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

Potential (co-)contamination of dairy milk with AFM1 and MC-LR and their synergistic interaction in inducing mitochondrial dysfunction in HepG2 cells

Several toxic metabolites, such as aflatoxin M1 (AFM1), are known to contaminate dairy milk. However, as mentioned in an external EFSA report, there is a knowledge gap regarding the carry-over of certain emerging toxins such as microcystin-LR (MC-LR). Therefore, this work aimed to develop an LC-MS/MS method for MC-LR quantification in dairy milk. Also, the method included AFM1 as a common fungal metabolite and applied to analyze 113 dairy milk samples collected directly after the end of the summer peak. Both toxins were below their LODs, keeping the question on MC-LR carry-over still unanswered. Moreover, an in silico analysis, using a 3D molecular modeling was performed, pointing to a possible interaction between MC-LR and milk proteins, especially β-lactoglobulin. Since AFM1 and MC-LR are hepatotoxic, their interaction in inducing mitochondrial dysfunction in HepG2 cells was investigated at low (subcytotoxic) concentrations. Live cell imaging-based assays showed an inhibition in cell viability, without involvement of caspase-3/7, and a hyperpolarization in the mitochondrial membrane potential after the exposure to a mixture of 100 ng mL-1 AFM1 and 1000 ng mL-1 MC-LR for 48h. Extracellular flux analysis revealed inhibitions of several key parameters of mitochondrial function (basal respiration, ATP-linked respiration, and spare respiratory capacity).

The biological functions of microcystins

Microcystins are potent hepatotoxins predominantly produced by bloom-forming freshwater cyanobacteria (e.g., Microcystis, Planktothrix, Dolichospermum). Microcystin biosynthesis involves large multienzyme complexes and tailoring enzymes encoded by the mcy gene cluster. Mutation, recombination, and deletion events have shaped the mcy gene cluster in the course of evolution, resulting in a large diversity of microcystin congeners and the natural coexistence of toxic and non-toxic strains. The biological functions of microcystins and their association with algal bloom formation have been extensively investigated over the past decades. This review synthesizes recent advances in decoding the biological role of microcystins in carbon/nitrogen metabolism, antioxidation, colony formation, and cell-to-cell communication. Microcystins appear to adopt multifunctional roles in cyanobacteria that reflect the adaptive plasticity of toxic cyanobacteria to changing environments.

Nodding syndrome: A role for environmental biotoxins that dysregulate MECP2 expression?

Nodding syndrome is an epileptic encephalopathy associated with neuroinflammation and tauopathy. This initially pediatric brain disease, which has some clinical overlap with Methyl-CpG-binding protein 2 (MECP2) Duplication Syndrome, has impacted certain impoverished East African communities coincident with local civil conflict and internal displacement, conditions that forced dependence on contaminated food and water. A potential role in Nodding syndrome for certain biotoxins (freshwater cyanotoxins plus/minus mycotoxins) with neuroinflammatory, excitotoxic, tauopathic, and MECP2-dysregulating properties, is considered here for the first time.

Congener-specific fate and impact of microcystins in the soil-earthworm system

Microcystins (MCs) have a significant influence on aquatic ecosystems, but little is known about their terrestrial fate and impact. Here, we investigated the fate of two MCs (MC-LR and MC-RR) in the soil-earthworm system, with consideration of their congener-specific impact on earthworm health, soil bacteria, and soil metabolome. Although MCs had little acute lethal effect on earthworms, they caused obvious growth inhibition and setae rupture. Relative to MC-RR, MC-LR exhibited higher bioaccumulation and the resulting dermal lesions and deformation of longitudinal muscles. While the incorporation of both MCs into soils stimulated pathogenic bacteria and depressed oxidative stress tolerant bacteria, the response among soil nitrification and glutathione metabolism differed between the two congeners. The dissipation kinetics of MCs obeyed the first-order model. Earthworms stimulated soil N-cycling enzyme activities, increased the abundance of MC-degrading bacteria, and promoted bacterial metabolic functions related to glutathione metabolism, xenobiotics biodegradation, and metabolism of amino acids that comprise MCs, which accelerated the dissipation of MC-LR and MC-RR by 227% and 82%, respectively. These results provide evidence of significant congener differences in the terrestrial fate and impact of MCs, which will enable a better understanding of their role in mediating soil functions and ecosystem services.

