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

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

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

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.

Microcystin influence on soil-plant microbiota: Unraveling microbiota modulations and assembly processes in the rhizosphere of Vicia faba

Microcystins (MCs) are frequently detected in cyanobacterial bloom-impacted waterbodies and introduced into agroecosystems via irrigation water. They are widely known as phytotoxic cyanotoxins, which impair the growth and physiological functions of crop plants. However, their impact on the plant-associated microbiota is scarcely tackled and poorly understood. Therefore, we aimed to investigate the effect of MCs on microbiota-inhabiting bulk soil (BS), root adhering soil (RAS), and root tissue (RT) of Vicia faba when exposed to 100 μg L-1 MCs in a greenhouse pot experiment. Under MC exposure, the structure, co-occurrence network, and assembly processes of the bacterial microbiota were modulated with the greatest impact on RT-inhabiting bacteria, followed by BS and, to a lesser extent, RAS. The analyses revealed a significant decrease in the abundances of several Actinobacteriota-related taxa within the RT microbiota, including the most abundant and known genus of Streptomyces. Furthermore, MCs significantly increased the abundance of methylotrophic bacteria (Methylobacillus, Methylotenera) and other Proteobacteria-affiliated genera (e.g., Paucibacter), which are supposed to degrade MCs. The co-occurrence network of the bacterial community in the presence of MCs was less complex than the control network. In MC-exposed RT, the turnover in community composition was more strongly driven by deterministic processes, as proven by the beta-nearest taxon index. Whereas in MC-treated BS and RAS, both deterministic and stochastic processes can influence community assembly to some extent, with a relative dominance of deterministic processes. Altogether, these results suggest that MCs may reshape the structure of the microbiota in the soil-plant system by reducing bacterial taxa with potential phytobeneficial traits and increasing other taxa with the potential capacity to degrade MCs.

Effect of linear alkylbenzene sulfonate on the uptake of microcystins by Brassica oleracea and Solanum tuberosum

Background

Globally, hypereutrophic conditions in major water reservoirs used for irrigation purposes, promote the co-existence of cyanotoxins and other pollutants such as linear alkylbenzene sulfonate (LAS). LAS is known to alter the permeability of membranes and promote the uptake of other pollutants by plants. In light of the potential human health risks and prevailing hypereutrophic conditions in some catchments in South Africa, we investigated the combined effects of LAS and microcystins (MCs) on food plants when cyanobacteria infested water is used to irrigate terrestrial crops.

Methods

To understand the potential risks, pot-culture experiments were conducted to assess the effect of LAS on the accumulation of MCs in Brassica oleracea (cabbage) and Solanum tuberosum (potato) plants. The plants were watered with dam water containing 3.48 mg L -1 of the LAS (sodium dodecyl sulfate) and MCs (MC-LR: 10.47 ± 3.879; 6.158 ± 4.127 for MC-RR and 8.160 ± 2.544 for MC-YR μg L -1) for 20 days.

Results

The presence of LAS, at environmentally relevant concentrations in the irrigation water, did not enhance the uptake of MCs in the two plants, as demonstrated by statistically insignificant differences in the means of the treatments (with and without LAS). In addition, the presence of LAS, high pH, electrical conductivity (EC), and cyanotoxins in the water did not affect the total chlorophyll or the well-being of the plants. However, in some cases the levels of MCs bioaccumulated by the two plants exceeded the WHO recommended tolerable daily intake (TDI).

Conclusions

These findings imply that the tested levels of LAS and MCs did not have any synergic effects on the two plant species, but irrigating food crops with such water still poses a human health risk.

Two duckweed species exhibit variable tolerance to microcystin-LR exposure across genotypic lineages

Cyanotoxins produced by harmful cyanobacteria blooms can damage freshwater ecosystems and threaten human health. Floating macrophytes may be used as a means of biocontrol by limiting light and resources available to cyanobacteria. However, genetic variation in macrophyte sensitivity to cyanotoxins could influence their suitability as biocontrol agents. We investigated the influence of such intraspecific variation on the response of two rapidly growing duckweed species, Lemna minor and Spirodela polyrhiza, often used in nutrient and metal bioremediation. We assessed two biomarkers related to productivity (biomass and chlorophyll A production) and two related to fitness measures (population size and growth rate). Fifteen genetic lineages of each species were grown in media containing common cyanotoxin microcystin-LR at ecologically relevant concentrations or control media for a period of twelve days. Genotype identity had a strong impact on all biomarker responses. Microcystin concentration slightly increased the final population sizes of both macrophyte species with a marginal effect on growth rate of L. minor and the chlorophyll A production of S. polyrhiza, but overall these species were very tolerant of microcystin. The strong tolerance supports the potential use of these plants as bioremediators of cyanobacterial blooms. However, differential impact of microcystin exposure discovered in single lineage models among genotypes indicates a potential for cyanotoxins to act as selective forces, necessitating attention to genotype selection for bioremediation.

