More than just an eagle killer: The freshwater cyanobacterium Aetokthonos hydrillicola produces highly toxic dolastatin derivatives.

Cyanobacteria are infamous producers of toxins. While the toxic potential of planktonic cyanobacterial blooms is well documented, the ecosystem level effects of toxigenic benthic and epiphytic cyanobacteria are an understudied threat. The freshwater epiphytic cyanobacterium Aetokthonos hydrillicola has recently been shown to produce the "eagle killer" neurotoxin aetokthonotoxin (AETX) causing the fatal neurological disease vacuolar myelinopathy. The disease affects a wide array of wildlife in the southeastern United States, most notably waterfowl and birds of prey, including the bald eagle. In an assay for cytotoxicity, we found the crude extract of the cyanobacterium to be much more potent than pure AETX, prompting further investigation. Here, we describe the isolation and structure elucidation of the aetokthonostatins (AESTs), linear peptides belonging to the dolastatin compound family, featuring a unique modification of the C-terminal phenylalanine-derived moiety. Using immunofluorescence microscopy and molecular modeling, we confirmed that AEST potently impacts microtubule dynamics and can bind to tubulin in a similar matter as dolastatin 10. We also show that AEST inhibits reproduction of the nematode Caenorhabditis elegans. Bioinformatic analysis revealed the AEST biosynthetic gene cluster encoding a nonribosomal peptide synthetase/polyketide synthase accompanied by a unique tailoring machinery. The biosynthetic activity of a specific N-terminal methyltransferase was confirmed by in vitro biochemical studies, establishing a mechanistic link between the gene cluster and its product.

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.

Cylindrospermopsin exposure promotes redox unbalance and tissue damage in the liver of Poecilia reticulata, a neotropical fish species.

There is a growing concern regarding the adverse risks exposure to cylindrospermopsin (CYN) might exert on animals and humans. However, data regarding the toxicity of this cyanotoxin to neotropical fish species are scarce. Using the fish species Poecilia reticulata, the influence of CYN concentrations equal to and above the tolerable for drinking water may produce on liver was determined by assessing biomarkers of antioxidant defense mechanisms and correlated to qualitative and semiquantitative histopathological observations. Adult females were exposed to 0.0 (Control); 0.5, 1 and 1.5 µg/L pure CYN for 24 or 96 hr, in triplicate. Subsequently the livers were extracted for biochemical assays and histopathological evaluation. Catalase (CAT) activity was significantly increased only by 1.5 µg/L CYN-treatment, at both exposure times. Glutathione -S-transferase (GST) activity presented a biphasic response for both exposure times. It was markedly decreased after exposure by 0.5 µg/L CYN treatment but significantly elevated by 1.5 µg/L CYN treatment. All CYN treatments produced histopathological alterations, as evidenced by hepatocyte cords degeneration, steatosis, inflammatory infiltration, melanomacrophage centers, vessel congestion, and areas with necrosis. Further, an IORG >35 was achieved for all treatments, indicative of the presence of severe histological alterations in P. reticulata hepatic parenchyma and stroma. Taken together, data demonstrated evidence that CYN-induced hepatotoxicity in P. reticulata appears to be associated with an imbalance of antioxidant defense mechanisms accompanied by histopathological liver alterations. It is worthy to note that exposure to low environmentally-relevant CYN concentrations might constitute a significant risk to health of aquatic organisms.

Blue Green Algae.

Blue green algae cyanotoxins have become increasingly more prevalent due to environmental, industrial, and agricultural changes that promote their growth into harmful algal blooms. Animals are usually exposed via water used for drinking or bathing, though specific cases related to equines are very limited. The toxic dose for horses has not been determined, and currently only experimental data in other animals can be relied upon to aid in case interpretation and treatment. Treatment is mostly limited to supportive care, and preventative control methods to limit exposures are more likely to aid in animal health until more research has been performed.

