Synthesis, configuration assignment, and simultaneous quantification by liquid chromatography coupled to tandem mass spectrometry, of dihydroanatoxin-a and dihydrohomoanatoxin-a together with the parent toxins, in axenic cyanobacterial strains and in environmental samples

Environmental Factors Impacting the Development of Toxic Cyanobacterial Proliferations in a Central Texas Reservoir

Cyanobacterial harmful algal proliferations (cyanoHAPs) are increasingly associated with dog and livestock deaths when benthic mats break free of their substrate and float to the surface. Fatalities have been linked to neurotoxicosis from anatoxins, potent alkaloids produced by certain genera of filamentous cyanobacteria. After numerous reports of dog illnesses and deaths at a popular recreation site on Lady Bird Lake, Austin, Texas in late summer 2019, water and floating mat samples were collected from several sites along the reservoir. Water quality parameters were measured and mat samples were maintained for algal isolation and DNA identification. Samples were also analyzed for cyanobacterial toxins using LC-MS. Dihydroanatoxin-a was detected in mat materials from two of the four sites (0.6-133 ng/g wet weight) while water samples remained toxin-free over the course of the sampling period; no other cyanobacterial toxins were detected. DNA sequencing analysis of cyanobacterial isolates yielded a total of 11 genera, including Geitlerinema, Tyconema, Pseudanabaena, and Phormidium/Microcoleus, taxa known to produce anatoxins, including dihydroanatoxin, among other cyanotoxins. Analyses indicate that low daily upriver dam discharge, higher TP and NO3 concentrations, and day of the year were the main parameters associated with the presence of toxic floating cyanobacterial mats.

Identification of Cyanobacteria and Its Potential Toxins in the Joanes I Reservoir, Bahia, Brazil

The Joanes I Reservoir is responsible for 40% of the drinking water supply of the Metropolitan Region of Salvador, Bahia, Brazil. For water sources such as this, there is concern regarding the proliferation of potentially toxin-producing cyanobacteria, which can cause environmental and public health impacts. To evaluate the presence of cyanobacteria and their cyanotoxins in the water of this reservoir, the cyanobacteria were identified by microscopy; the presence of the genes of the cyanotoxin-producing cyanobacteria was detected by molecular methods (polymerase chain reaction (PCR)/sequencing); and the presence of toxins was determined by liquid chromatography with tandem mass spectrometry (LC-MS/MS). The water samples were collected at four sampling points in the Joanes I Reservoir in a monitoring campaign conducted during the occurrence of phytoplankton blooms, and the water quality parameters were also analysed. Ten cyanobacteria species/genera were identified at the monitoring sites, including five potentially cyanotoxin-producing species, such as Cylindrospermopsis raciborskii, Cylindrospermopsis cf. acuminato-crispa, Aphanocapsa sp., Phormidium sp., and Pseudanabaena sp. A positive result for the presence of the cylindrospermopsin toxin was confirmed at two sampling points by LC-MS/MS, which indicated that the populations are actively producing toxins. The analysis of the PCR products using the HEPF/HEPR primer pair for the detection of the microcystin biosynthesis gene mcyE was positive for the analysed samples. The results of this study point to the worrisome condition of this reservoir, from which water is collected for public supply, and indicate the importance of the joint use of different methods for the analysis of cyanobacteria and their toxins in reservoir monitoring.

Rapid Quantitation of Anatoxins in Benthic Cyanobacterial Mats Using Direct Analysis in Real-Time-High-Resolution Tandem Mass Spectrometry

Toxic benthic cyanobacterial mats are increasingly reported worldwide as being responsible for animal mortalities due to their production of the potent neurotoxin anatoxin-a (ATX) and its analogues. Improved analytical methods for anatoxins are needed to address public health and watershed management challenges arising from extremely high spatial and temporal variability within impacted systems. We present the development, validation, and application of a direct analysis in real-time-high-resolution tandem mass spectrometry (DART-HRMS/MS) method for analysis of anatoxins in cyanobacterial field samples, including a simplified sample preparation approach. The method showed excellent sensitivity and selectivity for ATX, homoanatoxin-a, and dihydroanatoxin-a. Isotopically labeled ATX was used as an internal standard for all three analogues and successfully corrected for the matrix effects observed (86 ± 16% suppression). The limit of detection and recovery for ATX was estimated as 5 ng/g and 88%, respectively, using spiked samples. The total analysis time was ∼2 min, and excellent agreement was observed with results from a liquid chromatography-HRMS reference method. Finally, the DART-HRMS/MS method was applied to a set of 45 Microcoleus-dominated benthic cyanobacterial mat samples from the Wolastoq near Fredericton, Canada, demonstrating its power and applicability in enabling broad-scale field studies of ATX distribution.

