Effects of enteric bacterial and cyanobacterial lipopolysaccharides, and of microcystin-LR, on glutathione S-transferase activities in zebra fish (Danio rerio)

Establishing a Zebrafish Model for Borrelia burgdorferi Infection Using Immersion and Microinjection Methods

Borrelia burgdorferi is the spirochetal bacterium that causes Lyme disease. Even though antimicrobial sensitivity of B. burgdorferi has been widely studied, there is still a need to develop an affordable, practical, high-throughput in vivo model which can be used to find effective antibiotic therapies, especially for the recently discovered persister and biofilm forms. Here, we describe the immersion and microinjection methods to introduce B. burgdorferi spirochetes into zebrafish larvae. The B. burgdorferi-zebrafish model can be produced by immersing 5-day post-fertilization (dpf) zebrafish in a B. burgdorferi culture, or by injecting B. burgdorferi into the hindbrain of zebrafish at 28 h post-fertilization (hpf). To demonstrate that B. burgdorferi indeed infect the fish, nested polymerase chain reaction (PCR), reverse transcription PCR (RT-PCR), live fluorescence imaging, histological staining, and wholemount immunohistochemical (IHC) methods can be used on B. burgdorferi-infected zebrafish.

Analyzing eutrophication and harmful algal bloom dynamics in a deep Mediterranean hypereutrophic reservoir

Excessive point and non-point nutrient loadings accompanied with elevated temperatures have increased the prevalence of harmful algal bloom (HAB). HABs pose significant environmental and public health concerns, particularly for inland freshwater systems. In this study, the eutrophication and HAB dynamics in the Qaraoun Reservoir, a hypereutrophic deep monomictic reservoir suffering from poor water quality, were assessed. The reservoir was mostly phosphorus limited, and large algal particulates dominated light attenuation in the water column. During bloom events, surface chlorophyll-a concentrations increased up to 961.3 µg/L, while surface concentrations of ammonia and ortho-phosphate were rapidly depleted; surface dissolved oxygen reached supersaturation levels and surface pH levels were up to 3 units higher than those measured in the hypolimnion. Meanwhile, measured Microcystin-LR toxin concentrations in the reservoir exceeded the World Health Organization 1 μg/L provisional guideline 45% of the times. Yet, the results showed that most of the toxins were intra-cellular, suggesting that they decayed rapidly when released into the reservoir. Results from a random forests ensemble model indicated that tracking the changes in surface dissolved oxygen levels, ammonium, ortho-phosphate, and pH can be an effective program towards predicting the reservoir's trophic state and algae blooms.

Intrinsic mechanisms underlying the highly efficient removal of bacterial endotoxin and related risks in tailwater by dielectric barrier discharge plasma

Endotoxin is widely present in aquatic environments and can induce adverse health effects. In this study, dielectric barrier discharge (DBD) plasma was used to remove bacterial endotoxin from the tailwater of a wastewater treatment plant. The removal efficiency of total endotoxin activity was up to 92% with low electrical energy consumption (0.43 J mL^-1%^-1) after 180 s of the DBD plasma treatment, which was better than other previously reported methods. In the early stage of DBD plasma oxidation, the expression of genes related to cell morphology and bacterial antioxidant enzyme synthesis was distinctly down-regulated, suggesting that cell integrity was destroyed, leading to endotoxin release into the solution. Additionally, endotoxin synthesis in the cells was suppressed. The endotoxin in the solution was effectively removed by ·OH, ¹O₂, and O₂·^-generated by the DBD plasma, with second-order reaction rates of 2.69 × 10¹⁰, 2.20 × 10⁷, and 8.60 × 10⁸ mol^-1 L s^-1, respectively. The core toxic component of endotoxin (lipid A) was attacked by these strong oxidative species, generating smaller molecular fragments with low toxicity. Consequently, the inflammatory factors IL-6, IL-β, and TNF-α of endotoxin decreased by 3.4-4.8 folds after the DBD plasma treatment, implying that the health risks posed by endotoxin were greatly reduced. This study revealed the intrinsic mechanisms of the highly efficient removal of bacterial endotoxin by DBD plasma oxidation.

Effect of Dietary Lactobacillus casei on Physiometabolic Responses and Liver Histopathology in Common Carp (Cyprinus carpio) After Exposure to Iron Oxide Nanoparticles

A 60-day feeding trial was performed to assess the dietary effect of Lactobacillus casei as a probiotic supplement on some serum biochemical parameters and liver histopathology in common carp fry after exposure to iron oxide nanoparticles (IoNPs). Six treatments were prepared as follows: control (no IoNP exposure and no dietary probiotic), P6: 10⁶ CFU/g probiotic diet, P7: 10⁷ CFU/g probiotic diet, NPs: 0.15 mg/l IoNPs, NPs + P6: 0.15 mg/l IoNPs with 10⁶ CFU/g probiotic diet, and NPs + P7: 0.15 mg/l IoNPs with 10⁷ CFU/gprobiotic diet. Based on the results, serum aspartate aminotransferase and alanine aminotransferase levels were significantly increased in 0.15 mg/l IoNPs, P7, and NPs + P6 treatments compared to the control group. In addition, the examination of antioxidant enzymes showed a significant increase in the levels of cortisol and glutathione S-transferase as well as malondialdehyde level. IoNPs also caused significant histopathological changes in the fish liver during the experiment such as hyperemia in sinusoidal spaces, hepatocytes vacuolation and necrosis, pyknosis, and disruption of hepatic lobules and atrophy. Results revealed the protective effects of dietary L. casei to mitigate the adverse impacts of IoNPs on the physiological processes of common carp.

Antioxidant Responses in Copepods Are Driven Primarily by Food Intake, Not by Toxin-Producing Cyanobacteria in the Diet

The association between oxidative processes and physiological responses has received much attention in ecotoxicity assessment. In the Baltic Sea, bloom-forming cyanobacterium Nodularia spumigena is a significant producer of various bioactive compounds, and both positive and adverse effects on grazers feeding in cyanobacteria blooms are reported. To elucidate the effect mechanisms and species sensitivity to the cyanobacteria-dominating diet, we exposed two Baltic copepods, Acartia bifilosa and Eurytemora affinis, to a diet consisting of toxin-producing cyanobacteria N. spumigena and a high-quality food Rhodomonas salina at 0–300 μg C L⁻¹; the control food was R. salina provided as a monodiet at the same food levels. The subcellular responses to food type and availability were assayed using a suite of biomarkers – antioxidant enzymes [superoxide dismutases (SOD), catalase (CAT), and glutathione S-transferases (GST)] and acetylcholinesterase (AChE). In parallel, we measured feeding activity using gut content (GC) assayed by real-time PCR analysis that quantified amounts of the prey DNA in copepod stomachs. As growth and reproduction endpoints, individual RNA content (a proxy for protein synthesis capacity), egg production rate (EPR), and egg viability (EV%) were used. In both toxic and nontoxic foods, copepod GC, RNA content, and EPR increased with food availability. Antioxidant enzyme activities increased with food availability regardless of the diet type. Moreover, CAT (both copepods), SOD, and GST (A. bifilosa) were upregulated in the copepods receiving cyanobacteria; the response was detectable when adjusted for the feeding and/or growth responses. By contrast, the diet effects were not significant when food concentration was used as a co-variable. A bimodal response in AChE was observed in A. bifilosa feeding on cyanobacteria, with up to 52% increase at the lower levels (5–25 μg C L⁻¹) and 32% inhibition at the highest food concentrations. These findings contribute to the refinement of biomarker use for assessing environmental stress and mechanistic understanding of cyanobacteria effects in grazers. They also suggest that antioxidant and AChE responses to feeding activity and diet should be accounted for when using biomarker profiles in field-collected animals in the Baltic Sea and, perhaps other systems, where toxic cyanobacteria are common.

