Uptake and accumulation of dissolved, radiolabeled nodularin in Baltic Sea zooplankton

Incorporating Microbial Species Interaction in Management of Freshwater Toxic Cyanobacteria: A Systems Science Challenge

Water resources are critically important, but also pose risks of exposure to toxic and pathogenic microbes. Increasingly, a concern is toxic cyanobacteria, which have been linked to the death and disease of humans, domesticated animals, and wildlife in freshwater systems worldwide. Management approaches successful at reducing cyanobacterial abundance and toxin production have tended to be short-term solutions applied on small scales (e.g., algaecide application) or solutions that entail difficult multifaceted investments (e.g., modification of landscape and land use to reduce nutrient inputs). However, implementation of these approaches can be undermined by microbial species interactions that (a) provide toxic cyanobacteria with protection against the method of control or (b) permit toxic cyanobacteria to be replaced by other significant microbial threats. Understanding these interactions is necessary to avoid such scenarios and can provide a framework for novel strategies to enhance freshwater resource management via systems science (e.g., pairing existing physical and chemical approaches against cyanobacteria with ecological strategies such as manipulation of natural enemies, targeting of facilitators, and reduction of benthic occupancy and recruitment). Here, we review pertinent examples of the interactions and highlight potential applications of what is known.

(Eco)Toxicology of Cyanobacteria and Cyanotoxins: From Environmental Dynamics to Adverse Effects

The problem of artificial eutrophication, together with the effects of climate changes has led to an increase in the frequency of the occurrence of cyanobacterial blooms [...].

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.

Iningainema tapete sp. nov. (Scytonemataceae, Cyanobacteria) from greenhouses in central Florida (USA) produces two types of nodularin with biosynthetic potential for microcystin-LR and anabaenopeptin production

Iningainema is a recently described genus of heterocytous, false-branching cyanobacteria originally described from Australia. In this work, we present Iningainema tapete sp. nov., isolated from subaerial and terrestrial environments in central Florida (USA). In comparison to the sister species, our novel cyanobacterium produces nodularin-R (NOD-R) and a methylated isoform [MeAdda³] NOD previously not reported within this genus; in addition to possessing the biosynthetic gene clusters for microcystin and anabaenopeptins production. Nodularin accumulation by this cyanobacterium exceeded 500 µg g^-1 dry weight in cultures grown in nitrogen-depleted media. Such elevated toxin concentrations are alarming as the cyanobacterium was isolated from a food production greenhouse and poses a potential risk for food products and for workforce exposure. Using morphology, 16S rRNA gene phylogeny, and 16S-23S rRNA internal transcribed spacer (ITS) secondary structure, coupled with toxin detection and toxin gene presence, we provide evidence for the establishment of a novel toxic species of cyanobacteria, Iningainema tapete.

Seasonal variation of microcystins and their accumulation in fish in two large shallow lakes of China

Bioaccumulation of microcystins (MCs) has been widely observed in aquatic vertebrates and invertebrates, but its seasonal and specific variations remain unclear. In the present study, dissolved MCs in water, algal cell-bound MCs and muscle tissue MCs of nine fish species were investigated monthly in two of the largest shallow lakes in China: Lake Taihu and Lake Chaohu. The fish species were grouped as carnivorous, planktivorous, and omnivorous fish. Seasonal variations in dissolved and algal cell-bound MCs in water and MCs contents of fish hepatopancreas and muscle were investigated in the two lakes from 2009 to 2010. Dissolved MCs in water ranged from 0.35 to 2.56 µg l^-1 in Lake Taihu and 0.16 to 2.45 µg l^-1 in Lake Chaohu, and showed seasonally a unimodal distribution. Algal cell-bound MCs also showed a similar seasonal variation in both lakes, but dissolved MCs in water peaked about one month later than algal cell-bound MCs. The MCs content in the Fish muscle was higher MCs from October to December than in the other months. For most of the fish species, it exceeded the tolerable daily intake value established by the WHO. The averaged MCs content in the muscle of carnivorous, planktivorous, omnivorous fish was 48.2, 28.7 and 37.8 μg kg^-1 in Lake Taihu, respectively, and 27.8, 18.6 and 20.4 μg kg^-1 in Lake Chaohu. It was significantly higher in carnivorous fish than in planktivorous and omnivorous fish, indicating that carnivorous fish has a higher exposure risk to the local people when consuming the harvested fish. The average ratio of hepatopancreas to muscle MCs contents was 13.0, 25.2, 13.8 for carnivorous, planktivorous, omnivorous fishes in Lake Taihu, respectively, and 18.0, 24.9, 14.8 in Lake Chaohu. These ratio for planktivorous fish almost doubled that for carnivorous and omnivorous fish. High correlation of MC content in carnivorous, omnivorous and planktivorous fish indicates that MCs can be delivered along trophic levels in the food chains.

