The toxicology of microcystins

Deciphering the Natural Attenuation of Cyanotoxins: Dissipation, Transformation Pathways, and Genotoxicity

Microcystin-LR (MC-LR) and cylindrospermopsin (CYN) are toxic cyanotoxins frequently found in drinking water sources, posing significant health risks. This study conducted a microcosm experiment using surface lake water exposed to sunlight to investigate the natural attenuation processes of MC-LR and CYN. Results indicated that photodegradation plays a crucial role in the natural attenuation of cyanotoxins. The half-lives of MC-LR and CYN were 1 and 7 days in summer under a combined effect of direct and indirect photodegradation, respectively. The effectiveness of these natural processes varied seasonally, with faster dissipation rates observed during summer. Bacterial degradation notably affected only MC-LR in summer, with a negligible effect on CYN. The identified transformation products showed that the conversion of MC-LR involved oxidation, hydroxylation, and/or bond cleavage with Adda and Mdha moieties, while it entails the oxidation of the tricyclic guanidine moiety and opening of the uracil ring for CYN. The Ames assay confirmed that these transformation products from the natural attenuation of MC-LR and CYN did not induce genotoxicity or mutagenicity. While these findings enhance our understanding of natural attenuation mechanisms, they also offer valuable insights that could guide artificial control strategies or improve the efficiency of cyanotoxin management. However, natural degradation processes alone, particularly in large water bodies, may be insufficient to fully mitigate cyanotoxin risks, highlighting the continued need for comprehensive management approaches.

Coupling effect of cyanobacterial blooms with migration and transformation of typical pollutants in lake or reservoir: Enhanced or decreased?

Eutrophication of lake and reservoir caused by cyanobacterial harmful algal blooms (cyanoHABs) become a global ecological problem because of massive destruction of ecosystems, which have attracted attentions widely. In addition to the production of cyanotoxins by certain bloom-forming species, there may also be direct or indirect interactions between cyanobacteria blooms and various pollutants in lakes or reservoirs. Based on bibliometrics, 19110 papers in Web of Science (WOS) and 2998 papers in the China National Knowledge Infrastructure (CNKI) on eutrophication and cyanobacterial blooms in lakes and reservoirs were analyzed, which showed that research on this topic has been ongoing for nearly 80 years with a gradual increase in its popularity. The research on the coupling process of cyanobacterial blooms with five typical pollutants, including microcystins (MCs), heavy metals, viruses, antibiotics and antibiotic resistance genes (ARGs), indicate that the coupling process between cyanobacteria blooms and certain pollutants is indeed generated through direct or indirect interactions by adsorption, changing the physical and chemical conditions of water environment, and changing the structure of microbial community. For instance, the production, toxicity would be likely enhanced by cyanobacteria blooms directly. And the microorganisms may play a significant role in the interaction between cyanobacteria blooms and ARGs. Generally, the risk of some typical pollutants would be likely enhanced or decreased directly or indirectly by these processes. It is recommended that further attention be paid to the interrelationships between the process of cyanobacterial bloom and typical pollutants' migration and transformation, to provide the scientific basis for the risk assessment and thus multi-objective synergistic control and management of nutrients and typical pollutants in eutrophic lakes or reservoirs.

Synthesis of a Truncated Microcystin Tetrapeptide Molecule from a Partial Mcy Gene Cluster in Microcystis Cultures and Blooms

Microcystis spp. threaten freshwater ecosystems through the proliferation of cyanobacterial harmful algal blooms (cyanoHABs) and production of the hepatotoxin, microcystin. While microcystin and its biosynthesis pathway, encoded by the mcy genes, have been well studied for over 50 years, a recent study found that Microcystis populations in western Lake Erie contain a transcriptionally active partial mcy operon, in which the A2 domain of mcyA and mcyB-C are present but the mcyD-J genes are absent. Here, we investigate the potential biosynthetic products and the evolutionary history of this partial operon. Our results reveal two candidate tetrapeptide constructs, with an X variable position, to be produced by strains with the partial operon. The partial operon appears necessary and sufficient for tetrapeptide biosynthesis and likely evolved from a single ancestor hundreds to tens of thousands of years ago. Bioactivity screens using Hep3B cells indicate a mild elevation of some markers of hepatotoxicity and inflammation, suggesting the need to further assess the effects of these novel secondary metabolites on freshwater ecosystems and public health. The need to assess these effects is even more pressing given the detection of tetrapeptides in both culture and western Lake Erie, which is a vital source of fresh water. Results from this study emphasize previous findings in which novel bacterial secondary metabolites may be derived from the molecular evolution of existing biosynthetic machinery under different environmental forcings.

RNAseq analysis of whole zebrafish (Danio rerio) larvae revealed the main cellular biological effects of geosmin and microcystin exposure at environmentally relevant concentrations

Cyanobacterial blooms are common events that releases secondary metabolites into water posing considerable threats to the environment, wildlife, and public health. Some of these metabolites, such as microcystin, have been extensively studied and associated with harmful effects in mammals and aquatic organisms, while the biological effects of others, like geosmin, remain much less investigated. Enhancing our understanding of cyanotoxins effects on organisms is especially relevant facing the complex scenarios projected due to global warming. The aim of this study was to assess the transcriptional modulation in whole zebrafish (Danio rerio) larvae (n = 9) in response to a 7-days immersion exposure to 3 μg L-1 MCLR or 5 μg L-1 geosmin. No mortality or differences in length gain were observed in zebrafish larvae exposed to environmentally realistic doses of both cyanotoxins. The exposure to MCLR and to geosmin caused the differential expression of 164 and 172 genes respectively, being 23 upregulated by MCLR and 98 upregulated by geosmin. Among the upregulated genes, 16 were shared, while 42 were shared among the downregulated genes. Over-representation analysis identified three enriched GO terms only among the genes upregulated by geosmin: organic hydroxy compound metabolic process (1901615), small molecule biosynthetic process (0044283), and lipid metabolic process (0006629). In fact, the expression of 12 of the 13 genes directly involved in the synthesis of cholesterol from acetyl-CoA was upregulated by geosmin. A chronic upregulation of cholesterol biosynthetic pathway is linked to several diseases and metabolic disorders, including alterations in sex-related hormones. Moreover, our results indicate that geosmin and MCLR acts through different mechanisms. Geosmin does not appear to provoke short-term adverse effects as MCLR but could disrupt the endocrine system by altering the lipid and steroid metabolism.

Simultaneous electrochemical removal of three microcystin congeners and sulfamethoxazole in natural water

Microcystins (MCs), frequently detected in freshwater ecosystems, have raised significant human health and ecological concerns. New approaches are being developed to control and remove MCs. In this study, we examined factors influencing the efficacy of electrochemical oxidation as a means of control. Anode material (Pt/Ti, Ta2O5-IrO2/Ti, SnO2-SbO2/Ti, boron-doped diamond (BDD/Si), anode surface area ratios and solution volumes, initial pollutant concentrations, and the co-existing antibiotic sulfamethoxazole (SMX) were investigated. MCs and SMX were dissolved in filtered Taihu Lake water to simulate the natural aquatic environment. The results showed that non-active anodes, lower initial concentration of MC, larger surface area ratio of cathode to anode, and smaller ratio of reaction solution volume to anode surface area could promote the degradation target pollutants. Under optimal conditions in this study, the degradation rates of MC-LR, MC-YR, MC-RR, and SMX each reached more than 90% within 6 h, and the removal efficiency of MC-YR was the highest among three congeners. The effect of SMX on the degradation of MC congeners depended mainly on their concentration differences, such that when the initial concentration of SMX was one to two orders of magnitude lower than microcystin, the presence of SMX would promote the degradation of MCs. In contrast, when the initial concentration of SMX was higher than that of microcystin by approximately an order of magnitude, sulfamethoxazole would inhibit the degradation of MCs by between 4.6% and 24.5%. Ultra-high-performance liquid chromatography tandem mass spectrometry analysis revealed that the three MC congeners were electrochemically degraded through aromatic ring oxidation, alkene oxidation, and bond cleavage on the ADDA (3-amino-9-methoxy-2,6,8-trimethyl-10-phenyldeca-4,6-dienoic acid) side chain. Notably, the removal of MCs was accompanied by a decline in the hardness of the reaction water. This study provided insights into electrochemical degradation of microcystins and antibiotics in natural water, offering suggestions for its practical application.

