A contínua entrada de metais pesados nos ambientes aquáticos constitui uma potencial ameaça aos ecossistemas naturais devido à ação tóxica direta em organismos aquáticos. Nos ambientes aquáticos, os organismos estão expostos a metais tanto dissolvidos na água como aqueles presentes na cadeia trófica. Um maior conhecimento sobre o papel do alimento como rota adicional de exposição a metais ou como um possível retentor de sua toxicidade para invertebrados aquáticos é necessário. Considerando-se a importância dos metais na contaminação ambiental, bem como a necessidade de melhor entendimento das interações desses elementos nos sistemas aquáticos, o presente estudo visou a avaliar a sensibilidade de espécies fitoplanctônicas (Selenastrum capricornutum e Microcystis aeruginosa) e de espécies zooplanctônicas (Daphnia similis e Ceriodaphnia dubia) aos metais cádmio e cromo e os efeitos tóxicos desses elementos em tais organismos. O crescimento celular, a concentração de clorofila, o biovolume e o peso seco das algas foram analisados quando as espécies algais foram expostas aos metais por meio de testes de toxicidade aguda. Testes de toxicidade aguda e crônica com o zooplâncton aos metais também foram realizados e o efeito de diferentes densidades algais (alta, média e baixa) sobre a toxicidade dos metais aos cladóceros foi avaliado. Além disso, algas foram expostas aos metais, oferecidas como alimento a C. dubia e os efeitos tóxicos crônicos foram investigados. Os resultados demonstraram que S. capricornutum foi mais sensível ao cádmio e M. aeruginosa foi mais sensível ao cromo, sendo essa diferença relacionada à capacidade das algas para reter os metais. Com o aumento de ambos os metais, houve uma diminuição na densidade celular, na taxa de crescimento, na clorofila e no peso seco das algas. A presença de diferentes densidades de S. capricornutum não alterou significativamente o valor da CE(I)50; 48h aos metais para D. similis, mas a elevada densidade de M. aeruginosa reduziu a toxicidade do cádmio para o dafinídeo. A alta densidade de alimento (106 céls/mL) influenciou negativamente a reprodução e a sobrevivência de C. dubia quando exposta a concentrações subletais dos metais em solução. Alimento exposto à metais, quando fornecido em alta e em média densidade, também afetou a sobrevivência e a reprodução dos organismos-teste. Apesar de a água ser uma importante rota de exposição aos metais para os organismos aquáticos, o alimento deve ser considerado uma via de contaminação adicional. / The continuous input of heavy metals into aquatic systems constitutes a potential threat to natural ecosystems because of the direct toxic action on aquatic organisms. In aquatic ecosystems, the organisms are exposed to dissolved metals in the water as to metals presents in the food chain. A larger knowledge about paper of food as an additional route of exposure to metals or as possible retainer of its toxicity for aquatic organisms is necessary. Considering the importance of metals in contamination of aquatic ecosystems and the need of better understanding of the interactions of those elements in the aquatic ecosystems as well, the aim of this study was to evaluate the sensibility of phytoplankton species (Selenastrum capricornutum and Microcystis aeruginosa) and zooplankton species (Daphnia similis and Ceriodaphnia dubia) to cadmium and chromium metals and the toxic effects of those elements in such organisms. Analysed of cellular growth, chlorophyll concentration, biovolume and dry weight of the algae were carried out when algal species were exposed to metals. Acute and chronic toxicity tests with the zooplankton were also accomplished and the effect of different algal densities (high, middle and low) on toxicity of metals to cladoceran was evaluated. Alga S. capricornutum was exposed to metals, supplied as food to C. dubia and chronic toxicity effects were investigated. The results demonstrated that S. capricornutum was more sensitive to cadmium and M. aeruginosa was more sensitive to chromium, this difference was related the capacity of the algae to retain metals. Cell density, growth rate, chlorophyll and dry weight of the algae were reduced with increase of both metals. The presence of different density of S. capricornutum does not alter the value of EC50 to metals for D. similis, but high density of M. aeruginosa reduced the toxicity of cadmium for daphnid. High food density (106 cells/mL) influenced negatively on reproduction and survival of C. dubia when this organism was exposed to sublethal concentrations of metals in solution. Food exposed to metals, when it was supplied at high and middle density, also affected survival and reproduction of the test organisms. Although the water to be considered a important route of exposure of metals for aquatic organisms, the food should be considered an additional source of toxicity.