Global change-driven effects on dissolved organic matter composition: Implications for food webs of northern lakes

Northern ecosystems are experiencing some of the most dramatic impacts of global change on Earth. Rising temperatures, hydrological intensification, changes in atmospheric acid deposition and associated acidification recovery, and changes in vegetative cover are resulting in fundamental changes in terrestrial-aquatic biogeochemical linkages. The effects of global change are readily observed in alterations in the supply of dissolved organic matter (DOM)-the messenger between terrestrial and lake ecosystems-with potentially profound effects on the structure and function of lakes. Northern terrestrial ecosystems contain substantial stores of organic matter and filter or funnel DOM, affecting the timing and magnitude of DOM delivery to surface waters. This terrestrial DOM is processed in streams, rivers, and lakes, ultimately shifting its composition, stoichiometry, and bioavailability. Here, we explore the potential consequences of these global change-driven effects for lake food webs at northern latitudes. Notably, we provide evidence that increased allochthonous DOM supply to lakes is overwhelming increased autochthonous DOM supply that potentially results from earlier ice-out and a longer growing season. Furthermore, we assess the potential implications of this shift for the nutritional quality of autotrophs in terms of their stoichiometry, fatty acid composition, toxin production, and methylmercury concentration, and therefore, contaminant transfer through the food web. We conclude that global change in northern regions leads not only to reduced primary productivity but also to nutritionally poorer lake food webs, with discernible consequences for the trophic web to fish and humans.

Effect of Microcystins on Proto- and Metazooplankton Is More Evident in Artificial Than in Natural Waterbodies

The increasing proliferation of cyanobacterial blooms prolongs the impact of cyanobacteria on aquatic fauna, potentially altering trophic relationships. We hypothesized that any effect of dissolved microcystins (toxins produced by cyanobacteria) on plankton assemblages would be more evident in artificial reservoirs and ponds than in natural ones. The concentrations of dissolved microcystins in the waters we studied ranged widely from 0.07 to 0.81 μg/L. We showed that the artificial ponds were subjected to more frequent and longer-lasting harmful algal blooms. The plankton occurring in them were exposed to significantly higher concentrations of dissolved microcystins than those in natural oxbow lakes. Using a general linear model (GLM) regression, our study identified a significant relationship between dissolved microcystins and both the density and biomass of particular zooplankton groups (ciliates, rotifers, cladocerans, copepods). The density, biomass, and richness of the animal plankton were significantly lower in the artificial ponds than in the natural oxbow lakes. The impact of microcystins and the length of time that they remained in the water caused structural homogenization of the plankton.

Potential human health risk assessment of cylindrospermopsin accumulation and depuration in lettuce and arugula

The cyanobacterial toxin cylindrospermopsin (CYN) has become a globally important secondary metabolite due to the negative effect it has on human and animal health. As a means of evaluating the risk of human exposure to CYN, the bioaccumulation and depuration of the toxin in lettuce (Lactuca sativa L.) and arugula (Eruca sativa Mill.) were investigated, after irrigation with contaminated water. The vegetables were irrigated for 7days with CYN (3, 5 and 10μg/L) contaminated water (bioaccumulation phase), and subsequently, irrigated for 7days with uncontaminated distilled water (depuration phase). In general, the bioaccumulation of CYN in both vegetables decreased with increasing exposure concentration. Bioconcentration factor (BCF) of CYN increased with the progression of the experiment at 3.0μg/L CYN, while the reverse occurred at 5 and 10μg/L CYN. In arugula, BCF increased at all CYN exposure concentrations throughout the study. The depuration of CYN decreased with increasing exposure concentration but was highest in the plants of both species with the highest bioaccumulation of CYN. Specifically, in plants previously irrigated with water contaminated with 3, 5 and 10μg/L CYN, the depuration of the toxin was 60.68, 27.67 and 18.52% for lettuce, and 47, 46.21 and 27.67% for arugula, respectively. Human health risks assessment revealed that the consumption of approximately 10 to 40g of vegetables per meal will expose children and adults to 1.00-6.00ng CYN/kg body mass for lettuce and 2.22-7.70ng CYN/kg body mass for arugula. The irrigation of lettuce and arugula with contaminated water containing low CYN concentrations constitutes a potential human exposure route.