Characterization of Potential Threats from Cyanobacterial Toxins in Lake Victoria Embayments and during Water Treatment

Africa’s water needs are often supported by eutrophic water bodies dominated by cyanobacteria posing health threats to riparian populations from cyanotoxins, and Lake Victoria is no exception. In two embayments of the lake (Murchison Bay and Napoleon Gulf), cyanobacterial surveys were conducted to characterize the dynamics of cyanotoxins in lake water and water treatment plants. Forty-six cyanobacterial taxa were recorded, and out of these, fourteen were considered potentially toxigenic (i.e., from the genera Dolichospermum, Microcystis, Oscillatoria, Pseudanabaena and Raphidiopsis). A higher concentration (ranging from 5 to 10 µg MC-LR equiv. L−1) of microcystins (MC) was detected in Murchison Bay compared to Napoleon Gulf, with a declining gradient from the inshore (max. 15 µg MC-LR equiv. L−1) to the open lake. In Murchison Bay, an increase in Microcystis sp. biovolume and MC was observed over the last two decades. Despite high cell densities of toxigenic Microcystis and high MC concentrations, the water treatment plant in Murchison Bay efficiently removed the cyanobacterial biomass, intracellular and dissolved MC to below the lifetime guideline value for exposure via drinking water (<1.0 µg MC-LR equiv. L−1). Thus, the potential health threats stem from the consumption of untreated water and recreational activities along the shores of the lake embayments. MC concentrations were predicted from Microcystis cell numbers regulated by environmental factors, such as solar radiation, wind speed in the N−S direction and turbidity. Thus, an early warning through microscopical counting of Microcystis cell numbers is proposed to better manage health risks from toxigenic cyanobacteria in Lake Victoria.

Determination of Cyanotoxins and Prymnesins in Water, Fish Tissue, and Other Matrices: A Review

Harmful algal blooms (HABs) and their toxins are a significant and continuing threat to aquatic life in freshwater, estuarine, and coastal water ecosystems. Scientific understanding of the impacts of HABs on aquatic ecosystems has been hampered, in part, by limitations in the methodologies to measure cyanotoxins in complex matrices. This literature review discusses the methodologies currently used to measure the most commonly found freshwater cyanotoxins and prymnesins in various matrices and to assess their advantages and limitations. Identifying and quantifying cyanotoxins in surface waters, fish tissue, organs, and other matrices are crucial for risk assessment and for ensuring quality of food and water for consumption and recreational uses. This paper also summarizes currently available tissue extraction, preparation, and detection methods mentioned in previous studies that have quantified toxins in complex matrices. The structural diversity and complexity of many cyanobacterial and algal metabolites further impede accurate quantitation and structural confirmation for various cyanotoxins. Liquid chromatography–triple quadrupole mass spectrometer (LC–MS/MS) to enhance the sensitivity and selectivity of toxin analysis has become an essential tool for cyanotoxin detection and can potentially be used for the concurrent analysis of multiple toxins.

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.

Rapid quantitative screening of cyanobacteria for production of anatoxins using direct analysis in real time high-resolution mass spectrometry

RATIONALE

Anatoxins (ATXs) are a potent class of cyanobacterial neurotoxins that are increasingly problematic in drinking water reservoirs and recreational water bodies worldwide. Because of their high polarity and low molecular weight, analysis of ATXs is challenging and they can be considered underreported compared with other classes of cyanobacterial toxins. Improved screening methods are therefore needed to effectively assess their occurrence and concentrations in the environment.

METHODS

A rapid screening method was developed for ATXs in cyanobacteria using direct analysis in real time combined with high-resolution mass spectrometry (DART-HRMS), requiring less than 2 min per sample for triplicate analysis. The developed method was evaluated for its quantitative capabilities, applied to the screening of 30 cyanobacterial culture samples for the presence of anatoxin-a, homoanatoxin-a and dihydroanatoxin-a, and compared with a more typical liquid chromatography (LC)/HRMS method.

RESULTS

Excellent linearity was observed in the analysis of a matrix-matched calibration curve using DART-HRMS, with ionization suppression of about 50% and relative standard deviations between replicate analyses of approximately 30%. Limits of detection for both anatoxin-a and homoanatoxin-a were estimated as 1 ng/mL. Excellent agreement was observed between DART-HRMS and LC/HRMS with all ATX-producing cultures correctly identified and only one false positive culture by DART-HRMS.

CONCLUSIONS

DART-HRMS shows excellent promise for the rapid, quantitative screening of ATXs in cyanobacteria and could be expanded in the future to include the analysis of field samples and drinking water, as well as additional ATX analogues.

Acute toxicity of dihydroanatoxin-a from Microcoleus autumnalis in comparison to anatoxin-a

