobacteria lacked the major fatty acid degradative metabolic pathway β-oxidation, generally thought to be a universally occurring pathway. Lack of this pathway in cyanobacteria was confirmed by employing a range of analytical techniques. Bioinformatic analysis suggested that potential enzymes with β-oxidation activity were involved in other metabolic pathways. A sensitive assay was set up to detect acyl- CoAs, the substrates of β-oxidation, using liquid chromatography triple quadrupole mass spectrometry. None could be detected in cyanobacteria. No enzymatic activity from the rate-limiting acyl-CoA dehydrogenase/oxidase could be detected in cyanobacterial extracts. It was found that radiolabeled fatty acids fed to cyanobacteria were utilised for lipid membranes as opposed to being converted to CO2 by respiration or into other compounds by the TCA cycle. An element of the β-oxidation pathway, E. coli acyl-CoA synthetase was ectopically expressed in a strain of cyanobacteria and implications of the introduction of acyl-CoA synthesis were assessed. Finally, the regulation of the fatty acid biosynthetic pathway was investigated. It was determined that under conditions of excess fatty acid, the transcription of acetyl-CoA carboxylase and enoyl-ACP reductase was repressed and acyl-ACP synthetase involved in fatty acid recycling was induced. These results were discussed in relation to fatty acid oxidation and hydrocarbon biosynthesis in other organisms.

Estilos ABNT, Harvard, Vancouver, APA, etc.

16

Symes, Elizabeth Anne. "Freshwater Cyanobacteria within Extreme Environments." Thesis, The University of Sydney, 2016. http://hdl.handle.net/2123/15606.

Texto completo da fonte

Resumo:

The proliferation of undesirable cyanobacteria within eutrophic freshwaters is now reported on a global scale, however the factors triggering cyanobacteria bloom formation were found to be especially complex. Even within a single water body, physical, chemical and biological factors all influence the assemblage of phytoplankton found. Notwithstanding the body of research conducted over the past 50 years, where concerted efforts have been applied to observing bloom patterns and the drivers of cyanobacteria blooms, substantial knowledge gaps were identified. An examination of field methods, the factors promoting the growth of cyanobacteria blooms in modified inland aquatic ecosystems, modelling to predict the onset of a bloom using a 7 day positive model, and consideration of the likely effects increasing atmospheric CO2 could have on the development of surface dwelling species were key themes addressed. The thesis represents a combination of field based and controlled experimental laboratory research. A three-year case study was undertaken at an inland freshwater impoundment where cyanobacteria blooms had become a burgeoning issue. Standard surface monitoring and in situ multi-parameter instruments were used to determine environmental stressors. Importantly the water body was characterised as a well-mixed system. A hypertrophic classification was attributed to the water body due to nutrient super saturation, high water temperatures and suspended sediment measured in all years. A discrepancy between the available analysis methods was found, as the molecular method detected a diversity of microorganisms including several cyanobacteria species, whereas microscopy detected only one species. Notably harmful colonies of picocyanobacteria were not observed using standard microscopy. The molecular data also showed cyanobacteria represented 30% of the total bacterial community yet; molecular analyses may be limited when cell counts are required for a comparison with the alert level framework. The case study found the adoption of multi-monitoring and analysis methods constitutes best practice, and should therefore be integral to early detection, risk mitigation and system characterisation. A controlled laboratory study was undertaken to measure the efficacy of emerging technology as a water quality-monitoring stratagem, with emphasis placed on the accuracy of fluorometry in turbid waters above 50 nephelometric turbidity units (NTUs). The results found in vivo fluorometry using a Manta 2 probe was useful for detecting Microcystis aeruginosa at concentrations consistent with the National Health and Medical Research Council’s alert framework (Green, Amber and Red). Phycocyanin was found to be a more reliable measure of cyanobacteria than chlorophyll a, and by using a calibrated instrument it was possible to accurately detect cyanobacteria in turbid waters up to 220 NTUs. Cyanobacteria are highly effective at CO2 assimilation, with a remarkable capacity to adapt to different CO2 conditions, however scant research had previously focused on understanding how freshwater species may respond to increasing atmospheric CO2. Controlled laboratory experiments were performed and diazotrophic and non-diazotrophic cultures were exposed to past and projected atmospheric CO2 concentrations. Both experimental species adapted to the ambient low and high CO2 conditions, however, significantly higher bio volume was measured in the elevated CO2 chambers. The ability of freshwater ecosystems to maintain steady state water chemistry or base-neutralizing capacity if atmospheric CO2 concentrations reach levels projected for the latter part of this century is questionable, and furthermore, the study provided empirical evidence to support the theoretical position that increasing CO2 may lead to changes in water chemistry, particularly a decrease in pH values.

Estilos ABNT, Harvard, Vancouver, APA, etc.

17

Mesfin, Melaku. "Comparative study of cyanobacteria of desert and semi-desert crusts of two different continents: Africa (Ethiopa) and North America (USA)." Cleveland, Ohio : Cleveland State University, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=csu1245854204.

Texto completo da fonte

Resumo:

Thesis ( Ph.D.)--Cleveland State University, 2009. Abstract. Title from PDF t.p. (viewed on July 22, 2009). Includes bibliographical references (p. 154-160). Available online via the OhioLINK ETD Center and also avaliable in print.

Estilos ABNT, Harvard, Vancouver, APA, etc.

18

Dillon, Jesse Gardner. "Cyanobacterial responses to UV irradiance : the synthesis and protective role of scytonemin /." view abstract or download file of text, 2000. http://wwwlib.umi.com/cr/uoregon/preview?9977899.

Texto completo da fonte

Resumo:

Thesis (Ph. D.)--University of Oregon, 2000. Typescript. Includes vita and abstract. Includes bibliographical references (leaves 199-217). Also available for download via the World Wide Web; free to University of Oregon users.

Estilos ABNT, Harvard, Vancouver, APA, etc.

19

Mihali, Troco Kaan Biotechnology &amp Biomolecular Sciences Faculty of Science UNSW. "Biosynthesis of toxic alkaloids in cyanobacteria." Publisher:University of New South Wales. Biotechnology & Biomolecular Sciences, 2008. http://handle.unsw.edu.au/1959.4/41485.

Texto completo da fonte

Resumo:

Freshwater cyanobacteria produce a wealth of biologically active metabolites, which can adversely affect human and animal health, and cause great economic damage to the fishing, tourism and water-management industries on a global scale. We describe the molecular genetics and biochemistry of biosynthesis for the cyanobacterial toxic alkaloids cylindrospennopsin, paralytic shellfish toxins (PST) and anatoxin-a. Characterisation of the 43 kb cylindrospennopsin biosynthesis gene cluster (cyr), in Cylindrospermopsis raciborskii AWT205 is described. Biosynthesis is initiated via an amidinotransfer onto glycine followed by five polyketide extensions. Rings are formed via Michael additions, while the uracil ring is formed by a novel mechanism. Tailoring reactions, including sulfation and hydroxylation complete the biosynthesis. We describe the characterisation of PST biosynthesis gene clusters in Anabaena circinalis, Aphanizomenon sp. and Lyngbya wollei. These gene clusters span between 28 and 36 kb and contain genes coding for the biosynthesis and export of PSTs. The Lyngbya wollei PST gene cluster represents a 'natural combinatorial biosynthesis' event, explaining its unique toxin profile. A biosynthetic pathway leading to the formation of saxitoxin and its analogues in these organisms is proposed, and a putative insertion/excision site of the PST gene cluster in Anabaena circinalis 310F was identified. Interestingly, PSTs are produced by distantly related organisms via this unique biosynthesis pathway. We Investigated the phylogenetics of PST biosynthesis genes from four different genera of cyanobacteria. The results suggested that PST biosynthesis in cyanobacteria is an ancient trait, whereby the sporadic distribution of PST production in extant isolates of Anabaena circinalis and Aphanizomenon sp. is a result of the repeated loss of the biosynthetic gene cluster. Horizontal gene ransfer also appears to have had a critical influence on PST biosynthesis in Lyngbya wollei. We additionally propose a hypothetical, mixed non-ribosomal peptide synthetase (NRPS)/polyketide synthase (PKS) biosynthesis scheme for anatoxin-a. Degenerate PCR primers were developed, for the specific amplification of mixed NRPSIPKS hybrid ketosynthase (KS) domains. Gene-walking distally to a novel hybrid KS domain in the anatoxin-a producer Planktothrix rubescens, revealed an orphan gene cluster, denoted pro, which spans 24 kb and codes for a mixed NRPS/PKS system, putatively producing an acetylated and sulphated dipeptide.

