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Natália V Casquilho,
Giovanna M C Carvalho,
João L C R Alves,
Mariana N Machado,
Raquel M Soares, Sandra M F O Azevedo,
Lidia M Lima,
Eliezer J Barreiro,
Samuel S Valença,
Alysson R Carvalho,
Débora S Faffe,
Walter A Zin
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ABSTRACT: Cyanobacterial blooms that generate microcystins (MCYSTs) are increasingly recognized as an important health problem in aquatic ecosystems. We have previously reported the impairment of pulmonary structure and function by microcystin-LR (MCYST-LR) exposure as well as the pulmonary improvement by intraperitoneally injected (i.p.) LASSBio 596. In the present study, we aimed to evaluate the usefulness of LASSBio 596 per os on the treatment of pulmonary and hepatic injuries induced by MCYST-LR. Swiss mice received an intraperitoneal injection of 40 μl of saline (CTRL) or a sub-lethal dose of MCYST-LR (40 μg/kg). After 6 h the animals received either saline (TOX and CTRL groups) or LASSBio 596 (50 mg/kg, LASS group) by gavage. Eight hours after the first instillation, lung impedance (static elastance, elastic component of viscoelasticity and resistive, viscoelastic and total pressures) was determined by the end-inflation occlusion method. Left lung and liver were prepared for histology. In lung and hepatic homogenates MCYST-LR, TNF-α, IL-1β and IL-6 were determined by ELISA. LASSBio 596 per os (LASS mice) kept all lung mechanical parameters, polymorphonuclear (PMN) cells, pro-inflammatory mediators, and alveolar collapse similar to control mice (CTRL), whereas in TOX these findings were higher than CTRL. Likewise, liver structural deterioration (hepatocytes inflammation, necrosis and steatosis) and inflammatory process (high levels of pro-inflammatory mediators) were less evident in the LASS than TOX group. LASS and CTRL did not differ in any parameters studied. In conclusion, orally administered LASSBio 596 prevented lung and hepatic inflammation and completely blocked pulmonary functional and morphological changes induced by MCYST-LR.
Toxicon 06/2011; 58(2):195-201. · 2.51 Impact Factor
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ABSTRACT: The treatment of microcystin-LR (MCYST-LR)-induced lung inflammation has never been reported. Hence, LASSBio 596, an anti-inflammatory drug candidate, designed as symbiotic agent that modulates TNF-alpha levels and inhibits phosphodiesterase types 4 and 5, or dexamethasone were tested in this condition. Swiss mice were intraperitoneally (i.p.) injected with 60 microl of saline (CTRL) or a sub-lethal dose of MCYST-LR (40 micrg/kg). 6 h later they were treated (i.p.) with saline (TOX), LASSBio 596 (10 mg/kg, L596), or dexamethasone (1 mg/kg, 0.1 mL, DEXA). 8 h after MCYST-LR injection, pulmonary mechanics were determined, and lungs and livers prepared for histopathology, biochemical analysis and quantification of MCYST-LR. TOX showed significantly higher lung impedance than CTRL and L596, which were similar. DEXA could only partially block the mechanical alterations. In both TOX and DEXA alveolar collapse and inflammatory cell influx were higher than in CTRL and L596, being LASSBio 596 more effective than dexamethasone. TOX showed oxidative stress that was not present in CTRL and L596, while DEXA was partially efficient. MCYST-LR was detected in the livers of all mice receiving MCYST-LR and no recovery was apparent. In conclusion, LASSBio 596 was more efficient than dexamethasone in reducing the pulmonary functional impairment induced by MCYST-LR.
Toxicon 09/2010; 56(4):604-12. · 2.51 Impact Factor
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ABSTRACT: Bioassays using Daphnia pulex and Moina micrura were designed to detect cyanobacterial neurotoxins in raw water samples. Phytoplankton and cyanotoxins from seston were analyzed during 15 months in a eutrophic reservoir. Effective time to immobilize 50% of the exposed individuals (ET50) was adopted as the endpoint. Paralysis of swimming movements was observed between approximately 0.5-3 h of exposure to lake water containing toxic cyanobacteria, followed by an almost complete recovery of the swimming activity within 24 h after being placed in control water. The same effects were observed in bioassays with a saxitoxin-producer strain of Cylindrospermopsis raciborskii isolated from the reservoir. Regression analysis showed significant relationships between ET50 vs. cell density, biomass and saxitoxins content, suggesting that the paralysis of Daphnia in lake water samples was caused by saxitoxins found in C. raciborskii. Daphnia bioassay was found to be a sensitive method for detecting fast-acting neurotoxins in natural samples, with important advantages over mouse bioassays.
