Evaluation of cyanobacteria toxicity in tropical reservoirs using crude extracts bioassay with cladocerans

During a cyanobacterial bloom in a eutrophic environment, particularly at the end when decomposition occurs, toxic compounds such as the cyanotoxins and the lipopolysaccharides can be released in high concentrations into the water column damaging aquatic organisms. In this work, the effects of this release of toxic compounds during a cyanobacterial bloom were investigated. The acute and chronic toxicity of cyanobacterial crude extracts from two natural blooms in the Barra Bonita and Ibitinga reservoirs (Middle Tietê River, São Paulo State, Brazil) and of a toxic strain cultured in the laboratory were tested. The cladocerans Daphnia similis, Ceriodaphnia dubia and Ceriodaphnia silvestrii were used as test organisms. In the chronic toxicity tests, only a native cladoceran found in Brazilian freshwaters, Ceriodaphnia silvestrii, was used. Microcystins were detected in all cyanobacterial samples. The acute toxicity tests showed that the crude bloom material extract from the Ibitinga Reservoir (48-h EC(50) values between 32.6 and 35.8 microg microcystin g(-1) of freeze-dried material) exhibited higher toxicity to cladoceran than did the crude bloom material extract from Barra Bonita Reservoir (48-h EC(50) values between 46.0 and 80.2 microg microcystin g(-1) of freeze-dried material). The chronic toxicity test data showed that the three extracts reduced the fecundity of C. silvestrii, and the crude extract of Barra Bonita Reservoir bloom material also affected the survival of this cladoceran. Both acute and chronic tests effectively prognosticated possible changes in the cladoceran population, and probably other components of the biota due to cyanobacterial blooms in natural aquatic ecosystems.

In vitro effects of pure microcystin-LR on the lymphocyte proliferation in rainbow trout (Oncorhynchus mykiss)

The aim of this study was to determine the in vitro influence of microcystin-LR on the viability and mitogenic response of rainbow trout (Oncorhynchus mykiss) lymphocytes since few data are available in the literature on the influence of cyanotoxins on fish immunocompetent cells. Lymphocytes were isolated from blood and haematopoietic organs (pronephros and spleen) and cultivated in RPMI 1640 medium with different concentrations of the toxin (1, 5, 10, 20, 40 mg ml-1 of cell suspension). Dose-dependent effects of microcystin-LR on the lymphocyte viability were shown. The lymphocyte proliferation was inhibited after application of microcystin at a concentration of 40 mg ml-1 but significantly increased at a concentration of 1mg ml-1 in comparison to the control group. The results suggest the modulatory effects of microcystin-LR dependent on the applied concentration.

Toxicogenomic evaluation of microcystin-LR treated with ultrasonic irradiation

Microcystins are a family of toxins produced by cyanobacteria found throughout the world in marine and freshwater environments. The most commonly encountered form of microcystin is microcystin-LR (MC-LR). Humans are exposed to MC-LR by drinking contaminated water. The toxin accumulates rapidly in the liver where it exerts most of its damage. Treatment of water containing MC-LR by ultrasonic irradiation leads to the breakdown of the toxin. Both the parent toxin and the treated toxin reaction products (TTRP) were evaluated for toxic effects in mice. Animals were exposed to purified MC-LR or an equivalent dose of the TTRP and sacrificed after 4 h or 24 h. Serum was collected and assayed for lactate dehydrogenase (LDH) activity as an indicator of hepatotoxicity. LDH activity was detected in the serum of MC-LR exposed mice indicative of liver damage, but not in control mice. Only a fraction of that activity was detectable in mice exposed to TTRP. Liver RNA was used for microarray analysis and real-time PCR. Individual animals varied in their overall genomic response to the toxin; however, only 20 genes showed consistent changes in expression. These include chaperones which may be part of a generalized stress response; cytochrome P450 which may be involved in metabolizing the toxin; and lipid dystrophy genes such as lipin-2, uridine phosphorylase and a homolog to tribbles, a stress-inducible gene involved in cell death. Of the genes that responded to the MC-LR, none showed significant changes in expression profile in response to TTRP. Taken together, the data indicate that ultrasonic irradiation of MC-LR effectively reduces hepatotoxicity in mice and therefore may be a useful method for detoxification of drinking water.

