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Detrimental impacts of toxic Microcystis aeruginosa from Vietnam on life history traits of Daphnia magna / Ảnh hưởng tiêu cực của loài Microcystis aeruginosa có độc ở Việt Nam lên các đặc điểm vòng đời của Daphnia magnaVo, Thi My Chi, Pham, Thanh Luu, Dao, Thanh Son 24 August 2017 (has links) (PDF)
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.
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Reprotoxic effects of microcystins and secondary metabolites produced by cyanobacteria Microcystis in adult medaka fish / Effets reprotoxiques des microcystines et des métabolites secondaires produits par les cyanobactéries du genre Microcystis chez le poisson medaka adulteQiao, Qin 16 December 2016 (has links)
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.
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Detrimental impacts of toxic Microcystis aeruginosa from Vietnam on life history traits of Daphnia magna: Research articleVo, Thi My Chi, Pham, Thanh Luu, Dao, Thanh Son 24 August 2017 (has links)
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.
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The Effects of Nutrient Ratios and Forms on the Growth Of Microcystis aeruginosa and Anabaena flos-aquaeCrawford, Kathryn A. 17 June 2008 (has links)
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.
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Odstraňování microcystinů při úpravě pitné vody / Removal of microcystins during drinking water treatmentVaněčková, Hana January 2015 (has links)
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...
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Uptake and depuration of cyanotoxins in the common blue mussel Mytilus edulisWaack, Julia January 2017 (has links)
Cyanobacteria produce a variety of secondary metabolites which possess amongst others antifungal, antibacterial, and antiviral properties. Being primary producers they are also a vital component within the food web. However, certain strains also produce toxic metabolites such as the hepatotoxins microcystin (MC) and nodularin (NOD). Their toxicity in combination with the increasing global occurrence has resulted in a drinking water guideline limit of 1 μg L-1 being issued by the World Health Organisation (WHO). However, these toxins are not only present in water, but can be accumulated by fish and shellfish. Currently, no regulations regarding cyanotoxin contaminated seafood has been established despite similar toxicity to routinely monitored marine toxins such as domoic acid (DA). To facilitate regular monitoring, a high performance liquid chromatography photo diode array (HPLC-PDA) analysis method for the detection of DA was optimised to enable the simultaneous detection of DA and nine cyanotoxins. This method was then utilised to determine cyanotoxin concentration in laboratory cyanobacteria strains. To assess the accumulation and depuration of cyanotoxins in the common blue mussel Mytilus edulis, three feeding trials were performed. During these, mussels were exposed to two cyanobacteria strains, Nodularia spumigena KAC66, Microcystis aeruginosa PCC 7813, both individually and simultaneously. A rapid dose dependent accumulation of cyanotoxins was observed with maximum concentration of 3.4 -17 μg g-1 ww accumulated by M. edulis, which was followed by a much slower depuration observed. During the final feeding trial, with N. spumigena KAC 66 and M. aeruginosa PCC7813, cyanotoxins were still detectable following 27 days of depuration. Mortality in all studies was 7% or less indicating that most mussels were unaffected by the maximum dose of 480 μg L-1 NOD (feeding study 1), 390 μg L-1 MC (feeding study 2), or 130 μg L-1 total cyanotoxins (feeding trial 3), respectively. Mortality in negative control tanks was lower throughout all three feeding trials ( < 1 - 2.6%). Consumption of a typical portion size (20 mussels) would result in ingestion of cyanotoxins at levels significantly higher than the WHO recommended tolerable daily intake (TDI) of 2.4 μg NOD and/or MCs for a 60 kg adult. This value was exceeded not only during the exposure period (maximum levels 270 - 1370 μg cyanotoxins per 20 mussels), but also at the end of the depuration period 39-600 μg cyanotoxins per 20 mussels. These results illustrated that cyanotoxin monitoring of seafood should be considered not only during, but also following bloom events. In an attempt to investigate the cyanotoxin budget of the experimental system, not only mussels, but cyanobacteria cultures, the tank water, and the mussel faeces were also analysed for their cyanotoxin content. Results showed that large quantities of MCs and NOD were unaccounted for during all exposure trials. The combined effect of cyanotoxin metabolism in M. edulis, biotic and/or abiotic degradation, protein binding, and losses during the extraction and analysis were thought to have contributed to the unaccounted cyanotoxin fraction. Mussel flesh was analysed for the presence of glutathione or cysteine conjugates, however, there was no evidence of their occurrence in the samples tested. Due to these discrepancies in the toxin budget of the system, the introduction of correction factors for the analysis of cyanotoxins in M. edulis was suggested in order to protect the general public.
