The Diversity of Cyanobacterial Toxins on Structural Characterization, Distribution and Identification: A Systematic Review

Distribution of toxigenic cyanobacteria in Alpine lakes and rivers as revealed by molecular screening

The increasing frequency of cyanobacteria blooms in waterbodies caused by ecosystem eutrophication could endanger human health. This risk can be mitigated by effective monitoring incorporating molecular methods. To date, most molecular studies on toxigenic cyanobacteria have been limited to microcystins (MCs), disregarding other cyanotoxins, to freshwater planktic habitats while ignoring benthic habitats, and to limited geographic areas (usually one or a few specific waterbodies). In this study, we used PCR-based methods including PCR product sequencing and chemical-analytical methods (LC-MS/MS) to screen many plankton (n = 123) and biofilm samples (n = 113) originating from 29 Alpine lakes and 18 rivers for their cyanotoxin production potential. Both mcyE (indicating MC synthesis) and anaC (indicating anatoxin (ATX) synthesis) gene fragments were able to qualitatively predict MC or ATX occurrence. The abundance of mcyE gene fragments was significantly related to MC concentrations in plankton samples (R2 = 0.61). mcyE gene fragments indicative of MC synthesis were most abundant in planktic samples (65 %) and were assigned to the genera Planktothrix and Microcystis. However, mcyE rarely occurred in biofilms of lakes and rivers, i.e., 4 % and 5 %, respectively, and were assigned to Microcystis, Planktothrix, and Nostoc. In contrast, anaC gene fragments occurred frequently in planktic samples (14 % assigned to Tychonema, Phormidium (Microcoleus), and Oscillatoria), but also in biofilms of lakes (49 %) and rivers (18 %) and were assigned to the genera Phormidium, Oscillatoria, and Nostocales. The cyrJ gene fragment indicating cylindrospermopsin synthesis occurred only once in plankton (assigned to Dolichospermum), while saxitoxin synthesis potential was not detected. For plankton samples, monomictic and less eutrophic conditions were positively related to mcyE/MC occurrence frequency, while oligomictic conditions were related to anaC/ATX frequency. The anaC/ATX frequency in biofilm was related to the lake habitats generally showing higher biodiversity as revealed from metabarcoding in a parallel study.

Identification of a homoarginine biosynthetic gene from a microcystin biosynthetic pathway in Fischerella sp. PCC 9339

Microcystins (MCs) are a family of chemically diverse toxins produced by numerous distantly related cyanobacteria. They are potent inhibitors of eukaryotic protein phosphatases 1 and 2A and are responsible for the toxicosis and death of wild and domestic animals around the world. Microcystins are synthesized on large enzyme complexes comprised of peptide synthetases, polyketide synthases, and additional modifying enzymes. Bioinformatic analysis identified the presence of an additional uncharacterized enzyme in the microcystin (mcy) biosynthetic gene cluster in Fischerella sp. PCC 9339, which we named McyK, that lacked a clearly defined role in the biosynthesis of microcystin. Further bioinformatic analysis suggested that McyK belongs to the inosamine-phosphate amidinotransferase family and could be involved in synthesizing homo amino acids. Quadrupole time-of-flight tandem mass spectrometry (Q-TOFMS/MS) analysis confirmed that Fischerella sp. PCC 9339 produces MC-Leucine2-Homoarginine4(MC-LHar) and [Aspartic acid3]MC-Leucine2-Homoarginine4 ([Asp3]MC-LHar) as the dominant chemical variants. We hypothesized that the McyK enzyme might be involved in the production of microcystin variants containing homoarginine (Har) in the strain. Heterologous expression of a codon-optimized mcyK gene in Escherichia coli confirmed that McyK is responsible for the synthesis of L-Har. These results confirm the production of MC-LHar, a novel microcystin chemical variant [Asp3]MC-LHar, and a new microcystin biosynthetic enzyme involved in supply of the rare homo-amino acid Har to the microcystin biosynthetic pathway in Fischerella sp. PCC 9339. This study provides new insights into the logic underpinning the biosynthesis of microcystin chemical variants and broadens our knowledge of structural diversity of the microcystin family of toxins.

Environmentally related microcystin-LR-induced ovarian dysfunction via the CCL2-CCR10 axis in mice ameliorated by dietary mulberry

Microcystin-LR (MC-LR) is a reproductive toxin produced by cyanobacteria in the aquatic environment and can be ingested by humans through drinking water and the food chain, posing a threat to human reproductive health. However, the toxic mechanisms and prospective interventions for MC-LR-induced ovarian dysfunction at environmental doses are unknown. The mulberry fruit is a traditional natural product of plant origin, with various pharmacological effects, such as antioxidant and anti-inflammatory effects. Here, mice were exposed to MC-LR (10, 100 μg/L) in drinking water for 90 days, during which mice were gavage 600 mg/kg/week of mulberry fruit extract (MFE). It was found that MC-LR can accumulate in mouse ovaries, causing sexual hormone disturbance, inflammatory infiltration, and ovarian pathological damage. Results from RNA-seq were shown that CCL2, a chemokine associated with inflammatory response, was significantly increased in mouse ovary after MC-LR exposure. Further investigation revealed that MC-LR exposure aggravates apoptosis of granulosa cells via the CCL2-CCR10 axis-mediated Jak/Stat pathway. Importantly, MFE can significantly ameliorate these ovarian dysfunction phenotypes by inhibiting the activation of the CCL2-CCR10 axis. This study broadened new insights into the ovarian toxicity of MC-LR and clarified the pharmacological effects of mulberry fruit on ovarian function protection.

Single microcystin exposure impairs the hypothalamic-pituitary-gonadal axis at different levels in female rats

Microcystin (MC) is most common cyanobacterial toxin. Few studies have evaluated the MC effects on the hypothalamic-pituitary-gonadal (HPG) axis and metabolic function. In this study, we assessed whether MC exposure results in HPG axis and metabolic changes. Female rats were exposed to a single dose of MC at environmentally relevant levels (5, 20 and 40 μg/kg). After 24 h, we evaluated reproductive and metabolic parameters for 15 days. MC reduced the hypothalamic GnRH protein expression, increased the pituitary protein expression of GnRHr and IL-6. MC reduced LH levels and increased FSH levels. MC reduced the primary follicles, increased the corpora lutea, elevated levels of anti-Müllerian hormone (AMH) and progesterone, and decreased estrogen levels. MC increased ovarian VEGFr, LHr, AMH, ED1, IL-6 and Gp91-phox protein expression. MC increased uterine area and reduced endometrial gland number. A blunted estrogen-negative feedback was observed in MC rats after ovariectomy, with no changes in LH levels compared to intact MC rats. Therefore, these data suggest that a MC leads to abnormal HPG axis function in female rats.

Microcystin-RR promote lipid accumulation through CD36 mediated signal pathway and fatty acid uptake in HepG2 cells

Microcystins (MC)-RR is a significant analogue of MC-LR, which has been identified as a hepatotoxin capable of influencing lipid metabolism and promoting the progression of liver-related metabolic diseases. However, the toxicity and biological function of MC-RR are still not well understood. In this study, the toxic effects and its role in lipid metabolism of MC-RR were investigated in hepatoblastoma cells (HepG2cells). The results demonstrated that MC-RR dose-dependently reduced cell viability and induced apoptosis. Additionally, even at low concentrations, MC-RR promoted lipid accumulation through up-regulating levels of triglyceride, total cholesterol, phosphatidylcholines and phosphatidylethaolamine in HepG2 cells, with no impact on cell viability. Proteomics and transcriptomics analysis further revealed significant alterations in the protein and gene expression profiles in HepG2 cells treated with MC-RR. Bioinformatic analysis, along with subsequent validation, indicated the upregulation of CD36 and activation of the AMPK and PI3K/AKT/mTOR in response to MC-RR exposure. Finally, knockdown of CD36 markedly ameliorated MC-RR-induced lipid accumulation in HepG2 cells. These findings collectively suggest that MC-RR promotes lipid accumulation in HepG2 cells through CD36-mediated signal pathway and fatty acid uptake. Our findings provide new insights into the hepatotoxic mechanism of MC-RR.

