Occurrence and diversity of cyanotoxins in Greek lakes

Cyanobacteria respond to trophic status in shallow aquatic ecosystems

Small and shallow water bodies are particularly sensitive to adverse conditions connected with anthropogenic eutrophication. As model systems, ponds are a good object for ecological research and monitoring of global environmental changes. We examined cyanobacteria along with other groups of algae versus zooplankton and abiotic characteristics of water in 51 aquatic ecosystems exposed to anthropogenic pressure (from natural forest to highly disturbed field ponds) with 3 distinct trophic groups: meso-, eu- and hypertrophic. This study aimed to define how different levels of trophy affect pond-specific cyanobacteria assemblages and to identify species responding to particular trophic states. We demonstrated that trophic type determined the occurrence of certain cyanobacteria species. From among 78 identified taxa, shade- and turbid mixed adapted were the most numerous. Eutrophic ponds had the highest cyanobacteria species and diversity and abundance of zooplankon. Dominating species such as Chroococcus minimus, Anagnostidinema amphibium, Phormidium granulatum or Komvophoron minutum preferred mesotrophic, while e.g. Jaaginema subtilissimum, Limnolyngbya circumcreta, Limnothrix vacuolifera or Romeria leopolienis eutrophic waters and these were not grazed by filtrators. Only 3 species (Aphanizomenon flos-aquae, Dolichospermum circinale, Planktothrix agardhii) were associated with hypertrophic ponds. Therefore, we assume that cyanobacteria taxa have a high indicative potential to distinguish between trophic type of ponds. Reynolds Functional Groups also exhibit responses to changes in water quality. It was partucularly evident in the case of cyanobacteria representatives of codon M which was attributed to eutrophic ponds. Advancing our understanding about trophic preferences of cyanobacteria is crucial, especially in the era of global warming and the persistent issue of water eutrophication, when problems with harmful cyanobacterial blooms are intensifying. The research findings have ecological significance and management implications, highlighting the often-overlooked importance of pond ecosystems in maintaining overall water quality.

Risk quick sketch: Soil captured most anatoxin-a and microcystin-RR rather than cylindrospermopsin and microcystin-LA/-LY

Cyanobacteria proliferate in warm, nutrient-rich environments and release toxic secondary metabolites into natural waters. Using cyanotoxin-contaminated water to irrigate crops could expose humans and biota, but the risk may be low if agricultural soils can sorb and retain cyanotoxins. In this report, we compared the sorption and desorption capacities of multi-class cyanotoxins/anabaenopeptins in soils of variable properties with a batch sorption procedure. The target compounds were anabaenopeptin-A, anabaenopeptin-B, anatoxin-a, cylindrospermopsin, and microcystins -LR, -RR, -LA, -LY, -LW, and -LF. Based on solid-liquid distribution coefficients (Kd), we classified cylindrospermopsin and microcystin-LA/-LY as "very low sorptivity", anabaenopeptin-A, -B and microcystin-LR, -LF, and -LW as "low sorptivity", and anatoxin-a and microcystin-RR as "medium sorptivity". We remain concerned about irrigating agricultural land with water contaminated with high levels of CYN and MC-LA/-LY because of their relatively low affinity and high desorption proportion in soils. The results also suggest that soil sorption can be an effective immobilization pathway for anatoxin-a and microcystin-RR. The generated data will be useful for prioritizing research on the most bioavailable cyanotoxins/anabaenopeptins that are likely to be released by the soil matrix, for environmental risk assessment.

Untargeted LC-HRMS applied to microcystin-producing cyanobacterial cultures for the evaluation of the efficiency of chlorine-based treatments commonly used for water potabilization

Cyanobacteria in water supplies are considered an emerging threat, as some species produce toxic metabolites, cyanotoxins, of which the most widespread and well-studied are microcystins. Consumption of contaminated water is a common exposure route to cyanotoxins, making the study of cyanobacteria in drinking waters a priority to protect public health. In drinking water treatment plants, pre-oxidation with chlorinated compounds is widely employed to inhibit cyanobacterial growth, although concerns on its efficacy in reducing cyanotoxin content exists. Additionally, the effects of chlorination on abundant but less-studied cyanometabolites (e.g. cyanopeptolins whose toxicity is still unclear) remain poorly investigated. Here, two chlorinated oxidants, sodium hypochlorite (NaClO) and chlorine dioxide (ClO2), were tested on the toxic cyanobacterium Microcystis aeruginosa, evaluating their effect on cell viability, toxin profile and content. Intra- and extracellular microcystins and other cyanometabolites, including their degradation products, were identified using an untargeted LC-HRMS approach. Both oxidants were able to inactivate M. aeruginosa cells at a low dose (0.5 mg L-1), and greatly reduced intracellular toxins content (>90%), regardless of the treatment time (1-3 h). Conversely, a two-fold increase of extracellular toxins after NaClO treatment emerged, suggesting a cellular damage. A novel metabolite named cyanopeptolin-type peptide-1029, was identified based on LC-HRMSn (n = 2, 3) evidence, and it was differently affected by the two oxidants. NaClO led to increase its extracellular concentration from 2 to 80-100 μg L-1, and ClO2 induced the formation of its oxidized derivative, cyanopeptolin-type peptide-1045. In conclusion, pre-oxidation treatments of raw water contaminated by toxic cyanobacteria may lead to increased cyanotoxin concentrations in drinking water and, depending on the chemical agent, its dose and treatment duration, also of oxidized metabolites. Since the effects of such metabolites on human health remain unknown, this issue should be handled with extreme caution by water security agencies involved in drinking water management.

Biodegradation of the cyanobacterial toxin anatoxin-a by a Bacillus subtilis strain isolated from a eutrophic lake in Saudi Arabia

Anatoxin-a (ATX-a) is a neurotoxin produced by some species of cyanobacteria. Due to its water solubility and stability in natural water, it could pose health risks to human, animals, and plants. Conventional water treatment techniques are not only insufficient for the removal of ATX-a, but they also result in cell lysis and toxin release. The elimination of this toxin through biodegradation may be a promising strategy. This study examines for the first time the biodegradation of ATX-a to a non-toxic metabolite (Epoxy-ATX-a) by a strain of Bacillus that has a history of dealing with toxic cyanobacteria in a eutrophic lake. The Bacillus strain AMRI-03 thrived without lag phase in a lake water containing ATX-a. The strain displayed fast degradation of ATX-a, depending on initial toxin concentration. At the highest initial concentrations (50 & 100 µg L- 1), total ATX-a degradation took place in 4 days, but it took 6 & 7 days at lower concentrations (20, 10, and 1 µg L- 1, respectively). The ATX-a biodegradation rate was also influenced by the initial toxin concentration, reaching its maximum value (12.5 µg L- 1 day- 1) at the highest initial toxin concentrations (50 & 100 µg L- 1). Temperature and pH also had an impact on the rate of ATX-a biodegradation, with the highest rates occurring at 25 and 30 ºC and pH 7 and 8. This nontoxic bacterial strain could be immobilized within a biofilm on sand filters and/or sludge for the degradation and removal of ATX-a and other cyanotoxins during water treatment processes, following the establishment of mesocosm experiments to assess the potential effects of this bacterium on water quality.

Comprehensive analysis of cyanobacterial secondary metabolites distribution and toxicity in urban water bodies

This study addresses the increasing concern regarding cyanotoxin contamination of water bodies, highlighting the diversity of these toxins and their potential health implications. Cyanobacteria, which are prevalent in aquatic environments, produce toxic metabolites, raising concerns regarding human exposure and associated health risks, including a potential increase in cancer risk. Although existing research has primarily focused on well-known cyanotoxins, recent technological advancements have revealed numerous unknown cyanotoxins, necessitating a comprehensive assessment of multiple toxin categories. To enhance the cyanotoxin databases, we optimized the CyanoMetDB cyanobacterial secondary metabolites database by incorporating secondary fragmentation patterns using the Mass Frontier fragmentation data prediction software. Water samples from diverse locations in Shanghai were analyzed using high-resolution mass spectrometry. Subsequently, the toxicity of cyanobacterial metabolites in the water samples was examined through acute toxicity assays using the crustacean Thamnocephalus platyurus. After 24 h of exposure, the semi-lethal concentrations (LC50) of the water samples ranged from 0.31 mg L-1 to 1.78 mg L-1 (MC-LR equivalent concentration). Our findings revealed a critical correlation between the overall concentration of cyanobacterial metabolites and toxicity. The robust framework and insights of this study underscore the need for an inclusive approach to water quality management, emphasizing continuous efforts to refine detection methods and comprehend the broader ecological impact of cyanobacterial blooms on aquatic ecosystems.