Fungal biodegradation and removal of cyanobacteria and microcystins: potential applications and research needs

Harmful cyanobacterial blooms (HCB) have severe impacts on marine and freshwater systems worldwide. They cause oxygen depletion and produce potent cyanotoxins that have detrimental effects on human and environmental health and deteriorate the water quality. Biological treatment of the water for control of cyanobacterial blooms and removal of cyanotoxins can be a more economical and environment-friendly way, as they do not result in production of undesirable by-products. Most biological treatments of cyanobacteria and cyanotoxins have concentrated largely on bacteria, with little attention paid to algicidal fungi. Therefore, this review aims to provide an overview of the current status and the main progresses achieved in fungal biodegradation of HCB and cyanotoxin research. The available data revealed that 15 fungal species had high lytic activity against cyanobacteria, and 6 species were capable of degrading microcystins (MCs). Some fungal species (e.g., Aurobasidium pullulans and Trichoderma citrinoviride) have been identified to selectively inhibit the growth of cyanobacteria rather than beneficial species of other algal groups. Interestingly, some fungal strains (Trichaptum abietinum, Trichoderma citrinoviride) exhibited di-functional trait, being efficient in lysing cyanobacteria and degrading MCs released from the cells after decay. Beyond a comprehensive review of algicidal and toxin-degrading activities of fungi, this paper also identifies and prioritizes research gaps in algicidal fungi. The review also gives insights to the potential applications of algicidal fungi for removal of cyanobacterial blooms and their cyanotoxins from the aquatic environment.

DNA nanotechnology: A recent advancement in the monitoring of microcystin-LR

The Microcystin-Leucine-Arginine (MC-LR) is the most toxic and widely distributed microcystin, which originates from cyanobacteria produced by water eutrophication. The MC-LR has deleterious effects on the aquatic lives and agriculture, and this highly toxic chemical could severely endanger human health when the polluted food was intaken. Therefore, the monitoring of MC-LR is of vital importance in the fields including environment, food, and public health. Utilizing the complementary base pairing between DNA molecules, DNA nanotechnology can realize the programmable and predictable regulation of DNA molecules. In analytical applications, DNA nanotechnology can be used to detect targets via target-induced conformation change and the nano-assemblies of nucleic acids. Compared with the conventional analytical technologies, DNA nanotechnology has the advantages of sensitive, versatile, and high potential in real-time and on-site applications. According to the molecular basis for recognizing MC-LR, the strategies of applying DNA nanotechnology in the MC-LR monitoring are divided into two categories in this review: DNA as a recognition element and DNA-assisted signal processing. This paper introduces state-of-the-art analytical methods for the detection of MC-LR based on DNA nanotechnology and provides critical perspectives on the challenges and development in this field.

Exposure of Nile Tilapia (Oreochromis niloticus) Fingerlings to a Saxitoxin-Producing Strain of Raphidiopsis (Cylindrospermopsis) raciborskii (Cyanobacterium) Reduces Growth Performance and Increases Mortality Rate

Blooms of toxin-producing cyanobacteria have been more frequent and lasting because of the eutrophication of freshwater ecosystems, including those used for aquaculture. The aim of the present study was to investigate the effects of chronic exposure to a saxitoxin-producing strain of Raphidiopsis (Cylindrospermopsis) raciborskii on the performance of Nile tilapia (Oreochromis niloticus) fingerlings over a 60-d period. The fingerlings were cultivated under the following conditions: 1) water without cyanobacterium (WATER), 2) R. raciborskii in ASM-1 culture medium (CYANO), and 3) ASM-1 culture medium without cyanobacterium (ASM). Exposure to the CYANO treatment led to a significant increase in the mortality rate (p < 0.05) and a significant reduction in growth (p < 0.05) compared to fingerlings submitted to the ASM and WATER treatments, in which similar survival and growth were found (p > 0.05). Saxitoxin toxicity was dependent on the weight of the fingerling (p < 0.05), with maximum mortality caused by the ingestion of 13.66 μg saxitoxin equivalent L^-1  g^-1 . The present results clearly show the harm caused by saxitoxins to the production of Nile tilapia fingerlings in the early growth phase. These findings underscore the importance of maintaining adequate water quality in aquaculture activities to minimize the risk of saxitoxin-producing cyanobacterial blooms and avoid economic losses among producers. Environ Toxicol Chem 2020;39:1409-1420. © 2020 SETAC.

Biotransformations, Antioxidant System Responses, and Histopathological Indexes in the Liver of Fish Exposed to Cyanobacterial Extract

Radiocystis fernandoi, a microcystin (MC) producer, has been common in cyanobacterial blooms in tropical regions. Microcystin is a hepatotoxin that causes tissue damage and even death in animals, including humans; its detoxification process may involve biotransformation and activation of the antioxidant defense system. We evaluated the detoxification pathway, examined the antioxidant defense system responses, and determined the alterations and the organ histopathological indexes in the liver of the tropical fish Hoplias malabaricus after acute and subchronic intraperitoneal exposure to microcystin. The crude microcystin extract of R. fernandoi had predominantly MC-RR and MC-YR. The detoxification process was activated by increasing ethoxyresorufin-O-deethylase activity, whereas glutathione S-transferase was inhibited. The activity of the antioxidant defense enzymes superoxide dismutase (SOD) and glutathione peroxidase decreased after acute exposure; the SOD-catalase system and the glutathione level increased after subchronic exposure. The carbonyl protein level, lipid peroxidation (LPO), and DNA damage were unchanged after acute exposure, whereas protein carbonyl was unchanged, LPO decreased, and DNA damage increased after subchronic exposure. Histopathological alteration indexes differed between acute and subchronic exposure, but the histopathological organ indexes indicate liver dysfunction in both exposure periods. We conclude that MC-RR and MC-YR induce different liver responses depending on the time of exposure, and the antioxidant defense responses after subchronic exposure may help to partially restore the liver function. Environ Toxicol Chem 2020;39:1041-1051. © 2020 SETAC.

The effects of Microcystis aeruginosa cells lysate containing microcystins on physiological and molecular responses in the nematode Caenorhabditis elegans

Microcystins (MCs) are potent toxins produced by environmental cyanobacterial blooms. The present study evaluated the effects of a Microcystis aeruginosa cyanobacterial lysate containing 0.1, 1, and 10 μg L^-1 MC-LR equivalent in the C. elegans Bristol N2 wild-type and the effects caused by equivalent concentrations of a MC-LR standard. The lysate was prepared from a culture of toxic strain (RST9501) originated from the Patos Lagoon Estuary (RS, Brazil). The minimal concentration necessary to cause significant effects in C. elegans under exposure to M. aeruginosa lysate or to MC-LR standard were, respectively, 10 and 0.1 μg L^-1 MC-LR equivalent for growth and 10 and 1 μg L^-1 MC-LR equivalent for fertility. Reproduction (ie, brood size) was only affected by the exposure to 10 μg L^-1 MC-LR standard and was not affected by the lysate. The nematodes that were exposed to lysate containing 1 μg L^-1 MC-LR equivalent or MC-LR were also analyzed for pharyngeal pumping and gene expression using RT-qPCR. The worms' rhythmic contractions of the pharynx were similarly affected by the lysate containing 1 μg L^-1 of MC-LR equivalent and the MC-LR standard. The MC-LR standard caused down-regulation of genes related to growth (daf-16), fertility (spe-10), and biotransformation (gst-2). This is the first study to evaluate the effects of a toxic cyanobacterial lysate using the C. elegans model. This study suggests the organism as a potential biotest to evaluate toxicity of natural waters containing M. aeruginosa cells and to environmental risk assessment associated to cyanobacterial bloom events.