A zinc-air battery assisted self-powered electrochemical sensor for sensitive detection of microcystin-RR

Building a high-performance sensing platform is the key to developing sensitive sensors. Herein, a highly sensitive self-powered electrochemical sensor (SPES) was constructed using a WO3·H2O film as the cathode prepared by a hydrothermal method and Zn as the anode, and it could be applied to sensitive detection of microcystin (MC-RR). The WO3·H2O film with a larger specific surface area could boost the oxygen reduction reaction (ORR), which could achieve signal amplification and significantly increase the sensitivity of the sensors. Under the optimal conditions, there was a good linear relationship between the increased electrical power density and the logarithm of MC-RR concentration with a detection limit of 1.31 × 10-15 M (S/N = 3). This method had good anti-interference ability and stability when applied to the determination of MC-RR content in actual samples, which could boost the potential application of electrochemical sensors in the field of environmental monitoring.

Physico-chemical treatments for the removal of cyanotoxins from drinking water: Current challenges and future trends

Cyanobacteria are highly prevalent blue-green algae that grow in stagnant and nutrient-rich water bodies. Environmental conditions, such as eutrophication and human activities, increased the cyanobacterial blooms in freshwater resources worldwide. The excessive bloom formation has also resulted in an alarming surge of cyanobacterial toxins. Prolonged exposure to cyanotoxins is a potential threat to natural ecosystems, animal and human health by the spoilage of the quality of bathing and drinking water. Various molecular and analytical methods have been proposed to monitor their occurrence and understand their global distribution. Moreover, different physical, chemical, and biological approaches have been employed to control cyanobacterial blooms and their toxins to mitigate their occurrence. Numerous strategies have been engaged in drinking water treatment plants (DWTPs). However, the degree of treatment varies greatly and is primarily determined by the source, water properties, and operating parameters such as temperature, pH, and cyanotoxin variants and levels. A comprehensive compilation of methods, from traditional approaches to more advanced oxidation processes (AOPs), are presented for the removal of intracellular and extracellular cyanotoxins. This review discusses the effectiveness of various physicochemical operations and their limitations in a DWTP, for the removal of various cyanotoxins. These operations span from simple to advanced treatment levels with varying degrees of effectiveness and differing costs of implementation. Furthermore, mitigation measures applied in other toxin systems have been considered as alternative strategies.

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.

Characterization of driving factors for the long-term succession of bloom-forming cyanobacterial genera in Lake Erhai, southwest China

Cyanobacterial blooms pose a global environmental concern, with various genera contributing to their formation. The harmfulness of cyanobacterial blooms varies depending on the specific genus, yet the factors triggering their formation remain incompletely understood. This study conducted qPCR of sediment DNA in Lake Erhai to reconstruct the historical succession of three common bloom-forming cyanobacterial genera (i.e., Microcystis, Dolichospermum, and Aphanizomenon). The driving factors and their corresponding thresholds were identified, and human activities related to driving factors were evaluated. The results revealed two successions in the past century. The first succession transitioned from Aphanizomenon (1902-1978) to Microcystis and Dolichospermum (1978-1999), driven by TN:TP and TP. The second succession shifted from Microcystis and Dolichospermum (1978-1999) to Microcystis (1999-2010), driven by TP, TN:TP, and temperature. The thresholds of TP and TN:TP for the Microcystis bloom were 0.023 mg/L and 17, respectively. TN:TP was significantly influenced by domestic pollution and crop farming in both successions, while TP was significantly impacted by domestic pollution in the first succession and by pollution from crop and dairy farming in the second succession. These results shed light on the underlying mechanism responsible for the blooms of various cyanobacterial genera and could serve as a valuable reference for effectively preventing and controlling nutrient input in the watershed.

Cyanotoxins availability and detection methods in wastewater treatment plants: A review

Research interest in ecological significance, toxicity, and potential applications of cyanobacterial metabolites has grown as a result of the current extensive cyanobacterial blooms in water bodies. Under favourable conditions, specific cyanobacterial species release cyanotoxins, hepatotoxins, dermatoxins, neurotoxins, and cytotoxins, creating a heightened threat to aquatic ecosystems and human health. Wastewater treatment plants (WWTPs) offer one of the best culture media for cyanobacterial development and synthesis of cyanotoxins by providing optimum environmental conditions, including temperature, light intensity, lengthy water residence time, and nutrient-rich habitat. To discover the intricate relationships between cyanobacterial populations and other living organisms, it is important to comprehend the cyanobacterial communities in the ecology of WWTPs. Monitoring strategies of these cyanotoxins typically involved combined assessments of biological, biochemical, and physicochemical methodologies. Microscopic observations and physicochemical factors analysis cannot be carried out for toxicity potential analysis of blooms. Due to their high sensitivity, molecular-based approaches allow for the early detection of toxic cyanobacteria, while biological analysis is carried out by using water bloom material and cell extracts to screen cyanotoxins build up in organisms. As each approach has benefits and drawbacks, the development of an integrated multi-method laboratory system is essential to obtain trustworthy results and accurate detection of cyanotoxin levels in WWTPs allowing us to take necessary proactive and preventative approaches for effective wastewater treatment.

Cyanobacteria and cyanotoxins in the environment and water intakes: Reports, diversity of congeners, detection by mass spectrometry and their impact on health

Cyanobacteria are aquatic microorganisms of high interest for research due to the production of secondary metabolites, among which the most popular are cyanotoxins, responsible for causing severe poisoning in humans and animals through ingestion or contact with contaminated water bodies. Monitoring the number of cyanobacteria in water and concentrations of secreted cyanotoxins with the aid of sensitive and reliable methods is considered the primary action for evaluating potentially toxic blooms. There is a great diversity of methods to detect and identify these types of micro contaminants in water, differing by the degree of sophistication and information provided. Mass Spectrometry stands out for its accuracy and sensitivity in identifying toxins, making it possible to identify and characterize toxins produced by individual species of cyanobacteria, in low quantities. In this review, we seek to update some information about cyanobacterial peptides, their effects on biological systems, and the importance of the main Mass Spectrometry methods used for detection, extraction, identification and monitoring of cyanotoxins.

Morchella Effectively Removes Microcystins Produced by Microcystis aeruginosa

Microcystins (MCs) produced by Microcystis aeruginosa are harmful to animal and human health, and there is currently no effective method for their removal. Therefore, the development of biological approaches that inhibit cyanobacteria and remove MCs is needed. We identified strain MB1, confirmed as Morchella, using morphological and mole-cular evolution methods. To assess the impact of strain MB1 on M. aeruginosa, we conducted an experiment in which we inoculated M. aeruginosa with Morchella strain MB1. After their co-cultivation for 4‍ ‍d, the inoculation with 0.9696‍ ‍g MB1 completely inhibited and removed M. aeruginosa while concurrently removing up to 95% of the MC content. Moreover, within 3‍ ‍d of their co-cultivation, MB1 removed more than 50% of nitrogen and phosphorus from the M. aeruginosa solution. Therefore, the development of effective biological techniques for MC removal is paramount in safeguarding both the environment and human well-being. We herein successfully isolated MB1 from its natural habitat. This strain effectively inhibited and removed M. aeruginosa and also reduced the content of nitrogen and phosphorus in the M. aeruginosa solution. Most importantly, it exhibited a robust capability to eliminate MCs. The present results offer a new method and technical reference for mitigating harmful algal blooms.

