Cyanobacterial anabaenopeptin-B, microcystins and their mixture cause toxic effects on the behavior of the freshwater crustacean Daphnia magna (Cladocera)

Ecotoxicological assessment of cyclic peptides produced by a Planktothrix rubescens bloom: Impact on aquatic model organisms

Cyanobacterial blooms, a natural phenomenon in freshwater ecosystems, have increased in frequency and severity due to climate change and eutrophication. Some cyanobacteria are able to produce harmful substances called cyanotoxins. These metabolites possess different chemical structures and action mechanisms representing a serious concern for human health and the environment. The most studied cyanotoxins belong to the group of microcystins which are potent hepatotoxins. Anabaenopeptins are another class of cyclic peptides produced by certain species of cyanobacteria, including Planktothrix spp. Despite limited knowledge regarding individual effects of anabaenopeptins on freshwater organisms, reports have identified in vivo toxicity in representatives of freshwater zooplankton by cyanobacterial extracts or mixtures containing anabaenopeptins. This study focused on the isolation and toxicity evaluation of the cyanotoxins produced in the 2022 Planktothrix rubescens bloom in Averno lake, Italy. The three main cyclic peptides have been isolated and identified by nuclear magnetic resonance (NMR) spectroscopy, mass spectrometry (MS) and optical analyses as anabaenopeptins A and B, and oscillamide Y. Ecotoxicological tests on the aquatic model organisms Daphnia magna (crustacean), Raphidocelis subcapitata (algae), and Aliivibrio fischeri (bacterium) revealed that anabaenopeptins A and B do not generate significant toxicity at environmentally relevant concentrations, being also found a stimulatory effect on R. subcapitata in the case of anabaenopeptin A. By contrast, oscillamide Y displayed toxicity. Ecological implications based on ECOSAR predictions align with experimental data. Moreover, long-term exposure bioassays on different green unicellular algae species showed that R. subcapitata was not significantly affected, while Scenedesmus obliquus and Chlorella vulgaris exhibited altered growth patterns. These results, together with the already-known background in literature, highlight the complexity of interactions between organisms and the tested compounds, which may be influenced by species-specific sensitivities, physiological differences, and modes of action, possibly affected by parameters like lipophilicity.

Lethal and behavioral effects of semi-purified microcystins, Micropeptin and apolar compounds from cyanobacteria on freshwater microcrustacean Thamnocephalus platyurus

The mass proliferation of cyanobacteria, episodes known as blooms, is a concern worldwide. One of the most critical aspects during these blooms is the production of toxic secondary metabolites that are not limited to the four cyanotoxins recognized by the World Health Organization. These metabolites comprise a wide range of structurally diverse compounds that possess bioactive functions. Potential human and ecosystem health risks posed by these metabolites and co-produced mixtures remain largely unknown. We studied acute lethal and sublethal effects measured as impaired mobility on the freshwater microcrustaceans Thamnocephalus platyurus for metabolite mixtures from two cyanobacterial strains, a microcystin (MC) producer and a non-MC producer. Both cyanobacterial extracts, from the MC-producer and non-MC-producer, caused acute toxicity with LC50 (24 h) values of 0.50 and 2.55 mgdw_biomass/mL, respectively, and decreased locomotor activity. Evaluating the contribution of different cyanopeptides revealed that the Micropeptin-K139-dominated fraction from the MC-producer extract contributed significantly to mortality and locomotor impairment of the microcrustaceans, with potential mixture effect with other cyanopeptolins present in this fraction. In the non-MC-producer extract, compounds present in the apolar fraction contributed mainly to mortality, locomotor impairment, and morphological changes in the antennae of the microcrustacean. No lethal or sublethal effects were observed in the fractions dominated by other cyanopetides (Cyanopeptolin 959, Nostoginin BN741). Our findings contribute to the growing body of research indicating that cyanobacterial metabolites beyond traditional cyanotoxins cause detrimental effects. This underscores the importance of toxicological assessments of such compounds, also at sublethal levels.

Interactive effects of cyanobacterial metabolites aeruginosin-98B, anabaenopeptin-B and cylindrospermopsin on physiological parameters and novel in vivo fluorescent indicators in Chironomus aprilinus larvae

We aimed to determine the effects of single cyanobacterial metabolites aeruginosin-B (AER-B), anabaenopeptin-B (ANA-B), cylindrospermopsin (CYL), their binary and ternary mixtures on biomarkers of Chironomus aprilinus larvae: oxygen consumption, fat body structure and two novel fluorescent indicators: imaging of nuclei in cells of body integument, and the catecholamine level. The obtained results showed that oxygen consumption was inhibited by single tested cyanobacterial metabolites except for ANA-B at the lowest concentration (250 μg/L). Although the mixtures of the metabolites inhibited oxygen consumption with antagonistic interactions between the components stimulation was noted in the group exposed to the lowest concentrations of AER-B + CYL (125 μg/L + 125 μg/L, respectively) and the ternary mixture of AER-B + ANA-B + CYL (83.3 μg/L + 83.3 μg/L + 83.3 μg/L, respectively). In vivo fluorescent staining with Hoechst 34580 showed that single AER-B had lower cytotoxic potential on body integument cells than ANA-B and CYL and most binary mixtures except for AER-B + CYL induced synergistic toxicity. Catecholamine level was decreased in animals exposed to single metabolites, their binary and ternary mixtures; however, the interactions between the components in the ternary mixture were antagonistic. Fat body was found to be disrupted in the larvae exposed to single metabolites and their combinations. Antagonistic toxic interactions between the oligopeptide components were found in most binary and the ternary mixtures; however, synergistic effect was noted in the binary mixture of AER-B + CYL. The results suggest that in natural conditions Chironomus larvae and possibly other benthic invertebrates may be affected by cyanobacterial metabolites, however various components and in mixtures and their concentrations may determine varied physiological effects and diverse interactions.