Environmental pollution (Barking, Essex: 1987) 03/2010; 158(6):2084-93. · 3.43 Impact Factor
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ABSTRACT: Although reservoirs are similar to natural lakes in many respects, such driving forces as water retention time and watershed features can play important roles in the limnology of manmade lakes. With the goal of investigating how these factors influence the limnology of tropical reservoirs, physical and chemical variables were measured at four sampling sites in two reservoirs in southern Brazil, from June 2002 to June 2003. Funil Reservoir is located in one of the most-populated areas in the country, in the Paraíba do Sul river basin, which drains and drastically influences the water quality of the reservoir. In contrast, Lajes Reservoir is located in a well-preserved area, with its water retention time varying from six to 30 times longer than for Funil Reservoir. Funil Reservoir is a turbid (median euphotic zone = 4.3 m), eutrophic reservoir (median total phosphorus (TP) = 3.1 µm), with a high phytoplankton biomass (median chlorophyll-a concentration = 10.0 µg L−1). In contrast, Lajes Reservoir is a transparent (median euphotic zone = 9.2 m), mesotrophic water system (median TP = 1.0 µm), with a low phytoplankton biomass (median chlorophyll-a = 1.9 µg L−1). Both reservoirs were stratified during the summer months, but isothermy was only observed in Funil Reservoir. Because of its short water retention time, Funil Reservoir is a much more dynamic system than Lajes Reservoir, with a pronounced temporal pattern related to changes in its water column and its phytoplankton biomass. Spatial heterogeneity is more evident in Lajes Reservoir, mainly as a consequence of its location in a preserved area, long water retention time and the presence of net cages for fish culture in the waterbody. The typical spatial zonation found in reservoirs, related to nutrient sedimentation and light availability, however, is more evident in Funil Reservoir than in Lajes Reservoir. Despite the similarities between these two water systems, which are in the same geographical region with similar climate, and are comparable in size, the distinct watershed features and water retention time are responsible for marked differences between these reservoirs.
Lakes & Reservoirs Research & Management 11/2008; 13(4):257 - 269.
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Environmental Toxicology 07/2008; 23(3):422. · 2.41 Impact Factor
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ABSTRACT: This study evaluates the potential for the use of cladocerans in biomonitoring of cyanobacterial toxins. Two zooplankton species (Daphnia gessneri and Moina micrura) were cultivated in the laboratory for use in acute (48 h) and chronic (10 days) bioassays. Water samples were collected from two reservoirs and diluted in mineral water at four concentrations. Survivorship in the acute bioassays was used to calculate LC50, and survivorship and fecundity in chronic bioassays were used to calculate the intrinsic population growth rate (r) and the EC50. Analysis of phytoplankton in the water samples from one reservoir revealed that cyanobacteria were the dominant group, represented by the genera Anabaena, Cylindrospermopsis, and Microcystis. Results of bioassays showed adverse effects including death, paralysis, and reduced population growth rate, generally proportional to the reservoir water concentration. These effects may be related to the presence of cyanobacteria toxins (microcystins or saxitoxins) in the water.
Ecotoxicology and Environmental Safety 05/2008; 72(2):479-89. · 2.29 Impact Factor
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ABSTRACT: This study evaluated the effects of a saxitoxin-producer strain (T3) of the cyanobacteria species Cylindrospermopsis raciborskii on the swimming movements of three cladoceran species (Daphnia gessneri, D. pulex, and Moina micrura). Acute toxicity bioassays were designed to access the effects of T3 strain, of a nonsaxitoxin producer strain (NPLP-1) of the same species and of a raw water sample from Funil reservoir (Rio de Janeiro, Brazil), that contained this and other cyanobacteria. In the acute bioassays, animals were exposed to C. raciborskii filaments or Funil water for 24-48 h and then transferred to food suspensions without cyanobacterial filaments for a further 48 h. During the exposure time to T3 strain filaments there was a decrease in the number of swimming individuals, with animals showing progressive immobilization. The same effect was observed with Funil water sample. Animals stayed alive on the bottom of the test tube and recovered swimming movements when transferred to food suspensions without toxic cells. This effect was not observed with the strain NPLP-1. The cladoceran D. pulex showed to be extremely sensitive to T3 strain and to Funil water containing C. raciborskii filaments, showing complete paralysis after 24-h exposure to T3 cell densities of 10(3) and 10(4) cells mL(-1), and after 24-h exposure to only 10% of raw water. However, D. gessneri was not sensitive to both T3 and to Funil water, whereas M. micrura was intermediate in sensitivity. This is the first report on the effects of cyanobacterial saxitoxins on movements of freshwater cladocerans, showing also difference in sensitivity among closely related Daphnia species.
