Effects on growth and oxidative stress status of rice plants (Oryza sativa) exposed to two extracts of toxin-producing cyanobacteria (Aphanizomenon ovalisporum and Microcystis aeruginosa)

Aptameric photonic structure-based optical biosensor for the detection of microcystin

An optical photonic biosensor for the detection of microcystin (MC) has been developed using an aptamer-immobilized interpenetrating polymeric network (IPNaptamer) intertwined with solid-state cholesteric liquid crystals (CLCsolids). The IPN was constructed with a polyacrylic acid hydrogel (PAA). Aptamer immobilization enhances polarity while blocking hydrogen bonding between the carboxylic groups of PAA-IPN hydrogel, thereby increasing the swelling ratio of the PAA-IPN hydrogel. This leads to an expansion in the helical pitch of the corresponding IPNaptamer-CLCsolid biosensor chip and results in a red-shift in the reflected color. Upon exposure to an aqueous MC solution, the IPNaptamer-CLCsolid biosensor chip exhibits aptamer-mediated engulfment of MC, resulting in reduced polarity of the IPNaptamer complex and a consequential blue-shift in the biosensor chip color occurred. The wavelength shift of the IPNaptamer-CLCsolid biosensor chip demonstrates a linear change with an increase in MC concentration from 3.8 to 150 nM, with a limit of detection of 0.88 nM. This novel optical biosensor is characterized by its low cost, simplicity, selectivity, and sensitivity, offering a promising strategy for designing similar toxin biosensors through the modification of biological receptors.

Role of root plasma membrane H+-ATPase in enhancing Cucumis sativus adaptation to microcystins

Microcystins (MCs) are the most widespread and hazardous cyanotoxins posing a huge threat to agro-ecosystem by irrigation. Some adaptive metabolisms can be initiated at the cellular and molecular levels of plant to survive environmental change. To find ways to improve plant tolerance to MCs after recognizing adaptive mechanism in plant, we studied effects of MCs on root morphology, mineral element contents, root activity, H+-ATPase activity, and its gene expression level in cucumber during exposure and recovery (without MCs) periods. After being exposed to MCs (1, 10, 100 and 1000 μg L-1) for 7 days, we found 1 μg L-1 MCs did not affect growth and mineral elements in cucumber. MCs at 10 μg ·L-1 increased root activity and H+-ATPase activity partly from upregulation of genes (CsHA2, CsHA3, CsHA8, and CsHA9) expression, to promote nutrient uptake. Then, the increase in NO3-, Fe, Zn, and Mn contents could contribute to maintaining root growth and morphology. Higher concentration MCs (100 or 1000 µg L-1) inhibited root activity and H+-ATPase activity by downregulating expression of genes (CsHA2, CsHA3, CsHA4, CsHA8, CsHA9, and CsHA10), decreased contents of nutrient elements except Ca largely, and caused root growing worse. After a recovery, the absorption activity and H+-ATPase activity in cucumber treated with10 μg L-1 MCs were closed to the control whereas all parameters in cucumber treated 1000 μg L-1 MCs were even worse. All results indicate that the increase in H+-ATPase activity can enhance cucumber tolerance to MC stress by regulating nutrient uptake, especially when the MCs occur at low concentrations.

Co-cultures from Plants and Cyanobacteria: A New Way for Production Systems in Agriculture and Bioprocess Engineering

Due to the global increase in the world population, it is not possible to ensure a sufficient food supply without additional nitrogen input into the soil. About 30-50% of agricultural yields are due to the use of chemical fertilizers in modern times. However, overfertilization threatens biodiversity, such as nitrogen-loving, fast-growing species overgrow others. The production of artificial fertilizers produces nitrogen oxides, which act as greenhouse gases. In addition, overfertilization of fields also releases ammonia, which damages surface waters through acidification and eutrophication. Diazotrophic cyanobacteria, which usually form a natural, stable biofilm, can fix nitrogen from the atmosphere and release it into the environment. Thus, they could provide an alternative to artificial fertilizers. In addition to this, biofilms stabilize soils and thus protect against soil erosion and desiccation. This chapter deals with the potential of cyanobacteria as the use of natural fertilizer is described. Possible partners such as plants and callus cells and the advantages of artificial co-cultivation will be discussed later. In addition, different cultivation systems for studying artificial co-cultures will be presented. Finally, the potential of artificial co-cultures in the agar industry will be discussed.

Tracing the fate of microcystins from irrigation water to food chains: Studies with Fragaria vulgaris and Meriones shawi

Microcystins (MCs) are cyanobacterial toxins that can negatively impact human and animal health. This study investigated the bioaccumulation, transfer, depuration, and health risks of MCs in strawberry plants (Fragaria vulgaris) and Meriones shawi animals. The plants were irrigated with 1, 5, 10, and 20 μg/L MCs for 60 days (bioaccumulation phase) and then with clean water for 30 days (depuration phase). The harvested plants (roots and leaves) were then prepared in an aliquot form and used as feed for Meriones shawi. Liquid chromatography-mass spectrometry (LC/MS/MS) was used to measure MC concentrations in plant and animal tissues. The bioaccumulation of MCs was found to be highest in the roots, followed by leaves, fruits, liver, stomach, and fecal matter. The bioaccumulation factor (BAF) was highest in perlite (8.48), followed by roots (5.01), leaves (1.55), stomach (0.87), and fecal matter (1.18), indicating that the parts with high bioaccumulation factor had high translocation of MCs. The transfer of MCs to animal organs was low, and the daily toxin intake of adult consumers of strawberry fruit irrigated with 1, 5, 10, and 20 μg/L MC did not exceed the WHO-recommended limit of 0.04 μg MC-LR/Kg of bw/day. However, fruits from plants irrigated with 10 and 20 μg/L may pose a moderate health risk to children (25 Kg bw), and Meriones' consumption of leaves may pose a significant health risk. After the depuration phase, MC concentration in perlite, roots, leaves, and fruits decreased, indicating that depuration reduced the danger of MC transmission and bioaccumulation. The study also found that glutathione reductase and glutathione S-transferase activity were essential in the depuration of MCs in the tested plants. The findings suggest that legislation regulating the quality of irrigation water in terms of MC concentrations is necessary to prevent detrimental consequences to crops and human exposure.

Effect of cold food storage techniques on the contents of Microcystins and Cylindrospermopsin in leaves of spinach (Spinacia oleracea) and lettuce (Lactuca sativa)

The presence of Cylindrospermopsin (CYN) and Microcystins (MCs) in vegetables is considered as a significant worldwide toxicological risk. Thus, this work aims to assess for the first time the impact of refrigeration (4 °C) and freezing (-20 °C) on the levels of CYN, MCs and their mixtures (CYN + MCs) in lettuce and spinach. Samples were spiked with 750 μg cyanotoxins/g dry weight (d.w.). Several storage conditions were studied: refrigeration after 24, 48 h and 7 days, and freezing for 7 days, 1 and 3 months. Cyanotoxin concentrations were determined by Ultra Performance Liquid Chromatography-Tandem Mass Spectrometry (UPLC-MS/MS). For CYN, refrigeration at 48 h and 7 days was effective to decrease its concentrations up to 26% and 32%, respectively, in spinach. For MCs, refrigeration was only effective in lettuce compared to spinach, showing an important decrease of 80.3% MC-LR and 85.1% MC-YR. In spinach, CYN was stable after 3 months freezing, whereas MC contents were still reduced up to 44%. Overall, cyanotoxins were less stable in the mixture compared to individual toxins for both processes, and the effect of these storage techniques were toxin and food-specific. Further studies of cyanotoxins in foods are required for evaluating the risk for humans.