Identification of novel microcystins in algal extracts by a liquid chromatography-high-resolution mass spectrometry data analysis pipeline

BACKGROUND

Microcystins are an emergent public health problem. These toxins are secondary metabolites of harmful cyanobacterial blooms, with blooms becoming more prevalent with eutrophication of water. Exposure to microcystins can result in sickness, liver damage, and even death. Over 300 microcystins have been identified to date, with differences in toxicity based on the specific amino acid composition. Because of this diversity in microcystins, as well as the likelihood of detecting as yet undiscovered microcystins, it is vital to establish a methodological workflow to identify any microcystin in a complex sample, regardless of the availability of a reference standard. Additionally, ascribing varying levels of confidence to these identifications is critical to effectively communicate discoveries.

METHODS

A liquid-chromatography-high-resolution mass spectrometry method was utilized to identify microcystins present in cyanobacterial extracts from a strain of Microcystis aeruginosa and an Aphanizomenon sp. First, microcystin congeners with available standards were identified in the cyanobacterial extract. These known-unknown microcystins were considered to have the highest confidence identifications due to availability of accurate masses, retention times, and library spectra for comparison. Utilizing the spectra of these microcystins, relatively high-abundance diagnostic product-ions were identified and employed to screen the data for additional candidate microcystins. Microcystins without a standard that had an exact mass matching a microcystin published in CyanoMetDB were considered semi-known-unknown microcystins. The remaining microcystins were considered unknown-unknown microcystins. The identities of the microcystins determined herein were additionally supported by product-ion analysis, thiol reactivity, esterification reactions, neutral loss analysis, and literature contextualization.

RESULTS

In total, utilizing the systematic workflow presented herein, 23 microcystins were identified in the M. aeruginosa culture, including two not published previously: [d-Asp3]MC-LCit and the incompletely identified MC-L(C7H11NO3).

Responses of RTgill-W1 cells to cyanobacterial metabolites microcystin-LR, anabaenopeptin-A, cylindrospermopsin, their binary and ternary mixtures

The aim of our study was to investigate the effects of cyanobacterial metabolites: microcystin-LR (MC-LR) anabaenopeptin-A (ANA-A), cylindrospermopsin (CYL), their binary and ternary mixtures on rainbow trout (Oncorhynchus mykiss) gill (RTgill-W1) cell line. We determined the following cell parameters: Hoechst and propidium iodide (PI) double staining, intracellular ATP level with luminometric assay, glutathione level with ThiolTracker Violet®- glutathione detection reagent and cytoskeletal F-actin fluorescence. The results showed that although reduction of Hoechst fluorescence was observed in both binary and ternary combinations of cyanobacterial metabolites, the mixture of MC-LR + ANA-A + CYL was the most potent inhibitor (EC50 = 148 nM). PI fluorescence and ATP levels were more increased in the cells exposed to the mixtures than those exposed to the individual metabolites with synergistic toxic changes suggesting apoptosis as the mechanism of cell death. Reduced glutathione level was also decreased in cells exposed both to single metabolites and their mixtures with the highest decrease and synergistic effects at 334 nM MC-LR+334 nM ANA-A+ 334 nM CYL suggesting induction oxidative stress by the tested compounds. Reduction of F-actin fluorescence was found in the cells from all of the groups exposed to individual metabolites and their mixtures, however the highest level of inhibition showed the binary MC-LR + CYL and the ternary MC-LR + ANA-A + CYL with synergistic interactions. The study suggests that in natural conditions fish gill cells may be very sensitive to individual cyanobacterial metabolites and more prone to their binary and ternary mixtures.

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

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

Algae blooms with resistance in fresh water: Potential interplay between Microcystis and antibiotic resistance genes

Microcystis, a type of cyanobacteria known for producing microcystins (MCs), is experiencing a global increase in blooms. They have been recently recognized as potential contributors to the widespread of antibiotic resistance genes (ARGs). By reviewing approximately 150 pieces of recent studies, a hypothesis has been formulated suggesting that significant fluctuations in MCs concentrations and microbial community structure during Microcystis blooms could influence the dynamics of waterborne ARGs. Among all MCs, microcystin-LR (MC-LR) is the most widely distributed worldwide, notably abundant in reservoirs during summer. MCs inhibit protein phosphatases or increase reactive oxygen species (ROS), inducing oxidative stresses, enhancing membrane permeability, and causing DNA damage. This further enhances selective pressures and horizontal gene transfer (HGT) chances of ARGs. The mechanisms by which Microcystis regulates ARG dissemination have been systematically organized for the first time, focusing on the secretion of MCs and the alterations of bacterial community structure. However, several knowledge gaps remain, particularly concerning how MCs interfere with the electron transport chain and how Microcystis facilitates HGT of ARGs. Concurrently, the predominance of Microcystis forming the algal microbial aggregates is considered a hotspot for preserving and transferring ARGs. Yet, Microcystis can deplete the nutrients from other taxa within these aggregates, thereby reducing the density of ARG-carrying bacteria. Therefore, further studies are needed to explore the 'symbiotic - competitive' relationships between Microcystis and ARG-hosting bacteria under varied nutrient conditions. Addressing these knowledge gaps is crucial to understand the impacts of the algal aggregates on dynamics of waterborne antibiotic resistome, and underscores the need for effective control of Microcystis to curb the spread of antibiotic resistance. Constructed wetlands and photocatalysis represent advantageous strategies for halting the spread of ARGs from the perspective of Microcystis blooms, as they can effectively control Microcystis and MCs while maintaining the stability of aquatic ecosystem.

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

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

Ultrastructural, molecular and haemato-immunological changes: Multifaceted toxicological effects of microcystin-LR in rohu, Labeo rohita

No water body is resilient to afflicts of algal bloom, if goes unmanaged. With the increasing trend of intensification, eutrophication and climate change, Labeo rohita (rohu) is highly anticipated to suffer from the deleterious effects of bloom and eventually its toxins. A comprehensive study was conducted to understand the toxicopathological effects of microcystin-LR (MC-LR) in rohu following intraperitoneal injection of 96 h-LD50 dose i.e., 713 μg kg-1. Substantial changes in micro- and ultrastructural level were evident in histopathology and transmission electron microscope (TEM) study. The haematological, biochemical, cellular and humoral innate immune biomarkers were significantly altered (p < 0.05) in MC-LR treated fish. The mRNA transcript levels of IL-1β, IL-10, IgM and IgZ in liver and kidney tissues were significantly up-regulated in 12 hpi and declined in 96 hpi MC-LR exposed fish. The relative mRNA expression of caspase 9 in the liver and kidney indicates mitochondrial-mediated apoptosis which was strongly supported by TEM study. In a nutshell, our study illustrates for the first time MC-LR induced toxicological implications in rohu displaying immunosuppression, enhanced oxidative stress, pathophysiology, modulation in mRNA transcription, genotoxicity, structural and ultrastructural alterations signifying it as a vulnerable species for MC-LR intoxication.

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.

Alleviation of microcystin-leucine arginine -induced hepatotoxicity: An updated overview

OBJECTIVES

Contamination of surface waters is a major health threat for all living creatures. Some types of blue-green algae that naturally occur in fresh water, are able to produce various toxins, like Microcystins (MCs). Microcystin-leucine arginine (MC-LR) produced by Microcystis aeruginosa is the most toxic and abundant isoforms of MCs, and it causes hepatotoxicity. The present article reviews preclinical experiments examined different treatments, including herbal derivatives, dietary supplements and drugs against MC-LR hepatotoxicity.

METHODS

We searched scientific databases Web of Science, Embase, Medline (PubMed), Scopus, and Google Scholar using relevant keywords to find suitable studies until November 2023.

RESULTS

MC-LR through Organic anion transporting polypeptide superfamily transporters (OATPs) penetrates and accumulates in hepatocytes, and it inhibits protein phosphatases (PP1 and PP2A). Consequently, MC-LR disturbs many signaling pathways and induces oxidative stress thus damages cellular macromolecules. Some protective agents, especially plants rich in flavonoids, and natural supplements, as well as chemoprotectants were shown to diminish MC-LR hepatotoxicity.

CONCLUSION

The reviewed agents through blocking the OATP transporters (nontoxic nostocyclopeptide-M1, captopril, and naringin), then inhibition of MC-LR uptake (naringin, rifampin, cyclosporin-A, silymarin and captopril), and finally at restoration of PPAse activity (silybin, quercetin, morin, naringin, rifampin, captopril, azo dyes) exert hepatoprotective effect against MC-LR.