Diazotrophy modulates cyanobacteria stoichiometry through functional traits that determine bloom magnitude and toxin production.

Harmful cyanobacterial blooms are an increasing threat to water quality. The interactions between two eco-physiological functional traits of cyanobacteria, diazotrophy (nitrogen (N)-fixation) and N-rich cyanotoxin synthesis, have never been examined in a stoichiometric explicit manner. We explored how a gradient of resource N:phosphorus (P) affects the biomass, N, P stoichiometry, light-harvesting pigments, and cylindrospermopsin production in a N-fixing cyanobacterium, Aphanizomenon. Low N:P Aphanizomenon cultures produced the same biomass as populations grown in high N:P cultures. The biomass accumulation determined by carbon, indicated low N:P Aphanizomenon cultures did not have a N-fixation growth tradeoff, in contrast to some other diazotrophs that maintain stoichiometric N homeostasis at the expense of growth. However, N-fixing Aphanizomenon populations produced less particulate cylindrospermopsin and had undetectable dissolved cylindrospermopsin compared to non-N-fixing populations. The pattern of low to high cyanotoxin cell quotas across an N:P gradient in the diazotrophic cylindrospermopsin producer is similar to the cyanotoxin cell quota response in non-diazotrophic cyanobacteria. We suggest that diazotrophic cyanobacteria may be characterized into two broad functional groups, the N-storage-strategists and the growth-strategists, which use N-fixation differently and may determine patterns of bloom magnitude and toxin production in nature.

Liquid chromatography-high-resolution tandem mass spectrometry of anatoxins, including new conjugates and reduction products.

Anatoxins (ATXs) are a potent class of cyanobacterial neurotoxins for which only a handful of structural analogues have been well characterized. Here, we report the development of an LC-HRMS/MS method for the comprehensive detection of ATXs. Application of this method to samples of benthic cyanobacterial mats and laboratory cultures showed detection of several new ATXs. Many of these result from nucleophilic addition to the olefinic bond of the α,ß-unsaturated ketone functional group of anatoxin-a (ATX) and homoanatoxin-a (hATX), analogous to the conjugation chemistry of microcystins, which contain similar α,ß-unsaturated amide functionality. Conjugates with glutathione, γ-glutamylcysteine, methanethiol, ammonia, methanol and water were detected, as well as putative C-10 alcohol derivatives. Structural confirmation was obtained by simple and selective analytical-scale semisynthetic reactions starting from available ATX standards. Methanol, water and ammonia conjugates were found to result primarily from sample preparation. Reduction products were found to result from enzymatic reactions occurring primarily after cell lysis in laboratory cultures of Kamptonema formosum and Cuspidothrix issatschenkoi. The relative contributions of the identified analogues to the anatoxin profiles in a set of 22 benthic-cyanobacterial-mat field samples were estimated, showing conjugates to account for up to 15% of total ATX peak area and 10-hydroxyanatoxins up to 38%. The developed methodology, new analogues and insight into the chemical and enzymatic reactivity of ATXs will enable a more comprehensive study of the class than possible previously.

Chrysosporum ovalisporum is synonymous with the true-branching cyanobacterium Umezakia natans (Nostocales/Aphanizomenonaceae).

True branching is a facultative characteristic only known from two cyanobacteria in the Aphanizomenonaceae, Umezakia natans and Dolichospermum brachiatum. In both cases, its expression has been associated with environmental stress, and its practical use as a diacritical feature has been previously evaluated. In this study, we undertook further evaluation of the phylogeny of Umezakia natans and its relationship to Chrysosporum ovalisporum as a previous study suggested the two were potentially congeneric. We used combined morphological, phylogenetic, and phylogenomic approaches to determine their relatedness using new strains available from a broad geographic range. Phylogenetic analysis based on 16S rRNA gene sequences showed that Australian C. ovalisporum and Japanese U. natans strains clustered together with accessions of C. ovalisporum originating from Australia, Israel, and Spain, with high p-distance similarity values (99.5%-99.9%). Additionally, differences between the two species in the 16S-23S ITS region was low (0%-2.5%). The average nucleotide identity of the U. natans and C. ovalisporum strains was also high (ANI of > 99.5 and AF > 0.9) and supported a genus-level separation from Chrysosporum bergii (83 ANI between clusters). Furthermore, in culture, strains of both species grown in vitamin-free media showed facultative true branching, a feature not previously known in C. ovalisporum. Collectively, the results support unification of C. ovalisporum and U. natans according to the principle of priority as Umezakia ovalisporum.