The Beneficial Effects of Cyanobacterial Co-Culture on Plant Growth

Cyanobacteria are ubiquitous phototrophic prokaryotes that find a wide range of applications in industry due to their broad product spectrum. In this context, the application of cyanobacteria as biofertilizers and thus as an alternative to artificial fertilizers has emerged in recent decades. The benefit is mostly based on the ability of cyanobacteria to fix elemental nitrogen and make it available to the plants in a usable form. However, the positive effects of co-cultivating plants with cyanobacteria are not limited to the provision of nitrogen. Cyanobacteria produce numerous secondary metabolites that can be useful for plants, for example, they can have growth-promoting effects or increase resistance to plant diseases. The effects of biotic and abiotic stress can as well be reduced by many secondary metabolites. Furthermore, the biofilms formed by the cyanobacteria can lead to improved soil conditions, such as increased water retention capacity. To exchange the substances mentioned, cyanobacteria form symbioses with plants, whereby the strength of the symbiosis depends on both partners, and not every plant can form symbiosis with every cyanobacterium. Not only the plants in symbiosis benefit from the cyanobacteria, but also vice versa. This review summarizes the beneficial effects of cyanobacterial co-cultivation on plants, highlighting the substances exchanged and the strength of cyanobacterial symbioses with plants. A detailed explanation of the mechanism of nitrogen fixation in cyanobacterial heterocysts is given. Finally, a summary of possible applications of co-cultivation in the (agrar-)industry is given.

Plant-cyanobacteria interactions: Beneficial and harmful effects of cyanobacterial bioactive compounds on soil-plant systems and subsequent risk to animal and human health

Plant-cyanobacteria interactions occur in different ways and at many different levels, both beneficial and harmful. Plant-cyanobacteria interactions, as a beneficial symbiosis, have long been demonstrated in rice-growing areas (Poaceae) where the most efficient nitrogen-fixing cyanobacteria are present in paddies. Moreover, cyanobacteria may in turn produce and/or secrete numerous bioactive compounds that have plant growth-promoting abilities or that may make the plant more resistant to abiotic or biotic stress. In recent years, there has been a growing worldwide interest in the use of cyanobacterial biomass as biofertilizers to replace chemical fertilizers, in part to overcome increasing organic-farming demands. However, the potential presence of harmful cyanotoxins has delayed the use of such cyanobacterial biomass, which can be found in large quantities in freshwater ecosystems around the world. In this review, we describe the existing evidence for the positive benefit of plant-cyanobacteria interactions and discuss the use of cyanobacterial biomass as biofertilizers and its growing worldwide interest. Although mass cyanobacterial blooms and scums are a current and emerging threat to the degradation of ecosystems and to animal and human health, they may serve as a source of numerous bioactive compounds with multiple positive effects that could be of use as an alternative to chemical fertilizers in the context of sustainable development.

Co-occurrence of co-contaminants: Cyanotoxins and microplastics, in soil system and their health impacts on plant - A comprehensive review

Cyanotoxins (CTX) and micro/nanoplastics (M/NP) are ubiquitously distributed in every environmental compartment. But the distribution, abundance and associated ecological risks of CTX are still poorly understood in soil system. On the other hand, M/NP could serve as vectors for persistent organic/inorganic pollutants in the natural environment through the sorption of pollutants onto them. Thus, co-occurrence of CTX and M/NP in soils suggests the sorption of CTX onto M/NP. So, major aim of this review is to understand the relevance of CTX and M/NP in soils as co-contaminants, possible interactions between them and ecological risks of CTX in terms of phytotoxicity. In this study, we comprehensively discuss different sources and fate of CTX and the sorption of CTX onto M/NP in soil system, considering the partition coefficient of different phases of soil and mass balance. Phytotoxicity of CTX, CTX mixture and co-contaminants has also been discussed with insights on the mechanism of action. This study indicates the need for the evaluation of sorption between co-contaminants, especially CTX and M/NP, and their phytotoxicity assessment using environmentally relevant concentrations.

Diversity of bioactive compound content across 71 genera of marine, freshwater, and terrestrial cyanobacteria

Cyanobacterial blooms have increased in frequency, distribution, and intensity due to climate change and anthropogenic nutrient input. The release of bioactive compounds accumulated in these blooms can affect the health of humans and the environment. The co-occurrence of bioactive metabolites is well-documented in bloom samples from marine and freshwater ecosystems, with fewer reports from unialgal isolates. Cyanobacteria also are important terrestrial ecosystem components, especially in drylands, but reports on bioactive molecules from terrestrial cyanobacteria are sparse. This study determined bioactive metabolite profiles for 71 genera of cyanobacteria from seven orders isolated from freshwater (12 genera), marine (15 genera), and terrestrial (44 genera) habitats originally. Cultures were harvested for bioactive metabolites when entering the late-exponential phase for all 157 strains, and 33 were sampled at both early and late exponential phases. Bioactive metabolites were analyzed using an ultra high performance/pressure liquid chromatography in-line with a time-of-flight mass spectrometer. Overall, 12 bioactive classes of the 28 identified were ubiquitous in all samples. On average, each freshwater genus produced ∼12 bioactive classes, whereas each marine genus contained > 4 bioactive classes, and each terrestrial genus contained ∼6 bioactive classes. While 10 of 12 freshwater genera produced at least 10 bioactive classes, only a single genus each from marine and terrestrial habitats had the same number of bioactive classed accumulated. Aeruginosin was found in 58 of 71 total genera, carmabin in 51 of 71 genera, and anabaenopeptin in 48 of 71 genera. Chemotaxonomic use of these secondary metabolites may help resolve higher-level genetic classification(s). An additional growth curve experiment showed that bioactive metabolites were produced at both early and late exponential growth phases. The bioactive metabolite accumulation pattern between early and late exponential phases differed by bioactive classes, genera, and habitats. This survey of 55 bioactive classes in cyanobacteria isolated from freshwater, marine, and terrestrial habitats (71 genera) provides as one of the first systematic bioactive metabolite profiles for cyanobacteria, which should be useful in environmental and drinking water management. Further, it offers novel insights about the toxin potential of selected terrestrial cyanobacteria.

Oxidative stress induced in rice suspension cells exposed to microcystin-LR at environmentally relevant concentrations

Microcystins (MCs) are cyclic heptapeptide hepatotoxins that are highly soluble in water and can be transferred to farmland through irrigation with potentially substantial effects on crops, especially rice. In order to investigate the possible negative effects of microcystin-LR (MC-LR) on rice, the oxidative stress induced in rice suspension cells exposed to MC-LR at environmentally relevant concentrations (0.05, 0.5, 5.0, and 50.0 μg·L^-1) was investigated. Results showed that the exposure to MC-LR at 0.5-50.0 μg·L^-1 resulted in a significant decline in viability of rice suspension cells and an increase in malondialdehyde (MDA) contents. In the 50.0-μg·L^-1 MC-LR treatment group, the content of MDA was as much as 5.39 times that of the control group after 6 days of exposure. The excess MDA production indicated that MC-LR exposure has caused lipid peroxidation damage in rice cells, whereas these negative effects could be recovered over time when suspension cells were exposed to low concentration of MC-LR (0.05 μg·L^-1). When exposed to MC-LR for 3 days, the O₂^- content in all treatment groups increased significantly compared with the control group. Additionally, the antioxidant system of rice suspension cells initiated a positive stress response to MC-LR exposure. Indeed, peroxidase (POD) played an active role in the removal of reactive oxygen species (ROS) in rice suspension cells during the early period of exposure, while total superoxide dismutase (T-SOD) was induced after 6 days. Similarly, after 6 days of exposure, the anti-superoxide anion free radical activity (ASAFR), glutathione (GSH), and glutathione-S transferase (GST) in rice suspension cells were higher than that in the control group. These results provided a comprehensive understanding of the exposure time- and dose-dependent oxidative stress induced by the environmentally relevant concentrations of MC-LR in rice suspension cells.

Subcellular Alterations Induced by Cyanotoxins in Vascular Plants-A Review

Phytotoxicity of cyanobacterial toxins has been confirmed at the subcellular level with consequences on whole plant physiological parameters and thus growth and productivity. Most of the data are available for two groups of these toxins: microcystins (MCs) and cylindrospermopsins (CYNs). Thus, in this review we present a timely survey of subcellular cyanotoxin effects with the main focus on these two cyanotoxins. We provide comparative insights into how peculiar plant cellular structures are affected. We review structural changes and their physiological consequences induced in the plastid system, peculiar plant cytoskeletal organization and chromatin structure, the plant cell wall, the vacuolar system, and in general, endomembrane structures. The cyanotoxins have characteristic dose-and plant genotype-dependent effects on all these structures. Alterations in chloroplast structure will influence the efficiency of photosynthesis and thus plant productivity. Changing of cell wall composition, disruption of the vacuolar membrane (tonoplast) and cytoskeleton, and alterations of chromatin structure (including DNA strand breaks) can ultimately lead to cell death. Finally, we present an integrated view of subcellular alterations. Knowledge on these changes will certainly contribute to a better understanding of cyanotoxin–plant interactions.