The cyanobacterium Microcoleus autumnalis grows as thick benthic mats in rivers and is becoming increasingly prevalent around the world. M. autumnalis can produce high concentrations of anatoxins and ingestion of benthic mats has led to multiple dog deaths over the past two decades. M. autumnalis produces a suite of different anatoxin congeners including anatoxin-a (ATX), dihydroanatoxin-a, (dhATX), homoanatoxin-a and dihydrohomoanatoxin-a. Benthic mat samples often contain high levels of dhATX, but there is little toxicology information on this congener. In the present study, natural versions of dhATX and ATX were purified from cyanobacteria to determine the acute toxicity by different routes of administration using mice. Nuclear magnetic resonance spectroscopy was used to confirm the putative structure of dhATX. By intraperitoneal (ip) injection, the median lethal dose (LD₅₀) for dhATX was 0.73 mg/kg, indicating a reduced toxicity compared to ATX (LD₅₀ of 0.23 mg/kg). However, by oral administration (both gavage and feeding), dhATX was more toxic than ATX (gavage LD₅₀ of 2.5 mg/kg for dhATX and 10.6 mg/kg for ATX; feeding LD₅₀ of 8 mg/kg for dhATX and 25 mg/kg for ATX). The relative nicotinic acetylcholine receptor-binding affinities of ATX and dhATX were determined using the Torpedo electroplaque assay which showed consistency with the relative toxicity determined by ip injection. This work highlights that toxicity studies based solely on ip injection may not yield LD₅₀ values that are relevant to those derived via oral administration, and hence, do not provide a good estimate of the risk posed to human and animal health in situations where oral ingestion is the likely route of exposure. The high acute oral toxicity of dhATX, and its abundance in M. autumnalis proliferations, demonstrates that it is an important environmental contaminant that warrants further investigation.

Mass Occurrence of Anatoxin-a- and Dihydroanatoxin-a-Producing Tychonema sp. in Mesotrophic Reservoir Mandichosee (River Lech, Germany) as a Cause of Neurotoxicosis in Dogs

In August 2019, three dogs died after bathing in or drinking from Mandichosee, a mesotrophic reservoir of the River Lech (Germany). The dogs showed symptoms of neurotoxic poisoning and intoxication with cyanotoxins was considered. Surface blooms were not visible at the time of the incidents. Benthic Tychonema sp., a potential anatoxin-a (ATX)-producing cyanobacterium, was detected in mats growing on the banks, as biofilm on macrophytes and later as aggregations floating on the lake surface. The dogs' pathological examinations showed lung and liver lesions. ATX and dihydroanatoxin-a (dhATX) were detected by LC-MS/MS in the stomachs of two dogs and reached concentrations of 563 and 1207 µg/L, respectively. Anatoxins (sum of ATX and dhATX, ATXs) concentrations in field samples from Mandichosee ranged from 0.1 µg/L in the open water to 68,000 µg/L in samples containing a large amount of mat material. Other (neuro)toxic substances were not found. A molecular approach was used to detect toxin genes by PCR and to reveal the cyanobacterial community composition by sequencing. Upstream of Mandichosee, random samples were taken from other Lech reservoirs, uncovering Tychonema and ATXs at several sampling sites. Similar recent findings emphasize the importance of focusing on the investigation of benthic toxic cyanobacteria and applying appropriate monitoring strategies in the future.

Molecular and morphological characterization of a novel dihydroanatoxin-a producing Microcoleus species (cyanobacteria) from the Russian River, California, USA

Reports of anatoxins poisoning of wildlife and domestic animals by toxigenic cyanobacteria in streams and rivers are increasing globally. Little is known about the taxonomy, morphology and genomics of anatoxins producing species, limiting our knowledge about their environmental preferences. We isolated three benthic non-heterocystous filamentous cyanobacterial strains from the Russian River in Northern California (USA), which produce anatoxin-a and dihydroanatoxin-a. Both 16S rRNA and protein sequence phylogenetic analyses showed that the strains represent a distinct new member of the cyanobacterial genus Microcoleus (Oscillatoriales). A novel species, Microcoleus anatoxicus is described and accompanied with light microscope photomicrographs, toxin profiles and the complete anatoxin-a gene cassette with the first description of the anaK gene in Microcoleus.

Biosynthesis of Anatoxins in Cyanobacteria: Identification of the Carboxy-anatoxins as the Penultimate Biosynthetic Intermediates

Anatoxin-a, homoanatoxin-a, and dihydroanatoxin-a are potent cyanobacterial neurotoxins. They are biosynthesized in cyanobacteria from proline and acetate by a pathway involving three polyketide synthases. We report the identification of carboxy-anatoxin-a, carboxy-homoanatoxin-a, and carboxy-dihydroanatoxin-a in acidic extracts of Cuspidothrix issatschenkoi CHARLIE-1, Oscillatoria sp. PCC 6506, and Cylindrospermum stagnale PCC 7417, respectively, using liquid chromatography coupled to mass spectrometry. The structure of these carboxy derivatives was confirmed by mass spectrometry and by isotopic incorporation experiments using labeled proline and acetate. Each of these three cyanobacteria only produce one carboxy-anatoxin, suggesting that these metabolites are the product of the hydrolysis by AnaA, the type II thioesterase, of the thioesters bound to AnaG, the last polyketide synthase of the pathway. By measuring the rate of isotopic incorporation of labeled proline into carboxy-homoanatoxin-a and homoanatoxin-a produced by Oscillatoria sp. PCC 6506, we show that carboxy-homoanatoxin-a is the intracellular precursor of homoanatoxin-a, and that homoanatoxin-a is then excreted into the extracellular medium. The transformation of carboxy-homoanatoxin-a into homoanatoxin-a is a very slow two-step process, with accumulation of carboxy-homoanatoxin-a, suggesting that the decarboxylation is spontaneous and not enzymatically catalyzed. However, an unidentified and extracellular catalyst accelerates the decarboxylation when the cell extracts are prepared at neutral pH.