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

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

Snapshot of cyanobacterial toxins in Pakistani freshwater bodies

Cyanobacteria are known to produce diverse secondary metabolites that are toxic to aquatic ecosystems and human health. However, data about the cyanotoxins occurrence and cyanobacterial diversity in Pakistan's drinking water reservoirs is scarce. In this study, we first investigated the presence of microcystin, saxitoxin, and anatoxin in 12 water bodies using an enzyme-linked immunosorbent assay (ELISA). The observed cyanotoxin values for the risk quotient (RQ) determined by ELISA indicated a potential risk for aquatic life and human health. Based on this result, we made a more in-depth investigation with a subset of water bodies (served as major public water sources) to analyze the cyanotoxins dynamics and identify potential producers. We therefore quantified the distribution of 17 cyanotoxins, including 12 microcystin congeners using a high-performance liquid chromatography-high-resolution tandem mass spectrometry/mass spectrometry (HPLC-HRMS/MS). Our results revealed for the first time the co-occurrence of multiple cyanotoxins and the presence of cylindrospermopsin in an artificial reservoir (Rawal Lake) and a semi-saline lake (Kallar Kahar). We also quantified several microcystin congeners in a river (Panjnad) with MC-LR and MC-RR being the most prevalent and abundant. To identify potential cyanotoxin producers, the composition of the cyanobacterial community was characterized by shotgun metagenomics sequencing. Despite the noticeable presence of cyanotoxins, Cyanobacteria were not abundant. Synechococcus was the most abundant cyanobacterial genus found followed by a small amount of Anabaena, Cyanobium, Microcystis, and Dolichospermum. Moreover, when we looked at the cyanotoxins genes coverage, we never found a complete microcystin mcy operon. To our knowledge, this is the first snapshot sampling of water bodies in Pakistan. Our results would not only help to understand the geographical spread of cyanotoxin in Pakistan but would also help to improve cyanotoxin risk assessment strategies by screening a variety of cyanobacterial toxins and confirming that cyanotoxin quantification is not necessarily related to producer abundance.

Shifts in phytoplankton and zooplankton communities in three cyanobacteria-dominated lakes after treatment with hydrogen peroxide

Cyanobacteria can reach high densities in eutrophic lakes, which may cause problems due to their potential toxin production. Several methods are in use to prevent, control or mitigate harmful cyanobacterial blooms. Treatment of blooms with low concentrations of hydrogen peroxide (H2O2) is a promising emergency method. However, effects of H2O2 on cyanobacteria, eukaryotic phytoplankton and zooplankton have mainly been studied in controlled cultures and mesocosm experiments, while much less is known about the effectiveness and potential side effects of H2O2 treatments on entire lake ecosystems. In this study, we report on three different lakes in the Netherlands that were treated with average H2O2 concentrations ranging from 2 to 5 mg L-1 to suppress cyanobacterial blooms. Effects on phytoplankton and zooplankton communities, on cyanotoxin concentrations, and on nutrient availability in the lakes were assessed. After every H2O2 treatment, cyanobacteria drastically declined, sometimes by more than 99%, although blooms of Dolichospermum sp., Aphanizomenon sp., and Planktothrix rubescens were more strongly suppressed than a Planktothrix agardhii bloom. Eukaryotic phytoplankton were not significantly affected by the H2O2 additions and had an initial advantage over cyanobacteria after the treatment, when ample nutrients and light were available. In all three lakes, a new cyanobacterial bloom developed within several weeks after the first H2O2 treatment, and in two lakes a second H2O2 treatment was therefore applied to again suppress the cyanobacterial population. Rotifers strongly declined after most H2O2 treatments except when the H2O2 concentration was ≤ 2 mg L-1, whereas cladocerans were only mildly affected and copepods were least impacted by the added H2O2. In response to the treatments, the cyanotoxins microcystins and anabaenopeptins were released from the cells into the water column, but disappeared after a few days. We conclude that lake treatments with low concentrations of H2O2 can be a successful tool to suppress harmful cyanobacterial blooms, but may negatively affect some of the zooplankton taxa in lakes. We advise pre-tests prior to the treatment of lakes to define optimal treatment concentrations that kill the majority of the cyanobacteria and to minimize potential side effects on non-target organisms. In some cases, the pre-tests may discourage treatment of the lake.

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

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

What, How, When, and Where: Spatiotemporal Water Quality Hazards of Cyanotoxins in Subtropical Eutrophic Reservoirs

Though toxins produced during harmful blooms of cyanobacteria present diverse risks to public health and the environment, surface water quality surveillance of cyanobacterial toxins is inconsistent, spatiotemporally limited, and routinely relies on ELISA kits to estimate total microcystins (MCs) in surface waters. Here, we employed liquid chromatography tandem mass spectrometry to examine common cyanotoxins, including five microcystins, three anatoxins, nodularin, cylindrospermopsin, and saxitoxin in 20 subtropical reservoirs spatially distributed across a pronounced annual rainfall gradient. Probabilistic environmental hazard analyses identified whether water quality values for cyanotoxins were exceeded and if these exceedances varied spatiotemporally. MC-LR was the most common congener detected, but it was not consistently observed with other toxins, including MC-YR, which was detected at the highest concentrations during spring with many observations above the California human recreation guideline (800 ng/L). Cylindrospermopsin was also quantitated in 40% of eutrophic reservoirs; these detections did not exceed a US Environmental Protection Agency swimming/advisory level (15,000 ng/L). Our observations have implications for routine water quality monitoring practices, which traditionally use ELISA kits to estimate MC levels and often limit collection of surface samples during summer months near reservoir impoundments, and further indicate that spatiotemporal surveillance efforts are necessary to understand cyanotoxins risks when harmful cyanobacteria blooms occur throughout the year.

Effect of Metal Cations on Colloids-Microcystin-LR Interaction

Colloidal particles, mixture with continuous molecular weight distribution and multiple organic components, is widespread in lake and have significant impact on the retention, migration, transportation, and fate of contaminants in lake ecosystems. Here we extract sedimentary colloids from algal growth dominant area (AD) in Taihu Lake and further separated into four different particle size ranges by cross-flow ultra-filtration (CFUF). The interaction mechanism between colloids and Microcystin-LR (MC-LR) was investigated under different cation conditions by dialysis equilibrium experiment method. Adsorption kinetics research shows the adsorption of MC-LR by colloids follows second-order kinetics and can be simulated by Freundlich isotherms. The effects of different cations on colloids-MC-LR interaction shows the addition of Mg(II) decreased colloids-MC-LR interaction, while Cu(II) increased colloids-MC-LR binding. MC-LR also increased Cu(II) binding to colloids, while MC-LR decreased Mg(II) binding. Therefore, different effect of cations to colloids-MC-LR interaction was proposed.

Genomic Analysis of a New Freshwater Cyanophage Lbo240-yong1 Suggests a New Taxonomic Family of Bacteriophages

A worldwide ecological issue, cyanobacterial blooms in marine and freshwater have caused enormous losses in both the economy and the environment. Virulent cyanophages-specifically, infecting and lysing cyanobacteria-are key ecological factors involved in limiting the overall extent of the population development of cyanobacteria. Over the past three decades, reports have mainly focused on marine Prochlorococcus and Synechococcus cyanophages, while information on freshwater cyanophages remained largely unknown. In this study, a novel freshwater cyanophage, named Lbo240-yong1, was isolated via the double-layer agar plate method using Leptolyngbya boryana FACHB-240 as a host. Transmission electron microscopy observation illustrated the icosahedral head (50 ± 5 nm in diameter) and short tail (20 ± 5 nm in length) of Lbo240-yong1. Experimental infection against 37 cyanobacterial strains revealed that host-strain-specific Lbo240-yong1 could only lyse FACHB-240. The complete genome of Lbo240-yong1 is a double-stranded DNA of 39,740 bp with a G+C content of 51.99%, and it harbors 44 predicted open reading frames (ORFs). A Lbo240-yong1 ORF shared the highest identity with a gene of a filamentous cyanobacterium, hinting at a gene exchange between the cyanophage and cyanobacteria. A BLASTn search illustrated that Lbo240-yong1 had the highest sequence similarity with the Phormidium cyanophage Pf-WMP4 (89.67% identity, 84% query coverage). In the proteomic tree based on genome-wide sequence similarities, Lbo240-yong1, three Phormidium cyanophages (Pf-WMP4, Pf-WMP3, and PP), one Anabaena phage (A-4L), and one unclassified Arthronema cyanophage (Aa-TR020) formed a monophyletic group that was more deeply diverging than several other families. Pf-WMP4 is the only member of the independent genus Wumpquatrovirus that belongs to the Caudovircetes class. Pf-WMP3 and PP formed the independent genus Wumptrevirus. Anabaena phage A-4L is the only member of the independent Kozyakovvirus genus. The six cyanopodoviruses share similar gene arrangements. Eight core genes were found in them. We propose, here, to set up a new taxonomic family comprising the six freshwater cyanopodoviruses infecting filamentous cyanobacteria. This study enriched the field's knowledge of freshwater cyanophages.