Review on Cyanobacterial Studies in Portugal: Current Impacts and Research Needs

Cyanobacteria have long been associated with harmful effects on humans, animals and aquatic biota. Cyanotoxins are their most toxic metabolite. This review summarizes the current research, impacts and future needs in cyanobacterial studies undertaken in Portugal, the southernmost country of Europe, and with a recent multiplication of cyanotoxicity due to climate change events. Microcystins are still the most prevalent, studied and the only regulated cyanotoxins in Portuguese freshwater systems much like most European countries. With the development of some tools, particularly in molecular studies, the recent discovery of cylindrospermopsins, anatoxins and saxitoxins, both genes and toxins, in North and Center ecosystems of our country highlight current impacts that overall communities are facing with increased risks of exposure and uptake to cyanotoxins. Research needs encompass the expansion of studies at all aspects due to the uprising of these cyanotoxins and reinforces the urgent need of increasing the frequency of surveillance to achieve tangible effects of cyanotoxins in Portugal to ultimately implement regulations on cylindrospermopsins, anatoxins and saxitoxins worldwide.

Algal Toxic Compounds and Their Aeroterrestrial, Airborne and other Extremophilic Producers with Attention to Soil and Plant Contamination: A Review

The review summarizes the available knowledge on toxins and their producers from rather disparate algal assemblages of aeroterrestrial, airborne and other versatile extreme environments (hot springs, deserts, ice, snow, caves, etc.) and on phycotoxins as contaminants of emergent concern in soil and plants. There is a growing body of evidence that algal toxins and their producers occur in all general types of extreme habitats, and cyanobacteria/cyanoprokaryotes dominate in most of them. Altogether, 55 toxigenic algal genera (47 cyanoprokaryotes) were enlisted, and our analysis showed that besides the “standard” toxins, routinely known from different waterbodies (microcystins, nodularins, anatoxins, saxitoxins, cylindrospermopsins, BMAA, etc.), they can produce some specific toxic compounds. Whether the toxic biomolecules are related with the harsh conditions on which algae have to thrive and what is their functional role may be answered by future studies. Therefore, we outline the gaps in knowledge and provide ideas for further research, considering, from one side, the health risk from phycotoxins on the background of the global warming and eutrophication and, from the other side, the current surge of interest which phycotoxins provoke due to their potential as novel compounds in medicine, pharmacy, cosmetics, bioremediation, agriculture and all aspects of biotechnological implications in human life.

Beyond Microcystins: Cyanobacterial Extracts Induce Cytoskeletal Alterations in Rice Root Cells

Microcystins (MCs) are cyanobacterial toxins and potent inhibitors of protein phosphatases 1 (PP1) and 2A (PP2A), which are involved in plant cytoskeleton (microtubules and F-actin) organization. Therefore, studies on the toxicity of cyanobacterial products on plant cells have so far been focused on MCs. In this study, we investigated the effects of extracts from 16 (4 MC-producing and 12 non-MC-producing) cyanobacterial strains from several habitats, on various enzymes (PP1, trypsin, elastase), on the plant cytoskeleton and H₂O₂ levels in Oryza sativa (rice) root cells. Seedling roots were treated for various time periods (1, 12, and 24 h) with aqueous cyanobacterial extracts and underwent either immunostaining for α-tubulin or staining of F-actin with fluorescent phalloidin. 2,7-dichlorofluorescein diacetate (DCF-DA) staining was performed for H₂O₂ imaging. The enzyme assays confirmed the bioactivity of the extracts of not only MC-rich (MC+), but also MC-devoid (MC−) extracts, which induced major time-dependent alterations on both components of the plant cytoskeleton. These findings suggest that a broad spectrum of bioactive cyanobacterial compounds, apart from MCs or other known cyanotoxins (such as cylindrospermopsin), can affect plants by disrupting the cytoskeleton.

Toxic compounds produced by cyanobacteria belonging to several species of the order Nostocales: A review

Cyanobacteria are well recognised as producers of a wide range of natural compounds that are in turn recognised as toxins that have potential and useful applications in the future as pharmaceutical agents. The order Nostocales, which is largely overlooked in this regard, has become increasingly recognised as a source of toxin producers including Anabaena, Nostoc, Hapalosiphon, Fischerella, Anabaenopsis, Aphanizomenon, Gloeotrichia, Cylindrospermopsis, Scytonema, Raphidiopsis, Cuspidothrix, Nodularia, Stigonema, Calothrix, Cylindrospermum and Desmonostoc species. The toxin compounds (i.e., microcystins, nodularin, anatoxins, ambiguines, fischerindoles and welwitindolinones) and metabolites are about to have a destructive effect on both inland and aquatic environment aspects. The present review gives an overview of the various toxins that are extracted by the order Nostocales. The current research suggests that these compounds that are produced by cyanobacterial species have promising future considerations as potentially harmful algae and as promising leads for drug discovery.

Uptake and Effects of Cylindrospermopsin: Biochemical, Physiological and Biometric Responses in The Submerged Macrophyte Egeria densa Planch

Cylindrospermopsin (CYN) is being detected in surface waters more commonly and frequently worldwide. This stable, extracellular cyanotoxin causes protein synthesis inhibition, thus posing a risk to aquatic biota, including macrophytes, which serve as primary producers. Nevertheless, data regarding the effects caused by environmental concentrations of CYN is still limited. In the presented study, the uptake of CYN at environmental concentrations by the submerged macrophyte Egeria densa was investigated. Bioaccumulation, changes in the plant biomass, as well as shoot-length were assessed as responses. Variations in the cellular H2O2 levels, antioxidative enzyme activities, as well as concentrations and ratios of the photosynthetic pigments were also measured. E. densa removed 54% of CYN within 24 h and up to 68% after 336 h; however, CYN was not bioaccumulated. The antioxidative enzyme system was activated by CYN exposure. Pigment concentrations decreased with exposure but normalized after 168 h. The chlorophyll a to b ratio increased but normalized quickly thereafter. Carotenoids and the ratio of carotenoids to total chlorophylls increased after 96 h suggesting participation in the antioxidative system. Growth stimulation was observed. The ability to remove CYN and resistance to CYN toxicity within 14 days proved E. densa as suitable for phytoremediation; nonetheless, prolonged exposure (32 days) resulted in adverse effects related to CYN uptake, which needs to be studied further.

The effects of microcystin-LR in Oryza sativa root cells: F-actin as a new target of cyanobacterial toxicity

Microcystins are toxins produced by cyanobacteria, notorious for negatively affecting a wide range of living organisms, among which several plant species. Although microtubules are a well-established target of microcystin toxicity, its effect on filamentous actin (F-actin) in plant cells has not yet been studied. Τhe effects of microcystin-LR (MC-LR) and an extract of a microcystin-producing freshwater cyanobacterial strain (Microcystis flos-aquae TAU-MAC 1510) on the cytoskeleton (F-actin and microtubules) of Oryza sativa (rice) root cells were studied with light, confocal, and transmission electron microscopy. Considering the role of F-actin in endomembrane system distribution, the endoplasmic reticulum and the Golgi apparatus in extract-treated cells were also examined. F-actin in both MC-LR- and extract-treated meristematic and differentiating root cells exhibited time-dependent alterations, ranging from disorientation and bundling to the formation of ring-like structures, eventually resulting in a collapse of the F-actin network after longer treatments. Disorganization and eventual depolymerization of microtubules, as well as abnormal chromatin condensation were observed following treatment with the extract, effects which could be attributed to microcystins and other bioactive compounds. Moreover, cell cycle progression was inhibited in extract-treated roots, specifically affecting the mitotic events. As a consequence of F-actin network disorganization, endoplasmic reticulum elements appeared stacked and diminished, while Golgi dictyosomes appeared aggregated. These results support that F-actin is a prominent target of MC-LR, both in pure form and as an extract ingredient. Endomembrane system alterations can also be attributed to the effects of cyanobacterial bioactive compounds (including microcystins) on the F-actin cytoskeleton.