Estilos ABNT, Harvard, Vancouver, APA, etc.

20

Bury, Nicolas R. "The effects of cyanobacteria on fish." Thesis, University of Dundee, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.367494.

Texto completo da fonte

Estilos ABNT, Harvard, Vancouver, APA, etc.

21

Winder, Jula Susan. "Clycosidase inhibitors from microalgae and cyanobacteria." Thesis, University of Hertfordshire, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.303402.

Texto completo da fonte

Estilos ABNT, Harvard, Vancouver, APA, etc.

22

Bojadzija, Savic Gorenka. "Metabolic interactions between Daphnia and cyanobacteria." Thesis, Rennes 1, 2019. http://www.theses.fr/2019REN1B061.

Texto completo da fonte

Resumo:

Il n'est pas clair si la présence de zooplancton a un impact sur la production de métabolites secondaires chez les cyanobactéries, le stress oxydatif et la physiologie des cyanobactéries. Le zooplancton est capable de développer une tolérance en tant que réponse physiologique aux cyanobactéries et à leurs composés bioactifs, grâce à des mécanismes tels que l'augmentation de l'activité des enzymes antioxydants de stress et des enzymes de détoxification. Cependant, cela s'accompagne d'un coût énergétique qui, à son tour, influence les traits de vie des daphnies et peut nuire à leurs populations. L'objectif principal de cette thèse est de mieux comprendre la complexité de la co-acclimatation et de la coexistence mutuelle entre daphnies et cyanobactéries. Nous émettons l'hypothèse que : a) la présence de D. magna induira un mécanisme de défense chez M. aeruginosa par la production de composés bioactifs spécifiques et affectera sa physiologie et b) la présence de M. aeruginosa affectera les réponses physiologiques et les traits de vie chez D. magna. Afin de déconvoluer les interactions mutuelles, M. aeruginosa a été exposé à du filtrat de D. magna, et vice-versa, D. magna a été exposé à du filtrat de M. aeruginosa. Des interactions mutuelles entre M. aeruginosa et D.magna ont été observées dans une chambre de co-culture spécialement construite pour permettre l'échange des métabolites au travers d’une membrane de 0.2 μm sans contact direct entre les organismes. La croissance, l'activité photosynthétique, les ROS et la dynamique des métabolites secondaires intracellulaires et extracellulaires ont été suivis chez M. aeruginosa en présence de daphnies. Parallèlement, des réponses physiologiques et des réponses aux traits de vie de Daphnia ont été suivies, y compris la survie, le stress oxydatif, la biotransformation et la répartition de l'énergie en présence de M. aeruginosa. Les résultats ont montré que le filtrat de Daphnia avait un impact sur la physiologie des cyanobactéries et leur stress oxydatif, mais que la réponse dépendait du type d'exposition, des densités initiales et de la concentration des composés info-chimiques de Daphnia dans le filtrat. La souche M. aeruginosa, qui ne produit pas de microcystin (MC-) a mieux résisté au stress causé par le filtrat de D. magna, que la souche M. aeruginosa qui produit de la microcystin (MC+). Dans l’expérience de co-culture, la souche toxique (MC+) a réussi à s’acclimater aux composés de daphnies diffusant progressivement à travers la membrane. De plus, des concentrations extracellulaires élevées de MC-LR (en co-culture) et de Cyanopeptolin A (expérience de filtrat de Daphnia) pourraient jouer un rôle anti prédation, mais d'autres recherches sont nécessaires pour confirmer cette fonction. M. aeruginosa a affecté négativement la survie de la daphnie dans toutes les configurations d'exposition. La diminution de l'activité de la CAT, de la SOD et de la GST suggère l'épuisement enzymatique dû à la présence de MC-LR et d'autres composés dans le milieu lors de l’exposition en co-culture ou de l’exposition du filtrat de la souche toxique de M. aeruginosa. De plus, dans les deux types de setups expérimentaux, la diminution des paramètres énergétiques chez la Daphnie suggère une allocation d'énergie vers des mécanismes de réponse au stress qui n'ont pas été observés dans cette étude Freshwater ecosystems frequently experience cyanobacterial blooms, many of which produce toxic and bioactive metabolites that can affect zooplankton life traits. However if the presence of zooplankton influences the production of cyanobacterial bioactive compounds, oxidative stress and affects physiology in cyanobacteria is unclear. At the same time, zooplankton are able to develop tolerance as a physiological response to cyanobacteria and their bioactive compounds, through mechanisms such as increase of antioxidative stress enzymes and detoxification enzymes activity. However, this comes with energetic cost that in turn influence Daphnia life traits and may impair populations. The main aim of this project is a better understanding of the complexity of mutual acclimations and co-existence between Daphnia and cyanobacteria. The hypothesis are: a) the presence of D. magna will induce a defense mechanism in M. aeruginosa via the production of specific bioactive compounds and affect its physiology; and b) the presence of M. aeruginosa will affect physiological responses and life traits in D. magna. In order to disentangle mutual interactions, M. aeruginosa was exposed to D.magna spent medium, and vice-versa, D.magna was exposed to cell free cyanobacterial medium obtained from axenically grown M. aeruginosa. Mutual interactions between M. aeruginosa and D.magna were observed in a specially built co-culture chamber that allowed exchange of the metabolites via a membrane of 0.2 μm without direct contact of the organisms. Cyanobacterial growth, photosynthetic activity, ROS and the dynamics of intracellular and extracellular cyanobacterial secondary metabolites was monitored in the presence of Daphnia. In parallel, Daphnia physiological and life trait responses were recorded, including, survival, oxidative stress, biotransformation and energy allocation in the presence of M. aeruginosa. Daphnia spent medium impacted on cyanobacterial physiology and oxidative stress, and response depended on the type of exposure set-up (aquaria versus co-culture chamber), initial densities and concentration of Daphnia infochemicals in the spent medium. Non-microcystin (MC-) producing M. aeruginosa dealt better with the stress caused by D.magna spent medium, than microcystin producing (MC+) M. aeruginosa. In the co-culture chamber experiment, microcystin producing (MC+) M. aeruginosa was able to acclimate to D.magna infochemicals slowly diffused through the membrane, maintaining good physiology. Furthermore, elevated concentration of extracellular MC-LR (co-culture exposure), Cyanopeptolin A (exposure to D.magna spent medium) could have anti-grazing role, however, more research is needed to confirm this function. Microcystis negatively affected Daphnia survival in all exposure setups. Decrease of CAT, SOD and GST activity after 7 days of exposure suggests enzyme exhaustibility due to presence of MC-LR and other compounds in the medium in both co-culture chamber exposure, as well as direct exposure to (MC+) M. aeruginosa spent medium. Similarly, in both experimental set-ups, decreasing energetic resources in Daphnia suggest energy allocation towards mechanisms dealing with stress different of those observed in this study

Estilos ABNT, Harvard, Vancouver, APA, etc.