Biological HRPs in wastewater

Biological high-risk pollutants (HRPs) have become a serious threat to human health worldwide, and wastewater is one of the major sources of them in a natural environment. Despite the long history of wastewater research, comprehensive understanding of the role and behavior of HRPs during wastewater treatment is still limited owing to the complexity of the community. In recent decades, the rapid development of molecular tools, especially the wide application of next generation sequencing technologies, helps to unravel the community composition, structure, and dynamic variation in wastewater. Overall, this chapter mainly focuses on biological HRPs, including bacteria, viruses, protozoa, helminth, biotoxins, antibiotic resistance genes and antibiotic resistant bacteria in wastewater. The characteristics, classification, fates, functions, and health implications of these HRPs are introduced in detail. Moreover, the biogeography of HRPs is a research hotspot in recent years, and available information is also summarized in this chapter. Finally, we also propose the future research needs of HRPs in wastewater after the comprehensive summary of the existing research reports. This chapter is wished to be helpful for beginners to quickly understand the biological HRPs in wastewater.

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

The widespread distribution of cyanobacteria in the aquatic environment is increasing the risk of water pollution caused by cyanotoxins, which poses a serious threat to human health. However, the structural characterization, distribution and identification techniques of cyanotoxins have not been comprehensively reviewed in previous studies. This paper aims to elaborate the existing information systematically on the diversity of cyanotoxins to identify valuable research avenues. According to the chemical structure, cyanotoxins are mainly classified into cyclic peptides, alkaloids, lipopeptides, nonprotein amino acids and lipoglycans. In terms of global distribution, the amount of cyanotoxins are unbalanced in different areas. The diversity of cyanotoxins is more obviously found in many developed countries than that in undeveloped countries. Moreover, the threat of cyanotoxins has promoted the development of identification and detection technology. Many emerging methods have been developed to detect cyanotoxins in the environment. This communication provides a comprehensive review of the diversity of cyanotoxins, and the detection and identification technology was discussed. This detailed information will be a valuable resource for identifying the various types of cyanotoxins which threaten the environment of different areas. The ability to accurately identify specific cyanotoxins is an obvious and essential aspect of cyanobacterial research.

Endotoxin contamination, a potentially important inflammation factor in water and wastewater: A review

Endotoxins, also referred to as lipopolysaccharides or pyrogens, are major components embedded in the outer cell wall membrane of most Gram-negative bacteria and some cyanobacteria. As common pyrogens and strong immune stimulators, health hazards associated with endotoxins in water and wastewater have been attracting attention in recent years. In this paper, the characteristics, existing forms, and detection assays of endotoxins in water and wastewater are reviewed. Cellular response and pathophysiological effects, and main exposure tracts of endotoxins in water and wastewater are discussed. Levels of endotoxin contamination in water, wastewater, and their aerosols are presented. The removal effects of different water and wastewater treatment processes are summarized. Hence, it is important to: (i) Improve investigations into endotoxin contamination in water and wastewater in order to identify their source, occurrence, and fate. (ii) Implement water and wastewater treatment processes capable of ensuring low levels of endotoxins. This review aims to identify efficient water and wastewater treatment processes capable of ensuring the production of WTPs and WWTPs effluents with a low level of endotoxin activity, and to guarantee the reduction of endotoxin exposure risks to the consumers of water and wastewater.

Glutathione S-Transferase Protein Expression in Different Life Stages of Zebrafish (Danio rerio)

Zebrafish is a widely used animal model in biomedical sciences and toxicology. Although evidence for the presence of phases I and II xenobiotic defense mechanisms in zebrafish exists on the transcriptional and enzyme activity level, little is known about the protein expression of xenobiotic metabolizing enzymes. Given the important role of glutathione S-transferases (GSTs) in phase II biotransformation, we analyzed cytosolic GST proteins in zebrafish early life stages and different organs of adult male and female fish, using a targeted proteomics approach. The established multiple reaction monitoring-based assays enable the measurement of the relative abundance of specific GST isoenzymes and GST classes in zebrafish through a combination of proteotypic peptides and peptides shared within the same class. GSTs of the classes alpha, mu, pi and rho are expressed in zebrafish embryo as early as 4 h postfertilization (hpf). The majority of GST enzymes are present at 72 hpf followed by a continuous increase in expression thereafter. In adult zebrafish, GST expression is organ dependent, with most of the GST classes showing the highest expression in the liver. The expression of a wide range of cytosolic GST isoenzymes and classes in zebrafish early life stages and adulthood supports the use of zebrafish as a model organism in chemical-related investigations.

Effects of ocean acidification and solar ultraviolet radiation on physiology and toxicity of dinoflagellate Karenia mikimotoi

A batch culture experiment was conducted to study the interactive effects of ocean acidification (OA) and solar ultraviolet radiation (UVR, 280-400 nm) on the harmful dinoflagellate Karenia mikimotoi. Cells were incubated in 7-days trials under four treatments. Physiological (growth, pigments, UV_abc) and toxicity (hemolytic activity and its toxicity to zebrafish embryos) response variables were measured in four treatments, representing two factorial combinations of CO₂ (400 and 1000 μatm) and solar irradiance (with or without UVR). Toxic species K. mikimotoi showed sustained growth in all treatments, and there was not statistically significant difference among four treatments. Cell pigment content decreased, but UV_abc and hemolytic activity increased in all HC treatments and PAB conditions. The toxicity to zebrafish embryos of K. mikimotoi was not significantly different among four treatments. All HC and UVR conditions and the combinations of HC*UVR (HC-PAB) positively affected the UV_abc, hemolytic activity in comparison to the LC*P (LC-P) treatment, and negatively affected the pigments. Ocean acidification (OA) was probably the main factor that affected the chlorophyll-a (Chl-a) and UV_abc, but UVR was the main factor that affected the carotenoid (Caro) and hemolytic activity. There were no significant interactive effects of OA*UVR on growth, toxicity to zebrafish embryos. If these results are extrapolated to the natural environment, it can be hypothesized that this strain (DP-C32) of K. mikimotoi cells have the efficient mechanisms to endure the combination of ocean acidification and solar UVR. It is assumed that this toxic strain could form harmful bloom and enlarge the threatening to coastal communities, marine animals, even human health under future conditions.

GST transcriptional changes induced by a toxic Microcystis aeruginosa strain in two bivalve species during exposure and recovery phases

Previous studies have demonstrated the modulation of glutathione transferases (GSTs) induced by microcystin (MC) alone or in combination with other cyanobacterial secondary metabolites in bivalves. However, interspecies information about which and how GST isoforms are affected by these secondary metabolites is still scarce, especially considering the dynamic process involving their uptake and elimination routes. In this context, the role of GSTs gene expression changes in response to a toxic Microcystis aeruginosa extract were examined for Mytilus galloprovincialis and Ruditapes philippinarum during exposure and recovery phases. The expression levels of sigma 1, sigma 2, pi and mu-class GST genes were analyzed in the hepatopancreas of both bivalve species during cyanobacteria extract exposure (24 h) and post-exposure (24 and 72 h). Only a significant induction of sigma 1-class GST expression was observed for R. philippinarum upon 24-hour exposure of both bivalve species to Microcystis extract. During the recovery phase, GST transcriptional changes for M. galloprovincialis were characterized by an early induction (24 h) of sigma 1 and sigma 2 transcripts. On the other hand, GST transcriptional changes for R. philippinarum during post-exposure phase were characterized by an early induction (24 h) of sigma 1 and mu transcripts and a later induction (72 h) of the four analyzed GST transcripts. Such differences reflect variable GST response mechanisms to cope with MC-producing cyanobacterial blooms exposure between these two bivalve species, revealing a higher sensitivity of R. philippinarum to Microcystis-induced stress than M. galloprovincialis. The results also suggest a much higher level of activity of the GST detoxification system during the recovery phase compared to the period of the stress exposure for both bivalve species.