Detection of cylindrospermopsin and its decomposition products in raw and cooked fish (Oreochromis niloticus) by analytical pyrolysis (Py-GC/MS)

The presence of the toxin cylindrospermopsin is increasingly frequent in samples from different ecosystems and it is a serious problem both at environmental level and for animal and human health. To be able to prevent CYN exposure risk, it is important to have suitable analytical methods, but also quick and economical ones. Analytical pyrolysis coupled to GC/MS (Py-GC/MS) represents an important alternative for the rapid detection, characterization or "fingerprinting" of different materials. However, it has been less studied with cyanotoxins up to date. The present work aims to investigate: 1) the suitability of Py-GC/MS for detection of CYN and its decomposition products in raw and cooked fish samples before consumption and 2) the influence of the different cooking methods on the presence of different CYN degradation products detected by Py-GC/MS. For first time, these results present that Py-GC/MS could be a rapid and economical alternative for the detection and monitoring of CYN and its degradation products (DP. m/z 290.1, 169.1 and 336.2) in raw or cooked fish. Moreover, the changes induced in CYN and DP by cooking could be amenable and detected by Py-GC/MS.

Uptake, Growth, and Pigment Changes in Lemna minor L. Exposed to Environmental Concentrations of Cylindrospermopsin

Cylindrospermopsin (CYN)-producing cyanobacterial blooms such as Raphidiopsis, Aphanizomenon, Anabaena, Umezakia, and Lyngbya spp. are occurring more commonly and frequently worldwide. CYN is an environmentally stable extracellular toxin, which inhibits protein synthesis, and, therefore, can potentially affect a wide variety of aquatic biota. Submerged and floating macrophytes, as primary producers in oligotrophic habitats, are at risk of exposure and information on the effects of CYN exposure at environmentally relevant concentrations is limited. In the present study, we investigated CYN uptake in the floating macrophyte Lemna minor with exposure to reported environmental concentrations. The effects were evaluated in terms of bioaccumulation, relative plant growth, and number of fronds per day. Variations in the concentrations and ratios of the chlorophylls as stress markers and carotenoids as markers of oxidative stress defense were measured. With exposure to 25 μg/L, L. minor could remove 43% of CYN within 24 h but CYN was not bioaccumulated. Generally, the pigment concentrations were elevated with exposure to 0.025, 0.25, and 2.5 μg/L CYN after 24 h, but normalized quickly thereafter. Changes in relative plant growth were observed with exposure to 0.25 and 2.5 μg/L CYN. Adverse effects were seen with these environmentally realistic concentrations within 24 h; however, L. minor successfully recovered within the next 48-96 h.

Analysis of the Use of Cylindrospermopsin and/or Microcystin-Contaminated Water in the Growth, Mineral Content, and Contamination of Spinacia oleracea and Lactuca sativa

Cyanobacteria and cyanotoxins constitute a serious environmental and human health problem. Moreover, concerns are raised with the use of contaminated water in agriculture and vegetable production as this can lead to food contamination and human exposure to toxins as well as impairment in crop development and productivity. The objective of this work was to assess the susceptibility of two green vegetables, spinach and lettuce, to the cyanotoxins microcystin (MC) and cylindrospermopsin (CYN), individually and in mixture. The study consisted of growing both vegetables in hydroponics, under controlled conditions, for 21 days in nutrient medium doped with MC or CYN at 10 μg/L and 50 μg/L, or CYN/MC mixture at 5 + 5 μg/L and 25 + 25 μg/L. Extracts from M. aeruginosa and C. ovalisporum were used as sources of toxins. The study revealed growth inhibition of the aerial part (Leaves) in both species when treated with 50µg/L of MC, CYN and CYN/MC mixture. MC showed to be more harmful to plant growth than CYN. Moreover spinach leaves growth was inhibited by both 5 + 5 and 25 + 25 µg/L CYN/MC mixtures, whereas lettuce leaves growth was inhibited only by 25 + 25 µg/L CYN/MC mixture. Overall, growth data evidence increased sensitivity of spinach to cyanotoxins in comparison to lettuce. On the other hand, plants exposed to CYN/MC mixture showed differential accumulation of CYN and MC. In addition, CYN, but not MC, was translocated from the roots to the leaves. CYN and MC affected the levels of minerals particularly in plant roots. The elements most affected were Ca, K and Mg. However, in leaves K was the mineral that was affected by exposure to cyanotoxins.

A Comparative Study of Microcystin-LR Degradation by UV-A, Solar and Visible Light Irradiation Using Bare and C/N/S-Modified Titania

In an endeavor to tackle environmental problems, the photodegradation of microcystin-LR (MC-LR), one of the most common and toxic cyanotoxins, produced by the cyanobacteria blooms, was examined using nanostructured TiO2 photocatalysts (anatase, brookite, anatase–brookite, and C/N/S co-modified anatase–brookite) under UV-A, solar and visible light irradiation. The tailoring of TiO2 properties to hinder the electron–hole recombination and improve MC-LR adsorption on TiO2 surface was achieved by altering the preparation pH value. The highest photocatalytic efficiency was 97% and 99% with degradation rate of 0.002 mmol L−1 min−1 and 0.0007 mmol L−1 min−1 under UV and solar irradiation, respectively, using a bare TiO2 photocatalyst prepared at pH 10 with anatase to brookite ratio of ca. 1:2.5. However, the bare TiO2 samples were hardly active under visible light irradiation (25%) due to a large band gap. Upon UV, solar and vis irradiation, the complete MC-LR degradation (100%) was obtained in the presence of C/N/S co-modified TiO2 with a degradation rate constant of 0.26 min−1, 0.11 min−1 and 0.04 min−1, respectively. It was proposed that the remarkable activity of co-modified TiO2 might originate from its mixed-phase composition, mesoporous structure, and non-metal co-modification.

Glutathione biosynthesis plays an important role in microcystin-LR depuration in lettuce and spinach

Irrigation of crop plants with microcystins (MCs) contaminated water could be a threat to human health via bioaccumulation. Despite the fact MCs bioaccumulation in crop plants is well documented, MCs depuration, as well as the mechanism involved remains unclear. The objectives of the present study were to investigate the bioaccumulation and depuration of microcystin-LR (MC-LR) in lettuce (Lactuca sativa L.) and spinach (Spinacia oleracea L.), as well as to explore the role of glutathione (GSH) biosynthesis in MC-LR depuration. The tested plants were irrigated with deionized water containing 10 μg L-1 MC-LR for 12 days (bioaccumulation), and subsequently, with either deionized water only or deionized water containing 0.5 mM buthionine sulfoximine (BSO, a specific inhibitor of GSH biosynthesis) for 12 days (depuration). After bioaccumulation period, highest concentrations of MC-LR found in lettuce and spinach were 114.4 and 138.5 μg kg-1 dry weight (DW) respectively. Depuration rates of MC-LR in lettuce and spinach were 9.5 and 8.1 μg kg-1 DW d-1, which deceased to 3.7 and 4.6 μg kg-1 DW d-1 in treatments with BSO application. GSH content in both lettuce and spinach were not significantly affected during depuration without BSO; whereas after treatment with BSO, GSH content significantly decreased by 36.0% and 24.7% in lettuce and spinach on 15 d, and the decrease remained on 18 d and 21 d in lettuce. Moreover, during the bioaccumulation period, activities of glutathione reductase (GR) and glutathione S-transferase (GST) were enhanced in both plants. Our results suggested that GSH biosynthesis played an important role in MC-LR depuration in the tested plants. Concerning human health risk, most of the estimated daily intake (EDI) values during the bioaccumulation period exceeded the tolerable daily intake (TDI) guideline. However, the risk could be alleviated by irrigating with MCs-free water for a certain amount of time before harvest.