Sphingomonas lacusdianchii sp. nov., an attached bacterium inhibited by metabolites from its symbiotic cyanobacterium

An alpha-proteobacterial strain JXJ CY 53 T was isolated from the cyanosphere of Microcystis sp. FACHB-905 (MF-905) collected from Lake Dianchi, China. JXJ CY 53 T was observed to be an aerobic, Gram-stain-negative, oval shaped, and mucus-secreting bacterium. It had C18:1ω7c and C16:0 as the major cellular fatty acids, Q-10 as the predominant ubiquinone, and sphingoglycolipid, diphosphatidylglycerol, phosphatidylcholine, and phosphatidylmethylethanolamine as the polar lipids. The G + C content of DNA was 65.85%. The bacterium had 16S rRNA gene sequence identities of 98.9% and 98.7% with Sphingomonas panni DSM 15761 T and Sphingomonas hankookensis KCTC 22579 T, respectively, while less than 97.4% identities with other members of the genus. Further taxonomic analysis indicated that JXJ CY 53 T represented a new member of Sphingomonas, and the species epithet was proposed as Sphingomonas lacusdianchii sp. nov. (type strain JXJ CY 53 T = KCTC 72813 T = CGMCC 1.17657 T). JXJ CY 53 T promoted the growth of MF-905 by providing bio-available phosphorus and nitrogen, plant hormones, vitamins, and carotenoids. It could modulate the relative abundances of nonculturable bacteria associated with MF-905 and influence the interactions of MF-905 and other bacteria isolated from the cyanobacterium, in addition to microcystin production characteristics. Meanwhile, MF-905 could provide JXJ CY 53 T dissolved organic carbon for growth, and control the growth of JXJ CY 53 T by secreting specific chemicals other than microcystins. Overall, these results suggest that the interactions between Microcystis and its attached bacteria are complex and dynamic, and may influence the growth characteristics of the cyanobacterium. This study provided new ideas to understand the interactions between Microcystis and its attached bacteria. KEY POINTS: • A novel bacterium (JXJCY 53 T) was isolated from the cyanosphere of Microcystis sp. FACHB-905 (MF-905) • JXJCY 53 T modulated the growth and microcystin production of MF-905 • MF-905 could control the attached bacteria by specific chemicals other than microcystins (MCs).

Micrococcus lacusdianchii sp. nov., an attached bacterium inhibited by metabolites from its symbiotic algae

A novel actinobacterial strain, designated as JXJ CY 30 T, was isolated from the phycosphere of Microcystis aeruginosa FACHB-905 (Maf) collected from Lake Dianchi, China. The strain was a Gram-stain-positive, aerobic and coccus-shaped actinobacterium. It had alanine, glutamic acid, aspartic acid, and lysine in the peptidoglycan, and mannose, ribose and arabinose in its cell wall sugars, anteiso-C15:0 and iso-C15:0 as the main cellular fatty acids, MK-7 and MK-8 as the major respiratory quinones, and phosphatidylglycerol, diphosphatidylglycerol, phosphatidylinositol, glycolipid, and an unidentified phospholipid as the polar lipids. The DNA G + C content was 73.08%. Its 16 S rRNA gene sequence shared 99.14%, and 98.75% similarities with Micrococcus flavus DSM 19079 T and M. porci KD337-16T, respectively, and ≤98.41% similarities with other type strains of the genus Micrococcus. It formed independent clade with M. flavus DSM 19079 T on the phylogenetic trees. The digital DNA-DNA hybridization and average nucleotide identity values between strain JXJ CY 30 T and M. flavus DSM 19079 T and M. porci KD337-16T were 48.0% and 92.1%, 25.5% and 83.2%, respectively. These data above indicated that strain JXJ CY 30 T represented a new species of the genus Micrococcus, and the species epithet is proposed as Micrococcus lacusdianchii sp. nov. (type strain JXJ CY 30 T = KCTC 49378 T = CGMCC 1.17508 T). Strain JXJ CY 30 T can potentially provide Maf with various nutrients such as available phosphorus and nitrogen, plant hormones, various vitamins and carotenoids for growth, while it was inhibited by metabolites from its symbiotic algae Maf.

Mechanisms of harmful effects of Microcystis aeruginosa on a brackish water organism Moina mongolica based on physiological and transcriptomic responses

To investigate the detrimental impacts of cyanobacterial bloom, specifically Microcystis aeruginosa, on brackish water ecosystems, the study used Moina mongolica, a cladoceran species, as the test organism. In a chronic toxicology experiment, the survival and reproductive rates of M. mongolica were assessed under M. aeruginosa stress. It was observed that the survival rate of M. mongolica fed with M. aeruginosa significantly decreased with time and their reproduction rate dropped to zero, while the control group remained maintained stable and normal reproduction. To further explore the underlying molecular mechanisms of the effects of M. aeruginosa on M. mongolica, we conducted a transcriptomic analysis on newly hatched M. mongolica cultured under different food conditions for 24 h. The results revealed significant expression differences in 572 genes, with 233 genes significantly up-regulated and 339 genes significantly down-regulated. Functional analysis of these differentially expressed genes identified six categories of physiological functional changes, including nutrition and metabolism, oxidative phosphorylation, neuroimmunology, cuticle and molting, reproduction, and programmed cell death. Based on these findings, we outlined the basic mechanisms of microcystin toxicity. The discovery provides critical insights into the mechanisms of Microcystis toxicity on organisms and explores the response mechanisms of cladocerans under the stress of Microcystis.

Modulation of growth, microcystin production, and algal-bacterial interactions of the bloom-forming algae Microcystis aeruginosa by a novel bacterium recovered from its phycosphere

Harmful algal blooms (HABs) in natural waters are of escalating global concern due to their detrimental impact on environmental health. Emerging evidence indicates that algae-bacteria symbionts can affect HAB features, though much about this interplay remains largely unexplored. The current study isolated a new species of Mucilaginibacter (type strain JXJ CY 39T) from culture biomass of the bloom-causing Microcystis aeruginosa FACHB-905 (Maf) from Lake Dianchi, China. Strain JXJ CY 39T was an aerobic, Gram-stain-negative rod bacterium that grew at 5-38°C, pH 4.0-11.0, and 0-3.0% NaCl. Taxonomic evaluation proposed a new species, with Mucilaginibacter lacusdianchii sp. nov., as the species epithet. Experimental results revealed that strain JXJ CY 39T spurred the growth of Maf by supplying soluble phosphorus and nitrogen during cultivation, despite the unavailability of soluble phosphorus and nitrogen. Additionally, by producing the plant hormone indole-3-acetate, strain JXJ CY 39T possibly impacted Maf's functionality. Results from co-culture experiments with other strains from Maf biomass showed possible effects of strain JXJ CY 39T on the relationship between Maf and other cohabiting bacteria, as well as microcystin toxin production characteristics. Although Maf could foster the growth of strain JXJ CY 39T by supplying organic carbon, the strain's growth could be regulated via specific chemical compounds based on antibiotic assays. Community composition analysis disclosed that this Mucilaginibacter strain positively affected Maf's growth and modified densities and types of bacteria linked to Maf. Overall, these results suggest that the interactions between important HAB-causing organisms and their attached bacteria are complex, dynamic, and may influence the growth characteristics of algae.

Microcystin-LR-induced epithelial-mesenchymal transition-like cells acquire resistance to multi-toxins

The protein phosphatase inhibitor microcystin-LR (MC-LR), a hepatocyte-selective cyanotoxin, induces phenotypic changes in HEK293 OATP1B3-expressing (HEK293-OATP1B3) cells, which include cytoskeletal reorganization (HEK293-OATP1B3-AD) and anoikis resistance (HEK293-OATP1B3-FL) transformed cells, respectively. These cells acquire resistance to MC-LR and partial epithelial-mesenchymal transition (EMT) characteristics. In cancer cells, EMT is generally involved in multi-drug resistance. Here, we focused on the multi-drug resistance of HEK293-OATP1B3-AD and HEK293-OATP1B3-FL cells. The MTT assay and immunoblotting were conducted to examine the responses of HEK293-OATP1B3, HEK293-OATP1B3-AD, and HEK293-OATP1B3-FL cells to multiple toxins and drugs that function as substrates for OATP1B3, including MC-LR, nodularin (Nod), okadaic acid (OA), and cisplatin (CDDP). HEK293-OATP1B3-AD and HEK293-OATP1B3-FL cells were more resistant to MC-LR, Nod, and OA than HEK293-OATP1B3 cells. Conversely, the three cell types were equivalently sensitive to CDDP. By using protein phosphatase assay, the reduction of the inhibitory effect of MC-LR and Nod on phosphatase activity might be one reason for the resistance to MC-LR and Nod in HEK293-OATP1B3-AD and HEK293-OATP1B3-FL cells. Furthermore, the parental HEK293-OATP1B3 cells showed enhanced p53 phosphorylation and stabilization after MC-LR exposure, while p53 phosphorylation was attenuated in HEK293-OATP1B3-AD and HEK293-OATP1B3-FL cells. Moreover, in HEK293-OATP1B3-AD and HEK293-OATP1B3-FL cells, AKT phosphorylation was higher than that of the parental HEK293-OATP1B3 cell line. These results suggest that the multi-toxin resistance observed in HEK293-OATP1B3-AD and HEK293-OATP1B3-FL cells is associated with AKT activation and p53 inactivation.

