Uptake Of Microcystins Research Articles

Fate of Planktothrix-derived toxins in aquatic food webs: A case study in Lake Mindelsee (Germany)

Blooms of the red, filamentous cyanobacterium Planktothrix rubescens occur frequently in pre-alpine lakes in Europe, often with concomitant toxic microcystin (MC) production. Trophic transfer of MCs has been observed in bivalves, fish, and zooplankton species, while uptake of MCs into Diptera species could facilitate distribution of MCs into terrestrial food webs and habitats. In this study, we characterized a Planktothrix bloom in summer 2019 in Lake Mindelsee and tracked possible trophic transfer and/or bioaccumulation of MCs via analysis of phytoplankton, zooplankton (Daphnia) and emergent aquatic insects (Chaoborus, Chironomidae and Trichoptera). Using 16 S rRNA gene amplicon sequencing, we found that five sequence variants of Planktothrix spp. were responsible for bloom formation in September and October of 2019, and these MC-producing variants, provisionally identified as P. isothrix and/or P. serta, occurred exclusively in Lake Mindelsee (Germany), while other variants were also detected in nearby Lake Constance. The remaining cyanobacterial community was dominated by Cyanobiaceae species with high species overlap with Lake Constance, suggesting a well-established exchange of cyanobacteria species between the adjacent lakes. With targeted LC–HRMS/MS we identified two MC-congeners, MC-LR and [Asp3]MC-RR with maximum concentrations of 45 ng [Asp3]MC-RR/L in lake water in September. Both MC congeners displayed different predominance patterns, suggesting that two different MC-producing species occurred in a time-dependent manner, whereby [Asp3]MC-RR was clearly associated with the Planktothrix spp. bloom. We demonstrate an exclusive transfer of MC-LR, but not [Asp3]MC-RR, from phytoplankton into zooplankton reaching a 10-fold bioconcentration, yet complete absence of these MC congeners or their conjugates in aquatic insects. The latter demonstrated a limited trophic transfer of MCs from zooplankton to zooplanktivorous insect larvae (e.g., Chaoborus), or direct transfer into other aquatic insects (e.g. Chironomidae and Trichoptera), whether due to avoidance or limited uptake and/or rapid excretion of MCs by higher trophic emergent aquatic insects.

Effect of linear alkylbenzene sulfonate on the uptake of microcystins by Brassica oleracea and Solanum tuberosum.

Globally, hypereutrophic conditions in major water reservoirs used for irrigation purposes, promote the co-existence of cyanotoxins and other pollutants such as linear alkylbenzene sulfonate (LAS). LAS is known to alter the permeability of membranes and promote the uptake of other pollutants by plants. In light of the potential human health risks and prevailing hypereutrophic conditions in some catchments in South Africa, we investigated the combined effects of LAS and microcystins (MCs) on food plants when cyanobacteria infested water is used to irrigate terrestrial crops. To understand the potential risks, pot-culture experiments were conducted to assess the effect of LAS on the accumulation of MCs in Brassica oleracea (cabbage) and Solanum tuberosum (potato) plants. The plants were watered with dam water containing 3.48 mg L -1 of the LAS (sodium dodecyl sulfate) and MCs (MC-LR: 10.47 ± 3.879; 6.158 ± 4.127 for MC-RR and 8.160 ± 2.544 for MC-YR μg L -1) for 20 days. The presence of LAS, at environmentally relevant concentrations in the irrigation water, did not enhance the uptake of MCs in the two plants, as demonstrated by statistically insignificant differences in the means of the treatments (with and without LAS). In addition, the presence of LAS, high pH, electrical conductivity (EC), and cyanotoxins in the water did not affect the total chlorophyll or the well-being of the plants. However, in some cases the levels of MCs bioaccumulated by the two plants exceeded the WHO recommended tolerable daily intake (TDI). These findings imply that the tested levels of LAS and MCs did not have any synergic effects on the two plant species, but irrigating food crops with such water still poses a human health risk.