Ecological Implications in a Human-Impacted Lake-A Case Study of Cyanobacterial Blooms in a Recreationally Used Water Body

This study was aimed primarily at describing the planktonic assemblages with special attention to invasive and toxin-producing cyanobacterial species in the context of ecological and health threats. The second aim was to analyze the aspect of recreational pressure, which may enhance the cyanobacterial blooms, and, as a consequence, the negative changes and loss of planktonic biodiversity. This study was carried out in recreationally used Lake Sztynorckie throughout the whole growing season of 2020 and included an assessment of the abundance and biomass of phytoplankton (cyanobacteria and algae) in relation to environmental variables. The total biomass was in the range of 28-70 mg L^-1, which is typical for strong blooms. The dominant filamentous cyanobacteria were Pseudanabaena limnetica, Limnothrix redekei, Planktolyngbya limnetica, and Planktothrix agarhii, and three invasive nostocalean species Sphaerospermopsis aphanizomenoides, Cuspidothrix issatschenkoi, and Raphidiopsis raciborskii. They can pose a serious threat not only to the ecosystem but also to humans because of the possibility of cyanobacteria producing cyanotoxins, such as microcystins, saxitoxins, anatoxin-a, and cylindrospermopsins, having hepatotoxic, cytotoxic, neurotoxic, and dermatoxic effects. The water quality was assessed as water bodies had bad ecological status (based on phytoplankton), were highly meso-eutrophic (based on zooplankton), and had very low trophic efficiency and low biodiversity.

Biotransformation and detoxification of saxitoxin by Bacillus flexus in batch experiments

Saxitoxins (STXs) are carbamate alkaloid neurotoxins produced by some species of cyanobacteria. They are water soluble and relatively stable in the natural environment, and thereby represent a risk to animal and human health through a long-time exposure. STXs cannot be sufficiently removed by conventional water treatment methods. Therefore, this study investigates the potential STX biodegradation and detoxification by bacteria as a promising method for toxin removal. STX biodegradation experiments were conducted using Bacillus flexus SSZ01 strain in batch cultures. The results revealed that SSZ01 strain grew well and rapidly detoxified STX, with no lag phase observed. STX detoxification by SSZ01 strain was initial-toxin-concentration-dependent. The highest biotransformation rate (10 µg STX L^-1 day^-1) the pseudo-first-order kinetic constant (0.58 d^-1) were obtained at the highest initial toxin concentration (50 µg L^-1) and the lowest ones (0.06 µg STX L^-1 day^-1 and 0.14 d^-1, respectively) were recorded at the lowest initial concentration (0.5 µg L^-1). STX biotransformation rate increased with temperature, with highest occurred at 30 ºC. This rate was also influenced by pH, with highest obtained at pH8 and lowest at higher and lower pH values. HPLC chromatograms showed that STX biotransformation peak is corresponding to the least toxic STX analog (disulfated sulfocarbamoyl-C1 variant). The Artemia-based toxicity assay revealed that this biotransformation byproduct was nontoxic. This suggests the potential application of this bacterial strain in slow sand filters for cyanotoxin removal in water treatment plants. Being nontoxic, this byproduct needs to be assayed for its therapeutic effects toward neurodegenerative diseases.

Untargeted and targeted LC-MS and data processing workflow for the comprehensive analysis of oligopeptides from cyanobacteria

Cyanobacteria produce a plethora of structurally diverse bioactive secondary metabolites, including cyanotoxins which pose a serious threat to humans and other living organisms worldwide. Currently, a wide variety of mass spectrometry-based methods for determination of microcystins (MCs), the most commonly occurring and studied class of cyanotoxins, have been developed and employed for research and monitoring purposes. The scarcity of commercially available reference materials, together with the ever-growing range of mass spectrometers and analytical approaches, make the accuracy of quantitative analyses a critical point to be carefully investigated in view of a reliable risk evaluation. This study reports, a comparative investigation of the qualitative and quantitative MCs profile obtained using targeted and untargeted liquid chromatography-mass spectrometry approaches for the analyses of cyanobacterial biomass from Lake Kastoria, Greece. Comparison of the total MCs content measured by the two approaches showed good correlation, with variations in the range of 3.8-13.2%. In addition, the implementation of an analytical workflow on a hybrid linear ion trap/orbitrap mass spectrometer is described, based on combining data-dependent acquisition and a powerful database of cyanobacterial metabolites (CyanoMetDB) for the annotation of known and discovery of new cyanopeptides. This untargeted strategy proved highly effective for the identification of MCs, microginins, anabaenopeptins, and micropeptins. The systematic interpretation of the acquired fragmentation patterns allowed the elucidation of two new MC structural variants, MC-PrhcysR and MC-Prhcys(O)R, and proposal of structures for two new microginins, isomeric cyanostatin B and MG 821A, and three isomeric micropeptins at m/z 846.4715, 846.4711 and 846.4723.

Screening of pesticides and emerging contaminants in eighteen Greek lakes by using target and non-target HRMS approaches: Occurrence and ecological risk assessment

Lakes, albeit ecosystems of vital importance, are insufficiently investigated with respect to the degradation of water quality due to the organic micropollutants load. As regards Greece, screening of lake waters is scarce and concerns a limited number of contaminants. However, understanding the occurrence of contaminants of emerging concern (CECs) and other micropollutants in lakes is essential to appraise their potential ecotoxicological effects. The aim of this study was to deploy a multiresidue screening approach based on liquid chromatography-high-resolution mass spectrometry (HRMS) to get a first snapshot for >470 target CECs, including pesticides, pharmaceuticals, personal care products (PPCPs), per- and polyfluoroalkyl substances (PFASs), as well as organophosphate flame retardants (OPFRs) in eighteen Greek lakes in Central, Northern and West Northern Greece. The omnipresent compounds were DEET (N,N-diethyl-meta-toluamide), caffeine and TCPP (tris (1-chloro-2-propyl) phosphate). Maximum concentrations varied among the different classes. DEET was detected at a maximum average concentration of >1000 ng/L in Lake Orestiada, while its mean concentration was estimated at 233 ng/L. The maximum total concentrations for pesticides, PPCPs, PFASs, and OPFRs were 5807, 2669, 33.1, and 1214 ng/L, respectively, indicating that Greek lakes are still threatened by the intense agricultural activity. Besides, HRMS enabled a non-target screening by exploiting the rich content of the full-scan raw data, allowing the 'discovery' of tentative candidates, such as surfactants, pharmaceuticals, and preservatives among others, without reference standards. The potential ecotoxicity was assessed by both the risk quotient method and ECOSAR (Ecological Structure Activity Relationships) revealing low risk for most of the compounds.