Submitted by Renata Lopes (renatasil82@gmail.com) on 2016-07-15T18:16:10Z No. of bitstreams: 1 marcelaaparecidacamposnevesmiranda.pdf: 2269537 bytes, checksum: 9bf86ff2517e2014e98028114505af4e (MD5) / Approved for entry into archive by Adriana Oliveira (adriana.oliveira@ufjf.edu.br) on 2016-07-22T14:58:32Z (GMT) No. of bitstreams: 1 marcelaaparecidacamposnevesmiranda.pdf: 2269537 bytes, checksum: 9bf86ff2517e2014e98028114505af4e (MD5) / Made available in DSpace on 2016-07-22T14:58:32Z (GMT). No. of bitstreams: 1 marcelaaparecidacamposnevesmiranda.pdf: 2269537 bytes, checksum: 9bf86ff2517e2014e98028114505af4e (MD5) Previous issue date: 2011-04-12 / Alterações no padrão de distribuição de luz em ambientes aquáticos podem afetar as características fisiológicas das cianobactérias, e com isso, influenciar na ocorrência de suas florações. Microcystis e Cylindrospermopsis estão entre os gêneros mais comuns formadores de florações em sistemas brasileiros. Conhecer e entender os requerimentos por luz e seu efeito no crescimento dessas duas cianobactérias é de fundamental importância para a compreensão e manejo de florações em ambientes aquáticos continentais. Este trabalho buscou avaliar o efeito de diferentes intensidades luminosas (25, 50, 300, 600 μmol de fótons m-2 s-1) na ecofisiologia de M.aeruginosa (cepa MIRF-01) e de C. raciborskii (cepa CYRF-01) e a interação entre uma cepa de M. aeruginosa (MIRF-01) com duas cepas de C. raciborskii (CYRF-01 e T3) em duas intensidades luminosas (50 e 500 μmol de fótons m-2 s-1). Para avaliar a ecofisiologia as células das duas espécies foram previamente aclimatadas por três gerações as intensidades luminosas utilizadas e os parâmetros avaliados foram turbidez, densidade do fluxo de fótons, densidade celular, pigmentos totais, atividade fotossintética e a morfologia das duas espécies. A interação entre as espécies foi verificada através da taxa de crescimento. O aumento na densidade celular ao longo do tempo promoveu aumento da turbidez e reduziu a disponibilidade da intensidade luminosa por volta de 50% em todos os tratamentos, devido ao auto-sombreamento. MIRF apresentou taxa de crescimento maior do que CYRF (0,38 ± 0,015 e 0,29 ± 0,019 respectivamente) em todos os tratamentos. Em ambas as cepas houve um aumento na concentração de pigmentos ao longo do tempo e uma diminuição com o aumento da intensidade luminosa. O aumento na relação carotenóide/clorofila, nas culturas de CYRF cultivadas em alta intensidade luminosa (CYRF-300 e CYRF-600), justifica a mudança na coloração de “verde” viii para “verde-amarelada” das culturas de C. raciborskii. As duas espécies apresentaram taxa de transferência de elétrons semelhantes entre os tratamentos, não sendo verificados mecanismos de dissipação de energia. Em relação a morfologia MIRF apresentou agregação celular em baixas intensidade luminosas (25 e 50 μmol de fótons m-2 s-1) e CYRF apresentaram alterações nos tricomas cultivados as altas intensidade luminosas (300 e 600 μmol de fótons m-2 s-1), levemente curvados com diferenciação nas extremidades e filamentos bifurcados. A interação entre M.aeruginosa e C. raciborskii foi evidente para as cepas coexistentes MIRF e CYRF. Em baixa intensidade luminosa (50 μmol de fótons m-2 s-1), CYRF apresentou menor taxa de crescimento quando na presença de MIRF; em alta intensidade luminosa (500 μmol de fótons m-2 s-1) MIRF apresentou maiores taxas de crescimento quando na presença de CYRF do que quando em monocultura. M.aeruginosa e C. raciborskii quando aclimatadas não apresentaram diferenças em relação à ecofisiologia nas diferentes intensidades luminosas utilizadas. E a interação entre cepas coexistentes pode refletir no crescimento das espécies com a alteração da intensidade luminosa. / Changes in the distribution pattern of light in aquatic environments can affect the physiological characteristics of cyanobacteria and, thus, influence on the occurrence of blooms. Cylindrospermopsis and Microcystis are among the most common bloomforming genera in Brazilian systems. Knowing and understanding the requirements for light and its effect on the growth of these two cyanobacteria are important for the understanding and management of algal blooms in freshwater ecosystems. This study evaluated (1) the effect of different light intensities (25, 50, 300, 600, μmol photons m-2 s-1) on growth, physiology and morphology of the species M. aeruginosa (strain MIRF) and C. raciborskii (strain CYRF) and; (2) the interaction between one strain of M.aeruginosa (MIRF-01) with two strains of C. raciborskii (CYRF-01 and T3) at two light intensities (50 and 500 μmol photons m-2 s-1). Both strains were previously acclimated. Cell density, total pigments, turbidity, density of photon flux, photosynthetic activity and morphology of the two species were analized. The interaction between two species was verified by changes in growth rates. The increase in cell density over time promoted increase in turbidity and reduced the availability of light intensity by about 50% in all treatments, due to