Toxicity and microcystin content of extracts from a Planktothrix bloom and two laboratory strains

Cyanopeptides occurrence and diversity in a Brazilian tropical reservoir: Exploring relationships with water quality

Microcystins (MCs) are a class of toxic secondary metabolites produced by some cyanobacteria strains that endanger aquatic and terrestrial organisms in various freshwater systems. Although patterns in MC occurrence are being recognized, divergences in the global data still hamper our ability to predict the toxicity of cyanobacterial blooms. This study aimed (i) to determine the dynamics of MCs and other cyanopeptides in a tropical reservoir, (ii) to investigate the correlation between peptides and potential cyanotoxin producers (iii) identifying the possible abiotic factors that influence the peptides. We analyzed, monthly, eight MC variants (MC-RR, -LA, -LF, -LR, -LW, -YR, [D-Asp3]-RR and [D-Asp3]-LR) and other peptides in 47 water samples collected monthly, all season long, from two sampling sites in a tropical eutrophic freshwater reservoir, in southeastern Brazil. The cyanopeptides were assessed by liquid chromatography-tandem mass spectrometry (LC-MS/MS). The biomass of potential cyanobacterial producers and water quality variables were measured. MCs were detected in both sampling sites year-round; the total MC concentration varied from 0.21 to 4.04 μg L-1, and three MC variants were identified and quantified (MC-RR, [D-Asp3]-RR, -LR). Additionally, we identified 28 compounds belonging to three other cyanopeptide classes: aeruginosin, microginin, and cyanopeptolin. As potential MC producers, Microcystis spp. and Dolichospermum circinalis were dominant during the study, representing up to 75% of the total phytoplankton. Correlational and redundancy analysis suggested positive effects of dissolved oxygen, nitrate, and total phosphorus on MC and microginins concentration, while water temperature appeared to favor aeruginosins. A comparison between our results and historical data showed a reduction in total phosphorus and cyanobacteria, suggesting increased water quality in the reservoir. However, the current MC concentrations indicate a rise in cyanobacterial toxicity over the last eight years. Moreover, our study underscores the pressing need to explore cyanopeptides other than MCs in tropical aquatic systems.

Biotests in Cyanobacterial Toxicity Assessment-Efficient Enough or Not?

Cyanobacteria are a diverse group of organisms known for producing highly potent cyanotoxins that pose a threat to human, animal, and environmental health. These toxins have varying chemical structures and toxicity mechanisms and several toxin classes can be present simultaneously, making it difficult to assess their toxic effects using physico-chemical methods, even when the producing organism and its abundance are identified. To address these challenges, alternative organisms among aquatic vertebrates and invertebrates are being explored as more assays evolve and diverge from the initially established and routinely used mouse bioassay. However, detecting cyanotoxins in complex environmental samples and characterizing their toxic modes of action remain major challenges. This review provides a systematic overview of the use of some of these alternative models and their responses to harmful cyanobacterial metabolites. It also assesses the general usefulness, sensitivity, and efficiency of these models in investigating the mechanisms of cyanotoxicity expressed at different levels of biological organization. From the reported findings, it is clear that cyanotoxin testing requires a multi-level approach. While studying changes at the whole-organism level is essential, as the complexities of whole organisms are still beyond the reach of in vitro methodologies, understanding cyanotoxicity at the molecular and biochemical levels is necessary for meaningful toxicity evaluations. Further research is needed to refine and optimize bioassays for cyanotoxicity testing, which includes developing standardized protocols and identifying novel model organisms for improved understanding of the mechanisms with fewer ethical concerns. In vitro models and computational modeling can complement vertebrate bioassays and reduce animal use, leading to better risk assessment and characterization of cyanotoxins.

Sublethal exposure to Microcystis aeruginosa extracts during embryonic development reduces aerobic swimming capacity in juvenile zebrafish

In the last decades, cyanobacterial harmful algal blooms (CyanoHABs) pose an intensifying ecological threat. Microcystis aeruginosa is a common CyanoHAB species in freshwater ecosystems, with severe toxic effects in a wide range of organisms. In the present paper we examined whether transient and short (48 h) exposure of fish embryos to sublethal levels of M. aeruginosa crude extract (200 mg biomass dw L^-1) affects swimming performance at later life stages (end of metamorphosis, ca 12 mm TL, 22,23 days post-fertilization). Pre-exposed metamorphosing larvae presented a significant decrease in swimming performance (9.7 ± 1.6 vs 11.4 ± 1.7 TL s^-1 in the control group, p < 0.01), and a significant decrease in the ventricle length-to-depth ratio (1.23 ± 0.15 vs 1.42 ± 0.15 in control fish, p < 0.05). In addition, extract-exposed fish presented significantly elevated rates of vertebral abnormalities (82 ± 13% vs 7 ± 4% in the control group), mainly consisting of the presence of extra neural and haemal processes. No significant differences between groups were detected in survival and growth rates. Results are discussed in respect to the mechanisms that might mediate the detected cyanobacterial effects. This is the first evidence of a direct link between sublethal exposure to M. aeruginosa during the embryonic period and swimming performance at later life-stages. Decreased swimming performance, altered cardiac shape, and elevated vertebral abnormalities in response to early exposure to M. aeruginosa could have significant effects on fish populations in the wild.

Investigating the microbial dynamics of microcystin-LR degradation in Lake Erie sand

Cyanobacterial blooms and the associated hepatotoxins produced (e.g., microcystins, MCs) create a significant human health risk in freshwater lakes around the world, including Lake Erie. Though various physical and chemical treatment options are utilized, these are costly and their effectiveness decreases when other organics are present. Laboratory studies have identified a remediation option based on a mlr gene operon that can systematically degrade this toxin; however, studies on Lake Erie have been unable to amplify mlr genes from MC-degrading bacteria. These results suggest that either existing primers may be inefficient for broad identification of the mlr genes or that MC degradation genes and/or pathways may vary among bacterial taxa. To investigate the dynamics of the Lake Erie microbial community involved in the degradation of microcystin-LR (MC-LR), a flow-through column experiment using collected beach sand was conducted over a period of six weeks. Increasing concentrations of lake water spiked with MC-LR were continuously delivered to both biotic and abiotic (sterilized) sand columns, with influent and effluent MC-LR concentrations measured by LC-MS/MS. Despite the toxin concentrations far exceeding natural conditions during a bloom event (maximum dosage = 15.4 μg/L), MC-LR was completely removed within 21 h of contact time in the biotic columns. Stimulation of community taxa during the degradation process included Burkholderiaceae, Illumatobacteraceae, Pseudomonadaceae, Rhodocyclaceae and Nitrosomonadaceae. The overall results suggest several critical species may be required for the most complete and effective degradation of MC-LR.