Multi-class secondary metabolites in cyanobacterial blooms from a tropical water body: Distribution patterns and real-time prediction

Cyanobacterial blooms that produce toxins occur in freshwaters worldwide and yet, the occurrence and distribution patterns of many cyanobacterial secondary metabolites particularly in tropical regions are still not fully understood. Moreover, predictive models for these metabolites by using easily accessible water quality indicators are rarely discussed. In this study, we investigated the co-occurrence and spatiotemporal trends of 18 well-known and less-studied cyanobacterial metabolites (including [D-Asp3] microcystin-LR (DM-LR), [D-Asp3] microcystin-RR (DM-RR), microcystin-HilR (MC-HilR), microcystin-HtyR (MC-HtyR), microcystin-LA (MC-LA), microcystin-LF (MC-LF), microcystin-LR (MC-LR), microcystin-LW (MC-LW), microcystin-LY (MC-LY), microcystin-RR (MC-RR) and microcystin-WR (MC-WR), Anatoxin-a (ATX-a), homoanatoxin-a (HATX-a), cylindrospermospin (CYN), nodularin (NOD), anabaenopeptin A (AptA) and anabaenopeptin B (AptB)) in a tropical freshwater lake often plagued with blooms. Random forest (RF) models were developed to predict MCs and CYN and assess the relative importance of 22 potential predictors that determined their concentrations. The results showed that 11 MCs, CYN, ATX-a, HATX-a, AptA and AptB were found at least once in the studied water body, with MC-RR and CYN being the most frequently occurring, intracellularly and extracellularly. AptA and AptB were detected for the first time in tropical freshwaters at low concentrations. The metabolite profiles were highly variable at both temporal and spatial scales, in line with spatially different phytoplankton assemblages. Notably, MCs decreased with the increase of CYN, possibly revealing interspecific competition of cyanobacteria. The rapid RF prediction models for MCs and CYN were successfully developed using 4 identified drivers (i.e., chlorophyll-a, total carbon, rainfall and ammonium for MCs prediction; and chloride, total carbon, rainfall and nitrate for CYN prediction). The established models can help to better understand the potential relationships between cyanotoxins and environmental variables as well as provide useful information for making policy decisions.

Microcystins can be extracted from Microcystis aeruginosa using amino acid-derived biosurfactants

Microcystin, a cyanotoxin produced by Microcystis aeruginosa growing in eutrophic waters, can promote liver tumors in people ingesting contaminated water. To date, water treatment systems have not been effective in removing or degrading these cyanotoxins. In this work, we investigated the inhibitory activity of surfactants on the growth of M. aeruginosa and their application to extract the intracellular produced cyanotoxins. The experiments involving growth inhibition and extraction of cyanotoxins were carried out using the non-biodegradable surfactant cetyl trimethyl ammonium bromide (CTAB) in addition to other biodegradable surfactants. These were Tween 80 and surfactants derived from amino acids and peptides, respectively, from arginine, SDA, and hydrolyzed peptone, SDP. We demonstrated that the tested surfactants could be used to inhibit the growth of M. aeruginosa. At this point, CTAB and SDA proved to be the most competent surfactants in reducing cyanobacterial growth. Moreover, microcystins have been successfully removed from the water employing a cloud point extraction protocol based on the use of these surfactants and ammonium sulfate.

Co-occurrence of multiple cyanotoxins and taste-and-odor compounds in the large eutrophic Lake Taihu, China: Dynamics, driving factors, and challenges for risk assessment

Cyanobacterial blooms producing toxic metabolites occur frequently in freshwater, yet the environmental behaviors of complex cyanobacterial metabolites remain largely unknown. In this study, the seasonal and spatial variations of several classes of cyanotoxins (microcystins, cylindrospermopsins, saxitoxins) and taste-and-odor (T&O) compounds (β-cyclocitral, β-ionone, geosmin, 2-methylisoborneol) in Lake Taihu were simultaneously investigated for the first time. The total cyanotoxins were dominated by microcystins with concentrations highest in November (mean 2209 ng/L) and lowest in February (mean 48.7 ng/L). Cylindrospermopsins were abundant in May with the highest content of 622.8 ng/L. Saxitoxins only occurred in May (mean 19.2 ng/L) and November (mean 198.5 ng/L). Extracellular T&O compounds were most concentrated in August, the highest being extracellular β-cyclocitral (mean 240.6 ng/L) followed by 2-methylisoborneol (mean 146.6 ng/L). Environment variables play conflicting roles in modulating the dynamics of different groups of cyanotoxins and T&O compounds. Total phosphorus (TP), total nitrogen (TN), chlorophyll-a and cyanobacteria density were important factors affecting the variation of total microcystins, β-cyclocitral and β-ionone concentrations. In contrast, total cylindrospermopsins, 2-methylisoborneol and geosmin concentrations were significantly influenced by water temperature and TP. There was a significant and linear relationship between microcystins and β-cyclocitral/β-ionone, while cylindrospermopsins were positively correlated with 2-methylisoborneol and geosmin. The perceptible odors may be good indicators for the existence of cyanotoxins. Hazard quotients revealed that potential human health risks from microcystins were high in August and November. Meanwhile, the risks from cylindrospermopsins were at moderate levels. Cylindrospermopsins and saxitoxins were first identified in this lake, suggesting that diverse cyanotoxins might co-occur more commonly than previously thought. Hence, the risks from other cyanotoxins beyond microcystins shouldn't be ignored. This study also highlights that the necessity for further assessing the combination effects of these complex metabolites.

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

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

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

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

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

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

Four Decades of Surface Temperature, Precipitation, and Wind Speed Trends over Lakes of Greece

Climate change is known to affect world’s lakes in many ways. Lake warming is perhaps the most prominent impact of climate change but there is evidence that changes of precipitation and wind speed over the surface of the lakes may also have a significant effect on key limnological processes. With this study we explored the interannual trends of surface temperature, precipitation, and wind speed over 18 lakes of Greece using ERA5-Land data spanning over a period of almost four decades. We used generalized additive models (GAMs) to conduct time-series analysis in order to identify significant trends of change. Our results showed that surface temperature has significantly increased in all lakes with an average rate of change for annual temperature of 0.43 °C decade−1. With regard to precipitation, we identified significant trends for most lakes and particularly we found that precipitation decreased during the first two decades (1981–2000), but since 2000 it increased notably. Finally, wind speed did not show any significant change over the examined period with the exception for one lake. In summary, our work highlights the major climatic changes that have occurred in several freshwater bodies of Greece. Thus, it improves our understanding on how climate change may have impacted the ecology of these important ecosystems and may aid us to identify systems that are more vulnerable to future changes.

Killing effect of deinoxanthins on cyanobloom-forming Microcystis aeruginosa: Eco-friendly production and specific activity of deinoxanthins

Cyanobacterial blooms caused mainly by Microcystis aeruginosa could be controlled using chemical and biological agents such as H₂O₂, antagonistic bacteria, and enzymes. Little is known about the possible toxic effects of bacterial membrane pigments on M. aeruginosa cells. Deinococcus metallilatus MA1002 cultured under light increased the production of several carotenoid-like compounds by upregulating two deinoxanthin biosynthesis genes: crtO and cruC. The deinoxanthin compounds were identified using thin-layer chromatography, high-performance liquid chromatography, and liquid chromatography-mass spectrometry. D. metallilatus was cultured with agricultural by-products under light to produce the deinoxanthin compounds. Soybean meal, from six tested agricultural by-products, was selected as the single factor for making an economical medium to produce deinoxanthin compounds. The growth of axenic M. aeruginosa PCC7806, as well as other xenic cyanobacteria such as Cyanobium gracile, Trichormus variabilis, and Dolichospermum circinale, were inhibited by the deinoxanthin compounds. Scanning electron microscopic images showed the complete collapse of M. aeruginosa cells under deinoxanthin treatment, probably due to its interference with cyanobacterial membrane synthesis during cellular elongation. Deinoxanthins appeared to be nontoxic to other non-cyanobacteria such as Acinetobacter, Pseudomonas, Methylobacterium, and Bacillus species, suggesting that it can be a novel candidate for preventing cyanobacterial blooms through its specific activity against cyanobacteria.

Phototransformation of an emerging cyanotoxin (Aerucyclamide A) in simulated natural waters

Aerucyclamide A (ACA) is an emerging cyanopeptide toxin produced by cyanobacteria, and its transformation pathway has rarely been reported. In the present study, ACA was purified from cyanobacterial extracts, and photodegradation processes were investigated in dissolved organic matter (DOM) solutions. Under simulated solar irradiation, the photodegradation of ACA was dominated by ^•OH oxidation, accounting for ~72% of the indirect photodegradation. The bimolecular reaction rate constant of ACA with ^•OH was (6.4 ± 0.2) × 10⁹M ^- 1s ^- 1. Our results indicated that the major reactive sites of ACA toward ^•OH are thiazoline and thiazole moieties. Product analysis via high-resolution mass spectrometry suggested that hydrogen abstraction and gradual hydroxylation are the main photodegradation pathways. The acute toxicity assessment indicate that the products generated in photolysis process did not show any measurable toxicity to Thamnocephalus platyurus. Photodegradation experiments with various DOM-phycocyanin mixtures demonstrated that the half-life of ACA is much longer than that of microcystin-LR.