Environmental Toxicology 05/2008; 23(2):161-8. · 2.41 Impact Factor
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Sandra M F O Azevedo,
Neil Chernoff,
Ian R Falconer,
Michael Gage,
Elizabeth D Hilborn,
Michelle J Hooth,
Karl Jensen,
Robert MacPhail,
Ellen Rogers,
Glen R Shaw,
Ian Stewart,
John W Fournie
Advances in experimental medicine and biology 02/2008; 619:579-606. · 1.09 Impact Factor
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ABSTRACT: Toxic cyanobacteria blooms in drinking water supplies have been an increasing public health concern all over the world. Human populations can be exposed to microcystins, an important family of cyanotoxins, mainly by oral ingestion. However, inhalation from recreational water and hemodialysis can represent other routes. This study investigated changes in respiratory mechanics, histology, protein phosphatase (PP) 1 and 2A activity and microcystin in lung of adult mice injected intraperitoneally (i.p.) with microcystin-LR. Thirty-six mice were divided into control (CTRL) and test (CYANO) groups. CTRL group received an i.p. injection of saline and the CYANO group received 40 microg MCYST-LR/kg i.p. After 2 and 8 h, and 1, 2 and 4 days after toxin injection, six mice from each group were sampled for analyses. Resistive and viscoelastic pressures, static and dynamic elastances augmented at 2 h in CYANO and so remained until day 4. Alveolar collapse and inflammatory cell infiltration were found 2h after the injection, reaching peak values at 8 h. However, no microcystin or inhibition of PPases could be detected in mice lungs. In conclusion, MCYST-LR led to a rapid increase in lung impedance and an inflammatory response with interstitial edema and inflammatory cell recruitment in mice.
Toxicon 10/2007; 50(3):330-8. · 2.51 Impact Factor
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ABSTRACT: The methylated form of mercury (Hg), methylmercury (MeHg), is one of the most toxic pollutants. Biotic and/or abiotic methylation, often associated to sulfate-reducing bacteria metabolism, occurs in aquatic environments and in many tropical areas, mostly in the periphyton associated to floating macrophyte roots. Data about mercury methylation by phytoplankton are scarce and the aim of this study was to verify the biotic influence in the methylation process in Microcystis aeruginosa and Sineccocystis sp. laboratory strains and in natural populations of phytoplankton from two different aquatic systems, the mesotrophic Ribeirão das Lajes reservoir and hypereutrophic oligohaline Jacarepaguá lagoon, Rio de Janeiro state, Brazil. Adapted radiochemical techniques were used to measure sulfate-reduction, mercury methylation and bacterial activity in phytoplankton samples. Methyl-(203)Hg formation from added inorganic (203)Hg and (3)H-Leucine uptake were measured by liquid scintillation as well as sulfate-reduction, estimated as H(2)(35)S produced from added Na(2)(35)SO(4). There was no significant difference in low methylation potentials (0.37%) among the two cyanobacterium species studied in laboratory conditions. At Ribeirão das Lajes reservoir, there was no significant difference in methylation, bacterial activity and sulfate-reduction of surface sediment between the sampling points. Methylation in sediments (3-4%) was higher than in phytoplankton (1.5%), the opposite being true for bacterial activity (sediment mean 6.6 against 150.3 nmol gdw(-1) h(-1) for phytoplankton samples). At Jacarepaguá lagoon, an expressive bacterial activity (477.1 x 10(3) nmol gdw(-1) h(-1) at a concentration of 1000 nM leucine) and sulfate-reduction ( approximately 21% H(2)(35)S trapped) associated to phytoplankton (mostly cyanobacteria M. aeruginosa) was observed, but mercury methylation was not detected.