The cyanobacterial toxin, cylindrospermopsin, induces fetal toxicity in the mouse after exposure late in gestation

Cylindrospermopsin (cyn) is a cyanobacterial toxin implicated in human and wildlife poisonings. We have completed studies investigating the potential of purified cyn to induce developmental toxicity in mammals. The teratology study involved intraperitoneal injections (8.0-128 microg kg(-1)) on gestational days (GD) 8-12 with subsequent examination of term fetuses for viability, weight and morphological anomalies. Cyn was lethal to a significant portion of the dams receiving > or = 32 microg kg(-1). Surviving pregnant females were killed and fetuses removed for examination. Analysis indicates no adverse effects on litter size, fetal weight, or incidence of anomalies. Subsequently, 50 microg kg(-1) cyn was administered on GD 8-12 or 13-17. Animals were allowed to give birth and litters monitored for growth and viability. A reduction in litter size occurred in treated groups. Avg. pup wt. was only affected in the GD 13-17 group. GD 13-17 dams did not exhibit the toxicity noted in the GD 8-12 group but gave birth significantly earlier than controls. There was a significant number of dead GD 13-17 pups and incidences of blood in the gastrointestinal tract and hematomas in the tips of the tails in survivors. Pups were cross-fostered to control mothers in litters of 10. On postnatal days (PND) 5-6 there were no significant differences in weight gain or viability in GD 8-12 litters, while GD 13-17 litters had significantly reduced weight gain and viability. GD 13-17 exposed male pups still weighed significantly less than the controls after 15 months.

[Antagonism effects of green tea against microcystin induced oxidant damage on liver and kidney]

OBJECTIVE

To evaluate the antagonism effects of green tea (GT) against microcystin LR (MC-LR) induced hepatotoxicity and nephrotoxicity in mice.

METHODS

All 40 male mice were randomly divided into four groups. Mice in group III and IV were pretreated with green tea for free drink at doses of 2 g/L and 12 g/L prior to MC-LR intoxication, for consecutively 18 days. The toxin treatment mice were administered continually intraperitoneal injections of MC-LR at a dose of 10 microg x kg(-1) x d(-1) bw from day 6th till sacrifice, continually 13 days. Mice were sacrificed and immediately subjected to necropsy, and the body weight, relative organ weight, serum biochemical parameters, antioxidant enzyme levels (SOD and GSH), lipid peroxidation products (MDA) and histopathology were systematically evaluated.

RESULTS

MC-LR exposure led to increase the oxidative stress and organ injury was significantly observed through biochemical parameters and microscopic evaluation. However, high dose of GT pretreatment caused a significant elevation in serum GSH and SOD levels, and a decrease of serum MDA level as compared with MC-LR control. The mean values of GSH and SOD activities were separately 467.29 mg/L and 139.22 U/ml in group IV. Subsequently, GT pretreatment obviously diminished the serum ALT, AST and Cr activities. Those pathological damages in liver and kidney, were to a certain extent, lessened in GT pretreatment mice in correlation with the biochemical parameters.

CONCLUSION

GT might elevate antioxidant defense system, clean up free radicals, lessen oxidative damages and protect liver and kidney against MC-LR induced toxicity.

Biomonitoring Of Cyanobacterial Blooms In Polish Water Reservoir And The Cytotoxicity And Genotoxicity Of Selected Cyanobacterial Extracts

OBJECTIVES

Water pollution with toxic cyanobacterial blooms is a worldwide problem. Cyanobacteria species that mainly produce microcystins predominate in Polish water reservoirs.

MATERIALS AND METHODS

In our study, cyanobacterial blooms were monitored during summer of 2004 in the Sulejów reservoir. The concentration of microcystins in water and cyanobacterial cells were determined using liquid chromatography and immunobiotests, while the biological activity of microcystic cyanobacterial extracts was assessed using bacterial tests (SOS Chromotest, UMU test), the comet assay and micronucleus test with human lymphocytes.

