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

Microcystin-degrading bacteria reduce bioaccumulation in Fragaria vulgaris and enhance fruit yield and quality

In Morocco, red fruit production has thrived, primarily utilizing hydroponic methods to control crops, increase fruit yield and quality, and avoid soil-related problems. However, the irrigation of these expansive hydroponic farms relies heavily on water sourced from dams, many of which are contaminated with Microcystins (MCs). To address this contamination issue, ongoing research is focused on discovering effective and cost-efficient biological solutions for eliminating MCs. In this study, we isolate and identify bacterial strains capable of degrading MCs, evaluate the rate of degradation, and investigate how soil inoculated with these bacteria affects the accumulation of MCs in plant tissue. The partial 16S rRNA analyses of three bacterial sequences were conducted, identifying them through NCBI as follows: Ensifer sp. (B1) isolated from soil, Shinella sp. (B2) from a cyanobacterial bloom, and Stutzerimonas sp. (B3) from water. These bacteria exhibited the ability to degrade MCs, with approximately 34.75%, 73.75%, and 30.1% of the initial concentration (20 µg/L) being removed after a 6-day period for B1, B2, and B3, respectively. Moreover, strawberry plants were cultivated hydroponically in a greenhouse for a duration of 90 days. These plants were subjected to extracts of cyanobacteria containing 10 and 20 µg/L of Microcystins (MC), as well as water from an artificial lake contaminated with MC, both with and without the presence of isolated bacterial strains. Among these strains, Shinella sp. exhibited the highest efficacy in mitigating MC accumulation. Specifically, it resulted in a reduction of approximately 1.159 µg of MC per kilogram of root dry weight, leading to complete elimination in the leaves and fruits. The findings also indicated that the inoculation of perlite with the three MC-degrading bacterial strains significantly enhanced growth, photosynthetic pigments, yield, biochemical constituents, and quality attributes of strawberries (p ≤ 0.05). These promising outcomes suggest the potential of this approach for addressing the adverse impacts of crops irrigated with MC-contaminated water in future agricultural practices.

Monitoring of toxic cyanobacterial blooms in Lalla Takerkoust reservoir by satellite imagery and microcystin transfer to surrounding farms

Cyanobacterial harmful algal blooms (CyanoHABs) threaten public health and freshwater ecosystems worldwide. In this study, our main goal was to explore the dynamics of cyanobacterial blooms and how microcystins (MCs) move from the Lalla Takerkoust reservoir to the nearby farms. We used Landsat imagery, molecular analysis, collecting and analyzing physicochemical data, and assessing toxins using HPLC. Our investigation identified two cyanobacterial species responsible for the blooms: Microcystis sp. and Synechococcus sp. Our Microcystis strain produced three MC variants (MC-RR, MC-YR, and MC-LR), with MC-RR exhibiting the highest concentrations in dissolved and intracellular toxins. In contrast, our Synechococcus strain did not produce any detectable toxins. To validate our Normalized Difference Vegetation Index (NDVI) results, we utilized limnological data, including algal cell counts, and quantified MCs in freeze-dried Microcystis bloom samples collected from the reservoir. Our study revealed patterns and trends in cyanobacterial proliferation in the reservoir over 30 years and presented a historical map of the area of cyanobacterial infestation using the NDVI method. The study found that MC-LR accumulates near the water surface due to the buoyancy of Microcystis. The maximum concentration of MC-LR in the reservoir water was 160 µg L-1. In contrast, 4 km downstream of the reservoir, the concentration decreased by a factor of 5.39 to 29.63 µgL-1, indicating a decrease in MC-LR concentration with increasing distance from the bloom source. Similarly, the MC-YR concentration decreased by a factor of 2.98 for the same distance. Interestingly, the MC distribution varied with depth, with MC-LR dominating at the water surface and MC-YR at the reservoir outlet at a water depth of 10 m. Our findings highlight the impact of nutrient concentrations, environmental factors, and transfer processes on bloom dynamics and MC distribution. We emphasize the need for effective management strategies to minimize toxin transfer and ensure public health and safety.

Effects of microcystin-LR on purification efficiency of simulating drinking water source by Hydrocharis dubia (Bl.) backer