Multiple cyanotoxin congeners produced by sub-dominant cyanobacterial taxa in riverine cyanobacterial and algal mats

Benthic cyanobacterial proliferations in rivers are have been reported with increasing frequency worldwide. In the Eel and Russian rivers of California, more than a dozen dog deaths have been attributed to cyanotoxin toxicosis since 2000. Periphyton proliferations in these rivers comprise multiple cyanobacterial taxa capable of cyanotoxin production, hence there is uncertainty regarding which taxa are producing toxins. In this study, periphyton samples dominated by the cyanobacterial genera Anabaena spp. and Microcoleus spp. and the green alga Cladophora glomerata were collected from four sites in the Eel River catchment and one site in the Russian River. Samples were analysed for potential cyanotoxin producers using polymerase chain reaction (PCR) in concert with Sanger sequencing. Cyanotoxin concentrations were measured using liquid chromatography tandem-mass spectrometry, and anatoxin quota (the amount of cyanobacterial anatoxins per toxigenic cell) determined using droplet digital PCR. Sequencing indicated Microcoleus sp. and Nodularia sp. were the putative producers of cyanobacterial anatoxins and nodularins, respectively, regardless of the dominant taxa in the mat. Anatoxin concentrations in the mat samples varied from 0.1 to 18.6 μg g-1 and were significantly different among sites (p < 0.01, Wilcoxon test); however, anatoxin quotas were less variable (< 5-fold). Dihydroanatoxin-a was generally the most abundant variant in samples comprising 38% to 71% of the total anatoxins measured. Mats dominated by the green alga C. glomerata contained both anatoxins and nodularin-R at concentrations similar to those of cyanobacteria-dominated mats. This highlights that even when cyanobacteria are not the dominant taxa in periphyton, these mats may still pose a serious health risk and indicates that more widespread monitoring of all mats in a river are necessary.

Cyanobacterial bioactive metabolites-A review of their chemistry and biology

Cyanobacterial blooms occur when algal densities exceed baseline population concentrations. Cyanobacteria can produce a large number of secondary metabolites. Odorous metabolites affect the smell and flavor of aquatic animals, whereas bioactive metabolites cause a range of lethal and sub-lethal effects in plants, invertebrates, and vertebrates, including humans. Herein, the bioactivity, chemistry, origin, and biosynthesis of these cyanobacterial secondary metabolites were reviewed. With recent revision of cyanobacterial taxonomy by Anagnostidis and Komárek as part of the Süβwasserflora von Mitteleuropa volumes 19(1-3), names of many cyanobacteria that produce bioactive compounds have changed, thereby confusing readers. The original and new nomenclature are included in this review to clarify the origins of cyanobacterial bioactive compounds. Due to structural similarity, the 157 known bioactive classes produced by cyanobacteria have been condensed to 55 classes. This review will provide a basis for more formal procedures to adopt a logical naming system. This review is needed for efficient management of water resources to understand, identify, and manage cyanobacterial harmful algal bloom impacts.

Cyanobacterial bioactive metabolites-A review of their chemistry and biology

Cyanobacterial blooms occur when algal densities exceed baseline population concentrations. Cyanobacteria can produce a large number of secondary metabolites. Odorous metabolites affect the smell and flavor of aquatic animals, whereas bioactive metabolites cause a range of lethal and sub-lethal effects in plants, invertebrates, and vertebrates, including humans. Herein, the bioactivity, chemistry, origin, and biosynthesis of these cyanobacterial secondary metabolites were reviewed. With recent revision of cyanobacterial taxonomy by Anagnostidis and Komárek as part of the Süβwasserflora von Mitteleuropa volumes 19(1-3), names of many cyanobacteria that produce bioactive compounds have changed, thereby confusing readers. The original and new nomenclature are included in this review to clarify the origins of cyanobacterial bioactive compounds. Due to structural similarity, the 157 known bioactive classes produced by cyanobacteria have been condensed to 55 classes. This review will provide a basis for more formal procedures to adopt a logical naming system. This review is needed for efficient management of water resources to understand, identify, and manage cyanobacterial harmful algal bloom impacts.

Spatial and Temporal Variability in the Development and Potential Toxicity of Phormidium Biofilms in the Tarn River, France

Proliferation of Phormidium biofilms in rivers is becoming a worldwide sanitation problem for humans and animals, due to the ability of these bacteria to produce anatoxins. To better understand the environmental conditions that favor the development of Phormidium biofilms and the production of anatoxins, we monitored the formation of these biofilms and their toxins for two years in the Tarn River, biofilms from which are known to have caused the deaths of multiple dogs. As previously observed in New Zealand, Phormidium biofilm development occurred in riffle areas. The coverage of these biofilms at the bottom of the river exhibited strong spatial and temporal variations, but was positively correlated with water temperature and depth. Anatoxin-a was detected in less than 50% of the biofilms. The concentrations of these toxins in the biofilms exhibited high spatiotemporal variability, with the highest concentrations being recorded at the end of the summer period at the upstream sampling sites. These findings suggest that the maturity of the biofilms, combined with the local environmental conditions, have an impact on the production of anatoxin, making risk assessment for these benthic proliferations challenging.