Effect of different irrigation methods on the toxicity and bioavailability of microcystin-LR to lettuce and carrot

The use of cyanobacteria-polluted water for irrigation has become an increasing concern due to the potential contamination of microcystins (MCs). However, the effects of MCs on plant performance and food safety under different irrigation methods are not well understood. In this study, we investigated the effects of microcystin-LR (MC-LR) on the growth, food quality, and safety of lettuce and carrot using four irrigation methods (spray irrigation and three types of drip irrigation with different distances from the plant stem). Our results showed that exposure to 10 μg L-1 MC-LR negatively affected plant growth and food quality in treatments with spray irrigation (TS) and drip irrigation directly to the stem (TD0), but not in treatments with drip irrigation away from the plant stem (TD10 and TD20). Using soil as a filtration system, the bioavailability of MC-LR in soil was reduced in TD10 and TD20, resulting in less bioaccumulation in plant edible tissues. The estimated daily intake (EDI) values of TS and TD0 in both lettuce and carrot cultivation exceeded the tolerable daily intake (TDI) limit proposed by WHO, whereas the EDI values of TD10 and TD20 could be effectively reduced below the TDI limit. This study highlights the importance of drip irrigation away from the plant stem as a practical measure to mitigate the effects of cyanobacteria-polluted water in agricultural production.

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

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

Microcystin-Detoxifying Recombinant Saccharomyces cerevisiae Expressing the mlrA Gene from Sphingosinicella microcystinivorans B9

Contamination of water by microcystins is a global problem. These potent hepatotoxins demand constant monitoring and control methods in potable water. Promising approaches to reduce contamination risks have focused on natural microcystin biodegradation led by enzymes encoded by the mlrABCD genes. The first enzyme of this system (mlrA) linearizes microcystin structure, reducing toxicity and stability. Heterologous expression of mlrA in different microorganisms may enhance its production and activity, promote additional knowledge on the enzyme, and support feasible applications. In this context, we intended to express the mlrA gene from Sphingosinicella microcystinivorans B9 in an industrial Saccharomyces cerevisiae strain as an innovative biological alternative to degrade microcystins. The mlrA gene was codon-optimized for expression in yeast, and either expressed from a plasmid or through chromosomal integration at the URA3 locus. Recombinant and wild yeasts were cultivated in medium contaminated with microcystins, and the toxin content was analyzed during growth. Whereas no difference in microcystins content was observed in cultivation with the chromosomally integrated strain, the yeast strain hosting the mlrA expression plasmid reduced 83% of toxins within 120 h of cultivation. Our results show microcystinase A expressed by industrial yeast strains as a viable option for practical applications in water treatment.

The effects of secondary bacterial metabolites on photosynthesis in microalgae cells

Secondary metabolites of bacteria are regulatory molecules that act as "info-chemicals" that control some metabolic processes in the cells of microorganisms. These molecules provide the function of bacteria communication in microbial communities. As primary producers of organic matter in the biosphere, microalgae play a central ecological role in various ecosystems. Photosynthesis is a central process in microalgae cells, and it is exposed to various biotic and abiotic factors. Various secondary metabolites of bacteria confer a noticeable regulatory effect on photosynthesis in microalgae cells. The main purpose of this review is to highlight recent experimental results that demonstrate the impact of several types of common bacterial metabolites (volatile organic compounds, non-protein amino acids, and peptides) on photosynthetic activity in cells of microalgae. The use of these molecules as herbicides can be of great importance both for practical applications and for basic research.

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.

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.