RESULTS

It was revealed that cyanobacterial bloom was most intensive in mid August and lasted until the end of September. Microcystis aeruginosa and Aphanizomenon flos-aquae dominated in the blooms. The highest concentration of microcystins in cyanobacterial cells was also observed at that time. The concentration of microcystins in water did not exceed 1 microg/l. All cyanobacterial extracts showed weak genotoxicity only for Escherichia coli PQ37. The cyanobacterial extracts prepared at the beginning of September were most toxic to human lymphocytes, the effective microcystin extracts (EC50) concentration was about two or three times lower compared to the other extracts. The level of DNA damage in lymphocytes after short exposure to microcystic extracts (3 and 6 h) was significantly higher than respective levels after longer exposure. The microcystins of cyanobacterial blooms induced a slight increase in micronuclei frequencies in human lymphocytes.

CONCLUSION

Phytoplankton biomass and the genotoxicity of massive cyanobacterial blooms should be assessed for eucariotic cells in the Sulejów reservoir to avoid the hazard induced by cyanobacterial blooms.

[Effects of microcystins on expression of apoptosis-associated hepatocyte genes]

OBJECTIVE

To deeply explore the effects of microcystins (MC-LR) on Bax and Bcl-2 during the course of MC-LR promoting liver tumor.

METHODS

applied to set up the animal model, and the effect of MC-LR promoting liver tumor was evaluated by the Albertgamma-GT methods. And then, the immunohistochemical technique, RT-PCR and image analysis were used to study the expression of the Bcl-2 and Bax during the course of promoting tumor.

RESULTS

(1) MC-LR might enhance the positive reaction rate of GGT. The positive reaction rate of GGT in DEN + pure toxin group was 100%, it was significantly higher than the DEN control group 22.22% (P < 0.05). (2) The intension and areas of the protein expression of Bcl-2 in DEN + pure toxin group were 0.0977 and 0.0315, and in DEN control group were 0.0460 and 0.0205, respectively. The expression level of Bcl-2 protein in DEN + pure toxin group were significantly higher than in DEN control group (P < 0.05). Simultaneously, the protein expression of Bax was significantly decreased by MC-LR (P < 0.05). The intension and areas of the expression of Bax in DEN + pure toxin group were 0.0283 and 0.0073, and in DEN control group were 0.0655 and 0.0244 respectively. (3) The mRNA expression of Bcl-2 was significantly increased by MC-LR. The intension of Bcl-2 mRNA expression in DEN + pure toxin group was 2.244, being significantly higher than in the other groups (P < 0.05). However, the mRNA expression of Bax showed no significant difference between DEN + pure toxin and the other groups.

CONCLUSION

The expression change of Bcl-2 and Bax should possibly play an important role in the course of MC-LR promoting liver tumor.

In vivo exposure to microcystins induces DNA damage in the haemocytes of the zebra mussel, Dreissena polymorpha, as measured with the comet assay

The Comet assay was used to investigate the potential of the biotoxin microcystin (MC) to induce DNA damage in the freshwater zebra mussel, Dreissena polymorpha. Mussels maintained in the laboratory were fed daily, over a 21-day period, with one of four strains of the cyanobacterium, Microcystis aeruginosa. Three of the strains produced different profiles of MC toxin, while the fourth strain did not produce MCs. The mussels were sampled at 0, 7, 14, and 21 days by withdrawing haemocytes from their adductor muscle. In addition, a positive control was performed by exposing a subsample of the mussels to water containing cadmium chloride (CdCl(2)). Cell viability, measured with the Fluorescein Diacetate/Ethidium Bromide test, indicated that the MC concentrations, to which the mussels were exposed, were not cytotoxic to the haemocytes. The Comet assay performed on the haemocytes indicated that exposure to CdCl(2) produced a dose-responsive increase in DNA damage, demonstrating that mussel haemocytes were sensitive to DNA-damaging agents. DNA damage, measured as percentage tail DNA (%tDNA), was observed in mussels exposed to the three toxic Microcystis strains, but not in mussels exposed to the nontoxic strain. Toxin analysis of the cyanobacterial cultures confirmed that the three MC-producing strains exhibit different toxin profiles, with the two MC variants detected being MC-LF and MC-LR. Furthermore, the DNA damage that was observed appeared to be strain-specific, with high doses of MC-LF being associated with a higher level of genotoxicity than low concentrations of MC-LR. High levels of MC-LF also seemed to induce relatively more persistent DNA damage than small quantities of MC-LR. This study is the first to demonstrate that in vivo exposure to MC-producing strains of cyanobacteria induces DNA damage in the haemocytes of zebra mussels and confirms the sublethal toxicity of these toxins.