Survival and Accumulation of Microcystins in a Native Amphipod Shredder, Gammarus Pulex under Environmentally Relevant Cyanotoxin Exposure

Microcystin release in freshwaters is a major public health and ecological threat, affecting survival and trophic interactions across food web components. Although bioaccumulation has been suggested to represent an important pathway for microcystin uptake and trophic transfer across different food web compartments, it is rarely known how microcystin exposure may affect survival and accumulation among lower trophic levels under environmentally realistic scenario. Therefore, in this study, survival and microcystin accumulations in the UK native amphipod species, Gammarus pulex were monitored during a 96-hour static acute toxicity experiment. Animals were exposed to a range of environmentally relevant microcystin concentrations (0.01–10μg/L) across two treatment types, purified MC-LR and crude extract of microcystin-producing Microcystis aeruginosa. Survival of G. pulex individuals across the two treatments showed no evidence of significant difference from the control. Microcystin concentrations observed in G. pulex exposed to the purified MC-LR and crude extract ranged from (12.8 – 27.5) ng/g of MC-LR and (5.6-12.8) ng/g of MC-LR respectively. Microcystin concentrations measured in animals showed strong positive correlations with toxin concentrations in the experimental media across the two treatments, suggesting G. pulex can bioaccumulate microcystins, therefore may represent a potential vector for microcystin exposure to higher food web consumers. These results highlight the fact that exposure of benthic food web components to environmental microcystin concentrations may constitute an important route of toxin transfer within freshwater food webs.

Effect of linear alkylbenzene sulfonate on the uptake of microcystins by Brassica oleracea and Solanum tuberosum

Background Hypereutrophic conditions in major water reservoirs used for irrigation purposes in South Africa promote the co-existence of cyanotoxins and other pollutants such as linear alkylbenzene sulfonate (LAS). LAS is known to alter the permeability of membranes and promote the uptake of other pollutants by plants. In light of the potential human health risks and prevailing hypereutrophic conditions in some catchments in South Africa, we investigated the combined effects of LAS and microcystins (MCs) when cyanobacteria infested water is used to irrigate terrestrial crops. Methods To understand the potential risks, pot-culture experiments were conducted to assess the effect of LAS on the accumulation of MCs in Brassica oleracea (cabbage) and Solanum tuberosum (potato) plants. The plants were watered with dam water containing 3.48 mg L-1 of the LAS (sodium dodecyl sulfate) and MCs (MC-LR: 10.47 ± 3.879; 6.158 ± 4.127 for MC-RR and 8.160 ± 2.544 for MC-YR μg L-1) for 20 days. Results The presence of LAS, at environmentally relevant concentrations in the irrigation water, did not enhance the uptake of MCs in the two plants, as demonstrated by statistically insignificant differences in the means of the treatments (with and without LAS). In addition, the presence of LAS, high pH, electrical conductivity (EC), and cyanotoxins in the water did not affect the total chlorophyll or the well-being of the plants. However, in some cases the levels of MCs bioaccumulated by the two plants exceeded the WHO recommended tolerable daily intake (TDI). Conclusions These findings imply that the tested levels of LAS and MCs did not have any synergic effects on the two plant species, but irrigating food crops with such water still poses a human health risk.

Microcystin bioaccumulation in Limnoperna fortunei following Microcystis aeruginosa exposure, analysis of in vivo enzymatic phosphatase, acetylcholinesterase and carboxylesterase effects and in vitro experiments

Toxic cyanobacteria blooms have been reported in freshwater sources worldwide and may lead to aquatic biota toxin accumulation and trophic chain transfer, resulting in ecological and public health concerns. To assess cyanobacteria effects on microcystin uptake and accumulation and on phosphatase, acethylcholinesterase (AChE) and carboxylesterase (CarbE) enzymatic activities, an in vivo experiment was carried out employing the golden mussel Limnoperna fortunei. These mussels were exposed to a Microcystis aeruginosa NPLJ-4 strain (NPLJ-4) for 48 hours at different cell densities. Subsequently, algal cell counts were carried out and enzymatic activities were assayed. All three enzymes (Phosphatase, AChE and CarbE) were inhibited at the end of the exposure experiment. Mussels exposed to higher in vivo M. aeruginosa densities exhibited microcystin uptake and accumulation. In vitro assays were also carried out, exposing soluble L. fortunei enzyme fractions to M. aeruginosa extracts containing microcystin, and phosphatase inhibition was observed, whereas acetylcholinesterase and carboxylesterase were not inhibited. The results indicate that metabolites other than mycrocystin probably caused the observed in vivo esterase inhibitions, requiring further investigations.

