Effect of different microcystin profiles on toxin bioaccumulation in common carp (Cyprinus carpio) larvae via Artemia nauplii

Health risk assessment of lake water contaminated with microcystins for fruit crop irrigation and farm animal drinking

The health risks linked to the consumption of microcystin-accumulating crops have been increasing worldwide in toxic cyanobloom-occurring regions. The bioaccumulation of microcystins (MCs) in agricultural produce at environmentally realistic concentrations is poorly investigated. In this field study, we assessed the health risks of MCs in raw water used for irrigating fruit crops (bioaccumulation) and watering farm animals in the Lalla Takerkoust agricultural region (Marrakesh, Morocco). Thus, MCs were extracted from water and fruit samples and quantified by enzyme-linked immunosorbent assay in order to calculate the health risk indicators. MCs posed a high health-risk level to poultry and horses, with estimated daily intakes (EDI) being 14- and 19-fold higher than the recommended limits (3.1 and 2.3 μg MC-LR L-1), respectively. Furthermore, pomegranate posed the same level of risk, with EDI being 22- and 53-fold higher than the limit dose (0.04 μg MC-LR kg-1) for adults and children, respectively. There was an urgent need for guidelines regarding water use and management in MC-polluted areas, besides the setup of nature-based tools for toxin removal from raw water used in farming practices. Moreover, MCs could contaminate the human food chain, which implies further investigations of their potential accumulation in livestock- and poultry-based food.

Killing effect of deinoxanthins on cyanobloom-forming Microcystis aeruginosa: Eco-friendly production and specific activity of deinoxanthins

Cyanobacterial blooms caused mainly by Microcystis aeruginosa could be controlled using chemical and biological agents such as H₂O₂, antagonistic bacteria, and enzymes. Little is known about the possible toxic effects of bacterial membrane pigments on M. aeruginosa cells. Deinococcus metallilatus MA1002 cultured under light increased the production of several carotenoid-like compounds by upregulating two deinoxanthin biosynthesis genes: crtO and cruC. The deinoxanthin compounds were identified using thin-layer chromatography, high-performance liquid chromatography, and liquid chromatography-mass spectrometry. D. metallilatus was cultured with agricultural by-products under light to produce the deinoxanthin compounds. Soybean meal, from six tested agricultural by-products, was selected as the single factor for making an economical medium to produce deinoxanthin compounds. The growth of axenic M. aeruginosa PCC7806, as well as other xenic cyanobacteria such as Cyanobium gracile, Trichormus variabilis, and Dolichospermum circinale, were inhibited by the deinoxanthin compounds. Scanning electron microscopic images showed the complete collapse of M. aeruginosa cells under deinoxanthin treatment, probably due to its interference with cyanobacterial membrane synthesis during cellular elongation. Deinoxanthins appeared to be nontoxic to other non-cyanobacteria such as Acinetobacter, Pseudomonas, Methylobacterium, and Bacillus species, suggesting that it can be a novel candidate for preventing cyanobacterial blooms through its specific activity against cyanobacteria.

Role of Rhizospheric Microbiota as a Bioremediation Tool for the Protection of Soil-Plant Systems from Microcystins Phytotoxicity and Mitigating Toxin-Related Health Risk