Benthic periphyton from Pennsylvania, USA is a source for both hepatotoxins (microcystins/nodularin) and neurotoxins (anatoxin-a/homoanatoxin-a)

In 2016, the Pennsylvania Department of Environmental Protection conducted a limited survey of streams in the Susquehanna River basin in Pennsylvania, USA, to screen for microcystins/nodularins, anatoxin-a (ATX) and homoanatoxin-a (HTX). Testing revealed the presence of HTX in samples collected from the Pine Creek basin, with ATX present at lower levels. Microcystins/nodularins (MCs/NODs) were also tested and found to be concomitant, with NOD-R confirmed present by LC-MS/MS.

Monitoring of freshwater toxins in European environmental waters by using novel multi-detection methods

Monitoring the quality of freshwater is an important issue for public health. In the context of the European project μAqua, 150 samples were collected from several waters in France, Germany, Ireland, Italy, and Turkey for 2 yr. These samples were analyzed using 2 multitoxin detection methods previously developed: a microsphere-based method coupled to flow-cytometry, and an ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) method. The presence of microcystins, nodularin, domoic acid, cylindrospermopsin, and several analogues of anatoxin-a (ATX-a) was monitored. No traces of cylindrospermopsin or domoic acid were found in any of the environmental samples. Microcystin-LR and microcystin-RR were detected in 2 samples from Turkey and Germany. In the case of ATX-a derivatives, 75% of samples contained mainly H₂ -ATX-a and small amounts of H₂ -homoanatoxin-a, whereas ATX-a and homoanatoxin-a were found in only 1 sample. These results confirm the presence and wide distribution of dihydro derivatives of ATX-a toxins in European freshwaters. Environ Toxicol Chem 2017;36:645-654. © 2016 SETAC.

Molecular tools to detect anatoxin-a genes in aquatic ecosystems: Toward a new nested PCR-based method

Over the last few decades, cyanobacterial mass occurrence has become a recurrent feature of aquatic ecosystems. This has led to ecosystem exposure and health hazards associated with cyanotoxin production. The neurotoxin anatoxin-a and its homologs can be synthesized by benthic cyanobacterial species in lotic systems, but also by planktonic lacustrine species such as Dolichospermum (also known as Anabaena). However, only a few studies have focused on anatoxin-a occurrence and its biosynthesis genes in freshwater lakes. The initial aim of this study was to evaluate the molecular tools available in the literature to detect anatoxin-a biosynthesis genes in lacustrine environments. Having tested different sets of PCR primers, we found that that some sets of primers, such as anxC, were too specific and did not amplify anatoxin-a biosynthesis genes in all producing strains. On the other hand, some sets of primers, such as atxoa, seemed not to be specific enough, amplifying numerous non-specific bands in environmental samples, especially those from sediments. Furthermore, anaC and anaF amplification exhibited different band intensities during electrophoresis, suggesting a high variation in number of gene copies between samples. As a result, we proposed a new nested PCR-based method which considerably improved the amplification of the anaC gene in our environmental samples, eliminating non-specific bands and weak detections. Using this tool, our study also highlighted that anatoxin-a genes are widely distributed throughout freshwater lakes. This suggests the need for further ecological investigations into anatoxin-a in these ecosystems.

Dihydroanatoxin-a Is Biosynthesized from Proline in Cylindrospermum stagnale PCC 7417: Isotopic Incorporation Experiments and Mass Spectrometry Analysis

LC-MS and GC-MS analytical conditions have been developed to detect the cis- and trans-epimers (relative configuration of the carbon bearing the acetyl or propionyl group) of dihydroanatoxin-a and dihydrohomoanatoxin-a, in biological samples. These compounds epimerize under acidic conditions, yielding a major species that was tentatively assigned as the cis-epimer. Cylindrospermum stagnale PCC 7417 was definitively shown to produce dihydroanatoxin-a (1.2 mg/g dried cells). Oscillatoria sp. PCC 9107, Oscillatoria sp. PCC 6506, and C. stagnale PCC 7417, which produce anatoxin-a, homoanatoxin-a, and dihydroanatoxin-a, respectively, were cultivated in the presence of isotopically labeled proline, and the toxins were extracted. Interpretation of the GC-MS electron ionization mass spectra of these labeled anatoxins showed that they are all biosynthesized from proline and that the positions of the labels in these molecules are identical. These data and the fact that the ana cluster of genes is conserved in these cyanobacteria suggest that dihydroanatoxin-a is formed by the reduction of either anatoxin-a or its precursor in a specific step involving AnaK, an F420-dependent oxido-reductase whose gene is found in the ana gene cluster in C. stagnale PCC 7417. This is the first report of a cyanobacterium producing dihydroanatoxin-a, suggesting that other producers are present in the environment.