The safety of drinking water source directly affects human health. Microcystin-LR (MC-LR), a toxic and common pollutant in drinking water source, is released by algae and can impede the in-situ remediation effect of aquatic plant. Finding out the effect mechanism of MC-LR on the purification of drinking water by aquatic plant is the key to its application. This study aims to explore the performance and mechanism of MC-LR on drinking water source purification by Hydrocharis dubia (Bl.) backer. The optimum removal efficiency of NH4+-N, TP and COD were 90.7%, 93.2% and 77.3% at MC-LR concentration of 0.5 μg L-1, respectively. With the increase of MC-LR concentration, the pollutants removal rate was obviously inhibited causing by concentration-dependent. Furthermore, the growth and development of the Hydrocharis dubia (Bl.) backer roots were significantly promoted at the concentration of 0.1 μg L-1. The length, tips, surface area, and average diameter of the root increased by 71.3%, 271.4%, 265.5%, and 113.0%, respectively. Chlorophyll contents under low-concentration MC-LR show a 14.5%-15.7% promoting effect compared with the control group. The activities of POD and CAT were also stimulated with the MC-LR increasing (<1.0 μg L-1). Notably, the MDA contents increased with increasing MC-LR concentration (p < 0.01). This study indicates the effect mechanism of MC-LR on Hydrocharis dubia (Bl.) backer purification performance relies on the increased growth and enzyme activity of Hydrocharis dubia (Bl.) backer.

Cyanotoxins in African waterbodies: occurrence, adverse effects, and potential risk to animal and human health

Public concerns about cyanotoxins production in water and its detrimental impacts on human and animal health are growing primarily due to the widespread eutrophication observed in aquatic ecosystems. A review of relevant literature was done to determine the degree of cyanotoxin occurrence and its harmful effects in African waterbodies. Data were extracted from 64 published studies from 1990 to 2022 that quantified the concentration of cyanotoxins in African aquatic ecosystems. Cyanotoxins have been reported in 95 waterbodies (29 lakes, 41 reservoirs, 10 ponds, 9 rivers, 5 coastal waters, and 1 irrigation canal) from 15 African countries. Cyanotoxins were documented in all the regions of Africa except the central region. Microcystins have been reported in nearly all waterbodies (98.9%), but anatoxin-a (5.3%), cylindrospermopsin (2.1%), nodularins (2.1%), homoanatoxin-a (1.1%), and β-N-methylamino-L-alanine (1.1%) were encountered in a small number of water ecosystems, homoanatoxin-a and β-N-methylamino-L-alanine each occurred in one waterbody. The largest concentrations of microcystins and nodularins were reported in South African Lakes Nhlanganzwani (49,410 μg L-1) and Zeekoevlei (347,000 μg g-1). Microcystin concentrations exceeding the WHO guideline for lifetime drinking water (1 μg L-1) were reported in 63% of the aquatic ecosystems surveyed. The most frequently reported toxin-producing cyanobacteria genus is Microcystis spp. (73.7%), followed by Oscillatoria spp. (35.8%) and Dolichospermum spp. (33.7%). Cyanotoxin-related animal mortality and human illness were reported in the continent. Consequently, it is necessary to regularly monitor the level of nutrients, cyanobacteria, and cyanotoxins in African waterbodies in an integrated manner to devise a sustainable water resources management.

The osmotic stress of Vallisneria natans (Lour.) Hara leaves originating from the disruption of calcium and potassium homeostasis caused by MC-LR

Aquatic plants are potentially impacted by microcystins (MCs) in lakes experiencing harmful algal blooms. However, how these plants respond, and possibly adapt to osmotic stress caused by MCs is unclear. Vallisneria natans is a pioneer taxon with a global distribution in eutrophic lakes. In this study, we investigated the effect of MC-LR on morphological structure, water retention, osmoregulatory ability, and homeostasis of calcium (Ca2+) and potassium (K+) ions in V. natans leaves. Results showed that the morphological changes caused by MC-LR included increased volumes of epidermal and mesophyll cells, changes in their lignification level, and the degradation of chloroplast structure and dissolution of starch granules. The increased moisture content and water potential with MC-LR concentration were consistent with the occurrence of osmotic stress, and the decreased osmotic potential implied the activation of osmoregulation. Soluble sugar and free amino acid concentrations increased at MC-LR treatments ≥10 μg/L, while inorganic ion K+ content increased in all MC-LR treatments. Although instantaneous K+inflow and Ca2+outflow occurred at 10 μg/L and 100 μg/L MC-LR, respectively, ≥1 μg/L MC-LR resulted in continuous K+ inflow and Ca2+ outflow within 24 h. Moreover, plasma membrane hyperpolarization was caused by MC-LR, especially at 1 and 10 μg/L. We suggest that Ca2+ efflux served as a signal molecule from the cytoplasmic matrix via Ca2+-ATPase, and the uptake of K+ was activated passively through transporters in response to MC-LR-induced plasma membrane hyperpolarization. Therefore, the uptake of K+ was a part of the response but not an adaptation to MC-LR stress, and is considered the cause for the uptake of water in leaves. Ca2+ and K+ homeostasis of V. natans leaves was disrupted by MC-LR concentrations as low as 1 μg/L, suggesting that aquatic plants in most eutrophic lakes may experience negative impacts such as Ca2+ loss, impacts to cell water balance, and alteration in cellular morphology, due to osmotic stress caused by MC-LR.