Frequent toxic cyanoblooms in eutrophic freshwaters produce various cyanotoxins such as the monocyclic heptapeptides microcystins (MCs), known as deleterious compounds to plant growth and human health. Recently, MCs are a recurrent worldwide sanitary problem in irrigation waters and farmland soils due to their transfer and accumulation in the edible tissues of vegetable produce. In such cases, studies about the persistence and removal of MCs in soil are scarce and not fully investigated. In this study, we carried out a greenhouse trial on two crop species: faba bean (Vicia faba var. Alfia 321) and common wheat (Triticum aestivum var. Achtar) that were grown in sterile (microorganism-free soil) and non-sterile (microorganism-rich soil) soils and subjected to MC-induced stress at 100 µg equivalent MC-LR L⁻¹. The experimentation aimed to assess the prominent role of native rhizospheric microbiota in mitigating the phytotoxic impact of MCs on plant growth and reducing their accumulation in both soils and plant tissues. Moreover, we attempted to evaluate the health risk related to the consumption of MC-polluted plants for humans and cattle by determining the estimated daily intake (EDI) and health risk quotient (RQ) of MCs in these plants. Biodegradation was liable to be the main removal pathway of the toxin in the soil; and therefore, bulk soil (unplanted soil), as well as rhizospheric soil (planted soil), were used in this experiment to evaluate the accumulation of MCs in the presence and absence of microorganisms (sterile and non-sterile soils). The data obtained in this study showed that MCs had no significant effects on growth indicators of faba bean and common wheat plants in non-sterile soil as compared to the control group. In contrast, plants grown in sterile soil showed a significant decrease in growth parameters as compared to the control. These results suggest that MCs were highly bioavailable to the plants, resulting in severe growth impairments in the absence of native rhizospheric microbiota. Likewise, MCs were more accumulated in sterile soil and more bioconcentrated in root and shoot tissues of plants grown within when compared to non-sterile soil. Thereby, the EDI of MCs in plants grown in sterile soil was more beyond the tolerable daily intake recommended for both humans and cattle. The risk level was more pronounced in plants from the sterile soil than those from the non-sterile one. These findings suggest that microbial activity, eventually MC-biodegradation, is a crucial bioremediation tool to remove and prevent MCs from entering the agricultural food chain.

Microcystins: Biogenesis, Toxicity, Analysis, and Control

Microcystins are cyclic peptide toxins formed by cyanobacteria. These toxins are recognized for their association with algal blooms, posing a significant threat to ecosystems and drinking water quality. Due to the growing environmental concerns they raise, a comprehensive review on microcystins' genesis, toxicity, and analytical methods for their quantitative determination is outlined. Genes, including the mcyABC cluster, regulate microcystin biogenesis. Bioanalytical experiments have identified key environmental factors, such as temperature and nitrogen availability, that promote microcystin production. Microcystin toxicity is explored based on its modulatory effects on protein phosphatases 1 and 2A in specific tissues and organs. Additionally, biochemical mechanisms of chelation, transportation, resultant oxidative stress, and tumor promotion abilities of microcystins are also discussed. Various analytical methods to separate, detect, and quantify microcystins, including the quantitative real-time polymerase chain reaction, enzyme-linked immunosorbent assay, nuclear magnetic resonance spectroscopy, and chromatographic platforms-linked tandem mass spectrometry (LC-MS) for unequivocal structural identification, are also reviewed. Since control of microcystins in water is of great necessity, both water treatment and mechanisms of abiotic transformation and microbial degradation are also discussed.

A new method for the simultaneous determination of cyanotoxins (Microcystins and Cylindrospermopsin) in mussels using SPE-UPLC-MS/MS

The aim of this study was to optimize the extraction conditions of Microcystin-LR (MC-LR), Microcystin-RR (MC-RR), Microcystin-YR (MC-YR) and Cylindrospermopsin (CYN) simultaneously from mussels by using response surface methodology (RSM) and to validate the method by a dual solid phase extraction (SPE) system combined with ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). The optimal parameters were: 90% MeOH (% v/v) for the extraction, a solvent/sample ratio of 75 and 15% MeOH in the extract before loading onto SPE. Mussels were spiked at 10; 37.5 and 75 ng g^-1 fresh weight (f.w) of the 4 toxins, showing linear ranges of 0.5-75 ng g^-1 f.w; low values for the limits of detection (0.01-0.39 ng g^-1 f.w.) and quantification (0.23-0.40 ng g^-1 f.w.); acceptable recoveries (70.37-114.03%) and relative standard deviation (%RSD_IP) values (2.61-13.73%). The method was successfully applied to edible mussels exposed to cyanobacterial extracts under laboratory conditions, and it could allow the monitoring of these cyanotoxins in environmental mussel samples.