Sub-chronic exposure to waterborne extracellular microcystin-LR impairs calcium homeostasis in rainbow trout.

Fish mortality is associated with harmful algal blooms, although whether toxicity is related directly to the presence of cyanotoxins or the prevailing water chemistry remains unclear. Similarly, while planktivorous fish may be exposed to toxin through the diet, the hazard posed by waterborne extracellular toxin to carnivorous fish is less well understood. In this study rainbow trout (Oncorhynchus mykiss) were exposed for up to 28 d to waterborne microcystin-LR at nominal concentrations of 1.5 and 50 µg L-1 (measured values 2 and 49 µg L-1, respectively). The former represents the Canadian drinking water guideline, and the latter an elevated environmental level. This study hypothesised that waterborne toxin exposure would specifically impact gill function, and given the importance of this tissue in freshwater fish ion regulation, effects on plasma ions and branchial ion transporter activity would be observed. Microcystin-LR exposure resulted in a significant and persistent hypocalcaemia at the higher exposure concentration, but plasma sodium and branchial activities of the sodium/potassium ATPase, proton ATPase and calcium ATPase enzymes remained unaffected. An in vitro assessment failed to show any effect of microcystin-LR on branchial calcium ATPase activity even at exposure concentrations as high as 1000 µg L-1. A transient increase in hepatic alkaline phosphatase activity was also observed at 49 µg L-1, but there were no effects of toxin exposure on branchial or hepatic lactate dehydrogenase activity. These results suggest that microcystin-LR exposure does not have a general effect on ion regulation, but instead produces a novel and specific impact on calcium metabolism in rainbow trout, although the mechanism underlying this effect remains unknown.

Detection and Characterization of Nodularin by Using Label-Free Surface-Enhanced Spectroscopic Techniques.

Nodularin (NOD) is a potent toxin produced by Nodularia spumigena cyanobacteria. Usually, NOD co-exists with other microcystins in environmental waters, a class of cyanotoxins secreted by certain cyanobacteria species, which makes identification difficult in the case of mixed toxins. Herein we report a complete theoretical DFT-vibrational Raman characterization of NOD along with the experimental drop-coating deposition Raman (DCDR) technique. In addition, we used the vibrational characterization to probe SERS analysis of NOD using colloidal silver nanoparticles (AgNPs), commercial nanopatterned substrates with periodic inverted pyramids (KlariteTM substrate), hydrophobic Tienta® SpecTrimTM slides, and in-house fabricated periodic nanotrenches by nanoimprint lithography (NIL). The 532 nm excitation source provided more well-defined bands even at LOD levels, as well as the best performance in terms of SERS intensity. This was reflected by the results obtained with the KlariteTM substrate and the silver-based colloidal system, which were the most promising detection approaches, providing the lowest limits of detection. A detection limit of 8.4 × 10-8 M was achieved for NOD in solution by using AgNPs. Theoretical computation of the complex vibrational modes of NOD was used for the first time to unambiguously assign all the specific vibrational Raman bands.

Can correlational analyses help determine the drivers of microcystin occurrence in freshwater ecosystems? A meta-analysis of microcystin and associated water quality parameters.