self-shading. MIRF showed higher growth rate than CYRF (0.38 ± 0.29 ± 0.015 and 0.019 respectively) in all treatments. There was no difference in the growth rates between treatments for MIRF and CYRF in different light intensities. In both strains, there was an increase in pigment concentration over time and decrease with increasing irradiance. The increase in the ratio carotenoid/chlorophyll-a in cultures grown in high irradiance CYRF (CYRF-300 and CYRF-600) explains the change in color from green to green-yellow of cultures of C. raciborskii. The rapid light curves were similar among treatments, and was not verified x down regulation mechanisms. It was also noted that while MIRF showed cell aggregation at low light intensities (25 and 50 mmol photons.m-2.s-1), CYRF showed morphological changes in the trichomes at high light intensities (300 and 600 μmol photons.m-2.s-1), slightly curved filaments and bifurcate at the ends. The interaction between M.aeruginoa and C.raciborskii was evident for coexisting MIRF and CYRF strains. In low light intensity (50 μmol photons.m-2.s-1), CYRF showed a lower growth rate in the presence of MIRF. In high light-intensity (500 μmol photons.m-2.s-1) MIRF growth rates were higher in the presence of CYRF than in monoculture. When M.aeruginosa and C.raciborskii are acclimated there is no ecophysiology difference in different light intensities. The interaction between coexisting strains may reflect the growth of species in different light intensity.

Submitted by Renata Lopes (renatasil82@gmail.com) on 2016-07-20T14:13:23Z No. of bitstreams: 1 marianamendesemello.pdf: 1655122 bytes, checksum: 20f07a833562e4111886f134f6b2d724 (MD5) / Approved for entry into archive by Adriana Oliveira (adriana.oliveira@ufjf.edu.br) on 2016-07-22T15:20:26Z (GMT) No. of bitstreams: 1 marianamendesemello.pdf: 1655122 bytes, checksum: 20f07a833562e4111886f134f6b2d724 (MD5) / Made available in DSpace on 2016-07-22T15:20:26Z (GMT). No. of bitstreams: 1 marianamendesemello.pdf: 1655122 bytes, checksum: 20f07a833562e4111886f134f6b2d724 (MD5) Previous issue date: 2011-02-15 / Cianobactérias vêm sendo apontadas como um dos maiores problemas ambientais relacionados à água doce. Esses micro-organismos formadores de florações e potencialmente tóxicos estão relacionados à perda da qualidade da água e até a problemas de saúde em seres humanos. Alta afinidade por nitrogênio, estratégias para estocagem de fósforo e a capacidade de ajustarem sua posição na coluna d’água são algumas vantagens competitivas das cianobactérias sobre outros componentes do fitoplâncton. Mais recentemente, a ocorrência de processos de comunicação química, como alelopatia e quorum sensing, vêm sendo apontados como vantagens competitivas alternativas das cianobactérias. Desta forma, os objetivos do presente trabalho foram: (1) verificar se as espécies Cylindrospermopsis raciborskii e Microcystis aeruginosa interagem quimicamente e se situações de estresse por competição e luz influenciam nessa interação; (2) verificar como a competição entre C. raciborskii e M. aeruginosa pode alterar a morfologia de M. aeruginosa, através da formação de colônias, além de avaliar o papel da co-evolução neste processo. Para tal, experimentos em laboratório foram executados adicionando-se exudatos de culturas de C. raciborskii e M. aeruginosa, sob diferentes condições, em ambas as espécies como alvo. Os resultados apontaram que as cepas de C. raciborskii (CYRF) e M. aeruginosa (MIRF) provenientes do Reservatório do Funil (RJ) apresentaram um maior número de respostas às interações químicas do que cepas provenientes de outros locais. CYRF em estresse por competição produziu possíveis aleloquímicos capazes de inibir o crescimento de MIRF, enquanto MIRF quando cultivada sob estresse por luz (25 μmol fótons m-2s-1) produziu aleloquímicos capazes de inibir o crescimento de CYRF. Ambas as cepas também demonstraram a habilidade de se comunicarem por quorum sensing. Essa comunicação em CYRF induziu a inibição do seu próprio crescimento, enquanto que em MIRF induziu a formação de colônias. Quando a formação de colônia em M. aeruginosa foi testada, foi observado uma possível produção de moléculas para a formação de colônias em MIRF engatilhada pela competição com diferentes cepas de C. raciborskii, e não somente com CYRF. Os resultados apontaram também que, dentre dez cepas de M. aeruginosa testadas, somente MIRF foi capaz de formar colônias quando em contato com o exudato da competição entre CYRF e MIRF. Desta forma, o sinal para formação de colônia foi apontado como cepa-dependente, indicando a importância do papel da co-evolução nas interações químicas entre cianobactérias. Os resultados encontrados sugerem que interações químicas intra e interespecíficas podem desempenhar importante papel, ainda que pouco explorado, na dominância e substituição de espécies de cianobactérias. / Cyanobacteria have been pointed as one of the main problems in freshwater systems. These blooming microorganisms are potentially toxic and their occurrence have