The sensitivity of multiple ecotoxicological assays for evaluating Microcystis aeruginosa cellular algal organic matter and contribution of cyanotoxins to the toxicity

Secondary metabolites of cyanobacteria and algae released during algal blooms often exhibit toxic effects, but only a small number of the metabolites are the subject of routine analytical screenings. Alternatively, ecotoxicological assays offer a better representation of the overall negative effects. The aim of this work was to compare multiple assays in their sensitivity towards cellular algal organic matter (COM) of the toxin-producing cyanobacterium Microcystis aeruginosa. Multiple endpoints were investigated: mortality, growth inhibition, bioluminescence inhibition, genotoxicity, endocrine-disrupting effects, oxidative stress, and the induction of ethoxyresorufin-O-deethylase (EROD). Three rainbow trout (Oncorhynchus mykiss) cell lines as well as representatives of bacteria, yeasts, algae, vascular plants, and crustaceans were employed, and the results were expressed per mg of dissolved organic carbon (DOC) in the COM. M. aeruginosa COM was toxic to the RTgill-W1, RTG-2, and RTL-W1 cell lines (EC₅₀ values ranging from 0.48 ± 0.02 to 1.9 ± 0.1 mg_DOC/L), to the crustacean Thamnocephalus platyurus (LC₅₀ = 20 ± 1 mg_DOC/L), and to Lepidium sativum (IC₅₀ = 241 ± 13 mg_DOC/L). In contrast, no effect was observed for bacteria and yeasts, and the growth of the alga Desmodesmus subspicatus was even stimulated. No genotoxicity, endocrine-disrupting effects or increase in oxidative stress or EROD activity was detected. The content of six microcystins (MC-LR, MC-RR, MC-YR, MC-LY, MC-LW, and MC-LF), anatoxin-a, cylindrospermopsin, and nodularin in the M. aeruginosa COM was determined by liquid chromatography-tandem mass spectrometry. An artificially prepared mixture of the detected cyanotoxins in the corresponding concentrations did not induce response in the O. mykiss cell lines and T. platyurus, suggesting that other cyanobacterial metabolites are responsible for the toxicity of M. aeruginosa.

Presence of ß-N-methylamino-L-alanine in cyanobacteria and aquatic organisms from waters of Northern Poland; BMAA toxicity studies

BMAA (ß-N-methylamino-L-alanine) was originally found in the seeds of cycad Cycas micronesica in the 1960s. Some years later it was discovered that the amino acid is genuinely produced by endosymbiotic cyanobacteria. Further research has proven the neurotoxic activity of BMAA, leading to neurodegenerative disease diagnosed as amyotrophic lateral sclerosis/parkinsonism-dementia complex (ALS/PDC). The aim of the present work was to examine the occurrence of BMAA in samples from Polish waterbodies. Both, the field cyanobacterial samples and the isolated cyanobacterial strains were analyzed. Also mussel and fish samples were checked for the BMAA accumulation. The additional goal was to assess the biological activity of BMAA in in vivo and in vitro assays. In waters of Northern Poland, BMAA was detected in cyanobacteria from Synechococcales, Oscillatoriales and Nostocales orders. The free and protein-bound forms of BMAA were detected in 9 and 4 (of 37) environmental samples, respectively. Both forms of BMAA were also identified in 2 out of 21 cyanobacterial strains isolated from Polish waterbodies. Our analyses of cyanobacterial material did not confirm the presence of soluble protein-bound form of BMAA. The amino acid was detected neither in the tissues of fish nor in the mussels. Biological activity of BMAA was tested with the application of hippocampal neural cell line HT22 and crustaceans: Thamnocephalus platyurus, Artemia franciscana and Daphnia magna. Among them, only D. magna assay revealed toxic effects of BMAA. The results of our research did not demonstrate the widespread production of BMAA by cyanobacteria from Northern Poland waters.

The Comparative Toxicity of 10 Microcystin Congeners Administered Orally to Mice: Clinical Effects and Organ Toxicity

Microcystins (MCs) are common cyanobacterial toxins that occur in freshwaters worldwide. Only two of the >200 MC variants have been tested for potential toxicity after oral exposure. This paper reports on the toxicity of 10 different MC congeners identified in algal blooms, microcystin-LR (MCLR), MCLA, MCLF, MCLW, MCLY, MCRR, [Asp3]MCRR, [Asp3,Dhb7]MCRR, MCWR, and MCYR after single administrations to BALB/c mice. In a preliminary MCLR dose–response study of 3 to 9 mg/kg doses, ≥5 mg/kg induced clinical changes, increased serum levels of ALT, AST, and GLDH, liver congestion, increased liver/body weight ratios, and reduced serum glucose and total protein. Based on the extent of these effects, the 10 congeners were administered as single 7 mg/kg oral doses and toxicity evaluated. The greatest toxicity was observed with MCLA and MCLR including a high percentage of moribundity. In addition to eliciting effects similar to those listed above for MCLR, MCLA also induced serum alterations indicative of jaundice. MCLY, and MCYR induced changes like those noted with MCLR, but to lesser extents. MCLW and MCLF exhibited some serum and morphological changes associated with hepatic toxicity, while there were few indications of toxicity after exposures to MCRR, [Asp³]MCRR, [Asp³,Dhb⁷]MCRR, or MCWR. These data illustrate a wide spectrum of hepatic effects and different potencies of these MC congeners.

Microcystin-LR promotes zebrafish (Danio rerio) oocyte (in vivo) maturation by activating ERK1/2-MPF signaling pathways, and cAMP is involved in this process

Cyanobacterial blooms and their secondary metabolites, microcystins (MCs), are not only toxic to aquatic organisms, but also to humans. MCs exert reproductive toxicity in female fish by affecting the oocyte development. However, the mechanism behind MC-LR interference in oocyte development remains largely unknown. In our study, adult female zebrafish were exposed to MC-LR (0, 1, 5, 20 μg/L) for 30 d. After exposure to MC-LR for 30 d, fertilized eggs from the treated females and healthy males were collected and cultured in water without MC-LR. Histomorphological observations showed pathological damage in the ovary after MC-LR exposure, which was mainly characterized by enlarged intercellular spaces, detachment of follicular cells from oocytes, and vacuolation of parenchymal tissues. The 20 μg/L MC-LR treatment caused a remarkable increase in the rate of the zebrafish oocytes germinal vesicle breakdown (GVBD) and a significant decrease in the levels of cyclic adenosine monophosphate (cAMP) and vitellogenin (VTG). In addition, the phosphorylation levels of the extracellular signal-regulated kinases (ERK) were elevated in ovaries from zebrafish exposed to 5 and 20 μg/L MC-LR, and cyclinB phosphorylation levels were also upregulated notably in the 20 μg/L MC-LR group. However, MC-LR exposure did not cause any change in the levels of cAMP-dependent protein kinase (PKA) protein and cdc2 phosphorylation in all the treatments. All the doses of MC-LR reduced the number of eggs, prematurely hatched the fertilized eggs and increased the abnormal rate of offspring generation. In summary, the present study demonstrates that MC-LR promotes oocyte maturation by activating the ERK1/2 and MPF signaling pathways, and cAMP is involved in this process.