Bioaccumulation of the hepatotoxic microcystins in various organs of a freshwater snail from a subtropical Chinese lake, Taihu Lake, with dense toxic Microcystis blooms

In this paper, we describe the seasonal dynamics of three common microcystins (MCs; MC-RR, MC-YR, and MC-LR) in the whole body, hepatopancreas, intestine, gonad, foot, remaining tissue, and offspring of a freshwater snail, Bellamya aeruginosa, from Gonghu Bay of Lake Taihu, China, where dense toxic Microcystis blooms occur in the warm seasons. Microcystins were determined by liquid chromatography electrospray ionization mass spectrum. Microcystin (MC-RR + MC-YR + MC-LR) content of the offspring and gonad showed high positive correlation, indicating that microcystins could transfer from adult females to their young with physiological connection. This study is the first to report the presence of microcystins in the offspring of the adult snail. The majority of the toxins were present in the intestine (53.6%) and hepatopancreas (29.9%), whereas other tissues contained only 16.5%. If intestines are excluded, up to 64.3% of the toxin burden was allocated in the hepatopancreas. The microcystin content in the intestine, hepatopancreas, and gonad were correlated with the biomass of Microcystis and intracellular and extracellular toxins. Of the analyzed foot samples, 18.2% were above the tolerable daily microcystin intake recommended by the World Health Organization (WHO) for human consumption. This result indicates that public health warnings regarding human ingestion of snails from Taihu Lake are warranted. In addition, further studies are needed to evaluate the occurrence by Microcystis in relation to spatial and temporal changes in water quality.

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.

The role of ROS in microcystin-LR-induced hepatocyte apoptosis and liver injury in mice

Microcystin-LR (MC-LR) produced by cyanobacteria in diverse water systems is a potent specific hepatotoxin and has been documented to induce hepatocyte apoptosis and liver injury; however, the mechanisms have not been fully elucidated. In the present study, we investigated whether MC-LR stimulated ROS generation in the liver of mice and the role of ROS in the pathogenesis of MC-LR-induced liver injury in vivo. MC-LR treatment (60 microg/kg of body weight) for 12h prompted large amount of ROS generation in mice liver, upregulated the expression of Bax and Bid, caused the mitochondrial membrane potential (MMP) loss and hepatocyte apoptosis as well as liver injury. While pretreatment with antioxidants, oral administration of vitamin C (250mg/kg of body weight, dissolved in double distill water) and vitamin E (200mg/kg of body weight, dissolved in corn oil) per day for 3 days continually, significantly reduced the generation of ROS and effectively inhibited the MC-LR-induced hepatocyte apoptosis and liver injury, suggesting that ROS played a critical role in MC-LR-induced hepatocyte apoptosis and liver injury. The protective effect of vitamin C and E also suggested the potential interest in the clinical treatment of MC-LR-induced liver injury and hepatotoxicity.

Protection against the toxicity of microcystin-LR and cylindrospermopsin in Artemia salina and Daphnia spp. by pre-treatment with cyanobacterial lipopolysaccharide (LPS)

Purified cyanobacterial lipopolysaccharide (LPS) was not acutely toxic to three aquatic invertebrates (Artemia salina, Daphnia magna and Daphnia galeata) in immersion trials. However, pre-exposure (24 h) to 2 ngmL(-1) LPS increased the LC(50) of microcystin-LR significantly in all 3 species. Similar results were observed with A. salina pre-treated with the same concentration of cyanobacterial LPS and subsequently exposed to cylindrospermopsin, increasing the LC(50) by 8. The findings indicate the need to include exposures to defined combinations of cyanotoxins, and in defined sequences, to understand the contributions of individual cyanotoxins in accounting for cyanobacterial toxicity to invertebrates in natural aquatic environments.