Synthetic algocyanobacterial consortium as an alternative to chemical fertilizers

The use of unregulated pesticides and chemical fertilizers can have detrimental effects on biodiversity and human health. This problem is exacerbated by the growing demand for agricultural products. To address these global challenges and promote food and biological security, a new form of agriculture is needed that aligns with the principles of sustainable development and the circular economy. This entails developing the biotechnology market and maximizing the use of renewable and eco-friendly resources, including organic fertilizers and biofertilizers. Phototrophic microorganisms capable of oxygenic photosynthesis and assimilation of molecular nitrogen play a crucial role in soil microbiota, interacting with diverse microflora. This suggests the potential for creating artificial consortia based on them. Microbial consortia offer advantages over individual organisms as they can perform complex functions and adapt to variable conditions, making them a frontier in synthetic biology. Multifunctional consortia overcome the limitations of monocultures and produce biological products with a wide range of enzymatic activities. Biofertilizers based on such consortia present a viable alternative to chemical fertilizers, addressing the issues associated with their usage. The described capabilities of phototrophic and heterotrophic microbial consortia enable effective and environmentally safe restoration and preservation of soil properties, fertility of disturbed lands, and promotion of plant growth. Hence, the utilization of algo-cyano-bacterial consortia biomass can serve as a sustainable and practical substitute for chemical fertilizers, pesticides, and growth promoters. Furthermore, employing these bio-based organisms is a significant stride towards enhancing agricultural productivity, which is an essential requirement to meet the escalating food demands of the growing global population. Utilizing domestic and livestock wastewater, as well as CO2 flue gases, for cultivating this consortium not only helps reduce agricultural waste but also enables the creation of a novel bioproduct within a closed production cycle.

Bacterioplankton Associated with Toxic Cyanobacteria Promote Pisum sativum (Pea) Growth and Nutritional Value through Positive Interactions

Research on Plant Growth-Promoting Bacteria (PGPB) has focused much more on rhizospheric bacteria. However, PGPB associated with toxic cyanobacterial bloom (TCB) could enter the rhizosphere through irrigation water, helping plants such as Pisum sativum L. (pea) overcome oxidative stress induced by microcystin (MC) and improve plant growth and nutritional value. This study aimed to isolate bacteria associated with toxic cyanobacteria, test PGPB properties, and inoculate them as a consortium to pea seedlings irrigated with MC to investigate their role in plant protection as well as in improving growth and nutritional value. Two bacterioplankton isolates and one rhizosphere isolate were isolated and purified on a mineral salt medium supplemented with 1000 μg/L MC and identified via their 16S rRNA gene. The mixed strains were inoculated to pea seedlings in pots irrigated with 0, 50, and 100 μg/L MC. We measured the morphological and physiological parameters of pea plants at maturity and evaluated the efficiency of the plant’s enzymatic and non-enzymatic antioxidant responses to assess the role and contribution of PGPB. Both bacterioplankton isolates were identified as Starkeya sp., and the rhizobacterium was identified as Brevundimonas aurantiaca. MC addition significantly (p < 0.05) reduced all the growth parameters of the pea, i.e., total chlorophyll content, leaf quantum yield, stomatal conductance, carotenoids, and polyphenol contents, in an MC concentration-dependent manner, while bacterial presence positively affected all the measured parameters. In the MC treatment, the levels of the pea’s antioxidant traits, including SOD, CAT, POD, PPO, GST, and ascorbic acid, were increased in the sterile pots. In contrast, these levels were reduced with double and triple PGPB addition. Additionally, nutritional values such as sugars, proteins, and minerals (Ca and K) in pea fruits were reduced under MC exposure but increased with PGPB addition. Overall, in the presence of MC, PGPB seem to positively interact with pea plants and thus may constitute a natural alternative for soil fertilization when irrigated with cyanotoxin-contaminated water, increasing the yield and nutritional value of crops.

Effects of Irrigation with Microcystin-Containing Water on Growth, Physiology, and Antioxidant Defense in Strawberry Fragaria vulgaris under Hydroponic Culture