Moving towards adaptive management of cyanotoxin-impaired water bodies

The cyanobacteria are a phylum of bacteria that have played a key role in shaping the Earth's biosphere due to their pioneering ability to perform oxygenic photosynthesis. Throughout their history, cyanobacteria have experienced major biogeochemical changes accompanying Earth's geochemical evolution over the past 2.5+ billion years, including periods of extreme climatic change, hydrologic, nutrient and radiation stress. Today, they remain remarkably successful, exploiting human nutrient over‐enrichment as nuisance “blooms.” Cyanobacteria produce an array of unique metabolites, the functions and biotic ramifications of which are the subject of diverse ecophysiological studies. These metabolites are relevant from organismal and ecosystem function perspectives because some can be toxic and fatal to diverse biota, including zooplankton and fish consumers of algal biomass, and high‐level consumers of aquatic food sources and drinking water, including humans. Given the long history of environmental extremes and selection pressures that cyanobacteria have experienced, it is likely that that these toxins serve ecophysiological functions aimed at optimizing growth and fitness during periods of environmental stress. Here, we explore the molecular and ecophysiological mechanisms underlying cyanotoxin production, with emphasis on key environmental conditions potentially controlling toxin production. Based on this information, we offer potential management strategies for reducing cyanotoxin potentials in natural waters; for cyanotoxins with no clear drivers yet elucidated, we highlight the data gaps and research questions that are still lacking. We focus on the four major classes of toxins (anatoxins, cylindrospermopsins, microcystins and saxitoxins) that have thus far been identified as relevant from environmental health perspectives, but caution there may be other harmful metabolites waiting to be elucidated.

The genetics, biosynthesis and regulation of toxic specialized metabolites of cyanobacteria

The production of toxic metabolites by cyanobacterial blooms represents a significant threat to the health of humans and ecosystems worldwide. Here we summarize the current state of the knowledge regarding the genetics, biosynthesis and regulation of well-characterized cyanotoxins, including the microcystins, nodularin, cylindrospermopsin, saxitoxins and anatoxins, as well as the lesser-known marine toxins (e.g. lyngbyatoxin, aplysiatoxin, jamaicamides, barbamide, curacin, hectochlorin and apratoxins).

Health impacts from cyanobacteria harmful algae blooms: Implications for the North American Great Lakes

Harmful cyanobacterial blooms (cHABs) have significant socioeconomic and ecological costs, which impact drinking water, fisheries, agriculture, tourism, real estate, water quality, food web resilience and habitats, and contribute to anoxia and fish kills. Many of these costs are well described, but in fact are largely unmeasured. Worldwide cHABs can produce toxins (cyanotoxins), which cause acute or chronic health effects in mammals (including humans) and other organisms. There are few attempts to characterize the full health-related effects other than acute incidences, which may go unrecorded. At present these are difficult to access and evaluate and may be ascribed to other causes. Such information is fundamental to measure the full costs of cHABs and inform the need for often-costly management and remediation. This paper synthesizes information on cHABs occurrence, toxicology and health effects, and relates this to past and current conditions in the Great Lakes, a major global resource which supplies 84% of the surface water in North America. This geographic region has seen a significant resurgence of cHABs since the 1980s. In particular we focus on Lake Erie, where increased reporting of cHABs has occurred from the early 1990's. We evaluate available information and case reports of cHAB-related illness and death and show that cHABs occur throughout the basin, with reports of animal illness and death, especially dogs and livestock. Lake Erie has consistently experienced cHABs and cyanotoxins in the last decade with probable cases of human illness, while the other Great Lakes show intermittent cHABs and toxins, but no confirmed reports on illness or toxicity. The dominant toxigenic cyanobacterium is the genus Microcystis known to produce microcystins. The presence of other cyanotoxins (anatoxin-a, paralytic shellfish toxins) implicates other toxigenic cyanobacteria such as Anabaena (Dolichospermum) and Lyngbya.

Risk to human health associated with the environmental occurrence of cyanobacterial neurotoxic alkaloids anatoxins and saxitoxins

Cyanobacteria are ubiquitous photosynthetic micro-organisms forming blooms and scums in surface water; among them some species can produce cyanotoxins giving rise to some concern for human health and animal life. To date, more than 65 cyanobacterial neurotoxins have been described, of which the most studied are the groups of anatoxins and saxitoxins (STXs), comprising many different variants. In freshwaters, the hepatotoxic microcystins represent the most frequently detected cyanotoxin: on this basis, it could appear that neurotoxins are less relevant, but the low frequency of detection may partially reflect an a priori choice of target analytes, the low method sensitivity and the lack of certified standards. Cyanobacterial neurotoxins target cholinergic synapses or voltage-gated ion channels, blocking skeletal and respiratory muscles, thus leading to death by respiratory failure. This review reports and analyzes the available literature data on environmental occurrence of cyanobacterial neurotoxic alkaloids, namely anatoxins and STXs, their biosynthesis, toxicology and epidemiology, derivation of guidance values and action limits. These data are used as the basis to assess the risk posed to human health, identify critical exposure scenarios and highlight the major data gaps and research needs.