Occurrence and toxicity of microcystin congeners other than MC-LR and MC-RR: A review

The occurrence of cyanobacterial toxins is being increasingly reported. This is a reason for concern as they can induce toxic effects both in humans and in the environment. Among them, microcystins (MCs) are the best described and most diverse group of cyanobacterial toxins, and MC-LR and MC-RR are the congeners most widely investigated. However, the number of MC variants has also increased in recent years. Some of these minority variants have been shown to have a different toxicokinetic and toxicodynamic profile, but research focused on them is still limited. Moreover, in some water bodies these minority variants can be the predominant toxins. Nonetheless, MC-LR is the only one used for risk evaluation purposes at present. In order to contribute to more realistic risk assessments in the future, the aim of this review was to compile the available information in the scientific literature regarding the occurrence and concentration of minority MCs in water and food samples, and their toxic effects. The data retrieved demonstrate the congener-specific toxicity of MCs, as well as many data gaps in relation to analytical or mechanistic aspects, among others. Therefore, further research is needed to improve the toxicological characterization of these toxins and the exposure scenarios.

Development and single-laboratory validation of a UHPLC-MS/MS method for quantitation of microcystins and nodularin in natural water, cyanobacteria, shellfish and algal supplement tablet powders

A simple, rapid UHPLC-MS/MS method has been developed and optimised for the quantitation of microcystins and nodularin in wide variety of sample matrices. Microcystin analogues targeted were MC-LR, MC-RR, MC-LA, MC-LY, MC-LF, LC-LW, MC-YR, MC-WR, [Asp3] MC-LR, [Dha7] MC-LR, MC-HilR and MC-HtyR. Optimisation studies were conducted to develop a simple, quick and efficient extraction protocol without the need for complex pre-analysis concentration procedures, together with a rapid sub 5min chromatographic separation of toxins in shellfish and algal supplement tablet powders, as well as water and cyanobacterial bloom samples. Validation studies were undertaken on each matrix-analyte combination to the full method performance characteristics following international guidelines. The method was found to be specific and linear over the full calibration range. Method sensitivity in terms of limits of detection, quantitation and reporting were found to be significantly improved in comparison to LC-UV methods and applicable to the analysis of each of the four matrices. Overall, acceptable recoveries were determined for each of the matrices studied, with associated precision and within-laboratory reproducibility well within expected guidance limits. Results from the formalised ruggedness analysis of all available cyanotoxins, showed that the method was robust for all parameters investigated. The results presented here show that the optimised LC-MS/MS method for cyanotoxins is fit for the purpose of detection and quantitation of a range of microcystins and nodularin in shellfish, algal supplement tablet powder, water and cyanobacteria. The method provides a valuable early warning tool for the rapid, routine extraction and analysis of natural waters, cyanobacterial blooms, algal powders, food supplements and shellfish tissues, enabling monitoring labs to supplement traditional microscopy techniques and report toxicity results within a short timeframe of sample receipt. The new method, now accredited to ISO17025 standard, is simple, quick, applicable to multiple matrices and is highly suitable for use as a routine, high-throughout, fast turnaround regulatory monitoring tool.

Are We Underestimating Benthic Cyanotoxins? Extensive Sampling Results from Spain

Microcystins (MCs) are potent hepatotoxins, and their presence in water bodies poses a threat to wildlife and human populations. Most of the available information refers to plankton, and much less is known about microcystins in other habitats. To broaden our understanding of the presence and environmental distribution of this group of toxins, we conducted extensive sampling throughout Spain, under a range of conditions and in distinct aquatic and terrestrial habitats. More than half of the tested strains were toxic; concentrations of the hepatotoxin were low compared with planktic communities, and the number of toxic variants identified in each sample of the Spanish strains ranged from 1–3. The presence of microcystins LF and LY (MC-LF and MC-LY) in the tested samples was significant, and ranged from 21.4% to 100% of the total microcystins per strain. These strains were only detected in cyanobacteria Oscillatoriales and Nostocales. We can report, for the first time, seven new species of microcystin producers in high mountain rivers and chasmoendolithic communities. This is the first report of these species in Geitlerinema and the confirmation of Anatoxin-a in Phormidium uncinatum. Our findings show that microcystins are widespread in all habitat types, including both aerophytic and endolithic peat bogs and that it is necessary to identify all the variants of microcystins in aquatic bodies as the commonest toxins sometimes represent a very low proportion of the total.