Identification of Serine-Containing Microcystins by UHPLC-MS/MS Using Thiol and Sulfoxide Derivatizations and Detection of Novel Neutral Losses

Microcystins (MCs) are hepatotoxic cyclic heptapeptides produced by cyanobacteria, and their structural diversity has led to the discovery of more than 300 congeners to date. However, with known amino acid combinations, many more MC congeners are theoretically possible, suggesting many remain unidentified. Herein, two novel serine (Ser)-containing MCs were putatively identified in a Lake Erie cyanobacterial harmful algal bloom (cyanoHAB), using high-resolution UHPLC-MS as well as thiol and sulfoxide derivatization procedures. These MCs contain an α,β-unsaturated carbonyl on methyl dehydroalanine (Mdha) residue that undergoes Michael addition to produce a thiol-derivatized MC. Derivatization reactions using various thiolation reagents were followed by MS/MS, and two Python codes were used for data analysis and structural elucidation of MCs. Two novel MCs containing Ser at position 1 (i.e., next to Mdha) were putatively identified as [Ser1]MC-RR and [Ser1]MC-YR. Using thiol- and sulfoxide-modified [Ser1]MCs, identifications were confirmed by the observation of specific neutral losses of the oxidized thiols or sulfoxides in CID-MS/MS spectra in both positive and negative electrospray ionization (ESI) modes. These novel neutral losses are unique for MCs with Mdha and an adjacent Ser residue. Data suggest that a gas-phase reaction occurs between oxygen from adjacent Ser residue and sulfur of the Mdha-bonded thiol or sulfoxide, which leads to the formation and detection of stable cyclic MC ions in MS/MS spectra at m/z values corresponding to the loss of oxidized thiols or oxidized sulfoxides from Ser1-containing MCs.

Devosia lacusdianchii sp. nov., an attached bacterium inhibited by metabolites from its symbiotic Microcystis

A novel alphaproteobacterial strain JXJ CY 41T was isolated from a culture mass of Microcystis, collected from Lake Dianchi, south-west, China. Strain JXJ CY 41T was gram-strain-negative, aerobic, motile, with rod-shaped cells (0.4-1.0 × 1.7-3.5 μm). It was positive for catalase and starch hydrolysis, negative for oxidase and hydrolysis of Tweens (20, 40, and 80). Growth occurred at 10-44 °C, pH 5.0-10.0, and 0-5.0% (w/v) NaCl. Major fatty acids included C16:0 (28.1%), 11-methyl C18:1 ω7c (36.7%) and C18:1 ω7c (20.8%). Q10 was the sole ubiquinone. The polar lipids were diphosphatidylglycerol, phosphatidylglycerol, glycolipid, and an unidentified lipid. The DNA G + C content was 63.1%. Its 16S rRNA gene sequence showed high similarities with Devosia oryziradicis G19T (99.5%; not validly published), D. yakushimensis Yak96BT (98.3%) and D. ginsengisoli Gsoil 520T (98.1%), and less than 98.1% similarities with other members of the genus Devosia. The digital DNA-DNA hybridization (dDDH) and average nucleotide identity (ANI) values between strain JXJ CY 41T and its 5 closest similar strains were 19.9-24.1% and 75.7-80.5%, respectively. Based on the data above, strain JXJ CY 41T was identified as a novel species of the genus Devosia, for which the epithet Devosia lacusdianchii sp. nov. was proposed. The type strain is JXJ CY 41T (= KCTC 72812T = CGMCC 1.17502T). Strain JXJ CY 41T exhibited different interactions with Microcystis aeruginosa FACHB-905 (Maf) under different conditions, and Maf could control the bacterial cellular density by secreting unknown specific chemical compounds according to its nutritional requirements.

The mechanisms of microcystin-LR-induced genotoxicity and neurotoxicity in fish and mammals: Bibliometric analysis and meta-analysis

Microcystin-leucine arginine (MC-LR) is a typical cyanobacterial toxin, and the threat of this toxin is increasing among organisms. Despite extensive toxicological studies on MC-LR, there is no comprehensive analysis based on previously published data. Therefore, we conducted bibliometric analysis and meta-analysis to identify research hotspots and to elucidate the key mechanism of the relationship between MC-LR and genotoxicity and neurotoxicity among fish and mammals. One of the hotspots is toxic mechanisms (indicated by the frequent appearance of oxidative stress, DNA damage, apoptosis, neurotoxicity, genotoxicity, ROS, comet assay, signalling pathway, and gene expression indicate as keywords). The density visualization shows a high frequency of "microcystin-LR" and "toxicology," and the overlay visualization emphasizes the prominence of "neurotoxicity" in recent years. These findings confirm the importance of studying MC-LR toxicity. Meta-analysis indicated that in both fish and mammals, MC-LR exposure increased ROS levels by 294 % and increased DNA damage biomarkers by 174 % but decreased neurotoxicity biomarkers by 9 %. Intergroup comparisons revealed that the exposure concentration of MC-LR was significantly correlated with genotoxicity and neurotoxicity levels in both fish and mammals (p < 0.05). Furthermore, the random forest (RF) model revealed that exposure concentration was the primary determinant associated with the induction of ROS, genotoxicity, and neurotoxicity induced by MC-LR. This is likely the dominant mechanism by which excessive ROS production induced by MC-LR causes oxidative stress, ultimately leading to genotoxicity and neurotoxicity in both fish and mammals.

Analysis of the immune function of Caspase-3 in Cristaria plicata

Caspase-3 is generally considered to be the most important terminal shear enzyme in the process of apoptosis, as well as an important part of cytotoxic T lymphocytes (CTL) killing mechanism, which is confirmed to play an important role in vertebrate cell apoptosis and immune system, and is poorly reported in invertebrates. In this paper, we used bioinformatics to perform amino acid multiple sequence alignment and protein structural domain analysis, and constructed a phylogenetic tree to identify the full-length cDNA of the cloned caspase-3 of Cristaria plicata (Named CpCaspase-3). The expression of caspase-1, caspase-7, caspase-8, and caspase-9 was found to be down-regulated by double-stranded RNA interference of CpCaspase-3 in C. plicata. Some degree of disruption of the caspase signaling pathway occurs. The expression of CpCaspase-3 was affected after injection of Lipopolysaccharide (LPS), Peptidoglycan (PGN), polyinosinic-polycytidylic acid (poly(I:C)), and Aeromonas hydrophila. These results were suggested that CpCaspase-3 was involved in the immune response of C. plicata. The wound recovery process of C. plicata was simulated and CpCaspase-3 was found to promote wound recovery. An autophagy inhibition and autophagy activation model of mussels was constructed, where apoptosis and autophagy undergo crosstalk, and inhibition of autophagy induces the onset of apoptosis, and similarly autophagy activation inhibits the process of apoptosis instead. In addition, a recombinant CpCaspase-3-pEGFP-C1 plasmid was constructed for subcellular localization experiments and found that CpCaspase-3 was distributed in both the nucleus and the cytoplasm. This paper aims to unveil the immune mechanism of C. plicata and provide a theoretical basis for the healthy culture of shellfish.

Hepatic NLRP3-Derived Hsp70 Binding to TLR4 Mediates MASLD to MASH Progression upon Inhibition of PP2A by Harmful Algal Bloom Toxin Microcystin, a Second Hit

Harmful algal bloom toxin microcystin has been associated with metabolic dysfunction-associated steatotic liver disease (MASLD) progression and hepatocellular carcinoma, though the mechanisms remain unclear. Using an established mouse model of MASLD, we show that the NLRP3-Hsp70-TLR4 axis drives in part the inflammation of the liver lobule that results in the progression of MASLD to metabolic dysfunction-associated steatohepatitis (MASH). Results showed that mice deficient in NLRP3 exhibited decreased MASH pathology, blocked Hsp70 expression, and co-binding with NLRP3, a crucial protein component of the liver inflammasome. Hsp70, both in the liver lobule and extracellularly released in the liver vasculature, acted as a ligand to TLR4 in the liver, primarily in hepatocytes to activate the NF-κB pathway, ultimately leading to hepatic cell death and necroptosis, a crucial pathology of MASH progression. The above studies show a novel insight into an inflammasome-triggered Hsp70-mediated inflammation that may have broader implications in MASLD pathology. MASLD to MASH progression often requires multiple hits. One of the mediators of progressive MASLD is environmental toxins. In this research report, we show for the first time a novel mechanism where microcystin-LR, an environmental toxin, advances MASLD to MASH by triggering the release of Hsp70 as a DAMP to activate TLR4-induced inflammation in the liver.