Microcystin-LR, a cyanotoxin, modulates division of higher plant chloroplasts through protein phosphatase inhibition and affects cyanobacterial division

Microcystin-LR (MC-LR) is a harmful cyanotoxin that inhibits 1 and 2A serine-threonine protein phosphatases. This study examines the influence of MC-LR on chloroplast division and the underlying mechanisms and consequences in Arabidopsis. MC-LR increased the frequency of dividing chloroplasts in hypocotyls in a time range of 1-96 h. At short-term exposures to MC-LR, small-sized chloroplasts (longitudinal diameters ≤6 μm) were more sensitive to these stimulatory effects, while both small and large chloroplasts showed stimulations at long-term exposure. After 48 h, the cyanotoxin increased the frequency of small-sized chloroplasts, indicating the stimulation of division. MC-LR inhibited protein phosphatases in whole hypocotyls and isolated chloroplasts, while it did not induce oxidative stress. We show for the first time that total cellular phosphatases play important roles in chloroplast division and that particular chloroplast phosphatases may be involved in these processes. Interestingly, MC-LR has a protective effect on cyanobacterial division during methyl-viologen (MV) treatments in Synechococcus PCC6301. MC-LR production has harmful effects on ecosystems and it may have an ancient cell division regulatory role in stressed cyanobacterial cells, the evolutionary ancestors of chloroplasts. We propose that cytoplasmic (eukaryotic) factors also contribute to the relevant effects of MC-LR in plants.

Cyanotoxins in food: Exposure assessment and health impact

The intricate nature of cyanotoxin exposure through food reveals a complex web of risks and uncertainties in our dietary choices. With the aim of starting to unravel this intricate nexus, a comprehensive review of 111 papers from the past two decades investigating cyanotoxin contamination in food was undertaken. It revealed a widespread occurrence of cyanotoxins in diverse food sources across 31 countries. Notably, 68% of the studies reported microcystin concentrations exceeding established Tolerable Daily Intake levels. Cyanotoxins were detected in muscles of many fish species, and while herbivorous fish exhibited the highest recorded concentration, omnivorous species displayed a higher propensity for cyanotoxin accumulation, exemplified by Oreochromis niloticus. Beyond fish, crustaceans and bivalves emerged as potent cyanotoxin accumulators. Gaps persist regarding contamination of terrestrial and exotic animals and their products, necessitating further exploration. Plant contamination under natural conditions remains underreported, yet evidence underscores irrigation-driven cyanotoxin accumulation, particularly affecting leafy vegetables. Finally, cyanobacterial-based food supplements often harbored cyanotoxins (57 % of samples were positive) warranting heightened scrutiny, especially for Aphanizomenon flos-aquae-based products. Uncertainties surround precise concentrations due to methodological variations (chemical and biochemical) and extraction limitations, along with the enigmatic fate of toxins during storage, processing, and digestion. Nonetheless, potential health consequences of cyanotoxin exposure via contaminated food include gastrointestinal and neurological disorders, organ damage (e.g. liver, kidneys, muscles), and even elevated cancer risks. While microcystins received significant attention, knowledge gaps persist regarding other cyanotoxins' accumulation, exposure, and effects, as well as combined exposure via multiple pathways. Intriguing and complex, cyanotoxin exposure through food beckons further research for our safer and healthier diets.

Experimental accumulation and depuration kinetics and natural occurrence of microcystin-LR in basil (Ocimum basilicum L.)