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Remoção de células de Microcystis Aeruginosa em água de abastecimento por coagulação, floculação e sedimentação utilizando cloreto férrico e sulfato de alumínio e filtração por filtro de areiaOliveira, Erivanna Karlene dos Santos 11 April 2014 (has links)
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Previous issue date: 2014-04-11 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / The presence of cyanobacteria in reservoirs, lakes and rivers is a global environmental
health problem as a result ofanthropogenic eutrophication. These microorganisms
hinder water purifiers, to produce taste and odor difficult to remove and the cells at high
density clog the sand filters, reducing its time of use. In the conventional method of
water treatment, coagulation, flocculation and sedimentation are essential in the removal
of cells and determine the efficiency of the following operations. In this study we
analyzed the efficiency of removal of intact cells of Microcystis aeruginosaand
microcystin-LR in the stages of coagulation, flocculation and sedimentation, followed
by filtration through sand filters with the use of coagulants ferric chloride and aluminum
sulfate, evaluating four filtration rates: 15, 30, 50 and 100 m
3
.m
-2
.d
-1
at pH 7.5 and a
dosage of 40 mg.L
-1
tests with a bench-scale (Jartest) using treated water dechlorinated
and adadded with a pureculture of M. aeruginosa with approximate final densityof 10
cel.mL
-1
simulating a bloom. The parametres control were turbidity, apparent color and
cell concentration. It was observed that both the efficiency rates at 15 and 30 m
1
had similar removal of apparent color, turbidity and cellconcentration (79%, 80% and
92% and 80%, 80,5% and 89,10% respectively for the coagulant ferric chloride. And for
aluminum sulphate was the same for both rates removals of 81,48% for apparent color,
turbidity to 83,25% and to 90,50% for cell concentration, since the rate for 30 m
1
removals were 83,33%, 83,25% and 89,71%, respectively. Nocell lysiswas
observedandconsequently, no further increases in concentrationsofmicrocystin-LR
cyanotoxinduring treatment was observed. / A presença de cianobactérias em reservatórios, lagos e rios é um problema mundial de
saúde ambiental, em consequência da eutrofização antropogênica. Esses microrganismos
dificultam a potabilização da água, por produzir gosto e odor difíceis de remover e suas
células em alta densidade colmatam os filtros, diminuindo sua vida útil. No método
convencional de tratamento de água, coagulação, floculação e sedimentação são
fundamentais na remoção de células e determinam a eficiência das operações seguintes.
Neste trabalho analisou-se a eficiência na remoção de células intactas de Microcystis
aeruginosa e da microcistina-LR nas etapas de coagulação, floculação e sedimentação,
seguido por filtração em filtro de areia com uso dos coagulantes cloreto férrico e sulfato
de alumínio, avaliando quatro taxas de filtração de 15, 30, 50 e 100 m
3
.m
, em pH 7,5
e dosagem de 40 mg.L
-1
com testes em escala de bancada (Jartest) utilizando-se água
tratada de torneira desclorada e adicionada de uma cultura pura de M. aeruginosa com
densidade final aproximada de 10
5
cel.mL
-1
simulando uma floração. Os parâmetros de
referência foram turbidez, cor aparente e concentração celular. Observou-se que a
eficiência, tanto com as taxas de 15 e 30 m
3
.m
-2
.d
-1
tiveram remoções semelhantes para as
variáveis cor aparente, turbidez e concentração celular com 79%, 80% e 92%; e 80%,
80,5% e 89,10%, respectivamente para o coagulante cloreto férrico. Para o sulfato de
alumínio e para ambas as taxas, houve a mesma reposta com remoções de 81,48% para
cor aparente, 83,25% para turbidez e 90,50% para concentração celular, já para a taxa de
30 m3
.m
-2
.d
-1
as remoções foram de 83,33% , 83,25% e 89,71% respectivamente. Não foi
observada lise celular e consequentemente, não houve aumentos, ao longo do tratamento,
das concentrações da cianotoxina microcistina -LR.