Sorption, degradation and mobility of microcystins in Chinese agriculture soils: Risk assessment for groundwater protection

In the present paper, sorption, persistence, and leaching behavior of three microcystin variants in Chinese agriculture soils were examined. Based on this study, the values of capacity factor and slope for three MCs variants in three soils ranged from 0.69 to 6.00, and 1.01 to 1.54, respectively. The adsorption of MCs in the soils decreased in the following order: RR > Dha7 LR > LR. Furthermore, for each MC variant in the three soils, the adsorption rate in the soils decreased in the following order: soil A > soil C > soil B. The calculated half-time ranged between 7.9 and 17.8 days for MC-RR, 6.0-17.1 days for MC-LR, and 7.1-10.2 days for MC-Dha7 LR. Results from leaching experiments demonstrated that recoveries of toxins in leachates ranged from 0-16.7% for RR, 73.2-88.9% for LR, and 8.9-73.1% for Dha7 LR. The GUS value ranged from 1.48 to 2.06 for RR, 1.82-2.88 for LR, and 1.76-2.09 for Dha7 LR. Results demonstrated the use of cyanobacterial collections as plant fertilizer is likely to be unsafe in soils.

Inhibition of nucleotide excision repair (NER) by microcystin-LR in CHO-K1 cells

Microcystin-LR (MC-LR), a potent inhibitor of PP1 and PP2A protein phosphatases, is related to tumor promotion and initiation. Although the genotoxic properties of this toxin have been extensively investigated with a variety of non-mammalian and mammalian test systems, the existing results are contradictory. Based on our previous results regarding the impact of MC-LR on the processes of DNA repair we decided to examine in greater detail its effect on the capacity of nucleotide excision repair (NER). CHO-K1 cells were pre-treated with increasing doses of MC-LR (1, 10 and 20 microg/ml) and then exposed to UV radiation (25 J/m(2)). Apoptosis was analyzed to exclude the possibility of false positive results in the comet assay. The results suggest that MC-LR targets the nucleotide excision repair mechanisms by interference with the incision/excision phase as well as the rejoining phase of NER and leads to an increased level of UV-induced cytogenetic DNA damage in CHO-K1 cells.

Decrease in toxicity of microcystins LA and LR in drinking water by ozonation

Unchlorinated treated waters from two Australian reservoirs were spiked with microcystin-LA and -LR extracted from a toxic scum of Microcystis aeruginosa. The two waters had considerably different water quality and therefore ozone demands. The spiked sample waters were ozonated using the batch method of ozonation at a range of doses and the samples were analysed for toxins using high-performance liquid chromatography (HPLC). The toxin content of the samples was also determined using a protein phosphatase type 2A inhibition assay (PP2A) and toxicity via the standard mouse bioassay. The HPLC results correlated well with the PP2A results and toxicity tests for both waters. A loss of both toxins and toxicity was observed with increasing ozone dose, resulting in a complete loss of toxicity for both waters once an ozone residual had been achieved. At this ozone residual no toxin was detected using HPLC. The results indicate that microcystins are not transformed into toxic by-products.

The acute effects of microcystin LR on the transcription of nine glutathione S-transferase genes in common carp Cyprinus carpio L

The glutathione S-transferases play important roles in the detoxification of microcystin. In this experiment, nine glutathione S-transferase genes including cytosolic GSTs (rho, mu, theta, alpha and pi), mitochondrial GST (kappa) and microsomal GSTs (mGST1, mGST2 and mGST3) were cloned from common carp Cyprinus carpio. The mRNA abundance of each carp GST isoform in liver was analyzed by real time PCR. The relative changes after stimulation with microcystin LR were also analyzed: increased levels of transcription of GST alpha, rho and mGST3 isoforms were detected at 6h post stimulation; the transcription of mu, theta and mGST2 isoforms were relatively stable; and all the GST isoforms except GST kappa and rho recovered to original levels compared with controls at 72 h. It is suggested that MC-LR showed different effects on the transcription of nine carp GST isoforms.