Microcystin-LR (MC-LR) is a hepatotoxic metabolite that naturally occurs during some cyanobacterial blooms in eutrophic waterbodies, and irrigation of edible plants with MC-LR-contaminated water causes bioaccumulation of the toxin. However, sufficient information about accumulation and depuration mechanics in hydroculture-grown herb plants is still lacking. This work aimed at 1) investigating bioaccumulation and depuration of MC-LR in basil, 2) verifying the possible MC-LR detoxification mechanisms in the plant, and 3) detecting the natural occurrence of MC-LR in basil (n = 50) collected from the Belgian market. Basil plants grown in a hydroculture were exposed to MC-LR (5, 20, and 50 μg L-1) spiked in a Hoagland solution for seven days. MC-LR depuration was also studied by transferring the plants to a non-contaminated Hoagland solution after exposure to MC-LR for another seven days. MC-LR concentrations in Hoagland solution, basil leaves, and roots were quantified using a validated UHPLC-MS/MS method. In addition, ELISA and LC-HRMS (only basil leaves) were used for confirmation. The results showed an increase in the accumulated levels of MC-LR at higher exposure doses, with higher MC-LR levels in roots than in leaves for all the treatment conditions. For MC-LR depuration, significant reductions were observed in all the treatment conditions for roots only. No MC-LR conjugates, potentially related to metabolism, were detected by LC-HRMS. Finally, MC-LR was detected in one store-bought basil sample, representing the first occurrence of cyanotoxins in an edible crop from Belgium.

Capillary electrophoresis tandem mass spectrometry to determine multiclass cyanotoxins in reservoir water and spinach samples

Cyanotoxins constitute a group of toxic secondary metabolites, the presence of which in any water body poses a major health risk. Moreover, advanced organisms such as edible plants exposed to these toxins, are a possible pathway for human exposure. Green analytical chemistry is demanding environmentally friendly analytical techniques. In this sense, we propose the use of capillary electrophoresis coupled to tandem mass spectrometry (CE-MS/MS) to determine a mixture of eight cyanotoxins belonging to three different classes: cyclic peptides (microcystin-LR, microcystin-RR and nodularin), alkaloids (cylindrospermopsin and anatoxin-a) and three isomeric non-protein amino acids (β-methylamino-l-alanine, 2,4-diaminobutyric acid and N-(2-aminoethyl)glycine). Separation was achieved by using an acidic background electrolyte consisting of 2 M formic acid and 20% acetonitrile in water. Parameters affecting MS/MS detection and the sheath-liquid interface were also studied. Finally, a combination of pH-junction, field-amplified sample stacking (FASS) and acid barrage as online preconcentration strategies, was employed to improve sensitivity and efficiency. The online preconcentration applied, in combination with a dual cartridge solid-phase extraction (SPE) system, allows to obtain limits of detection in the very low range of µg·L-1 for these multiclass cyanotoxins in reservoir water samples (from 0.005 to 0.10 µg·L-1). Furthermore, for the first time cyanotoxins are analysed in spinach samples through CE-MS/MS using the same SPE procedure, following lyophilisation and solid-liquid extraction with 6 mL 80 % aqueous MeOH.

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.

Biochemical and transcriptomic responses of buckwheat to polyethylene microplastics

The ubiquity of microplastic is widely recognized as pollution. Microplastic can affect the growth performances of plants. Buckwheat is a potential model crop to investigate plant responses to hazardous materials. Still, little is known about the response of buckwheat to microplastics. Thus, this study investigated the effect and uptake of polyethylene (PE) in buckwheat plant growth by monitoring the morphological and photosynthetic merits, antioxidant systems and transcriptome analysis of gene expression. Results confirmed that the impacts of PE on buckwheat growth were dose-dependent, while the highest concentration (80 mg/L) exposure elicited significantly negative responses of buckwheat. PE can invade buckwheat roots and locate in the vascular tissues. PE exposure disturbed the processes of carbon fixation and the synthesis of ATP from ADP + Pi in buckwheat leaves. The promotion of photosynthesis under PE exposure could generate extra energy for buckwheat leaves to activate antioxidant systems by increasing the antioxidant enzyme activities at an expense of morphological merits under microplastic stresses. Further in-depth study is warranted about figuring out the interactions between microplastics and biochemical responses (i.e., photosynthesis and antioxidant systems), which have great implications for deciphering the defense mechanism of buckwheat to microplastic stresses.