Science of The Total Environment 08/2006; 364(1-3):188-99. · 3.29 Impact Factor
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ABSTRACT: In November 2001, a cyanobacterial bloom dominated by Microcystis and Anabaena occurred in the Funil Reservoir and the Guandu River, both of which supply drinking water to Rio de Janeiro, Brazil. Using ELISA, microcystins were detected at a concentration of 0.4 microg/L in the drinking water, whereas a concentration of 0.32 microg/L was detected in activated carbon column-treated water for use at the renal dialysis center of Clementino Fraga Filho Hospital (HUCFF) at the Federal University of Rio de Janeiro. A total of 44 hemodialysis patients who received care at this center were believed to be exposed. Initial ELISA analyses confirmed the presence of serum microcystin concentrations > or = 0.16 ng/mL in 90% of serum samples collected from these patients. Twelve patients were selected for continued monitoring over the following 2-month period. Serum microcystin concentrations ranged from < 0.16 to 0.96 ng/mL during the 57 days after documented exposure. ELISA-positive samples were found throughout the monitoring period, with the highest values detected 1 month after initial exposure. ESI LC/MS analyses indicated microcystins in the serum; however, MS/MS fragmentation patterns typical of microcystins were not identified. LC/MS analyses of MMPB for control serum spiked with MCYST-LR. and patient sera revealed a peak at retention time of 8.4 min and a mass of 207 m/z. These peaks are equivalent to the peak observed in the MMPB standard analysis. Taken together ELISA, LC/MS, and MMPB results indicate that these renal dialysis patients were exposed to microcystins. This documents another incident of human microcystin exposure during hemodialysis treatment.
Environmental Toxicology 05/2006; 21(2):95-103. · 2.41 Impact Factor
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ABSTRACT: Toxic cyanobacteria are contaminants of surface waters worldwide. Microcystins are some of the most commonly detected cyanotoxins. Biological evidence of human exposure may be difficult to obtain due to limitations associated with cost, laboratory capacity, analytic support, and expertise. We investigated the application of an enzyme-linked immunosorbant assay (ELISA) to detect microcystins in human serum. We analyzed ten serum samples collected from dialysis patients who were known to be exposed to a mixture of microcystins during a 1996 outbreak in Brazil. We applied a commercially available ELISA method to detect microcystins in serum, and we compared the ELISA results to a more specific method, liquid chromatography/mass spectrometry (LC/MS) that was also used to detect microcystins in serum. The Spearman correlation coefficient was calculated using serum microcystin concentrations in split samples obtained by the two methods. Serum microcystin concentrations were similar, and we found good correlation of microcystin concentrations between the two methods. The ELISA detected total microcystins, median=19.9 ng/ml; LC/MS detected microcystin-LR equivalents, median=21.2 ng/ml; Spearman r=0.96, p<0.0001. We found that ELISA is a simple, accessible method to screen human serum for evidence of microcystin exposure.
Toxicon 09/2005; 46(2):218-21. · 2.51 Impact Factor
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ABSTRACT: Toxic cyanobacteria in aquatic environments have been implicated in many poisoning incidents of livestock, wildlife, and domestic animals. Microcystins (MCYSTs) in water supplies represent a risk to public health. This work investigated the effect of water composition on the quantitation and biological activity of MCYSTs analyzed by different methods (HPLC, ELISA, and protein phosphatase 1 inhibition assay). Different MCYST concentrations were added to deionized water and quantified, confirming the efficiency of these analytical methods. MCYST concentrations diluted in drinking water had reduced detection by all methods tested. The drinking water used contained a free chlorine concentration of 2.5 mg/L and an Fe concentration of 0.45 mg/L, and the conductivity was 69.8 microS cm(-1), whereas in deionized water, free chlorine and Fe were not detectable, and the conductivity was 1.6 microS cm(-1). Drinking water also interfered with the biological activity of MYCSTs, as these toxins showed reduced protein phosphatase-1 inhibition. A free chlorine concentration of 2.5 mg/L in deionized water was completely effective in preventing any detection of 10 microg/L of added MCYSTs. Fe and Al ions also were very effective in reducing MCYST detection. The chemical composition of drinking water thus affected MCYST detection, indicating a significant reduction in quantitation of this molecule either because of its decomposition or through complexation with metal ions.