Iningainema pulvinus gen nov., sp nov. (Cyanobacteria, Scytonemataceae) a new nodularin producer from Edgbaston Reserve, north-eastern Australia

A new nodularin producing benthic cyanobacterium Iningainema pulvinus gen nov., sp nov. was isolated from a freshwater ambient spring wetland in tropical, north-eastern Australia and characterised using combined morphological and phylogenetic attributes. It formed conspicuous irregularly spherical to discoid, blue-green to olive-green cyanobacterial colonies across the substratum of shallow pools. Morphologically Iningainema is most similar to Scytonematopsis Kiseleva and Scytonema Agardh ex Bornet & Flahault. All three genera have isopolar filaments enveloped by a firm, often layered and coloured sheath; false branching is typically geminate, less commonly singly. Phylogenetic analyses using partial 16S rRNA sequences of three clones of Iningainema pulvinus strain ES0614 showed that it formed a well-supported monophyletic clade. All three clones were 99.7-99.9% similar, however they shared less than 93.9% nucleotide similarity with other cyanobacterial sequences including putatively related taxa within the Scytonemataceae. Amplification of a fragment of the ndaF gene involved in nodularin biosynthesis from Iningainema pulvinus confirmed that it has this genetic determinant. Consistent with these results, analysis of two extracts from strain ES0614 by HPLC-MS/MS confirmed the presence of nodularin at concentrations of 796 and 1096μgg^-1 dry weight. This is the third genus of cyanobacteria shown to produce the cyanotoxin nodularin and the first report of nodularin synthesis from the cyanobacterial family Scytonemataceae. These new findings may have implications for the aquatic biota at Edgbaston Reserve, a spring complex which has been identified as a priority conservation area in the central Australian arid and semiarid zones, based on patterns of endemicity.

Evidence of freshwater algal toxins in marine shellfish: Implications for human and aquatic health

The occurrence of freshwater harmful algal bloom toxins impacting the coastal ocean is an emerging threat, and the potential for invertebrate prey items to concentrate toxin and cause harm to human and wildlife consumers is not yet fully recognized. We examined toxin uptake and release in marine mussels for both particulate and dissolved phases of the hepatotoxin microcystin, produced by the freshwater cyanobacterial genus Microcystis. We also extended our experimental investigation of particulate toxin to include oysters (Crassostrea sp.) grown commercially for aquaculture. California mussels (Mytilus californianus) and oysters were exposed to Microcystis and microcystin toxin for 24h at varying concentrations, and then were placed in constantly flowing seawater and sampled through time simulating riverine flushing events to the coastal ocean. Mussels exposed to particulate microcystin purged the toxin slowly, with toxin detectable for at least 8 weeks post-exposure and maximum toxin of 39.11ng/g after exposure to 26.65μg/L microcystins. Dissolved toxin was also taken up by California mussels, with maximum concentrations of 20.74ng/g after exposure to 7.74μg/L microcystin, but was purged more rapidly. Oysters also took up particulate toxin but purged it more quickly than mussels. Additionally, naturally occurring marine mussels collected from San Francisco Bay tested positive for high levels of microcystin toxin. These results suggest that ephemeral discharge of Microcystis or microcystin to estuaries and the coastal ocean accumulate in higher trophic levels for weeks to months following exposure.

Harmful algae: Effects of cyanobacterial cyclic peptides on aquatic invertebrates-a short review

Cyanotoxins are secondary metabolites produced by cyanobacteria. Cyclic peptides, microcystins and nodularin commonly detected in water reservoirs of different parts of the world may induce various detrimental effects in a wide range of organisms from bacteria to humans. This paper presents the current state of knowledge on the effects of microcystins and nodularin on aquatic invertebrates: zooplankton, decapods and mollusks. Accumulation of microcystins and nodularin in these organisms and possible transfer of the cyanotoxins through the food web and possible threat to humans as consumers are also discussed.