Aerosolized Cyanobacterial Harmful Algal Bloom Toxins: Microcystin Congeners Quantified in the Atmosphere

Cyanobacterial harmful algal blooms (cHABs) have the potential to adversely affect public health through the production of toxins such as microcystins, which consist of numerous molecularly distinct congeners. Microcystins have been observed in the atmosphere after emission from freshwater lakes, but little is known about the health effects of inhaling microcystins and the factors contributing to microcystin aerosolization. This study quantified total microcystin concentrations in water and aerosol samples collected around Grand Lake St. Marys (GLSM), Ohio. Microcystin concentrations in water samples collected on the same day ranged from 13 to 23 μg/L, dominated by the d-Asp3-MC-RR congener. In particulate matter <2.5 μm (PM2.5), microcystin concentrations up to 156 pg/m3 were detected; the microcystins were composed primarily of d-Asp3-MC-RR, with additional congeners (d-Asp3-MC-HtyR and d-Asp3-MC-LR) observed in a sample collected prior to a storm event. The PM size fraction containing the highest aerosolized MC concentration ranged from 0.44 to 2.5 μm. Analysis of total bacteria by qPCR targeting 16S rDNA revealed concentrations up to 9.4 × 104 gc/m3 in aerosol samples (≤3 μm), while a marker specific to cyanobacteria was not detected in any aerosol samples. Concentrations of aerosolized microcystins varied even when concentrations in water were relatively constant, demonstrating the importance of meteorological conditions (wind speed and direction) and aerosol generation mechanism(s) (wave breaking, spillway, and aeration systems) when evaluating inhalation exposure to microcystins and subsequent impacts on human health.

Microcystin Concentrations, Partitioning, and Structural Composition during Active Growth and Decline: A Laboratory Study

Microcystin can be present in variable concentrations, phases (dissolved and particulate), and structural forms (congeners), all which impact the toxicity and persistence of the algal metabolite. Conducting incubation experiments with six bloom assemblages collected from the Chowan River, North Carolina, we assessed microcystin dynamics during active growth and biomass degradation. Upon collection, average particulate and dissolved microcystin ranged between 0.2 and 993 µg L-1 and 0.5 and 3.6 µg L-1, respectively. The presence of congeners MC-LA, -LR, -RR, and -YR was confirmed with MC-RR and MC-LR being the most prevalent. Congener composition shifted over time and varied between dissolved and particulate phases. Particulate microcystin exponentially declined in five of six incubations with an average half-life of 10.2 ± 3.7 days, while dissolved microcystin remained detectable until the end of the incubation trials (up to 100 days). Our findings suggest that concerns about food-web transfer via intracellular toxins seem most warranted within the first few weeks of the bloom peak, while dissolved toxins linger for several months in the aftermath of the event. Also, it was indicated there were differences in congener profiles linked to the sampling method. We believe this study can inform monitoring strategies and aid microcystin-exposure risk assessments for cyanobacterial blooms.

A Direct Analysis of β-N-methylamino-l-alanine Enantiomers and Isomers and Its Application to Cyanobacteria and Marine Mollusks

Of the wide variety of toxic compounds produced by cyanobacteria, the neurotoxic amino acid β-N-methylamino-l-alanine (BMAA) has attracted attention as a result of its association with chronic human neurodegenerative diseases such as ALS and Alzheimer's. Consequently, specific detection methods are required to assess the presence of BMAA and its isomers in environmental and clinical materials, including cyanobacteria and mollusks. Although the separation of isomers such as β-amino-N-methylalanine (BAMA), N-(2-aminoethyl)glycine (AEG) and 2,4-diaminobutyric acid (DAB) from BMAA has been demonstrated during routine analysis, a further compounding factor is the potential presence of enantiomers for some of these isomers. Current analytical methods for BMAA mostly do not discriminate between enantiomers, and the chiral configuration of BMAA in cyanobacteria is still largely unexplored. To understand the potential for the occurrence of D-BMAA in cyanobacteria, a chiral UPLC-MS/MS method was developed to separate BMAA enantiomers and isomers and to determine the enantiomeric configuration of endogenous free BMAA in a marine Lyngbya mat and two mussel reference materials. After extraction, purification and derivatization with N-(4-nitrophenoxycarbonyl)-l-phenylalanine 2-methoxyethyl ester ((S)-NIFE), both L- and D-BMAA were identified as free amino acids in cyanobacterial materials, whereas only L-BMAA was identified in mussel tissues. The finding of D-BMAA in biological environmental materials raises questions concerning the source and role of BMAA enantiomers in neurological disease.

α-LA attenuates microcystin-LR-induced hepatocellular oxidative stress in mice through Nrf2-mediated antioxidant and detoxifying enzymes

Microcystins constitute a class of toxins synthesized by cyanobacteria and are known to inflict significant damage on the antioxidant defense system of living organisms, primarily targeting the liver. α-Lipoic acid (α-LA) is universally recognized as a potent antioxidant in biological systems. It exerts its beneficial effects through multiple mechanisms-directly neutralizing reactive oxygen species (ROS) and free radicals, and indirectly enhancing antioxidant defenses by facilitating the regeneration of glutathione (GSH). However, the precise modus operandi of α-LA's protective effect against Microcystin-LR-induced hepatotoxicity remains incompletely elucidated. The present study, therefore, employed α-LA to explore its protective role against Microcystin-LR exposure in mice. A model of Microcystin-LR-induced hepatic injury was established by administering Microcystin-LR into the peritoneal cavity of BALB/c mice daily over a two-week period. Thereafter, BALB/c mice were pre-treated with varying concentrations of α-LA via oral gavage for a duration of 7 days, followed by a 7-day exposure to Microcystin-LR. Our findings reveal that α-LA pre-treatment significantly mitigated hepatic pathologies in Microcystin-LR-exposed mice. Furthermore, α-LA administration led to a notable elevation in the activities and expression levels of nuclear factor erythroid 2-related factor 2, superoxide dismutase, glutathione peroxidase, glutathione S-transferase, and glutathione-indicative of its antioxidative capacity. Concurrently, a significant decrease was observed in the activities and expression levels of malondialdehyde and cytochrome P450 2E1. Consequently, α-LA emerges as a promising therapeutic candidate for the amelioration of liver oxidative damage subsequent to Microcystin-LR exposure.

A Review of the Antimicrobial Properties of Cyanobacterial Natural Products

The development of multiple-drug-resistant pathogens has prompted medical research toward the development of new and effective antimicrobial therapies. Much research into novel antibiotics has focused on bacterial and fungal compounds, and on chemical modification of existing compounds to increase their efficacy or reactivate their antimicrobial properties. In contrast, cyanobacteria have been relatively overlooked for antibiotic discovery, and much more work is required. This may be because some cyanobacterial species produce environmental toxins, leading to concerns about the safety of cyanobacterial compounds in therapy. Despite this, several cyanobacterial-derived compounds have been identified with noteworthy inhibitory activity against bacterial, fungal and protozoal growth, as well as viral replication. Additionally, many of these compounds have relatively low toxicity and are therefore relevant targets for drug development. Of particular note, several linear and heterocyclic peptides and depsipeptides with potent activity and good safety indexes have been identified and are undergoing development as antimicrobial chemotherapies. However, substantial further studies are required to identify and screen the myriad other cyanobacterial-derived compounds to evaluate their therapeutic potential. This study reviews the known phytochemistry of cyanobacteria, and where relevant, the effects of those compounds against bacterial, fungal, protozoal and viral pathogens, with the aim of highlighting gaps in the literature and focusing future studies in this field.

Understanding the Risks of Diffusion of Cyanobacteria Toxins in Rivers, Lakes, and Potable Water

Blue-green algae, or cyanobacteria, may be prevalent in our rivers and tap water. These minuscule bacteria can grow swiftly and form blooms in warm, nutrient-rich water. Toxins produced by cyanobacteria can pollute rivers and streams and harm the liver and nervous system in humans. This review highlights the properties of 25 toxin types produced by 12 different cyanobacteria genera. The review also covered strategies for reducing and controlling cyanobacteria issues. These include using physical or chemical treatments, cutting back on fertilizer input, algal lawn scrubbers, and antagonistic microorganisms for biocontrol. Micro-, nano- and ultrafiltration techniques could be used for the removal of internal and extracellular cyanotoxins, in addition to powdered or granular activated carbon, ozonation, sedimentation, ultraviolet radiation, potassium permanganate, free chlorine, and pre-treatment oxidation techniques. The efficiency of treatment techniques for removing intracellular and extracellular cyanotoxins is also demonstrated. These approaches aim to lessen the risks of cyanobacterial blooms and associated toxins. Effective management of cyanobacteria in water systems depends on early detection and quick action. Cyanobacteria cells and their toxins can be detected using microscopy, molecular methods, chromatography, and spectroscopy. Understanding the causes of blooms and the many ways for their detection and elimination will help the management of this crucial environmental issue.