Microcystin-LR retards gonadal maturation through disrupting the growth hormone/insulin-like growth factors system in zebrafish

Recent studies have documented that microcystins (MCs) have potential toxic effects on growth and reproduction in fish. However, no systematic data exist on whether MCs cause gonadal development retardation through disrupting the growth hormone/insulin-like growth factors (GH/IGFs) system. To this end, zebrafish hatchlings (5 d post-fertilization) were exposed to 0, 0.3, 3 and 30µg/L microcystin-LR (MC-LR) for 90 d until they reached sexual maturity. Life-cycle exposure to MC-LR caused delayed ovarian maturation and sperm development along with ultrapathological lesions in the brain and liver. Moreover, the retarded gonadal development was accompanied by an inhibition of the GH/IGFs system, which was characterized by significant decreases in the transcriptional levels of brain gh (males only), hepatic igf2a and igf2b as well as gonadal igf1 (males only), igf3 and igf2r. These findings for the first time point to the influence of MC-LR on fish gonadal development via the GH/IGFs system. Also, sex-differential impairments suggested that gonadal development of males is more vulnerable than that of female to MC-LR. Our results provide evidence that MC-LR at environmentally relevant concentrations is able to induce impairments on fish gonadal development.

Toxicity of benthic dinoflagellates on grazing, behavior and survival of the brine shrimp Artemia salina

Harmful algae may differently affect their primary grazers, causing sub-lethal effects and/or leading to their death. The present study aim to compare the effects of three toxic benthic dinoflagellates on clearance and grazing rates, behavioral changes, and survival of Artemia salina. Feeding assays consisted in 1-h incubations of brine shrimps with the toxic Prorocentrum lima, Gambierdiscus excentricus and Ostreopsis cf. ovata and the non-toxic Tetraselmis sp. Brine shrimps fed unselectively on all toxic and non-toxic algal preys, without significant differences in clearance and ingestion rates. Acute toxicity assays were performed with dinoflagellate cells in two growth phases during 7-h to assess differences in cell toxicity to A. salina. Additionally, exposure to cell-free medium was performed to evaluate its effects on A. salina survival. The behavior of brine shrimps significantly changed during exposure to the toxic dinoflagellates, becoming immobile at the bottom by the end of the trials. Dinoflagellates significantly affected A. salina survival with 100% mortality after 7-h exposure to cells in exponential phase (all treatments) and to P. lima in stationary phase. Mortality rates of brine shrimps exposed to O. cf. ovata and G. excentricus in stationary phase were 91% and 75%, respectively. However, incubations of the brine shrimps with cell-free medium did not affect A. salina survivorship. Significant differences in toxic effects between cell growth phases were only found in the survival rates of A. salina exposed to G. excentricus. Acute exposure to benthic toxic dinoflagellates induced harmful effects on behavior and survival of A. salina. Negative effects related to the toxicity of benthic dinoflagellates are thus expected on their primary grazers making them more vulnerable to predation and vectors of toxins through the marine food webs.