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

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

A Systematic Review of Phytochemistry, Nutritional Composition, and Pharmacologic Application of Species of the Genus Viola in Noncommunicable Diseases (NCDs)

Viola L. is the largest genus of the Violaceae family with more than 500 species across the globe. The present extensive literature survey revealed Viola species to be a group of important nutritional and medicinal plants used for the ethnomedicinal treatment of noncommunicable diseases (NCDs) such as diabetes, asthma, lung diseases, and fatigue. Many plant species of this genus have also received scientific validation of their pharmacological activities including neuroprotective, immunomodulatory, anticancer, antihypertensive, antidyslipidemic, analgesic, antipyretic, diuretic, anti-inflammatory, anthelmintic, and antioxidant. Viola is highly rich in different natural products some of which have been isolated and identified in the past few decades; these include flavonoids terpenoids and phenylpropanoids of different pharmacological activities. The pharmacokinetics and clinical studies on this genus are lacking, and the present review is aimed at summarizing the current understanding of the ethnopharmacology, phytochemistry, nutritional composition, and pharmacological profile of medicinal plants from the Viola genus to reveal its therapeutic potentials, gaps, and subsequently open a new window for future pharmacological research.

Co-occurrence of marine and freshwater phycotoxins in oysters, and analysis of possible predictors for management

Oysters (Crassostrea virginica) were screened for 12 phycotoxins over two years in nearshore waters to collect baseline phycotoxin data and to determine prevalence of phycotoxin co-occurrence in the commercially and ecologically-relevant species. Trace to low concentrations of azaspiracid-1 and -2 (AZA1, AZA2), domoic acid (DA), okadaic acid (OA), and dinophysistoxin-1 (DTX1) were detected, orders of magnitude below seafood safety action levels. Microcystins (MCs), MC-RR and MC-YR, were also found in oysters (maximum: 7.12 μg MC-RR/kg shellfish meat wet weight), warranting consideration of developing action levels for freshwater phycotoxins in marine shellfish. Oysters contained phycotoxins that impair shellfish health: karlotoxin1-1 and 1-3 (KmTx1-1, KmTx1-3), goniodomin A (GDA), and pectenotoxin-2 (PTX2). Co-occurrence of phycotoxins in oysters was common (54%, n = 81). AZAs and DA co-occurred most frequently of the phycotoxins investigated that are a concern for human health (n = 13) and PTX2 and KmTxs co-occurred most frequently amongst the phycotoxins of concern for shellfish health (n = 9). Various harmful algal bloom (HAB) monitoring methods and tools were assessed for their effectiveness at indicating levels of phycotoxins in oysters. These included co-deployed solid phase adsorption toxin tracking (SPATT) devices, toxin levels in particulate organic matter (POM, >1.5 μm) and whole water samples and cell concentrations from water samples as determined by microscopy and quantitative real-time PCR (qPCR). The dominant phycotoxin varied between SPATTs and all other phycotoxin sample types, and out of the 11 phycotoxins detected in oysters, only four and seven were detected in POM and whole water respectively, indicating phycotoxin profile mismatch between ecosystem compartments. Nevertheless, there were correlations between DA in oysters and whole water (simple linear regression [LR]: R² = 0.6, p < 0.0001, n = 40), and PTX2 in oysters and SPATTs (LR: R² = 0.3, p = 0.001, n = 36), providing additional monitoring tools for these phycotoxins, but oyster samples remain the best overall indicators of seafood safety.

Chlorination of microcystin-LR in natural water: Kinetics, transformation products, and genotoxicity

Microcystin-LR (MC-LR), a type of cyanotoxin commonly found in natural water bodies (sources of drinking water), poses a threat to human health due to its high toxicity. It is essential to successfully remove this cyanotoxin from drinking water sources. In this study, chlorine was used to oxidize MC-LR in Milli-Q water (MQ) (control test) and natural water collected from Lake Longhu (LLW) as a drinking water source. The removal efficiency, proposed transformation pathways, and genotoxicity were investigated. In the chlorine dose range investigated (4.0 mg L^-1 - 8.0 mg L^-1), the apparent second-order rate constants for MC-LR chlorination varied from 21.3 M^-1s^-1 to 31.9 M^-1s^-1 in MQ, higher than that in LLW (9.06 M^-1s^-1 to 17.7 M^-1s^-1) due to a faster chlorine decay attributed to the water matrix (e.g., natural organic matter) of LLW. Eleven transformation products (TPs) of MC-LR were identified in the two waters. The conjugated diene moieties and benzene ring of Adda moiety (3-amino-9-methoxy-2,6,8-trimethyl-10-phenyldeca-4,6-dienoic acid), and the double bond of Mdha moiety (N-methyldehydroalanine) were the major susceptible reaction sites. Attacking unsaturated bonds by hydroxyl and chlorine radicals to generate monochloro-hydroxy-MC-LR was the primary initial transformation pathway, followed by nucleophilic substitution, dehydration, and cleavage in MC-LR. Chlorine substitution on the benzene ring was also observed. Based on the bacterial reverse-mutation assay (Ames assay), TPs in treated natural water did not induce genotoxicity/mutagenicity. These findings shed light on the role of chlorination in controlling the risk of cyanotoxins in drinking water treatment plants.

Microcystins-Loaded Aged Nanoplastics Provoke a Metabolic Shift in Human Liver Cells

Studies concerning the toxicity of pollutant-loaded nanoplastics (NPs) toward humans are still in their infancy. Here, we evaluated the adsorption of microcystins (MCs) by pristine and aged polystyrene nanoplastics (PSNPs), prepared MCs-loaded aged PSNPS (1, 5, 10, 15, and 19 μg/mg), and systematically mapped the key molecular changes induced by aged and MCs-loaded PSNPs to human hepatoblastoma (HepG2) cells. According to the results, MC-LR adsorption is increased 2.64-fold by aging, and PSNP accumulation is detected in HepG2 cells. The cytotoxicity of the MC-LR-loaded aged PSNPs showed a positive relationship with the MC-LR amount, as the cell viability in the 19 μg/mg loading treatment (aPS-MC19) was 10.84% lower than aged PSNPs; meanwhile, more severe oxidative damage was observed. Primary approaches involved stressing the endoplasmic reticulum and reducing protein synthesis that the aged PSNPs posed for HepG2 cells, while the aggravated cytotoxicity in aPS-MC19 treatment was a combined result of the metabolic energy disorder, oxidative damage, endoplasmic reticulum stress, and downregulation of the MC-LR target protein. Our results confirm that the aged PSNPs could bring more MC-LR into the HepG2 cells, significantly interfere with biological processes, and provide new insight into deciphering the risk of NPs to humans.

Microbial communities in aerosol generated from cyanobacterial bloom-affected freshwater bodies: an exploratory study in Nakdong River, South Korea

Toxic blooms of cyanobacteria, which can produce cyanotoxins, are prevalent in freshwater, especially in South Korea. Exposure to cyanotoxins via ingestion, inhalation, and dermal contact may cause severe diseases. Particularly, toxic cyanobacteria and their cyanotoxins can be aerosolized by a bubble-bursting process associated with a wind-driven wave mechanism. A fundamental question remains regarding the aerosolization of toxic cyanobacteria and cyanotoxins emitted from freshwater bodies during bloom seasons. To evaluate the potential health risk of the aerosolization of toxic cyanobacteria and cyanotoxins, the objectives of this study were as follows: 1) to quantify levels of microcystin in the water and air samples, and 2) to monitor microbial communities, including toxic cyanobacteria in the water and air samples. Water samples were collected from five sites in the Nakdong River, South Korea, from August to September 2022. Air samples were collected using an air pump with a mixed cellulose ester membrane filter. Concentrations of total microcystins were measured using enzyme-linked immunosorbent assay. Shotgun metagenomic sequencing was used to investigate microbial communities, including toxic cyanobacteria. Mean concentrations of microcystins were 960 μg/L ranging from 0.73 to 5,337 μg/L in the water samples and 2.48 ng/m³ ranging from 0.1 to 6.8 ng/m³ in the air samples. In addition, in both the water and air samples, predominant bacteria were Microcystis (PCC7914), which has a microcystin-producing gene, and Cyanobium. Particularly, abundance of Microcystis (PCC7914) comprised more than 1.5% of all bacteria in the air samples. This study demonstrates microbial communities with genes related with microcystin synthesis, antibiotic resistance gene, and virulence factors in aerosols generated from cyanobacterial bloom-affected freshwater body. In summary, aerosolization of toxic cyanobacteria and cyanotoxins is a critical concern as an emerging exposure route for potential risk to environmental and human health.