Effects of microcystin-LR on mammalian ovaries

The ovaries play critical roles in regulating oocyte maturation and sex steroid hormone production and thus are critical for female reproduction. Ovarian function relies on hormone receptors and signaling pathways, making the ovaries potential targets for environmental factors, such as microcystins (MCs). MCs are a diverse group of cyanobacterial toxins generally found in eutrophic water or algal blooms. Here, we review relevant research on the associations between MC exposure and ovarian dysfunction, including their effects on ovarian morphology, folliculogenesis, steroid production, oxidative stress, endoplasmic reticulum stress, apoptosis, autophagy, and fertility. This review covers the most recent in vitro and in vivo studies in mammals. We also discuss important gaps in the literature. Overall, current evidence indicates that MC exposure causes impairments in ovarian function, but further studies are needed to elucidate the mechanisms through which MCs affect ovarian function and other female endocrine functions.

Cyanotoxins, biosynthetic gene clusters, and factors modulating cyanotoxin biosynthesis

Cyanobacterial harmful algal blooms (CHABs) are a global environmental concern that encompasses public health issues, water availability, and water quality owing to the production of various secondary metabolites (SMs), including cyanotoxins in freshwater, brackish water, and marine ecosystems. The frequency, extent, magnitude, and duration of CHABs are increasing globally. Cyanobacterial species traits and changing environmental conditions, including anthropogenic pressure, eutrophication, and global climate change, together allow cyanobacteria to thrive. The cyanotoxins include a diverse range of low molecular weight compounds with varying biochemical properties and modes of action. With the application of modern molecular biology techniques, many important aspects of cyanobacteria are being elucidated, including aspects of their diversity, gene-environment interactions, and genes that express cyanotoxins. The toxicological, environmental, and economic impacts of CHABs strongly advocate the need for continuing, extensive efforts to monitor cyanobacterial growth and to understand the mechanisms regulating species composition and cyanotoxin biosynthesis. In this review, we critically examined the genomic organization of some cyanobacterial species that lead to the production of cyanotoxins and their characteristic properties discovered to date.

Microcystin-LR-Exposure-Induced Kidney Damage by Inhibiting MKK6-Mediated Mitophagy in Mice

Previous studies have reported that microcystin-LR (MC-LR) levels are highly correlated with abnormal renal function indicators, suggesting that MC-LR is an independent risk factor for kidney damage. However, the evidence for the exact regulation mechanism of MC-LR on kidney damage is still limited, and further in-depth exploration is needed. In addition, the mitochondria-related mechanism of MC-LR leading to kidney damage has not been elucidated. To this end, the present study aimed to further explore the mechanism of mitophagy related to kidney damage induced by MC-LR through in vitro and in vivo experiments. Male C57BL/6 mice were fed with a standard rodent pellet and exposed daily to MC-LR (20 μg/kg·bw) via intraperitoneal injections for 7 days. Moreover, HEK 293 cells were treated with MC-LR (20 μM) for 24 h. The histopathological results exhibited kidney damage after MC-LR exposure, characterized by structurally damaged nephrotomies, with inflammatory cell infiltration. Similarly, a significant increase in renal interstitial fibrosis was observed in the kidneys of MC-LR-treated mice compared with those of the control group (CT) mice. MC-LR exposure caused impaired kidney function, with markedly increased blood urea nitrogen (BUN), creatinine (Cr), and uric acid (UA) levels in mice. Ultrastructural analysis exhibited obviously swollen, broken, and disappearing mitochondrial crests, and partial mitochondrial vacuoles in the MC-LR-treated HEK 293 cells. The Western blotting results demonstrated that exposure to MC-LR significantly increased the protein expressions of MKK6, p-p38, and p62, while the expression of mitophagy-related proteins was significantly inhibited in the kidneys of mice and HEK293 cells, including parkin, TOM20, and LC3-II, indicating the inhibition of mitophagy. Therefore, our data suggest that the inhibition of MKK6-mediated mitophagy might be the toxicological mechanism of kidney toxicity in mice with acute exposure to MC-LR.

Microcystin-LR immersion caused sequential endocrine disruption and growth inhibition in zebrafish (Danio rerio) from fertilization to sexual differentiation completion

Microcystin-LR (MC-LR) is a highly toxic congener and is also one of the most commonly found. Recent studies have demonstrated that MC-LR can disrupt growth and endocrine in fish, but how it works at the stage of the sex differentiation period had not been determined to date. In this study, zebrafish (Danio rerio) embryos were exposed to MC-LR (0 and 10μg/L), and sampled at 14, 28, and 42 days post fertilization (dpf), respectively. The results demonstrated that MC-LR caused the growth inhibition of zebrafish at 42 dpf. The expression levels of genes related to the growth hormone/insulin-like growth factor (GH/IGF) and hypothalamic-pituitary-thyroid (HPT) axes, as well as the levels of hormone 3,5,3'- Triiodothyronine (T3) and thyroxine (T4), were significantly decreased at all time points. A Significant decrease in the ratio of testosterone and estradiol (T/E2) were detected at 28 and 42 dpf in MC-LR group along with changes in genes related to the hypothalamic-pituitary-gonadal (HPG) axis. The result of sex ratio showed that the percentage of females was up to 61.84%, indicating a estrogenic effect induced by MC-LR. The significant changes on hormone levels and gene transcripts occurred mainly in the stage of sex differentiation. The correlation analysis further suggested that key cross-talks among three endocrine axes may be the growth hormone releasing hormone (GHRH), Transthyretin (TTR) and gonadotropin releasing hormone (GnRH) signaling molecules. Overall, our findings provide a new insight for understanding the mechanisms by which MC-LR affects fish growth and reproduction during gonadal development.

Light and carbon: Synthetic biology toward new cyanobacteria-based living biomaterials

Cyanobacteria are ideal candidates to use in developing carbon neutral and carbon negative technologies; they are efficient photosynthesizers and amenable to genetic manipulation. Over the past two decades, researchers have demonstrated that cyanobacteria can make sustainable, useful biomaterials, many of which are engineered living materials. However, we are only beginning to see such technologies applied at an industrial scale. In this review, we explore the ways in which synthetic biology tools enable the development of cyanobacteria-based biomaterials. First we give an overview of the ecological and biogeochemical importance of cyanobacteria and the work that has been done using cyanobacteria to create biomaterials so far. This is followed by a discussion of commonly used cyanobacteria strains and synthetic biology tools that exist to engineer cyanobacteria. Then, three case studies-bioconcrete, biocomposites, and biophotovoltaics-are explored as potential applications of synthetic biology in cyanobacteria-based materials. Finally, challenges and future directions of cyanobacterial biomaterials are discussed.