Photocatalytic degradation of Microcystin-LR by visible light active and magnetic, ZnFe2O4-Ag/rGO nanocomposite and toxicity assessment of the intermediates

In this work, we aimed to study photocatalytic degradation of Microcystin-LR (MC-LR), a cyanotoxin known to cause acute as well as chronic toxicity and even mortality. The nanocomposite (NC) based on zinc ferrite (ZnFe₂O₄) was modified with graphene oxide (GO) and Ag nanoparticles (NPs) to enhance its photocatalytic properties under visible light. The so-formed ZnFe₂O₄-Ag/rGO NC exhibited superior performance in visible light allowing complete degradation of MC-LR within 120 min of treatment with pseudo rate constant, k = 0.0515 min^-1, several times greater than other photocatalysts, TiO₂ (k = 0.0009 min^-1), ZnFe₂O₄ (k = 0.0021 min^-1), ZnFe₂O₄-Ag (k = 0.0046 min^-1) and ZnFe₂O₄/rGO (k = 0.007 min^-1) respectively. The total organic carbon analysis revealed that only 22% of MC-LR was mineralized on 120 min of treatment time indicating presence of different intermediate by-products. The intermediates formed during photocatalytic treatment were identified using liquid chromatography-mass spectrometry (LCMS) based on which probable degradation pathways were proposed. The attack from OH radicals formed during the photocatalytic process resulted to hydroxylation and subsequent cleavage of diene bond. The toxicity assessment with Daphnia magna revealed that the degradation process has alleviated toxicity of the MC-LR and no toxic intermediates were formed during the treatment which is very important from eco-toxicological view point. Therefore, ZnFe₂O₄-Ag/rGO has a good potential in the field of environmental applications as visible light active and magnetic photocatalyst with enhanced performance.

Cytotoxic and morphological effects of microcystin-LR, cylindrospermopsin, and their combinations on the human hepatic cell line HepG2

Cylindrospermopsin (CYN) and Microcystin-LR (MC-LR) are toxins produced by different cyanobacterial species, which are found mainly in freshwater reservoirs. Both of them can induce, separately, toxic effects in humans and wildlife. However, little is known about the toxic effects of the combined exposure, which could likely happen, taking into account the concomitant occurrence of the producers. As both cyanotoxins are well known to induce hepatic damage, the human hepatocellular HepG2 cell line was selected for the present study. Thus, the cytotoxicity of both pure cyanotoxins alone (0-5 μg/mL CYN and 0-120 μg/mL MC-LR) and in combination for 24 and 48 h was assayed, as long as the cytotoxicity of extracts from CYN-producing and nonproducing cyanobacterial species. The potential interaction of the combination was evaluated by the isobologram or Chou-Talalay's method, which provides a combination index as a quantitative measure of the two cyanotoxins interaction's degree. Moreover, a morphological study of the individual pure toxins and their combinations was also performed. Results showed that CYN was the most toxic pure cyanotoxin, being the mean effective concentrations obtained ≈4 and 90 μg/mL for CYN and MC-LR, respectively after 24 h. However, the simultaneous exposure showed an antagonistic effect. Morphologically, autophagy, at low concentrations, and apoptosis, at high concentrations were observed, with affectation of the rough endoplasmic reticulum and mitochondria. These effects were more pronounced with the combination. Therefore, it is important to assess the toxicological profile of cyanotoxins combinations in order to perform more realistic risk evaluations.

New Method for Simultaneous Determination of Microcystins and Cylindrospermopsin in Vegetable Matrices by SPE-UPLC-MS/MS

Cyanotoxins are a large group of noxious metabolites with different chemical structure and mechanisms of action, with a worldwide distribution, producing effects in animals, humans, and crop plants. When cyanotoxin-contaminated waters are used for the irrigation of edible vegetables, humans can be in contact with these toxins through the food chain. In this work, a method for the simultaneous detection of Microcystin-LR (MC-LR), Microcystin-RR (MC-RR), Microcystin-YR (MC-YR), and Cylindrospermopsin (CYN) in lettuce has been optimized and validated, using a dual solid phase extraction (SPE) system for toxin extraction and ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) for analysis. Results showed linear ranges (5⁻50 ng g-1 f.w.), low values for limit of detection (LOD) (0.06⁻0.42 ng g-1 f.w.), and limit of quantification (LOQ) (0.16⁻0.91 ng g-1 f.w.), acceptable recoveries (41⁻93%), and %RSDIP values for the four toxins. The method proved to be robust for the three variables tested. Finally, it was successfully applied to detect these cyanotoxins in edible vegetables exposed to cyanobacterial extracts under laboratory conditions, and it could be useful for monitoring these toxins in edible vegetables for better exposure estimation in terms of risk assessment.

Bioaccessibility and decomposition of cylindrospermopsin in vegetables matrices after the application of an in vitro digestion model

Research on the human exposure to Cylindrospermopsin (CYN) via consumption of contaminated food is of great interest for risk assessment purposes. The aim of this work is to evaluate for the first time the CYN bioaccessibility in contaminated vegetables (uncooked lettuce and spinach, and boiled spinach) after an in vitro digestion model, including the salivar, gastric and duodenal phases and, colonic fermentation under lactic acid bacteria. The results obtained showed that the digestion processes are able to diminish CYN levels, mainly in the colonic phase, especially in combination with the boiling treatment, decreasing CYN levels in a significant way. Moreover, the potential decomposition products in a pure CYN solution and in CYN-contaminated vegetables were evaluated using UHPLC-MS/MS Orbitrap. Under the conditions assayed, only two diastereoisomers of the same fragment with m/z 292.09617 have been detected in all the analysed samples, with the exception of digested vegetables. Therefore, in terms of risk assessment, the digestion seems to play an important role in reducing the final bioaccesibility of CYN, and the consumption of cooked vegetables (spinach) would be safer in comparison to raw vegetables.

Optimization of extraction methods for quantification of microcystin-LR and microcystin-RR in fish, vegetable, and soil matrices using UPLC-MS/MS

Human-driven environmental change has increased the occurrence of harmful cyanobacteria blooms in aquatic ecosystems. Concomitantly, exposure to microcystin (MC), a cyanobacterial toxin that can accumulate in animals, edible plants, and agricultural soils, has become a growing public health concern. For accurate estimation of health risks and timely monitoring, availability of reliable detection methods is imperative. Nonetheless, quantitative analysis of MCs in many types of biological and environmental samples has proven challenging because matrix interferences can hinder sample preparation and extraction procedures, leading to poor MC recovery. Herein, controlled experiments were conducted to enhance the use of ultra-performance liquid-chromatography tandem-mass spectrometry (UPLC-MS/MS) to recover MC-LR and MC-RR at a range of concentrations in seafood (fish), vegetables (lettuce), and environmental (soil) matrices. Although these experiments offer insight into detailed technical aspects of the MC homogenization and extraction process (i.e., sonication duration and centrifugation speed during homogenization; elution solvent to use during the final extraction), they centered on identifying the best (1) solvent system to use during homogenization (2-3 tested per matrix) and (2) single-phase extraction (SPE) column type (3 tested) to use for the final extraction. The best procedure consisted of the following, regardless of sample type: centrifugation speed = 4200 × g; elution volume = 8 mL; elution solvent = 80% methanol; and SPE column type = hydrophilic-lipophilic balance (HLB), with carbon also being satisfactory for fish. For sonication, 2 min, 5 min, and 10 min were optimal for fish, lettuce, and soil matrices, respectively. Using the recommended HLB column, the solvent systems that led to the highest recovery of MCs were methanol:water:butanol for fish, methanol:water for lettuce, and EDTA-Na₄P₂O₇ for soils. Given that the recommended procedures resulted in average MC-LR and MC-RR recoveries that ranged 93 to 98%, their adoption for the preparation of samples with complex matrices before UPLC-MS/MS analysis is encouraged.