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.

Toxic effects of Microcystis cell extracts on the reproductive system of male mice

In this paper, the reproductive toxicity of male mice treated with Microcystis aeruginosa cell extracts containing microcystins was examined. In contrast to the control group, male mice exposed intraperitoneally to 3.33 or 6.67 microg microcystins/kg body weight for 14 days had decreased mean body weight, and the mean absolute weight of the testes and epididymides was decreased. However, the mean relative weight of the testes increased compared to the controls. In addition, histological examination of microcystin-treated mice indicated that the testes were damaged and the space between the seminiferous tubules was more pronounced compared to control mice. The quality of mature sperm in the seminiferous tubules was also decreased in treated mice compared with the control group. Further studies showed that motility and viability of the sperm from microcystin-treated mice were reduced, but no significant difference was found in the concentration and abnormality of the sperm from treated mice compared to the control. This study indicated that microcystins had numerous toxic effects on the reproductive system of male mice.

Effect of process variables and natural organic matter on removal of microcystin-LR by PAC-UF

The release of cyanobacterial toxins, such as microcystin-LR, in drinking water supplies is of increasing concern. In this study, we investigated the use of ultrafiltration (UF) combined with adsorption on powdered activated carbon (PAC) for the removal of microcystin-LR from drinking water. Process variables examined included PAC type, PAC dosage, membrane characteristics (material and pore size), and the presence of natural organic matter (NOM). Due to greater mesopore volume, wood-based activated carbon was up to 4-times more effective at removing microcystin-LR than coconut-based carbon, depending on contact time. Cellulose acetate (CA) membranes with a molecular weight cutoff (MWCO) of 20,000 Da did not reject or adsorb microcystin-LR. Membranes composed of polyethersulfone (PES) of similar pore size, on the other hand, adsorbed microcystin-LR presumably through hydrophobic interactions. A PES membrane with a MWCO of 5000 Da sorbed microcystin-LR, and also rejected 8.4% of the toxin through a size exclusion mechanism. When PAC was coupled to UF using PES membranes, greater removal of microcystin-LR occurred compared to when CA membranes were used due to sorption of the toxin to the PES membrane surface. The presence of Suwannee River fulvic acid (SRFA) reduced microcystin-LR removal by PAC-UF, primarily due to competition between SRFA and microcystin-LR for sites on the PAC surface.

Reciprocal allelopathic responses between toxic cyanobacteria (Microcystis aeruginosa) and duckweed (Lemna japonica)

We examined cyanobacterial toxin production in response to direct exposure to an axenically cultured aquatic plant (Lemna japonica Landolt) using two toxic monoclonal strains of Microcystis aeruginosa Küzing (NIES strains 103 and 107). The patterns of nutrient concentrations were similar between the controls and treatments. The exposure to toxic M. aeruginosa inhibited growth in L. japonica, and exposure to the aquatic plant caused an increase in microcystin (MC) production and inhibited growth in M. aeruginosa. The respective biomasses of M. aeruginosa and L. japonica differed significantly between control and treatments (p<0.05). Both intracellular MC and extracellular MC productions were significantly higher in the treatment than in the control for both strains (p<0.01). Increased MC production in response to direct exposure to this aquatic plant could be an induced defense mediated by the release of allelochemicals from the plant. This study revealed reciprocal allelopathic responses between Microcystis and Lemna, which can be applied to the management of eutrophic waters as well as an important information concerning strategies for recovering eutrophic waters.

Impacts of microcystins on the feeding behaviour and energy balance of zebra mussels, Dreissena polymorpha: a bioenergetics approach