Multi-class determination of intracellular and extracellular cyanotoxins in freshwater samples by ultra-high performance liquid chromatography coupled to high resolution mass spectrometry

In the past decades, the intensity and duration of cyanobacterial blooms are increasing due to anthropogenic factors. These phenomena worry drinking water companies and water managers because cyanobacteria produce a diverse range of cyanotoxins, which can cause liver, digestive and neurological diseases. The main exposure routes for humans are the consumption of drinking water that has not been effectively treated and the recreational use of polluted waters. For risk assessment and to conduct studies on large-scale occurrence, the development of reliable but simple, sensitive and cost-effective analytical approaches able to cover a wide range of cyanotoxins is essential. Additionally, the determination of intracellular and extracellular toxins separately is advantageous for risk management. To the best of our knowledge, this is the first time that a method for the multi-class determination of cyanotoxins in fresh water, which is able to separately report intra- and extracellular toxins, meet the criteria of simplicity (not requiring multiple sample preparation procedures or time-consuming steps) and it is based on highly specific high resolution mass spectrometry (potential for wide screening and retrospective analysis). Matrix effects, trueness and precision met general validation criteria for a group of nine cyanotoxins, including anatoxins, cylindrospermopsin and microcystins. Considering a 50 mL sample, the method quantification limits were within the range of 8-45 ng L^-1 and 25-129 ng L^-1 for intra- and extracellular cyanotoxins, respectively. Anatoxin-a, cylindrospermopsin and some microcystins were found in three out of four Dutch lakes included in the study, at concentrations up to 52 μg L^-1.

Spatial and Temporal Diversity of Cyanometabolites in the Eutrophic Curonian Lagoon (SE Baltic Sea)

This work aims to determine the profiles of cyanopeptides and anatoxin synthetized by cyanobacteria in the Lithuanian part of the Curonian Lagoon (SE Baltic Sea) and to characterize their spatial and temporal patterns in this ecosystem. Cyanometabolites were analysed by a LC-MS/MS system and were coupled to a hybrid triple quadrupole/linear ion trap mass spectrometer. During the investigation period (2013–2017), 10 microcystins, nodularin, anatoxin-a, 16 anabaenopeptins, including 1 oscillamide, 12 aeruginosins, 1 aeruginosamide, 3 cyanopeptolins and 4 microginins were detected. The most frequently detected metabolites were found at all investigated sites. Demethylated microcystin variants and anabaenopeptins had the strongest relationship with Planktothrix agardhii, while non-demethylated microcystin variants and anatoxin had the strongest relationship with Microcystis spp. Low concentrations of some microcystins: [Asp3]MC-RR, MC-RR, MC-LR, as well as a few other cyanopeptides: AP-A and AEG-A were found during the cold period (December–March). Over the study period, Aphanizomenon, Planktothrix and Microcystis were the main dominant cyanobacteria species, while Planktothrix, Microcystis, and Dolichospermum were potentially producers of cyanopeptides and anatoxin detected in samples from the Curonian Lagoon.

Cyanobacterial Toxins and Peptides in Lake Vegoritis, Greece

Cyanotoxins (CTs) produced by cyanobacteria in surface freshwater are a major threat for public health and aquatic ecosystems. Cyanobacteria can also produce a wide variety of other understudied bioactive metabolites such as oligopeptides microginins (MGs), aeruginosins (AERs), aeruginosamides (AEGs) and anabaenopeptins (APs). This study reports on the co-occurrence of CTs and cyanopeptides (CPs) in Lake Vegoritis, Greece and presents their variant-specific profiles obtained during 3-years of monitoring (2018–2020). Fifteen CTs (cylindrospermopsin (CYN), anatoxin (ATX), nodularin (NOD), and 12 microcystins (MCs)) and ten CPs (3 APs, 4 MGs, 2 AERs and aeruginosamide (AEG A)) were targeted using an extended and validated LC-MS/MS protocol for the simultaneous determination of multi-class CTs and CPs. Results showed the presence of MCs (MC-LR, MC-RR, MC-YR, dmMC-LR, dmMC-RR, MC-HtyR, and MC-HilR) and CYN at concentrations of <1 μg/L, with MC-LR (79%) and CYN (71%) being the most frequently occurring. Anabaenopeptins B (AP B) and F (AP F) were detected in almost all samples and microginin T1 (MG T1) was the most abundant CP, reaching 47.0 μg/L. This is the first report of the co-occurrence of CTs and CPs in Lake Vegoritis, which is used for irrigation, fishing and recreational activities. The findings support the need for further investigations of the occurrence of CTs and the less studied cyanobacterial metabolites in lakes, to promote risk assessment with relevance to human exposure.

Four decades of progress in cylindrospermopsin research: The ins and outs of a potent cyanotoxin

The cyanotoxin cylindrospermopsin (CYN), a toxic metabolite from cyanobacteria, is of particular concern due to its cosmopolitan occurrence, aquatic bioaccumulation, and multi-organ toxicity. CYN is the second most often recorded cyanotoxin worldwide, and cases of human morbidity and animal mortality are associated with ingestion of CYN contaminated water. The toxin poses a great challenge for drinking water treatment plants and public health authorities. CYN, with the major toxicity manifested in the liver, is cytotoxic, genotoxic, immunotoxic, neurotoxic and may be carcinogenic. Adverse effects are also reported for endocrine and developmental processes. We present a comprehensive review of CYN over the past four decades since its first reported poisoning event, highlighting its global occurrence, biosynthesis, toxicology, removal, and monitoring. In addition, current data gaps are identified, and future directions for CYN research are outlined. This review is beneficial for understanding the ins and outs of this environmental pollutant, and for robustly assessing health hazards posed by CYN exposure to humans and other organisms.

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

Microcystins are cyanotoxins produced by many species of cyanobacteria. They are specific inhibitors of serine/threonine protein phosphatases and are phytotoxic to agricultural plants. This study used a formal meta-analysis to estimate the phytotoxicity and bioconcentration rates of agricultural plants exposed to microcystins, and the human health risk from consuming microcystin-contaminated plants. Among the 35 agricultural plants investigated, microcystins were most phytotoxic to durum wheat, corn, white mustard and garden cress. Leafy vegetables such as dill, parsley and cabbage could bioconcentrate ∼3 times more microcystins in their edible parts than other agricultural plants. Although the human health risk from ingesting microcystins could be greater for leafy vegetables than other agricultural plants, further work is needed to confirm bioconcentration of microcystins in realistic water-soil-plant environments. Still, we should avoid growing leafy vegetables, durum wheat and corn on agricultural land that is irrigated with microcystins-contaminated water and be attentive to the risk of microcystins contamination in the agricultural food supply.

Occurrence of microcystins, anabaenopeptins and other cyanotoxins in fish from a freshwater wildlife reserve impacted by harmful cyanobacterial blooms

Harmful algal blooms of cyanobacteria (CyanoHABs) can lead to the release of potent toxins that can seriously affect ecosystem integrity. Some freshwater watersheds are particularly at risk considering the threats to already imperiled wildlife. The consumption of tainted drinking water and contaminated food also raises concerns for human health. In the present study, a pilot survey was conducted in the riverine ecosystem of the Pike River Ecological Reserve (QC, Canada) near Missisquoi Bay, Lake Champlain. We examined the occurrence of multiclass cyanotoxins including 12 microcystins, anatoxins, cylindrospermopsin (CYN), anabaenopeptins (AP-A, AP-B), and cyanopeptolin-A in surface waters and wild-caught fish during the summer 2018. Out of the 18 targeted cyanotoxins, 14 were detected in bloom-impacted surface water samples; toxins peaked during early-mid September with the highest concentrations for MC-LR (3.8 μg L^-1) and MC-RR (2.9 μg L^-1). Among the 71 field-collected fish from 10 species, 30% had positive detections to at least one cyanotoxin. In positive samples, concentration ranges in fish muscle were as follows for summed microcystins (∑MCs: 0.16-9.2 μg kg^-1), CYN (46-75 μg kg^-1), AP-A (1.1-5.4 μg kg^-1), and AP-B (0.12-5.0 μg kg^-1). To the best of our knowledge, this is one the first reports of anabaenopeptins occurrence in wildlife. The maximum ∑MCs in fish was 1.15-fold higher than the World Health Organization (WHO) daily intake recommendation for adults and nearly equated the derived value for young children. The concentration of CYN was also about 3-fold higher than the limit derived from the human health guideline values.