Extreme rainfall drives early onset cyanobacterial bloom

The increasing prevalence of cyanobacteria-dominated harmful algal blooms is strongly associated with nutrient loading and changing climatic patterns. Changes to precipitation frequency and intensity, as predicted by current climate models, are likely to affect bloom development and composition through changes in nutrient fluxes and water column mixing. However, few studies have directly documented the effects of extreme precipitation events on cyanobacterial composition, biomass, and toxin production. We tracked changes in a eutrophic reservoir following an extreme precipitation event, describing an atypically early toxin-producing cyanobacterial bloom and successional progression of the phytoplankton community, toxins, and geochemistry. An increase in bioavailable phosphorus by more than 27-fold in surface waters preceded notable increases in Aphanizomenon flos-aquae throughout the reservoir approximately 2 weeks postevent and ∼5 weeks before blooms typically occur. Anabaenopeptin-A and three microcystin congeners (microcystin-LR, -YR, and -RR) were detected at varying levels across sites during the bloom period, which lasted between 3 and 5 weeks. These findings suggest extreme rainfall can trigger early cyanobacterial bloom initiation, effectively elongating the bloom season period of potential toxicity. However, effects will vary depending on factors including the timing of rainfall and reservoir physical structure.

Dhb Microcystins Discovered in USA Using an Online Concentration LC-MS/MS Platform

Based on current structural and statistical calculations, thousands of microcystins (MCs) can exist; yet, to date, only 246 MCs were identified and only 12 commercial MC standards are available. Standard mass spectrometry workflows for known and unknown MCs need to be developed and validated for basic and applied harmful algal bloom research to advance. Our investigation focuses on samples taken in the spring of 2018 from an impoundment fed by Oser and Bischoff Reservoirs, Indiana, United States of America (USA). The dominant cyanobacterium found during sampling was Planktothrix agardhii. The goal of our study was to identify and quantify the MCs in the impoundment sample using chemical derivatization and mass spectrometry. Modifying these techniques to use online concentration liquid chromatography tandem mass spectrometry (LC-MS/MS), two untargeted MCs have been identified, [d-Asp3, Dhb7]-MC-LR and [Dhb7]-MC-YR. [Dhb7]-MC-YR is not yet reported in the literature to date, and this was the first reported incidence of Dhb MCs in the United States. Furthermore, it was discovered that the commercially available [d-Asp3]-MC-RR standard was [d-Asp3, Dhb7]-MC-RR. This study highlights a workflow utilizing online concentration LC-MS/MS, high-resolution MS (HRMS), and chemical derivatization to identify isobaric MCs.

Microcystin-LR Degradation and Gene Regulation of Microcystin-Degrading Novosphingobium sp. THN1 at Different Carbon Concentrations

The bacterium Novosphingobium sp. THN1 (THN1) is capable of degrading microcystin-LR (MC-LR). To study the ability of THN1 to degrade MC-LR and its possible mechanism(s) of regulation, we analyzed the effect of carbon concentrations on the degradation process. The MC-LR degradation rate peaked early and then declined during MC-LR biodegradation. Decreased levels of carbon in the medium caused the degradation peak to occur earlier. The expression of the functional gene mlrA, encoding a microcystinase, showed a similar trend to the MC-LR degradation rate at various carbon concentrations (r² = 0.717, p < 0.05), suggesting that regulation of mlrA expression may play an important role in MC-LR degradation by THN1. The total bacterial biomass decreased when the carbon source was limited and did not correlate with the MC-LR degradation rate. Transcriptomic analysis showed that MC-LR degradation differentially regulated 62.16% (2597/4178) of THN1 genes. A considerable number of differentially expressed genes (DEGs) during MC-LR degradation encoded proteins related to carbon-, nitrogen-, and amino acid-related pathways. At 2 h of MC-LR degradation, most DEGs (29/33) involved in carbon and nitrogen metabolism were downregulated. This indicated that MC-LR may regulate carbon and nitrogen pathways of Novosphingobium sp. THN1. KEGG pathway analysis indicated that the upregulated DEGs during MC-LR degradation were mainly related to amino acid degradation and substrate metabolism pathways. Particularly, we detected increased expression of glutathione metabolism-related genes from transcriptomic data at 2 h of MC-LR degradation compared with the gene expression of 0 h, such as GST family protein, glutathione peroxidase, S-(hydroxymethyl) glutathione dehydrogenase, and glutathione-dependent disulfide-bond oxidoreductase that have been reported to be involved in microcystin degradation.

Cyanobacterial peptides beyond microcystins - A review on co-occurrence, toxicity, and challenges for risk assessment

Cyanobacterial bloom events that produce natural toxins occur in freshwaters across the globe, yet the potential risk of many cyanobacterial metabolites remains mostly unknown. Only microcystins, one class of cyanopeptides, have been studied intensively and the wealth of evidence regarding exposure concentrations and toxicity led to their inclusion in risk management frameworks for water quality. However, cyanobacteria produce an incredible diversity of hundreds of cyanopeptides beyond the class of microcystins. The question arises, whether the other cyanopeptides are in fact of no human and ecological concern or whether these compounds merely received (too) little attention thus far. Current observations suggest that an assessment of their (eco)toxicological risk is indeed relevant: First, other cyanopeptides, including cyanopeptolins and anabaenopeptins, can occur just as frequently and at similar nanomolar concentrations as microcystins in surface waters. Second, cyanopeptolins, anabaenopeptins, aeruginosins and microginins inhibit proteases in the nanomolar range, in contrast to protein phosphatase inhibition by microcystins. Cyanopeptolins, aeruginosins, and aerucyclamide also show toxicity against grazers in the micromolar range comparable to microcystins. The key challenge for a comprehensive risk assessment of cyanopeptides remains their large structural diversity, lack of reference standards, and high analytical requirements for identification and quantification. One way forward would be a prevalence study to identify the priority candidates of tentatively abundant, persistent, and toxic cyanopeptides to make comprehensive risk assessments more manageable.