Microcystins are produced by bloom-forming cyanobacteria and pose significant health and ecological problems. To investigate the impacts of these biotoxins on the physiology of the zebra mussels, Dreissena polymorpha, a series of short-term feeding experiments were conducted in the laboratory. We used five microalgal diets consisting of single-cell suspensions of the green algae, Chlorella vulgaris, the diatom, Asterionella formosa, the cryptophyte, Cryptomonas sp. and two strains of the toxic cyanobacterium, Microcystis aeruginosa (strains CCAP 1450/06 and CCAP 1450/10). A sixth diet was a mixture of the diatom and the CCAP 1450/10 cyanobacterial strain. The low-toxicity strain CCAP 1450/06 contained 7.4 microg l(-1) of the MC-LR variant while the very toxic strain CCAP 1450/10 contained 23.8 microg l(-1) of MC-LR and 82.9 microg l(-1) of MC-LF. A flow-through system was designed to measure the following feeding parameters: clearance, filtration, ingestion and absorption rates. Ultimately the scope for growth (SFG) was determined as a net energy balance. We observed that mussels cleared the cyanobacterial species containing MC-LF (mean+/-95% confidence interval) at a significant lower rate (498+/-82 ml h(-1) g(-1) for the single cell suspension and 663+/-100 ml h(-1) g(-1) for the mixture diet) than all of the non-toxic species and the cyanobacterium containing MC-LR (all above 1l h(-1) g(-1)). The same pattern was observed with all the feeding parameters, particularly absorption rates. Furthermore, MC-LF caused an acute irritant response manifested by the production of 'pseudodiarrhoea', unusually fluid pseudofaeces, rich in mucus and MC-LF-producing Microcystis cells, ejected through the pedal gape of the mussels. This overall response therefore demonstrates selective rejection of MC-LF-producing cyanobacteria by zebra mussels, enhancing the presence of the very toxic MC-LF-producing M. aeruginosa in mixed cyanobacterial blooms and in the benthos. Finally, we observed that the SFG (mean+/-95% confidence interval) of mussels feeding on M. aeruginosa containing MC-LF was significantly lower (34.0+/-18.8 J h(-1) g(-1) for the single cell suspension and 83.1+/-53.0 J h(-1) g(-1) for the mixture diet) than for mussels ingesting non-toxic diets, except for C. vulgaris (all above 200 J h(-1)g(-1)). This reveals a sublethal, stressful effect of microcystins (particularly MC-LF) on the feeding behaviour and energy balance of the zebra mussel.

Mediation of glutamatergic receptors and nitric oxide on striatal dopamine release evoked by anatoxin-a. An in vivo microdialysis study

In this work, the involvement of ionotropic glutamatergic receptors and nitric oxide on striatal dopamine release induced by anatoxin-a was investigated in conscious and freely-moving rats. To study the participation of glutamatergic receptors, the effects of alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA)/kainate receptors antagonist, 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), and N-methyl-D-aspartate (NMDA) receptor antagonists, dizocilpine (MK-801) and d(-)-2-amino-5-phosphonopentanoic acid (APV), were examined. The perfusion of 3.5 mM anatoxin-a increased the extracellular dopamine levels to 701% relative to the basal. When CNQX was administered with 3.5 mM anatoxin-a, the increase of dopamine levels was 29% smaller than that observed with anatoxin-a alone. When MK-801 and APV were administered, the effect of anatoxin-a was attenuated 26% and 25% respectively in terms of that observed with anatoxin-a alone. And with CNQX plus MK-801, the effect of anatoxin-a was 53% inhibited in terms of the effect of anatoxin-a alone. These results suggest that the striatal dopamine release induced by anatoxin-a is partly mediated by activation of both ionotropic glutamatergic receptors. Since the neuronal form of nitric oxide synthase (nNOS) produces nitric oxide (NO) primarily in response to activation of NMDA receptors, it was tested if NO could play any role in the effect of anatoxin-a. Treatment with NOS inhibitors, L-nitro-arginine methyl ester (L-NAME) and d(-)-2-amino-5-phosphonopentanoic acid (7-NI), induced decreased anatoxin-a effects of 22% and 26% respectively. In conclusion, the present in vivo results demonstrate that anatoxin-a induced an indirect activation of ionotropic glutamatergic receptors (NMDA and AMPA/kainite receptors), which stimulate striatal dopamine release. On the other hand, activation of NMDA receptors may elicit NO increased levels enhancing dopamine release.