Interannual and Spatial Variability of Cyanotoxins in the Prespa Lake Area, Greece

The Prespa Lakes area in Greece—comprised partly of lake Great and lake Lesser Prespa and the Vromolimni pond—has a global importance for biodiversity. Although the waters show regular cyanobacteria blooms, assessments of water quality threats are limited. Samples collected in 2012 revealed scattered and low microcystin (MC) concentrations in Great Prespa (<0.2 μg MC L−1) whereas considerable spatial heterogeneity in both total chlorophyll (2.4–93 µg L−1) and MC concentrations (0.04–52.4 µg MC L−1) was detected in Lesser Prespa. In 2013, there was far less spatial variability of MC concentrations in Lesser Prespa (0.4–1.53 µg L−1), however in 2014, increased concentrations were detected near the lakeshore (25–861 µg MC L−1). In Vromolimni pond the MC concentrations were on average 26.6 (±6.4) µg MC L−1 in 2012, 2.1 (±0.3) µg MC L−1 in 2013 and 12.7 (±12.5) µg MC L−1 in 2014. In 2013, no anatoxins, saxitoxins, nor cylindrospermopsins were detected in Lesser Prespa and Vromolimni waters. Tissue samples from carps, an otter and Dalmatian Pelicans contained 0.4–1.9 µg MC g−1 dry weight. These results indicate that cyanotoxins could be a threat to the ecosystem functions of particularly Lesser Prespa and Vromolimni.

Photocatalytic treatment of natural waters. Reality or hype? The case of cyanotoxins remediation

This review compiles recent advances and challenges in the photocatalytic treatment of natural water by analyzing the remediation of cyanotoxins. The review frames the treatment need based on the occurrence, geographical distribution, and legislation of cyanotoxins in drinking water while highlighting the underestimated global risk of cyanotoxins. Next, the fundamental principles of photocatalytic treatment for remediating cyanotoxins and the complex degradation pathway for the most widespread cyanotoxins are presented. The state-of-the-art and recent advances on photocatalytic treatment processes are critically discussed, especially the modification strategies involving TiO₂ and the primary operational conditions that determine the scalability and integration of photocatalytic reactors. The relevance of light sources and light delivery strategies are shown, with emphasis on novel biomimicry materials design. Thereafter, the seldomly-addressed role of water-matrix components is thoroughly and critically explored by including natural organic matter and inorganic species to provide future directions in designing highly efficient strategies and scalable reactors.

Microcystis aeruginosa and M. wesenbergii Were the Primary Planktonic Microcystin Producers in Several Bulgarian Waterbodies (August 2019)

The rising interest in harmful cyanoprokaryote blooms promotes an increase of phycological and ecological research on potentially toxic species and their hazardous substances. The present study aimed to identify the main microcystin (MC) producers and their contribution to the phytoplankton of shallow waterbodies in Bulgaria, applying different methods. The sampling was performed in August 2019 in nine lakes and reservoirs, two of which (reservoirs Kriva Reka and Izvornik 2) were studied for the first time. The high contribution of cyanoprokaryotes to the total species composition and phytoplankton abundance was proved by light microscopic (LM) observations and HPLC analysis of marker pigments. The LM identification of potential MC-producers was supported by PCR amplification of mcyE and mcyB genes. The MCs amounts, detected by HPLC-DAD, varied by sites with a range from undetectable concentrations to 0.46 µg L−1 with only one recorded variant, namely MC-LR. It was found only in the reservoirs Mandra and Durankulak, while toxigenic MC-strains were obtained by PCR from five more waterbodies. Both LM and PCR demonstrated that the MC-producers were Microcystis aeruginosa and M. wesenbergii, despite their occurrence in low amounts (<0.5–5% of the total biomass) when filamentous cyanoprokaryotes dominated.

Distribution of Toxic Cyanobacteria in Volcanic Lakes of the Azores Islands

Eutrophication and global climate change gather advantageous conditions for cyanobacteria proliferation leading to bloom formation and cyanotoxin production. In the Azores, eutrophication is a major concern, mainly in lakes where fertilizers and organic matter discharges have increased nutrient concentration. In this study, we focused on understanding the influence of environmental factors and lake characteristics on (i) cyanobacteria diversity and biomass and (ii) the presence of toxic strains and microcystin, saxitoxin, anatoxin-a, and cylindrospermopsin cyanotoxin-producing genes. Fifteen lakes from the Azores Archipelago were sampled seasonally, environmental variables were recorded in situ, cyanobacteria were analyzed with microscopic techniques, and cyanotoxin-producing genes were targeted through conventional PCR. Statistical analysis (DistLM) showed that lake typology-associated variables (lake’s depth, area, and altitude) were the most explanatory variables of cyanobacteria biomass and cyanotoxin-producing genes presence, although trophic variables (chlorophyll a and total phosphorus) influence species distribution in each lake type. Our main results revealed higher cyanobacteria biomass/diversity, and higher toxicity risk in lakes located at lower altitudes, associated with deep anthropogenic pressures and eutrophication scenarios. These results emphasize the need for cyanobacteria blooms control measures, mainly by decreasing anthropogenic pressures surrounding these lakes, thus decreasing eutrophication. We also highlight the potential for microcystin, saxitoxin, and anatoxin-a production in these lakes, hence the necessity to implement continuous mitigation protocols to avoid environmental and public health toxicity events.

Irrigation of radish (Raphanus sativus L.) with microcystin-enriched water holds low risk for plants and their associated rhizopheric and epiphytic microbiome

Microcystins (MCs) are toxins produced during cyanobacterial blooms. They reach soil and translocated to plants through irrigation of agricultural land with water from MC-impacted freshwater systems. To date we have good understanding of MC effects on plants, but not for their effects on plant-associated microbiota. We tested the hypothesis that MC-LR, either alone or with other stressors present in the water of the Karla reservoir (a low ecological quality and MC-impacted freshwater system), would affect radish plants and their rhizospheric and phyllospheric microbiome. In this context a pot experiment was employed where radish plants were irrigated with tap water without MC-LR (control) or with 2 or 12 μg L^-1 of pure MC-LR (MC2 and MC12), or water from the Karla reservoir amended (12 μg L^-1) or not with MC-LR. We measured MC levels in plants and rhizospheric soil and we determined effects on (i) plant growth and physiology (ii) the nitrifying microorganisms via q-PCR, (ii) the diversity of bacterial and fungal rhizospheric and epiphytic communities via amplicon sequencing. MC-LR and/or Karla water treatments resulted in the accumulation of MC in taproot at levels (480-700 ng g^-1) entailing possible health risks. MC did not affect plant growth or physiology and it did not impose a consistent inhibitory effect on soil nitrifiers. Karla water rather than MC-LR was the stronger determinant of the rhizospheric and epiphytic microbial communities, suggesting the presence of biotic or abiotic stressors, other than MC-LR, in the water of the Karla reservoir which affect microorganisms with a potential role (i.e. pathogens inhibition, methylotrophy) in the homeostasis of the plant-soil system. Overall, our findings suggest that MC-LR, when applied at environmentally relevant concentrations, is not expected to adversely affect the radish-microbiota system but might still pose risk for consumers' health.