P62/SQSTM1 upregulates NQO1 transcription via Nrf2/Keap1a signaling pathway to resist microcystins-induced oxidative stress in freshwater mussel Cristaria plicata

Microcystins (MCs) are the most frequent and widely distributed type of cyanotoxin in aquatic systems, and they cause an imbalance of the body's oxidative system. In a previous experiment, we demonstrated that the mollusk Cristaria plicata can protect against MC-induced oxidative damage through the nuclear factor erythroid 2-related factor 2(Nrf2)/Kelch-like epichlorohydrin-related protein-1 (Keap1) pathway. Here, we evaluated whether selective autophagy affects the Nrf2/Keap1a anti-oxidative stress pathway in C. plicata. Full-length cDNA sequences of p62/SQSTM1 from C. plicata (Cpp62) were divided into 2484 bp fragments. From N-terminal to C-terminal, the amino acid sequence of Cpp62 contained PB1 (Phox and Bem1p domain), ZNF (zinc finger domain) chain, LIR (LC3 interacting region) and UBA (ubiquitin-associated domain) domains, but not the KIR (Keap1 interacting region) domain. We confirmed that Cpp62 did not bind to CpKeap1a in vitro, and the relative level of Cpp62 was the highest in the hepatopancreas. Moreover, MCs significantly upregulated the mRNA and protein levels of Cpp62 in the hepatopancreas after CpKeap1a knockdown, whereas Nrf2 upregulated the transcription levels of Cpp62, suggesting that MCs increased Cpp62 expression via the Nrf2/Keap1a signaling pathway. Moreover, Cpp62 and CpNrf2 proteins have a strong affinity for the NQO1 promoter, but MCs inhibited the ability of CpNrf2 and Cpp62 to upregulate luciferase activity. The results show that Nrf2 and the p62 protein induced p62 expression by binding to ARE (antioxidant response element) sequences in the p62 promoter of C. plicata, thereby promoting p62 to resist MC-induced oxidative stress. Therefore, we speculate that MCs induce p62-dependent autophagy in C. plicata, resulting in the inhibition of Nrf2 transcription and Cpp62 promoter activity. These findings help to reveal the mechanism by which the p62-Nrf2/Keap1 pathway mitigates MC-induced oxidative damage in mussels.

PI3K/AKT/mTOR pathway mediated-cell cycle dysregulation contribute to malignant proliferation of mouse spermatogonia induced by microcystin-leucine arginine

Environmental cyanotoxin exposure may be a trigger of testicular cancer. Activation of PI3K/AKT/mTOR signaling pathway is the critical molecular event in testicular carcinogenesis. As a widespread cyanotoxin, microcystin-leucine arginine (MC-LR) is known to induce cell malignant transformation and tumorigenesis. However, the effects of MC-LR on the regulatory mechanism of PI3K/AKT/mTOR pathway in seminoma, the most common testicular tumor, are unknown. In this study, mouse spermatogonia cell line (GC-1) and nude mice were used to investigate the effects and mechanisms of MC-LR on the malignant transformation of spermatogonia by nude mouse tumorigenesis assay, cell migration invasion assay, western blot, and cell cycle assay, and so forth. The results showed that, after continuous exposure to environmentally relevant concentrations of MC-LR (20 nM) for 35 generations, the proliferation, migration, and invasion abilities of GC-1 cells were increased by 120%, 340%, and 370%, respectively. In nude mice, MC-LR-treated GC-1 cells formed tumors with significantly greater volume (0.998 ± 0.768 cm³ ) and weight (0.637 ± 0.406 g) than the control group (0.067 ± 0.039 cm³ ; 0.094 ± 0.087 g) (P < .05). Furthermore, PI3K inhibitor Wortmannin inhibited the PI3K/AKT/mTOR pathway and its downstream proteins (c-MYC, CDK4, CCND1, and MMP14) activated by MC-LR. Blocking PI3K alleviated MC-LR-induced cell cycle disorder and malignant proliferation, migration and invasive of GC-1 cells. Altogether, our findings suggest that MC-LR can induce malignant transformation of mouse spermatogonia, and the PI3K/AKT/mTOR pathway-mediated cell cycle dysregulation may be an important target for malignant proliferation. This study provides clues to further reveal the etiology and pathogenesis of seminoma.

Different environmental factors drive the concentrations of microcystin in particulates, dissolved water, and sediments peaked at different times in a large shallow lake

Global distribution and health threats of microcystins (MCs) have received much more attention, but there are still significant knowledge gaps in the peak periods and driving factors of MC in different phases of freshwater ecosystems. Thus, we systematically analyzed the annual variation of different MC congeners (-LR, -RR, and -YR, where L, R, and Y respectively represent leucine, arginine, and tyrosine) in particulates, dissolved water, and sediments in three eutrophic bays of Lake Taihu, China. The results indicated that particulate MCs concentration was the highest, followed by dissolved and sediment MC, with the mean concentration of 7.58 μg/L, 1.48 μg/L, and 0.15 μg/g (DW), respectively. Except for particulate MC, the concentrations of the other two types of MC showed significant differences among the three bays. The dominant congeners of the three types of MCs were different, with the highest proportion of MC-LR being observed in sediment MCs and the lowest in particulate MCs. The peak period of the three types of MC was also different, with particulate MCs reaching their peak in July and October, dissolved MCs in May to July and October, and sediment MCs reaching their peak in September. Consistent with our hypothesis, the dynamics of different types of MCs were driven by different environmental factors. Particulate MCs were primarily related to biological parameters, followed by TP and dissolved carbon. By contrast, dissolved MCs strongly correlated with water temperature and dissolved oxygen. While sediment MCs were primarily driven by properties of sediments, followed by different forms of nitrogen in the water column. Our results suggested that particulate and dissolved MCs in northern Lake Taihu pose high health threats, especially in the peak period. Moreover, a more detailed and targeted risk management strategy should be designed to prevent the possible hazards posed by different types of MC.

Metabolomics Applied to Cyanobacterial Toxins and Natural Products

The biological and chemical diversity of Cyanobacteria is remarkable. These ancient prokaryotes are widespread in nature and can be found in virtually every habitat on Earth where there is light and water. They are producers of an array of secondary metabolites with important ecological roles, toxic effects, and biotechnological applications. The investigation of cyanobacterial metabolites has benefited from advances in analytical tools and bioinformatics that are employed in metabolomic analyses. In this chapter, we review selected articles highlighting the use of targeted and untargeted metabolomics in the analyses of secondary metabolites produced by cyanobacteria. Here, cyanobacterial secondary metabolites have been didactically divided into toxins and natural products according to their relevance to toxicological studies and drug discovery, respectively. This review illustrates how metabolomics has improved the chemical analysis of cyanobacteria in terms of speed, sensitivity, selectivity, and/or coverage, allowing for broader and more complex scientific questions.

Scientists' warning of threats to mountains

Mountains are an essential component of the global life-support system. They are characterized by a rugged, heterogenous landscape with rapidly changing environmental conditions providing myriad ecological niches over relatively small spatial scales. Although montane species are well adapted to life at extremes, they are highly vulnerable to human derived ecosystem threats. Here we build on the manifesto 'World Scientists' Warning to Humanity', issued by the Alliance of World Scientists, to outline the major threats to mountain ecosystems. We highlight climate change as the greatest threat to mountain ecosystems, which are more impacted than their lowland counterparts. We further discuss the cascade of "knock-on" effects of climate change such as increased UV radiation, altered hydrological cycles, and altered pollution profiles; highlighting the biological and socio-economic consequences. Finally, we present how intensified use of mountains leads to overexploitation and abstraction of water, driving changes in carbon stock, reducing biodiversity, and impacting ecosystem functioning. These perturbations can provide opportunities for invasive species, parasites and pathogens to colonize these fragile habitats, driving further changes and losses of micro- and macro-biodiversity, as well further impacting ecosystem services. Ultimately, imbalances in the normal functioning of mountain ecosystems will lead to changes in vital biological, biochemical, and chemical processes, critically reducing ecosystem health with widespread repercussions for animal and human wellbeing. Developing tools in species/habitat conservation and future restoration is therefore essential if we are to effectively mitigate against the declining health of mountains.