Nodularia spumigena peptides--accumulation and effect on aquatic invertebrates

Thus far, the negative effects of Nodularia spumigena blooms on aquatic organisms have been mainly attributed to the production of the hepatotoxic nodularin (NOD). In the current work, the accumulation of other N. spumigena metabolites in blue mussels and crustaceans, and their effect on Thamnocephalus platyurus and Artemia franciscana, were examined. The liquid chromatography-tandem mass spectrometry (LC-MS/MS) analyses provided evidence that both blue mussels collected after a cyanobacterial bloom in the Baltic Sea and the crustaceans exposed under laboratory conditions to N. spumigena extract accumulated the cyclic anabaenopeptins (APs). In the crustaceans, the linear peptides, spumigins (SPUs) and aeruginosins (AERs), were additionally detected. Exposure of T. platyurus and A. franciscana to N. spumigena extract confirmed the negative effect of nodularin on the organisms. However, high numbers of dead crustaceans were also recorded in the nodularin-free fraction, which contained protease inhibitors classified to spumigins and aeruginosins. These findings indicate that cyanobacterial toxicity to aquatic organisms is a complex phenomenon and the induced effects can be attributed to diverse metabolites, not only to the known hepatotoxins.

Effects of the naturally-occurring contaminant microcystins on the Azolla filiculoides-Anabaena azollae symbiosis

Harmful algal blooms (HABs) contaminate aquatic ecosystems and are responsible for animal poisoning worldwide. We conducted a toxicity test with the aquatic fern and the biofertilizer, Azolla filiculoides. The sporophytes were exposed to three concentrations (0.01, 0.1 and 1μgmL(-1)) of a microcystin (MC) cyanobacterial crude extract and purified MC-LR. The growth of A. filiculoides decreased only at 1μgmL(-1) crude extract concentration while with MC-LR it decreased at all the tested concentrations, indicating that the presence of other compounds in the crude extract altered toxicity and stimulated the fern growth at lower concentrations (0.01 and 0.1μgmL(-1)). Both phycoerythrocyanin and allophycocyanin levels decreased in all the concentrations of crude extract and MC-LR. The phycocyanin had a marked increase at 0.1μgmL(-1) crude extract concentration and a marked decrease at 1μgmL(-1) MC-LR concentration. These changes in the phycobiliprotein content indicate a shift in the antenna pigments of the cyanobionts of A. filiculoides. The changes in two oxidative stress enzymes, glutathione reductase for the crude extract assay and glutathione peroxidase for MC-LR assay, points towards the induction of stress defense responses. The low bioconcentration factor in both crude extract and MC-LR treatments can suggest the low uptake of microcystins, and indicates that the aquatic fern can be used as a biofertilizer and as animal feed but is not suitable for MC phytoremediation.

Microcystin accumulation in cladocerans: first evidence of MC uptake from aqueous extracts of a natural bloom sample

Bioaccumulation of microcystins (MC) in zooplankton has been shown in several studies, mainly in field samples. A few studies, however, have demonstrated MC bioaccumulation in laboratory experiments. Although ingestion of cell-bound MC is considered the main route of MC accumulation, another important source is the MC from the dissolved fraction (DMC). This study reports the accumulation of DMC from aqueous extracts of natural bloom samples in three cladoceran species: Moina micrura, Daphnia laevis and Daphnia similis. Animals were exposed for 96 h to aqueous extracts of lyophilized matter from two bloom samples from Colombian reservoirs in different concentrations (25-1000 mg DW L(-1)). Analysis by HPLC-MS detected MC-LR in these samples at concentrations of 434-538 μg g(-1). For the analysis of MC in animal tissues the samples were homogenized and sonicated in methanol:water (75%) and analyzed by ELISA. Results showed that the animals uptake of MC increased with increasing exposure concentrations of aqueous extracts, with M. micrura and D. laevis clones presenting the highest MC concentrations in their tissues (up to 1170-1260 μg g(-1)) while D. similis the lowest (184 μg g(-1)). This study shows, for the first time, that MC uptake from dissolved fraction by zooplankton is possible, not only from the ingestion of seston or cell-bound MC as previously demonstrated.