Over the last years, the use of artificial lakes and ponds to irrigate agricultural crops has been intensified and cultivation methods have been diversified. Hydroponics is a type of hydroculture which usually involves growing plants in an inert substrate, by using nutrient-enriched water to support plant growth. However, irrigating plants in hydroponic-based culture must be accompanied by monitoring the quality of irrigation water. The human health risks involved are mainly related to the proliferation of microcystin-producing cyanobacteria that contaminate water used for irrigation purposes. Strawberry (Fragaria vulgaris L.) is a widely cultivated plant of an increased economically importance worldwide. Its fruits provide essential elements for human nutrition; therefore, the study of its sensitivity to microcystins (MCs) is of paramount importance. The objective of this study was to evaluate the effects of MCs in irrigation water on the growth, physiology, and antioxidant defense system in F. vulgaris. In this study, strawberry seedlings at the three-leaf stage were grown in pots containing perlite under controlled conditions. Plants were exposed to a crude extract of Microcystis aeruginosa bloom at different concentrations of MCs (1, 5, 10, and 20 μg/L) for 60 days of exposure. The results showed that the highest concentrations of 10 and 20 μg/L induced a decrease in growth parameters. They resulted in root/shoot length decrease as well as number of leaves, roots/leaves dry and fresh weight. Furthermore, MCs reduced chlorophyll/carotenoid content, stomatal conductance, fluorescence, and total protein content of strawberry plants. At the same time, a significant increase in Malondialdehyde (MDA) (an indicator of lipid peroxidation), polyphenol, and sugar content were recorded in strawberry plants exposed to MCs at 5, 10, and 20 μg/L compared with the control. Additionally, superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), Polyphenoloxydase (PPO), and ascorbate peroxidase (APX) activities significantly increased in plants under MCs exposure. The oxidative stress was higher in plants exposed to 10 and 20 μg/L of MCs from the second harvest (after 60 days of exposure) compared to those from the first harvest (after 30 days). Overall, the results obtained in this study indicate an increasingly negative effect of MCs on strawberry plants grown in hydroponics even at concentrations (10 and 20 µg/L). This effect is more damaging on the roots after exposure (60 days).

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.

Effect of microcystins at different rice growth stages on its yield, quality, and safety

Microcystins (MCs) in water for irrigation may damage crop growth and enter food chains to threaten human health. To evaluate the potential risk of irrigation water contaminated with MCs, we exposed rice at each of the seedling, booting, and filling stages to irrigation water spiked with MCs at 1, 10, 100, and 1000 μg/L for 7 days. Afterwards, all rice underwent a recovery (without MCs) till the harvest. Low MCs (1 or10 μg/L) during different rice growth stages did not affect its yield and nutritional quality and had no risk to human health. High-concentration MCs (100 or 1000 μg/L) during the seedling or booting stage caused a larger decrease in the nutritional quality and yield of rice grains than that during the filling stage. In addition, MCs at 100 μg/L during the booting stage or at 1000 μg/L during the filling stage potentially threatened human health. The effect of MCs on rice yield, quality, and health risk was associated with the MC concentration and rice growth stage. Irrigation water contaminated with moderate-concentration MCs should be of concern at the early growth stage of rice.

Phytotoxicity and bioconcentration of microcystins in agricultural plants: Meta-analysis and risk assessment

Microcystins are cyanotoxins produced by many species of cyanobacteria. They are specific inhibitors of serine/threonine protein phosphatases and are phytotoxic to agricultural plants. This study used a formal meta-analysis to estimate the phytotoxicity and bioconcentration rates of agricultural plants exposed to microcystins, and the human health risk from consuming microcystin-contaminated plants. Among the 35 agricultural plants investigated, microcystins were most phytotoxic to durum wheat, corn, white mustard and garden cress. Leafy vegetables such as dill, parsley and cabbage could bioconcentrate ∼3 times more microcystins in their edible parts than other agricultural plants. Although the human health risk from ingesting microcystins could be greater for leafy vegetables than other agricultural plants, further work is needed to confirm bioconcentration of microcystins in realistic water-soil-plant environments. Still, we should avoid growing leafy vegetables, durum wheat and corn on agricultural land that is irrigated with microcystins-contaminated water and be attentive to the risk of microcystins contamination in the agricultural food supply.

Irrigation of radish (Raphanus sativus L.) with microcystin-enriched water holds low risk for plants and their associated rhizopheric and epiphytic microbiome

Microcystins (MCs) are toxins produced during cyanobacterial blooms. They reach soil and translocated to plants through irrigation of agricultural land with water from MC-impacted freshwater systems. To date we have good understanding of MC effects on plants, but not for their effects on plant-associated microbiota. We tested the hypothesis that MC-LR, either alone or with other stressors present in the water of the Karla reservoir (a low ecological quality and MC-impacted freshwater system), would affect radish plants and their rhizospheric and phyllospheric microbiome. In this context a pot experiment was employed where radish plants were irrigated with tap water without MC-LR (control) or with 2 or 12 μg L^-1 of pure MC-LR (MC2 and MC12), or water from the Karla reservoir amended (12 μg L^-1) or not with MC-LR. We measured MC levels in plants and rhizospheric soil and we determined effects on (i) plant growth and physiology (ii) the nitrifying microorganisms via q-PCR, (ii) the diversity of bacterial and fungal rhizospheric and epiphytic communities via amplicon sequencing. MC-LR and/or Karla water treatments resulted in the accumulation of MC in taproot at levels (480-700 ng g^-1) entailing possible health risks. MC did not affect plant growth or physiology and it did not impose a consistent inhibitory effect on soil nitrifiers. Karla water rather than MC-LR was the stronger determinant of the rhizospheric and epiphytic microbial communities, suggesting the presence of biotic or abiotic stressors, other than MC-LR, in the water of the Karla reservoir which affect microorganisms with a potential role (i.e. pathogens inhibition, methylotrophy) in the homeostasis of the plant-soil system. Overall, our findings suggest that MC-LR, when applied at environmentally relevant concentrations, is not expected to adversely affect the radish-microbiota system but might still pose risk for consumers' health.