Cylindrospermopsin induces biochemical changes leading to programmed cell death in plants

In the present study we provide cytological and biochemical evidence that the cyanotoxin cylindrospermopsin (CYN) induces programmed cell death (PCD) symptoms in two model vascular plants: the dicot white mustard (Sinapis alba) and the monocot common reed (Phragmites australis). Cytological data include chromatin fragmentation and the increase of the ratio of TUNEL-positive cells in roots, the latter being detected in both model systems studied. The strongest biochemical evidence is the elevation of the activity of several single-stranded DNA preferring nucleases-among them enzymes active at both acidic and alkaline conditions and are probably directly related to DNA breaks occurring at the initial stages of plant PCD: 80 kDa nucleases and a 26 kDa nuclease, both having dual (single- and double-stranded nucleic acid) specificity. Moreover, the total protease activity and in particular, a 53-56 kDa alkaline protease activity increases. This protease could be inhibited by PMSF, thus regarded as serine protease. Serine proteases are detected in all organs of Brassicaceae (Arabidopsis) having importance in differentiation of specialized plant tissue through PCD, in protein degradation/processing during early germination and defense mechanisms induced by a variety of biotic and abiotic stresses. However, knowledge of the physiological roles of these proteases and nucleases in PCD still needs further research. It is concluded that CYN treatment induces chromatin fragmentation and PCD in plant cells by activating specific nucleases and proteases. CYN is proposed to be a suitable molecule to study the mechanism of plant apoptosis.

Validation of a Method for Cylindrospermopsin Determination in Vegetables: Application to Real Samples Such as Lettuce (Lactuca sativa L.)

Reports on the occurrence of the cyanobacterial toxin cylindrospermopsin (CYN) have increased worldwide because of CYN toxic effects in humans and animals. If contaminated waters are used for plant irrigation, these could represent a possible CYN exposure route for humans. For the first time, a method employing solid phase extraction and quantification by ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) of CYN was optimized in vegetables matrices such as lettuce (Lactuca sativa). The validated method showed a linear range, from 5 to 500 ng CYN g-1 of fresh weight (f.w.), and detection and quantitation limits (LOD and LOQ) of 0.22 and 0.42 ng CYN g-1 f.w., respectively. The mean recoveries ranged between 85 and 104%, and the intermediate precision from 12.7 to 14.7%. The method showed to be robust for the three different variables tested. Moreover, it was successfully applied to quantify CYN in edible lettuce leaves exposed to CYN-contaminated water (10 µg L-1), showing that the tolerable daily intake (TDI) in the case of CYN could be exceeded in elderly high consumers. The validated method showed good results in terms of sensitivity, precision, accuracy, and robustness for CYN determination in leaf vegetables such as lettuce. More studies are needed in order to prevent the risks associated with the consumption of CYN-contaminated vegetables.

Floating rice-culture system for nutrient remediation and feed production in a eutrophic lake

The increased inputs of nutrients have been demonstrated to be a major contributing factor to the eutrophication of lakes and reservoirs which can lead to the production of harmful algal/cyanobacterial blooms and deleteriously affect the aesthetics of water-bodies. Floating plant-culture systems have been widely used for the ecological remediation of eutrophic water in a cost-effective manner. We investigated the applicability of Korean japonica rice variety 'Nampyeong' in a floating-culture system in a eutrophic lake for nutrient uptake and biomass production. Chemical and organic compound compositions were analyzed two times during the growth stages of the rice plant: 98 DAT (days after transplanting) and 165 DAT. Total nitrogen and phosphorus contributed around 1.36 and 0.15 (% dry weight), respectively, in rice plant components at 165 DAT. Crude protein, lipids, fiber and ash were 4.35, 1.91, 23.66 and 5.55 (% dry weight), respectively. In addition, microcystin levels in the rice plant components ranged from 0.0008 to 0.002 μg/g and did not exceed the recommended tolerable limits. These results suggested that the developed floating rice-culture system showed a good potential as a holistic management approach in terms of nutrient reduction, rice production for further use as feed and for bloom control.

Lettuce facing microcystins-rich irrigation water at different developmental stages: Effects on plant performance and microcystins bioaccumulation

This study investigated the microcystins (MCs)-rich irrigation water effect on lettuce of different developmental stages, i.e. during a two months period, covering the whole period from seed germination to harvest at marketable size of the plant. We followed four lettuce plant groups receiving MCs-rich water (1.81μgl-1 of dissolved MCs), originating from the Karla Reservoir, central Greece: 1) from seeds, 2) the cotyledon, 3) two true leaves and 4) four true leaves stages, all of which were compared to control plants that received tap water. Lettuce growth, photosynthetic performance, biochemical and mineral characteristics, as well as MCs accumulation in leaves, roots and soil were measured. The overall performance of lettuce at various developmental stages pointed to increased tolerance since growth showed minor alterations and non-enzymatic antioxidants remained unaffected. Plants receiving MCs-rich water from the seed stage exhibited higher photosynthetic capacity, chlorophylls and leaf nitrogen content. Nevertheless, considerable MCs accumulation in various plant tissues occurred. The earlier in their development lettuce plants started receiving MCs-rich water, the more MCs they accumulated: roots and leaves of plants exposed to MCs-rich water from seeds and cotyledons stage exhibited doubled MCs concentrations compared to respective tissues of the 4 Leaves group. Furthermore, roots accumulated significantly higher MCs amounts than leaves of the same plant group. Concerning human health risk, the Estimated Daily Intake values (EDI) of Seed and Cotyledon groups leaves exceeded Tolerable Daily Intake (TDI) by a factor of 6, while 2 Leaves and 4 Leaves groups exceeded TDI by a factor of 4.4 and 2.4 respectively. Our results indicate that irrigation of lettuce with MCs-rich water may constitute a serious public health risk, especially when contaminated water is received from the very early developmental stages (seed and cotyledon). Finally, results obtained for the tolerant lettuce indicate that MCs bioaccumulation in edible tissues is not necessarily coupled with phytotoxic effects.

Potential human health risk assessment of cylindrospermopsin accumulation and depuration in lettuce and arugula

The cyanobacterial toxin cylindrospermopsin (CYN) has become a globally important secondary metabolite due to the negative effect it has on human and animal health. As a means of evaluating the risk of human exposure to CYN, the bioaccumulation and depuration of the toxin in lettuce (Lactuca sativa L.) and arugula (Eruca sativa Mill.) were investigated, after irrigation with contaminated water. The vegetables were irrigated for 7days with CYN (3, 5 and 10μg/L) contaminated water (bioaccumulation phase), and subsequently, irrigated for 7days with uncontaminated distilled water (depuration phase). In general, the bioaccumulation of CYN in both vegetables decreased with increasing exposure concentration. Bioconcentration factor (BCF) of CYN increased with the progression of the experiment at 3.0μg/L CYN, while the reverse occurred at 5 and 10μg/L CYN. In arugula, BCF increased at all CYN exposure concentrations throughout the study. The depuration of CYN decreased with increasing exposure concentration but was highest in the plants of both species with the highest bioaccumulation of CYN. Specifically, in plants previously irrigated with water contaminated with 3, 5 and 10μg/L CYN, the depuration of the toxin was 60.68, 27.67 and 18.52% for lettuce, and 47, 46.21 and 27.67% for arugula, respectively. Human health risks assessment revealed that the consumption of approximately 10 to 40g of vegetables per meal will expose children and adults to 1.00-6.00ng CYN/kg body mass for lettuce and 2.22-7.70ng CYN/kg body mass for arugula. The irrigation of lettuce and arugula with contaminated water containing low CYN concentrations constitutes a potential human exposure route.