been directly related to the lost of water quality and human health problems. High nitrogen affinity, strategies to storage phosphorus and the ability to adjust their position in the water column are some competitive advantages of cyanobacteria over other phytoplankton components. Recently, mechanisms of chemical communication, such as allelopathy and quorum sensing, have been indicated as an alternative advantage of cyanobacteria. The aim of this study was: 1. to evaluate if Cylindrospermopsis raciborskii and Microcystis aeruginosa can interact chemically, and if stressed conditions caused by competition and light can interfere in this relationship; 2. to evaluate how the competition between C. raciborskii and M. aeruginosa can induce morphological variation (colony formation) in M. aeruginosa and how the role of coevaluation. Laboratory experiments were performed and exudates from C. raciborskii and M. aeruginosa, cultivated in different conditions, were added to the same species as target. The results revealed that the strains of C. raciborskii (CYRF) and M. aeruginosa (MIRF), isolated from Funil Reservoir (RJ), showed more responses to chemical interactions than the strains from different places. When CYRF was grown in regular light (100 μmol quanta m-2s-1) and stressed by competition, this strain produced allelochemicals that inhibited the growth of MIRF, while MIRF cultivated in light stress (25 μmol quanta m-2s-1) produced allelochemicals that inhibited the growth of CYRF. It was also observed that both strains have the ability to communicate by quorum sensing. This communication induced growth self-inhibition in CYRF, while it induced colony formation in MIRF. When colony formation was evaluated, the production of inducible molecules to colony formation in MIRF was triggered by the competition with different strains of C. raciborskii, and not only by the competition with CYRF. The results also showed that, among ten strains of M. aeruginosa, only MIRF was able to form colonies when in contact with exudates from competition between CYRF and MIRF. The colony formation signal was pointed as strain-dependent, highlighting the importance of the co-evolution in chemical interactions among cyanobacteria. These results suggest that chemical interactions among species can play an important role, still unexplored, in the dominance and successional pattern of species.

In this study, we tested the long-term and negative effects of microcystin-producing cyanobacterium Microcystis aeruginosa from Vietnam on Daphnia magna under the laboratory conditions. The test organisms were fed with mixtures of green alga Scenedesmus armatus. and toxic M. aeruginosa at different ratios (10% Microcystis + 90% Scenedesmus, 50% Microcystis + 50% Scenedesmus, 100% Microcystis, and 100% Scenedesmus) for over a period of 21 days. The life history traits of the organisms such as, survival, maturation, fecundity were daily recorded. Besides, the intrinsic population rate of D. magna in each treatment was also calculated based on the survivorship, the reproductive age and the clutch size of the animals. The results showed that survival, maturation and reproduction of the D. magna fed with 10, 50 and 100% M. aeruginosa was impaired. Additionally, the intrinsic population rate of the exposed D. magna was lower than that of the control. This study evidenced the adverse effects of toxic M. aeruginosa on both the individual and intrinsic population levels of D. magna. To our knowledge, this is the first report on the chronically detrimental impacts of toxic M. aeruginosa isolated from Vietnam on D. magna and contributed the scientific information on the severe influences of toxic cyanobacteria world wide. / Trong bài viết này, chúng tôi nghiên cứu ảnh hưởng xấu mãn tính của loài vi khuẩn lam Microcystis aeruginosa có khả năng sản sinh độc tố microcysin từ Việt Nam lên Daphnia magna trong điều kiện phòng thí nghiệm. Sinh vật thí nghiệm được cho ăn với hỗn hợp tảo lục Scenedesmus armatus và M. aeruginosa có độc ở các tỷ lệ khác nhau (10% Microcystis + 90% Scenedesmus, 50% Microcystis + 50% Scenedesmus, 100% Microcystis, và 100% Scenedesmus) trong thời gian 21 ngày. Các đặc điểm vòng đời của sinh vật bao gồm sức sống, sự thành thục, sức sinh sản được theo dõi hàng ngày. Bên cạnh đó, tỷ lệ phát triển quần thể của D. magna trong từng lô thí nghiệm cũng được tính toán dựa vào sức sống, tuổi sinh sản và kích cỡ sinh sản của sinh vật. Kết quả cho thấy, sức sống, tuổi thành thục và sự sinh sản của D. magna cho ăn với 10, 50 và 100% M. aeruginosa bị ảnh hưởng xấu. Bên cạnh đó, tỷ lệ phát triển quần thể của D. magna trong lô phơi nhiễm thấp hơn so với đối chứng. Nghiên cứu này chứng minh ảnh hưởng xấu của M. aeruginosa có độc lên cả hai mức độ cá thể và quần thể của D. magna. Theo hiểu biết của chúng tôi, đây là báo cáo đầu tiên về ảnh hưởng xấu mãn tính của M. aeruginosa có độc phân lập từ Việt Nam lên D. magna and đóng góp thêm thông tin khoa học cho những ảnh hưởng nghiêm trọng của vi khuẩn lam có độc trên khắp thế giới.