Trace determination of multiple hydrophilic cyanotoxins in freshwater by off- and on-line solid phase extraction coupled to liquid chromatography-tandem mass spectrometry

Hydrophilic cyanotoxins (HCTs), such as paralytic shellfish toxins (PSTs), anatoxin-a (ATX-a), and cylindrospermopsin (CYN) are highly toxic and toxin-producing algae are widely distributed worldwide. However, HCTs, especially PSTs, are rarely reported in freshwater due to analytical limitations. This may result in an underestimation of the ecological risks and health risks. This study developed a new method to detect ATX-a, CYN, and thirteen common PSTs in freshwater simultaneously by using off-line solid phase extraction (SPE) and liquid chromatography-tandem mass spectrometry (LC-MS/MS). The limits of detection (LODs) of all targets were lower than 0.05 μg/L, which could meet the regulatory requirements for monitoring of HCTs in drinking water in different countries and regions. To improve the detection sensitivities for trace PSTs, a method based on off-line SPE and on-line SPE-LC-MS/MS was established with LOD around 0.001 μg/L. GTX1&4, GTX2&3, and GTX5 were detected in freshwater in China for the first time, highlighting that overall communities are facing potential risks of exposure to various PSTs in China. High concentrations of ATX-a and CYN were also detected in freshwater from Northern China. The proposed method helps to understand the pollution status of HCT in water bodies, especially during the non-algal bloom period.

A new identity of microcystins: Environmental endocrine disruptors? An evidence-based review

Microcystins (MCs) are widely distributed cyanobacterial toxins in eutrophic waters. At present, the endocrine-disrupting effects of MCs have been extensively studied, but whether MCs can be classified as environmental endocrine disruptors (EDCs) is still unclear. This review is aimed to evaluate the rationality for MCs as to be classified as EDCs based on the available evidence. It has been identified that MCs meet eight of ten key characteristics of chemicals that can be classified as EDCs. MCs interfere with the six processes, including synthesis, release, circulation, metabolism, binding and action of natural hormones in the body. Also, they are fit two other characteristics of EDC: altering the fate of producing/responding cells and epigenetic modification. Further evidence indicates that the endocrine-disrupting effect of MCs may be an important cause of adverse health outcomes such as metabolic disorders, reproductive disorders and effects on the growth and development of offspring. Generally, MCs have endocrine-disrupting properties, suggesting that it is reasonable for them to be considered EDCs. This is of great importance in understanding and evaluating the harm done by MCs on humans.

A review and assessment of cyanobacterial toxins as cardiovascular health hazards

Eutrophicated waters frequently support bloom-forming cyanobacteria, many of which produce potent cyanobacterial toxins (cyanotoxins). Cyanotoxins can cause adverse health effects in a wide range of organisms where the toxins may target the liver, other internal organs, mucous surfaces and the skin and nervous system. This review surveyed more than 100 studies concerning the cardiovascular toxicity of cyanotoxins and related topics. Over 60 studies have described various negative effects on the cardiovascular system by seven major types of cyanotoxins, i.e. the microcystin (MC), nodularin (NOD), cylindrospermopsin (CYN), anatoxin (ATX), guanitoxin (GNTX), saxitoxin (STX) and lyngbyatoxin (LTX) groups. Much of the research was done on rodents and fish using high, acutely toxin concentrations and unnatural exposure routes (such as intraperitoneal injection), and it is thus concluded that the emphasis in future studies should be on oral, chronic exposure of mammalian species at environmentally relevant concentrations. It is also suggested that future in vivo studies are conducted in parallel with studies on cells and tissues. In the light of the presented evidence, it is likely that cyanotoxins do not constitute a major risk to cardiovascular health under ordinary conditions met in everyday life. The risk of illnesses in other organs, in particular the liver, is higher under the same exposure conditions. However, adverse cardiovascular effects can be expected due to indirect effects arising from damage in other organs. In addition to risks related to extraordinary concentrations of the cyanotoxins and atypical exposure routes, chronic exposure together with co-existing diseases could make some of the cyanotoxins more dangerous to cardiovascular health.

Environmental Exposure to Cyanobacteria Hepatotoxins in a Pacific Island Community: A Cross-Sectional Assessment

(1) Background: Cyanobacteria produce a wide range of secondary metabolites, including tumor-promoting hepatotoxins. We recently reported evidence of an independent association between oral cyanobacteria and hepatocellular carcinoma in a U.S. population. We sought to characterize the nature, sources, and health correlates of cyanotoxin exposure in the U.S. Pacific Island territory of Guam, which has a high incidence of liver cancer. (2) Methods: Seventy-four adult males and females were enrolled in a cross-sectional study to quantify cyanotoxins in saliva, urine, and blood and their correlation with health behaviors, medical history, and environmental exposures. Plant samples were collected from locations throughout the island. Microcystin/nodularin (MC/NOD), cylindrospermopsin (CYN), and anabaenopeptin (AB) were measured in biospecimens and in plant extracts by ELISA. (3) Results: Overall, among study participants MC/NOD were detected in 53.9% of saliva, 7.5% of urine, and 100% of serum.; CYN in 40.0% of saliva, 100.0% of urine, and 70.4% of serum; AB in 30.8% of saliva, 85% of urine, and 92.6% of serum. Salivary MC/NOD levels were significantly higher in individuals using municipal tap water as their primary source of drinking water; both salivary and urinary MC/NOD levels were higher in those not using store-bought/commercial water. Urine MC/NOD levels were highest among individuals consuming fruits and vegetables exclusively from local sources. Urine MC/NOD levels were elevated in individuals with hypertension and hyperlipidemia and salivary MC/NOD in those with recent alcohol consumption. Cyanotoxins were prevalent in plant samples including MC/NOD (46.6%), CYN (35.1%), and AB (51.7%). (4) Conclusions: Our study provides evidence that exposure to cyanobacterial hepatotoxins, including tumor promoters, may be prevalent in Guam and may originate from environmental sources. Population-based epidemiologic studies are needed to investigate the role of cyanotoxins in liver cancer development.

Non-Proteinogenic Amino Acid β-N-Methylamino-L-Alanine (BMAA): Bioactivity and Ecological Significance

Research interest in a non-protein amino acid β-N-methylamino-L-alanine (BMAA) arose due to the discovery of a connection between exposure to BMAA and the occurrence of neurodegenerative diseases. Previous reviews on this topic either considered BMAA as a risk factor for neurodegenerative diseases or focused on the problems of detecting BMAA in various environmental samples. Our review is devoted to a wide range of fundamental biological problems related to BMAA, including the molecular mechanisms of biological activity of BMAA and the complex relationships between producers of BMAA and the environment in various natural ecosystems. At the beginning, we briefly recall the most important facts about the producers of BMAA (cyanobacteria, microalgae, and bacteria), the pathways of BMAA biosynthesis, and reliable methods of identification of BMAA. The main distinctive feature of our review is a detailed examination of the molecular mechanisms underlying the toxicity of BMAA to living cells. A brand new aspect, not previously discussed in any reviews, is the effect of BMAA on cyanobacterial cells. These recent studies, conducted using transcriptomics and proteomics, revealed potent regulatory effects of BMAA on the basic metabolism and cell development of these ancient photoautotrophic prokaryotes. Exogenous BMAA strongly influences cell differentiation and primary metabolic processes in cyanobacteria, such as nitrogen fixation, photosynthesis, carbon fixation, and various biosynthetic processes involving 2-oxoglutarate and glutamate. Cyanobacteria were found to be more sensitive to exogenous BMAA under nitrogen-limited growth conditions. We suggest a hypothesis that this toxic diaminoacid can be used by phytoplankton organisms as a possible allelopathic tool for controlling the population of cyanobacterial cells during a period of intense competition for nitrogen and other resources in various ecosystems.

Harmonizing science and management options to reduce risks of cyanobacteria

Management of cyanobacteria has become an increasingly complex venture. Cyanobacteria risks have amplified as society moves forward in an era of accelerated global changes. The cyanobacteria management "pendulum" has progressively shifted from prevention to mitigation, with management considerations often put forth after bloom formation. A universal system (i.e., one-size-fits-all management) fails to provide a management path forward due to the inherent complexities of each lake. A tailored management plan is needed: the right species at the right time in the right place (i.e., the three Rs). The three Rs represent a customizable management strategy that is flexible and informed by advances in scientific understanding to lower cyanobacteria-associated risks. Identifying thresholds in risk tolerance, where thresholds are defined by community collectives, is essential to frame cyanobacteria management targets and to decide on what management interventions are warranted.