23

Dryden, Robert Cumming. "Predation of cyanobacteria by Acanthamoeba spp." Thesis, University of Bath, 1987. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.376341.

Texto completo da fonte

Estilos ABNT, Harvard, Vancouver, APA, etc.

24

Axmann, Ilka Maria. "The regulatory potential of marine cyanobacteria." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, 2007. http://dx.doi.org/10.18452/15598.

Texto completo da fonte

Resumo:

Das Leben auf der Erde wird maßgeblich durch die Kraft der oxygenen Photosythese bestimmt, die Sonnen- in chemische Energie umwandelt. Cyanobakterien wie Prochloro- und Synechococcus zählen zu den wichtigsten primären Produzenten der Ozeane und werden zunehmend als Modelle für photosynthetische Organismen genutzt. Um die Regulationsmechanismen dieser Picocyanobakterien besser zu verstehen, wurde hier die Information von vier Genomen hochgradig verwandter aber dennoch ökologisch unterschiedlich angepasster mariner Stämme genutzt in einer Kombination aus computer-gestützten und experimentellen Untersuchungen. Sequenzsignale und RNA-kodierende Gene wurden als neuartige Regulationselemente identifiziert und entlang des phylogenetischen Gradienten verglichen. Mittels ''phylogenetic footprinting'' konnte ein minimales, konserviertes Set möglicher Transkriptionsfaktoren, deren Bindestellen und Regulons aufgedeckt werden. NtcA-, LexA- und ArsR-ähnliche Motive wurden ebenso gefunden wie neue regulatorische Elemente. Mit Hilfe von RACE Experimenten wurden einige der vorhergesagten Bindestellen Promotorregionen zugeordnet. Eine Suche nach konservierten Sekundärstrukturen detektierte mehrere nicht-kodierende RNAs, benannt Yfr für cYanobacterial Functional RNA. Eine vergleichende Analyse von Yfr7 innerhalb der cyanobakteriellen Linie ergab, dass diese RNA wahrscheinlich ein Homolog der E. coli 6S RNA ist. Zwei verschiedene Yfr7 Transkripte mit einem zirkadianen aber zeitversetzten Akkumulationsmuster lassen eine Verknüpfung ihrer Expression mit dem zirkadianen Rhythmus oder der Lichtintensität vermuten. Experimente in Synechocystis deckten einen neuartigen Regulationsmechanismus durch eine antisense RNA auf, welche die Menge der isiA mRNA kontrolliert und die Assemblierung von IsiA-Superkomplexen beeinflusst. Die funktionelle Zuordnung dieser neuen Elemente wird zu einem besseren Verständnis regulatorischer Netzwerke in marinen Cyanobakterien und darüber hinaus führen. Life on Earth is driven by the power of oxygenic photosynthesis transforming solar into chemical energy. Cyanobacteria such as Prochlorococcus and Synechococcus belong to the most important primary producers within the oceans and increasingly serve as models for photosynthetic organisms. To better understand the regulatory mechanisms in these picocyanobacteria, here the information from four genomes of closely related and even so ecologically divergent marine strains was used in a combined computational and experimental approach. Sequence signals and RNA-coding genes as novel elements in the regulation of gene expression were identified and their distribution along the phylogenetic gradient compared. Phylogenetic footprinting revealed a minimal conserved set of putative transcription factors, their binding sites and regulons. Sites for NtcA, LexA and ArsR-like regulators were found as well as new cis elements. RACE experiments verified several of these predicted sites belonging to the promoter region. A search, focussing on conserved secondary structures, detected several non-coding RNAs named Yfr for cYanobacterial Functional RNA. A comparative analysis of Yfr7 structures, transcript types and accumulation throughout the cyanobacterial radiation indicated this RNA as the likely homologue of the E. coli 6S RNA. Two distinct Yfr7 transcripts with a circadian but time-shifted expression pattern suggested a coupling of their expression to the circadian rhythm or light intensity. Experiments in Synechocystis discovered a novel antisense RNA-mediated regulatory mechanism that controls isiA mRNA abundance and assembly of IsiA-photosystem I supercomplexes. Functional assignments of these new elements in the future will contribute to a deeper understanding of the regulatory network of marine cyanobacteria and promote new studies on bacterial ncRNAs.

Estilos ABNT, Harvard, Vancouver, APA, etc.

25

Mascia, Francesco. "Engineering ferredoxin-dependent oxyfunctionalization in cyanobacteria." Electronic Thesis or Diss., Aix-Marseille, 2022. http://www.theses.fr/2022AIXM0648.

Texto completo da fonte

Resumo:

Les cyanobactéries drainent une attention grandissante en tant que photo-biocatalyseurs répondant aux critères de la Chimie Verte. Elles sont capables de croître en utilisant uniquement la lumière et le CO2 comme sources d’énergie et de carbone. L’ajout de donneurs d’électrons sacrificiels (ie glucose) pour le recyclage du cofacteur NADPH d’oxydoréductases n’est pas nécessaire car celui-ci est régénéré par des électrons issus de l'oxydation photosynthétique de l'eau tandis que les oxygenases peuvent utiliser le dioxygène produit in-situ lors de la photosynthèse. Une souche de Synechocystis sp. PCC 6803, modifiée pour exprimer CYP153A6, un cytochrome P450, hydroxyle sélectivement le limonène, substrat bon marché et largement disponible, en l'alcool périllylique, utilisable comme arôme ou médicament. Une autre souche, exprimant le seul CYP110D1 et non les protéines porteuses d'électrons de ce cytochrome P450, catalyse l'hydroxylation regiosélective de la testostérone en 15β-hydroxytestostérone, davantage biodisponible et adapté aux formulations orales. L’activité (1 U gCDW-1) est deux fois plus grande que celle des réactions biocatalysées par la bactérie Escherichia coli. Une protéine de fusion CYP110D1- Fed1, une des ferrédoxines natives de Synechocystis, a également été conçue, visant à canaliser plus efficacement les électrons du photosystème I vers la monooxygénase.Ce travail a démontré l'efficacité des cyanobactéries modifiées exprimant des cytochromes P450 lorsqu’elles sont utilisés en tant que biocatalyseurs dans des procédés à cellules entières. Elles permettent la production durable de produits de grande valeur, tels que les produits pharmaceutiques Cyanobacteria are attracting growing attention as photo-biocatalysts meeting the criteria of Green Chemistry. They are able to grow using only light and CO2 as energy and carbon sources. The addition of sacrificial electron donors (i.e. glucose) for the recycling of the NADPH cofactor of oxidoreductases is not necessary because it is regenerated by electrons from the photosynthetic oxidation of water, while the oxygenases can use the oxygen produced in-situ during photosynthesis. A strain of Synechocystis sp. PCC 6803, modified to express CYP153A6, a cytochrome P450, selectively hydroxylates limonene, a cheap and widely available substrate, to perillyl alcohol, usable as a flavor or drug. Another strain, expressing only CYP110D1 without any electron-carrier proteins of this cytochrome P450, catalyzes the regioselective hydroxylation of testosterone to 15β-hydroxytestosterone, which is more bioavailable and suitable for oral formulations. The activity (1 U gCDW-1) is twice as high as that of the reactions biocatalyzed by the bacterium Escherichia coli. A CYP110D1-Fed1 fusion protein, one of the native Synechocystis ferredoxins, was also designed, aiming to channel photosystem I electrons more efficiently to monooxygenase. This work demonstrated the efficacy of modified cyanobacteria expressing cytochromes P450 when used as biocatalysts in whole-cell processes. They enable the sustainable production of high-value products, such as pharmaceuticals

Estilos ABNT, Harvard, Vancouver, APA, etc.

26

Liu, Xuejun, and 劉學軍. "An eco-physiological study of the edible terrestrial cyanobacterium Nostoc flagelliforme: towards successfulartificial cultivation." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2004. http://hub.hku.hk/bib/B29514836.