Les efflorescences de cyanobactéries sont susceptibles d’avoir des effets néfastes sur les organismes des écosystèmes aquatiques, ainsi que sur les populations environnantes, notamment à travers la production de nombreuses molécules potentiellement toxiques (appelées cyanotoxines). Jusqu'à présent, une des cyanotoxines les plus étudiées est la microcystine (MC). Cette thèse a pour objectif d’évaluer la toxicité potentielle sur la reproduction de la MC-LR et de l'extrait d'une souche de Microcystis productrice de MCs en étudiant leurs effets toxiques sur le foie et les gonades de poissons medaka adultes exposés de manière aiguë ou chronique.Une étude complète du foie des poissons médaka deux sexes a été menés par ailleurs, attestant d'un fort dimorphisme sexuel aussi bien au niveau cellulaire que moléculaire et souligne les importantes spécificités métaboliques du foie entre les deux sexes, notamment pour le maintien de la compétence de reproduction chez les poissons medaka adultes femelles.Dans l'étude des effets induits par une exposition aiguë, les poissons medaka adultes ont été exposés par gavage à 10 μg.g-1 bw de MC-LR pure pendant 1 heure. L'examen histologique et l'immunolocalisation des MCs du foie de poisson traité par la MC-LR ont révélé des lésions hépatiques sévères ainsi qu'une distribution intense de la MC-LR dans le foie, localisée particulièrement dans le cytoplasme et dans le noyau des hépatocytes. Dans la gonade des poissons traités, la MC-LR a été détectée dans les tissus conjonctifs de l'ovaire et des testicules. De plus, l’observation par microscopie électronique couplé à la technique d’immunogold a révélé, pour la première fois, que la MC-LR était également détectable dans le chorion, le cytoplasme et le vitellus des ovocytes matures.Au cours des études des effets induits par l’exposition chronique, les poissons medaka adultes ont été exposés durant 28 jours par balnéation à 1 et 5 μg.L-1 de MC-LR et à un extrait de la souche de Microcystis aeruginosa (PCC 7820) productrice de microcystines (5 μg.L-1 équivalent MC-LR). Ces résultats ont révélé que la MC-LR et l'extrait de Microcystis induisent des effets délétères sur différents paramètres de reproduction, tels la fécondité et le taux d’éclosion des embryons. La cause principale de ces perturbations de la reproduction semblent principalement résulté d’un dysfonction hépatique globale induite par les traitements aux MCs (hépatotoxiques, notoires), plutôt qu’à des effets directs sur les gonades. Dans l'ensemble, les résultats de cette thèse démontrent que même si les microcystines pourraient avoir un impact direct, mais modéré, sur la fonction gonadique en induisant une cytotoxicité dans les cellules somatiques gonadiques et les cellules reproductrices, elle semble avoir principalement avoir un impact indirect sur la fonction reproductrice en perturbant la fonction hépatique générale. Ces données améliorent notre compréhension des processus liés à la toxicité potentielle des cyanotoxines pour la reproduction chez un poisson modèle, et fait d’une manière générale progresser questionnement quant à la protection des populations exposées à ces cyanotoxines. / Cyanobacterial blooms threaten human health as well as other living organisms of the aquatic environment, particularly due to the production of natural toxic components (called cyanotoxins). So far, one of the most studied cyanotoxins is the microcystin (MC). This thesis evaluated the potential reproductive toxicity of MC-LR and the extract of one Microcystis strain (MC-producing) by investigating their toxic effects on the liver and gonad of adult medaka fish with one acute and one chronic study.An investigation of the metabolic specificities of the liver in two genders of medaka fish was performed prior to the MC-containing exposure, which attests to a strong sexual dimorphism of medaka liver, and highlights the importance of metabolic adjustments of the liver for maintaining the reproductive competency in adult medaka fish.In the acute study, adult medaka fish were administered with 10 μg.g-1 bw of pure MC-LR for 1 hour by gavage. The histological examination and immunolocalization of the MC-treated fish liver revealed a severe liver lesion along with an intense distribution of MC-LR in the liver, being particularly localized in the cytoplasm and nucleus of hepatocytes. In the gonad of MC-treated fish, MC-LR was shown to be present in the connective tissue of ovary and testis. Additionally, immunogold electron microscopy, for the first time, revealed that MC-LR was also localized in the chorion, cytoplasm and yolk vesicles of oocytes.Overall, the results of this thesis demonstrates that MC might directly impact gonadal function by inducing cytotoxicity in gonadal somatic cells and reproductive cells, and it could also impact the reproductive function indirectly by disturbing the general liver function. This improves our understanding of the potential reproductive toxicity of cyanotoxins in model fish, and advances our current knowledge on the protection of aquatic organism populations as well as human health from cyanotoxin issues.