Removal Characteristics of Organic Pollutants from Eutrophic Raw Water by Biological Pretreatment Reactors

Two biological contact oxidation reactors, cascade biofilm reactor (CSBR) and one-step biofilm reactor (OSBR), were used in this paper for pretreatment of eutrophic water from Lake Taihu in China. The CSBR was more effective and stable for eutrophic water treatment than OSBR, in terms of extracellular microcystin-LR,chlorophyll-a, DOC, and biodegradable dissolved organic carbon (BDOC) removal. Removal efficiencies of extracellular microcystin-LR andchlorophyll-a were 75.8% and 59.7% in CSBR and 60.5% and 53.0% after 2 h in OSBR. CSBR had much higher removal efficiency (34.3%) than OSBR (22.7%) for DOC, and CSBR could remove 67% BDOC, accounting for 34% of total DOC in source water. 11.5% of DOC was removed through means other than biological degradation, such as biofilm adsorption and bioflocculation. In CSBR at 5.5~13°C, 57.5% of atrazine was removed at 2 h hydraulic retention time, with background concentration of 136.5 ng/L. Meanwhile, removal efficiencies of three phthalic acid esters (PAEs) (dimethyl phthalate, di-(2-ethylhexyl) phthalate, and di-n-butyl phthalate) were 78.7%, 52.4%, and 85.3%, respectively. Only 35.2% of polycyclic aromatic hydrocarbons (PAHs) could be removed by CSBR with initial concentration of 21.5 μg/L. The results indicated that CSBR is effective in low-molecular-weight organic pollution pretreatment and provides benefits in terms of effluent quality.

Nodularia spumigena peptides--accumulation and effect on aquatic invertebrates

Thus far, the negative effects of Nodularia spumigena blooms on aquatic organisms have been mainly attributed to the production of the hepatotoxic nodularin (NOD). In the current work, the accumulation of other N. spumigena metabolites in blue mussels and crustaceans, and their effect on Thamnocephalus platyurus and Artemia franciscana, were examined. The liquid chromatography-tandem mass spectrometry (LC-MS/MS) analyses provided evidence that both blue mussels collected after a cyanobacterial bloom in the Baltic Sea and the crustaceans exposed under laboratory conditions to N. spumigena extract accumulated the cyclic anabaenopeptins (APs). In the crustaceans, the linear peptides, spumigins (SPUs) and aeruginosins (AERs), were additionally detected. Exposure of T. platyurus and A. franciscana to N. spumigena extract confirmed the negative effect of nodularin on the organisms. However, high numbers of dead crustaceans were also recorded in the nodularin-free fraction, which contained protease inhibitors classified to spumigins and aeruginosins. These findings indicate that cyanobacterial toxicity to aquatic organisms is a complex phenomenon and the induced effects can be attributed to diverse metabolites, not only to the known hepatotoxins.

Ciliate Nassula sp. grazing on a microcystin-producing cyanobacterium (Planktothrix agardhii): impact on cell growth and in the microcystin fractions

The proliferation of microcystins (MCs)-producing cyanobacteria (MCs) can have detrimental effects on the food chain in aquatic environments. Until recently, few studies had focused on the fate of MCs in exposed organisms, such as primary consumers of cyanobacteria. In this study, we investigate the impact of an MC-producing strain of the cyanobacterium Planktothrix agardhii on the growth and physiology of a Nassula sp. ciliate isolated from a non-toxic cyanobacterial bloom. We show that this Nassula sp. strain was able to consume and grow while feeding exclusively on an MC-producing cyanobacterium over a prolonged period of time (8 months). In short-term exposure experiments (8 days), ciliates consuming an MC-producing cyanobacterial strain displayed slower growth rate and higher levels of antioxidant enzymes than ciliates feeding on two non-MC-producing strains. Three high-performance methods (LC/MS, LC/MS-MS and ELISA) were used to quantify the free and bound MCs in the culture medium and in the cells. We show that ciliate grazing led to a marked decrease in free MCs (methanol extractable) in cells, the MCs were therefore no longer found in the surrounding culture medium. These findings suggest that MCs may have undergone redistribution (free vs bound MCs) or chemical degradation within the ciliates.

Detection of microcystins in Pamvotis lake water and assessment of cyanobacterial bloom toxicity

Lake Pamvotis is a shallow, eutrophic Mediterranean lake with ecological significance. This paper deals with the evaluation of cyanobacterial toxicity in Lake Pamvotis. ELISA and HPLC revealed the presence of significant amounts of MCYST-LR. Danio rerio bioassay confirmed the toxic nature of the bloom. Cyanobacterial extracts had adverse toxic effects on development of D. rerio. Also, it was shown that cyanobacterial extracts containing environmentally detected concentrations of MCYST can cause reduced survival rate of fish species. The results clearly indicate that cyanobacterial blooms in Lake Pamvotis may be regarded as human and fish health hazard. Continuous monitoring of the lake is suggested, in order to prevent future possible intoxications.

Use of chlorophyll a fluorescence to detect the effect of microcystins on photosynthesis and photosystem II energy fluxes of green algae

The phenomenon of cyanobacteria bloom occurs widely in lakes, reservoirs, ponds and slow flowing rivers. Those blooms can have important repercussions, at once on recreational and commercial activities but also on the health of animals and human beings. Indeed, many species are known to produce toxins which are released in water mainly at cellular death. The cyanotoxin most frequently encountered is the microcystin (MC), a hepatotoxin which counts more than 70 variants. The use of fast tests for the detection of this toxin is thus a necessity for the protection of the ecosystems and the human health. A promising method for their detection is a bioassay based on the chlorophyll a fluorescence of algae. Many studies have shown that algae are sensible to diverse pollutants, but were almost never used for cyanotoxins. Therefore, our goals were to evaluate the effect of microcystin on the fluorescence of different species of algae and how it can affect the flow of energy through photosystem II. To reach these objectives, we exposed four green algae (Scenedesmus obliquus CPCC5, Chlamydomonas reinhardtii CC125, Pseudokirchneriella subcapitata CPCC37 and Chlorella vulgaris CPCC111) to microcystin standards (variants MC-LF, LR, RR, YR) and to microcystin extracted from Microcystis aeruginosa (CPCC299), which is known to produce mainly MC-LR. Chlorophyll a fluorescence was measured by PEA (Plant Efficiency Analyzer) and LuminoTox. The results of our experiment showed that microcystins affect the photosynthetic efficiency and the flow of energy through photosystem II from 0.01 μg/mL, within only 15 min. From exposure to standard of microcystin, we showed that MC-LF was the most potent variant, followed by MC-YR, LR and RR. Moreover, green algae used in this study demonstrated different sensitivity to MCs, S. obliquus being the more sensitive. We finally demonstrated that LuminoTox was more sensitive to MCs than parameters measured with PEA, although the latter brings indication on the mode of action of MCs at the photosynthetic apparatus level. This is the first report showing a photosynthetic response within 15 min of exposure. Our results suggest that bioassay based on chlorophyll fluorescence can be used as a rapid and sensitive tool to detect microcystin.