Effects of depuration on histopathological changes in tilapia (Oreochromis niloticus) after exposure to cylindrospermopsin

Cylindrospermopsin (CYN) is a highly water-soluble cytotoxin produced by several species of freshwater cyanobacteria and it is considered the second most studied cyanotoxin worldwide. CYN acts as a potent protein and glutathione synthesis inhibitor, as well as inducing genotoxicity, oxidative stress and histopathological alterations. Studies concerning the depuration of cyanobacterial toxins in aquatic organisms, especially in fish, are of great interest for fish economy and public health, but are scarce in the case of CYN. This is the first study reporting the ability of depuration (3 - 7 days) in reversing or ameliorating the histopathological lesions induced in liver, kidney, heart, intestines, and gills of tilapia (Oreochromis niloticus) due to exposure by immersion to repeated doses of a CYN-containing culture of A. ovalisporum for 14 days. The main histopathological changes induced by CYN were glucogenic degeneration and loss of the normal hepatic cord-structure (liver), hyperemia, dilated Bowman's capsule and cellular tumefaction (kidney), myofibrolysis, hemorrhages and edema (heart), necrosis and partial loss of microvilli (gastrointestinal tract), and hyperemia and inflammatory cells infiltrates (gills). After 3 days of depuration, gills were totally recovered, while the liver, kidney, and gastrointestinal tract required 7 days, and longer depuration periods may be needed for a full recovery of the heart. In addition, the morphometric study indicated that depuration managed to reverse the affectation in the hepatocytes nuclear diameters and cross sections of the proximal and distal convoluted tubules induced in CYN-exposed fish. In general, these results validate depuration as an effective practice for detoxification of fish contaminated with CYN. © 2016 Wiley Periodicals, Inc. Environ Toxicol 32: 1318-1332, 2017.

Cyanobacterial Toxins in Freshwater and Food: Important Sources of Exposure to Humans

A recent ecological study demonstrated a significant association between an increased risk of nonalcoholic liver disease mortality and freshwater cyanobacterial blooms. Moreover, previous epidemiology studies highlighted a relationship between cyanotoxins in drinking water with liver cancer and damage and colorectal cancer. These associations identified cyanobacterial blooms as a global public health and environmental problem, affecting freshwater bodies that are important sources for drinking water, agriculture, and aquafarms. Furthermore, as a result of climate change, it is expected that our freshwater environments will become more favorable for producing harmful blooms that produce various cyanotoxins. Food is an important source of cyanotoxin exposure to humans, but it has been less addressed. This paper synthesizes information from the studies that have investigated cyanotoxins in freshwater and food on a global scale. We also review and summarize the health effects and exposure routes of cyanotoxins and candidates for cyanotoxin treatment methods that can be applied to food.

Effects of microcystin-LR and cylindrospermopsin on plant-soil systems: A review of their relevance for agricultural plant quality and public health

Toxic cyanobacterial blooms are recognized as an emerging environmental threat worldwide. Although microcystin-LR is the most frequently documented cyanotoxin, studies on cylindrospermopsin have been increasing due to the invasive nature of cylindrospermopsin-producing cyanobacteria. The number of studies regarding the effects of cyanotoxins on agricultural plants has increased in recent years, and it has been suggested that the presence of microcystin-LR and cylindrospermopsin in irrigation water may cause toxic effects in edible plants. The uptake of these cyanotoxins by agricultural plants has been shown to induce morphological and physiological changes that lead to a potential loss of productivity. There is also evidence that edible terrestrial plants can bioaccumulate cyanotoxins in their tissues in a concentration dependent-manner. Moreover, the number of consecutive cycles of watering and planting in addition to the potential persistence of microcystin-LR and cylindrospermopsin in the environment are likely to result in groundwater contamination. The use of cyanotoxin-contaminated water for agricultural purposes may therefore represent a threat to both food security and food safety. However, the deleterious effects of cyanotoxins on agricultural plants and public health seem to be dependent on the concentrations studied, which in most cases are non-environmentally relevant. Interestingly, at ecologically relevant concentrations, the productivity and nutritional quality of some agricultural plants seem not to be impaired and may even be enhanced. However, studies assessing if the potential tolerance of agricultural plants to these concentrations can result in cyanotoxin and allergen accumulation in the edible tissues are lacking. This review combines the most current information available regarding this topic with a realistic assessment of the impact of cyanobacterial toxins on agricultural plants, groundwater quality and public health.

Microcystin accumulation and potential effects on antioxidant capacity of leaves and fruits of Capsicum annuum

Surface water, often used for irrigation purposes, may sometimes be contaminated with blooming cyanobacteria and thereby may contain their potent and harmful toxins. Cyanotoxins adversely affect many terrestrial plants, and accumulate in plant tissues that are subsequently ingested by humans. Studies were undertaken to (1) examine the bioaccumulation of microcystins (MCs) in leaves and fruits of pepper Capsicum annuum and (2) examine the potential effects of MCs on antioxidant capacity of these organs. Plants were irrigated with water containing MCs for a period of 3 mo. Data showed that MCs did not accumulate in leaves; however, in fruits the presence of the MC-LR (0.118 ng/mg dry weight) and dmMC-LR (0.077 ng/mg dry weight) was detected. The concentrations of MC-LR in fruit approached the acceptable guideline values and tolerable daily intake for this toxin. Lipid peroxidation levels and flavonoids content were significantly enhanced in both organs of treated plants, while total phenolic concentrations were not markedly variable between control and treated plants. Significant decrease in 1,1-diphenyl-2-picrylhydrazyl (DPPH) scavenging capacity was noted for both organs. The levels of superoxide anion in fruits and hydroxyl radical in leaves were markedly reduced. Data suggest that exposure to MCs significantly reduced antioxidant capacity of experimental plants, indicating that MCs affected antioxidant systems in C. annuum.

Analysis of the use of microcystin-contaminated water in the growth and nutritional quality of the root-vegetable, Daucus carota

Toxic cyanobacterial blooms are often observed in freshwaters and may reflect the increased eutrophication of these environments and alterations in climate. Cyanotoxins, such as microcystins (MCs), are an effective threat to many life forms, ranging from plants to humans. Despite the research conducted to date on cyanotoxins, the risks associated to the use of contaminated water in agriculture require further elucidation. To tackle this aim, a research was conducted with the root-vegetable Daucus carota. The specific aims of this work were the following: (i) to evaluate the effects of MC-LR on the plant growth and photosynthesis; (ii) to evaluate the nutritional quality of carrot roots; and (iii) to measure bioaccumulation. To this purpose, young carrots were grown in soil during 1 month in natural conditions and exposed to Mycrocystis aeruginosa aqueous extracts containing environmentally realistic concentrations of MC-LR (10 and 50 MC-LR μg/L). The results showed that MC-LR may decrease root growth after 28 days of exposure to 50 μg/L and increase photosynthetic efficiency. We also observed changes in mineral and vitamin content in carrots as a result of the exposure to contaminated water. Moreover, MC-LR was detected in carrot roots by ELISA at very low concentration 5.23 ± 0.47 ng MC eq./g FW. The soil retained 52.7 % of the toxin potentially available for plants. This result could be attributed to MC-LR adsorption by soil particles or due to microbial degradation of the toxin. We conclude that the prolonged use of MC-LR-contaminated water may affect crop growth, alter the nutritional value of vegetable products, and potentiate contamination.

Effects of Chrysosporum (Aphanizomenon) ovalisporum extracts containing cylindrospermopsin on growth, photosynthetic capacity, and mineral content of carrots (Daucus carota)

Natural toxins produced by freshwater cyanobacteria, such as cylindrospermopsin, have been regarded as an emergent environmental threat. Despite the risks for food safety, the impact of these water contaminants in agriculture is not yet fully understood. Carrots (Daucus carota) are root vegetables, extensively consumed worldwide with great importance for human nourishment and economy. It is, therefore, important to evaluate the possible effects of using water contaminated with cyanotoxins on carrot cultivation. The aim of this work was to investigate cylindrospermopsin effects on D. carota grown in soil and irrigated for 30 days, with a Chrysosporum ovalisporum extract containing environmentally relevant concentrations of cylindrospermopsin (10 and 50 μg/L). The parameters evaluated were plant growth, photosynthetic capacity, and nutritional value (mineral content) in roots of carrots, as these are the edible parts of this plant crop. The results show that, exposure to cylindrospermopsin did not have a clear negative effect on growth or photosynthesis of D. carota, even leading to an increase of both parameters. However, alterations in mineral contents were detected after exposure to crude extracts of C. ovalisporum containing cylindrospermopsin. A general decline was observed for most minerals (Ca, Mg, Na, Fe, Mn, Zn, Mo, and P), although an increase was shown in the case of K and Cu, pointing to a possible interference of the cyanobacterial extract in mineral uptake. This study is the first to evaluate the effects of C. ovalisporum extracts on a root vegetable, however, more research is necessary to understand the effects of this toxin in environmentally relevant scenarios.