Texto completo da fonte

Estilos ABNT, Harvard, Vancouver, APA, etc.

27

Nagarkar, Sanjay. "The ecology of intertidal epilithic biofilms with special reference to cyanobacteria /." Hong Kong : University of Hong Kong, 1996. http://sunzi.lib.hku.hk/hkuto/record.jsp?B19667218.

Texto completo da fonte

Estilos ABNT, Harvard, Vancouver, APA, etc.

28

Sadeghi, Abbas. "Gene Expression in Two Cyanobacteria, Freshwater Synechococcus sp. PCC 7942 and Oceanic Synechococcus sp. WH 7803, in response to ammonium, nitrate or iron." PDXScholar, 1998. https://pdxscholar.library.pdx.edu/open_access_etds/74.

Texto completo da fonte

Resumo:

The transcriptional response of freshwater Synechococcus sp. PCC 7942 and oceanic Synechococcus sp. WH 7803 to ammonium, nitrate or iron was studied in single or multiple factor limited cultures. Both strains showed maximum production of NiR mRNA when grown in nitrate-containing media. When grown in ammonium-containing medium, they did not show any signal for NiR mRNA synthesis. The influence on the transcription of NiR mRNA by iron as sole limiting nutrient was also evaluated. Iron increased the NiR mRNA whether or not the positive effect of nitrate was already present. The hybridization signal of mRNA for the large subunit of ribulose bisphosphate carboxylase/oxygenase enzyme (rbcl), was increased in both strains when iron was added. The relative response of NiA was larger than that of rbcL to iron addition. In the final set of experiments, combinations of iron, ammonium, or nitrate nutrient limitation were studied to understand their interactive effect on NiR and rbcL mRNA production. The ammonium-grown cells were allowed to starve for iron and then transferred to +iron+nitrate, +iron-nitrate, or -iron+nitrate cultures. rbcL mANA was increased gradually up to 168 hr. NiR mRNA increased initially but, for unknown reasons, decreased after 24 hr to a minimum that was similar for +iron+nitrate, +iron-nitrate, and -iron+nitrate cultures. A comparison of the rbcL or NiR mRNA from multiple nutrient limitation with that of single nutrient limitation showed different time dependent patterns of synthesis. The response to iron starvation could be different when cells experience a co-limitation with nitrate. This response is also influenced by species specific differences by evolutionary adaptation to different environments. This difference is confirmed in the NiR and rbcL mRNA response in two strains of marine and freshwater Synechococcus for single (iron) or multiple (iron+nitrate) limitation. Physiological studies commonly assume a single factor will constrain cell growth at any moment and when conditions change, the limiting factor will switch. The differential response in the synthesis of NiA and rbcl mANA observed shows that cells exhibit unique responses to combined limitations.

Estilos ABNT, Harvard, Vancouver, APA, etc.

29

Ferreira, Ana Helena Ferreira. "Peptides in Cyanobacteria under different environmental conditions." [S.l.] : [s.n.], 2006. http://deposit.ddb.de/cgi-bin/dokserv?idn=979948371.

Texto completo da fonte

Estilos ABNT, Harvard, Vancouver, APA, etc.

30

Zakrisson, Anna. "External Growth Control of Baltic Sea Cyanobacteria." Licentiate thesis, Stockholms universitet, Institutionen för ekologi, miljö och botanik, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-90086.

Texto completo da fonte

Resumo:

In the Himmerfjärden Bay a large excess of nitrogen over phosphorus in the discharge from a large sewage treatment plant (STP) has suppressed growth of diazotrophic cyanobacteria in its inner parts. Implementation of nitrogen removal in the STP in 1997 drastically reduced nitrogen load and triggered growth of diazotrophs, mainly Aphanizomenon sp. This study is part of a long-term series of experiments with the overall aim to test how algal biomass and production in a receiving area can be reduced, without stimulating nitrogen fixation and biomass growth by diazotrophic cyanobacteria. Nitrogen removal was discontinued in the STP during two years (2007-8) and resumed in 2009, and the discharge shifted from 25 to 10 m depth, above the seasonal pycnocline. Cellular 15N showed that N2 was the most important N source for diazotrophic cyanobacteria, and that uptake of combined nitrogen was insignificant. As biomass was declining and at the end of the productive season, we could detect a small, but significant, increase in cellular δ15N at the inner bay stations (H3 and H4). However, this coincided with an increased proportion of Anabaena spp. of the total diazotrophic biomass. This may indicate that Anabaena spp. has a higher uptake of combined nitrogen compared with Aphanizomenon sp. or that declining populations of Aphanizomenon sp. take up combined nitrogen. We also found no evidence of uptake of combined nitrogen during the winter months when nitrogen supply is ample and Aphanizomenon sp. is devoid of heterocysts. During the first half of summer (week 21-27) heterocyst frequencies were higher at the outer stations B1 and H2, compared to the inner bay stations (H4 and H5). The lower frequencies at the inner bay stations are likely due to the reduced growth rate suffered by the Aphanizomenon sp. due to stronger competition for phosphorus by non-diazotrophs at these stations and hence lower need for heterocysts. Towards the end of summer conditions even out along the bay, as the surplus phosphorus from the spring bloom is used up at the outer stations and no heterocyst gradient is present. Heterocyst frequency varied significantly over the summer, with minimum values in the beginning of July, coinciding with the highest water temperatures, and higher frequencies in early and late summer. We suggest this is primarily due to a more efficiently functioning nitrogenase enzyme at high temperatures with a reduced need for “expensive” heterocysts. Spring heterocyst differentiation occurred around 4-6 weeks after depletion of dissolved inorganic nitrogen (DIN) and only when water temperature was 5-9 oC and a pycnocline established. It seems that temperature and light in concert will initiate growth, leading to an internal nitrogen deficiency which starts heterocyst differentiation. Himmerfjärden eutrophication study

Estilos ABNT, Harvard, Vancouver, APA, etc.

31

Alambo, Katherine I. "Cyanobacteria North of 60°: Environmental DNA Approaches." Thesis, Université d'Ottawa / University of Ottawa, 2017. http://hdl.handle.net/10393/35665.

Texto completo da fonte

Resumo:

Cyanobacterial blooms, such as those recently reported in Great Slave Lake (GSL, NWT), have sparked concern over the occurrence of toxic blooms in the North. This study investigated past and present incidences of cyanobacteria in lakes above latitude 60° N. The abundance of the toxin (microcystin) gene mcyE, as well as genes common to all cyanobacteria (16S rRNA) and bacteria (glnA) were quantified from lake sediment cores using ddPCR. Individual colony isolates from a surface bloom in Yellowknife Bay (GSL) in August 2015 were amplified and identified as non-toxigenic Dolichospermum lemmermannii. Very low levels of microcystin genes were detected through the sediment archives (over ~100-150 yr) of GSL and other lakes, as well as in the plankton of GSL. While recent increases in mcyE were not observed, an increase in the cyanobacterial 16S rRNA and glnA genes was seen through time. In the high Arctic Meretta Lake, gene abundance profiles reflected the effects of past eutrophication and recovery.

Estilos ABNT, Harvard, Vancouver, APA, etc.

32

Bloor, Stephen. "Investigation of extracellular metabolite production by cyanobacteria." Thesis, University of Central Lancashire, 1989. http://clok.uclan.ac.uk/20913/.

Texto completo da fonte

Estilos ABNT, Harvard, Vancouver, APA, etc.

33

Cavaliere, Rosalia Biotechnology &amp Biomolecular Sciences Faculty of Science UNSW. "The regulation of Saxitoxin production in Cyanobacteria." Publisher:University of New South Wales. Biotechnology & Biomolecular Sciences, 2008. http://handle.unsw.edu.au/1959.4/44403.