Effects of silver nanoparticles on the development and histopathology biomarkers of Japanese medaka (Oryzias latipes) using the partial-life test

Silver nanoparticles (AgNPs) have emerged as an important class of nanomaterials and are currently used in a wide range of industrial and commercial applications. This has caused increasing concern about their effects on the environment and to human health. Using Japanese medaka (Oryzias latipes) at early-life stages as experimental models, the developmental toxicity of silver nanoparticles was investigated following exposure to 100-1000 μg/L homogeneously dispersed AgNPs for 70 days, and developmental endpoints were evaluated by microscopy during embryonic, larval and juvenile stages of development in medaka. Meanwhile, histopathological changes in the larval eye were evaluated. Retarded development and reduced pigmentation were observed in the treated embryos by AgNPs at high concentrations (≥ 400 μg/L). Maximum width of the optic tectum, as an indicator of midbrain development, decreased significantly in a dose-related manner. Furthermore, silver nanoparticles exposure at all concentrations induced a variety of morphological malformations such as edema, spinal abnormalities, finfold abnormalities, heart malformations and eye defects. Histopathological observations also confirmed the occurrence of abnormal eye development induced by AgNPs. The data showed non-linear or U-shaped dose-response patterns for growth retardation at 5 days of postfertilization, as well as the incidence of abnormalities. Preliminary results suggested that the developmental process of medaka may be affected by exposure to silver nanoparticles. Morphological abnormalities in early-life stages of medaka showed the potential developmental toxicities of silver nanoparticles. Further research should be focused on the mechanisms of developmental toxicity in fish exposed to silver nanoparticles.

Microcystis toxigenic strains in urban lakes: a case of study in Mexico City

Microcystis is a bloom-forming, common cyanobacterium in urban lakes of Mexico City. To assess the presence of potentially cyanotoxin-producing Microcystis, molecular techniques were applied and acute toxicity bioassays were performed with Daphnia magna neonates exposed to cyanobacterial crude extracts. Toxigenic potential of isolated strains was inferred by amplifying the mcyA-Cd genes and their identity as Microcystis was confirmed through the 16S rDNA and phycocyanin operon amplification. Microcystins synthesized under culture conditions were quantified through ELISA. The acute toxicity bioassays revealed that mortality was independent from the cyanotoxin concentration in some strains; this suggests the presence of other metabolites (different from microcystins) that also exerted an important biological effect. Isolated strains had the mcyA-Cd gene and most of them produced variable amounts of microcystins in the culture conditions used, confirming their toxigenic potential. Results warn about possible toxic effect risks for aquatic biota, neighboring areas, visitors and users of these sites, due to the constant presence of these blooms in the studied water bodies.

Microcystin-LR toxicity on dominant copepods Eurytemora affinis and Pseudodiaptomus forbesi of the upper San Francisco Estuary

This study investigates the toxicity and post-exposure effects of dissolved microcystin (MC-LR) on the dominant copepods of the upper San Francisco Estuary (SFE), where blooms of the toxic cyanobacteria Microcystis aeruginosa coincide with record low levels in the abundance of pelagic organisms including phytoplankton, zooplankton, and fish. The potential negative impact of Microcystis on the copepods Eurytemora affinis and Pseudodiaptomus forbesi has raised concern for further depletion of high quality fish food. Response of copepods to MC-LR (MC) was determined using a 48-h standard static renewal method for acute toxicity testing. Following exposure, a life table test was performed to quantify any post-exposure impacts on survival and reproduction. The 48-h LC-50 and LC-10 values for MC were 1.55 and 0.14 mg/L for E. affinis; and 0.52 and 0.21 mg/L for P. forbesi. Copepod populations recovered once dissolved MC was removed and cultures returned to optimal conditions, suggesting no post-exposure effects of MC on copepod populations. Dissolved microcystin above 0.14 mg/L proved likely to have chronic effects on the survival of copepods in the SFE. Since such high concentrations are unlikely, toxicity from dissolved microcystin is not a direct threat to zooplankton of the SFE, and other mechanisms such as dietary exposure to Microcystis constitute a more severe risk.

Development of an mlrA gene-directed TaqMan PCR assay for quantitative assessment of microcystin-degrading bacteria within water treatment plant sand filter biofilms

We report for the first time a quantitative mlrA gene-directed TaqMan PCR assay for the rapid detection of microcystin-degrading bacteria. This was applied, in combination with 16S ribosomal DNA-directed quantitative PCR and denaturing gradient gel electrophoresis, to study virgin sand filter column biofilm development and to correlate mlrA gene abundance with microcystin removal efficiency.

Development of an analytical method for the unambiguous structure elucidation of cyclic peptides with special appliance for hepatotoxic desmethylated microcystins

The periodical occurrence of harmful algal blooms (HABs) in freshwater lakes requires the determination of potential cyanobacterial toxins, especially microcystins (MCs). On demand of an adequate risk assessment, the high diversity of these hepatotoxic cyclic heptapeptides implicates the need of an unambiguous detection of their specific structural variants. Therefore, LC-MS and LC-MS/MS methods are the approaches of choice for determination of MCs. In contrast, even tandem mass spectromic fragmentation patterns are not even sufficient in any kind of structural determination requirements, whereas NMR methods require very high amounts of MCs. In this study, we present a novel method for chromatographic separation of desmethylated microcystins (dm-MCs). Based on the isolation of the specific structural variants using semi-preparative HPLC, a method was developed for the structure elucidation of cyclic peptides with special appliance for the determination of dm-MCs via analysis of the specific amino acid composition after peptide hydrolysis followed by stereospecific detection of the amino acids and resulting keto acids. On the basis of this method it is demonstrated that dm-MC-RR with the structure [Dha(7)]MC-RR represented the major compound in the microcystin pattern of Microcystis aeruginosa bloom events in 2005 and 2006 in Lake Senftenberg, Germany.

Compensatory growth induced in zebrafish larvae after pre-exposure to a Microcystis aeruginosa natural bloom extract containing microcystins

Early life stage tests with zebrafish (Danio rerio) were used to detect toxic effects of compounds from a Microcystis aeruginosa natural bloom extract on their embryolarval development. We carried out the exposure of developing stages of fish to complex cyanobacterial blooms containing hepatotoxic molecules - microcystins. Fish embryo tests performed with the bloom extract containing 3 mg·L⁻¹ Eq microcystin-LR showed that after 24 h of exposure all fish embryos died. The same tests performed with other diluted extracts (containing 0.3, 0.1 and 0.03 mg·L⁻¹ Eq microcystin-LR) were shown to have an influence on zebrafish development and a large number of embryos showed malformation signs (edema, bent and curving tail). After hatching the larvae were transferred to a medium without toxins to follow the larval development under the new conditions. The specific growth of the pre-exposed larvae was significantly more important than that of the control larvae. This may represent a compensatory growth used to reduce the difference in size with the control fish noted after hatching.

