Thesis (M.Sc.). / Written for the Dept. of Biology. Title from title page of PDF (viewed 2009/13/07). Includes bibliographical references.

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Mn was found to reduce the toxicity of Cu to the marine diatom Thalassiosira pseudonana (clone 3H) in the chemically well defined medium Aquil (Morel et al., 1979), verifying the results of Sunda and Huntsman (1983). A cation-exchange resin technique developed by Zorkin (1983) was modified for use in natural seawater samples to estimate the biologically active Cu and Mn. Seawater samples taken from the bottom waters of a local fjord were found to support better growth of the test organism than samples from shallow waters, although the concentration of the biologically active Cu as estimated by the resin technique was similar for samples collected from all depths. The biologically active Mn concentration was found to be higher in the bottom water samples, indicating that the bioassay organism was probably responding to the interaction between the ionic forms of Cu and Mn, rather than to changes in the biologically active Cu concentration. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

Thesis (M.S.)--University of North Carolina Wilmington, 2009. / Title from PDF title page (January 14, 2010) Includes bibliographical references (p. 28-30)

Submitted by Eduarda Figueiredo (eduarda.ffigueiredo@ufpe.br) on 2015-03-12T14:19:33Z No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) Dissertação_oceanografia.pdf: 1445279 bytes, checksum: 3027171fff7f9f76800597b9c4f442b7 (MD5) / Made available in DSpace on 2015-03-12T14:19:33Z (GMT). No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) Dissertação_oceanografia.pdf: 1445279 bytes, checksum: 3027171fff7f9f76800597b9c4f442b7 (MD5) Previous issue date: 2012-02 / CAPES / As microalgas estão dentre os organismos mais recomendados para avaliação de toxicidade aquática, pois fornecem informações sobre possíveis alterações qualitativas e quantitativas das populações, tornando-se importantes em monitoramento ambiental. Este estudo teve por objetivo avaliar a sensibilidade da microalga Thalassiosira weissflogii à possível toxicidade das águas do complexo portuário de Suape e ao dicromato de potássio durante os meses de julho, setembro e novembro de 2010 e janeiro e setembro de 2011, além de comparar com os resultados obtidos para o ouriço do mar Lytechinus variegatus. Os testes de toxicidade crônica para as duas espécies seguiram normas padronizadas, onde após o período de exposição, foi avaliado o crescimento populacional da microalga, através de dados de densidade celular e taxas de crescimento, tendo sido avaliado, também, o percentual de larvas pluteus de L. variegatus apresentando desenvolvimento normal e anômalo. Os resultados, baseados no crescimento algal e no percentual de pluteus, evidenciaram que a toxicidade nos pontos analisados variou de acordo com os meses. O estudo verificou que o melhor momento para encerramento do teste com a microalga T. weissflogii foi com 72 horas de exposição. Os resultados baseados na densidade celular da microalga, em 72 horas, foram eficientes para avaliação da toxicidade de amostras de águas superficiais e foram mais significativos do que para as taxas de crescimento. A microalga T. weissflogii demonstrou ser um organismo-teste sensível ao tóxico de referência. Setembro foi o mês mais comprometido, nos dois anos estudados.

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Thalassiosira oceanica, a marine centric diatom, possesses an extracellular reductase that reduces iron (Fe(III)) bound to organic complexes as part of a high-affinity Fe transport mechanism. A number of Fe(III) organic complexes are reduced, including siderophores---effective Fe chelates produced by microorganims in response to Fe stress. Reduction rates are inversely related to the relative stability constants of the oxidized and reduced Fe chelates (log Kox/Kred), and vary by a factor of 2.4 in accordance with theoretical predictions. Under Fe-limiting conditions, reduction rates increase and the ability of T. oceanica to transport Fe from siderophores is enhanced. Iron bound to the siderophore desferrioxamine B (DFB) is reduced 2 times faster than it is taken up, suggesting that the reductase is well coupled to the Fe transporter, and can provide all the inorganic Fe to account for the measured Fe uptake rates in the presence of excess DFB. The efficacy of the reductase in providing inorganic Fe for uptake and growth is ultimately dependent on the relative concentrations of excess ligands in solution and cell surface Fe transporters competing for inorganic Fe. The rates of Fe reduction and uptake are twice as fast in cells grown in NO3- compared to those grown in NH 4+, suggesting a link with cellular N metabolism and with NO3- utilization in particular. Enhanced Fe reductase activity in NO3--grown cells enables them to maintain a 1.6-fold higher cellular Fe concentration under low Fe conditions. / Experiments conducted in the subarctic Pacific, an Fe-limited oceanic region, demonstrated that even indigenous plankton (both prokaryotic and eukaryotic plankton) have the ability to acquire Fe bound to strong organic chelates. Large phytoplankton species (>3 mum) reduce Fe bound to siderophores extracellularly. Because the predominant form of dissolved Fe in the sea is bound to strong organic complexes, a reductive mechanism as described here may be a critical step in Fe acquisition by phytoplankton.