Texto completo da fonte

Resumo:

Aquatic microalgae produce a variety of toxic secondary metabolites, which are a concern for public health and seafood industries, while also presenting a source of pharmacologically valuable compounds. The present study deals with the physiology and molecular genetics of saxitoxin (STX), a cyanobacterial neurotoxic alkaloid. Ecological and chemical parameters have been investigated for their effects on growth and STX production in the cyanobacterium Cylindrospermopsis raciborskii T3, in order to better understand the physiological responses of this cyanobacterium to the anthropogenic eutrophication of water bodies. The results indicated that phosphate, in particular, had an incremental effect on STX production, as well as promoting the up-regulation of transcription of the STX biosynthetic gene cluster (sxt). High temperature was found to negatively affect growth and STX production in this organism. The effects of the plant hormone, jasmonic acid, were also tested, since it has previously been shown to affect plant alkaloid production. The hypothesised similarity between cyanobacterial and plant secondary metabolism in response to this plant hormone was confirmed in the neurotoxic cyanobacterium, C. raciborskii T3, as well as the non-toxic Anabaena sp. PCC7120. Furthermore, investigation of the sxt gene cluster transcriptional map in C. raciborskii T3 was carried out, with identification of three main polycistronic and one monocistronic transcripts. Promoter regions putatively involved in the regulation of STX production in C. raciborskii T3 were also identified. Transcription factor consensus motifs, the pho boxes, were identified in the main promoter region. These conserved motifs are the binding regions for the transcriptional regulator, PhoB, to the pho regulon genes, involved in phosphate uptake during conditions of its depletion in the environment. Moreover, a genomic region adjacent to the sxt gene cluster in C. raciborskii T3 was identified and characterised, putatively encoding a regulatory two-component system. This system appears to be involved in the sensing of environmental signals, in particular depleted phosphate, while activating the transcription of genes involved in its uptake and transport. The results of this study lead to a greater understanding of the complex factors associated with the regulation of STX biosynthesis and bloom-formation, by the cyanobacterium C. raciborskii T3.

Estilos ABNT, Harvard, Vancouver, APA, etc.

34

Yeremenko, Nataliya Genadievna. "Functional flexibility of photosystem I in cyanobacteria." [Amsterdam] : Amsterdam : Universiteit van Amsterdam ; Universiteit van Amsterdam [Host], 2004. http://dare.uva.nl/document/73922.

Texto completo da fonte

Estilos ABNT, Harvard, Vancouver, APA, etc.

35

Joshua, Sarah. "Mobility of pigment-protein complexes in cyanobacteria." Thesis, University College London (University of London), 2005. http://discovery.ucl.ac.uk/1444430/.

Texto completo da fonte

Resumo:

Phycobilisomes, the light harvesting complexes of cyanobacteria are highly mobile, fluorescent complexes known to diffuse freely on the thylakoid membranes, interacting with the reaction centre complexes to mediate efficient photosynthesis. The primary aim of this project is to establish what processes require this rapid movement of the complexes using a number of genetic, biochemical and microscopic techniques. The cyanobacterial species used extensively in the work presented in this thesis are the fully sequenced, naturally transformable Synechocystis sp. PCC 6803 and Synechococcus sp. PCC 7942. The latter lends itself particularly well to quantitatively elucidating the diffusion rate of fluorescent complexes, but qualitative detection of mobile fluorescent complex is also feasible with Synechocystis 6803. State transitions are observed in cyanobacteria upon the alteration of illumination conditions. A rapid redistribution of excitation energy between the reaction centres is observed. This was investigated using high osmotic strength buffers to fix phycobilisomes to reaction centres they were associating with upon their addition, thus inhibiting their mobility, as adjudged by spectroscopy and microscopy using the Fluorescence Recovery after Photobleaching (FRAP) technique. It was found that mobile phycobilisomes are required for cells to be capable of state transitions. Non-Photochemical Quenching (NPQ) is a protective mechanism seen in iron- deprived cyanobacteria. Extensively studied in plants, its supposed function is to dissipate excess energy as heat to prevent photodamage to the reaction centres. Using Synechocystis 6803 and the techniques described above, phycobilisome mobility was determined to be critical to NPQ induction, and the interaction with IsiA in cyanobacteria was proposed as being involved in the process. A previously inactivated gene thought to be involved in state transitions, rpaC, was over-expressed in Synechocystis 6803 and knocked out in Synechococcus 7942 and gave pleiotropic effects. The conclusion that the binding of phycobilisomes to PSII is predictably stronger than to PSI was exploited by comparing the strength of the binding in the Synechococcus 7942 mutant with the wild type. Data were suggestive of the protein being involved in phycobilisome to PSII binding. Psb28* mutants of both species used in this thesis were extensively characterised, as the cells also presented a highly unusual mobile PSII phenotype. Psb28 is possibly involved in maintaining thylakoid membrane organisation.

Estilos ABNT, Harvard, Vancouver, APA, etc.

36

Aly, Wafaa S. M. "Novel aspects of iron acquisition in cyanobacteria." Thesis, University of Reading, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.553637.

Texto completo da fonte

Resumo:

Database searches revealed that some species of cyanobacteria, such as Synechocystis sp. PCC 6803 and Nostoc sp. PCC 7120, contain homologues of the Fet3p-Ftrlp high-affinity ferrous-iron uptake system, defined originally in the yeast Saccharomyces cerevisiae. These homologues include the ftr (ferric permease homologue, encoding a protein similar to Ftr 1 p) gene in both Synechocystis and Nostoc, and mco (a1l3942 a multicopper oxidase homologue- encoding a protein somewhat similar to Fet3p) found only in Nostoc where it is close to ftr. RT-PCR analysis indicated that ftr and mco in Nostoc are induced upon iron restriction as is fir in Synechocystis, thus supporting a role for these genes in iron uptake. Phenotypic studies in E. coli JC28 (a strain deficient in iron uptake) revealed that Ftr from Synechocystis is not functional in compensating for lack of iron-uptake capacity in E. coli. However, phenotypic studies revealed that the mco-all3941-bfr-ftr fragment of Nostoc causes a major enhancement of growth under aerobic iron restriction in E. coli JC28. However, the mco gene was not required for this growth promotion effect although inclusion of bfr (encoding the iron-storage protein, bacterioferritin) upstream of fir enhanced the effect of fir, and the inclusion of all3941-bfr upstream of fir raised growth still further. Thus, the Ftr of Nostoc does not require a Mco protein for its activity, but may instead use a bacterioferritin. Ftr-mediated growth enhancement was promoted by low pH and by the reductant ascobate, suggesting ferrous iron is the preferred Ftr substrate. In addition, the Ftr system had a weaker iron- restriction growth benefit anaerobically than that seen aerobically. Bioinformatics analysis indicated that All3942 (Mco) is a Tat exported periplasmic protein containing two cupredoxin domains with the blue copper and tri-nuclear inter-domain copper binding sites characteristic of multi copper oxidases. Overproduced and purified MalE-Mco was able to bind 5.8, 1.2 and 3.1 atoms of Cu, Zn and Fe, respectively, per subunit which is consistent with its Mco designation. UV-visible and EPR spectroscopy revealed the likely presence of Tl, T2, and T3 copper centres. Upon addition of ferrous iron to the copper-containing Mal-Mco, Tl signals were lost, presumably due to reduction of the centre, suggesting ferroxidase activity. Copper- soaked MalE-Mco showed phenoloxidase activity, as found for other Mco proteins, as well as limited ferroxidase activity indicating that it may, like Fet3p, oxidise ferrous iron in vivo. However, no requirement for the All3942/Mco protein in Ftr-mediated iron uptake was found in E. coli JC28 which suggests that the Nostoc Ftr protein may transport ferrous iron using a mechanism distinct from that of the yeast Ftr1p.