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On the ecology of hyperscum-forming Microsystis aeruginosa in a hypertrophic African lake.Zohary, Tamar. January 1987 (has links)
Light is the primary source of energy in most of earth's ecosystems .
In freshwater ecosystems the major interacting factors that determine
the abundance and species composition of planktonic phototrophs, the
primary utilizers of light, are nutrients, temperature and light.
With increasing eutrophication and declining geographical latitude,
nutrient availability becomes in excess of the organisms'
requirements, water temperature is more favourable for growth, and
community structure depends to a greater extent on light availability.
This study focuses on the population dynamics of the bloom-forming
cyanobacterium Microcystis aeruginosa Kutz. emend. Elenkin in subtropical
Hartbeespoort Dam, South Africa. The objectives of the study
were: to investigate the annual cycle, and the factors leading to the
dominance and success of the cyanobacterium in this hypertrophic, warm
monomictic lake, where light availability is the major factor limiting
phytoplankton growth rates; to study the surface blooms and ultimately
hyperscums that this species forms; and to assess the ecological significance
of hyperscums.
A 4. 5-years field study of phytoplankton abundance and species composition
in relation to changes in the physical environment, was
undertaken. The hypothesis was that M. aeruginosa dominated the
phytoplankton population (> 80 % by volume) up to 10 months of every
year because it maintained itself within shallow diurnal mixed layers
and was thus ensured access to light. It was shown that wind speeds
over Hartbeespoort Dam were strong enough to mix the epilimnion (7 -
18 m depth) through Langmuir circulations only 12 % of the time. At
other times solar heating led to the formation of shallow ( < 2 m)
diurnal mixed layers (Z[1]) that were usually shallower than the
euphotic zone (Zeu; x = 3.5 m), while the seasonal mixed layer (zrn)
was always deeper than Zeu. From the correspondence between vertical
gradients of chlorophyll a concentrations and density gradients, when
M. aeruginosa was dominant, it was implied that this species maintained the bulk of its population within Z[1]. Under the same mixing
conditions non-buoyant species sank into dark layers. These data
point out the importance of distinguishing between Zrn and Z[1], and show
the profound effect that the daily pattern of Z[1], as opposed to the
seasonal pattern of Zrn can have on phytoplankton species composition Adaptation to strong light intensities at the surface was implicated
from low cellular chlorophyll a content (0.132 μg per 10[6] cells) and
high I[k ](up to 1230 μE m⁻² S¯¹). Ensured access to light, the postmaximum
summer populations persisted throughout autumn and winter,
despite suboptimal winter temperatures, by sustaining low losses.
Sedimentation caused a sharp decline of the population at the end of
winter each year and a short ( 2-3 months) successional episode
follCMed, rut by late spring M. aeruginosa. was again dominant.
The mixing regime in Hartbeespoort Dam and the buoyancy mechanism of
M. aeruginosa led to frequent formation of surface bloons and ultimately
hyperscums. Hyperscums were defined as thick (decimeters),
crusted, buoyant cyanobacterial mats, in which the organisms are so
densely packed that free water is not evident. In Hartbeespoort Dam
in winter M. aeruginosa formed hyperscums that measured up to 0.75 m
in thickness, covered more than a hectare, contained up to 2 tonnes of
chlorophyll a, and persisted for 2 - 3 monnths. Hyperscum formation
was shown to depend upon the coincidence of the following
preconditions: a large, pre-existing standing crop of positively
buoyant cyanobacteria; turbulent mixing that is too weak to overcome
the tendency of the cells to float, over prolonged periods (weeks);
lake morphometry with wind-protected sites on lee shores; and high incident
solar radiation. The infrequent occurrence of hyperscums can
be attributed to the rare co-occurrence of these conditions.