A Summer of Cyanobacterial Blooms in Belgian Waterbodies: Microcystin Quantification and Molecular Characterizations

In the context of increasing occurrences of toxic cyanobacterial blooms worldwide, their monitoring in Belgium is currently performed by regional environmental agencies (in two of three regions) using different protocols and is restricted to some selected recreational ponds and lakes. Therefore, a global assessment based on the comparison of existing datasets is not possible. For this study, 79 water samples from a monitoring of five lakes in Wallonia and occasional blooms in Flanders and Brussels, including a canal, were analyzed. A Liquid Chromatography with tandem mass spectrometry (LC-MS/MS) method allowed to detect and quantify eight microcystin congeners. The mcyE gene was detected using PCR, while dominant cyanobacterial species were identified using 16S RNA amplification and direct sequencing. The cyanobacterial diversity for two water samples was characterized with amplicon sequencing. Microcystins were detected above limit of quantification (LOQ) in 68 water samples, and the World Health Organization (WHO) recommended guideline value for microcystins in recreational water (24 µg L⁻¹) was surpassed in 18 samples. The microcystin concentrations ranged from 0.11 µg L⁻¹ to 2798.81 µg L⁻¹ total microcystin. For 45 samples, the dominance of the genera Microcystis sp., Dolichospermum sp., Aphanizomenon sp., Cyanobium/Synechococcus sp., Planktothrix sp., Romeria sp., Cyanodictyon sp., and Phormidium sp. was shown. Moreover, the mcyE gene was detected in 75.71% of all the water samples.

Multiclass cyanotoxin analysis in reservoir waters: Tandem solid-phase extraction followed by zwitterionic hydrophilic interaction liquid chromatography-mass spectrometry

The presence of cyanobacteria and cyanotoxins in all water bodies, including ocean water and fresh water sources, represents a risk for human health as eutrophication and climate change are enhancing their level of proliferation. For risk assessment and studies on occurrence, the development of reliable and sensitive analytical approaches able to cover a wide range of cyanotoxins is essential. This work describes the development of an HILIC-MS/MS multiclass method for the simultaneous analysis of eight cyanotoxins in reservoir water samples belonging to three different classes according to their chemical structure: cyclic peptides (microcystin-LR, microcystin-RR and nodularin), alkaloids (cylindrospermopsin, anatoxin-a) and three non-protein amino acids isomers such as β-methylamino-L-alanine, 2,4-diaminobutyric acid and N-(2-aminoethyl)glycine). A SeQuant ZIC-HILIC column was employed to achieve the chromatographic separation in less than 12 min. Previously, a novel sample treatment based on a tandem solid-phase extraction (SPE) system using mixed cation exchange (MCX) and Strata-X cartridges was investigated with the aim of extracting and preconcentrating this chemically diverse group of cyanotoxins. The Strata-X cartridge, which was configured first in the line of sample flow, retained the low polar compounds and the MCX cartridge, which was at the bottom of the dual system, retained mainly the non-protein amino acids. The optimization procedure highlighted the importance of sample ion content for the recoveries of some analytes such as the isomers β-N-methylamino-L-alanine and 2-4-diaminobutyric acid. Method validation was carried out in terms of linearity, limit of detection (LOD) and quantification (LOQ), recoveries, matrix effect and precision in terms of repeatability and intermediate precision. This work represents the first analytical method for the simultaneous analysis of these multiclass cyanotoxins in reservoir water samples, achieving LOQs in the very low range of 7·10^-3 - 0.1 μg L^-1. Despite high recoveries obtained at the LOQ concentration levels (101.0-70.9%), relative standard deviations lower than 17.5% were achieved.

3D Impedimetric Biosensor for Cyanobacteria Detection in Natural Water Sources

The excessive growth of cyanobacteria in freshwater sources produces the development of toxic blooms mainly due to the production of cyanotoxins. Here, a novel impedimetric biosensor based on a three-dimensional interdigitated electrode array (3D-IDEA) for detection of cyanobacteria cells is reported. The 3D-IDEA sensor surface biofunctionalization was performed by means of the layer-by-layer method using polyethyleneimine (PEI) as the anchoring layer and concanavalin A (Con A) as the bioreceptor to lipopolysaccharides of cyanobacteria cells. The developed PEI-Con A 3D-IDEA sensors show a linear response (R2 = 0.992) of the impedance changes (RS) versus the logarithm of cyanobacteria concentrations in the range of 102–105 cells·mL−1 with the detection limit of 100 cells·mL−1. Moreover, to prevent the interference from components that may be present in real water samples and minimize a possible sample matrix effect, a filtration methodology to recover cyanobacterial cells was developed. The proposed methodology allows 91.2% bacteria recovery, permitting to obtain results similar to controlled assays. The developed system can be used in aquatic environments to detect cyanobacteria and consequently to prevent the formation of blooms and the production of cyanotoxins. Con A can bind to most polysaccharides and so react with other types of bacteria. However, currently, on the market, it is not possible to find specific biorecognition elements for cyanobacteria. Taking into consideration the specificity of samples to be analyzed (natural water resources), it is difficult to expect high concentration of other bacteria. In this sense, the developed methodology may be used as an alarm system to select samples for more thorough and precise laboratory analysis.

Investigation of the Occurrence of Cyanotoxins in Lake Karaoun (Lebanon) by Mass Spectrometry, Bioassays and Molecular Methods

Lake Karaoun is the largest artificial lake in Lebanon and serves multiple purposes. Recently, intensive cyanobacterial blooms have been reported in the lake, raising safety and aesthetic concerns related to the presence of cyanotoxins and cyanobacterial taste and odor (T&O) compounds, respectively. Here, we communicate for the first time results from a recent investigation by LC-MS/MS covering multiple cyanotoxins (microcystins (MCs), anatoxin-a, cylindrospermopsin, nodularin) in water and fish collected between 2019 and 2020. Eleven MCs were identified reaching concentrations of 211 and 199 μg/L for MC-LR and MC-YR, respectively. Cylindrospermopsin, anatoxin-a and nodularin were not detected. The determination of the total MCs was also carried out by ELISA and Protein Phosphatase Inhibition Assay yielding comparable results. Molecular detection of cyanobacteria (16S rRNA) and biosynthetic genes of toxins were carried out by qPCR. Untargeted screening analysis by GC-MS showed the presence of T&O compounds, such as β-cyclocitral, β-ionone, nonanal and dimethylsulfides that contribute to unpleasant odors in water. The determination of volatile organic compounds (VOCs) showed the presence of anthropogenic pollutants, mostly dichloromethane and toluene. The findings are important to develop future monitoring schemes in order to assess the risks from cyanobacterial blooms with regard to the lake’s ecosystem and its uses.

Cyanotoxins and the Nervous System

Cyanobacteria are capable of producing a wide range of bioactive compounds with many considered to be toxins. Although there are a number of toxicological outcomes with respect to cyanobacterial exposure, this review aims to examine those which affect the central nervous system (CNS) or have neurotoxicological properties. Such exposures can be acute or chronic, and we detail issues concerning CNS entry, detection and remediation. Exposure can occur through a variety of media but, increasingly, exposure through air via inhalation may have greater significance and requires further investigation. Even though cyanobacterial toxins have traditionally been classified based on their primary mode of toxicity, increasing evidence suggests that some also possess neurotoxic properties and include known cyanotoxins and unknown compounds. Furthermore, chronic long-term exposure to these compounds is increasingly being identified as adversely affecting human health.