Global scanning of cylindrospermopsin: Critical review and analysis of aquatic occurrence, bioaccumulation, toxicity and health hazards

Cylindrospermopsin (CYN), a cyanotoxin produced by harmful algal blooms, has been reported worldwide; however, there remains limited understanding of its potential risks to surface water quality. In the present study, we critically reviewed available literature regarding the global occurrence, bioaccumulation, and toxicity of CYN in aquatic systems with a particular focus on freshwater. We subsequently developed environmental exposure distributions (EEDs) for CYN in surface waters and performed probabilistic environmental hazard assessments (PEHAs) using guideline values (GVs). PEHAs were performed by geographic region, type of aquatic system, and matrix. CYN occurrence was prevalent in North America, Europe, and Asia/Pacific, with lakes being the most common system. Many global whole water EEDs exceeded guideline values (GV) previously developed for drinking water (e.g., 0.5 μg L-1) and recreational water (e.g., 1 μg L-1). GV exceedances were higher in the Asia/Pacific region, and in rivers and reservoirs. Rivers in the Asia/Pacific region exceeded the lowest drinking water GV 73.2% of the time. However, lack of standardized protocols used for analyses was alarming, which warrants improvement in future studies. In addition, bioaccumulation of CYN has been reported in mollusks, crustaceans, and fish, but such exposure information remains limited. Though several publications have reported aquatic toxicity of CYN, there is limited chronic aquatic toxicity data, especially for higher trophic level organisms. Most aquatic toxicity studies have not employed standardized experimental designs, failed to analytically verify treatment levels, and did not report purity of CYN used for experiments; therefore, existing data are insufficient to derive water quality guidelines. Considering such elevated exceedances of CYN in global surface waters and limited aquatic bioaccumulation and toxicity data, further aquatic monitoring, environmental fate and mechanistic toxicology studies are warranted to robustly assess and manage water quality risks to public health and the environment.

Improved Estimations of Nitrate and Sediment Concentrations Based on SWAT Simulations and Annual Updated Land Cover Products from a Deep Learning Classification Algorithm

The agricultural sector and natural resources are heavily interdependent, comprising a coherent but complex system. The soil and water assessment tool (SWAT) is widely used in assessing these interdependencies for regional watershed management. However, long-term simulations of agricultural watersheds are considered as not realistic since they have often been performed assuming constant land use over time and are based on the coarse resolution of the existing global or national data. This work presents the first insights of the synergy among SWAT model and deep learning classification algorithms to provide annually updated and realistic model’s parameterization and simulations. The proposed hybrid modelling approach couples the physical process SWAT model with the versatility of Earth observation data-driven non-linear deep learning algorithms for land use classification (Overall Accuracy (OA) = 79.58% and Kappa = 0.79), giving a strong advantage to decision makers for efficient management planning. A validation case at an agricultural watershed located in Northern Greece is provided to demonstrate their synergistic use to estimate nitrate and sediment concentrations that load in Zazari Lake. The SWAT model has been implemented under two different simulations; one with the use of a static coarse land use map and the other with the use of the annual updated land use maps for three consecutive years (2017–2019). The results indicate that the land use changes affect the final estimations resulting to an enhanced prediction performance of 1% and 2% for sediment and nitrate, respectively, when the annual land use maps are incorporated into SWAT simulations. In this context, a hybrid approach could further contribute to addressing challenges and support a data-centric scheme for informed decision making with regard to environmental and agricultural issues on the river basin scale.

Insight into Unprecedented Diversity of Cyanopeptides in Eutrophic Ponds Using an MS/MS Networking Approach

Man-made shallow fishponds in the Czech Republic have been facing high eutrophication since the 1950s. Anthropogenic eutrophication and feeding of fish have strongly affected the physicochemical properties of water and its aquatic community composition, leading to harmful algal bloom formation. In our current study, we characterized the phytoplankton community across three eutrophic ponds to assess the phytoplankton dynamics during the vegetation season. We microscopically identified and quantified 29 cyanobacterial taxa comprising non-toxigenic and toxigenic species. Further, a detailed cyanopeptides (CNPs) profiling was performed using molecular networking analysis of liquid chromatography-tandem mass spectrometry (LC-MS/MS) data coupled with a dereplication strategy. This MS networking approach, coupled with dereplication, on the online global natural product social networking (GNPS) web platform led us to putatively identify forty CNPs: fourteen anabaenopeptins, ten microcystins, five cyanopeptolins, six microginins, two cyanobactins, a dipeptide radiosumin, a cyclooctapeptide planktocyclin, and epidolastatin 12. We applied the binary logistic regression to estimate the CNPs producers by correlating the GNPS data with the species abundance. The usage of the GNPS web platform proved a valuable approach for the rapid and simultaneous detection of a large number of peptides and rapid risk assessments for harmful blooms.

Limnological Differences in a Two-Basin Lake Help to Explain the Occurrence of Anatoxin-a, Paralytic Shellfish Poisoning Toxins, and Microcystins

Chautauqua Lake, New York, is a two-basin lake with a deeper, cooler, and less nutrient-rich Northern Basin, and a warmer, shallower, nutrient-replete Southern Basin. The lake is populated by a complex mixture of cyanobacteria, with toxigenic strains that produce microcystins, anatoxins, and paralytic shellfish poisoning toxins (PSTs). Samples collected from 24 sites were analyzed for these three toxin classes over four years spanning 2014-2017. Concentrations of the three toxin groups varied widely both within and between years. During the study, the mean and median concentrations of microcystins, anatoxin-a, and PSTs were 91 and 4.0 μg/L, 0.62 and 0.33 μg/L, and 32 and 16 μg/L, respectively. Dihydro-anatoxin was only detected once in Chautauqua Lake, while homo-anatoxin was never detected. The Northern Basin had larger basin-wide higher biomass blooms with higher concentrations of toxins relative to the more eutrophied Southern Basin, however blooms in the North Basin were infrequent. Chlorophyll concentrations and toxins in the two basins were correlated with different sets of environmental and physical parameters, suggesting that implementing controls to reduce toxin loads may require applications focused on more than reductions in cyanobacterial bloom density (e.g., reduction of phosphorus inputs), and that lake limnological factors and morphology are important determinants in the selection of an appropriate management strategy. Chautauqua Lake is a drinking water source and is also heavily used for recreation. Drinking water from Chautauqua Lake is unlikely to be a significant source of exposure to cyanotoxins due to the location of the intakes in the deeper North Basin, where there were generally low concentrations of toxins in open water; however, toxin levels in many blooms exceeded the US Environmental Protection Agency's recreational guidelines for exposure to cyanotoxins. Current cyanotoxin monitoring in Chautauqua Lake is focused on microcystins. However, the occurrence of blooms containing neurotoxic cyanotoxins in the absence of the microcystins indicates this restricted monitoring may not be sufficient when aiming to protect against exposure to cyanotoxins. The lake has a large number of tourist visitors; thus, special care should be taken to prevent recreational exposure within this group.

High Levels of Anabaenopeptins Detected in a Cyanobacteria Bloom from N.E. Spanish Sau-Susqueda-El Pasteral Reservoirs System by LC-HRMS

The appearance of a bloom of cyanobacteria in the Sau-Susqueda-El Pasteral system (River Ter, NE Spain) in the autumn of 2015 has been the most recent episode of extensive bloom detected in Catalonia. This system is devoted mainly to urban supply, regulation of the river, irrigation and production of hydroelectric energy. In fact, it is one of the main supply systems for the metropolitan area of cities such as Barcelona and Girona. An assessment and management plan was implemented in order to minimize the risk associated to cyanobacteria. The reservoir was confined and periodic sampling was carried out. Low and high toxicity was detected by cell bioassays with human cell lines. Additionally, analysis studies were performed by enzyme-linked immunosorbent assay (ELISA) and liquid chromatography–high resolution mass spectrometry (LC–HRMS). A microcystin target analysis and suspect screening of microcystins, nodularins, cylindrosperpmopsin and related cyanobacterial peptides by LC–HRMS were applied. The results for the analysis of microcystins were negative (<0.3 μg/L) in all the surface samples. Only traces of microcystin-LR, -RR and -dmRR were detected by LC–HRMS in a few ng/L from both fractions, aqueous and sestonic. In contrast, different anabaenopeptins and oscillamide Y at unusually high concentrations (µg-mg/L) were observed. To our knowledge, no previous studies have detected these bioactive peptides at such high levels. The reliable identification of these cyanobacterial peptides was achieved by HRMS. Although recently these peptides are detected frequently worldwide, these bioactive compounds have received little attention. Therefore, more studies on these substances are recommended, especially on their toxicity, health risk and presence in water resources.