[D-Leu1]MC-LR and MC-LR: A Small-Large Difference: Significantly Different Effects on Phaseolus vulgaris L. (Fabaceae) Growth and Phototropic Response after Single Contact during Imbibition with Each of These Microcystin Variants

[D-Leu¹]MC-LR and MC-LR, two microcystins differing in one amino acid, constitute a sanitary and environmental problem owing to their frequent and concomitant presence in water bodies of the Americas and their association with human intoxication during recreational exposure to cyanobacterial bloom. Present in reservoirs used for irrigation as well, they can generate problems in the development of crops such as Phaseolus vulgaris, of nutritional and economic interest to the region. Although numerous works address the toxic effects of MC-LR, information on the toxicity of [D-Leu¹]MC-LR is limited. Our objective was to study the toxic effects of [D-Leu¹]MC-LR and MC-LR (3.5 µg/ml) on P. vulgaris after a single contact at the imbibition stage. Our findings indicate that 10 days post treatment, [D-Leu¹]MC-LR generates morphological and physiological alterations more pronounced than those caused by MC-LR. In addition to the alterations produced by [D-Leu¹]MC-LR in the development of seedlings and the structure of the leaves, roots and stems, we also found alterations in leaf stomatal density and conductivity, a longer delay in the phototropic response and a decrease in the maximum curvature angles achieved with respect to that observed for MC-LR. Our findings indicate that these alterations are linked to the greater inhibition of phosphatase activity generated by [D-Leu¹]MC-LR, rather than to oxidative damage. We observed that 30 days after treatment with MC-LR, plants presented better development and recovery than those treated with [D-Leu¹]MC-LR. Further studies are required on [D-Leu¹]MC-LR and MC-LR toxicity and their underlying mechanisms of action.

Remote sensing of cyanobacterial blooms in a hypertrophic lagoon (Albufera of València, Eastern Iberian Peninsula) using multitemporal Sentinel-2 images

Eutrophy in Albufera of Valencia (Eastern Iberian Peninsula) is a quite old problem since after the intense eutrophication processes throughout the 1960s. The system shifted to a turbid stable state consolidated by the virtual disappearance of macrophytes by the early 1970s. The lagoon has been studied extensively since the 1980s, but efforts to revert the system to a clear state have not yielded the expected results because cultural eutrophication due to the growth of population in its area of influence and the effects of climate change, decreasing rainfall and increasing evaporation. This has driven to an increase in water retention times in the lagoon in recent years, resulting in a phytoplanktonic shift towards potentially toxic cyanobacteria species, often forming blooms. Cyanobacterial blooms severely affect water quality for human use, ranging from recreation and fishing to drinking water resources, as indicated in the surveillance protocol of World Health Organization (WHO). The current state of the lake requires constant monitoring and remote sensing is an optimal tool for the continuous monitoring of the whole water mass. This work is included in the ESAQS project (Ecological Status of AQuatic systems with Sentinel satellites), to establish a protocol for regular and frequent monitoring of the ecological status of reservoirs, lakes and lagoons. Algorithms are developed using the images provided by the Sentinel-2 (A and B), provided with a spatial resolution of 10 m and a temporal frequency of 5 days. In this work we demonstrate that using this new earth observation satellite is possible to develop a consistent and suitable algorithm to estimate the phycocyanin concentration [PC] and establish a protocol for regular and frequent monitoring. Calibrating (R² = 0.841; n = 21; p < 0.001) and validating (R² = 0.775; n = 55; p < 0.001; RMSE% = 40) the algorithm with field data are also demonstrated.

Assessment of Constructed Wetlands’ Potential for the Removal of Cyanobacteria and Microcystins (MC-LR)