Meta-analysis reveals cyanotoxins risk across African inland waters

Global eutrophication and climate warming exacerbate production of cyanotoxins such as microcystins (MCs), presenting risks to human and animal health. Africa is a continent suffering from severe environmental crises, including MC intoxication, but with very limited understanding of the occurrence and extent of MCs. By analysing 90 publications from 1989 to 2019, we found that in various water bodies where MCs have been detected so far, the concentrations were 1.4-2803 times higher than the WHO provisional guideline for human lifetime exposure via drinking water (1 µg/L) in 12 of 15 African countries where data were available. MCs were relatively high in the Republic of South Africa (averaged 2803 μg/L) and Southern Africa as a whole (702 μg/L) when compared to other regions. Values were higher in reservoirs (958 μg/L) and lakes (159 μg/L) than in other water types, and much higher in temperate (1381 μg/L) than in arid (161 μg/L) and tropical (4 μg/L) zones. Highly significant positive relationships were found between MCs and planktonic chlorophyll a. Further assessment revealed high ecological risk for 14 of the 56 water bodies, with half used as human drinking water sources. Recognizing the extremely high MCs and exposure risk in Africa, we recommend routine monitoring and risk assessment of MCs be prioritized to ensure safe water use and sustainability in this region.

Expression of Microcystis Biosynthetic Gene Clusters in Natural Populations Suggests Temporally Dynamic Synthesis of Novel and Known Secondary Metabolites in Western Lake Erie

Microcystis spp. produce diverse secondary metabolites within freshwater cyanobacterial harmful algal blooms (cyanoHABs) around the world. In addition to the biosynthetic gene clusters (BGCs) encoding known compounds, Microcystis genomes harbor numerous BGCs of unknown function, indicating a poorly understood chemical repertoire. While recent studies show that Microcystis produces several metabolites in the lab and field, little work has focused on analyzing the abundance and expression of its broader suite of BGCs during cyanoHAB events. Here, we use metagenomic and metatranscriptomic approaches to track the relative abundance of Microcystis BGCs and their transcripts throughout the 2014 western Lake Erie cyanoHAB. The results indicate the presence of several transcriptionally active BGCs that are predicted to synthesize both known and novel secondary metabolites. The abundance and expression of these BGCs shifted throughout the bloom, with transcript abundance levels correlating with temperature, nitrate, and phosphorus concentrations and the abundance of co-occurring predatory and competitive eukaryotic microorganisms, suggesting the importance of both abiotic and biotic controls in regulating expression. This work highlights the need for understanding the chemical ecology and potential risks to human and environmental health posed by secondary metabolites that are produced but often unmonitored. It also indicates the prospects for identifying pharmaceutical-like molecules from cyanoHAB-derived BGCs. IMPORTANCE Microcystis spp. dominate cyanobacterial harmful algal blooms (cyanoHABs) worldwide and pose significant threats to water quality through the production of secondary metabolites, many of which are toxic. While the toxicity and biochemistry of microcystins and several other compounds have been studied, the broader suite of secondary metabolites produced by Microcystis remains poorly understood, leaving gaps in our understanding of their impacts on human and ecosystem health. We used community DNA and RNA sequences to track the diversity of genes encoding synthesis of secondary metabolites in natural Microcystis populations and assess patterns of transcription in western Lake Erie cyanoHABs. Our results reveal the presence of both known gene clusters that encode toxic secondary metabolites as well as novel ones that may encode cryptic compounds. This research highlights the need for targeted studies of the secondary metabolite diversity in western Lake Erie, a vital freshwater source to the United States and Canada.

Room temperature synthesis of flower-like hollow covalent organic framework for efficient enrichment of microcystins

The morphology of nanomaterials is one of essential factors for their unique properties. Herein, a hollow covalent organic framework with a flower-like structure (HFH-COF) was synthesized at room temperature. The synthesized HFH-COF has a very large specific surface area, mesoporous structure, excellent chemical stability, and good crystallinity. The special morphology endowed HFH-COF with high specific surface area utilization and rapid mass transfer rate, resulting in faster equilibration time and better extraction performance than spherical COF (S-COF). Subsequently, combined with high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS), an efficient and sensitive method was established for microcystins (MCs) detection. The developed method has low detection limits (0.6-0.8 pg mL^-1), wide linear ranges (1.5-1000.0 pg mL^-1, R ≥ 0.9993), and acceptable reproducibility (RSD ≤ 7.6%, n = 6). Real biological samples were analyzed by the developed method, and trace levels of MC-YR, MC-RR and MC-LR were detected. The results indicate that the synthesized HFH-COF is an ideal sorbent for efficient extraction of MCs from complex biological samples.

Behavioral disturbances induced by cyanobacterial oligopeptides microginin-FR1, anabaenopeptin-A and microcystin-LR are associated with neuromotoric and cytotoxic changes in Brachionus calyciflorus

Aquatic animals are exposed to various cyanobacterial products released concomitantly to the environment by decaying blooms. Although there exist results on the toxicity of cyanobacterial extracts little is known on the influence of pure oligopeptides or their mixtures and elucidated mechanisms of behavioral toxicity in zooplanktonic organisms. Therefore, the aim of the present study was to assess the effects of single and mixed pure cyanobacterial oligopeptides: microginin FR-1 (MG-FR1), anabaenopeptin-A (ANA-A) and microcystin-LR (MC-LR) at various concentrations on the swimming behavior and catecholamine neurotransmitter activity, muscular F-actin structure, DNA nuclear content and cell viability of a model rotifer Brachionus calyciflorus. Swimming behavior was analyzed with the use of video digital analysis. Fluorescent microscopy imaging was used to analyze neuromotoric biomarkers in the whole organisms: neuromediator release (by staining with EC517 probe), muscle F-actin filaments (by staining with blue phalloidin dye). DNA content and cytotoxicity was also determined by Hoechst 34580 and propidium iodide double staining, respectively. The results showed that single oligopeptides inhibited all the tested endpoints. The binary mixtures induced synergistic interaction on swimming speed except for MG-FR1 +MC-LR which was nearly additive. Both binary and ternary mixtures also synergistically degraded F-actin and triggered cytotoxic effects visible in the whole organisms. Antagonistic inhibitory effects of all the binary mixtures were found on catecholamine neurotransmitter activity, however the ternary mixture induced additive toxicity. Antagonistic effects of both binary and ternary mixtures were also noted on nuclear DNA content. The results of the study suggest that both depression of neurotransmission and impairment of muscle F-actin structure in muscles may contribute to mechanisms of Brachionus swimming speed inhibition by the tested single cyanobacterial oligopeptides and their mixtures. The study also showed that natural exposure of rotifers to mixtures of these cyanobacterial metabolites may result in different level of interactive toxicity with antagonistic, additive synergistic effects depending on the variants and concentrations present in the environment.

Excluding interference and detecting Microcystin-LR in the natural lakes and cells based a unique fluorescence method

Cyanobacteria blooms that cause the death of aquatic and terrestrial organisms have attracted considerable attention since the 19th century. The most typical toxin in cyanobacteria blooms is cyanobacteria toxin, particularly microcystin-LR (MC-LR). Therefore, a simple and highly efficient method for detecting MC-LR plays a role in studying the ecological toxicology of MC-LR. However, as MC-LR itself is located in a complex environment, traditional techniques present complex and false-positive defects. To address the above issues, novel technologies should be explored and discovered. Herein, we describe the development of MC-BDKZ as the first paradigm of probes that can concurrently report MC-LR in natural lakes and cells. This novel material shows large Stokes Shift and possesses good photostability and high sensitivity. Considering the properties mentioned above, MC-BDKZ not only achieves the detection of MC-LR in the lake water samples, but also completes the imaging of exogenous MC-LR in cells. Moreover, the interference of many factors in the lake and cells is excluded completely in the process of MC-LR detection. We comprehensively analyzed the response principle and potential application of MC-BDKZ in the process of MC-LR detection. Compared with the conventional MC-LR detection technologies, fluorescence probe technology shows better convenience and greatly reduces distance from the practical application in vitro and in vivo. We envisioned that the development of this visual research tool could provide crucial clues for exploring the pathogenesis of MC-LR in body.

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.

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.