Aerobic-heterotrophic nitrogen removal through nitrate reduction and ammonium assimilation by marine bacterium Vibrio sp. Y1-5

An aerobic marine bacterium Vibrio sp. Y1-5 was screened to achieve efficient nitrate and ammonium removal simultaneously and fix nitrogen in cells without N loss. Approximately 98.0% of nitrate (100mg/L) was removed in 48h through assimilatory nitrate reduction and nitrate reductase was detected in the cytoplasm. Instead of nitrification, the strain assimilated ammonium directly, and it could tolerate as high as 1600mg/L ammonium concentration while removing 844.6mg/L. In addition, ammonium assimilation occurred preferentially in the medium containing nitrate and ammonium with a total nitrogen (TN) removal efficiency of 80.4%. The results of nitrogen balance and Fourier infrared spectra illustrated that the removed nitrogen was all transformed to protein or stored as organic nitrogen substances in cells and no N was lost in the process. Toxicological studies with the brine shrimp species Artemia naupliia indicated that Vibrio sp. Y1-5 can be applied in aquatic ecosystems safely.

Determination of microcystin-LR in clams (Tapes decussatus) of two Sardinian coastal ponds (Italy)

The presence of microcystin-LR (MC-LR) was monitored in Tapes decussatus harvested in two Sardinian ponds (Cabras and Tortolì, Italy) in spring and summer. After solid phase extraction, samples were analyzed using a screening enzyme-linked immunosorbent assay (ELISA) followed by a liquid chromatographic coupled to tandem mass spectrometer (LC-MS/MS) analysis. Results obtained through the ELISA test showed the presence of microcystins with a maximum concentration in August for Cabras pond (0.55ng/g) and in September for Tortolì pond (0.85ng/g). The LC-MS/MS analysis did not confirm the presence of MC-LR suggesting that results obtained with the ELISA technique could be due to the presence of other microcystins. According to the tolerable daily intake suggested by the World Health Organization, these results hint that clams harvested in these ponds are safe for human health. These data can contribute to enrich the knowledge about the healthiness of Sardinian ponds and of their products.

Microcystin-tolerant Rhizobium protects plants and improves nitrogen assimilation in Vicia faba irrigated with microcystin-containing waters

Irrigation of crops with microcystins (MCs)-containing waters-due to cyanobacterial blooms-affects plant productivity and could be a way for these potent toxins entering the food chain. This study was performed to establish whether MC-tolerant rhizobia could benefit growth, nodulation, and nitrogen metabolism of faba bean plants irrigated with MC-containing waters. For that, three different rhizobial strains-with different sensitivity toward MCs-were used: RhOF96 (most MC-sensitive strain), RhOF125 (most MC-tolerant strain), or Vicz1.1 (reference strain). As a control, plants grown without rhizobia and fertilized by NH4NO3 were included in the study. MC exposure decreased roots (30-37 %) and shoots (up to 15 %) dry weights in un-inoculated plants, whereas inoculation with rhizobia protects plants toward the toxic effects of MCs. Nodulation and nitrogen content were significantly impaired by MCs, with the exception of plants inoculated with the most tolerant strain RhOF125. In order to deep into the effect of inoculation on nitrogen metabolism, the nitrogen assimilatory enzymes (glutamine synthetase (GS) and glutamate synthase (GOGAT)) were investigated: Fertilized plants showed decreased levels (15-30 %) of these enzymes, both in shoots and roots. By contrast, inoculated plants retained the levels of these enzymes in shoots and roots, as well as the levels of NADH-GOGAT activity in nodules. We conclude that the microcystin-tolerant Rhizobium protects faba bean plants and improves nitrogen assimilation when grown in the presence of MCs.

Microbiote shift in the Medicago sativa rhizosphere in response to cyanotoxins extract exposure