The Potential of Allelochemicals from Microalgae for Biopesticides

Improvements in agricultural productivity are required to meet the demand of a growing world population. Phytopathogens, weeds, and insects are challenges to agricultural production. The toxicity and widespread application of persistent synthetic pesticides poses a major threat to human and ecosystem health. Therefore, sustainable strategies to control pests are essential for agricultural systems to enhance productivity within a green paradigm. Allelochemicals are a less persistent, safer, and friendly alternative to efficient pest management, as they tend to be less toxic to non-target organisms and more easily degradable. Microalgae produce a great variety of allelopathic substances whose biocontrol potential against weeds, insects, and phytopathogenic fungi and bacteria has received much attention. This review provides up-to-date information and a critical perspective on allelochemicals from microalgae and their potential as biopesticides.

A meta-analysis on the toxicity of microcystin-LR to fish and mammals

Microcystin-leucine arginine (MC-LR), the most prevalent and dangerous microcystin, poses high risks to living organisms, especially fish and mammals. Although many studies have focused on the toxic effect on fish and mammals exposed to MC-LR, works that incorporate published data into a comprehensive comparison and analysis are still limited. Here, the adverse effects of oxidative stress markers, health, functional traits, and performance traits in fish and mammals were systematically verified by collecting data from 67 studies for the first time. Notably, we first found that the activities of malondialdehyde (MDA) (p < 0.05) and lactoperoxidase (LPO) always showed increases, whereas the growth (performance traits) always had a significant decrease (p < 0.001) under all variables of MC-LR exposure, i.e., exposure time, exposure concentration, exposure route, and even life stage. Additionally, our study first verified that the activities of MDA and LPO can be employed as oxidative stress indicators of MC-LR effects in fish and mammals instead of other biomarkers of oxidative stress, such as superoxide dismutase (SOD) and catalase (CAT), considered by previous studies. Growth may be regarded as a highly sensitive indicator of MC-LR toxicity in mammals and fish. At the same time, we first found that the impact of MC-LR exposure concentration on LPO, MDA, and growth is higher than that of exposure time, exposure route, and different life stages using the random forest (RF) model. In short, this work sheds light on the potential biochemical and individual toxicity of MC-LR exposure in fish and mammals.

Environmental microcystin exposure triggers the poor prognosis of prostate cancer: Evidence from case-control, animal, and in vitro studies

Microcystin-leucine-arginine (MC-LR) is positively linked with multiple cancers in humans. However, the association between MC-LR and the risk and prognosis of prostate cancer has not been conducted in epidemiological studies. No reported studies have linked MC-LR exposure to the poor prognosis of prostate cancer by conducting experimental studies. The content of MC-LR was detected in most of the aquatic food in wet markets and supermarkets in Nanjing and posed a health risk for consumers. MC-LR levels in both prostate cancer tissues and serum were significantly higher than controls. The adjusted odds ratio (OR) for prostate cancer risk by serum MC-LR was 1.75 (95%CI: 1.21-2.52) in the whole subjects, and a positive correlation between MC-LR and advanced tumor stage was observed. Survival curve analysis indicated patients with higher MC-LR levels in tissues exhibited poorer overall survival. Human, animal, and cell studies confirmed that MC-LR exposure increases the expression of estrogen receptor-α (ERα) and promotes epithelial-mesenchymal transition (EMT) in prostate cancer. Moreover, MC-LR-induced decreased E-cadherin levels, increased vimentin levels, and increased migratory and invasive capacities of prostate cancer cells were markedly suppressed upon ERα knockdown. MC-LR-induced xenograft tumor growth and lung metastasis in BALB/c nude mice can be effectively alleviated with ERα knockdown. Our data demonstrated that MC-LR upregulated vimentin and downregulated E-cadherin through activating ERα, promoting migration and invasion of prostate cancer cells. Our findings highlight the role of MC-LR in prostate cancer, providing new perspectives to understand MC-LR-induced prostatic toxicity.