Cyanobakterien bilden zahlreiche bioaktive Substanzen mit zum Teil humantoxischer Relevanz. Nicht selten spielen dabei zyklische Peptide, zu denen unter anderem die Microcystine (MCYST) gehören, eine Schlüsselrolle. MCYST werden u.a. von Microcystis KÜTZING EX LEMMERMANN 1907 gebildet. Erkenntnisse zur ökophysiologischen Funktion der MCYST, die zweifelsfrei bei den Produzenten selbst zu suchen ist, liegen bisher kaum vor. Mit Hilfe von Freilanduntersuchungen sollten im Rahmen der vorliegenden Arbeit Kenntnisse zu einer möglichen ökologischen Funktion der MCYST erweitert und vertieft werden. Grundlage stellte dabei die Phänologie von Microcystis als einer der bedeutendsten limnischen MCYST-Produzenten dar. Microcystis zeigt im Freiland einen charakteristischen annuellen Lebenszyklus mit benthisch-pelagischer Kopplung. Ziel der vorliegenden Arbeit war es, die phänologischen Phasen des Lebenszyklus von Microcystis im Freiland zu differenzieren sowie die Dynamik der MCYST während dieser Phasen kompartimentübergreifend gesamtheitlich zu erfassen. Über eine MCYST-Massenbilanzierung sollen anschließend die dem annuellen Zyklus zugrundeliegenden Teilprozesse quantifiziert und zusammengeführt werden. Vordergründiges Anliegen war es, Phasen einzugrenzen, bei denen MCYST möglicherweise eine ökophysiologische Funktion haben könnte. Der annuelle Lebenszyklus von Microcystis wurde anhand von Biomasseänderungen am Sediment und im Pelagial der TS Quitzdorf in die phänologischen Phasen Überwinterung, Reinvasion, pelagisches Wachstum und Sedimentation unterteilt: Intakte, im Herbst aus dem Freiwasser aussedimentierte, Microcystis-Kolonien überwintern am Sediment und steigen im Frühjahr und Frühsommer zurück ins Freiwasser auf. Dort erfolgt der Wachstumsprozess, dem sich im darauffolgenden Herbst erneut ein Zusammenbruch und die Sedimentation der Freiwassergemeinschaft anschließt. Die benthisch-pelagische Kopplung wirkt dabei als interannuelles Bindeglied. Zwischen dem annuellen Lebenszyklus von Microcystis und der MCYST-Dynamik wurde eine enge Bindung nachgewiesen: Änderungen der absoluten MCYST-Konzentrationen während der Übergangsphasen Aufstieg (Frühjahr) und Sedimentation (Herbst) zeigen, dass MCYST mit den aufsteigenden bzw. aussedimentierenden Microcystis-Kolonien aus dem bzw. in das Sediment ‚transportiert’ werden. Ausschließlich während der pelagischen Phase, die sich dem Reinvasionsprozess anschließt, kommt es in Abhängigkeit vom Wachstum der Produzenten und deren Sukzession zur Neubildung von MCYST. Während den Wintermonaten wurden MCYST am Sediment intrazellulär ‚konserviert’. Der Verlauf der pelagischen MCYST-Konzentration wurde mit Hilfe eines Wachstumsmodells nachgebildet. In dieses Modell wurde die genetische Variabilität der MCYST-Produzenten sowie eine mögliche physiologische Steuerung der MCYST-Synthese über die Verfügbarkeit des anorganischen Kohlenstoffs integriert. Der prinzipielle Verlauf zeigte dabei weitestgehend Koinzidenz zwischen den real gemessenen und den simulierten MCYST-Konzentrationswerten. Abweichungen zwischen beiden konnten mit Hilfe des gesamtheitlich kompartimentübergreifenden MCYST-Bilanzierungsansatzes – in erster Linie über benthisch-pelagische Kopplungsprozesse – plausibel erklärt werden. Der Habitatwechsel ist für Microcystis prinzipiell mit Verlusten (Seneszenz/Lyse oder möglicherweise Apoptose) verbunden, sowohl für MCYST-Produzenten und Nichtproduzenten. Die auffallende Stabilität der benthischen MCYST-Zellquote während der Überwinterung gibt Grund zur Annahme, dass eine Funktion von MCYST am/im Sediment eher unwahrscheinlich ist. Da MCYST über derart lange Zeiträume am Sediment intrazellulär ‚konserviert’ werden, ist eine Bedeutung der MCYST während der Reinvasionsphase und in der frühen pelagischen Phase nicht auszuschließen. Im Speziellen wurde eine mögliche ökologische Funktion von MCYST in Zusammenhang mit der Variation der Koloniegröße bzw. dem epiphytischen Bewuchs von Microcystis-Kolonien mit Pseudanabaena mucicola geprüft: Aus dem