Biochemical and physiological responses after exposure to microcystins in the crab Chasmagnathus granulatus (Decapoda, Brachyura)

Microcystins are usually the predominant cyanotoxins present in both drinking and recreational waters after cyanobacterial blooms. Their classic toxic effect is hepatotoxicity through inhibition of serine/threonine phosphatases. However, recent studies also reported oxidative stress generation and disruption of ion regulation in aquatic organisms after microcystins exposure. In the present study, aqueous extracts of Microcystis aeruginosa were administered to the estuarine crab Chasmagnathus granulatus (Decapoda, Brachyura) by gavage in variable doses (from 34 to 860 microg kg(-1)) and exposure times (6, 12, and 72 h). A control group was exposed to saline solution. Analyzed variables included oxygen consumption, lipid peroxidation (LPO), enzyme activities (glutathione S-transferases or GST; alanine aminotransferase or ALT; aspartate aminotransferase or AST; and lactate dehydrogenase or LDH), glycogen, and microcystins content. Oxygen consumption increased in organisms exposed for 12h to 860 microg kg(-1) of microcystins and a similar result was observed after 72 h at doses equal to or higher than 34 microg kg(-1). LPO levels increased in doses equal to or higher than 34 microg kg(-1) after 72 h. GST and LDH activities increased after 12 h (at a dose of 860 microg kg(-1)), but ALT and AST activities remained unaltered in all experimental conditions. Glycogen content decreased after 72 h exposure at doses equal to or higher than 172 microg kg(-1). After 12h of exposure to 860 microg kg(-1) of microcystins, the concentration found in the hepatopancreas of C. granulatus was 13.17+/-0.56 microg kg(-1). In crabs exposed to doses higher than 172 microg kg(-1) during 72 h this value raised to 32.14+/-4.12 microg kg(-1). The obtained results indicated that microcystins exposure led the tissue to an oxidative stress condition (high LPO levels), at least in part favored by the augment of oxygen consumption, altering the glycogen metabolism. GST responses were only observed in the short-term experiment (12 h) and no effect on classical markers of vertebrate liver damage (ALT and AST) was observed. Although the hepatopancreas from C. granulatus accumulated a relatively low concentration of toxins, it was enough to induce physiological and biochemical disturbances.

Interactions between cyanobacteria and gastropods I. Ingestion of toxic Planktothrix agardhii by Lymnaea stagnalis and the kinetics of microcystin bioaccumulation and detoxification

The last two decades have been marked by an increasing occurrence of toxic cyanobacterial blooms in aquatic ecosystems. These pose an expanding threat to the environment and to human health. Among the intracellular toxins produced by cyanobacteria, microcystins (hepatotoxins) are the most frequent and widely studied. As an ubiquitous herbivore living in eutrophic freshwaters, the freshwater snail Lymnaea stagnalis (Gastropoda: Pulmonata) is particularly exposed to cyanobacteria. The toxic filamentous Planktothrix agardhii is common in temperate lakes and is, therefore, a potential food resource for gastropods. We have studied the consumption of P. agardhii by L. stagnalis juveniles and adults in the presence or absence of non-toxic food (lettuce) over a 5-weeks period. Intoxication was followed by a 3-week detoxification period when snails were fed only on lettuce. The kinetics of microcystin accumulation and detoxification in the gastropods were established using the ELISA analytical method. The results showed an ingestion of toxic P. agardhii by L. stagnalis, even in the presence of lettuce, and the absence of food selection regardless of the age of the snails. Juveniles and adults consumed the same number of cells per millilitre and consumption was proportional to food availability. On average, 63% of cyanobacteria available were taken up during the first 24h. After 5 weeks of intoxication, 61% of the toxins present in the ingested cyanobacterial cells had accumulated in snail tissues (95% in the digestive-genital gland complex) with a concentration up to 80.4+/-4.9microggDW(-1). Toxin accumulation was greater in the gastropods fed on P. agardhii alone than those fed on the mixed diet, and was also greater in juveniles than in adults. After the removal of toxic cyanobacteria, detoxification was rapid: 64% of the toxins disappeared from snail tissues during the first week, but microcystins were still detected after 3 weeks (on average, 3.5+/-0.9microggDW(-1)). These results are discussed in terms of potential contamination to the food web.

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.