Estilos ABNT, Harvard, Vancouver, APA, etc.

37

Zakrisson, Anna. "External Growth Control of Baltic Sea Cyanobacteria." Doctoral thesis, Stockholms universitet, Institutionen för ekologi, miljö och botanik, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-112753.

Texto completo da fonte

Resumo:

The overall aim of the study was to provide better insights to the ecological role and impact of cyanobacteria in Baltic Sea (BS) bay, coastal and open sea areas. Biomass and heterocyst development of diazotrophic, heterocystous cyanobacteria were monitored over several years simultaneously as physical parameters such as nutrients and temperature. Nitrogen fixation was estimated as well as its transfer in the BS food web. Even after decades of debate there is still controversy whether eutrophication of lakes and estuaries/coastal areas should be managed by reducing phosphorus only or also nitrogen. Central to this debate is whether nitrogen fixation by cyanobacteria can replace shortages of combined nitrogen quickly enough to make phosphorus the limiting nutrient and nitrogen removal pointless or even harmful. Also, it is not clear if available combined nitrogen inhibits heterocystous cyanobacterial nitrogen fixation and if it is used for their growth in situ. A large ecosystem-wide experiment started in Himmerfjärden bay in year 1997, where the N-loadings and release depth from a modern sewage treatment plant (STP), located in the inner part of the bay, were modulated. The STP creates a steep gradient of nutrients and stable nitrogen isotopes, which can be used to study uptake of combined nitrogen, as well as biomass development and primary productivity. A 35-year long data series was used to achieve good insights into phytoplankton development and primary productivity in the Baltic Sea over the last couple of decades. These in vivo long time series, based on monitoring data, in combination with shorter series (2-3 seasons, including measurements of colony stoichiometry and stable isotopes), have resulted in a unique meta-dataset, allowing for high-resolution observations into the role of the cyanobacteria in the Baltic Sea ecosystem. At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Manuscript. Paper 4: Manuscript.

Estilos ABNT, Harvard, Vancouver, APA, etc.

38

Huang, Hsin-Ho. "Promoter Engineering for Cyanobacteria : An Essential Step." Doctoral thesis, Uppsala universitet, Institutionen för kemi - Ångström, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-206901.

Texto completo da fonte

Resumo:

Synthetic biology views a complex biological system as an ensemble in the hierarchy of parts, devices, systems, and networks. The practice of using engineering rules such as decoupling and standardization to understand, predict, and re-build novel biological functions from model-driven designed genetic circuits is emphasized. It is one of the top ten technologies that could help solving the current and potential risks in human society. Cyanobacteria have been considered as a promising biological system in conducting oxygenic photosynthesis to convert solar energy into reducing power, which drives biochemical reactions to assimilate and generate chemicals for a specific purpose such as CO2 fixation, N2 fixation, bioremediation, or fuels production. The promoter is a key biological part to construct feedback loops in genetic circuits for a desired biological function. In this thesis, promoters that don't work in the cyanobacterium Synechocystis PCC 6803 in terms of promoter strength, and dynamic range of gene regulation are identified. Biological parts, such as ribosome binding sites, and reporter genes with and without protease tags were also characterized with the home-built broad-host-range BioBrick shuttle vector pPMQAK1. The strong L03 promoter, which can be tightly regulated in a wide dynamic range by the foreign Tet repressor, was created through an iterative promoter engineering cycle. The iteration cycle of DNA breathing dynamic simulations and quantification of a reporting signal at a single-cell level should guide through the engineering process of making promoters with intended regulatory properties. This thesis is an essential step in creating functional promoters and it could be applied to create more diverse promoters to realize the emphasized practices of synthetic biology to build synthetic cyanobacteria for direct fuel production and CO2 assimilation.

Estilos ABNT, Harvard, Vancouver, APA, etc.

39

Cranenburgh, Rocky M. "HIP1 and gene re-arrangement in cyanobacteria." Thesis, University of Newcastle Upon Tyne, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.339458.

Texto completo da fonte

Estilos ABNT, Harvard, Vancouver, APA, etc.

40

Terasaki, Satoshi. "Phosphorus sensing/acquisition mechanisms in marine cyanobacteria." Thesis, University of Warwick, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.416188.

Texto completo da fonte

Estilos ABNT, Harvard, Vancouver, APA, etc.

41

Cozens, A. L. "ATP synthase genes in cyanobacteria and chloroplasts." Thesis, University of Cambridge, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.383121.

Texto completo da fonte

Estilos ABNT, Harvard, Vancouver, APA, etc.

42

Ridley, Matthew John. "Molecular genetics of coproporphyrinogen oxidase in cyanobacteria." Thesis, University of Cambridge, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.621544.

Texto completo da fonte

Estilos ABNT, Harvard, Vancouver, APA, etc.

43

Aspinwall, Caroline Liesel. "Photosystem I monomers and trimers in cyanobacteria." Thesis, University College London (University of London), 2005. http://discovery.ucl.ac.uk/1445270/.

Texto completo da fonte

Resumo:

Photosystem I (PSI) is one of the chlorophyll-protein complexes located in the thylakoid membranes of photosynthetic organisms. It catalyses the oxidation of reduced plastocyanin or cytochrome C6 and reduction of ferredoxin or flavodoxin during photosynthesis. The complex is composed of two core subunits, PsaA and PsaB, which bind electron-carrying cofactors, and numerous low molecular weight subunits. The precise composition of small subunits varies between prokaryotic and eukaryotic PSI and the function of many of these subunits remains unclear. This thesis describes studies of cyanobacterial mutants lacking small subunits in order to clarify the function of the PsaL and PsaE subunits. The subunit PsaE has been implicated in the interaction of PSI with ferredoxin and in cyclic electron transport. In cyanobacteria a trimeric form of PSI predominates, with PsaL acting as the point of contact between three monomer units. Cyanobacterial mutants lacking this subunit therefore produce only monomeric PSI. No evidence of trimerisation has been found for PSI in eukaryotic organisms. This study has established growth conditions in which PsaL-lacking mutants are disadvantaged compared to wild type. An investigation into the interaction of monomeric PSI with light-harvesting structures such as the phycobilisomes and the iron stress-induced CP43' antenna ring revealed that trimerisation of PSI is not required for interaction with either structure. However, the rates of state transitions and phycobilisome diffusion were measured and compared to those of wild type cells, revealing an increase in rate in both cells when PSI is monomeric. This suggests a change in the stability of the phycobilisome-PSI interaction. EPR analysis of electron transfer processes in cyanobacterial mutants lacking the PsaE subunit and of PSI in either monomeric (PsaL-lacking) or trimeric (wild type) forms has been conducted. Possible functional roles for PSI trimerisation are discussed.

Estilos ABNT, Harvard, Vancouver, APA, etc.

44

Neves, Fabiana Marisa Vieira das. "Cyanobacteria dynamics at Vela lake during 2008." Master's thesis, Universidade de Aveiro, 2009. http://hdl.handle.net/10773/882.