Microcystin (MC) is a toxic secondary metabolite produced by select cyanobacteria that threatens aquatic and terrestrial organisms over a diverse range of freshwater systems. To assess the relationship between environmental parameters and MC, researchers frequently utilize correlational analyses. This statistical methodology has proved useful when summarizing complex water quality monitoring datasets, but the correlations between select parameters and MC have been documented to vary widely across studies and systems. Such variation within the peer-reviewed literature leaves uncertainty for resource managers when developing a MC monitoring program. The objective of this research is to determine if correlational analyses between environmental parameters and MC are helpful to resource managers desiring to understand the drivers of MC. Environmental (i.e., physical, chemical, and biological) and MC correlation data were retrieved from an estimated 2,643 waterbodies (largely from the north temperate region) and synthesized using a Fisher's z meta-analysis. Common water quality parameters, such as chlorophyll, temperature, and pH, were positively correlated with MC, while transparency was negatively correlated. Interestingly, 12 of the 15 studied nitrogen parameters, including total nitrogen, were not significantly correlated with MC. In contrast, three of the four studied phosphorus parameters, including total phosphorus, were positively related to MC. Results from this synthesis quantitatively reinforces the usefulness of commonly measured environmental parameters to monitor for conditions related to MC occurrence; however, correlational analyses by themselves are often ineffective and considering what role a parameter plays in the ecology of cyanobacterial blooms in addition to MC production is vital.

The mechanism of ß-N-methylamino-l-alanine inhibition of tRNA aminoacylation and its impact on misincorporation.

ß-N-methylamino-l-alanine (BMAA) is a nonproteinogenic amino acid that has been associated with neurodegenerative diseases, including amyotrophic lateral sclerosis (ALS) and Alzheimer's disease (AD). BMAA has been found in human protein extracts; however, the mechanism by which it enters the proteome is still unclear. It has been suggested that BMAA is misincorporated at serine codons during protein synthesis, but direct evidence of its cotranslational incorporation is currently lacking. Here, using LC-MS-purified BMAA and several biochemical assays, we sought to determine whether any aminoacyl-tRNA synthetase (aaRS) utilizes BMAA as a substrate for aminoacylation. Despite BMAA's previously predicted misincorporation at serine codons, following a screen for amino acid activation in ATP/PPi exchange assays, we observed that BMAA is not a substrate for human seryl-tRNA synthetase (SerRS). Instead, we observed that BMAA is a substrate for human alanyl-tRNA synthetase (AlaRS) and can form BMAA-tRNAAla by escaping from the intrinsic AlaRS proofreading activity. Furthermore, we found that BMAA inhibits both the cognate amino acid activation and the editing functions of AlaRS. Our results reveal that, in addition to being misincorporated during translation, BMAA may be able to disrupt the integrity of protein synthesis through multiple different mechanisms.

Highlighting the promise of qPCR-based environmental monitoring: response of the ribosomal RNA:DNA ratio of calanoid copepods to toxic cyanobacteria.

Calanoid copepods are integral to aquatic food webs and may drive the bioaccumulation of toxins and heavy metals, spread of infectious diseases, and occurrence of toxic cyanobacterial harmful algal blooms (HABs) in freshwater aquatic systems. However, interrelationships between copepod and cyanobacterial population dynamics and ecophysiology remain unclear. Insights into these relationships are important to aquatic resource management, as they may help guide mitigation efforts. We developed a calanoid copepod qPCR assay to investigate how copepod abundance and physiological status relate to the abundance of cyanobacteria and the concentration of total microcystin in a HAB-prone freshwater multi-use eutrophic lake. Through in silico and in vitro validation of primers and analyses of time series, we demonstrate that our assay can be used as a reliable tool for environmental monitoring. Importantly, copepod RNA:DNA ratios on and shortly after the day when microcystin concentration was at its highest within the lake were not significantly lower (or higher) than before or after this period, suggesting that copepods may have been tolerant of microcystin levels observed and capable of perpetuating bloom events by consuming competitors of toxic cyanobacteria.

DNA damage induced by cylindrospermopsin on different tissues of the biomonitor fish Poecilia reticulata.