The bloom-containing water bodies may have an impact due to cyanotoxins production on other microorganisms and aquatic plants. Where such water is being used for crops irrigation, the presence of cyanotoxins may also have a toxic impact on terrestrial plants and their rhizosphere microbiota. For that purpose, PCR-based 454 pyrosequencing was applied to phylogenetically characterize the bacterial community of Medicago sativa rhizosphere in response to cyanotoxins extract. This analysis revealed a wide diversity at species level, which decreased from unplanted soil to root tissues indicating that only some populations were able to compete for nutrients and niches in this selective habitat. Gemmatimonas, Actinobacteria, Deltaproteobacteria and Opitutae mainly inhabited the bulk soil, whereas, the root-adhering soil and the root tissues were inhabited by Gammaproteobacteria and Alphaproteobacteria. The proportion of these populations fluctuated in response to cyanotoxins extract exposure. Betaproteobacteria proportion increased in the three studied compartments, whereas Gammaproteobacteria proportion decreased except in the bulk soil. This study revealed the potential toxicity of cyanotoxins extract towards Actinobacteria, Gemmatimonas, Deltaproteobacteria, and Gammaproteobacteria, however Clostridia, Opitutae and bacteria related with Betaproteobacteria, were stimulated denoting their tolerance. Altogether, these data indicate that crop irrigation using cyanotoxins containing water might alter the rhizosphere functioning.

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.

Evidence of trophic transfer of microcystins from the gastropod Lymnaea stagnalis to the fish Gasterosteus aculeatus

According to our previous results the gastropod Lymnaea stagnalis exposed to MC-producing cyanobacteria accumulates microcystins (MCs) both as free and covalently bound forms in its tissues, therefore representing a potential risk of MC transfer through the food web. This study demonstrates in a laboratory experiment the transfer of free and bound MCs from L. stagnalis intoxicated by MC-producing Planktothrix agardhii ingestion to the fish Gasterosteus aculeatus. Fish were fed during five days with digestive glands of L. stagnalis containing various concentrations of free and bound MCs, then with toxin-free digestive glands during a 5-day depuration period. MC accumulation was measured in gastropod digestive gland and in various fish organs (liver, muscle, kidney, and gills). The impact on fish was evaluated through detoxification enzyme (glutathion-S-transferase, glutathion peroxydase and superoxyde dismutase) activities, hepatic histopathology, and modifications in gill ventilation, feeding and locomotion. G. aculeatus ingestion rate was similar with intoxicated and toxin-free diet. Fish accumulated MCs (up to 3.96±0.14μgg^-1DW) in all organs and in decreasing order in liver, muscle, kidney and gills. Hepatic histopathology was moderate. Glutathion peroxydase was activated in gills during intoxication suggesting a slight reactive oxygen species production, but without any impact on gill ventilation. Intoxication via ingestion of MC-intoxicated snails impacted fish locomotion. Intoxicated fish remained significantly less mobile than controls during the intoxication period possibly due to a lower health condition, whereas they showed a greater mobility during the depuration period that might be related to an acute foraging for food. During depuration, MC elimination was total in gills and kidney, but partial in liver and muscle. Our results assess the MC transfer from gastropods to fish and the potential risk induced by bound MCs in the food web.

New potential antitumor pyrazole derivatives: synthesis and cytotoxic evaluation

New pyrazole derivatives were designed and synthesized as potential protein kinase inhibitors in the view to develop specific antitumor therapies. The structures of the compounds were elucidated using spectral and elemental analyses. The antitumor potential was estimated using wheat seeds and the general toxicity was evaluated by alternative methods, using invertebrate animals. One 3-aminopyrazole derivative emerged as a potential candidate for the development of future cytotoxic compounds.

Physiological and antioxidant responses of Medicago sativa-rhizobia symbiosis to cyanobacterial toxins (Microcystins) exposure