Environmental Toxicology 05/2005; 20(2):126-30. · 2.41 Impact Factor
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ABSTRACT: In order to understand accumulation and depuration of microcystins (MCYSTs) in Tilapia rendalli, three experiments with juveniles were done. The experiments simulated the fish diet during a Microcystis aeruginosa bloom in three different situations. In the first one each fish received daily, during 15 days, fish food plus toxic cells of M. aeruginosa (20.4 microg MCYSTs fish(-1) day(-1)). In the following 15 days they were fed without toxic cells. In the second experiment, fish were fed only with toxic cells during 28 days (14.6 microg MCYSTs fish(-1) day(-1)) and in the third experiment, during 42 days, fish were fed with fish food plus toxic cells (29.2 microg MCYSTs fish(-1) day(-1)) previously disrupted (to simulate a senescent bloom). MCYSTs analyses were done by enzyme-linked immunosorbent assay (ELISA) in liver and muscle samples in all experiments and in faeces in the first one (only in the depuration period). The results demonstrated different profiles of MCYSTs accumulation in liver and muscle of T. rendalli. Comparing the experiments, the highest MCYSTs accumulation in the liver (2.8 microg g(-1)) occurred in the second one, where fish had only toxic cells as feeding source. In the first experiment, the highest MCYSTs accumulation in liver (0.6 microg MCYSTs g(-1)) was observed during the accumulation period, while in muscle, interestingly, the highest concentration (0.05 microg MCYSTs g(-1)) occurred in the depuration period. In this same period, it was also observed elimination of toxins through faeces. The second and third experiments showed almost the same average concentrations in tissues although fish have received more MCYSTs in third one. With respect to implications of the fish comsumption, MCYSTs accumulation in muscle of T. rendalli in all three experiments reached concentrations that would represent an intake of these toxins above the tolerable limit for humans and these results confirmed our previous observations from a field study. In conclusion, in this study it was observed that T. rendalli is able to accumulate MCYSTs and the availability of other feeding sources, besides toxic cells, probably interferes with the accumulation rate. Therefore, the occurrence of toxic cyanobacterial blooms produncing MCYSTs in aquaculture ponds could represent a risk to the quality of fish to the consumers.
Aquatic Toxicology 11/2004; 70(1):1-10. · 3.76 Impact Factor
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ABSTRACT: In February 1996, an outbreak of illness occurred at a hemodialysis clinic in Caruaru, Pernambuco State-Brazil. At this clinic 116 (89%) of 131 patients experienced visual disturbances, nausea, vomiting, and muscle weakness, following routine haemodialysis treatment. Subsequently, 100 patients developed acute liver failure. As of December 1996, 52 of the deaths could be attributed to a common syndrome now called 'Caruaru Syndrome'. Examination of previous years' phytoplankton counts showed that cyanobacteria were dominant in the water supply reservoir since 1990. Analyses of carbon and other resins from the clinic's water treatment system plus serum and liver tissue of patients led to the identification of two groups of hepatotoxic cyanotoxins: microcystins (cyclic heptapeptides) in all of these samples and cylindrospermopsin (alkaloid hepatotoxic) in the carbon and resins. Comparison of victims symptoms and pathology with animal studies on these two cyanotoxins, leads us to conclude that the major contributing factor to death of the dialysis patients was intravenous exposure to microcystins, specifically microcystin-YR, -LR and -AR. In 2000, a review of the Brazilian regulation for drinking water quality, promoted by Brazilian Health Ministry with collaboration of PAHO, incorporated cyanobacteria and cyanotoxins into this new regulation as parameters that must to be monitored for water quality control.
Toxicology 01/2003; 181-182:441-6. · 3.68 Impact Factor
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ABSTRACT: In the current study, the hepatotoxic peptide microcystins, were measured in the zooplankton community of Jacarepaguá Lagoon during a 6-month period. Concurrent phytoplankton and seston samples were obtained. Microcystins were measured in seston and phytoplankton by High Performance Liquid Chromatography (HPLC), and in zooplankton by an Enzyme-Linked Immunosorbant Assay (ELISA). Zooplankton community was comprised mainly by the rotifers Brachionus angularis and B. plicatilis, the cladocerans Moina micrura and Ceriodaphnia cornuta and the copepod Metacyclops mendocinus. Phytoplankton was dominated by Microcystis aeruginosa during all the studied period. Microcystins in zooplankton ranged from 0.3 to 16.4 microg g(-1) DW, while in the sestonic samples they ranged from undetectable values to 5.8 ng g(-1) DW. Microcystins in net phytoplankton ranged from 0.3 to 3.9 mg g(-1) DW. We conclude that zooplankton from Jacarepaguá Lagoon were efficient accumulators of microcystins from seston and that these animals can be potential vectors in the transferring of such toxins to higher trophic levels in the aquatic food chain.