Co-occurrence of microcystin and anatoxin-a in the freshwater lake Aydat (France): Analytical and molecular approaches during a three-year survey

Cyanobacterial mass occurrence is becoming a growing concern worldwide. They notably pose a threat to water users when cyanotoxins are produced. The aim of this study was to evaluate the occurrence and the dynamics of two cyanotoxins: microcystin (MC) and anatoxin-a (ANTX-a), and of two of the genes responsible for their production (respectively mcyA and anaC) during three consecutive bloom periods (2011, 2012 and 2013) in Lake Aydat (Auvergne, France). MC was detected at all sampling dates, but its concentration showed strong inter- and intra-annual variations. MC content did not correlate with cyanobacterial abundance, nor with any genera taken individually, but it significantly correlated with mcyA gene abundance (R²=0.51; p=0.042). MC content and mcyA gene abundance were maximal when cyanobacterial abundance was low, either at the onset of the bloom or during a trough of biomass. The LC-MS/MS analysis showed the presence of ANTX-a in the 2011 samples. To our knowledge, this is the first report of the presence of this neurotoxin in a French lake. The presence of ANTX-a corresponded to the only year for which Anabaena did not dominate the cyanobacterial community alone, and several cyanobacterial genera were present, including notably Aphanizomenon. anaC gene detection by PCR was not coherent with ANTX-a presence, both gene and toxin were never found for a same sample. This implies that molecular tools to study genes responsible for the production of anatoxin-a are still imperfect and the development of new primers is needed. This study also highlights the need for better monitoring practices that would not necessarily focus only on the peak of cyanobacterial abundance and that would take cyanotoxins other than MC into account.

Pharmacological studies confirm neurotoxic metabolite(s) produced by the bloom-forming Cylindrospermopsis raciborskii in Hungary

A rapid cyanobacterial bloom of Cylindrospermopsis raciborskii (3.2 × 10(4) filaments/mL) was detected early November, 2012, in the Fancsika pond (East Hungary). The strong discoloration of water was accompanied by a substantial fish mortality (even dead cats were seen on the site), raising the possibility of some toxic metabolites in the water produced by the bloom-forming cyanobacteria (C. raciborskii). The potential neuronal targets of the toxic substances in the bloom sample were studied on identified neurons (RPas) in the central nervous system of Helix pomatia. The effects of the crude aqueous extracts of the Fancsika bloom sample (FBS) and the laboratory isolate of C. raciborskii from the pond (FLI) were compared with reference samples: C. raciborskii ACT 9505 (isolated in 1995 from Lake Balaton, Hungary), the cylindrospermopsin producer AQS, and the neurotoxin (anatoxin-a, homoanatoxin-a) producer Oscillatoria sp. (PCC 6506) strains. Electrophysiological tests showed that both FBS and FLI samples as well the ACT 9505 extracts modulate the acetylcholine receptors (AChRs) of the neurons, evoking ACh agonist effects, then inhibiting the ACh-evoked neuronal responses. Dose-response data suggested about the same range of toxicity of FBS and FLI samples (EC50  = 0.397 mg/mL and 0.917 mg/mL, respectively) and ACT 9505 extracts (EC50  = 0.734 mg/mL). The extract of the neurotoxin-producing PCC 6506 strain, however, proved to be the strongest inhibitor of the ACh responses on the same neurons (EC50  = 0.073 mg/mL). The presented results demonstrated an anatoxin-a-like cholinergic inhibitory effects of cyanobacterial extracts (both the environmental FBS sample, and the laboratory isolate, FLI) by some (yet unidentified) toxic components in the matrix of secondary metabolites. Previous pharmacological studies of cyanobacterial samples collected in other locations (Balaton, West Hungary) resulted in similar conclusions; therefore, we cannot exclude that this chemotype of C. raciborskii which produce anatoxin-a like neuroactive substances is more widely distributed in this region.

Effects of nitrogen and phosphorus on anatoxin-a, homoanatoxin-a, dihydroanatoxin-a and dihydrohomoanatoxin-a production by Phormidium autumnale

Anatoxins are powerful neuromuscular blocking agents produced by some cyanobacteria. Consumption of anatoxin-producing cyanobacterial mats or the water containing them has been linked to numerous animal poisonings and fatalities worldwide. Despite this health risk, there is a poor understanding of the environmental factors regulating anatoxin production. Non-axenic Phormidium autumnale strain CAWBG557 produces anatoxin-a (ATX), homoanatoxin-a (HTX) and their dihydrogen-derivatives dihydroanatoxin-a (dhATX) and dihydrohomoanatoxin-a (dhHTX). The effects of varying nitrogen and phosphorus concentrations on the production of these four variants were examined in batch monocultures. The anatoxin quota (anatoxin per cell) of all four variants increased up to four fold in the initial growth phase (days 0-9) coinciding with the spread of filaments across the culture vessel during substrate attachment. Dihydroanatoxin-a and dhHTX, accounted for over 60% of the total anatoxin quota in each nitrogen and phosphorus treatment. This suggests they are being internally synthesised and not just derived following cell lysis and environmental degradation. The four anatoxin variants differed in their response to varying nitrogen and phosphorus concentrations. Notably, dhATX quota significantly decreased (P ≤ 0.03) when nitrogen and phosphorus concentrations were elevated (nitrogen = 21 mg L(-1); phosphorus = 3 mg L(-1)), while HTX quota increased when the phosphorus concentrations were reduced (ca. < 0.08 mg L(-1)). This is of concern as HTX has a high toxicity and anatoxin producing P. autumnale blooms in New Zealand usually occur in rivers with low water column dissolved reactive phosphorus.