Texto completo da fonte

Resumo:

Mestrado em Microbiologia A lagoa da Vela, localizada no litoral Centro Português (Figueira da Foz), é uma lagoa superficial com características típicas de estado trófico avançado, utilizada para actividades recreativas e como fonte de água para a agricultura e pecuária. No presente estudo foi efectuada uma recolha anual (bimensal) de forma a compreender a variação sazonal dos parâmetros ambientais e fitoplâncton, e a influência dos primeiros na variação do fitoplâncton. Os parâmetros ambientais, como temperatura, pH, condutividade, oxigénio (% e dissolvido), nutrientes (nitratos, amónia, fósforo, sílica), clorofila a e sólidos totais, foram determinados também para, comparando com trabalhos anteriores sobre esta lagoa, compreender a evolução do estado trófico desta massa de água. O fitoplâncton foi dominado por Cianobactérias durante todo o período do estudo, com densidades entre 1,0x105 (Fevereiro) e 1,0x106 células/mL (Setembro). Este domínio foi acompanhado por valores baixos de oxigénio e nutrientes, e por valores elevados de pH, condutividade, clorofila a e sólidos totais. As espécies Aphanizomenon flos-aquae e Cilyndrospermopsis raciborskii foram registadas em Abril e, desde Junho até Dezembro. Este trabalho também demonstra, por comparação com outros trabalhos, que o fitoplâncton e as variações de nutrientes observadas são muito diferentes daqueles descritos anteriormente na lagoa da Vela. No período em estudo identificaram-se as classes de fitoplâncton Bacillariophyceae, Chlorophyceae, Cyanophyceae, Euglenophyceae and Cryptophyceae sendo que a classe dominante durante todo o ano foi a Cyanophyceae. Relativamente aos nutrientes, estes apresentavam valores muito baixos, especialmente fósforo, nitratos e amónia. ABSTRACT: Vela Lake located in Portuguese littoral-centre (Figueira da Foz), is a shallow lake with typical characteristics of advanced trophic state used for recreational proposes and as a water source for agriculture and livestock. An annual sampling (bi-monthly) was carry out in the present study in order to understand the seasonal variation of environmental parameters and phytoplankton, and the influence of the first-one on the phytoplankton variation. Environmental parameters such as temperature, pH, conductivity, oxygen (% and dissolved), nutrients (nitrate, ammonium, soluble reactive phosphorus, silica), chlorophyll a and Total suspended solids, were determined also to, by comparing with previous works on this lake, comprehend the evolution of the trophic status of this water bodie. The phytoplankton composition was dominated by Cyanobacteria during all study period, with densities between 1.0x105 (February) and 1.0x106 cells/mL (September). This dominance was accompanied by lowest values of oxygen and nutrients, and by highest values of pH, conductivity, chlorophyll a, and Total suspended solids. The taxa Aphanizomenon flos-aquae and Cilyndrospermopsis raciborskii were recorded in April and since June do December. This work also demonstrates, by comparing with further works, that the phytoplankton and nutrients variations observed are very different than those described in Vela Lake. In the present study period were identified phytoplankton classes Bacillariophyceae, Chlorophyceae, Cyanophyceae, Euglenophyceae and Cryptophyceae and the ruling class throughout the year was the Cyanophyceae. For nutrients, these had very low levels, especially phosphorus, nitrates and ammonium.

Estilos ABNT, Harvard, Vancouver, APA, etc.

45

Ribeiro, Maria João Xavier. "Marine cyanobacteria: evaluation of the anticancer potential." Master's thesis, Universidade de Aveiro, 2012. http://hdl.handle.net/10773/10491.

Texto completo da fonte

Resumo:

Mestrado em Biotecnologia Molecular Durante as últimas décadas, as cianobactérias têm ganho importância devido à sua capacidade de sintetizar metabolitos secundários com actividade biológica, úteis no tratamento de inúmeras doenças, tal como o cancro. A caracterização dos metabolitos secundários com aplicações farmacológicas tem sido maioritariamente feita com cianobactérias filamentosas marinhas, do género Lyngbya, Microcoleus e Symploca, recolhidas em áreas tropicais. Contudo, a investigação em cianobactérias marinhas que ocorrem em baixas densidades e em regiões temperadas, como a costa Portuguesa, tem sido largamente negligenciada. Neste sentido, este trabalho teve como objectivo avaliar o potencial anticancerígeno de cianobactérias isoladas da costa Portuguesa e mantidas no laboratório de Ecotoxicologia, Genómica e Evolução do Centro Interdisciplinar de Investigação Marinha e Ambiental, Porto. Cinco estirpes de cianobactérias pertencentes aos géneros Cyanobium, Leptolyngbya, Romeria e Synechocystis, LEGE06098 (Cyanobium sp.), LEGE06113 (Cyanobium sp.), LEGE06102 (Leptolyngbya cf. halophila), LEGE06013 (Romeria sp.) e LEGE06155 (Synechocystis salina), foram cultivadas em condições laboratoriais. A partir da biomassa liofilizada foi obtido um extracto bruto usando metanol e diclorometano, o qual foi posteriormente fraccionado usando hexano, acetato de etilo e metanol, originando as fracções A, B e C, respectivamente, de forma a separar compostos com polaridades crescentes. Com o extracto bruto e as fracções foram realizados ensaios de citotoxicidade em quatro linhagens humanas tumorais: osteosarcoma (MG63), adenocardinoma de cólon (RKO e HT29) e neuroblastoma (SH-SY5Y). A citotoxicidade foi avaliada através da redução do bromide 3-(4,5-dimetil-tiazol-2-il)-2,5-difenil-tetrazolio (MTT) e do ensaio da lactato desidrogenase (LDH). A ocorrência de Apoptose/Necrose foi investigada pelo método de exclusão dos corantes, usando Iodeto de Propídeo e Hoechst 33342. De entre o extracto bruto e as fracções preparadas de cada estirpe de cianobactérias, a fracção com a maior percentagem de acetato de etilo, fracção B, revelou uma maior percentagem de inibição das células tumorais, sendo, portanto, promissora relativamente ao isolamento de compostos bioactivos. De entre as estirpes de cianobactérias incluídas no estudo, a estirpe Synechocystis salina, LEGE06155, revelou ser a mais interessante para o isolamento de potenciais compostos bioactivos. In the last few decades, cyanobacteria have gained significant importance due to their ability to synthesize secondary metabolites with biological activity, useful in the treatment of a role of diseases, such as cancer. Characterization of bioactive metabolites with pharmacological applications has mainly been performed with marine filamentous cyanobacteria of the genera Lyngbya, Microcoleus and Symploca collected in tropical areas. However, the research on marine cyanobacteria that occur in low densities in temperate regions such as the Portuguese coast has been largely overlooked. In this work we aimed to assess the anticancer potential of marine cyanobacteria isolated from the Portuguese coast. Five cyanobacteria strains from the genera Cyanobium, Leptolyngbya, Romeria and Synechocystis, LEGE06098 (Cyanobium sp.) and LEGE06113 (Cyanobium sp.), LEGE06102 (Leptolyngbya cf. halophila), LEGE06013 (Romeria sp.), and LEGE06155 (Synechocystis salina), respectively, were cultivated under laboratory conditions. From freeze dried biomass a crude extract was obtained using methanol and dichloromethane and fractionated using hexane, ethyl acetate and methanol, yielding fractions A, B and C with increasing polarity. The crude extract and the fractions were tested for cytotoxicity in four human tumor cell lines: osteosarcoma (MG63), colon adenocarcinoma (RKO and HT29) and neuroblastoma (SH-SY5Y). Cytotoxicity was evaluated by the reduction of the bromide 3-(4,5-dimetil-tiazol-2-il)-2,5-difenil-tetrazolio (MTT) and the Lactate Dehydrogenase (LDH) assay. Apoptosis/Necrosis was investigated by the dye exclusion method, using both Propidum Iodide and Hoechst 33342. Among the crude extract and prepared fractions, the fraction containing the higher percentage of ethyl acetate, fraction B, from each cyanobacteria strain revealed the highest percentage of inhibition of tumor cells growth, and is, therefore, promising in terms of isolation of bioactive compounds. Among the cyanobacteria strains, the Synechocystis salina strain, LEGE06155, revealed to be an interesting strain for the isolation of bioactive compounds.

Estilos ABNT, Harvard, Vancouver, APA, etc.