Global quantitative analysis of protein expression and phosphorylation status in the liver of the medaka fish (Oryzias latipes) exposed to microcystin-LR I. Balneation study

Microcystins (MCs) are hepatotoxins with potent inhibitor activity of protein phosphatases PP1 and PP2A. These non-ribosomal peptides are getting more and more attention due to their acute toxicity and potent tumor-promoting activity. These toxins are produced by freshwater cyanobacteria. The most toxic and most commonly encountered variant in aquatic environment is MC-LR (MC Leucine-Arginine). It has been used for toxicological investigations on the liver of intoxicated medaka. Differential proteome as well as differential phosphoproteome analyses have been performed for providing new information on early responses to the toxin. The experiments are also aiming at selecting biomarkers of MC-LR exposure. In the 2D electrophoresis gel protein maps from cytosol of liver cells of animals exposed or non-exposed to the cyanotoxin, 15 spots showed a significant increase or decrease of their stain signal either in specific phosphoprotein stain or total protein stain. Thirteen of these proteins have been identified by mass spectrometry. Among them, phenylalanine hydroxylase (PAH) and keratin 18 type I showed variations in phosphorylation stain in possible agreement with inhibition of PP2A activity. The other identified proteins exhibited variations in their expression level. The identified proteins appear to be involved in cytoskeleton assembly, cell signalling, oxidative stress and apoptosis. Such results confirm that proteomics and phosphoproteomics approaches may become valuable tools to identify signalling pathways implied in MC-LR effects. From accumulated data, specific pools of biomarkers could possibly be selected as specific for toxin exposure.

Isolation and identification of a novel microcystin-degrading bacterium from a biological sand filter

A novel bacterium capable of degrading two microcystin analogues, microcystin-LR and -LA (MCLR and MCLA), was isolated from a biological sand filter which was previously shown to effectively remove these toxins from source waters. Based on phylogenetic analysis of the 16S rRNA gene sequence, the isolated organism, LH21, most likely belonged to the genus Sphingopyxis and of the previously cultured species clustered with Sphingopyxis witflariensis. Using polymerase chain reaction (PCR), isolate LH21 was shown to contain homologues to each of the four genes, mlrA, mlrB, mlrC and mlrD previously associated with the degradation of MCLR by Sphingomonas sp. ACM-3962. Isolate LH21 was able to effectively degrade MCLR and MCLA in batch experiments under environmentally relevant conditions, with complete removal observed within 5h after re-exposure of the toxins.

Microcystin ecotypes in a perennial Planktothrix agardhii bloom

The dynamics and microcystins (MC) concentrations of a perennial Planktothrix agardhii bloom were investigated in a eutrophic lake (Viry-Châtillon, France). A weak relationship was observed between P. agardhii population biomass and the MC concentrations in a 1-year survey. To further investigate the causes of MC concentration changes, we concurrently conducted experiments on 41 strains isolated from this lake. We first checked the clonal diversity of P. agardhii population (i) by molecular techniques, to assess the presence of MC synthetase gene (mcyB), (ii) by biochemical assay (PP2A inhibition assay), for MC production, and (iii) by mass spectrometry (MS), to identify the MC chemotypes. Our results illustrated the diversity of genotype and MC chemotypes within a P. agardhii natural population. Eleven chemotypes among the 16 possible ones were found by MS. Furthermore, we noticed major differences in the MC content of isolated strains (from 0.02 to 1.86 microg equiv. MC-LR mg DW(-1), n=25). Growth and MC production of one MC-producing strain and one non-MC-producing strain were also assessed at two temperatures (10 and 20 degrees C). We showed that growth capacities of these strains were similar at the two tested temperatures, and that the MC production rate was correlated to the growth rate for the MC-producing strain. On the basis of these results, several hypotheses are discussed to explain the weakness of relationships between natural P. agardhii biomass and MC concentration. One of the main reasons could lie in the proportion of MC-producing clones and non-MC-producing clones that may change during the sampling period. Also, the MC-producing clones may present different intracellular MC content due to (i) MC chemotypes diversity, (ii) changes in MC variants proportions within a strain, and (iii) changes in MC rate production depending on the physiological state of cells. Finally, we concluded that various biological organization levels have to be considered (population, cellular and molecular), through an integrative approach, in order to provide a better understanding of P. agardhii in situ MC production.

Bacterial degradation of microcystin toxins in drinking water eliminates their toxicity

Microcystin-LR and -LA were readily biodegraded by a bacterium, Sphingpoyxis sp. LH21, in a treated reservoir water. Detection of the microcystins was conducted using high-performance liquid chromatography (HPLC), protein phosphatase 2A (PP2A) inhibition assay and a cell-based cytotoxicity assay. The HPLC results correlated well with the two assays. The decrease in cytotoxicity, coupled with the associated decrease in microcystin concentrations, indicated that no cytotoxic by-products were being generated, highlighting the applicability of biodegradation as a feasible treatment option for effective microcystin removal.

Toxicity to medaka fish embryo development of okadaic acid and crude extracts of Prorocentrum dinoflagellates

Chronic and subchronic toxicity following exposure to the DSP (Diarrhetic shellfish poisoning) toxin okadaic acid (OA) is receiving increasing attention as a public human health biohazard. However information on ecological impacts induced by proliferation of the OA producing dinoflagellate Prorocentrum is scarce. In order to analyse the toxicity of these substances, in vivo experiments were conducted on medaka fish (Oryzias latipes) embryos used as an experimental model. The study was focused on two strains of benthic Prorocentrum species, P. arenarium and P. emarginatum, naturally found in the Indian Ocean. Sample extracts (crude extracts, CE) were obtained from algal cultures and their toxic potential was explored. Their OA (and derivatives) content was evaluated by two methods: one based on chemical analysis using HPLC-MS, the other based on screening the inhibiting effect on protein phosphatase PP2A. P. arenarium extracts inhibit PP2A and the active toxin was confirmed as being OA by HPLC-MS. In contrast, P. emarginatum showed negative results regardless of the method used. The development of medaka fish embryos kept in medium containing pure OA or Prorocentrum CE was examined. Survival rates were reduced up to 100% depending on the concentrations used of both OA and CE of P. arenarium, while no effect was observed with CE of P. emarginatum. Anatomopathological studies of surviving embryos indicate that OA treatment resulted in significant increases in liver and digestive tract areas compared to controls. P. arenarium treated surviving embryos exhibited significant quantitative increases of global body and vitellus areas. Together, our results indicate that the toxic effects to medaka embryos development of pure OA and P. arenarium extracts containing OA are distinguishable. The differences may indicate the presence of additional toxic substance(s) (or molecules able to modulate OA impact) in the P. arenarium CE that probably are not present in P. emarginatum.