The link between microcystin levels in groundwater and surface Nile water, and assessing their potential risk to human health

Although groundwater is an important source for drinking and irrigation water worldwide, particularly in arid countries, they have been paid little attention to their contamination with microcystins (MCs) compared to surface water. Our study is the fourth one reporting existence of MCs in groundwater due to surface-water and groundwater interaction. Dissolved MCs in groundwater were found with higher concentrations in summer (0.1 to 0.84 μg L^-1) than in winter (0-0.06 μg L^-1), in association with MCs detected in nearby surface Nile water. The chronic daily intake (CDI) of MCs for both adults and children (0-0.003 μg kg^-1 body weight d^-1) in groundwater were lower than the chronic reference dose (RfD, 0.003 μg kg^-1 body weight d^-1) during winter, with hazard quotient less than 1. Conversely, CDI values exceeded the reference dose during summer for both adults (0.005-0.024 μg kg^-1 body weight d^-1) and children (0.012-0.05 μg kg^-1 body weight d^-1), with hazard quotient greater than 1. This indicates that MCs concentrations in these groundwater wells might pose adverse health effects to both adults and children during summer, but not during winter. The study provides evidence for the risk of cyanotoxins in groundwater close to cyanobacteria-contaminated surface water. Therefore, regular monitoring for cyanotoxins in groundwater supplies used for drinking-water should be undertaken when cyanobacteria bloom events are noted in nearby surface waters.

Using soil amendments to reduce microcystin-LR bioaccumulation in lettuce

Contamination of microcystins (MCs) in plant-soil system have become a serious problem worldwide, however, it remains largely unknown how to alleviate the potential risk of consuming MCs-contaminated plants. In the present study, attapulgite, biochar and peat were used as soil amendments to reduce MCs bioaccumulation in lettuce. Lettuce irrigated with 10 μg L-1 microcystin-LR (MC-LR) were growing in two different kinds of soils with or without soil amendments. Results showed that all soil amendments effectively reduced MC-LR bioaccumulation in lettuce roots and leaves. Compared with the control treatment, the MC-LR concentrations in leaves in treatments with attapulgite, biochar and peat decreased by 41.5%, 30.6%, 57.0% in soil A and 38.9%, 43.2%, 54.7% in soil B, respectively. Peat application was most effective in reducing MC-LR bioaccumulation. The decreased soil free MC-LR concentrations were positively correlated with MC-LR concentrations in lettuce, indicating decreased bioavailability of MC-LR by soil amendments. It is noteworthy that soil total MC-LR concentration in peat treatment significantly decreased by 33.3% and 29.4% in soil A and soil B, respectively, compared with the controls. According to the results from high-throughput sequencing, peat amendment increased the α-diversity of soil bacterial community and boosted the abundance of Sphingomonas and Methylobacillus (dozens of MC-degrading bacteria belong to these genera). This was in line with the results of soil total MC-LR concentration. It can be speculated that peat application directly and/or indirectly promoted microbial degradation of MC-LR in soils. This work proposed an effective way to alleviate the potential risks of MCs contamination in plant-soil system.

Microcystin-LR, a Cyanobacterial Toxin, Induces DNA Strand Breaks Correlated with Changes in Specific Nuclease and Protease Activities in White Mustard (Sinapis alba) Seedlings

There is increasing evidence for the induction of programmed cell death (PCD) in vascular plants by the cyanobacterial toxin microcystin-LR (MC-LR). Our aim was to detect the occurrence of PCD-related DNA strand breaks and their possible connections to specific nuclease and protease activities. DNA breaks were studied by the deoxynucleotidyl transferase mediated dUTP nick end labeling (TUNEL) method in the photoperiodically grown dicot model of white mustard (Sinapis alba). In-gel nuclease and protease activity assays showed changes in the activities of specific isoenzymes during treatments with MC-LR. Strand breaks occurred both in the developing root epidermis and cortex. Several isoenzyme activities were related to these breaks, for example: an increase in the activity of neutral 80–75 kDa, acidic high MW (100–120 kDa) and, most importantly, an increase in the activity of neutral 26–20 kDa nucleases, all of them having single-stranded DNA cleaving (SSP nuclease) activities. Increases in the activities of alkaline proteases in the 61–41 kDa range were also detected and proved to be in relation with MC-LR-induced PCD. This is one of the first pieces of evidence on the correlation of PCD-related DNA strand breaks with specific hydrolase activities in a model dicot treated with a cyanobacterial toxin known to have environmental importance.

Subcellular Alterations Induced by Cyanotoxins in Vascular Plants-A Review

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