Toxic cyanobacteria in freshwaters can induce potent harmful effects on growth and development of plants irrigated with contaminated water. In this study, the effect of cyanobacteria extract containing Microcystins (MC) on Medicago sativa-rhizobia symbiosis was investigated in order to explore plants response through biomass production, photosynthetic pigment and antioxidant enzymes analysis: Peroxidase (POD), Polyphenoloxidase (PPO) and Catalase (CAT). Alfalfa plants were inoculated with two endosymbiotic rhizobial strains: RhOL1 (MC less sensitive strain) and RhOL3 (MC more sensitive strain), to evaluate the rhizobial contribution on the plant response cultured under cyanobacterial toxins stress. The two rhizobia strains were identified as Ensifer meliloti by sequence analysis of their rrs and atpD genes. The chronic exposure to MC extract showed shoot, root and nodules dry weight decrease, in both symbiosis cultures. The rate of decline in plants inoculated with RhOL3 was higher than that in symbiosis with RhOL1 mainly at 20 μg L(-1) of MC. Cyanotoxins also reduced photosynthetic pigment content and generated an oxidative stress observed at cellular level. POD, PPO and CAT activities were significantly increased in leaves, roots and nodules of alfalfa plants exposed to MC. These enzyme activities were higher in plants inoculated with RhOL3 especially when alfalfa plants were exposed to 20 μg L(-1) of MC. The present paper reports new scientific finding related to the behavior of rhizobia-M. sativa associations to MC (Microcystins) for later recommendation concerning the possible use of these symbiosis face to crops exposure to MC contaminated water irrigation.

Phytotoxic effects of a natural bloom extract containing microcystins on Lycopersicon esculentum

The cyanobacterial toxins microcystins (MC) are known to affect many processes in plants. Their presence in the water used for irrigation may have considerable impact on the survivorship, growth and development of plants. In this study, a crude extract of a toxic cyanobacterial bloom from "Lalla Takerkoust" reservoir (Morocco) was used to study the effects of extract containing MC on tomato plants (Lycopersicon esculentum). Five MC variants: MC-LR, MC-FR, MC-LY, MC-(H4)-YR and DMC-LR were identified by HPLC in the cyanobacterial extract. Exposure of the seeds to the crude extract (containing 22.24 μg MC mL(-1)) caused a reduction of germination up to 85%. Experiments showed that 30 days exposure of plant to the cyanobacterial extract containing MC caused inhibition of L. esculentum growth and productivity, as well as harmful effects on photosystem II activity, measured by Fv/Fm fluorescence. An accumulation of nutrients Na(+), K(+) and Ca(2+) was also registered. The activity of peroxidase and phenolic content indicated that the extract caused an oxidative stress. The tissue necrosis of leaves was also a consequence of MC exposure indicating a disorder in the exposed plant metabolism.

Bioaccumulation of microcystins by fish associated with a persistent cyanobacterial bloom in Lago de Patzcuaro (Michoacan, Mexico)

Lago de Patzcuaro is a historically important freshwater fishery in Mexico. The lake is presently characterized by a persistent bloom of cyanobacteria, specifically dominated by recognized producers of toxic microcystins (MCYSTs). We evaluated MCYSTs in sestonic and dissolved fractions of the water column, as well as representative fish species (silversides, Chirostoma spp.; Goodea sp.; and carp, Cyprinus carpio) obtained from local markets and small commercial catches during the bloom. Samples were evaluated primarily by enzyme-linked immunosorbent assay (ELISA), and secondarily by protein phosphatase (PPase) inhibition assay and liquid chromatography-mass spectrometry (LC-MS). Sestonic MCYST concentration (0.02-0.36 µg/L) generally correlated inversely with distance from the bloom, supporting the bloom as the source of the toxin. Several MCYST variants, including MC-LR, -LA and -LY, as well as didemethyl variants, were identified by LC-MS/MS analysis. All three species of fish bioaccumulated MCYSTs in relevant tissues, and toxin content correlated with trophic level, with highest and lowest levels measured in phytoplanktivorous and zooplanktivorous representatives, respectively. Detection of MCYST in silversides and Goodea sp. is particularly relevant because both are consumed in their entirety, including viscera (e.g., liver) known to primarily accumulate MCYST. These results indicate that Lago de Patzcuaro is indeed characterized by a toxigenic bloom, and that commercially important fish species from the lake accumulate toxic MCYST in tissues relevant to human consumption. As such, this system may represent an ideal model of the trophic transfer of MCYSTs and its relevance to human and environmental health.