The cyanotoxin cylindrospermopsin (CYN) is the second biggest cause of poisoning worldwide, both in humans and animals. Although CYN primarily affects the aquatic environments and can be absorbed in fishes by multiple routes, data reporting its toxicity and mechanism of action are still scarce in this group. Using P. reticulata as model species, it was evaluated whether CYN promotes mutagenic and genotoxic effects in different fish target tissues. Adult females were exposed in a static way to 0 (control), 0.5, 1.0, and 1.5 µg L-1 of pure CYN for 24 and 96 hours. For the first time, DNA damage was detected in fish brain after CYN exposition. In brain cells, a concentration-response DNA damage was observed for both exposure times, suggesting a direct or indirect action of CYN in neurotoxicity. For the liver cells, 96 hours caused an increase in DNA damage, as well the highest percentage of DNA in the tail was reached when used 1.5 µg L-1 of CYN. In peripheral blood cells, an increase in DNA damage was observed for all tested concentrations after 96 hours. In erythrocytes, micronuclei frequency was higher at 1.5 µg L-1 treatment while the erythrocyte nuclear abnormalities (ENA) frequency was significantly higher even at the lowest CYN concentration. Such data demonstrated that acute exposition to CYN promotes genotoxicity in the brain, liver, and blood cells of P. reticulata, as well mutagenicity in erythrocytes. It rises an alert regarding to the toxic effects of CYN for aquatic organisms as well as for human health.

Cyanobacteria, cyanotoxins, and their histopathological effects on fish tissues in Fehérvárcsurgó reservoir, Hungary.

Cyanobacteria are important members of lake plankton, but they have the ability to form blooms and produce cyanotoxins and thus cause a number of adverse effects. Freshwater ecosystems around the world have been investigated for the distribution of cyanobacteria and their toxins and the effects they have on the ecosystems. Similar research was performed on the Fehérvárcsurgó reservoir in Hungary during 2018. Cyanobacteria were present and blooming, and the highest abundance was recorded in July (2,822,000 cells/mL). The species present were Aphanizomenon flos-aquae, Microcystis flos-aquae, Microcystis wesenbergii, Cuspidothrix issatschenkoi, Dolichospermum flos-aquae, and Snowella litoralis. In July and September, the microcystin encoding gene mcyE and the saxitoxin encoding gene sxtG were amplified in the biomass samples. While a low concentration of microcystin-RR was found in one water sample from July, analyses of Abramis brama and Carassius gibelio caught from the reservoir did not show the presence of the investigated microcystins in the fish tissue. However, several histopathological changes, predominantly in gills and kidneys, were observed in the fish, and the damage was more severe during May and especially July, which coincides with the increase in cyanobacterial biomass during the summer months. Cyanobacteria may thus have adverse effects in this ecosystem.

Physical drivers facilitating a toxigenic cyanobacterial bloom in a major Great Lakes tributary.

The Maumee River is the primary source for nutrients fueling seasonal Microcystis-dominated blooms in western Lake Erie's open waters though such blooms in the river are infrequent. The river also serves as source water for multiple public water systems and a large food services facility in northwest Ohio, USA. On 20 September 2017, an unprecedented bloom was reported in the Maumee River estuary within the Toledo metropolitan area, which triggered a recreational water advisory. Here we (1) explore physical drivers likely contributing to the bloom's occurrence, and (2) describe the toxin concentration and bacterioplankton taxonomic composition. A historical analysis using ten-years of seasonal river discharge, water level, and local wind data identified two instances when high-retention conditions occurred over ≥10 days in the Maumee River estuary: in 2016 and during the 2017 bloom. Observation by remote sensing imagery supported the advection of cyanobacterial cells into the estuary from the lake during 2017 and the lack of an estuary bloom in 2016 due to a weak cyanobacterial bloom in the lake. A rapid-response survey during the 2017 bloom determined levels of the cyanotoxins, specifically microcystins, in excess of recreational contact limits at sites within the lower 20 km of the river while amplicon sequencing found these sites were dominated by Microcystis. These results highlight the need to broaden our understanding of physical drivers of cyanobacterial blooms within the interface between riverine and lacustrine systems, particularly as such blooms are expected to become more prominent in response to a changing climate.