Interactive effect of nitrogen source and high CO2 concentration on the growth of the dinoflagellate Alexandrium tamarense and its toxicity to zebrafish (Danio rerio) embryos

The effects and interactive effects of different nitrogen (N) sources (ammonium, nitrate, and urea) and carbon dioxide (CO₂) concentrations were investigated on Alexandrium tamarense, a harmful marine dinoflagellate, by measuring its growth (μ), extracellular carbonic anhydrase (CA), and its toxicity to zebrafish (Danio rerio) embryo. The μ and CA were influenced more strongly by CO₂ concentrations rather than by N sources; significant effects of CO₂ on μ and CA were observed under low CO₂ concentration (LC) conditions compared to high CO₂ concentration (HC) conditions. The ammonium and nitrate media under LC conditions had the maximum μ and CA, which was inhibited under HC conditions. The embryotoxic effects were influenced more strongly by the N sources than by CO₂ concentrations, thus excluding the lower deformation in urea under HC conditions. Moreover, the antioxidant enzymes superoxide dismutase (SOD), glutathione peroxidase (GPX), glutathione S-transferase (GST), and catalase (CAT) were detected in normal (untreated) zebrafish embryos, and among them, the level of SOD was the highest. In summary, this study provides a clear insight for understanding the effects and interactive effects of N sources and CO₂ concentrations on the growth and toxicity of harmful dinoflagellates.

Allelopathic and Bloom-Forming Picocyanobacteria in a Changing World

Picocyanobacteria are extremely important organisms in the world's oceans and freshwater ecosystems. They play an essential role in primary production and their domination in phytoplankton biomass is common in both oligotrophic and eutrophic waters. Their role is expected to become even more relevant with the effect of climate change. However, this group of photoautotrophic organisms still remains insufficiently recognized. Only a few works have focused in detail on the occurrence of massive blooms of picocyanobacteria, their toxicity and allelopathic activity. Filling the gap in our knowledge about the mechanisms involved in the proliferation of these organisms could provide a better understanding of aquatic environments. In this review, we gathered and described recent information about allelopathic activity of picocyanobacteria and occurrence of their massive blooms in many aquatic ecosystems. We also examined the relationships between climate change and representative picocyanobacterial genera from freshwater, brackish and marine ecosystems. This work emphasizes the importance of studying the smallest picoplanktonic fractions of cyanobacteria.

Extraction, separation and characterization of endotoxins in water samples using solid phase extraction and capillary electrophoresis-laser induced fluorescence

This study focuses on one of the key environmental threats, endotoxins, also known as lipopolysaccharides (LPS). A capillary electrophoresis method in combination with laser induced fluorescence (LIF) detection was developed for the analysis of endotoxins from 16 different bacterial strains. LPSs were derivatized with the amino-reactive fluorescent dye, fluorescein isothiocyanate (FITC), separated by capillary zone electrophoresis (CZE) under the optimized conditions with the use of 50 mM sodium tetraborate buffer (pH 9.30), and detected by LIF detector. To improve the sensitivity of CZE-LIF detection for the determination of trace amounts of endotoxins and to remove possible interference materials in environmental samples, a solid phase extraction (SPE) pre-concentration technique was applied successfully. The SPE targeted at polysaccharide moieties of LPSs and showed LPS enrichment effects too. CE migration time could also reveal the O-antigen chain lengths of LPSs. This CE method and SPE pretreatment showed linearity at 99.84%, and repeatabilities at 8.44% and 11.0% for endotoxins from E. Coli O55:B5 and E. Coli O26:B6. The limit of detection (LOD) could reach around 5 ng/mL at optimized condition. The method was applied successfully to the determination of LPS levels in tap water and wastewater, and demonstrated sensitive, reproducible and reliable results.

Tissue-specific bioconcentration and biotransformation of cypermethrin and chlorpyrifos in a native fish (Jenynsia multidentata) exposed to these insecticides singly and in mixtures

The aim of the present study was to evaluate the accumulation of cypermethrin and chlorpyrifos when the fish Jenynsia multidentata was exposed to these pesticides singly and in technical and commercial mixtures. Adult female fish were exposed over 96 h to 0.04 μg/L of cypermethrin; 0.4 μg/L of chlorpyrifos; 0.04 μg/L of cypermethrin + 0.4 μg/L of chlorpyrifos in a technical mixture; and 0.04 μg/L of cypermethrin + 0.4 μg/L of chlorpyrifos in a mixture of commercial products. Fish exposed to cypermethrin accumulated this compound only in muscle, probably because of the low biotransformation capacity of this organ and the induction of cytochrome P4501A1 (CYP1A1) expression in the liver. The accumulation of chlorpyrifos occurred in fish exposed to the insecticide (intestine > liver > gills) even when these fish had higher gluthatione-S-transferase (GST) activity in gills and P-glycoprotein (P-gp) expression in the liver, compared with the control. Fish exposed to the technical mixture showed cypermethrin accumulation (liver > intestine > gills) with higher levels than those measured in fish after only cypermethrin exposure. Higher expression levels of CYP1A1 in the liver were also observed compared with the Control. Fish exposed to the commercial mixture accumulated both insecticides (cypermethrin: intestine > gills and chlorpyrifos: liver > intestine > gills > muscle). In the organs where accumulation occurred, biotransformation enzymes were inhibited. Consequently, the commercial formulation exposure provoked the highest accumulation of cypermethrin and chlorpyrifos in J. multidentata, possibly associated with the biotransformation system inhibition. Environ Toxicol Chem 2017;36:1764-1774. © 2016 SETAC.

Identification and characterization of the zebrafish glutathione S-transferase Pi-1

Zebrafish has in recent years emerged as a popular vertebrate model for use in pharmacological and toxicological studies. While there have been sporadic studies on the zebrafish glutathione S-transferases (GSTs), the zebrafish GST gene superfamily still awaits to be fully elucidated. We report here the identification of 15 zebrafish cytosolic GST genes in NCBI GenBank database and the expression, purification, and enzymatic characterization of the zebrafish cytosolic GST Pi-1 (GSTP1). The cDNA encoding the zebrafish GSTP1 was cloned from a 3-month-old female zebrafish, expressed in Eschelichia coli host cells, and purified. Purified GSTP1 displayed glutathione-conjugating activity toward 1-chloro-2,4-dinitrobenzene as a representative substrate. The enzymatic characteristics of the zebrafish GSTP1, including pH-dependency, effects of metal cations, and kinetic parameters, were studied. Moreover, the expression of zebrafish GSTP1 at different developmental stages during embryogenesis, throughout larval development, onto maturity was examined.

Cyanobacterial Toxins in Freshwater and Food: Important Sources of Exposure to Humans

A recent ecological study demonstrated a significant association between an increased risk of nonalcoholic liver disease mortality and freshwater cyanobacterial blooms. Moreover, previous epidemiology studies highlighted a relationship between cyanotoxins in drinking water with liver cancer and damage and colorectal cancer. These associations identified cyanobacterial blooms as a global public health and environmental problem, affecting freshwater bodies that are important sources for drinking water, agriculture, and aquafarms. Furthermore, as a result of climate change, it is expected that our freshwater environments will become more favorable for producing harmful blooms that produce various cyanotoxins. Food is an important source of cyanotoxin exposure to humans, but it has been less addressed. This paper synthesizes information from the studies that have investigated cyanotoxins in freshwater and food on a global scale. We also review and summarize the health effects and exposure routes of cyanotoxins and candidates for cyanotoxin treatment methods that can be applied to food.