Evidence of trophic transfer of microcystins from the gastropod Lymnaea stagnalis to the fish Gasterosteus aculeatus

According to our previous results the gastropod Lymnaea stagnalis exposed to MC-producing cyanobacteria accumulates microcystins (MCs) both as free and covalently bound forms in its tissues, therefore representing a potential risk of MC transfer through the food web. This study demonstrates in a laboratory experiment the transfer of free and bound MCs from L. stagnalis intoxicated by MC-producing Planktothrix agardhii ingestion to the fish Gasterosteus aculeatus. Fish were fed during five days with digestive glands of L. stagnalis containing various concentrations of free and bound MCs, then with toxin-free digestive glands during a 5-day depuration period. MC accumulation was measured in gastropod digestive gland and in various fish organs (liver, muscle, kidney, and gills). The impact on fish was evaluated through detoxification enzyme (glutathion-S-transferase, glutathion peroxydase and superoxyde dismutase) activities, hepatic histopathology, and modifications in gill ventilation, feeding and locomotion. G. aculeatus ingestion rate was similar with intoxicated and toxin-free diet. Fish accumulated MCs (up to 3.96±0.14μgg^-1DW) in all organs and in decreasing order in liver, muscle, kidney and gills. Hepatic histopathology was moderate. Glutathion peroxydase was activated in gills during intoxication suggesting a slight reactive oxygen species production, but without any impact on gill ventilation. Intoxication via ingestion of MC-intoxicated snails impacted fish locomotion. Intoxicated fish remained significantly less mobile than controls during the intoxication period possibly due to a lower health condition, whereas they showed a greater mobility during the depuration period that might be related to an acute foraging for food. During depuration, MC elimination was total in gills and kidney, but partial in liver and muscle. Our results assess the MC transfer from gastropods to fish and the potential risk induced by bound MCs in the food web.

Global warming and hepatotoxin production by cyanobacteria: what can we learn from experiments?

Global temperature is expected to rise throughout this century, and blooms of cyanobacteria in lakes and estuaries are predicted to increase with the current level of global warming. The potential environmental, economic and sanitation repercussions of these blooms have attracted considerable attention among the world's scientific communities, water management agencies and general public. Of particular concern is the worldwide occurrence of hepatotoxic cyanobacteria posing a serious threat to global public health. Here, we highlight plausible effects of global warming on physiological and molecular changes in these cyanobacteria and resulting effects on hepatotoxin production. We also emphasize the importance of understanding the natural biological function(s) of hepatotoxins, various mechanisms governing their synthesis, and climate-driven changes in food-web interactions, if we are to predict consequences of the current and projected levels of global warming for production and accumulation of hepatotoxins in aquatic ecosystems.

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.

Effects on growth and oxidative stress status of rice plants (Oryza sativa) exposed to two extracts of toxin-producing cyanobacteria (Aphanizomenon ovalisporum and Microcystis aeruginosa)

Toxic cyanobacteria are considered emerging world threats, being responsible for the degradation of the aquatic ecosystems. Aphanizomenon ovalisporum produces the toxin Cylindrospermopsin (CYN) being a concern in fresh water habitats. This work aims to increase our knowledge on the effects of this toxic cyanobacterium in plants by studying the alterations in growth parameters and oxidative stress status of rice (Oriza sativa) exposed to the cyanobacteria cell extracts containing CYN. Significant increases in glutathione S-transferase (GST) and glutathione peroxidase (GPx) activities were detected in the different experiments performed. The roots showed to be more sensitive than leaves regarding the enzyme activities. A reduction in the leaf tissue fresh weight was observed after 9 days of plant treatment suggesting a major physiological stress. The exposure of rice plants to a mixture of A. ovalisporum and Microcystis aeruginosa cell extracts containing CYN and microcystins including microcystin-LR, resulted in a significant increase in the GST and GPx activities, suggesting a synergistic effect of both extracts. Together these results point out the negative effects of cyanotoxins on plant growth and oxidative status, induced by A. ovalisporum cell extracts, raising also concerns in the accumulation of CYN.

Cyanobacterial toxins: a qualitative meta-analysis of concentrations, dosage and effects in freshwater, estuarine and marine biota