Interactive effects of cadmium and Microcystis aeruginosa (cyanobacterium) on the growth, antioxidative responses and accumulation of cadmium and microcystins in rice seedlings

Cadmium pollution and harmful cyanobacterial blooms are two prominent environmental problems. The interactive effects of cadmium(II) and harmful cyanobacteria on rice seedlings remain unknown. In order to elucidate this issue, the interactive effects of cadmium(II) and Microcystis aeruginosa FACHB905 on the growth and antioxidant responses of rice seedling were investigated in this study, as well as the accumulation of cadmium(II) and microcystins. The results showed that the growth of rice seedlings was inhibited by cadmium(II) stress but promoted by inoculation of M. aeruginosa FACHB905. cadmium(II) stress induced oxidative damage on rice seedlings. Inoculation of M. aeruginosa FACHB905 alleviated the toxicity of cadmium(II) on rice seedlings. The accumulation of cadmium(II) in rice seedlings was decreased by M. aeruginosa FACHB905, but the translocation of cadmium(II) from root to shoot was increased by this cyanobacterium. The accumulation of microcystins in rice seedlings was decreased by cadmium(II). Results presented in this study indicated that cadmium(II) and M. aeruginosa had antagonistic toxicity on rice seedlings. The findings of this study throw new light on evaluation of ecological- and public health-risks for the co-contamination of cadmium(II) and harmful cyanobacteria.

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.

Growth inhibition and oxidative damage of Microcystis aeruginosa induced by crude extract of Sagittaria trifolia tubers

Aquatic macrophytes are considered to be promising in controlling harmful cyanobacterial blooms. In this research, an aqueous extract of Sagittaria trifolia tubers was prepared to study its inhibitory effect on Microcystis aeruginosa in the laboratory. Several physiological indices of M. aeruginosa, in response to the environmental stress, were analyzed. Results showed that S. trifolia tuber aqueous extract significantly inhibited the growth of M. aeruginosa in a concentration-dependent way. The highest inhibition rate reached 90% after 6 day treatment. The Chlorophyll-a concentration of M. aeruginosa cells decreased from 343.1 to 314.2μg/L in the treatment group. The activities of superoxide dismutase and peroxidase and the content of reduced glutathione in M. aeruginosa cells initially increased as a response to the oxidative stress posed by S. trifolia tuber aqueous extract, but then decreased as time prolonged. The lipid peroxidation damage of the cyanobacterial cell membranes was reflected by the malondialdehyde level, which was notably higher in the treatment group compared with the controls. It was concluded that the oxidative damage of M. aeruginosa induced by S. trifolia tuber aqueous extract might be one of the mechanisms for the inhibitory effects.

The interactive effects of microcystin-LR and cylindrospermopsin on the growth rate of the freshwater algae Chlorella vulgaris

Microcystin-LR (MC-LR) and cylindrospermopsin (CYN) are the most representative cyanobacterial cyanotoxins. They have been simultaneously detected in aquatic systems, but their combined ecotoxicological effects to aquatic organisms, especially microalgae, is unknown. In this study, we examined the effects of these cyanotoxins individually and as a binary mixture on the growth rate of the freshwater algae Chlorella vulgaris. Using the MIXTOX tool, the reference model concentration addition (CA) was selected to evaluate the combined effects of MC-LR and CYN on the growth of the freshwater green algae due to its conservative prediction of mixture effect for putative similar or dissimilar acting chemicals. Deviations from the CA model such as synergism/antagonism, dose-ratio and dose-level dependency were also assessed. In single exposures, our results demonstrated that MC-LR and CYN had different impacts on the growth rates of C. vulgaris at the highest tested concentrations, being CYN the most toxic. In the mixture exposure trial, MC-LR and CYN showed a synergistic deviation from the conceptual model CA as the best descriptive model. MC-LR individually was not toxic even at high concentrations (37 mg L(-1)); however, the presence of MC-LR at much lower concentrations (0.4-16.7 mg L(-1)) increased the CYN toxicity. From these results, the combined exposure of MC-LR and CYN should be considered for risk assessment of mixtures as the toxicity may be underestimated when looking only at the single cyanotoxins and not their combination. This study also represents an important step to understand the interactions among MC-LR and CYN detected previously in aquatic systems.

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.

Antioxidative stress responses in the floating macrophyte Lemna minor L. with cylindrospermopsin exposure

Cylindrospermopsin toxicity and oxidative stress have been examined in aquatic animals, however, only a few studies with aquatic plants have been conducted focusing on the potential for bioaccumulation of cylindrospermopsin. The oxidative stress effects caused by cylindrospermopsin on macrophytes have not yet been specifically studied. The oxidative stress response of Lemna minor L. with exposure to cylindrospermopsin, was therefore tested in this study. The hydrogen peroxide concentration together with the activities of the antioxidant enzymes (catalase, peroxidase, glutathione reductase and glutathione S-transferase) were determined after 24h (hours) of exposure to varying concentrations (0.025, 0.25, 2.5 and 25μg/L) of cylindrospermopsin. Responses with longer exposure periods (48, 96, 168h) were tested only with exposure to 2.5 and 25μg/L cylindrospermopsin. Additionally, the content of the carotenoids was determined as a possible non-enzymatic antioxidant defence mechanism against cylindrospermopsin. The levels of hydrogen peroxide increased after 24h even at the lowest cylindrospermopsin exposure concentrations. Catalase showed the most representative antioxidant response observed after 24h and maintained its activity throughout the experiment. Catalase activity corresponded with the contents of hydrogen peroxide at 2.5 and 25μg/L cylindrospermopsin. The data suggest that glutathione S-transferase, glutathione reductase and the carotenoid content act together with catalase but are more sensitive to higher concentrations of cylindrospermopsin and after a longer exposure period (168h). The results indicate that cylindrospermopsin promotes oxidative stress in L. minor at concentrations of 2.5 and 25μg/L. However, L. minor has sufficient defence mechanisms in place against this cyanobacterial toxin. Even though L. minor exhibits the potential to managing and control cylindrospermopsin contamination in aquatic systems, further studies in tolerance limits to cylindrospermopsin, uptake and experiments with prolonged exposure periods of more than 7 days are required.

Effects of microcystin-LR, cylindrospermopsin and a microcystin-LR/cylindrospermopsin mixture on growth, oxidative stress and mineral content in lettuce plants (Lactuca sativa L.)

Toxic cyanobacterial blooms are documented worldwide as an emerging environmental concern. Recent studies support the hypothesis that microcystin-LR (MC-LR) and cylindrospermopsin (CYN) produce toxic effects in crop plants. Lettuce (Lactuca sativa L.) is an important commercial leafy vegetable that supplies essential elements for human nutrition; thus, the study of its sensitivity to MC-LR, CYN and a MC-LR/CYN mixture is of major relevance. This study aimed to assess the effects of environmentally relevant concentrations (1, 10 and 100 µg/L) of MC-LR, CYN and a MC-LR/CYN mixture on growth, antioxidant defense system and mineral content in lettuce plants. In almost all treatments, an increase in root fresh weight was obtained; however, the fresh weight of leaves was significantly decreased in plants exposed to 100 µg/L concentrations of each toxin and the toxin mixture. Overall, GST activity was significantly increased in roots, contrary to GPx activity, which decreased in roots and leaves. The mineral content in lettuce leaves changed due to its exposure to cyanotoxins; in general, the mineral content decreased with MC-LR and increased with CYN, and apparently these effects are time and concentration-dependent. The effects of the MC-LR/CYN mixture were almost always similar to the single cyanotoxins, although MC-LR seems to be more toxic than CYN. Our results suggest that lettuce plants in non-early stages of development are able to cope with lower concentrations of MC-LR, CYN and the MC-LR/CYN mixture; however, higher concentrations (100 µg/L) can affect both lettuce yield and nutritional quality.