Effects of exposure to microcystin-LR at environmentally relevant concentrations on the metabolism of thyroid hormones in adult zebrafish (Danio rerio)

Microcystin-LR (MC-LR) has the potential to disturb thyroid hormone homeostasis. However, the effects of MC-LR at environmentally relevant concentrations on the thyroid system in adult fish are still unclear. In this study, adult zebrafish were exposed to 0, 1, 5, and 25 μg/L MC-LR for 7, 14, 21, and 28 days. Whole-body thyroid hormones (THs) levels and thyroid follicle histology were used to assess thyroid function. The transcription of corticotropin-releasing hormone (crh), thyroid-stimulating hormone (tsh), transthyretin (ttr), thyroid hormone receptors (trs) genes, and the activities of iodothyronine deiodinases (IDs) were investigated to study the process of TH metabolism disruption. No differences in the histopathology of thyroid follicles and unchanged T₄ levels were observed in adult zebrafish. A significant decline in T₃ levels associated with a decrease in ID2 activity in male zebrafish was observed at 21 days exposure. Moreover, the mRNA expression of tsh, ttr and trs appeared to be a dynamic process as expression first decreased and then increased with continued exposure. These results indicated that exposure to MC-LR did not inhibit the production of TH. The decrease in ID2 activity may be an important factor in the decline of T₃ levels. Furthermore, it seems that the fish triggered a compensatory mechanism to maintain TH homeostasis in respond to environmental concentrations of MC-LR which induced TH disruption.

Enhancing the Feasibility of Microcystis aeruginosa as a Feedstock for Bioethanol Production under the Influence of Various Factors

Microcystis aeruginosa, a freshwater microalga, is capable of producing and accumulating different types of sugars in its biomass which make it a good feedstock for bioethanol production. Present study aims to investigate the effect of different factors increasing growth rate and carbohydrates productivity of M. aeruginosa. MF media (modified BG11 media) and additional ingredients such as aminolevulinic acid (2 mM), lysine (2.28 mM), alanine (1 mM), and Naphthalene acetic acid (1 mM) as cytokine promoted M. aeruginosa growth and sugar contents. Salmonella showed growth-assisting effect on M. aeruginosa. Enhanced growth rate and carbohydrates contents were observed in M. aeruginosa culture grown at 25°C under red LED light of 90 μmolm⁻²s⁻¹ intensity. More greenish and carbohydrates rich M. aeruginosa biomass was prepared (final OD_660 nm = 2.21 and sugar contents 10.39 mM/mL) as compared to control (maximum OD_660 nm = 1.4 and sugar contents 3 mM/mL). The final algae biomass was converted to algae juice through a specific pretreatment method. The resulted algae Juice was used as a substrate in fermentation process. Highest yield of bioethanol (50 mM/mL) was detected when Brettanomyces custersainus, Saccharomyces cerevisiae, and Pichia stipitis were used in combinations for fermentation process as compared to their individual fermentation. The results indicated the influence of different factors on the growth rate and carbohydrates productivity of M. aeruginosa and its feasibility as a feedstock for fermentative ethanol production.

Behavioral swimming effects and acetylcholinesterase activity changes in Jenynsia multidentata exposed to chlorpyrifos and cypermethrin individually and in mixtures

The pesticides cypermethrin (CYP) and chlorpyrifos (CPF) were found together in water bodies located in agricultural and urban areas. However, the impact to non-target biota from exposure to mixtures has received little attention. In the current study, we evaluated changes in swimming behavior and cholinesterase enzymes activity in Jenynsia multidentata, to investigate the possible effects of these insecticides individually and in mixtures. Moreover, differences between technical and commercial mixtures of the pesticides were evaluated. Females of J. multidentata were exposed over 96-h to CYP (0.04 and 0.4µgL(-1)), CPF (0.4 and 4µgL(-1)), individually and in a technical and commercial mixtures. Swimming behavior was recorded after 24h and 96h of exposure. Also, we measured cholinesterase enzymes activity in brain and muscle after 96h of exposure. Exposure to CYP increased the exploratory activity of J. multidentata in the upper area of the aquarium. Fish exposed to CPF (4µg L(-1)) showed a decrease in swimming activity and an increase in the time spent at the bottom of the aquarium. Interestingly, fish exposed to the technical and commercial mixture of CYP and CPF displayed a different behavior based on the concentration of exposure. Low concentration of pesticides elicited an increase in J. multidentata swimming activity with preference for the upper area of the aquarium, and high concentrations caused decrease in swimming activity with preference for the bottom area of the aquarium. Based on the response of cholinesterase enzymes, acetylcholinesterase in muscle was more sensitive to exposure to CYP, CPF and their mixtures than in brain. A decrease in swimming behavior correlates significantly with the inhibition of acetylcholinesterase activity in muscle of J. multidentata exposed to high concentrations of pesticides. These results draw attention to the need of more studies on the potential ecotoxicological impact of pesticides and its mixtures at environmental relevant concentrations.

The interactive effects of microcystin-LR and cylindrospermopsin on the growth rate of the freshwater algae Chlorella vulgaris

Microcystin-LR (MC-LR) and cylindrospermopsin (CYN) are the most representative cyanobacterial cyanotoxins. They have been simultaneously detected in aquatic systems, but their combined ecotoxicological effects to aquatic organisms, especially microalgae, is unknown. In this study, we examined the effects of these cyanotoxins individually and as a binary mixture on the growth rate of the freshwater algae Chlorella vulgaris. Using the MIXTOX tool, the reference model concentration addition (CA) was selected to evaluate the combined effects of MC-LR and CYN on the growth of the freshwater green algae due to its conservative prediction of mixture effect for putative similar or dissimilar acting chemicals. Deviations from the CA model such as synergism/antagonism, dose-ratio and dose-level dependency were also assessed. In single exposures, our results demonstrated that MC-LR and CYN had different impacts on the growth rates of C. vulgaris at the highest tested concentrations, being CYN the most toxic. In the mixture exposure trial, MC-LR and CYN showed a synergistic deviation from the conceptual model CA as the best descriptive model. MC-LR individually was not toxic even at high concentrations (37 mg L(-1)); however, the presence of MC-LR at much lower concentrations (0.4-16.7 mg L(-1)) increased the CYN toxicity. From these results, the combined exposure of MC-LR and CYN should be considered for risk assessment of mixtures as the toxicity may be underestimated when looking only at the single cyanotoxins and not their combination. This study also represents an important step to understand the interactions among MC-LR and CYN detected previously in aquatic systems.

An overview of diversity, occurrence, genetics and toxin production of bloom-forming Dolichospermum (Anabaena) species

The new genus name Dolichospermum, for most of the planktonic former members of the genus Anabaena, is one of the most ubiquitous bloom-forming cyanobacterial genera. Its dominance and persistence have increased in recent years, due to eutrophication from anthropogenic activities and global climate change. Blooms of Dolichospermum species, with their production of secondary metabolites that commonly include toxins, present a worldwide threat to environmental and public health. In this review, recent advances of the genus Dolichospermum are summarized, including taxonomy, genetics, bloom occurrence, and production of toxin and taste-and-odor compounds. The recent and continuing acquisition of genome sequences is ushering in new methods for monitoring and understanding the factors regulating bloom dynamics.