Mycolicibacterium lacusdiani sp. nov., an Attached Bacterium of Microcystis aeruginosa

In eutrophic water, attached bacteria of Microcystis play an important role in the formation, development, and degradation of Microcystis blooms. A novel actinobacterium, designated as JXJ CY 35^T, was isolated from the culture mass of Microcystis aeruginosa FACHB-905 (Maf) collected from Lake Dianchi, Yunnan Province, China. Strain JXJ CY 35^T was gram-positive, acid-fast staining, aerobic, with short rod-shaped cells, positive for catalase, and negative for oxidase. The isolate was able to grow at 10.0–36.0°C, pH 4.0–10.0, and tolerate up to 5.0% (w/v) NaCl, with optimal growth at 28°C, pH 7.0–8.0, and 0% (w/v) NaCl. Cell-wall peptidoglycan contains aspartic acid, glutamic acid, glycine, and alanine, with mannose, ribose, galactose, and arabinose as whole-cell sugars. Polar lipids consist of diphosphatidylglycerol (DPG), phosphatidylethanolamine (PE), glycolipid (GL1-3), phosphoglycolipid (PGL), phosphatidylinositol (PI), and unidentified lipid (L1). The predominant menaquinone was MK-9. Major fatty acids (>10%) were C_17:1ω7c (37.0%) and C_18:1ω9c (18.9%). The complete genome sequence of strain JXJ CY 35^T was 6,138,096 bp in size with a DNA G + C content of 68.3%. Based on 16S rRNA gene sequences, it has 98.2% similarity to Mycolicibacterium arabiense JCM 18538^T. The digital DNA-DNA hybridization (dDDH) and average nucleotide identity (ANI) values between strain JXJ CY 35^T and the closest five type strains M. arabiense JCM 18538^T, M. goodii ATCC 700504^T, M. mageritense DSM 44476^T, M. austroafricanum DSM 44191^T, and Mycobacterium neglectum CECT 8778^T were 52.1, 20.3, 20.3, 20.6, and 19.8%, and 92.7, 75.5, 75.6, 76.0, and 75.2%, respectively. On the basis of the above taxonomic data and differences in physiological characteristics from the closely related type strain, strain JXJ CY 35^T was determined to represent a novel species of genus Mycolicibacterium, for which the name Mycolicibacterium lacusdiani sp. nov., is proposed. The type strain is JXJ CY 35^T (=KCTC 49379^T = CGMCC 1.17501^T). Different inoculation dosages of the type strain JXJ CY 35^T could exhibit different effects on the growth of Maf and its toxin synthesis and release. Strain JXJ CY 35^T could promote the growth of Maf by providing it with available phosphorus, nitrogen, probably vitamins, and plant growth hormones.

Simultaneous electrochemical removal of Microcystis aeruginosa and sulfamethoxazole and its ecologic impacts on Vallisneria spiralis

In this study, the simultaneous removal effects of electrochemical oxidation with boron-doped diamond anodes at different current densities were tested on Microcystis aeruginosa and sulfamethoxazole. Flow cytometry and non-invasive micro-test technology were applied to study the physiological states of M. aeruginosa and Vallisneria spiralis leaf cells. As the current density increased, the degradation effect of electrochemical oxidation on sulfamethoxazole and microcystin-LR increased and exceeded 60% within 6 h. In addition, population density of M. aeruginosa, fluorescence response of chlorophyll a, and cytoplasmic membrane integrity decreased, whereas the proportion of cells with excessive accumulation of intracellular reactive oxygen species (ROS) increased. The effect of electrochemical oxidation on the cell population of M. aeruginosa continued after the power was turned off. The physiological state of V. spiralis leaf cells was not severely affected at 10 mA/cm² for 24 h. Higher current intensity and longer electrolysis time would induce apoptosis or necrosis. In order to achieve a higher target pollutant removal effect and simultaneously avoid damage to the lake ecosystem, the current intensity of the electrochemical oxidation device should not exceed 10 mA/cm², and a single electrolysis treatment should range from 6 h to 24 h.

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.

Inonotus obliquus aqueous extract prevents histopathological alterations in liver induced by environmental toxicant Microcystin

Environmental toxicants like microcystins are known to adversely impact liver physiology and lead to the increased risk for abnormal liver function and even liver carcinoma. Chaga mushroom (Inonotus obliquus) is reported for various properties mainly antibacterial, antiallergic, anti-inflammatory, antioxidant, and anticancer properties. This study was aimed to assess the effect microcystin (MC-LR) on histopathology of liver in mice and a preventive measure by using aqueous extract of Inonotus obliquus (IOAE). Adult Balb/c mice were administered with MC-LR at 20 ​μg/kg body weight, per day, intraperitoneal (i.p.) for 4 weeks. IOAE was treated to one group of MC-LR mice at 200 ​mg/kg body weight, per oral, for 4 weeks. Histological staining for liver structural details and biochemical assays for functions were assessed. The results of the study showed that MC-LR drastically reduced the body weight of mice which were restored close to the range of control by IOAE treatment. MC-LR exposed mice showed 1.9, 1.7 and 2.2-fold increase in the levels of SGOT, SGPT and LDH which were restored by IOAE treatment as compared to control (one-fold). MC-LR exposed mice showed reduced level of GSH (19.83 ​± ​3.3 ​μM) which were regained by IOAE treatment (50.83 ​± ​3.0 ​μM). Similar observations were noted for catalase activity. Histological examinations show that MC-LR exposed degenerative changes in the liver sections which were restored by IOAE supplementation. The immunofluorescence analysis of caspase-3 counterstained with DAPI showed that MC-LR led to the increased expression of caspase-3 which were comparatively reduced by IOAE treatment. The cell viability decreased on increasing the concentration of MC-LR with 5% cell viability at concentration of 10 ​μg MC-LR/mL as that of control 100% Cell viability. The IC₅₀ was calculated to be 3.6 ​μg/ml, indicating that MC-LR is chronic toxic to AML12 mouse hepatocytes. The molecular docking interaction of NF-κB-NIK with ergosterol peroxidase showed binding interaction between the two and showed the plausible molecular basis for the effects of IOAE in MC-LR induced liver injury. Collectively, this study revealed the deleterious effects of MC-LR on liver through generation of oxidative stress and activation of caspase-3, which were prevented by treatment with IOAE.

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Microcystin-LR is a potent hepatotoxic agent acting by inducing lipid peroxidation and oxidative damages.

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MC-LR exhibited significant deleterious alteration in liver by histopathological and biochemical signatures.

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Inonotus obliquus aqueous extract (IOAE) suppressed inflammation and oxidative damage in the liver induced by microcystin-LR.

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IOAE suppressed caspase-3 and p53 expression in MC-LR-induced liver.

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Chaga mushroom is suggested for using as a supplement in prevention of liver toxicity and inflammation.

Nocardioides lacusdianchii sp. nov., an attached bacterium of Microcystis aeruginosa

Attached bacteria of Microcystis play important roles in the occurence, outbreak and decline of Microcystis water blooms. In this study, a novel actinobacterium, designated strain JXJ CY 38 ^T, was isolated from the culture mass of Microcystis aeruginosa FACHB-905 (MAF), collected from Lake Dianchi, south-west, China. The strain was found to be a Gram-stain positive, short rod, catalase positive and oxidase negative. The isolate was found to be able to grow at 5.0-38.0 °C (optimum, 28.0 °C), pH 4.0-11.0 (optimum, 7.0-8.0) and 0-3.0% (w/v, optimum, 0%) NaCl. Based on 16S rRNA gene sequences, strain JXJ CY 38 ^T shows high similarities to Nocardioides furvisabuli JCM 13813 ^T (99.0%) and Nocardioides alpinus JCM 18960 ^T (98.7%), and less than 98.2% similarities to other members of the genus. The major cellular fatty acids (> 10.0%) were identified as iso-C_16:0 (23.6%), C_18:1ω9c (18.2%) and C_17:1ω8c (16.4%), while the predominant menaquinone was found to be MK-8 (H₄). The diagnostic diamino acids in the cell wall peptidoglycan were identified as aspartic acid, glutamic acid, glycine and alanine, with mannose, ribose and arabinose as whole cell sugars. The polar lipids were found to be diphosphatidylglycerol, phosphatidylglycerol, a phospholipid, phosphatidylcholine and an unidentified lipid. The DNA G + C content was determined to be 71.3%. The digital DNA-DNA hybridization and average nucleotide identity values between strain JXJ CY 38 ^T and the type strains N. furvisabuli JCM 13813 ^T and N. alpinus JCM 18960 ^T were 49.4% and 37.7%, and 92.0% and 83.4%, respectively. On the basis of the above taxonomic data and differences in physiological characteristics from the closely related type strains, strain JXJ CY 38 ^T was determined to represent a novel species of genus Nocardioides, for which the name Nocardioides lacusdianchii sp. nov. is proposed. The type strain is JXJ CY 38 ^T (= KCTC 49381 ^T = CGMCC 4.7665 ^T). Strain JXJ CY 38 ^T apparently exhibits complex effects on the interactions between MAF and other attached bacteria, including the promotion or inhibition of the growth of MAF and bacteria, and the synthesis and release of microcystins by MAF.