Selective interaction of microcystin congeners with zebrafish (Danio rerio) Oatp1d1 transporter

Microcystins (MCs) are the most studied cyanotoxins. The uptake of MCs in cells and tissues of mammals and fish species is mostly mediated by organic anion-transporting polypeptides (OATPs in humans and rodents; Oatps in other species), and the Oatp1d1 appears to be a major transporter for MCs in fish. In this study, six MC congeners of varying physicochemical properties (MC-LR, -RR, -YR, -LW, -LF, -LA) were tested by measuring their effect on the uptake of model Oatp1d1 fluorescent substrate Lucifer yellow (LY) in HEK293T cells transiently or stably overexpressing zebrafish Oatp1d1. MC-LW and -LF showed the strongest interaction resulting in an almost complete inhibition of LY transport with IC50 values of 0.21 and 0.26 μM, while congeners -LR, -YR and -LA showed lower inhibitory effects. To discern between Oatp1d1 substrates and inhibitors, results were complemented by Michaelis–Menten kinetics and chemical analytical determinations of MCs uptake, along with molecular docking studies performed using the developed zebrafish Oatp1d1 homology model. Our study showed that Oatp1d1-mediated transport of MCs could be largely dependent on their basic physicochemical properties, with log POW being the most obvious determinant. Finally, apart from determination of the chemical composition of cynobacterial blooms, a reliable risk assessment should take into account the interaction of identified MC congeners with Oatp1d1 as their primary transporter, and herewith we demonstrated that such a comprehensive approach could be based on the use of highly specific in vitro models, accompanied by chemical assessment and in silico molecular docking studies.

Long-term environmental exposure to microcystins increases the risk of nonalcoholic fatty liver disease in humans: A combined fisher-based investigation and murine model study

Microcystins (MCs) produced by cyanobacteria pose serious threats to human health. However, the contribution of long-term exposure to MCs to the development of nonalcoholic fatty liver disease (NAFLD) remains poorly documented. In this study, we estimated the environmental uptake of MCs by a small population of fishers who have lived for many years on Meiliang Bay of Lake Taihu, where cyanobacterial blooms occur frequently. Serum biochemical indices of liver function and their relationships with MC contamination in these people were also investigated. Moreover, to mimic the long-term effects of MC on the livers of fishers, an animal model was established in which mice were exposed to MC-LR at an environmentally relevant level, a reference level (the no-observed adverse effect level, NOAEL), and three times the NOAEL through drinking water for 12 months. We estimated the total daily intake of MCs by fishers through contaminated lake water and food to be 5.95 μg MC-LReq, far exceeding the tolerable daily intake (2.40 μg MC-LReq) proposed by the World Health Organization (WHO). More than 80% of participants had at least one abnormal serum marker. The indices of aspartate aminotransferase (AST)/alanine aminotransferase (ALT), triglyceride (TG), globulin (GLB), and lactate dehydrogenase (LDH) had close positive associations with MC contamination, indicating that both liver damage and lipid metabolism dysfunction were induced by chronic MC exposure. Furthermore, the animal experimental results showed that long-term exposure to MC-LR at the environmentally relevant level led to hepatic steatosis with molecular alterations in circadian rhythm regulation, lipid metabolic processes, and the cell cycle pathway. Exposure to MC-LR at or above the NOAEL worsened the pathological phenotype towards nonalcoholic steatohepatitis disease (NASH) or fibrosis. These results suggest that prolonged exposure to the reference level (NOAEL) of MC-LR could cause severe liver injury to mammals. People with long-term environmental exposure to MCs might be at high risk for developing NAFLD.