Structure and Effects of Cyanobacterial Lipopolysaccharides

Lipopolysaccharide (LPS) is a component of the outer membrane of mainly Gram-negative bacteria and cyanobacteria. The LPS molecules from marine and terrestrial bacteria show structural variations, even among strains within the same species living in the same environment. Cyanobacterial LPS has a unique structure, since it lacks heptose and 3-deoxy-d-manno-octulosonic acid (also known as keto-deoxyoctulosonate (KDO)), which are present in the core region of common Gram-negative LPS. In addition, the cyanobacterial lipid A region lacks phosphates and contains odd-chain hydroxylated fatty acids. While the role of Gram-negative lipid A in the regulation of the innate immune response through Toll-like Receptor (TLR) 4 signaling is well characterized, the role of the structurally different cyanobacterial lipid A in TLR4 signaling is not well understood. The uncontrolled inflammatory response of TLR4 leads to autoimmune diseases such as sepsis, and thus the less virulent marine cyanobacterial LPS molecules can be effective to inhibit TLR4 signaling. This review highlights the structural comparison of LPS molecules from marine cyanobacteria and Gram-negative bacteria. We discuss the potential use of marine cyanobacterial LPS as a TLR4 antagonist, and the effects of cyanobacterial LPS on humans and marine organisms.

Toxic picoplanktonic cyanobacteria--review

Cyanobacteria of a picoplanktonic cell size (0.2 to 2.0 µm) are common organisms of both freshwater and marine ecosystems. However, due to their small size and relatively short study history, picoplanktonic cyanobacteria, in contrast to the microplanktonic cyanobacteria, still remains a poorly studied fraction of plankton. So far, only little information on picocyanobacteria toxicity has been reported, while the number of reports concerning their presence in ecosystems is increasing. Thus, the issue of picocyanobacteria toxicity needs more researchers' attention and interest. In this report, we present information on the current knowledge concerning the picocyanobacteria toxicity, as well as their harmfulness and problems they can cause.

An overview of the toxic effect of potential human carcinogen Microcystin-LR on testis

The worldwide occurrence of cyanobacterial blooms due to water eutrophication evokes extreme concerns. These blooms produce cyanotoxins which are hazardous to living organisms. So far among these toxins, Microcystin-LR (MC-LR) is the most toxic and the most frequently encountered toxin produced by the cyanobacteria in the contaminated aquatic environment. Microcystin-LR is a potential carcinogen for animals and humans, and the International Agency for Research on Cancer has classified Microcystin-LR as a possible human carcinogen. After liver, testis has been considered as one of the most important target organs of Microcystin-LR toxicity. Microcystin-LR crosses the blood–testis barrier and interferes with DNA damage repair pathway and also increases expression of the proto-oncogenes, genes involved in the response to DNA damage, cell cycle arrest, and apoptosis in testis. Toxicity of MC-LR disrupts the motility and morphology of sperm and also affects the hormone levels of male reproductive system. MC-LR treated mice exhibit oxidative stress in testis through the alteration of antioxidant enzyme activity and also affect the histopathology of male reproductive system. In the present review, an attempt has been made to comprehensively address the impact of MC-LR toxicity on testis.

Damage and recovery of the ovary in female zebrafish i.p.-injected with MC-LR

Up to now, in vivo studies on toxic effects of microcystins (MCs) on the reproductive system are limited and the underlying molecular mechanisms of MCs-induced reproductive toxicity remain to be elucidated. In an acute toxic experiment, female zebrafish (Danio rerio) were injected intraperitoneally (i.p.) at doses of 50 and 200 μg MC-LR/kg body weight (BW) respectively, and histopathological lesions and antioxidant enzymatic activities and gene expression in the ovary were studied at 1, 3, 12, 24, 48 and 168 h post injection (hpi). Pathological lesions of zebrafish ovary progressed in severity and extent with the increasing exposure time and dose within 12 hpi. Concurrently, the increases in malondialdehyde (MDA) contents as well as the enzymatic activities and transcriptional levels of antioxidant enzymes catalase (CAT), superoxide dismutase (SOD) and glutathione peroxidase (GPx) showed the occurrence of oxidative stress, indicating that MC-LR induced adverse effects on the structure and functional activity of zebrafish ovary. Oxidative stress plays a significant role in the reproductive toxicity of MC-LR. The significant decrease of glutathione (GSH) content in zebrafish ovary suggested the importance of MC-LR detoxification by glutathione S-transferases (GST) via GSH. The final recovery of histostructure and antioxidative indices indicated that ovarian efficient antioxidant defense system might be an important mechanism of zebrafish to counteract MC-LR. Although the negative effects of MC-LR can be overcome by ovarian antioxidant system in this study, the potential reproductive risks of MC-LR should not be neglected because of its wide occurrence.

Protective role of oligomeric proanthocyanidin complex against hazardous nodularin-induced oxidative toxicity in Carassius auratus lymphocytes

Nodularin (NOD) is a hazardous material widely detected in water blooms. Fish immune cells are extremely vulnerable to NOD-induced oxidative stress. Oligomeric proanthocyanidin complex (OPC), extracted from grapeseed, was used as an antioxidant to eliminate reactive oxygen species and prevent apoptotic effects. Carassius auratus lymphocytes were treated with different concentrations (0, 10, 100, and 1,000 μg/L) of OPC and a constant dose (100 μg/L) of NOD for 12h in vitro. OPC inhibited mitosis by decreasing intracellular levels of oxidative stress, regulating antioxidant enzymes (CAT, SOD, GPx, GR, and GST), mediating bcl-2 family proteins, and deactivating caspase-3. Glutathione (GSH) levels in group V (NOD 100 μg/L; OPC 1,000 μg/L) showed a twofold increase compared with corresponding levels in group II (NOD 100 μg/L). Structure parameters of NOD and NOD-GSH were calculated using SYBYL 7.1 software. ClogP and HINK logP values of NOD-GSH decreased by 10.4- and 2.3-fold, respectively, compared with corresponding values of NOD. OPC-stimulated GSH can lower the lipophilicity and polarity of NOD. OPC, as a protective agent, can alleviate NOD-induced toxicity in C. auratus lymphocytes by regulating oxidative stress and inducing NOD-GSH detoxification.

Effects of Cylindrospermopsis raciborskii (cyanobacteria) on the swimming behavior of Daphnia (cladocera)

The present study aimed to test the effects of raw water samples from a eutrophic reservoir and of a saxitoxin-producing strain of Cylindrospermopsis raciborskii on the swimming behavior of 2 key herbivore species of Daphnia. Two complementary approaches were used, acute bioassays and behavioral assays using an automated movement tracking system for measuring the following activity parameters: swimming time, resting time, distance traveled, and mean velocity. In both assays, animals were exposed to field samples or to toxic filaments in different concentrations and observed for 2 h to 3 h. In the acute bioassays, there was a decrease in the number of swimming individuals during the exposure period and a recovery following removal from toxic algae. A significant relationship was found between median effective concentration and the saxitoxin content of seston (r(2)  = 0.998; p = 0.025) in the acute bioassays with raw water samples. Behavioral assays also showed significant effects in the activity parameters with both field samples and the strain of C. raciborskii, with some recovery during the exposure period. Both approaches corroborated previous research on the effects of neurotoxic C. raciborskii on the swimming activity of Daphnia, and these effects are compatible with the mechanism of action of saxitoxins. The present study showed that activity parameters of aquatic organisms may be a useful tool in the evaluation of sublethal toxicity and detection of neurotoxins in raw water.