New insights into toxicity of microcystins produced by cyanobacteria using in silico ADMET prediction

In silico methodologies can be used in the discovery of new drugs for measuring toxicity, predicting effects of substances not yet analyzed by in vivo methodologies. The ADMET Predictor® software (absorption, distribution, metabolism, elimination, and toxicity [ADMET]) was used in this work to predict toxic effects of microcystin variants MC-LR, MC-YR, MC-RR, and MC-HarHar. In the case of rodents, predictive results for all analyzed variants indicated carcinogenic potential. The predictive model of respiratory sensitivity in this group differentiated microcystins into 2 categories: sensitizer (MC-LR and -YR) and non-sensitizer (MC-HarHar and -RR). Predictive results for humans indicated that MC-LR and -RR are phospholipidosis inducers; on the other hand, MC-LR showed the highest predictive value of permeability in rabbit cornea and probability of crossing lipoprotein barriers (MC-LR>-YR>-HarHar>-RR). Considering bioavailable fractions, microcystins are more likely to cause biological effects in rats than humans, showing significant differences between models. The results of ADMET predictions add valuable information on microcystin toxicity, especially in the case of variants not yet studied experimentally.

The Toxicity Testing of Cyanobacterial Toxins In Vivo and In Vitro by Mouse Bioassay: A Review

Different biological methods based on bioactivity are available to detect cyanotoxins, including neurotoxicity, immunological interactions, hepatotoxicity, cytotoxicity, and enzymatic activity. The mouse bioassay is the first test employed in laboratory cultures, cell extracts, and water bloom materials to detect toxins. It is also used as a traditional method to estimate the LD50. Concerning the ease of access and low cost, it is the most common method for this purpose. In this method, a sample is injected intraperitoneally into adult mice, and accordingly, they are assayed and monitored for about 24 hours for toxic symptoms. The toxin can be detected using this method from minutes to a few hours; its type, e.g., hepatotoxin, neurotoxin, etc., can also be determined. However, this method is nonspecific, fails to detect low amounts, and cannot distinguish between homologues. Although the mouse bioassay is gradually replaced with new chemical and immunological methods, it is still the main technique to detect the bioactivity and efficacy of cyanotoxins using LD50 determined based on the survival time of animals exposed to the toxin. In addition, some countries oppose animal use in toxicity studies. However, high cost, ethical considerations, low-sensitivity, non-specificity, and prolonged processes persuade researchers to employ chemical and functional analysis techniques. The qualitative and quantitative analyses, as well as high specificity and sensitivity, are among the advantages of cytotoxicity tests to investigate cyanotoxins. The present study aimed at reviewing the results obtained from in-vitro and in-vivo investigations of the mouse bioassay to detect cyanotoxins, including microcystins, cylindrospermopsin, saxitoxins, etc.

Aptamer-functionalized metal-organic framework-based electrospun nanofibrous composite coating fiber for specific recognition of ultratrace microcystin in water

A novel aptamer@AuNPs@UiO-66-NH₂ electrospun nanofibrous coating fiber for specific recognition of microcystin-LR (MC-LR) was proposed by using electrospinning, metal-organic frameworks (MOF) seed growth and AuNPs bridging aptamer strategies. Characterization of morphology, structure and stability of the obtained affinity nanofibrous coating fiber were investigated. High loading of MOFs and aptamers on the nanofibrous fiber were achieved and successfully applied for accurate identification of MC-LR by solid-phase microextraction (SPME) coupled with LC-MS. Highly specific recognition of MC-LR with little interference of analogs was achieved with extremely low LOD (0.004 ng/mL), good precision (CV% < 11.0%) and low relative error (RE% = -1.5% to -10.0%), which was rather better than that of the traditional SPME or SPE protocols. Satisfactory recoveries of MC-LR were obtained in the range of 92.0-96.8% (n = 3) in fortified tap water, raw pond water and river water samples. This work revealed an attractive alternative access to specific recognition and super-sensitive analysis of MC-LR in water.

ELISA-Based Method for Variant-Independent Detection of Total Microcystins and Nodularins via a Multi-immunogen Approach

Required routine monitoring of microcystins (MCs) and nodularins (NODs) in water samples, as posed by U.S. EPA Unregulated Contaminant Monitoring Rule 4, demands cost-effective, reliable, and sensitive detection methods. To target as many MC and NOD variants as possible, we developed an indirect competitive enzyme-linked immunosorbent assay (ELISA) with group-specific monoclonal antibodies for variant-independent detection of total MCs and NODs. In this ELISA method, the mice monoclonal antibodies presenting both high affinities and broad-spectrum recognition capabilities against MCs and NODs were self-produced by designing MC hapten-based multi-immunogens to minimize specificity for the particular variant. Their high affinities and variant-independent binding capabilities against MCs and NODs were validated by both wet lab and in silico methods. The developed ELISA method achieved a limit of detection of below 0.3 μg/L for 13 MC/NOD variants, well with the reported best cross-reactivities of 60-127% relative to MC-LR. As a case study, this ELISA method was used to map the variations of intracellular and extracellular total MCs/NODs in the Luoma Lake drinking water source, China, in July, 2020. Its capability to measure total MCs/NODs with high sensitivity and high throughput in a simple and affordable way would truly be a disruptive technology capable of changing our understanding of bloom/toxin dynamics and having obvious implications for monitoring efforts.

Repeated exposure to microcystin-leucine-arginine potentiates excitotoxicity induced by a low dose of kainate

Microcystin-leucine-arginine (MLCR) is a cyanobacterial toxin, and has been demonstrated to cause neurotoxicity. In addition, MCLR has been identified as an inhibitor of protein phosphatase (PP)1 and PP2A, which are known to regulate the phosphorylation of various molecules related to synaptic excitability. Thus, in the present study, we examined whether MCLR exposure affects seizures induced by a low dose of kainic acid (KA; 0.05 μg, i.c.v.) administration. KA-induced seizure occurrence and seizure score significantly increased after repeated exposure to MCLR (2.5 or 5.0 μg/kg, i.p., once a day for 10 days), but not after acute MCLR exposure (2.5 or 5.0 μg/kg, i.p., 2 h and 30 min prior to KA administration), and hippocampal neuronal loss was consistently facilitated by repeated exposure to MCLR. In addition, repeated MCLR significantly elevated the membrane expression of kainate receptor GluK2 subunits, p-pan-protein kinase C (PKC), and p-extracellular signal-related kinase (ERK) at 1 h after KA. However, KA-induced membrane expression of Ca²⁺/calmodulin-dependent kinase II (CaMKII) was significantly reduced by repeated MCLR exposure. Consistent with the enhanced seizures and neurodegeneration, MCLR exposure significantly potentiated KA-induced oxidative stress and microglial activation, which was accompanied by increased expression of p-ERK and p-PKCδ in the hippocampus. The combined results suggest that repeated MCLR exposure potentiates KA-induced excitotoxicity in the hippocampus by increasing membrane GluK2 expression and enhancing oxidative stress and neuroinflammation through the modulation of p-CaMKII, p-PKC, and p-ERK.

Bonsecamin: A New Cyclic Pentapeptide Discovered through Heterologous Expression of a Cryptic Gene Cluster

The intriguing structural complexity of molecules produced by natural organisms is uncontested. Natural scaffolds serve as an important basis for the development of molecules with broad applications, e.g., therapeutics or agrochemicals. Research in recent decades has demonstrated that by means of classic metabolite extraction from microbes only a small portion of natural products can be accessed. The use of genome mining and heterologous expression approaches represents a promising way to discover new natural compounds. In this paper we report the discovery of a novel cyclic pentapeptide called bonsecamin through the heterologous expression of a cryptic NRPS gene cluster from Streptomyces albus ssp. chlorinus NRRL B-24108 in Streptomyces albus Del14. The new compound was successfully isolated and structurally characterized using NMR. The minimal set of genes required for bonsecamin production was determined through bioinformatic analysis and gene deletion experiments. A biosynthetic route leading to the production of bonsecamin is proposed in this paper.