This paper reviews the rapidly expanding literature on the ecological effects of cyanobacterial toxins. The study employs a qualitative meta-analysis from the literature examining results from a large number of independent studies and extracts general patterns from the literature or signals contradictions. The meta-analysis is set up by putting together two large tables--embodying a large and representative part of the literature (see Appendix A). The first table (Table A.1) reviews the presence (concentrations) of different cyanobacterial toxins in the tissues of various groups of aquatic biota after exposure via different routes, experimentally in the lab or via natural routes in the environment. The second table (Table A.2) reviews the dose dependent effect of toxins on biota. The great majority of studies deal with the presence and effects of microcystin, especially of the MC-LR congener. Although this may partly be justified--MC-LR is an abundant and highly toxic protein--our review also emphasizes what is known about (i) other MC congeners (a number of studies showed a preferred accumulation of the less toxic variant MC-RR in animal tissues), (ii) nodularin (data on a range of biota from studies on the Baltic Sea), (iii) neurotoxins like anatoxin-a(s), which are conspicuously often present at times when mass mortalities of birds occur, (iv) a few studies on the presence and effects of cylindrospermposin, as well as (v) the first examples of ecological effects of newly identified bioactive compounds, like microviridin-J. Data were reorganized to assess to what extent bioconcentration (uptake and concentration of toxins from the water) or biomagnification (uptake and concentration via the food) of cyanobacterial toxins occurs in ecosystems. There is little support for the occurrence of biomagnification, and this reduces the risk for biota at higher trophic levels. Rather than biomagnification biodilution seems to occur in the foodweb with toxins being subject to degradation and excretion at every level. Nevertheless toxins were present at all tropic levels, indicating that some vectorial transport must take place, and in sufficient quantities for effects to possibly occur. Feeding seemed to be the most important route for exposure of aquatic biota to cyanobacterial toxins. A fair number of studies focus on dissolved toxins, but in those studies purified toxin typically is used, and biota do not appear very sensitive to this form of exposure. More effects are found when crude cyanobacterial cell lysates are used, indicating that there may be synergistic effects between different bioactive compounds. Aquatic biota are by no means defenseless against toxic cyanobacteria. Several studies indicate that those species that are most frequently exposed to toxins in their natural environment are also the most tolerant. Protection includes behavioral mechanisms, detoxication of MC and NODLN by conjugation with glutathione, and fairly rapid depuration and excretion. A common theme in much of the ecological studies is that of modulating factors. Effects are seldom straightforward, but are dependent on factors like the (feeding) condition of the animals, environmental conditions and the history of exposure (acclimation and adaptation to toxic cyanobacteria). This makes it harder to generalize on what is known about ecological effects of cyanobacterial toxins. The paper concludes by summarizing the risks for birds, fish, macroinvertebrates and zooplankton. Although acute (lethal) effects are mentioned in the literature, mass mortalities of--especially--fish are more likely to be the result of multiple stress factors that co-occur during cyanobacterial blooms. Bivalves appear remarkably resistant, whilst the harmful effects of cyanobacteria on zooplankton vary widely and the specific contribution of toxins is hard to evaluate.

Accumulation of cyanobacterial toxins in freshwater "seafood" and its consequences for public health: a review

This review summarizes and discusses the current understanding of human exposure to cyanobacterial toxins in "seafood" collected from freshwater and coastal areas. The review consists of three parts: (a) the existing literature on concentrations of cyanobacterial toxins in seafood is reviewed, and the likelihood of bioaccumulation discussed; (b) we derive cyanotoxin doses likely to occur through seafood consumption and propose guideline values for seafood and compare these to guidelines for drinking water; and (c) we discuss means to assess, control or mitigate the risks of exposure to cyanotoxins through seafood consumption. This is discussed in the context of two specific procedures, the food specific HACCP-approach and the water-specific Water Safety Plan approach by the WHO. Risks of exposure to cyanotoxins in food are sometimes underestimated. Risk assessments should acknowledge this and investigate the partitioning of exposure between drinking-water and food, which may vary depending on local circumstances.

Toxins of cyanobacteria

Blue-green algae are found in lakes, ponds, rivers and brackish waters throughout the world. In case of excessive growth such as bloom formation, these bacteria can produce inherent toxins in quantities causing toxicity in mammals, including humans. These cyanotoxins include cyclic peptides and alkaloids. Among the cyclic peptides are the microcystins and the nodularins. The alkaloids include anatoxin-a, anatoxin-a(S), cylindrospermopsin, saxitoxins (STXs), aplysiatoxins and lyngbyatoxin. Both biological and chemical methods are used to determine cyanotoxins. Bioassays and biochemical assays are nonspecific, so they can only be used as screening methods. HPLC has some good prospects. For the subsequent detection of these toxins different detectors may be used, ranging from simple UV-spectrometry via fluorescence detection to various types of MS. The main problem in the determination of cyanobacterial toxins is the lack of reference materials of all relevant toxins. In general, toxicity data on cyanotoxins are rather scarce. A majority of toxicity data are known to be of microcystin-LR. For nodularins, data from a few animal studies are available. For the alkaloids, limited toxicity data exist for anatoxin-a, cylindrospermopsin and STX. Risk assessment for acute exposure could be relevant for some types of exposure. Nevertheless, no acute reference doses have formally been derived thus far. For STX(s), many countries have established tolerance levels in bivalves, but these limits were set in view of STX(s) as biotoxins, accumulating in marine shellfish. Official regulations for other cyanotoxins have not been established, although some (provisional) guideline values have been derived for microcystins in drinking water by WHO and several countries.