Zusammenhang zwischen extra-/intrazellulärer MCYST-Konzentration und der Microcystis-Koloniegrößenverteilung waren keine konsistenten Schlussfolgerungen abzuleiten, welche auf eine Steuerung der Koloniebildung durch MCYST deuten. Vor dem Hintergrund, dass MCYST keinen nachweislich allelopathischen Effekt auf den Epibionten Pseudanabaena mucicola ausüben, wurde postuliert, dass zwischen dem beobachteten epiphytischen Besiedlungs-/Verteilungsmuster und der MCYST-Produktion ein indirekter Zusammenhang besteht, welcher die zeitweise Einnischung von Pseudanabaena mucicola auf Microcystis-Kolonien ermöglicht. Die Ergebnisse der vorliegenden Untersuchung lassen weder unmittelbar noch mittelbar eine Variabilität der ökophysiologischen Bedeutung von MCYST, die im Zusammenhang mit der raum-zeitlichen Verteilung potentieller Produzenten steht, erkennen. Eine divergierende Funktion der MCYST auf intra- bzw. extrazellulärer Ebene kann nicht zwingend ausgeschlossen werden. Die Mehrzahl der aus der MCYST-Phänologie und MCYST-Bilanzierung abzuleitenden Schlussfolgerungen deutet allerdings eher auf eine Funktion auf (intra-)zellulärer Ebene hin, wie etwa die Effizienzsteigerung des Kohlenstoffmetabolismus (d.h. der intrazellulä-ren Akkumulation anorganischen Kohlenstoffs) während der pelagischen (Wachstums-)Phase der Produzenten.

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In this study, we tested the long-term and negative effects of microcystin-producing cyanobacterium Microcystis aeruginosa from Vietnam on Daphnia magna under the laboratory conditions. The test organisms were fed with mixtures of green alga Scenedesmus armatus. and toxic M. aeruginosa at different ratios (10% Microcystis + 90% Scenedesmus, 50% Microcystis + 50% Scenedesmus, 100% Microcystis, and 100% Scenedesmus) for over a period of 21 days. The life history traits of the organisms such as, survival, maturation, fecundity were daily recorded. Besides, the intrinsic population rate of D. magna in each treatment was also calculated based on the survivorship, the reproductive age and the clutch size of the animals. The results showed that survival, maturation and reproduction of the D. magna fed with 10, 50 and 100% M. aeruginosa was impaired. Additionally, the intrinsic population rate of the exposed D. magna was lower than that of the control. This study evidenced the adverse effects of toxic M. aeruginosa on both the individual and intrinsic population levels of D. magna. To our knowledge, this is the first report on the chronically detrimental impacts of toxic M. aeruginosa isolated from Vietnam on D. magna and contributed the scientific information on the severe influences of toxic cyanobacteria world wide. / Trong bài viết này, chúng tôi nghiên cứu ảnh hưởng xấu mãn tính của loài vi khuẩn lam Microcystis aeruginosa có khả năng sản sinh độc tố microcysin từ Việt Nam lên Daphnia magna trong điều kiện phòng thí nghiệm. Sinh vật thí nghiệm được cho ăn với hỗn hợp tảo lục Scenedesmus armatus và M. aeruginosa có độc ở các tỷ lệ khác nhau (10% Microcystis + 90% Scenedesmus, 50% Microcystis + 50% Scenedesmus, 100% Microcystis, và 100% Scenedesmus) trong thời gian 21 ngày. Các đặc điểm vòng đời của sinh vật bao gồm sức sống, sự thành thục, sức sinh sản được theo dõi hàng ngày. Bên cạnh đó, tỷ lệ phát triển quần thể của D. magna trong từng lô thí nghiệm cũng được tính toán dựa vào sức sống, tuổi sinh sản và kích cỡ sinh sản của sinh vật. Kết quả cho thấy, sức sống, tuổi thành thục và sự sinh sản của D. magna cho ăn với 10, 50 và 100% M. aeruginosa bị ảnh hưởng xấu. Bên cạnh đó, tỷ lệ phát triển quần thể của D. magna trong lô phơi nhiễm thấp hơn so với đối chứng. Nghiên cứu này chứng minh ảnh hưởng xấu của M. aeruginosa có độc lên cả hai mức độ cá thể và quần thể của D. magna. Theo hiểu biết của chúng tôi, đây là báo cáo đầu tiên về ảnh hưởng xấu mãn tính của M. aeruginosa có độc phân lập từ Việt Nam lên D. magna and đóng góp thêm thông tin khoa học cho những ảnh hưởng nghiêm trọng của vi khuẩn lam có độc trên khắp thế giới.