The isolation and characterization of lipopolysaccharides from Microcystis aeruginosa, a prominent toxic water bloom forming cyanobacteria

Massive toxic blooms of cyanobacteria represent a major threat to water supplies worldwide, yet serious gaps exist in understanding their complex toxic effects, including the role of lipopolysaccharides (LPS). The present comparative study focused on the levels and biological activities of LPS isolated from Microcystis aeruginosa, which is one of the most globally distributed toxic species. Using hot phenol extraction, LPS was isolated from 3 laboratory cultures and 11 natural water blooms. It formed 0.2-0.7% of the original dry biomass of the cyanobacteria, based on gravimetry. Additional analyses by commercial anti-LPS ELISA were correlated with gravimetry but showed concentrations that were about 7-times lower, which indicated either impurities in isolated LPS or the poor cross-reactivity of the antibodies used. LPS isolates from M. aeruginosa were potent pyrogens in the traditional Limulus amebocyte lysate (LAL)-test, but comparison with the PyroGene test demonstrated the limited selectivity of LAL with several interferences. The determined pyrogenicity (endotoxin units, EU) ranged from very low values in laboratory cultures (less than 0.003 up to 0.008-EU per 100 pg LPS) to higher values in complex bloom samples (0.01-0.078 EU per 100 pg of LPS), which suggested the role of bloom-associated bacteria in the overall effects. Potent pro-inflammatory effects of the studied LPS from both cultures and bloom samples were observed in a highly-relevant ex vivo human blood model by studying reactive oxygen species production in phagocytes as well as increased productions of interleukin 8, IL-8, and tumor necrosis factor α, TNF-α. LPS from M. aeruginosa seem to modulate several pathways involved in the regulation of both innate immunity and specific responses. In comparison to the standard pathogenic bacterial LPS (World Health Organization Escherichia coli O113:10 endotoxin; activity 1 EU per 100 pg), the studied cyanobacterial samples had pyrogenicity potencies that were at least 12-times lower. However, the health risks associated with LPS from M. aeruginosa should not be underestimated, especially with respect to diverse biological effects observed ex vivo and in the case of massive blooms in drinking water reservoirs, where the estimated pyrogenicity can reach up to 46,000 EU per mL of water.

Toxicological evaluation of microcystins in aquatic fish species: current knowledge and future directions

Microcystins (MCs) are algal toxins produced intracellularly within the algal cells, and are subsequently released into the aquatic systems. An increase in the frequency and intensity of occurrence of harmful algal blooms has directed the global attention towards the presence of MCs in aquatic systems. The effects of MCs on fish have been verified in a number of studies including histological, biochemical and behavioral effects. The toxicological effects of MCs on different organs of fish are related to the exposure route (intraperitoneal injection, feeding or immersion), the mode of uptake (passive or active transport) as well as biotransformation and bioaccumulation capabilities by different organs. This paper reviews the rapidly expanding literature on the toxicological evaluation of MCs in fish from both field studies and controlled laboratory experimental investigations, integrates the current knowledge available about the mechanisms involved in MC-induced effects on fish, and points out future research directions from a cross-disciplinary perspective. In addition, the need to carry out systematic fish toxicity studies to account for possible interactions between MCs and other environmental pollutants in aquatic systems is discussed.

Cytotoxic effects and changes in cytokine gene expression induced by microcystin-containing extract in fish immune cells--an in vitro and in vivo study

Blooms of cyanobacteria producing very toxic secondary metabolites (especially microcystins) are potent environmental stressors, hazardous not only to aquatic animals but also to public health. The purpose of this study was to investigate the effects of an extract containing microcystins on immune cells isolated from the common carp (Cyprinus carpio L.). In the present study it has been found that the extract induced apoptosis and inhibited in vitro lymphocyte proliferation. In addition, the results indicated the possible role of oxidative stress in this cytotoxicity and apoptosis. The in vivo investigations showed that the extract containing microcystins had greater suppressive effects on the essential functions of immune cells (intracellular reactive oxygen species production and lymphocyte proliferation) than the pure toxin alone. Moreover, immersion of fish in the toxic extract caused changes in the mRNA levels of various pro- and anti-inflammatory cytokines in carp leukocytes, while after exposure to the pure toxin, only IL1-β expression was markedly up-regulated. The observed modulatory effects on immune cells could have important implications for the health of planktivorous fish, which feed more frequently on toxic cyanobacteria.

Amino acid neurotoxins in feathers of the Lesser Flamingo, Phoeniconaias minor

The Lesser Flamingo (Phoeniconaias minor) is known to use cyanobacteria (primarily Arthrospira) as a major food source in the East African Rift Valley lakes. Periodically, mass mortalities have occurred, associated with the cyanobacterial toxins (cyanotoxins), microcystins and anatoxin-a. Deposition of these cyanotoxins into P. minor feathers has been shown to occur, consistent with the presence of cyanotoxins in the livers, stomach and faecal contents after dietary intake. As cyanobacteria have been shown to also produce the neurotoxins β-N-methylamino-L-alanine (BMAA) and 2,4-diaminobutyric acid (DAB), stored wing feathers, previously recovered from flamingos which had been exposed to microcystins and anatoxin-a and had subsequently died, were analysed for these neurotoxic amino acids. Trace amounts of BMAA were detected in extracts from Lake Nakuru flamingo feathers, with DAB also present at concentrations between 3.5 and 8.5 μg g(-1) dry weight in feathers from both lakes. Toxin recovery by solid-phase extraction of feather digests was tested with spiked deuterated BMAA and showed good recovery when analysed by LC-MS/MS (80-94%). This is the first report of these neurotoxic amino acids in birds. We discuss the origin and significance of DAB, alongside other cyanotoxins of dietary origin, in the feathers of the Lesser Flamingo.

Short-term uptake of microcystin-LR by Coregonus lavaretus: GST activity and genotoxicity

In the present study, juvenile whitefish weighing 2 g were exposed by force-feeding to two ecologically relevant doses (0.05 and 0.5 μg per fish) of microcystin-LR (MC-LR). Then over 96 h the MC uptake in fish liver and muscle was measured, as the activity of the detoxification enzyme glutathione S-transferase (GST) in the liver, and the genotoxicity impact on red blood cells. Results show that (1) the MC-LR equivalent concentrations increased for both doses and in both organs of whitefish with approximately threefold lower concentrations for the low dose compared to the high dose in both organs and threefold lower concentrations in the muscle compared to the liver for each dose (2) the liver GST activity increased during the first 48 h of exposure with fivefold higher GST activity for the highest dose at 48 h compared to control and (3) MC-LR leads to deoxyribonucleic acid strand breaks that were detected by the comet assay and shown to be partially repaired. This work demonstrates that European whitefish could be impacted by cyanobacteria toxins due to rapid microcystin uptake, especially in the context of chronic contamination, which can occur during long bloom episodes.

Oxidative stress and detoxification biomarker responses in aquatic freshwater vertebrates exposed to microcystins and cyanobacterial biomass

Cyanobacterial blooms represent a serious threat to the aquatic environment. Among other effects, biochemical markers have been studied in aquatic vertebrates after exposures to toxic cyanobacteria. Some parameters such as protein phosphatases may serve as selective markers of exposure to microcystins, but under natural conditions, fish are exposed to complex mixtures, which affect the overall biomarker response. This review aims to provide a critical summary of biomarker responses in aquatic vertebrates (mostly fish) to toxic cyanobacteria with a special focus on detoxification and oxidative stress. Detoxification biomarkers such as glutathione (GSH) and glutathione-S-transferase (GST) showed very high variability with poor general trends. Often, stimulations and/or inhibitions and/or no effects at GSH or GST have been reported, even within a single study, depending on many variables, including time, dose, tissue, species, etc. Most of the oxidative stress biomarkers (e.g., superoxide dismutase, catalase, glutathione peroxidase, and glutathione reductase) provided more consistent responses, but only lipid peroxidation (LPO) seemed to fulfill the criteria needed for biomarkers, i.e., a sufficiently long half-life and systematic response. Indeed, reviewed papers demonstrated that toxic cyanobacteria systematically elevate levels of LPO, which indicates the important role of oxidative damage in cyanobacterial toxicity. In summary, the measurement of biochemical changes under laboratory conditions may provide information on the mode of toxic action. However, comparison of different studies is very difficult, and the practical use of detoxification or oxidative stress biomarkers as diagnostic tools or early warnings of cyanobacterial toxicity is questionable.