Ecosystem consequences of cyanobacteria in the northern Baltic Sea

Cyanobacteria of the Baltic Sea have multiple effects on organisms that influence the food chain dynamics on several trophic levels. Cyanobacteria contain several bioactive compounds, such as alkaloids, peptides, and lipopolysaccharides. A group of nonribosomally produced oligopeptides, namely microcystins and nodularin, are tumor promoters and cause oxidative stress in the affected cells. Zooplankton graze on cyanobacteria, and when ingested, the hepatotoxins (nodularin) decrease the egg production of, for example, copepods. However, the observed effects are very variable, because many crustaceans are tolerant to nodularin and because cyanobacteria may complement the diet of grazers in small amounts. Cyanobacterial toxins are transferred through the food web from one trophic level to another. The transfer rate is relatively low in the pelagic food web, but reduced feeding and growth rates of fish larvae have been observed. In the benthic food web, especially in blue mussels, nodularin concentrations are high, and benthic feeding juvenile flounders have been observed to disappear from bloom areas. In the littoral ecosystem, gammarids have shown increased mortality and weakening of reproductive success under cyanobacterial exposure. In contrast, mysid shrimps seem to be tolerant to cyanobacterial exposure. In fish larvae, detoxication of nodularin poses a metabolic cost that is reflected as decreased growth and condition, which may increase their susceptibility to predation. Cyanobacterial filaments and aggregates also interfere with both hydromechanical and visual feeding of planktivores. The feeding appendages of mysid shrimps may clog, and the filaments interfere with prey detection of pike larvae. On the other hand, a cyanobacterial bloom may provide a refuge for both zooplankton and small fish. As the decaying bloom also provides an ample source of organic carbon and nutrients for the organisms of the microbial loop, the zooplankton species capable of selective feeding may thrive in bloom conditions. Cyanobacteria also compete for nutrients with other primary producers and change the nitrogen (N): phosphorus (P) balance of their environment by their N-fixation. Further, the bioactive compounds of cyanobacteria directly influence other primary producers, favoring cyanobacteria, chlorophytes, dinoflagellates, and nanoflagellates and inhibiting cryptophytes. As the selective grazers also shift the grazing pressure on other species than cyanobacteria, changes in the structure and functioning of the Baltic Sea communities and ecosystems are likely to occur during the cyanobacterial bloom season.

Quantitative real-time PCR detection of toxic Nodularia cyanobacteria in the Baltic Sea

A specific quantitative real-time PCR (qPCR) method was developed for the quantification of hepatotoxin nodularin-producing Nodularia, one of the main bloom-forming cyanobacteria in the Baltic Sea. Specific PCR primers were designed for subunit F of the nodularin synthetase gene (ndaF), which encodes the NdaF subunit of the nodularin synthetase gene complex needed for nodularin production. The qPCR method was applied to water samples (a total of 120 samples) collected from the Baltic Sea in July 2004. As few as 30 ndaF gene copies ml(-1) of seawater could be detected, and thus, the method was very sensitive. The ndaF gene copy numbers and nodularin concentrations were shown to correlate in the Baltic seawater, indicating the constant production of nodularin by Nodularia. This qPCR method for the ndaF gene can be used for detailed studies of Nodularia blooms and their formation. ndaF gene copies and nodularin were detected mostly in the surface water but also in deeper water layers (down to 30 m). Toxic Nodularia blooms are not only horizontally but also vertically widely distributed, and thus, the Baltic fauna is extensively exposed to nodularin.