Colonies in the hyperscum were arranged in a steep vertical gradient,
where colony compaction increased exponentially with decreasing distance
form the surface. This structure was caused by evaporative
dehydration at the surface, and by the buoyancy regulation mechanism
of M. aeruginosa., which results with cells being unable to lose
boyancy when deprived access to light from above. The mean
chlorophyll a concentration and water content were 3.0 g 1¯¹ and 14 %
at the surface crust, 1.0 g 1¯¹ and 77 % at a few mm depth, and 0.3 g
1¯¹ and 94 % at 10 cm depth, where M. aeruginosa cell concentration
exceeded 109 ml¯¹.
A consequence of the high cell and pigment concentrations was that
light penetrated only 3 mm or less, below which anaerobic, highly
reduced conditions developed. Nutrient concentrations in hyperscum
interstitial water, collected by dialysis, increased dramatically with
time (phosphate: 30-fold over 3 months; ammonia: 260-fold). Volatile
fatty acids, intermediate metabolites in anaerobic decomposition
processes, were present. Gas bubbles trapped within the hyperscum contained methane (28 %) , and CO[2] (19 %), the major end products of
anaerobic decomposition, and no oxygen.
The structure and function of M. aeruginosa in hyperscum was examined
in relation to the vertical position of colonies and the duration of
exposure to hyperscum condition. Colonies and cells collected from 10
em depth in the hyperscum were similar in their morphology (light and
fluorescent microscopy) and ultrastructure (transmission and scanning
electron microscopy) to those of colonies from surface blooms in the
main basin of the lake. With declining depth over the uppermost 10 mm
of the hyperscum cells appeared increasingly dehydrated, decomposed
and' colonized by bacteria.
studies employing microelectrode techniques demonstrated that
photosynthetic activity of colonies at the surface of a newly accumulated
hyperscum rapidly photoinhibited, substrate-limited, and
then ceased within hours of exposure to light intensities > 625 μE m⁻²
S¯¹. Photooxidative death followed. The dead cells dehydrated to
form the dry crust,
from underneath.
and space was thus created for colonies rising
Cells collected from 10 cm depth retained their
photosynthetic capacity ([14]C-uptake experiments) throughout the hyperscum
season, although a considerable decline in this capacity was
noted over the last (third) month.
Altogether the data indicated that spatial separation developed within
the hyperscum, between a zone at the surface of lethal physical
conditions, a zone beneath the surface of stressful and probably
lethal chemical conditions, and a deeper zone of more moderate
conditions, which nevertheless, deteriorated after 2 - 3 months. A
conceptual model describing the fate of a colony entering a hyperscum
was then proposed. According to this model, a colony that arrives
below a hyperscum and is not carried away by currents, becomes over-buoyant
in the dark and floats into the bottom of the hyperscum. With
time it migrates towards, due to its own positive buoyancy, the
buoyancy of colonies rising from underneath, and the collapse of cells
at the top. It survives in the dark, anaerobic environment by maintaining
low levels of basal metabolism while utilizing stored
reserves. Depending on weather conditions, the colony mayor may not
remain within the hyperscum long enough to reach the zone of decomposition
near the surface, where it would die. With the aging of the
hyperscum and the accumulation of trapped decomposition products, the
zone of decomposition expands. Thus, a hyperscum is essentially a
site of a continuous cycle of death and dehydration at the surface and upward migration of colonies from below to replace those that died,
although not all colonies entering the hyperscum necessarily reach the
lethal zone.
The formation of hyperscums was shown to have no major influence on
the annual cycle of M. aeruginosa in Hartbeespoort Dam. The
seasonality of increase and decline of the planktonic population was
similar from year to year, irrespective of whether or not hyperscums
formed. The phenomenon of hyperscums demonnstrated that, as Reynolds
and Walsby (1975) claimed, thick cyanobacterial water-blooms do form
incidentally and have no vital function in the biology of the organism.
water temperature did have a major effect on the annual cycle of this
species in Hartbeespoort Dam. In temperate lakes the low water temperatures
in autumn and winter (<10° C) cause M. aeruginosa to lose
its ability to regain buoyancy in the dark, and consequently it sinks
to bottom sediments. The higher ( > l2°C) minimum winter temperature
in Hartbeespoort Dam leads to the maintenance of a relatively large
residual planktonic population throughout the winter. Unlike the case
in temperate lakes, the long-term survival of M. aeruginosa in warm-water
lakes probably does not depend on winter benthic stocks for the
provision of an inoculum for the following growth season. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1987.