The Ascidian-Derived Metabolites with Antimicrobial Properties

Among the sub-phylum of Tunicate, ascidians represent the most abundant class of marine invertebrates, with 3000 species by heterogeneous habitat, that is, from shallow water to deep sea, already reported. The chemistry of these sessile filter-feeding organisms is an attractive reservoir of varied and peculiar bioactive compounds. Most secondary metabolites isolated from ascidians stand out for their potential as putative therapeutic agents in the treatment of several illnesses like microbial infections. In this review, we present and discuss the antibacterial activity shown by the main groups of ascidian-derived products, such as sulfur-containing compounds, meroterpenes, alkaloids, peptides, furanones, and their derivatives. Moreover, the direct evidence of a symbiotic association between marine ascidians and microorganisms shed light on the real producers of many extremely potent marine natural compounds. Hence, we also report the antibacterial potential, joined to antifungal and antiviral activity, of metabolites isolated from ascidian-associate microorganisms by culture-dependent methods.

New microginins from cyanobacteria of Greek freshwaters

Cyanobacteria can form extensive blooms in water with concurrent production and release of a large number of chemically diverse and bioactive metabolites, including hazardous toxins. Significant number of the metabolites belongs to non-ribosomal peptides, with unique residues, unusual structures and great potential for biotechnological application. The biosynthetic pathways of the peptides generate tens of variants, but only part of them has been identified. Microginins are an understudied class of cyanobacterial linear peptides with a characteristic decanoic acid derivative amino acid residue in their structure. In this study, cyanobacterial blooms and isolated strains from Greek lakes were analyzed for the presence of microginins by liquid chromatography coupled to hybrid triple quadrupole/linear ion trap mass spectrometer (LC-qTRAP MS/MS). Microginin structures were elucidated based on the obtained fragmentation spectra. A large number of microginins occurred in blooms of Greek freshwaters and the most frequently detected were Microginin FR1 (70% of samples), Microginin T1 (52%), Microginin 565B (52%), Microginin T2 (43%), and Microginin 565A (43%). Additionally, nine cyanobacterial strains i.e. Nostoc oryzae, Synechococcus sp., Microcystis aeruginosa, Microcystis viridis, and five Microcystis sp., were found to produce microginins. Thirty-six new microginin structures were characterized out of fifty-one totally detected variants. This is the first time that such a diversity of microginins is reported to be present in water bodies. Results clearly demonstrate the great metabolomic potential of cyanobacteria that inhabit Greek freshwaters and significantly expand the knowledge of cyanobacterial secondary metabolites with regards to the class of microginins.

Bioprospecting Sponge-Associated Marine Cyanobacteria to Produce Bioactive Compounds

Marine cyanobacteria are considered a prolific source of bioactive natural products with a range of biotechnological and pharmacological applications. However, data on the production of natural compounds from sponge-associated cyanobacteria are scarce. This study aimed to assess the potential of sponge-associated cyanobacteria strains representing different taxonomic groups for the production of bioactive compounds and the biological activity of their extracts. Phylogenetic analysis of sponge-associated cyanobacteria and screening for the presence of genes encoding non-ribosomal peptide synthetases (NRPSs) and polyketide synthases (PKSs) were performed. Methanol extracts of the sponge-associated strains were analyzed for cyanotoxin production and tested for antioxidant activity and cytotoxic activity against several human cancer cell lines and pathogenic bacteria. PKS were detected in all sponge-associated strains examined, indicating the metabolic potential of the isolates. PKS genes were more ubiquitous than NRPS genes. Cyanotoxins (i.e., cylindrospermopsin, anatoxin-a, nodularin, and microcystins) were not detected in any of the sponge-associated cyanobacterial strains. Strains belonging to Leptothoe, Pseudanabaena, and Synechococcus were found to have activity mainly against Staphylococcus aureus. In addition, sponge-associated Leptothoe strains (TAU-MAC 0915, 1015, 1115, and 1215) were found to be highly cytotoxic and in most cases more effective against human cancer cell lines than against normal cells. Extracts with the most promising bioactivity deserve further investigation in order to isolate and identify the bioactive molecule(s).

¿Son las cianotoxinas un peligro emergente en las aguas de baño y de abastecimiento?

El cambio ambiental global incrementa la proliferación de cianobacterias y la liberación de cianotoxinas muy peligrosas en aguas de abastecimiento y recreo. Estas citotoxinas pueden ocasionar graves problemas de salud, por lo que se hace necesario incrementar el control, especialmente en las aguas de baño, para evitar eventos indeseables en la población. Se analizaron cianobacterias productoras de toxinas y cianotoxinas (microcistinas) en muestras de columnas agua y de la superficie de las zonas de baño autorizadas por la Comunidad de Madrid, así como en embalses para abastecimiento de agua de consumo. Los muestreos se realizaron en los meses desde mayo a octubre de 2018. De cada lugar se realizaron, al menos, dos determinaciones en diferentes tiempos. Con excepción de la Playa de Presillas (Rascafría), en las zonas muestreadas se han detectado cianobacterias productoras de cianotoxinas, así como niveles de microcistina mayores de 1μg/L, considerado perjudicial para la salud. Los máximos tanto de microcistinas como de cianobacterias se encuentran en los meses de julio y agosto. El estudio confirma que hay presencia de microcistinas en concentraciones tóxicas en época de baño. Se hace necesario establecer controles de las cianotoxinas estableciendo un sistema de aviso de aparición de los blooms tóxicos en aguas de recreo.

Ecological Connectivity in Two Ancient Lakes: Impact Upon Planktonic Cyanobacteria and Water Quality

The ancient lakes Mikri Prespa and Megali Prespa are located in SE Europe at the transnational triangle and are globally recognized for their ecological significance. They host hundreds of flora and fauna species, and numerous types of habitat of conservational interest. They also provide a variety of ecosystem services. Over the last few decades, the two lakes have been interconnected through a surface water channel. In an attempt to explore whether such a management practice might alter the ecological properties of the two lakes, we investigated a series of community metrics for phytoplankton by emphasizing cyanobacteria. Our results demonstrate that the cyanobacterial metacommunity structure was affected by directional hydrological connectivity and high dispersal rates, and to a lesser extent, by cyanobacterial species sorting. Cyanobacterial alpha diversity was twofold in the shallow upstream Lake Mikri Prespa (Simpson index average value: 0.70) in comparison to downstream Lake Megali Prespa (Simpson index average value: 0.37). The cyanobacterial assemblage of the latter was only a strict subset of that in Mikri Prespa. Similarly, beta diversity components clearly showed a homogenization of cyanobacteria, supporting the hypothesis that water flow enhances fluvial translocation of potentially toxic and bloom-forming cyanobacteria. Degrading of the water quality in the Lake Megali Prespa in anticipation of improving that of the Lake Mikri Prespa is an issue of great concern for the Prespa lakes’ protection and conservation.

Diversity, Cyanotoxin Production, and Bioactivities of Cyanobacteria Isolated from Freshwaters of Greece

Cyanobacteria are a diverse group of photosynthetic Gram-negative bacteria that produce an array of secondary compounds with selective bioactivity against a broad spectrum of organisms and cell lines. In this study, 29 strains isolated from freshwaters in Greece were classified using a polyphasic approach and assigned to Chroococcales, Synechococcales, and Nostocales, representing 11 genera and 17 taxa. There were good agreements between 16S ribosomal RNA (rRNA)-cpcBA-internal genetic spacer (IGS) characterization and morphological features, except for the Jaaginema-Limnothrix group which appears intermixed and needs further elucidation. Methanol extracts of the strains were analyzed for cyanotoxin production and tested against pathogenic bacteria species and several cancer cell lines. We report for the first time a Nostoc oryzae strain isolated from rice fields capable of producing microcystins (MCs) and a Chlorogloeopsis fritschii strain isolated from the plankton of a lake, suggesting that this species may also occur in freshwater temperate habitats. Strains with very high or identical 16S rRNA gene sequences displayed different antibacterial and cytotoxic activities. Extracts from Synechococcus cf. nidulans showed the most potent antibacterial activity against Staphylococcus aureus, whereas Jaaginema sp. strains exhibited potent cytotoxic activities against human colorectal adenocarcinoma and hepatocellular carcinoma cells. Jaaginema Thessaloniki Aristotle University Microalgae and Cyanobacteria (TAU-MAC) 0110 and 0210 strains caused pronounced changes in the actin network and triggered the formation of numerous lipid droplets in hepatocellular carcinoma and green monkey kidney cells, suggesting oxidative stress and/or mitochondrial damage leading to apoptosis.