Advances in the toxicology research of microcystins based on Omics approaches

Microcystins (MCs) are the most widely distributed cyanotoxins, which can be ingested by animals and human body in multiple ways, resulting in a threat to human health and the biodiversity of wildlife. Therefore, the study on toxic effects and mechanisms of MCs is one of the focuses of attention. Recently, the Omics techniques, i.e. genomics, transcriptomics, proteomics and metabolomics, have significantly contributed to the comprehensive understanding and revealing of the molecular mechanisms about the toxicity of MCs. This paper mainly reviews current literature using the Omics approaches to explore the toxicity mechanism of MCs in liver, gonad, spleen, brain, intestine and lung of multiple species. It was found that MCs can exert strong toxic effects on various metabolic activities and cell signal transduction in cell cycle, apoptosis, destruction of cell cytoskeleton and redox disorder, at protein, transcription and metabolism level. Meanwhile, it was also revealed that the alteration of non-coding RNAs (miRNA, circRNA and lncRNA, etc.) and gut microbiota plays an essential regulatory role in the toxic effects of MCs, especially in hepatotoxicity and reproductive toxicity. In addition, we summarized current research gaps and pointed out the future directions for research. The detailed information in this paper shows that the application and development of Omics techniques have significantly promoted the research on MCs toxicity, and it is also a valuable resource for exploring the toxic mechanism of MCs.

Emerging Optical Materials in Sensing and Discovery of Bioactive Compounds

Optical biosensors are used in numerous applications and analytical fields. Advances in these sensor platforms offer high sensitivity, selectivity, miniaturization, and real-time analysis, among many other advantages. Research into bioactive natural products serves both to protect against potentially dangerous toxic compounds and to promote pharmacological innovation in drug discovery, as these compounds have unique chemical compositions that may be characterized by greater safety and efficacy. However, conventional methods for detecting these biomolecules have drawbacks, as they are time-consuming and expensive. As an alternative, optical biosensors offer a faster, simpler, and less expensive means of detecting various biomolecules of clinical interest. In this review, an overview of recent developments in optical biosensors for the detection and monitoring of aquatic biotoxins to prevent public health risks is first provided. In addition, the advantages and applicability of these biosensors in the field of drug discovery, including high-throughput screening, are discussed. The contribution of the investigated technological advances in the timely and sensitive detection of biotoxins while deciphering the pathways to discover bioactive compounds with great health-promoting prospects is envisaged to meet the increasing demands of healthcare systems.

Cyanobacteria, Cyanotoxins, and Neurodegenerative Diseases: Dangerous Liaisons

The prevalence of neurodegenerative disease (ND) is increasing, partly owing to extensions in lifespan, with a larger percentage of members living to an older age, but the ND aetiology and pathogenesis are not fully understood, and effective treatments are still lacking. Neurodegenerative diseases such as Alzheimer’s disease, Parkinson’s disease, and amyotrophic lateral sclerosis are generally thought to progress as a consequence of genetic susceptibility and environmental influences. Up to now, several environmental triggers have been associated with NDs, and recent studies suggest that some cyanotoxins, produced by cyanobacteria and acting through a variety of molecular mechanisms, are highly neurotoxic, although their roles in neuropathy and particularly in NDs are still controversial. In this review, we summarize the most relevant and recent evidence that points at cyanotoxins as environmental triggers in NDs development.

A Brief Review of the Structure, Cytotoxicity, Synthesis, and Biodegradation of Microcystins

Harmful cyanobacterial blooms pose an environmental health hazard due to the release of water-soluble cyanotoxins. One of the most prevalent cyanotoxins in nature is microcystins (MCs), a class of cyclic heptapeptide hepatotoxins, and they are produced by several common cyanobacteria in aquatic environments. Once released from cyanobacterial cells, MCs are subjected to physical chemical and biological transformations in natural environments. MCs can also be taken up and accumulated in aquatic organisms and their grazers/predators and induce toxic effects in several organisms, including humans. This brief review aimed to summarize our current understanding on the chemical structure, exposure pathway, cytotoxicity, biosynthesis, and environmental transformation of microcystins.

Does the Kis-Balaton Water Protection System (KBWPS) Effectively Safeguard Lake Balaton from Toxic Cyanobacterial Blooms?

Lake Balaton is the largest shallow lake in Central Europe. Its water quality is affected by its biggest inflow, the Zala River. During late 20th century, a wetland area named the Kis-Balaton Water Protection System (KBWPS) was constructed in the hopes that it would act as a filter zone and thus ameliorate the water quality of Lake Balaton. The aim of the present study was to test whether the KBWPS effectively safeguards Lake Balaton against toxic cyanobacterial blooms. During April, May, July and September 2018, severe cyanobacterial blooming was observed in the KBWPS with numbers reaching up to 13 million cells/mL at the peak of the bloom (July 2018). MC- and STX-coding genes were detected in the cyanobacterial biomass. Five out of nine tested microcystin congeners were detected at the peak of the bloom with the concentrations of MC-LR reaching 1.29 µg/L; however, accumulation of MCs was not detected in fish tissues. Histopathological analyses displayed severe hepatopancreas, kidney and gill alterations in fish obtained throughout the investigated period. In Lake Balaton, on the other hand, cyanobacterial numbers were much lower; more than 400-fold fewer cells/mL were detected during June 2018 and cyanotoxins were not detected in the water. Hepatic, kidney and gill tissue displayed few alterations and resembled the structure of control fish. We can conclude that the KBWPS acts as a significant buffering zone, thus protecting the water quality of Lake Balaton. However, as MC- and STX-coding genes in the cyanobacterial biomass were detected at both sites, regular monitoring of this valuable ecosystem for the presence of cyanobacteria and cyanotoxins is of paramount importance.

Multibiomarker-based assessment of toxicity of central European strains of filamentous cyanobacteria Aphanizomenon gracile and Raphidiopsis raciborskii to zebrafish Danio rerio

The global increase in cyanobacterial blooms poses environmental and health threats. Selected cyanobacterial strains reveal toxicities despite a lack of synthesis of known toxic metabolites, and the mechanisms of these toxicities are not well understood. Here we investigated the toxicity of non-cylindrospermopsin and non-microcystin producing Aphanizomenon gracile and Raphidiopsis raciborskii of Central European origin to zebrafish exposed for 14 days to their extracts. Toxicological screening revealed the presence of anabaenopeptins and a lack of anatoxin-a, ß-methylamino-L-alanine or saxitoxins in examined extracts. The responses were compared to 20 μg L^-1 of common cyanobacterial toxins cylindrospermopsin (CYN) and microcystin-LR (MC-LR). The expression of the marker genes involved in apoptosis (caspase 3a and 3b, Bcl-2, BAX, p53, MAPK, Nrf2), DNA damage detection and repair (GADD45, RAD51, JUN, XPC), detoxification (CYP1A, CYP26, EPHX1), lipid metabolism (PPARa, FABP1, PLA2), phosphorylation/dephosphorylation (PPP6C, PPM1) and cytoskeleton (actin, tubulin) were examined using targeted transcriptomics. Cellular stress and toxicity biomarkers (oxidative injury, antioxidant enzymes, thiol pool status, and lactate dehydrogenase activity) were measured in the liver, and acetylcholinesterase activity was determined as an index of neurotoxicity in the brain. The extracts of three cyanobacterial strains that produce no known cyanotoxins caused marked toxicity in D. rerio, and the biomarker profiles indicate different toxic mechanisms between the bioactive compounds extracted from these strains and the purified cyanotoxins. All studied cyanobacterial extracts and purified cyanotoxins induced oxidative stress and neurotoxicity, downregulated Nrf2 and CYP26B1, disrupted phosphorylation/dephosphorylation processes and actin/tubulin cytoskeleton and upregulated apoptotic activity in the liver. The tested strains and purified toxins displayed distinctively different effects on lipid metabolism. Unlike CYN and MC-LR, the Central European strain of A. gracile and R. raciborskii did not reveal a genotoxic potential. These findings help to further understand the ecotoxicological consequences of toxic cyanobacterial blooms in freshwater ecosystems.