Toxicity of complex cyanobacterial samples and their fractions in Xenopus laevis embryos and the role of microcystins

This work evaluated the effects of various cyanobacterial fractions in Frog Embryo Teratogenesis Assay Xenopus (FETAX) with African clawed frog embryos. Fractions were prepared from five biomasses with different dominant genera (Microcystis, Aphanizomenon, Anabaena, Planktothrix) and different microcystin content. Effects of following fractions were investigated: (I) homogenate of complex cyanobacterial biomass, (II) cell debris (pellet) after centrifugation of complex biomass, (III) supernatant after centrifugation of complex biomass (= crude aqueous extract), (IV) permeate after passing of crude extract through C-18 column (fraction devoid of microcystins), and (V) eluate from C-18 column (containing microcystins, if present). Besides classical parameters evaluated in 96 h FETAX (mortality, growth inhibition, malformations), we have also assessed the effects on biochemical markers of oxidative stress and detoxification (glutathione pool, GSH; activity of glutathione peroxidase, GPx; glutathione reductase, GR; activity of glutathione-S-transferase, GST). Complex biomass (I) and aqueous extract (III) were generally the most toxic fractions in terms of mortality and growth inhibition, whereas eluates containing microcystins (V) were generally less toxic. On the other hand, the same fraction (eluates) induced significant malformations in low concentrations but the effects were not related to the content of microcystins. Biomarkers were affected in variable manner but no significant effect or clear relation to microcystin content was observed. Our data support the hypothesis that microcystins are not the only or major toxic compounds in the complex cyanobacterial samples (at least for some species) and that more attention should be paid to other components of complex cyanobacterial biomass including non-specific parameters such as oxygen content or toxic ammonia released during bacterial decay of organic material.

Microcystins cause embryonic toxicity in mice

Microcystins produced by freshwater cyanobacteria are potent hepatotoxins and can cause animal intoxications and human illnesses. In the present study, the effects of microcystins on the embryonic development of Kunming mice were determined using cell extracts of Microcystis aeruginosa from the Nanwan reservoir, China. Forty-eight pregnant mice were divided into four groups of 12 mice. Pregnant mice in three experimental groups were injected intraperitoneally with cell extracts at doses equivalent to 3, 6, or 12 microg microcystins/kg body weight daily from gestational days 6-15, while the mice in the control group were injected on the same schedule with sterilized saline. Mice were killed on the 18th day of gestation and embryonic and fetal developmental indexes checked. The fetal mice were also examined for anomalies of external, skeletal, and internal organs. The results demonstrated a significant decrease in body weight gain of pregnant mice in the 12 microg/kg dose group when compared to the control group (p<0.05). Differences in mean body weight, body length, and tail length of the fetuses were also found in these two groups (p<0.05). However, no significant difference in these characteristics was detected in the 6 or 3 microg/kg dose groups when compared to the control group (p>0.05). Four fetuses in the 6 microg/kg body dose group were found to have a curving tail. Additionally, petechial hemorrhage and hydropic degeneration were observed in the livers of fetuses in the 6 and 12 microg/kg experimental groups. These results suggested that microcystins had both maternal and embryonic toxicity in mice.

Oral toxicity of the microcystin-containing cyanobacterium Planktothrix rubescens in European whitefish (Coregonus lavaretus)

The microcystin-producing cyanobacterium Planktothrix is one of the most widespread genera amongst toxin producing cyanobacteria in European lakes. In particular, the metalimnic blooms of Planktothrix rubescens have been associated with growing problems in the professional freshwater fishery as a decrease in yearly yields in the important coregonids fishery often coincides with the appearance of P. rubescens. P. rubescens is a cyanobacterial species known to produce toxic compounds, e.g. microcystins. Although microcystins have been reported to affect fish health, behaviour, development and growth and have also been associated with feral fish kills, there is currently no specific information on the effects of toxic Planktothrix filaments in fish and especially coregonids. Therefore, the aim of this study was to investigate the effects of an environmentally relevant dose of P. rubescens filaments orally applied to coregonids and to discuss the findings in the context of microcystin toxicity previously reported in carp and trout. A single dose of P. rubescens culture, at a density of 80,000 cells per 120 microl, was applied to coregonids thus corresponding to 0.6-0.9 microg microcystin-LR(equiv.)/kg body weight. Behavioural changes and opercular beat rates, growth, hepatosomatic index, condition and plasma glucose were determined. Liver, kidney, gill and the gastrointestinal tract were assessed histopathologically and immunohistologically. Exposed fish showed behavioural changes, increased opercular beat rates and elevated plasma glucose levels, possibly representing a physiological stress response. Histopathological alterations in liver, gastrointestinal tract and kidney, also immunopositive for microcystin suggested causality of tissue damage and the in situ presence of microcystins. The observed combination of stress and organ damage may explain the frequently reduced weight and thus the fitness noted in coregonids subjected to regular occurrences of stratified and dispersed P. rubescens blooms, e.g. in lake Ammersee, Bavaria, Germany.

Differences in the chlorine reactivity of four microcystin analogues

The presence of microcystin toxins in drinking water is highly undesirable as they have the potential to adversely affect human health. Consequently, effective removal of these toxins from water is a major goal for water authorities. In this study, four microcystin analogues were chlorinated in two treated waters, and two of the analogues were chlorinated in deionised water. The oxidation of the microcystins was related to the chlorine exposure (CT) of the sample waters with the ease of oxidation following the trend: microcystin-YR > microcystin-RR > microcystin-LR > or = microcystin-LA. This trend was in agreement with published data on model compounds and free amino acids. Values of CT of up to 25 mg min L(-1) were required for oxidation of all microcystin analogues to below the World Health Organization guideline value of 1.0 microg L(-1). Results from this study indicate that for some water resources it is important to determine the speciation of the microcystin analogues to optimise chlorination practices.

Bacterial degradation of microcystin toxins within a biologically active sand filter

Microcystin toxins are a problem for water authorities as they are recalcitrant to conventional water treatment. In this study, biological sand filtration was assessed in laboratory column experiments for its ability to remove two microcystin analogues, microcystin-LR and microcystin-LA. A lag period of 3 days was evident prior to the commencement of degradation. Contact times were varied during the experiment; however, no microcystin was detected in the effluent after 4 days, even under conditions similar to those of a rapid sand filter. Removals of microcystin through the sand filters were shown to be primarily through biological degradation processes. Using polymerase chain reaction (PCR), biofilm, extracted from one of the sand filters that had effectively removed the microcystins, was shown to contain bacteria with the mlrA gene. Detection of this gene provided additional evidence that biological degradation of microcystin was the primary removal mechanism.