Accumulation of nodularin in sediments, mussels, and fish from the Gulf of Gdańsk, southern Baltic Sea

In the Gulf of Gdańsk, as in other parts of the Baltic Sea, toxic blooms of Nodularia spumigena are an annual phenomenon. In the present work, the accumulation of nodularin (NOD), a cyanobacterial pentapeptide hepatotoxin, in sediments, blue mussels, and flounders from the Gulf of Gdańsk was studied by enzyme-linked immunosorbent assay (ELISA). In the surface layers of the sediments NOD concentration ranged from 2.3 ng/g dry weight (dw) several months after cyanobacterial bloom to 75 ng/g dw during the bloom. The highest toxin content in mussels was 139 ng/g dw. In two sampling stations situated in the coastal waters of the Gulf of Gdańsk the concentrations of NOD in sediments and mussels were significantly lower than those measured in the Gulf of Finland. In sediments and mussels collected in the Gulf of Gdańsk, the toxin was also detected in March when N. spumigena did not occur. In flounder, NOD accumulated in the liver (489 ng/g dw), guts (21 ng/g dw), and gonads (21 ng/g dw). Hybride quadrupole-time-of-flight liquid chromatography/mass spectrometry/mass spectrometry (TOF-LC/MS/MS) confirmed the presence of NOD in sediment, mussel, and fish samples. Additionally, other NOD analogues, ([DMAdda(3)]NOD and [dhb(5)]NOD), were detected in sediments and mussel tissue. No NOD conjugates with reduced glutathione or cysteine were found in fish and mussels.

Trophic transfer of cyanobacterial toxins from zooplankton to planktivores: consequences for pike larvae and mysid shrimps

The aim of this study was to evaluate the potentially harmful effects of zooplankton preexposed to cyanobacteria on two planktivorous animals: a fish larva (pike, Esox lucius) and a mysid shrimp (Neomysis integer). The planktivores were fed zooplankton from a natural community that had been preexposed to cell-free extract or to purified toxin (nodularin) of the cyanobacterium Nodularia spumigena, and the growth, feeding, and pellet production of the planktivores, as well as the toxin content of the pellets, were measured. In addition, radiolabeled nodularin ((3)H-dihydronodularin) was used in separate experiments to measure the vector transfer of nodularin from zooplankton to their predators. During 11-day exposures, dissolved nodularin was transferred to pike larvae and N. integer via zooplankton at very low rates of accumulation. Treatment with N. spumigena extract decreased the ingestion and feces production rates of pike larvae. With purified nodularin alone, no such effect could be observed. No effect on molting cycle length, fecal pellet production, C:N ratio, or growth of N. integer was detected. The results suggest that dissolved cyanobacterial toxins released during bloom decay can have a negative impact on feeding and, hence, on the growth of fish larvae via zooplankton, even without direct contact between cyanobacteria and the fish.

Quantitative LC-ESI-MS analyses of microcystins and nodularin-R in animal tissue--matrix effects and method validation

The matrix effects and signal response in LC-MS analysis of six microcystins and nodularin-R were studied in mussels and liver samples from the common eider and rainbow trout. The instrumentation used in the study was a triple quadrupole MS with electrospray ionization. The results from the spiked tissue samples showed that both signal suppression and enhancement occurred. The recorded matrix effects were not severe; all studied toxins could be detected with sufficient limit of detection in all matrices. The results indicate, however, that matrix effects must be monitored for accurate quantification of microcystin and nodularin in tissue samples. Matrix effects can be studied with standard additions in the studied matrix, as was done in this study. Solid-phase extraction (SPE) resulted in a lower limit of detection compared to no cleanup in the sample preparation. SPE also prolonged the chromatographic stability. SPE cleanup is therefore strongly recommeded. Also described in this article are the chromatographic and mass spectrometric details of glutathione and cysteine conjugates, which are the detoxification products of the toxins. LC-MS analysis is suitable for detoxification studies of microcystins and nodularins. Cysteine conjugate was identified as the main detoxification product in a mussel sample that was exposed to toxic cyanobacteria in an aquarium.

Ecotoxicological effects of selected cyanobacterial secondary metabolites: a short review

Cyanobacteria are one of the most diverse groups of gram-negative photosynthetic prokaryotes. Many of them are able to produce a wide range of toxic secondary metabolites. These cyanobacterial toxins can be classified in five different groups: hepatotoxins, neurotoxins, cytotoxins, dermatotoxins, and irritant toxins (lipopolysaccharides). Cyanobacterial blooms are hazardous due to this production of secondary metabolites and endotoxins, which could be toxic to animals and plants. Many of the freshwater cyanobacterial blooms include species of the toxigenic genera Microcystis, Anabaena, or Plankthotrix. These compounds differ in mechanisms of uptake, affected organs, and molecular mode of action. In this review, the main focus is the aquatic environment and the effects of these toxins to the organisms living there. Some basic toxic mechanisms will be discussed in comparison to the mammalian system.