Harmful cyanobacteria-diatom/dinoflagellate blooms and their cyanotoxins in freshwaters: A nonnegligible chronic health and ecological hazard

Human and ecological health depends on the vitality of freshwater systems, but these are increasingly threatened by cyanotoxins released from harmful algal blooms (HABs). Periodic cyanotoxin production, although undesirable, may be tolerable when there is enough time for cyanotoxins to degrade and dissipate in the environment, but the year-round presence of these toxins will be a chronic health for humans and ecosystems. The purpose of this critical review is to document the seasonal shifts of algal species and their ecophysiological acclimatation to dynamic environmental conditions. We discuss how these conditions will create successive occurrences of algal blooms and the release of cyanotoxins into freshwater. We first review the most common cyanotoxins, and evaluate the multiple ecological roles and physiological functions of these toxins for algae. Then, the annual recurring patterns HABs are considered in the context of global change, which demonstrates the capacity for algal blooms to shift from seasonal to year-round growth regimes that are driven by abiotic and biotic factors, leading to chronic loading of freshwaters with cyanotoxins. At last, we illustrate the impacts of HABs on the environment by compiling four health issues and four ecology issues emanating from their presence in the that covers atmosphere, aquatic ecosystems and terrestrial ecosystems. Our study highlights the annual patterns of algal blooms, and proposes that a "perfect storm" of events is lurking that will cause the 'seasonal toxicity' to become a full-blown, 'chronic toxicity' in the context of the deterioration of HABs, highlighting a non-negligible chronic health and ecological hazard.

Adaptation of protein phosphatases in Oryza sativa and Cucumis sativus to microcystins

Microcystins (MCs) in irrigation water could inhibit crop growth and yield. Protein phosphatases (PPs) play an important role in regulating physiological mechanisms in plants to adapt abiotic stresses. To clarify the adaptation mechanism in plants to MCs stress, we compared PPs in rice and cucumber leaves by analyzing PPs total activity, protein phosphatase-2A (PP2A) activity and expression, as well as related growth and gas exchange parameters. After 7-day exposure of MCs (5 ~ 100 µg/L) and 7-day recovery without MCs, rice showed higher tolerance to MCs by analyzing dry weight and gas exchange parameters. Both crops may regulate PPs activity to adapt MCs stress by increasing the expression of genes encoding PPs. Among them, PP2A activity in two crops showed more sensitivity to MCs than total PPs activity. In addition, the higher expressions of PP2A catalytic and regulatory subunits and lower decrease PP2A activity were observed in rice leaves compared to cucumber. All results suggest that the expression levels of PP2A subunits could play a role in maintaining the activity of PP2A to regulating plant tolerance to MCs stress.

Behavior and fate of microcystin-LR in soils amended with biochar and peat

Activities such as irrigation with cyanobacteria-polluted water can lead to microcystins (MCs) migration from soil surface to the deeper layers, which could pose a potential risk to ground drinking water safety. The present study evaluated the sorption, degradation and leaching behavior of microcystin-LR (MC-LR) in two different soils amended with biochar and peat. Results showed that both biochar and peat could significantly increase MC-LR sorption in both soils. The Freundlich unit capacity coefficient (K_f) of 2% biochar treatment were 2-3 times higher than those of the control treatment. Amendment of 2% peat greatly boosted the biodegradation of MC-LR, whereas amendment of 2% biochar significantly reduced the biodegradation of MC-LR in both soils. The half-lives of MC-LR were 4.99 d (Control), 5.59 d (2% Biochar) and 3.50 d (2% Peat) in soil A and 6.66 d (Control), 6.93 d (2% Biochar) and 5.13 d (2% Peat) in soil B, respectively. All the amendments, except treatment 1% Peat, could significantly reduce the recovery rates of MC-LR in the leachate of columns with both soils. Amendment of 2% biochar and 2% peat reduced the recovery rates of MC-LR by 15.87% and 8.6% in soil A and 18.4% and 10.3% in soil B, compared with the controls. This work provides a better understanding of the environmental behavior of MC-LR in soils with different amendments, which is also meaningful for groundwater protection in cyanobacterial-polluted areas.