Microcystis blooms and the subsequent release of hepatotoxic microcystins (MCs) pose a serious threat to the safety of water for human and livestock consumption, agriculture irrigation, and aquaculture worldwide. Microcystin-LR (MC-LR), the most toxic variant of MCs, has been widely detected in a variety of environments such as water, sediments, plants, and many aquatic organisms. Conventional solutions of water treatment are costly, requiring specific infrastructure, as well as specialized personnel and equipment. Therefore, these solutions are not feasible in many rural areas or in the treatment of large reservoirs. In this regard, low-cost and low-technology solutions, such as constructed wetlands (CWs), are attractive solutions to treat surface waters contaminated with toxic cyanobacteria blooms from lakes, ponds, reservoirs, and irrigation systems. In line with this, the main aim of this work was to evaluate the potential of CWs for the treatment of water contaminated with MC-LR produced by Microcystis aeruginosa—LEGE 91094. For that, microcosms (0.4 × 0.3 × 0.3 m) simulating CWs were assembled with Phragmites australis to treat lake water contaminated with Microcystis aeruginosa cells and MCs. Results showed removal percentages of M. aeruginosa cells above 94% and about 99% removal of MC-LR during 1 week treatment cycles. CWs maintained their functions, regardless the presence of MC-LR in the system, and also showed significant removal of nutrients (ammonium ion removal up to 86%) and organic matter (removal reaching 98%). The present work indicates that CWs have the potential for removal of cyanobacterial cells and cyanotoxins, which can be useful for the treatment of eutrophic waters and provide water of sufficient quality to be used, for instance, in agriculture.

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.

Mode of action and fate of microcystins in the complex soil-plant ecosystems

Over the last decades, global warming has increasingly stimulated the expansion of cyanobacterial blooms in freshwater ecosystems worldwide, in which toxic cyanobacteria produce various congeners of cyanotoxins, mainly dominated by microcystins (MCs). MCs introduced into agricultural soils have deleterious effects on the germination, growth and development of plants and their associated microbiota, leading to remarkable yield losses. Phytotoxicity of MCs may refer to the inhibition of phosphatases activity, generating deleterious reactive oxygen species, altering gene functioning and phytohormones translocation within the plant. It is also known that MCs can pass through the root membrane barrier, translocate within plant tissues and accumulate into different organs, including edible ones. Also, MCs impact the microbial activity in soil via altering plant-bacterial symbioses and decreasing bacterial growth rate of rhizospheric microbiota. Moreover, MCs can persist in agricultural soils through adsorption to clay-humic acid particles and results in a long-term contact with the plant-microflora complex. However, their bioavailability to plants and half-life in soil seem to be influenced by biodegradation process and soil physicochemical properties. This review reports the latest and most relevant information regarding MCs-phytotoxicity and impact on soil microbiota, the persistence in soil, the degradation by native microflora and the bioaccumulation within plant tissues.

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.

Effects of microcystin-LR on the tissue growth and physiological responses of the aquatic plant Iris pseudacorus L

The release of cyanobacterial toxins during algal bloom has adverse effects on aquatic plants and animals. This study aimed to understand the toxic effects and mechanism of microcystin-LR (MC-LR) on the seedling growth and physiological responses of Iris pseudacorus L. (calamus). After a one-month exposure experiment, the growth and development of the calamus leaves were significantly inhibited, and this inhibitory effect was verified to be concentration dependent. Furthermore, the cell membrane system was damaged, and the photosynthesis was also adversely affected by MC-LR. The relative conductivity of the leaves increased from 10.96% to 97.51%, and the total chlorophyll content decreased from 0.89 mg/g to 0.09 mg/g. Notably, the behavior of the roots in the presence of MC-LR was different from that of the leaves. The seedlings needed to absorb more nutrients to maintain the normal growth at low-toxin concentrations, but the high concentration of (over 250 μg/L) MC-LR exceeded the tolerance of plants and inhibited the growth of roots. In addition, MC-LR led to an excessive accumulation of H₂O₂, and the seedlings enhanced the activities of catalase, peroxidase, and superoxide dismutase to resist oxidative stress. The presence of MC-LR also affected the capacity of the plants to absorb nitrogen and phosphorus. The removal efficiency of NO₃^--N, the main source of nitrogen, was 63.53% in the presence of 100 μg/L MC-LR. As a result, the pH increased, and the growth of plants was indirectly inhibited. Therefore, the presence of MC-LR could affect the purification efficiency of calamus in eutrophic water. This study provides theoretical support for the selection of plants in the eutrophic water.

Seaweed Bioactive Compounds against Pathogens and Microalgae: Potential Uses on Pharmacology and Harmful Algae Bloom Control

Cyanobacteria are found globally due to their adaptation to various environments. The occurrence of cyanobacterial blooms is not a new phenomenon. The bloom-forming and toxin-producing species have been a persistent nuisance all over the world over the last decades. Evidence suggests that this trend might be attributed to a complex interplay of direct and indirect anthropogenic influences. To control cyanobacterial blooms, various strategies, including physical, chemical, and biological methods have been proposed. Nevertheless, the use of those strategies is usually not effective. The isolation of natural compounds from many aquatic and terrestrial plants and seaweeds has become an alternative approach for controlling harmful algae in aquatic systems. Seaweeds have received attention from scientists because of their bioactive compounds with antibacterial, antifungal, anti-microalgae, and antioxidant properties. The undesirable effects of cyanobacteria proliferations and potential control methods are here reviewed, focusing on the use of potent bioactive compounds, isolated from seaweeds, against microalgae and cyanobacteria growth.