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Iron, light and microcystin : the environmental modulation of growth and toxin production by microcystis species in the Bay of Quinte (Lake Ontario) and in culture /Forrester, Lauren. January 2008 (has links)
Thesis (M.Sc.)--York University, 2008. Graduate Programme in Biology. / Typescript. Includes bibliographical references (leaves 120-136). Also available on the Internet. MODE OF ACCESS via web browser by entering the following URL: http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&res_dat=xri:pqdiss&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&rft_dat=xri:pqdiss:MR38772
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Degradação bacteriana da MOD excretada por Microcystis aeruginosa (Cyanobacteria) em culturas, fracionada e submetida à radiação UVMoreira, Ingritt Caroline 31 July 2009 (has links)
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Previous issue date: 2009-07-31 / Solar radiation can change DOM in aquatic environments making compounds more labile or recalcitrant to biodegradation. Thus, solar radiation, especially UV, indirectly interfere in the microbial community in order to increase or decrease their growth. The objective was to verify the interference of UV-A + B on the bioavailability of DOM separated into different fractions (molecular weight), from release of cells in stationary phase of M. aeruginosa. DOM released from cyanobacteria was separated by tangential ultra-filtration and these were inoculated bacterial community of Barra Bonita reservoir. Bacterial community dynamic was monitored by measures of density and biomass and bacterial consumption of carbon from DOM by measures of DOC. Frequency of bacterial morphotypes were also calculated. All three fractions of DOM investigated were highly available to the bacterial community. The fraction of cultures with DOM<3 kDa and DOM>30 kDa demonstrated to be more vulnerable to UV radiation, corroborated by many statistical differences found for bacterial density during 27 days of incubation. At 15 days of incubation, the cultures with irradiated DOM>30 kDa showed a second peak in bacterial density and biomass that can be understood as an event of succession in bacterial community. Changes in relative frequency of bacterial morphotypes over incubation period suggest an episode of succession during the different stages of degradation of DOM. It was suggested that the majority of DOC released from a bloom of cyanobacteria is rapidly mineralized. Furthermore, the constant blooms, or ever high biomass of M. aeruginosa during the year, mean that such bacterial consortia are always available. / A radiação solar pode alterar a MOD em um ambiente aquático tornando os compostos mais lábeis ou recalcitrantes à biodegradação. Desta forma, a radiação solar, principalmente a radiação UV, interfere indiretamente na comunidade microbiana de forma a incrementar ou diminuir seu crescimento. O objetivo deste trabalho foi verificar a interferência da radiação UV-A+B na biodisponibilidade da MOD separada em diferentes frações (massa molecular), oriundas da liberação de células na fase estacionária de Microcystis aeruginosa. A MOD liberada pela cianobactéria foi separada por ultra-filtração tangencial e a estas foram inoculadas a comunidade bacteriana do reservatório de Barra Bonita. A dinâmica da comunidade bacteriana foi acompanhada por medidas de densidade e biomassa bacteriana e o consumo de carbono das frações de MOD por medidas de COD. Também foram calculadas as frequências dos morfotipos bacterianos. Todas as três frações de MOD investigadas apresentaram-se altamente disponíveis à comunidade bacteriana. As culturas com fração de MOD<3 kDa e MOD>30 kDa revelaram-se mais vulneráveis à radiação UV, fato corroborado pelas numerosas diferenças estatísticas encontradas para as densidades bacterianas durante os 27 dias de incubação. Aos 15 dias de incubação, as culturas com fração de MOD>30 kDa irradiada apresentaram um segundo pico na densidade e biomassa bacteriana que pode ser interpretado como um evento de sucessão na comunidade bacteriana. As mudanças na frequência relativa dos morfotipos bacterianos ao longo do período de incubação sugerem um episódio de sucessão durante as distintas fases de degradação da MOD. Sugeriu-se que a maior parte do COD liberado por um bloom desta cianobactéria é mineralizado rapidamente. Além disso, com os constantes blooms, ou a sempre alta biomassa de M. aeruginosa ao longo do ano, inferem que tais consórcios bacterianos estejam sempre disponíveis.
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