Chronic Exposure to Environmentally Relevant Concentrations of Microcystin-Leucine Arginine Causes Lung Barrier Damage through PP2A Activity Inhibition and Claudin1 Ubiquitination

Microcystin-leucine arginine (MC-LR), ubiquitous in water and food, is a threat to public health. In the present study, after C57BL/6J mice were fed with environmental concentrations of MC-LR (0, 1, 30, 60, 90, and 120 μg/L) for 6, 9, and 12 months, it was found that MC-LR could enter into mouse lung tissues and cause microstructural damage, as shown by western blotting and HE staining. Electron microscopy examination showed that MC-LR could damage the lung barrier by disruption of the tight junctions, which was confirmed by the decreased expression of tight junction markers, including Occludin, Claudin1, and ZO-1. In addition, MC-LR also increased the ubiquitination of Claudin1, indicating that MC-LR could disrupt tight junctions by promoting the degradation of Claudin1. Furthermore, MC-LR increased the levels of TNF-α and IL-6 in mouse lung tissues, leading to pneumonia. Importantly, pretreatment with PP2A activator D-erythro-sphingosine (DES) was found to significantly alleviate MC-LR-induced decrease of Occludin and Claudin1 by inhibiting the P-AKT/Snail pathway in vitro. Together, this study revealed that chronic exposure to MC-LR causes lung barrier damage, which involves PP2A activity inhibition and enhancement of Claudin1 ubiquitination. This study broadens the awareness of the toxic effects of MC-LR on the respiratory system, which has deep implications for public health.

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.

Subacute and sublethal ingestion of microcystin-LR impairs lung mitochondrial function by an oligomycin-like effect

Microcystin-LR (MC-LR) is a potent cyanotoxin that can reach several organs. However subacute exposure to sublethal doses of MC-LR has not yet well been studied. Herein, we evaluated the outcomes of subacute and sublethal MC-LR exposure on lungs. Male BALB/c mice were exposed to MC-LR by gavage (30 µg/kg) for 20 consecutive days, whereas CTRL mice received filtered water. Respiratory mechanics was not altered in MC-LR group, but histopathology disclosed increased collagen deposition, immunological cell infiltration, and higher percentage of collapsed alveoli. Mitochondrial function was extensively affected in MC-LR animals. Additionally, a direct in vitro titration of MC-LR revealed impaired mitochondrial function. In conclusion, MC-LR presented an intense deleterious effect on lung mitochondrial function and histology. Furthermore, MC-LR seems to exert an oligomycin-like effect in lung mitochondria. This study opens new perspectives for the understanding of the putative pulmonary initial mechanisms of damage resulting from oral MC-LR intoxication.

Microcystin Contamination and Toxicity: Implications for Agriculture and Public Health

Microcystins are natural hepatotoxic metabolites secreted by cyanobacteria in aquatic ecosystems. When present at elevated concentrations, microcystins can affect water quality aesthetics; contaminate drinking water reservoirs and recreational waters; disrupt normal ecosystem functioning; and cause health hazards to animals, plants, and humans. Animal and human exposures to microcystins generally result from ingesting contaminated drinking water or physically contacting tainted water. Much research has identified a multitude of liver problems from oral exposure to microcystins, varying from hepatocellular damage to primary liver cancer. Provisional guidelines for microcystins in drinking and recreational water have been established to prevent toxic exposures and protect public health. With increasing occurrences of eutrophication in freshwater systems, microcystin contamination in groundwater and surface waters is growing, posing threats to aquatic and terrestrial plants and agricultural soils used for crop production. These microcystins are often transferred to crops via irrigation with local sources of water, such as bloom-forming lakes and ponds. Microcystins can survive in high quantities in various parts of plants (roots, stems, and leaves) due to their high chemical stability and low molecular weight, increasing health risks for consumers of agricultural products. Studies have indicated potential health risks associated with contaminated fruits and vegetables sourced from irrigated water containing microcystins. This review considers the exposure risk to humans, plants, and the environment due to the presence of microcystins in local water reservoirs used for drinking and irrigation. Additional studies are needed to understand the specific health impacts associated with the consumption of microcystin-contaminated agricultural plants.