Increment of root membrane permeability caused by microcystins result in more elements uptake in rice (Oryza sativa)

We conducted an indoor culture experiment to evaluate the phytotoxic effect of microcystins (MCs) on rice. After a 30day exposure, MCs induced a clear inhibition in rice growth, as well as a disruption of its antioxidant system and lipid peroxidation. We observed an increase in root membrane permeability; the conductivity of the leakage solution of the roots at 50 and 500μgL^-1 was significantly increased by 77% and 136%, respectively, compared to the control. Uptake of microelements (Fe, Mn, Cu and Zn) was generally not affected after the 30day exposure to MCs. In contrast, uptake of macroelements, with the exception of K, was stimulated by MCs. Ca content in roots exposed to 500μgL^-1 showed the greatest increase, by 47%, compared to the control. We propose the following mechanisms to explain our experimental results: exposure of rice roots to MCs leads to root damage and loss of membrane integrity, resulting in greater permeability and uptake of elements.

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.

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.

Lettuce irrigated with contaminated water: Photosynthetic effects, antioxidative response and bioaccumulation of microcystin congeners

The use of microcystins (MCs) contaminated water to irrigate crop plants represents a human health risk due to their bioaccumulation potential. In addition, MCs cause oxidative stress and negatively influence photosynthetic activities in plants. The present study was aimed at investigating the effect of MCs on photosynthetic parameters and antioxidative response of lettuce. Furthermore, the bioaccumulation factor (BAF) of total MCs, MC-LR and MC-RR in the vegetable after irrigation with contaminated water was determined. Lettuce crops were irrigated for 15 days with water containing cyanobacterial crude extracts (Microcystis aeruginosa) with MC-LR (0.0, 0.5, 2.0, 5.0 and 10.0 µg L(-1)), MC-RR (0.0, 0.15, 0.5, 1.5 and 3.0 µg L(-1)) and total MCs (0.0, 0.65, 2.5, 6.5 and 13.0 µg L(-1)). Increased net photosynthetic rate, stomatal conductance, leaf tissue transpiration and intercellular CO2 concentration were recorded in lettuce exposed to different MCs concentrations. Antioxidant response showed that glutathione S-transferase activity was down-regulated in the presence of MCs. On the other hand, superoxide dismutase, catalase and peroxidase activities were upregulated with increasing MCs concentrations. The bioaccumulation factor (BAF) of total MCs and MC-LR was highest at 6.50 and 5.00 µg L(-1), respectively, while for MC-RR, the highest BAF was recorded at 1.50 µg L(-1) concentration. The amount of total MCs, MC-LR and MC-RR bioacumulated in lettuce was highest at the highest exposure concentrations. However, at the lowest exposure concentration, there were no detectable levels of MC-LR, MC-RR and total MCs in lettuce. Thus, the bioaccumulation of MCs in lettuce varies according to the exposure concentration. In addition, the extent of physiological response of lettuce to the toxins relies on exposure concentrations.

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.

Evaluation of phytotoxicity and ecotoxicity potentials of a cyanobacterial extract containing microcystins under realistic environmental concentrations and in a soil-plant system

The impact of a crude extract of Microcystis aeruginosa (PCC7820) containing 14 microcystin variants was investigated on seeds germination and radicles development of four agricultural plants: two tomato varieties Solanum lycopersicum (MicroTom and Saint-Pierre), the wheat Triticum aestivum and the lettuce Lactuca sativa. In addition, the effect of 14 d-exposure to irrigation water containing realistic concentrations of microcystins (0-0.1 mg eq. microcystin-LRL(-1)) on the tomato MicroTom seedling growth was further evaluated on roots and aerial part biomasses. Impacts on soil bacterial parameters, as such extracellular enzymatic activities, nitrification activity and abundances of ammonia-oxidizing microorganisms were also investigated. In germination-test, the cyanobacterial extract inhibited only the germination of the wheat seeds, with an EC50 of 11 mg eq. microcystin-LRL(-1); which is 13 times lower than that of the cadmium chloride (EC50 of 145 mg L(-1)). Moreover, the cyanobacterial extract containing low concentrations of microcystins increased the growth of primary roots; however, high concentrations decreased it for all plants except for the wheat. In the soil-plant approach, only aerial part biomass of the tomato MicroTom was enhanced significantly. In addition, only soil nitrification potential and ammonia-oxidizing bacterial abundances were consistently impacted. A significant positive correlation (r=0.56) was found between the increase of nitrification potential and abundances of ammonia-oxidizing bacteria. This work suggested, that exposure to a cyanobacterial extract containing realistic environmental microcystins concentrations could affect seed germination, depending plant species. It was also highlighted, for the first time, disturbances in soil bacteria functioning, evidences on soil nitrification process.

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.