Biosynthesis of anatoxin-a and analogues (anatoxins) in cyanobacteria

Freshwater cyanobacteria produce secondary metabolites that are toxic to humans and animals, the so-called cyanotoxins. Among them, anatoxin-a and homoanatoxin-a are potent neurotoxins that are agonists of the nicotinic acetylcholine receptor. These alkaloids provoke a rapid death if ingested at low doses. Recently, the cluster of genes responsible for the biosynthesis of these toxins, the ana cluster, has been identified in Oscillatoria sp. PCC 6506, and a biosynthetic pathway was proposed. This biosynthesis was reconstituted in vitro using purified enzymes confirming the predicted pathway. One of the enzymes, AnaB a prolyl-acyl carrier protein oxidase, was crystallized and its three dimensional structure solved confirming its reaction mechanism. Three other ana clusters have now been identified and sequenced in other cyanobacteria. These clusters show similarities and some differences suggesting a common evolutionary origin. In particular, the cluster from Cylindrospermum stagnale PCC 7417, possesses an extra gene coding for an F420-dependent oxidoreductase that is likely involved in the biosynthesis of dihydroanatoxin-a. This review summarizes all these new data and discusses them in relation to the production of anatoxins in the environment.

Detection of anatoxin-a and three analogs in Anabaena spp. cultures: new fluorescence polarization assay and toxin profile by LC-MS/MS

Anatoxin-a (ATX) is a potent neurotoxin produced by several species of Anabaena spp. Cyanobacteria blooms around the world have been increasing in recent years; therefore, it is urgent to develop sensitive techniques that unequivocally confirm the presence of these toxins in fresh water and cyanobacterial samples. In addition, the identification of different ATX analogues is essential to later determine its toxicity. In this paper we designed a fluorescent polarization (FP) method to detect ATXs in water samples. A nicotinic acetylcholine receptor (nAChR) labeled with a fluorescein derivative was used to develop this assay. Data showed a direct relationship between the amount of toxin in a sample and the changes in the polarization degree of the emitted light by the labeled nAChR, indicating an interaction between the two molecules. This method was used to measure the amount of ATX in three Anabaena spp. cultures. Results indicate that it is a good method to show ATXs presence in algal samples. In order to check the toxin profile of Anabaena cultures a LC-MS/MS method was also developed. Within this new method, ATX-a, retention time (RT) 5 min, and three other molecules with a mass m/z 180.1 eluting at 4.14 min, 5.90 min and 7.14 min with MS/MS spectra characteristic of ATX toxin group not previously identified were detected in the Anabaena spp. cultures. These ATX analogues may have an important role in the toxicity of the sample.

The ecotoxicological evaluation of Cylindrospermopsis raciborskii from Lake Balaton (Hungary) employing a battery of bioassays and chemical screening

Ecotoxicity of four Cylindrospermopsis raciborskii strains (ACT 9502, ACT 9503, ACT 9504, ACT 9505) isolated from Lake Balaton (Hungary) was evaluated in four aquatic bioassays including the Thamnocephalus platyurus acute lethality test; Daphnia magna acute immobilization assay; D. magna feeding inhibition assay and Danio rerio embryo developmental toxicity assay, assisted by chemical screening for known toxins by HPLC-MS. For reference, we analyzed in parallel the toxin content and toxic effects of two previously characterized toxin-producing strains: the Australian cylindrospermopsin producer AQS C. raciborskii and the anatoxins producer Oscillatoria sp. PCC 6506. Bioassays were used to evaluate the overall toxicity of the hydrophilic bioactive metabolites pool synthesized by the selected cyanobacteria. Chemical screening has proven that the ACT C. raciborskii extracts investigated did not contained cylindrospermopsins and anatoxins. The relative toxicity of the ACT C. raciborskii aqueous extracts observed in each bioassay was comparable to the effects recorded for the anatoxins producer PCC 6506 strain while toxicity values (EC50/LC50) calculated for the AQS extract were in general one order of magnitude lower. Concerning sublethal effects of ACT C. raciborskii extracts to the D. rerio embryogenesis, the general morphological abnormality observed was a significant retardation of development. Overall, our results suggest that C. raciborskii populating Lake Balaton produce metabolites with significant bioactive potencies. Therefore, continued investigation of these unknown compounds is required.