Cyanobacteria: A Natural Source for Controlling Agricultural Plant Diseases Caused by Fungi and Oomycetes and Improving Plant Growth

Cyanobacteria, also called blue-green algae, are a group of prokaryotic microorganisms largely distributed in both terrestrial and aquatic environments. They produce a wide range of bioactive compounds that are mostly used in cosmetics, animal feed and human food, nutraceutical and pharmaceutical industries, and the production of biofuels. Nowadays, the research concerning the use of cyanobacteria in agriculture has pointed out their potential as biofertilizers and as a source of bioactive compounds, such as phycobiliproteins, for plant pathogen control and as inducers of plant systemic resistance. The use of alternative products in place of synthetic ones for plant disease control is also encouraged by European Directive 2009/128/EC. The present up-to-date review gives an overall view of the recent results on the use of cyanobacteria for both their bioprotective effect against fungal and oomycete phytopathogens and their plant biostimulant properties. We highlight the need for considering several factors for a proper and sustainable management of agricultural crops, ranging from the mechanisms by which cyanobacteria reduce plant diseases and modulate plant resistance to the enhancement of plant growth.

Cerium exposure in Lake Taihu water aggravates microcystin pollution via enhancing endocytosis of Microcystis aeruginosa

Aggravating the pollution of microcystins (MCs) in freshwater environments is detrimental to aquatic living organisms and humans, and thus threatens the stability of ecosystems. Some environmental factors have been verified to promote the production of MCs in Microcystis aeruginosa, thereby aggravating the pollution of MCs. However, the effects of cerium (Ce), the most abundant rare earth element in global water environments, on the production of MCs in M. aeruginosa are unknown. Here, Lake Taihu water was selected as a representative of freshwater environments. By using interdisciplinary methods, it was found that: (1) the exposure level of Ce [Ce(III) and Ce(IV)] in Lake Taihu water is in the range of 0.271-0.282 μg/L; (2) Ce exposure in Lake Taihu water promoted the contents of three main MCs (MC-LR, MC-LW and MC-YR) in M. aeruginosa and water; (3) a cellular mechanism of Ce promoting the production of MCs in M. aeruginosa in Lake Taihu water was suggested: Ce enhanced endocytosis in cells of M. aeruginosa to promote the essential element uptake by M. aeruginosa for MC synthesis. Thus, Ce exposure in Lake Taihu water aggravates the pollution of MCs via enhancing endocytosis in cells of M. aeruginosa. The results provide reference for assessing the environmental risk of Ce in water environments, investigating the mechanism of the pollution of MCs induced by environmental factors, and developing strategies aimed at preventing and controlling the pollution of MCs.

Cyanotoxins and Food Contamination in Developing Countries: Review of Their Types, Toxicity, Analysis, Occurrence and Mitigation Strategies

Cyanotoxins have gained global public interest due to their potential to bioaccumulate in food, which threatens human health. Bloom formation is usually enhanced under Mediterranean, subtropical and tropical climates which are the dominant climate types in developing countries. In this context, we present an up-to-date overview of cyanotoxins (types, toxic effects, analysis, occurrence, and mitigation) with a special focus on their contamination in (sea)food from all the developing countries in Africa, Asia, and Latin America as this has received less attention. A total of 65 publications have been found (from 2000 until October 2021) reporting the contamination by one or more cyanotoxins in seafood and edible plants (five papers). Only Brazil and China conducted more research on cyanotoxin contamination in food in comparison to other countries. The majority of research focused on the detection of microcystins using different analytical methods. The detected levels mostly surpassed the provisional tolerable daily intake limit set by the World Health Organization, indicating a real risk to the exposed population. Assessment of cyanotoxin contamination in foods from developing countries still requires further investigations by conducting more survey studies, especially the simultaneous detection of multiple categories of cyanotoxins in food.