46

Engström-Öst, Jonna. "Effects of cyanobacteria on plankton and planktivores." Helsinki : University of Helsinki, 2002. http://ethesis.helsinki.fi/julkaisut/mat/ekolo/vk/engstrom-ost/.

Texto completo da fonte

Estilos ABNT, Harvard, Vancouver, APA, etc.

47

Hutchins, David Allen. "Nitrogen and iron interactions in filamentous cyanobacteria." PDXScholar, 1989. https://pdxscholar.library.pdx.edu/open_access_etds/3934.

Texto completo da fonte

Resumo:

The investigations described in this paper are an attempt to further define and quantify the interrelationship of nitrogen fixation and iron nutritional physiology in these two species. Chapter II will present and compare data on nutritional ratios of field collected Trichodesmium colonies and laboratory Anabaena cultures, with the intent of examining possible correlations between observed iron levels and protein nitrogen and chlorophyll concentrations, as well as nitrogen fixation rates. Chapter Ill is an examination of nitrogen fixation and siderophore production in Anabaena with emphasis on the possible implications of hypothesized synergistic effects of these two physiological capabilities on cyanobacterial dominance and bloom formation. Chapter IV will deal with the possibility of gratuitous manganese repression of Anabaena siderophore production in the manner described by Hantke (1987) for regulation of siderophore production in E. coli. The Conclusions chapter (Chapter V) will present a discussion of the results of these experiments in the context of current problems in cyanobacterial physiology, ecology and evolution. It is hoped that a significant contribution can be made to our understanding of the related problems of cyanobacterial dominance in freshwater ecosysytems and the scarcity of cyanobacterial nitrogen fixation in marine ecosystems.

Estilos ABNT, Harvard, Vancouver, APA, etc.

48

Overman, Corina Christina Mae. "Modeling Vertical Migration of Cyanobacteria and Zooplankton." PDXScholar, 2019. https://pdxscholar.library.pdx.edu/open_access_etds/5178.

Texto completo da fonte

Resumo:

Cyanobacteria, also known as blue-green algae, often cause harmful algal blooms and release toxic substances that can harm humans and other animals. Accurately modeling these phytoplankton is a step towards predicting, preventing, and controlling such blooms. Cyanobacteria and zooplankton species are known to migrate vertically in the water column on a daily cycle. Capturing this behavior is one aspect of correctly modeling their dynamics. Here, several models of cyanobacteria vertical movement were tested in proof-of-concept models before being applied to data from field studies. These models included both continuum and particle-tracking frameworks. Four continuum-framework models of cyanobacteria vertical migration were chosen to add to the numerical hydrodynamic, water-quality model CE-QUAL-W2. These were tested using a model of Dexter Reservoir (Oregon), where they predicted vertical migratory movement seen in cyanobacteria. Models of zooplankton migration were also tested in proof-of-concept models as a steppingstone towards future incorporation into CE-QUAL-W2. Preliminary models of cyanobacteria and zooplankton vertical migration using a particle-tracking framework also provided information to be used in future model developments that will incorporate vertical migration of plankton into the particle-tracking module of CE-QUAL-W2.

Estilos ABNT, Harvard, Vancouver, APA, etc.

49

GASTOLDI, LUCIA. "Cyanobacteria Sulfur Metabolism under Precambrian environmental Conditions." Doctoral thesis, Università Politecnica delle Marche, 2020. http://hdl.handle.net/11566/274568.

Texto completo da fonte

Resumo:

Durante il Precambriano, le variazioni di SO42- negli oceani sono state così importanti da ipotizzare che la disponibilità di S abbia influenzato l’evoluzione del fitoplancton. Ho investigato come la regolazione del suo metabolismo nei cianobatteri possa essere cambiata nel tempo, concentrandomi sul primo step della catena assimilativa controllato dalla ATP sulforilasi (ATPS). I cambiamenti ambientali preistorici hanno influenzato la chimica oceanica portando ad un aumento del SO42- disponibile, a una diminuzione del Fe disciolto e ad un aumento nel consumo di equivalenti riducenti. Questi fattori avrebbero potuto influenzare l'uso di equivalenti riducenti negli organismi unicellulari primitivi, con evidenti ripercussioni sulla regolazione del metabolismo e sulla distribuzione delle risorse. Poiché la prima produzione primaria dipendeva principalmente dai cianobatteri fotossigenici, mi sono concentrata su di essi, studiandone le prestazioni fisiologiche, la composizione chimica e la ripartizione di risorse in ambiente proterozoico ricostruito e in quello moderno. Per comprendere l'impatto che i cambiamenti ambientali potrebbero aver avuto sull'ecologia degli oceani, ho analizzato le conseguenze sulla qualità della biomassa cianobatterica. I risultati ottenuti indicano 1) che le variazioni della disponibilità di O2 influenzano il tasso di crescita nei cianobatteri, 2) che la limitazione dei nutrienti unita alla variazione del potere riducente disponibile ha un effetto sull'attività delle ATPS (la concentrazione di nutrienti sembra avere un effetto più forte), e 3) che la limitazione dei nutrienti influenza l'assimilazione degli elementi e il pool macromolecolare. È possibile concludere che l'ossigenazione del pianeta potrebbe non essere stata l'unico vincolo evolutivo per lo sviluppo di una regolazione redox nelle ATPS. Inoltre i risultati biochimici supportano la teoria per cui i cianobatteri evolvendosiin acqua dolce hanno conquistato solo secondariamente l'oceano. During Precambrian, sulfate variations were so strong that one hypothesis guesses that S availability influenced phytoplankton evolution/radiation in the oceans. Considering this concept, I investigated how sulfate metabolism regulation in cyanobacteria may have changed through geological times focusing on the first step of the S assimilation pathway, which is controlled by the ATP sulfurylase (ATPS) protein. Precambrian environmental changes caused variation in the ocean chemistry, leading to an increase of sulfate availability, a decrease of dissolved Fe and, an increase in sinks for reducing equivalents in cell metabolism. Since all these factors could have influenced the usage of reducing equivalents in primitive unicellular organisms, evident repercussions on their metabolism regulation and resource/energy allocation/distribution are ensuing. Since the early primary production mostly depended on photo-oxygenic cyanobacteria, I focused on them studying their physiological performance, their chemical composition, and their resource and energy partitioning in the reconstructed proterozoic environment and in the modern one. To understand the impact that environmental changes may have had on ocean ecology, I also studied consequences on cyanobacterial biomass quality, to comprehend the consequences on the trophic webs. Present results point out that (1) oxygen availability variations influence growth rate in cyanobacteria, (2) nutrient limitation combined with redox power variation has an effect on the ATPS activity, but the nutrient concentration seems to be the strongest one, (3) nutrient limitation influences elements assimilation and macromolecular pool in cyanobacteria. It is possible to conclude that the oxygenation of the planet may not have been the only evolutive constraint for redox regulation in ATPS enzymes. Moreover, biochemical results support the theory stating cyanobacteria evolved in the freshwater environment and only secondly conquered the ocean.

Estilos ABNT, Harvard, Vancouver, APA, etc.

50

Everroad, Richard Craig. "Diversification of marine picocyanobacteria : the ecology and evolution of spectral phenotype and phycoerythrin /." view abstract or download file of text, 2007. http://proquest.umi.com/pqdweb?did=1324371891&sid=1&Fmt=2&clientId=11238&RQT=309&VName=PQD.

Texto completo da fonte

Resumo:

Thesis (Ph. D.)--University of Oregon, 2007. Typescript. Includes vita and abstract. Includes bibliographical references (leaves 117-137). Also available for download via the World Wide Web; free to University of Oregon users.

Estilos ABNT, Harvard, Vancouver, APA, etc.

Teses / dissertações sobre o tema "Cyanobacteria"

Crie uma referência precisa em APA, MLA, Chicago, Harvard, e outros estilos