Crude extract of cyanobacterium Radiocystis fernandoi strain R28 induces anemia and oxidative stress in fish erythrocytes

The cyanobacterium Radiocystis fernandoi has been frequently identified in cyanobacterial blooms in Brazil. Recently, R. fernandoi strain R28, which produces microcystin (MC)-RR and MC-YR, was isolated from the Furnas reservoir, Minas Gerais, Brazil. The present study evaluated the hematological variables and erythrocyte antioxidant responses, lipid peroxidation (LPO), and genotoxicity in a neotropical fish (Hoplias malabaricus) after acute and subchronic exposure to a crude extract (CE) of R. fernandoi strain R28. Acute exposure (12 or 96 h) consisted of a single intraperitoneal (i.p.) CE injection, and subchronic exposure consisted of one i.p. CE injection every 72 h for 30 days. After acute exposure, fish exhibited macrocytic anemia (12 h post-injection) followed by normocytic anemia (96 h post-injection). The increased activity of superoxide dismutase, glutathione peroxidase, glutathione-S-transferase, and the glutathione level in the erythrocytes did not prevent oxidative stress, manifested as lipid peroxidation and elevated DNA damage after acute exposure. After subchronic exposure, the hematological variables recovered, and the absence of erythrocyte oxidative stress suggests possible modulation by other biological factors, including a possible decrease in MC uptake by the cells and/or increasing detoxification efficiency that precludes erythrocyte damage.

Characterization of Microcystin‐Induced Apoptosis in HepG2 Cells

Microcystins (MCs) are a class of hepatotoxins produced by freshwater cyanobacteria. Hepatocytes possess the organic anion transporting polypeptide 1B2, which results in the uptake of microcystins followed by inhibition of protein phosphatase 1 and 2A. Previously, programmed cell death, i.e., apoptosis, has been observed in MC‐treated hepatocytes, but, there is still a knowledge gap regarding the pathway adopted for apoptosis observed in hepatic cells. MC‐LR, the most common form of MCs, was administered to HepG2 cells at a 5μM final concentration, and microscopic observation along with Alamar Blue assay was performed to evaluate the induction of cytotoxicity. MC‐LR treated hepatic cells were also stained with caspases specific stains and the presence of caspases was determined based on flow cytometric analysis. Loss of viability and confluency was observed in MC‐LR exposed (24 hrs) HepG2 cells by microscopic analysis and Alamar Blue assay. Caspases 8, 9 and 3 were induced after 24 hrs of MC‐LR treatment. Expression of these caspases indicated the presence of both extrinsic and intrinsic pathway in MC‐LR induced apoptosis, where, extrinsic apoptotic pathway was triggered before the intrinsic apoptotic pathway.Support or Funding InformationKent State UniversityThis abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Development of a silicone-membrane passive sampler for monitoring cylindrospermopsin and microcystin LR-YR-RR in natural waters

Silicone membrane tubes were functionalised by filling them with synthesised γ-Fe2O3 nanoparticles and used as a passive sampling device for monitoring microcystins and cylindrospermopsin in aquatic environments. This novel device was calibrated for the measurement of microcystin and cylindrospermopsin concentrations in water. The effect of temperature and hydrodynamics on the sampler performance was studied in a flow-through system under controlled conditions. The chemical uptake of microcystins (MCs) and cylindrospermopsin (CYN) into the passive sampler remained linear and integrative throughout the exposure period. The rate of accumulation of most of the MC compounds tested was dependent on temperature and flow velocity. The use of 13C labelled polychlorinated biphenyls as performance reference compounds (PRCs) in silicone membrane/γ-Fe2O3 nanoparticle passive sampler, Chemcatcher and polar organic chemical integrative sampler (POCIS) was evaluated. The majority of PRCs improved the semi quantitative nature of water concentration estimated by the three samplers. The corrected sampling rate values of model biotoxin compounds were used to estimate the time-weighted average concentrations in natural cyanobacterial water blooms of the Hartbeespoort dam. The corrected sampling rates RScorr values varied from 0.1140 to 0.5628 Ld−1 between samplers with silicone membrane having the least RScorr values compared to the Chemcatcher and POCIS. The three passive sampling devises provided a more relevant picture of the biotoxin concentration in the Hartbeespoort dam. The results suggested that the three sampling devices are suitable for use in monitoring microcystins and cylindrospermopsin concentrations in aquatic environments.