Cyanobacteria are ancient prokaryotic organisms capable of performing oxygenic photosynthesis. An increase in the temporal and spatial distribution of cyanobacteria blooms worldwide has drawn considerable research attention in recent decades because of the health risks cyanobacteria pose to humans and wildlife through the production of cyanotoxins, interference with recreation, and ecosystem changes. A variety of hypotheses have sought to explain the increasing frequency and severity of cyanobacteria blooms around the world, with the relationship between cyanobacteria abundance and eutrophication receiving considerable attention. While the impacts of phosphorus concentration on cyanobacteria success are relatively well-studied, less is known about how nutrient stoichiometry and nitrogen uptake kinetics of different species contribute to cyanobacteria dominance. The underlying mechanism for the impacts of nitrogen to phosphorus (N:P) ratio and nitrogen form on cyanobacteria involves internal cycling of nitrogen within lakes and aspects of cyanobacteria cell physiology. The primary objective of this study was to assess the impacts of N:P ratios and nitrogen form on the growth of Microcystis aeruginosa and Anabaena flos-aquae in both axenic cultures and natural phytoplankton assemblages from Missisquoi Bay, Lake Champlain. A second objective was to determine whether treatment condition affected the production of the cyanotoxin microcystin. A final objective was to document the presence of benthic ammonium in Missisquoi Bay and the vertical migration of cyanobacteria throughout the water column in the bay, to provide evidence in support of the underlying mechanisms that might provide advantages to cyanobacteria in the bay. In laboratory culture experiments with M. aeruginosa and A. flos-aquae alone and in a mixed community, N:P ratios were varied between 5, 15, 30 and 45:1, and nitrogen was supplied as both nitrate and ammonium at each ratio. Triplicate samples were preserved after one, three and six days for cell enumeration using the standard Ütermohl method. Differences in density between initial and later times were used as an estimate of growth. Microcystin concentration was measured with the ELISA method. Weekly field sampling was conducted in the summer of 2006 in Missisquoi Bay to measure benthic nitrogen concentrations. Nocturnal sampling at varied depths in the bay was used to explore the vertical migration of cyanobacteria throughout the water column. There were weak associations between ammonium-nitrogen and M. aeruginosa growth and nitrate-nitrogen and A. flos-aquae growth, while the effects of N:P ratio on growth was highly variable across time and treatment condition. Ammonium-nitrogen was documented in the benthic water of Missisquoi Bay throughout the growing season, and M. aeruginosa dominated the vertical migration of cyanobacteria throughout the water column. The lack of clear trends visible within the data from laboratory experiments can be in part attributed to high variability of cell density within treatment conditions and the limitations of the methodology used for cell enumeration. Taken together these data suggest that the distribution of nitrogen within an aquatic system and the ability of M. aeruginosa to vertically migrate may contribute to the M. aeruginosa dominance of the summer phytoplankton community.

The aim of this diploma thesis is to explore the coagulation phase in water treatment process from two perspectives, the removal of cyanotoxin microcystin and the responses of ecotoxicological indicator species Daphnia magna to different concentration of this toxin, contained in a sample of cyanobacterial water bloom, which was extracted from a dam and was dominated by cyanobacteria Microcystis aeruginosa. The sample was administered in three environmentally relevant concentrations to 6 clones of Daphnia magna, 3 of which had previous experience with M. aeruginosa. Coagulation process was performed under optimal conditions: pH = 6.36; KNK4,5 = 0.26 mmol.l-1 ; Fe = 0.162 mg.l-1 ; DOC = 2.83 mg.l-1 using 10 ml of 0.125M NaHCO3 in two litres of ultrapure water. Individual forms of microcystin were detected in this ratio: 31.6 % MC-LR, 53.6 % MC-RR and 14.8 % MC-YR. The study has shown that under these conditions coagulation does not remove microcystin, e.g. the efficiency of the process is zero. In ecotoxicological study, with growing concentration of cyanobacterial mixture the negative impact on Daphnia magna increased. We have found interclonal variability in responses of D. magna, however, the previous experience with M. aeruginosa had no effect. With growing concentration of cyanobacterial water...