Degradation of microcystin-LR and cylindrospermopsin by continuous flow UV-A photocatalysis over immobilised TiO2.

The increasing presence of freshwater toxins have brought new challenges to preserve water quality due to their potential impact on the environment and human health. Two commonly occurring cyanotoxins, microcystin-LR and cylindrospermopsin, with different physico-chemical properties were used to evaluate the efficiency of photocatalysis using a continuous-flow reactor with immobilized TiO2 on glass tubes and UV-A light. The effect of flow rate and hydrogen peroxide addition on the efficiency of cyanotoxin removal were evaluated. An analysis of the effects on microcystin-LR removal efficiency showed that low flow rates (1 mL/min) and high H2O2 concentrations (120 mg/L) were needed to provide effective degradation. Up to 27.9% and 39.1% removal of MC-LR and CYN, respectively were achieved by UV-A/TiO2 after a single pass through the reactor. A slight increase of the removal of both cyanotoxins was observed when they were in a mixture (35.5% of MC-LR and 51.3% of CYN). The addition of H2O2 to the UV/TiO2 system led to an average removal enhancement of 92.6% of MC-LR and of 29.5% of CYN compared to the UV/TiO2 system. Photolysis assisted by H2O2 degraded MC-LR by up to 77.7%. No significant removal (<10%) was observed by photolysis alone or physical adsorption. This study presents a proof-of-principle that demonstrates the feasibility for this technology to be integrated in large-scale applications.

Novel Microcystins from Planktothrix prolifica NIVA-CYA 544 Identified by LC-MS/MS, Functional Group Derivatization and 15N-labeling.

Microcystins are cyclic heptapeptides from cyanobacteria that are potent inhibitors of protein phosphatases and are toxic to animals and humans. At present, more than 250 microcystin variants are known, with variants reported for all seven peptide moieties. While d-glutamic acid (d-Glu) is highly-conserved at position-6 of microcystins, there has been only one report of a cyanobacterium (Anabaena) producing microcystins containing l-Glu at the variable 2- and 4-positions. Liquid chromatography-mass spectrometry analyses of extracts from Planktothrix prolifica NIVA-CYA 544 led to the tentative identification of two new Glu-containing microcystins, [d-Asp3]MC-ER (12) and [d-Asp3]MC-EE (13). Structure determination was aided by thiol derivatization of the Mdha7-moiety and esterification of the carboxylic acid groups, while 15N-labeling of the culture and isotopic profile analysis assisted the determination of the number of nitrogen atoms present and the elemental composition of molecular and product-ions. The major microcystin analog in the extracts was [d-Asp3]MC-RR (1). A microcystin with an unprecedented high-molecular-mass (2116 Da) was also detected and tentatively identified as a sulfide-linked conjugate of [d-Asp3]MC-RR (15) by LC-HRMS/MS and sulfide oxidation, together with its sulfoxide (16) produced via autoxidation. Low levels of [d-Asp3]MC-RW (14), [d-Asp3]MC-LR (4), [d-Asp3,Mser7]MC-RR (11), [d-Asp3]MC-RY (17), [d-Asp3]MC-RF (18), [d-Asp3]MC-RR-glutathione conjugate (19), and [d-Asp3]MC-RCit (20), the first reported microcystin containing citrulline, were also identified in the extract, and an oxidized derivative of [d-Asp3]MC-RR and the cysteine conjugate of 1 were partially characterized.

Potential of biological approaches for cyanotoxin removal from drinking water: A review.