Calibration of a passive, in situ, integrative sampler for monitoring of microbial biotoxins in aquatic environments

In this work, an integrative passive sampler based on a silicone membrane filled with a suspension of γ-Fe2O3 at pH 3.5 was developed. The novel device was calibrated for the measurement of microcystin concentrations in water. Laboratory calibration studies of the passive sampling devises under controlled conditions of temperature, water turbulence, and analyte concentration were conducted in order to establish how variable environmental conditions affect the novel sampler's performance. The chemical uptake of microcystin (MC)-RR, -LR, and -YR into the passive sampler remained linear and integrative throughout the 28-day exposure. The relative standard deviations of mean concentrations obtained using silicone-based sampler ranged from 1.42 to 3.74% for microcystin-LR, -RR, and -YR. The values for reproducibility from triplicate samplers ranged from 3.5 to 7.1% for microcystin-LR, -RR, and -YR. The detection limits on high performance liquid chromatography (HPLC) with PDA detection for microcystins LR, RR, and YR were 24.7, 17.2, and 23.8 μg L−1 respectively, calculated as three times the signal to noise ratio. The rate of accumulation of most of the MC compounds tested was dependent on temperature and flow velocity. Furthermore, the sample matrix, e.g. humic substances, had no significant effect on the concentration of compounds trapped in the acceptor solution and once these MC compounds were trapped in the acceptor phase they did not diffuse back during the deployment period.

Effects of the naturally-occurring contaminant microcystins on the Azolla filiculoides–Anabaena azollae symbiosis

Harmful algal blooms (HABs) contaminate aquatic ecosystems and are responsible for animal poisoning worldwide. We conducted a toxicity test with the aquatic fern and the biofertilizer, Azolla filiculoides. The sporophytes were exposed to three concentrations (0.01, 0.1 and 1μgmL−1) of a microcystin (MC) cyanobacterial crude extract and purified MC-LR. The growth of A. filiculoides decreased only at 1μgmL−1 crude extract concentration while with MC-LR it decreased at all the tested concentrations, indicating that the presence of other compounds in the crude extract altered toxicity and stimulated the fern growth at lower concentrations (0.01 and 0.1μgmL−1). Both phycoerythrocyanin and allophycocyanin levels decreased in all the concentrations of crude extract and MC-LR. The phycocyanin had a marked increase at 0.1μgmL−1 crude extract concentration and a marked decrease at 1μgmL−1 MC-LR concentration. These changes in the phycobiliprotein content indicate a shift in the antenna pigments of the cyanobionts of A. filiculoides. The changes in two oxidative stress enzymes, glutathione reductase for the crude extract assay and glutathione peroxidase for MC-LR assay, points towards the induction of stress defense responses. The low bioconcentration factor in both crude extract and MC-LR treatments can suggest the low uptake of microcystins, and indicates that the aquatic fern can be used as a biofertilizer and as animal feed but is not suitable for MC phytoremediation.

Microcystin uptake and biochemical responses in the freshwater clam Corbicula leana P. exposed to toxic and non-toxic Microcystis aeruginosa: Evidence of tolerance to cyanotoxins

We investigated the accumulation and adverse effects of toxic and non-toxic Microcystis in the edible clam Corbicula leana. Treated clams were exposed to toxic Microcystis at 100μg of MC (microcystin)-LReqL−1 for 10 days. The experimental organism was then placed in toxin-free water and fed on non-toxic Microcystis for the following 10 days for depuration. Filtering rates (FRs) by C. leana of toxic and non-toxic Microcystis and of the green alga Chlorella vulgaris as a control were estimated. Adverse effects were evaluated though the activity of catalase (CAT), superoxide dismutase (SOD) and glutathione S-transferase (GST). Clam accumulated MCs (up to 12.7±2.5μgg−1 dry weight (DW) of free MC and 4.2±0.6μgg−1 DW of covalently bound MC). Our results suggest that although both toxic and non-toxic cyanobacteria caused adverse effects by inducing the detoxification and antioxidant defense system, the clam was quite resistant to cyanotoxins. The estimated MC concentration in C. leana was far beyond the World Health Organization's (WHO) provisional tolerable daily intake (0.04μgkg−1day−1), suggesting that consuming clams harvested during cyanobacterial blooms carries a high health risk.

Protonated mesoporous graphitic carbon nitride for rapid and highly efficient removal of microcystins

A novel biomaterial, protonated mesoporous graphitic carbon nitride (mpg-C3N4–H+) which is fabricated by treating mpg-C3N4with concentrated hydrochloric acid, is applied as a promising bioadsorbent for the uptake of microcystins (MCs).