Productivity in large areas of the world's oceans is limited by low concentrations of dissolved iron in surface waters. Phytoplankton have adapted to persist in these environments by reducing their requirements for iron (Fe) in key metabolic pathways, in some cases by replacing Fe-containing catalysts with their iron-free functional equivalents. This thesis examines the requirements and biochemical roles for copper (Cu) and manganese (Mn) in Fe-limited centric marine diatoms. A major finding of my research is that diatoms have elevated requirements for Mn and Cu when grown in Fe-deficient seawater. Iron deficiency induces oxidative stress and increases the cellular concentrations of toxic oxygen radicals and damage products in Thalassiosira pseudonana. The increased Mn-requirement is used, in part, to activate Mn-containing isoforms of the antioxidant enzyme superoxide dismutase. Cultures co-limited by Fe and Mn exhibit high levels of oxidative stress and an inefficient detoxification pathway that further reduces cell growth. Diatoms isolated from the metal poor open ocean require more Cu to divide than related species from metal-rich coastal waters. This pattern is in stark contrast to all other known nutritive trace metals. One part of the diatom Cu requirement that is independent of provenance is for efficient Fe transport. The additional Cu requirement of oceanic species appears to be due to the constitutive expression of a Cu-containing electron transport protein, possibly plastocyanin. Coastal species, which have higher Fe-requirements for growth, retain the Fe-containing functional homologue cytochrome c6. By employing metals other than Fe within photosynthesis and antioxidant pathways, marine diatoms are able to increase their fitness in Fe-deficient environments. However, Mn and Cu also occur in low concentrations in the open ocean and thus may co-limit growth of natural populations of phytoplankton. Metal enrichment experiments i

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Since the 18th-century scientists are studying diatoms, fascinated by their beauty and diversity. Their nano- and micropatterned biosilica cell walls are outstanding examples of biologically controlled mineral formation. Although the knowledge about diatom cell wall formation increased over the last 60 years, the process is still far away from being completely understood. Diatom cell walls exhibit highly interesting material properties, making them appealing to material scientists. Due to those properties, diatom cell walls are on the brink of becoming powerful tools in nanotechnology. However, the production of tailored silica structures for nanotechnology requires a much better understanding of the processes and components involved in cell wall morphogenesis. Recent studies set the focus on insoluble organic matrices as important parts of this process, suggesting that they act as templates in silica morphogenesis. Therefore, in this study, the occurrence of insoluble organic matrices and their possible silica precipitation activity was analyzed in the three diatom species T. pseudonana, T. oceanica and C. cryptica. For all three species girdle band and valve derived insoluble organic matrices could be identified. The extracted insoluble organic matrices exhibited structural features present in the corresponding biosilica cell walls. The highest similarities were found in the valve derived matrices of C. cryptica. Accessibility studies showed that the biosilica associated insoluble organic matrices of T. pseudonana were only partially accessible, arguing for an entrapment of insoluble organic matrices in the silica, rather than an attachment to the surface of the cell wall. All examined insoluble organic matrices of the three species exhibited intrinsic silica precipitation activity. The most intriguing structures were formed by the insoluble organic matrices of C. cryptica, yielding a porous silica pattern. The addition of biosilica derived soluble components or long-chain polyamines promoted this process and moreover lead to the reconstitution of biosilica-like hierarchical silica pore patterns. The generated silica structures were templated by the underlying structure of the insoluble organic matrix. The result presented in this thesis make this the first study reporting the in vitro generation of diatom biosilica-like hierarchical silica pore patterns using all natural cell wall components. It supports the hypothesis of microplates acting as templates for biosilica morphogenesis and introduces an interesting experimental setup for silica-based in vitro studies on the mechanism of pore formation in diatoms.