Biological treatment of cyanotoxins has gained much importance in recent decades and holds a promise to work in coordination with various physicochemical treatments. In drinking water treatment plants (DWTPs), effective removal of cyanotoxins with reduced toxicity is a primary concern. Commonly used treatments, such as ozonation, chlorination or activated carbon, undergo significant changes in their operating conditions (mainly dosage) to counter the variation in different environmental parameters, such as pH, temperature, and high cyanotoxin concentration. Presence of metal ions, natural organic matter (NOM), and other chemicals demand higher dosage and hence affect the activation energy to efficiently break down the cyanotoxin molecule. Due to these higher dose requirements, the treatment leads to the formation of toxic metabolites at a concentration high enough to break the guideline values. Biological methods of cyanotoxin removal proceed via enzymatic pathway where the protein-encoding genes are often responsible for the compound breakdown into non-toxic metabolites. However, in contrast to the chemical treatment, the biological processes advance at a much slower kinetic rate, predominantly due to a longer onset period (high lag phase). In fact, more than 90% of the studies reported on the biological degradation of the cyanotoxins attribute the biodegradation to the bacterial suspension. This suspended growth limits the mass transfer kinetics due to the presence of metal ions, NOMs and, other oxidizable matter, which further prolongs the lag phase and makes biological process toxic-free, albeit less efficient. In this context, this review attempts to bring out the importance of the attached growth mechanism, in particular, the biofilm-based treatment approaches which can enhance the biodegradation rate.

Genetic toxicity of water contaminated by microcystins collected during a cyanobacteria bloom.

Microcystin-LR (MCLR) is a toxin mainly produced by Microcystis aeruginosa, cyanobacteria most commonly found in eutrophic environments. Cyanobacteria blooms have affected Salto Grande reservoir (Americana, State of São Paulo/Brazil) for several decades, often observed during periods of drought. In this study, the genotoxic effects of MCLR (95% purity) and water samples contaminated by this toxin were evaluated during cyanobacteria bloom using assays with the test organism Allium cepa. The results showed genotoxic action for pure microcystin and cytotoxic, genotoxic and mutagenic action for water samples collected during flowering. Chromosomal aberration assays have shown that MCLR induces chromosomal breaks that persist in the daughter cells as MN. Therefore, it is possible to infer a clastogenic action for this toxin. The MCLR present in the environmental samples was shown to be more cytogenotoxic for the cells than the different concentrations tested in this study with the pure substance. This amplified toxic action can be related to a synergistic effect between the MCLR and other compounds present in the environmental samples. The genotoxicity studies with MCLR show inconsistent and inconclusive results, so this toxin needs to be better investigated in order to obtain further information about the action mode of it is on the biological system.

Simple and practical on-site treatment of high microcystin levels in water using polypropylene plastic.

Microcystin (MC) is a hepatotoxin produced by various cyanobacteria during harmful algal blooms (HAB's) in freshwater environments. Advanced treatment methods can remove MC from drinking water, but are costly and do not address recreational water exposure and ecosystem health concerns. Here we investigate the feasibility of utilizing plastics as a MC-adsorbing material, for use in water resources used for recreation, agriculture, aquaculture and drinking water. Water containing 20 µg/L MC-LR was exposed to polypropylene (PP) plastic for a six-day period at varying temperatures (22, 37, 65°C). Water samples were then collected at 0, 1, 2, and 6 hour-intervals to examine short term treatment feasibility. Samples were also taken at 24 hours, 3 days, and 6 days to determine long-term treatment effectiveness. MC concentrations were analyzed using ELISA. Results showed a maximal reduction of nearly 70% of MC-LR after a 6-day treatment with PP at 65°C. Temperature enhanced MC-LR reduction over a 6-day period: 70% reduction at 65°C; 50% at 37°C; 38% at 22°C. We propose an inexpensive intervention strategy which can be deployed rapidly on-site in various source waters, including in resource-limited settings. During the high peak of HAB season, the strategy can be applied in source waters, alleviating water treatment burden for treatment plants, lowering treatment costs and reducing chemical usage.