Exposure of Lycopersicon esculentum to microcystin-LR: effects in the leaf proteome and toxin translocation from water to leaves and fruits

Natural toxins such as those produced by freshwater cyanobacteria have been regarded as an emergent environmental threat. However, the impact of these water contaminants in agriculture is not yet fully understood. The aim of this work was to investigate microcystin-LR (MC-LR) toxicity in Lycopersicon esculentum and the toxin accumulation in this horticultural crop. Adult plants (2 month-old) grown in a greenhouse environment were exposed for 2 weeks to either pure MC-LR (100 μg/L) or Microcystis aeruginosa crude extracts containing 100 μg/L MC-LR. Chlorophyll fluorescence was measured, leaf proteome investigated with two-dimensional gel electrophoresis and Matrix Assisted Laser Desorption Ionization Time-of-Flight (MALDI-TOF)/TOF, and toxin bioaccumulation assessed by liquid chromatography-mass spectrometry (LC-MS)/MS. Variations in several protein markers (ATP synthase subunits, Cytochrome b6-f complex iron-sulfur, oxygen-evolving enhancer proteins) highlight the decrease of the capacity of plants to synthesize ATP and to perform photosynthesis, whereas variations in other proteins (ribulose-1,5-bisphosphate carboxylase/oxygenase large subunit and ribose-5-phosphate isomerase) suggest an increase of carbon fixation and decrease of carbohydrate metabolism reactions in plants exposed to pure MC-LR and cyanobacterial extracts, respectively. MC-LR was found in roots (1635.21 μg/kg fw), green tomatoes (5.15–5.41 μg/kg fw), mature tomatoes (10.52–10.83 μg/kg fw), and leaves (12,298.18 μg/kg fw). The results raise concerns relative to food safety and point to the necessity of monitoring the bioaccumulation of water toxins in agricultural systems affected by cyanotoxin contamination.

Early physiological and biochemical responses of rice seedlings to low concentration of microcystin-LR

Microcystin-leucine and arginine (microcystin-LR) is a cyanotoxin produced by cyanobacteria like Microcystis aeruginosa, and it's considered a threat to water quality, agriculture, and human health. Rice (Oryza sativa) is a plant of great importance in human food consumption and economy, with extensive use around the world. It is therefore important to assess the possible effects of using water contaminated with microcystin-LR to irrigate rice crops, in order to ensure a safe, high quality product to consumers. In this study, 12 and 20-day-old plants were exposed during 2 or 7 days to a M. aeruginosa extract containing environmentally relevant microcystin-LR concentrations, 0.26-78 μg/L. Fresh and dry weight of roots and leaves, chlorophyll fluorescence, glutathione S-transferase and glutathione peroxidase activities, and protein identification by mass spectrometry through two-dimensional gel electrophoresis from root and leaf tissues, were evaluated in order to gauge the plant's physiological condition and biochemical response after toxin exposure. Results obtained from plant biomass, chlorophyll fluorescence, and enzyme activity assays showed no significant differences between control and treatment groups. However, proteomics data indicates that plants respond to M. aeruginosa extract containing environmentally relevant microcystin-LR concentrations by changing their metabolism, responding differently to different toxin concentrations. Biological processes most affected were related to protein folding and stress response, protein biosynthesis, cell signalling and gene expression regulation, and energy and carbohydrate metabolism which may denote a toxic effect induced by M. aeruginosa extract and microcystin-LR. The implications of the metabolic alterations in plant physiology and growth require further elucidation.

Cyanobacterial toxins: modes of actions, fate in aquatic and soil ecosystems, phytotoxicity and bioaccumulation in agricultural crops

The occurrence of harmful cyanobacterial blooms in surface waters is often accompanied by the production of a variety of cyanotoxins. These toxins are designed to target in humans and animals specific organs on which they act: hepatotoxins (liver), neurotoxins (nervous system), cytotoxic alkaloids, and dermatotoxins (skin), but they often have important side effects too. When introduced into the soil ecosystem by spray irrigation of crops they may affect the same molecular pathways in plants having identical or similar target organs, tissues, cells or biomolecules. There are also several indications that terrestrial plants, including food crop plants, can bioaccumulate cyanotoxins and present, therefore, potential health hazards for human and animals. The number of publications concerned with phytotoxic effects of cyanotoxins on agricultural plants has increased recently. In this review, we first examine different cyanotoxins and their modes of actions in humans and mammals and occurrence of target biomolecules in vegetable organisms. Then we present environmental concentrations of cyanotoxins in freshwaters and their fate in aquatic and soil ecosystems. Finally, we highlight bioaccumulation of cyanotoxins in plants used for feed and food and its consequences on animals and human health. Overall, our review shows that the information on the effects of cyanotoxins on non-target organisms in the terrestrial environment is particularly scarce, and that there are still serious gaps in the knowledge about the fate in the soil ecosystems and phytotoxicity of these toxins.