Effects of cyanobacterial lipopolysaccharides from microcystis on glutathione-based detoxification pathways in the zebrafish (Danio rerio) embryo

Cyanobacteria ("blue-green algae") are recognized producers of a diverse array of toxic secondary metabolites. Of these, the lipopolysaccharides (LPS), produced by all cyanobacteria, remain to be well investigated. In the current study, we specifically employed the zebrafish (Danio rerio) embryo to investigate the effects of LPS from geographically diverse strains of the widespread cyanobacterial genus, Microcystis, on several detoxifying enzymes/pathways, including glutathione-S-transferase (GST), glutathione peroxidase (GPx)/glutathione reductase (GR), superoxide dismutase (SOD), and catalase (CAT), and compared observed effects to those of heterotrophic bacterial (i.e., E. coli) LPS. In agreement with previous studies, cyanobacterial LPS significantly reduced GST in embryos exposed to LPS in all treatments. In contrast, GPx moderately increased in embryos exposed to LPS, with no effect on reciprocal GR activity. Interestingly, total glutathione levels were elevated in embryos exposed to Microcystis LPS, but the relative levels of reduced and oxidized glutathione (i.e., GSH/GSSG) were, likewise, elevated suggesting that oxidative stress is not involved in the observed effects as typical of heterotrophic bacterial LPS in mammalian systems. In further support of this, no effect was observed with respect to CAT or SOD activity. These findings demonstrate that Microcystis LPS affects glutathione-based detoxification pathways in the zebrafish embryo, and more generally, that this model is well suited for investigating the apparent toxicophore of cyanobacterial LPS, including possible differences in structure-activity relationships between heterotrophic and cyanobacterial LPS, and teleost fish versus mammalian systems.

Artificial neural network modeling of biomarkers to infer characteristics of contaminant exposure in Clarias gariepinus

This study examined the potential of artificial neural network (ANN) modeling to infer timing, route and dose of contaminant exposure from biomarkers in a freshwater fish. Hepatic glutathione S-transferase (GST) activity and biliary concentrations of BaP, 1-OH BaP, 3-OH BaP and 7,8D BaP were quantified in juvenile Clarias gariepinus injected intramuscularly or intraperitoneally with 10-50 mg/kg benzo[a]pyrene (BaP) 1-3 d earlier. A feedforward multilayer perceptron (MLP) ANN resulted in more accurate prediction of timing, route and exposure dose than a linear neural network or a radial basis function (RBF) ANN. MLP sensitivity analyses revealed contribution of all five biomarkers to predicting route of exposure but no contribution of hepatic GST activity or one of the two hydroxylated BaP metabolites to predicting time of exposure and dose of exposure. We conclude that information content of biomarkers collected from fish can be extended by judicious use of ANNs.

Estrogenic activity in extracts and exudates of cyanobacteria and green algae

Here is presented some of the first information on interactions of compounds produced by cyanobacteria and green algae with estrogen receptor signaling. Estrogenic potency of aqueous extracts and exudates (culture spent media with extracellular products) of seven species of cyanobacteria (10 different laboratory strains) and two algal species were assessed by use of in vitro trans-activation assays. Compounds produced by cyanobacteria and algae, and in particular those excreted from the cells, were estrogenic. Most exudates were estrogenic with potencies expressed at 50% of the maximum response under control of the estrogen receptor ranging from 0.2 to 7.2 ng 17β-estradiol (E(2)) equivalents (EEQ)/L. The greatest estrogenic potency was observed for exudates of Microcystis aerigunosa, a common species that forms water blooms. Aqueous extracts of both green algae, but only one species of cyanobacteria (Aphanizomenon gracile) elicited significant estrogenicity with EEQ ranging from 15 to 280 ng 17β-estradiol (E(2))/g dry weight. Scenedesmus quadricauda exudates and extracts of Aphanizomenon flos-aquae were antagonistic to the ER when coexposed to E(2). The EEQ potency was not correlated with concentrations of cyanotoxins, such as microcystin and cylindrospermopsin, which suggests that the EEQ was comprised of other compounds. The study demonstrates some differences between the estrogenic potency of aqueous extracts prepared from the same species, but of different origin, while the effects of exudates were comparable within species. The observed estrogenic potencies are important namely in relation to the possible mass expansion of cyanobacteria and release of the active compounds into surrounding water.

Early biochemical effects of Microcystis aeruginosa extracts on juvenile rainbow trout (Oncorhynchus mykiss)

Microcystins (MC) are usually the predominant cyanotoxins associated with cyanobacterial blooms in natural surface waters. These toxins are well-known hepatotoxic agents that proceed by inhibiting protein phosphatase in aquatic biota; recent studies have also reported oxidative stress and disruption of ion regulation in aquatic organisms. In the present study, young trout (Oncorhynchus mykiss) were exposed to crude extracts of Microsystis aeruginosa for four days at 15 °C. The level of microcystins was calculated to confirm the presence of toxins in these crude extracts: 0, 0.75, 1.8 and 5 μg/L. Protein phosphatase measured in the liver increased by at least 3-fold and is significantly as a result of exposure to these sublethal concentrations of crude extract, his indicates an early defense response against protein phosphatase inhibition from cyanotoxins. This was corroborated by the decreased phosphate content in proteins found in the liver and brain. No increase in glutathione-S transferase (GST) activity was observed and lipid peroxidation was unaffected in both liver and brain tissue exposed to the cyanobacterial extracts. The data revealed that the proportion of the reduced (metal-binding) form of metallothionein (MT) decreased by two-fold relative to the control group (with a concomitant increase in the proportion of the oxidized form). The level of phosphate associated with MT increased by 1.5-fold at the highest concentration of crude extract. Acetylcholinesterase (AChE) activity in brain tissue was decreased after exposure to the highest concentration of crude extract, suggesting a slowdown in neural activity. However, no biotransformation processes or detoxification of GST was triggered. Our findings show early sign of biochemical effects of MC-LR in young trout.

Cyanotoxins: bioaccumulation and effects on aquatic animals

Cyanobacteria are photosynthetic prokaryotes with wide geographic distribution that can produce secondary metabolites named cyanotoxins. These toxins can be classified into three main types according to their mechanism of action in vertebrates: hepatotoxins, dermatotoxins and neurotoxins. Many studies on the effects of cyanobacteria and their toxins over a wide range of aquatic organisms, including invertebrates and vertebrates, have reported acute effects (e.g., reduction in survivorship, feeding inhibition, paralysis), chronic effects (e.g., reduction in growth and fecundity), biochemical alterations (e.g., activity of phosphatases, GST, AChE, proteases), and behavioral alterations. Research has also focused on the potential for bioaccumulation and transferring of these toxins through the food chain. Although the herbivorous zooplankton is hypothesized as the main target of cyanotoxins, there is not unquestionable evidence of the deleterious effects of cyanobacteria and their toxins on these organisms. Also, the low toxin burden in secondary consumers points towards biodilution of microcystins in the food web as the predominant process. In this broad review we discuss important issues on bioaccumulation and the effects of cyanotoxins, with emphasis on microcystins, as well as drawbacks and future needs in this field of research.