Variant-Specific Adsorption, Desorption, and Dissipation of Microcystin Toxins in Surface Soil

Microcystins (MCs) are hepatotoxic heptapeptides identified in cyanobacterial bloom-impacted waters and soils. However, their environmental fate in soils is poorly understood, preventing reliable site assessment. This study aims to clarify the variant-specific adsorption, desorption, and dissipation of MC-LR and MC-RR in agricultural soils. Results revealed that their adsorption isotherms followed the Freundlich model (R² ≥ 0.96), exhibiting a higher nonlinear trend and lower adsorption capacity for MC-LR than for MC-RR. The soils had low desorption rates of 8.14-21.06% and 3.06-34.04%, respectively, following a 24 h desorption cycle. Pairwise comparison indicated that soil pH and clay played key roles in MC-LR adsorption and desorption, while organic matter and cation exchange capacity played key roles in those of MC-RR. MC-LR dissipation half-lives in soils were 27.18-42.52 days, compared with 35.19-43.87 days for MC-RR. Specifically, an appreciable decrease in MC concentration in sterile soils suggested the significant role of abiotic degradation. This study demonstrates that the minor structural changes in MCs might have major effects on their environmental fates in agricultural soil and indicates that the toxic effects of MCs should be of high concern due to high adsorption, low desorption, and slow dissipation.

Impacts of Microcystins on Morphological and Physiological Parameters of Agricultural Plants: A Review

Cyanobacteria are a group of photosynthetic prokaryotes that pose a great concern in the aquatic environments related to contamination and poisoning of wild life and humans. Some species of cyanobacteria produce potent toxins such as microcystins (MCs), which are extremely aggressive to several organisms, including animals and humans. In order to protect human health and prevent human exposure to this type of organisms and toxins, regulatory limits for MCs in drinking water have been established in most countries. In this regard, the World Health Organization (WHO) proposed 1 µg MCs/L as the highest acceptable concentration in drinking water. However, regulatory limits were not defined in waters used in other applications/activities, constituting a potential threat to the environment and to human health. Indeed, water contaminated with MCs or other cyanotoxins is recurrently used in agriculture and for crop and food production. Several deleterious effects of MCs including a decrease in growth, tissue necrosis, inhibition of photosynthesis and metabolic changes have been reported in plants leading to the impairment of crop productivity and economic loss. Studies have also revealed significant accumulation of MCs in edible tissues and plant organs, which raise concerns related to food safety. This work aims to systematize and analyze the information generated by previous scientific studies, namely on the phytotoxicity and the impact of MCs especially on growth, photosynthesis and productivity of agricultural plants. Morphological and physiological parameters of agronomic interest are overviewed in detail in this work, with the aim to evaluate the putative impact of MCs under field conditions. Finally, concentration-dependent effects are highlighted, as these can assist in future guidelines for irrigation waters and establish regulatory limits for MCs.

Protective Role of Native Rhizospheric Soil Microbiota Against the Exposure to Microcystins Introduced into Soil-Plant System via Contaminated Irrigation Water and Health Risk Assessment

Microcystins (MCs) produced in eutrophic waters may decrease crop yield, enter food chains and threaten human and animal health. The main objective of this research was to highlight the role of rhizospheric soil microbiota to protect faba bean plants from MCs toxicity after chronic exposure. Faba bean seedlings were grown in pots containing agricultural soil, during 1 month under natural environmental conditions of Marrakech city in Morocco (March–April 2018) and exposed to cyanobacterial extracts containing up to 2.5 mg·L⁻¹ of total MCs. Three independent exposure experiments were performed (a) agricultural soil was maintained intact “exposure experiment 1”; (b) agricultural soil was sterilized “exposure experiment 2”; (c) agricultural soil was sterilized and inoculated with the rhizobia strain Rhizobium leguminosarum RhOF34 “exposure experiment 3”. Overall, data showed evidence of an increased sensitivity of faba bean plants, grown in sterilized soil, to MCs in comparison to those grown in intact and inoculated soils. The study revealed the growth inhibition of plant shoots in both exposure experiments 2 and 3 when treated with 2.5 mg·L⁻¹ of MCs. The results also showed that the estimated daily intake (EDI) of MCs, in sterilized soil, exceeded 2.18 and 1.16 times the reference concentrations (0.04 and 0.45 µg of microcysin-leucine arginine (MC-LR). Kg⁻¹ DW) established for humans and cattle respectively, which raises concerns about human food chain contamination.