Aquatic Toxicology 10/2002; 59(3-4):201-8. · 3.76 Impact Factor
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ABSTRACT: Chronic and subchronic toxicity from exposure to microcystins, cyclic peptide liver toxins from certain cyanobacteria, poses an important hazard, which has received little study. No in vivo information exists on accumulation and transfer of microcystin from the food chain to humans. This paper present results of a 3-year study that demonstrates bioaccumulation of microcystins by fish and potential rates of microcystin ingestion by humans. The study was carried out in a shallow coastal lagoon in the city of Rio de Janeiro (Jacarepaguá Lagoon). Fish (Tilapia rendalli) were collected every 2 weeks from August 1996 to November 1999. Microcystins were analyzed by HPLC in phytoplankton, fish liver and viscera while fish muscle tissue was analyzed by enzyme linked immunosorbant assay (ELISA). Phytoplankton samples, dominated by the genus Microcystis, were confirmed to contain microcystins as were fish livers, viscera and muscle tissue. During the entire study period, including times of low water bloom densities, fish muscle tissue contained concentrations of microcystins close to or above the recommended limit for human consumption (0.04 μg kg−1 day). Our findings demonstrate that microcystins can accumulate in fish tissue used for human consumption. Rates of ingestion routinely exceed the TDI guidelines as set by the WHO for drinking water. Appropriate epidemiology and risk assessment should be undertaken so that an acceptable TDI and appropriate risk management decisions can be made for human consumption of fish which are harvested from cyanobacterial blooms that contain cyanotoxins.
Toxicon 08/2001; · 2.51 Impact Factor
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ABSTRACT: This is the first report on microcystins, cyclic heptapeptide hepatotoxins, from Brazilian water supplies. A colony isolate (NPJB-1) of the colonial cyanobacteriumMicrocystis aeruginosa from Lagoa das Garas, So Paulo, was cultured under non-axenic conditions. Exponential phase cells were harvested, concentrated and lyophilized for mouse bioassays and toxin extraction. The LD100 of lyophilized cell suspensions was approximately 31 mg kg–1 (dry cell weight/animal weight). Isolation, purification and characterization of the toxins were carried out by reversed phase HPLC, HPLC amino acid analysis and fast atom bombardment mass spectrometry. Strain NPJB-1 produces two different hepatotoxic heptapeptide microcystins. The main one was microcystin-LR, the most commonly reported microcystin from cyanobacteria. The other was microcystin-LF, the phenylalanine variant of microcystin-LR. This is the first published report for microcystin-LF.
Journal of Applied Phycology 05/1994; 6(3):261-265. · 2.41 Impact Factor
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ABSTRACT: The methylated form of mercury (Hg), methylmercury (MeHg), is one of the most toxic pollutants. Biotic and/or abiotic methylation, often associated to sulfate-reducing bacteria metabolism, occurs in aquatic environments and in many tropical areas, mostly in the periphyton associated to floating macrophyte roots. Data about mercury methylation by phytoplankton are scarce and the aim of this study was to verify the biotic influence in the methylation process in Microcystis aeruginosa and Sineccocystis sp. laboratory strains and in natural populations of phytoplankton from two different aquatic systems, the mesotrophic Ribeirão das Lajes reservoir and hypereutrophic oligohaline Jacarepaguá lagoon, Rio de Janeiro state, Brazil. Adapted radiochemical techniques were used to measure sulfate-reduction, mercury methylation and bacterial activity in phytoplankton samples. Methyl-203Hg formation from added inorganic 203Hg and 3H-Leucine uptake were measured by liquid scintillation as well as sulfate-reduction, estimated as H235S produced from added Na235SO4. There was no significant difference in low methylation potentials (0.37%) among the two cyanobacterium species studied in laboratory conditions. At Ribeirão das Lajes reservoir, there was no significant difference in methylation, bacterial activity and sulfate-reduction of surface sediment between the sampling points. Methylation in sediments (3–4%) was higher than in phytoplankton (1.5%), the opposite being true for bacterial activity (sediment mean 6.6 against 150.3 nmol gdw− 1 h− 1 for phytoplankton samples). At Jacarepaguá lagoon, an expressive bacterial activity (477.1 × 103 nmol gdw− 1 h− 1 at a concentration of 1000 nM leucine) and sulfate-reduction (∼21% H235S trapped) associated to phytoplankton (mostly cyanobacteria M. aeruginosa) was observed, but mercury methylation was not detected.
Science of The Total Environment.