Germination and seedling growth of Brassica juncea and Medicago sativa under exposure to microcystinscontaminated water from Dau Tieng reservoir

Occurrence of toxic cyanobacteria and their toxins has been a root of many consequently serious problems to aquatic plants, animals, and human in the world. However, the toxicity of cyanobacterial toxins from Vietnam waters to the germination and growth of plants has not studied yet. In this study, we investigated the effects of microcystins (MC) (at the concentrations of 20 and 200 µg MC L–1) from field water and crude extract of cyanobacterial scum (mainly Microcystis spp.) from the Dau Tieng Reservoir, on the germination and seedling of Brassica juncea and Medicago sativa during 7 days. The results showed that MC inhibited the germination of the exposed seeds from 10 – 35% compared to the control. The fresh weight of exposed B. juncea and M. sativa compared to the control was from 44 – 89% and from 55 – 90%, respectively. Root length of the plants reduced from 12 – 73% for B. juncea and from 17 – 54% for M. sativa during toxin exposures. Similarly, the decrease of the shoot length, compared to the control, was from 20 – 80% for B. juncea and 13 – 52% for M. sativa. Therefore, the use of water contaminated with MC for irrigation may negatively influence on the quality and yield of agricultural crops. It could be inferred that there should be an uptake of MC by the exposed seeds and th toxin might be transferred to the next consumers via the food chain.

The fate of microcystins in the environment and challenges for monitoring.

Microcystins are secondary metabolites produced by cyanobacteria that act as hepatotoxins in higher organisms. These toxins can be altered through abiotic processes, such as photodegradation and adsorption, as well as through biological processes via metabolism and bacterial degradation. Some species of bacteria can degrade microcystins, and many other organisms metabolize microcystins into a series of conjugated products. There are toxicokinetic models used to examine microcystin uptake and elimination, which can be difficult to compare due to differences in compartmentalization and speciation. Metabolites of microcystins are formed as a detoxification mechanism, and little is known about how quickly these metabolites are formed. In summary, microcystins can undergo abiotic and biotic processes that alter the toxicity and structure of the microcystin molecule. The environmental impact and toxicity of these alterations and the metabolism of microcystins remains uncertain, making it difficult to establish guidelines for human health. Here, we present the current state of knowledge regarding the alterations microcystins can undergo in the environment.

4-Methylproline guided natural product discovery: co-occurrence of 4-hydroxy- and 4-methylprolines in nostoweipeptins and nostopeptolides.

4-methylproline (4-mPro) is a rare nonproteinogenic amino acid produced by cyanobacteria through the action of a zinc-dependent long-chain dehydrogenase and a Δ(1)-pyrroline-5-carboxylic acid (P5C) reductase homologue. Here, we used the presence of 4-mPro biosynthetic genes to discover new bioactive compounds from cyanobacteria. Eight biosynthetic gene clusters containing the 4-mPro biosynthetic genes nosE and nosF were found from publicly available cyanobacteria genomes, showing that 4-mPro is a good marker to discover previously unknown nonribosomal peptides. A combination of polymerase chain reaction (PCR) and liquid chromatography-mass spectroscopy (LC-MS) methods was used to screen 116 cyanobacteria strains from 8 genera. The 4-mPro biosynthetic genes were detected in 30 of the 116 cyanobacteria strains, 12 which were confirmed to produce 4-mPro by amino acid analysis. Species from the genus Nostoc were responsible for 80% of the positive results. Altogether, 11 new nonribosomal cyclic peptides, nostoweipeptin W1-W7 and nostopeptolide L1-L4, were identified from Nostoc sp. XPORK 5A and Nostoc sp. UK2aImI, respectively, and their chemical structure was elucidated. Interestingly, screening with 4-mPro genes resulted in the detection of peptides that do not contain just one 4-mPro but also 4-hydroxylproline (nostopeptolides) and, in case of nostoweipeptins, two 4-mPros and two 4-hydroxyprolines. Peptides from both groups inhibit microcystin-induced apoptosis of hepatocytes HEK293. The cell experiments indicated that these cyclic peptides inhibit the uptake of microcystin by blocking the organic anion-transporters OATP1B1/B3. This study enriches the drug library of microcystin antitoxin.