Distribution of microcystins in a lake foodweb: no evidence for biomagnification

Microcystins, toxins produced by cyanobacteria, may play a role in fish kills, although their specific contribution remains unclear. A better understanding of the eco-toxicological effects of microcystins is hampered by a lack of analyses at different trophic levels in lake foodwebs. We present 3 years of monitoring data, and directly compare the transfer of microcystin in the foodweb starting with the uptake of (toxic) cyanobacteria by two different filter feeders: the cladoceran Daphnia galeata and the zebra mussel Dreissena polymorpha. Furthermore foodwebs are compared in years in which the colonial cyanobacterium Microcystis aeruginosa or the filamentous cyanobacterium Planktothrix agardhii dominated; there are implications in terms of the types and amount of microcystins produced and in the ingestion of cyanobacteria. Microcystin concentrations in the seston commonly reached levels where harmful effects on zooplankton are to be expected. Likewise, concentrations in zooplankton reached levels where intoxication of fish is likely. The food chain starting with Dreissena (consumed by roach and diving ducks) remained relatively free from microcystins. Liver damage, typical for exposure to microcystins, was observed in a large fraction of the populations of different fish species, although no relation with the amount of microcystin could be established. Microcystin levels were especially high in the livers of planktivorous fish, mainly smelt. This puts piscivorous birds at risk. We found no evidence for biomagnification of microcystins. Concentrations in filter feeders were always much below those in the seston, and yet vectorial transport to higher trophic levels took place. Concentrations of microcystin in smelt liver exceeded those in the diet of these fish, but it is incorrect to compare levels in a selected organ to those in a whole organism (zooplankton). The discussion focuses on the implications of detoxication and covalent binding of microcystin for the transfer of the toxin in the foodweb. It seems likely that microcystins are one, but not the sole, factor involved in fish kills during blooms of cyanobacteria.

Tissue distributions and seasonal dynamics of the hepatotoxic microcystins-LR and -RR in two freshwater shrimps, Palaemon modestus and Macrobrachium nipponensis, from a large shallow, eutrophic lake of the subtropical China

So far no information is available on microcystin (MC) contents in shrimps, prawns or crayfish from natural freshwaters. Tissue distributions and seasonal dynamics of the hepatotoxic MC-LR and -RR in two freshwater shrimps, Palaemon modestus and Macrobrachium nipponensis were studied monthly (during June-November, 2003) in a Chinese lake containing toxic cyanobacterial blooms. The shrimps P. modestus and M. nipponensis accumulated high MCs not only in the hepatopancreas (mean 4.29 and 0.53 microg g(-1) DW, respectively) but also in the gonad (mean 1.17 and 0.48 microg g(-1) DW, respectively), and the crayfish Procambarus clarkii accumulated as much as 0.93 microg g(-1) DW in the gonad. This indicates that gonads of these invertebrates are the second important target organ of MCs. P. modestus apparently accumulated more MCs in their organs than M. nipponensis, which might be a reflection of their difference in trophic niche. Eggs of the shrimps accumulated 8.4% (M. nipponensis, 0.27 microg g(-1) DW) and 29.0% (P. modestus, 2.34 microg g(-1) DW) of total toxin burden, indicating that MCs had been transferred into offspring from their adults. Among the shrimp muscle samples analyzed, 31% were above the provisional WHO TDI level, suggesting the risk of consuming shrimps in Lake Chaohu.

Comparison of 17 biotests for detection of cyanobacterial toxicity

The aim of the present study was to compare the sensitivity of 17 acute bioassays of cyanobacterial toxicity by assessment of crude extracts of three cyanobacterial samples (all dominated by Microcystis sp. but substantially differing in microcystin-LR content). Toxicity of the fractions prepared by solid-phase extraction (SPE) for microcystins was also determined. The most sensitive bioassay was the 24-h test with crustacean Thamnocephalus platyurus, which elicited high lethality in the samples and also in fractions without microcystins. The fruit fly Drosophila melanogaster, protozoans Spirostomum ambiguum and Tetrahymena termophyla, and the crustacean Daphnia pulex formed the second group of sensitive bioassays. Good selective toxicity response to microcystins also was observed in the weakly sensitive biotests with the oligochaete Tubifex tubifex and the rotifer Brachionus calyciflorus. Preconcentration of microcystins by SPE substantially decreased variation of the results in bioassays and improved the discriminating potential of most assays employed.

Effects of microcystin-LR on development of medaka fish embryos (Oryzias latipes)

Chronic and subchronic toxicity from exposure to microcystins, cyclic hepatotoxic heptapeptides from cyanobacteria, receives increasing attention as a public human health biohazard. So far, the effects of microcystin on fish have been studied mainly in adults, rather than during early life stages. Limitations of direct ambient exposure experiments to fish egg have resulted from the difficult access of microcystin through the egg chorion. Using a microinjection technology, we have introduced microcystin-LR (MC-LR) directly into one-cell stage embryos or into the vitellus of late neurula embryos (stage 19) or into the vitellus of stage 25 embryos of medaka (Oryzias latipes) at the onset of the liver anlage. Microinjection (100 pl; stage 1 or 2 nl; stage 19 or 25) of MC-LR resulted in a dose dependent mortality of embryos. Survival rates were reduced up to 90% with microcystin concentrations of 10 or 1 microg/ml (corresponding to 1-20 pg or 0.1-2 pg of toxin injected), injected either at stages 1, 19 or 25. Also, a dose dependent advanced embryonic hatching processing was observed; hatching being brought forward from 2 or 3 days compared to controls in most of the microcystin injected groups. In agreement with the known hepatotoxic effects of microcystin, injected embryos consistently displayed hepatobiliary abnormalities such as liver hypertrophy and hepatic hemorrhage, also evidenced in post-hatching juveniles. Thus, the methodology presented in this paper should be valuable tool to analyze the effects of toxins on the development of aquatic vertebrate embryos.

Oscillapeptin J, a new grazer toxin of the freshwater cyanobacterium Planktothrix rubescens

Oscillapeptin J (1), a new and highly potent crustacean grazer toxin, was isolated from the axenic cyanobacterium Planktothrix rubescens, which frequently forms blooms in freshwater lakes. Chemical and spectroscopic analyses, including high resolving MS and two-dimensional NMR, were used to elucidate the compound's structure as a depsiheptapeptide of the oscillapeptin type. Strict application of a bioassay-guided isolation procedure proved this compound to be one of the major causative agents (besides [d-Asp(3),(E)-Dhb(7)]microcystin-RR) of the acute grazer toxicity of P. rubescens from Lake Zürich. The LC(50) value of oscillapeptin J as determined for the freshwater crustacean Thamnocephalus platyurus was 15.6 microM.