Inhibitory effect of naringin on microcystin-LR uptake in the freshwater snail Sinotaia histrica

Gastropods are an important food source for aquatic animals, and have been demonstrated to transfer microcystin (MC) to higher trophic levels through the food web. In this study, we performed an oral administration experiment to evaluate whether naringin can inhibit MC-LR uptake in the freshwater snail Sinotaia histrica. We also observed the effect of MC-LR on the organizational pathology of the hepatopancreas in S. histrica. Following exposure to cells of Microcystis ichthyoblabe, S. histrica showed vacuolization and separation of the basal lamina from cells in the hepatopancreas. Initial treatment with 1mM naringin resulted in the prevention of MC-LR uptake rate by approximately 60% over 8days, whereas initial treatment with 10mM naringin suppressed microcystin uptake in 2days, despite an increase in MC-LR levels in the snail from days 5 to 8. With continuous treatment of 10mM naringin, the uptake prevention rate was 100%. Overall, we observed a strong inhibitory effect against MC-LR with naringin treatment. This study provides a potential mechanism to prevent the uptake of microcystin in the aquatic food web, thereby limiting its toxicity in cyanobacterial bloom-polluted areas where the environment can be controlled and may have further applications in the aquaculture of gastropods.

Microcystin accumulation in cladocerans: First evidence of MC uptake from aqueous extracts of a natural bloom sample

Bioaccumulation of microcystins (MC) in zooplankton has been shown in several studies, mainly in field samples. A few studies, however, have demonstrated MC bioaccumulation in laboratory experiments. Although ingestion of cell-bound MC is considered the main route of MC accumulation, another important source is the MC from the dissolved fraction (DMC). This study reports the accumulation of DMC from aqueous extracts of natural bloom samples in three cladoceran species: Moina micrura, Daphnia laevis and Daphnia similis. Animals were exposed for 96 h to aqueous extracts of lyophilized matter from two bloom samples from Colombian reservoirs in different concentrations (25–1000 mg DW L−1). Analysis by HPLC-MS detected MC-LR in these samples at concentrations of 434–538 μg g−1. For the analysis of MC in animal tissues the samples were homogenized and sonicated in methanol:water (75%) and analyzed by ELISA. Results showed that the animals uptake of MC increased with increasing exposure concentrations of aqueous extracts, with M. micrura and D. laevis clones presenting the highest MC concentrations in their tissues (up to 1170–1260 μg g−1) while D. similis the lowest (184 μg g−1). This study shows, for the first time, that MC uptake from dissolved fraction by zooplankton is possible, not only from the ingestion of seston or cell-bound MC as previously demonstrated.

Accumulation of microcystin congeners in different aquatic plants and crops – A case study from lake Amatitlán, Guatemala

Microcystins (MCs) fate in natural environments can lead to its transfer into aquatic organisms, e.g. aquatic plants. Moreover, lakes in several countries sustain agriculture activities posing a serious health threat for the public. The case of Lake Amatitlán in Guatemala, was addressed to better understand MCs accumulation of four aquatic plants (Polygonum portoricensis, Eichhornia crassipes, Typha sp. and Hydrilla verticillata) coexisting with Microcystis aeruginosa blooms. These findings were further corroborated with an uptake/accumulation laboratory study. Finally crop products (Solanum lycopersicum and Capsicum annuum) irrigated with lake water were also evaluated for MCs. The obtained results suggest that Lake Amatitlán is highly contaminated with MCs (intra- and extracellular 1931 and 90µg/L, respectively). In fruits of S. lycopersicum and C. annuum a concentration of 1.16 and 1.03µg/kg dry weight (DW), respectively could be detected. All four aquatic plants showed a high MCs uptake capacity based on obtained bioconcentration factors (BCF) 165, 18, 16 and 11, respectively. These results were further corroborated in a laboratory study with 30 percent of total MCs taken up by H. verticillata within just 7 days. Additionally it was evidenced that all plants accumulated more MC-LR than other MCs congeners. Monitoring of crop products irrigated with lake water needs further consideration.