Effects of Harmful Cyanobacteria on Drinking Water Source Quality and Ecosystems

A seasonal plethora of cyanobacteria in the plankton community can have severe implications, not only for water ecosystems but also for the availability of treated water. The catchment of the Obrzyca River (a source of drinking water) is seasonally exposed to harmful cyanobacterial bloom. Previous studies (2008-2012; 2019) revealed that the most polluted water of the Obrzyca River was Uście, close to the outlet of Rudno Lake (at the sampling point). Therefore, the effect on this lake was specifically examined in this study. Sampling was performed from May to September at that site and from July to September 2020 at Rudno Lake. The conducted analysis revealed a massive growth of Aphanizomenon gracile, especially in Rudno Lake. The results showed not only the distinct impact of cyanobacterial bloom on phytoplankton biodiversity but also the presence of microcystins and other cyanopeptides in both sampling points. The maximal total concentration of microcystins (dmMC-RR, MC-RR, dmMC-LR, MC-LR, MC-LY, MC-YR) equaled 57.3 μg/L and the presence of cyanopeptides (aeruginosin, anabaenopeptin) was originally determined in Rudno Lake, August 2021. The presence of these toxins was highlighted in our results for the first time. The same samples from the lake were the most toxic in biotoxicological investigations using the planarian Dugesia tigrina. The performed bioassays proved that D. tigrina is a sensitive bioindicator for cyanotoxins. The physical and chemical indicators of water quality, i.e., color, temperature, total suspended solids, and total nitrogen and phosphorus, showed a significant correlation among each other and towards cyanobacterial abundance and microcystin concentrations.

Cyanobacterial metabolites: aeruginosin 98A, microginin-FR1, anabaenopeptin-A, cylindrospermopsin and their mixtures affect behavioral and physiological responses of Daphnia magna

We determined the effects influence of cyanobacterial products metabolites: aeruginosin-A (AER-A), microginin-FR1 (MG-FR1), anabaenopeptin-A (ANA-A), cylindrospermopsin (CYL) and their binary and quadruple mixtures on swimming behavior, heart rate, thoracic limb activity, oxygen consumption and in vivo cell health of Daphnia magna. The study showed that CYL induced mortality of daphnids at the highest concentrations, however three oligopeptides had no lethal effect. All the tested Each single metabolites inhibited swimming speed. The mixtures AER+MG-FR1 and AER-A+ANA-A induced antagonistic and the quadruple mixture synergistic effects. Physiological endpoints were depressed by CYL, however they were simulated by the oligopeptides and their binary mixtures. The quadruple mixture inhibited the physiological parameters with antagonistic interactions between the components were antagonistic. Single CYL, MG-FR1 and ANA-A induced cytotoxicity with synergistic interactions and the metabolites in mixtures showed. The study suggests that swimming behavior and physiological parameters may be affected by single cyanobacterial oligopeptides, however their mixtures may induce different total effects.

Effects of cyanobacterial metabolites: Aeruginosin 98A, microginin-FR1, anabaenopeptin-A, cylindrospermopsin in binary and quadruple mixtures on the survival and oxidative stress biomarkers of Daphnia magna

The aim of our study was to determine the effects of aeruginosin 98 A (ARE-A), microginin-FR1 (MG-FR1), anabaenopeptin-A (ANA-A) cylindrospermopsin (CYL) and their binary and quadruple mixtures on the survival and the levels of oxidative stress biomarkers in Daphnia magna: total glutathione (GSH), catalase (CAT), dismutase (SOD) and malondialdehyde (MDA). The biochemical indicators were measured with ELISA kits and the interactive effects were determined by isobole and polygonal analysis with Compusyn® computer software. The study revealed that oligopeptides did not decrease daphnid survival, only CYL inhibited this parameter, with synergistic effects when it was used as a component. The single metabolites at the two highest concentrations and all the binary and quadruple mixtures at all concentrations diminished GSH level, however both in the binary and in the quadruple mixtures most of the interactions between the metabolites were antagonistic. Nearly additive effects were found only in AER-A + CYL and MG-FR1+CYL. On the other hand, CAT activity was slightly increased in daphnids exposed to the binary mixtures with antagonistic interactions, however nearly addivive effects were found in animals exposed to the mixture of AER-A + ANA-A and synergistic in the quadruple mixture. SOD was elevated in daphnids exposed to single AER-A and MG-FR1, however it was diminished in the animals exposed to ANA-A and CYL. Binary mixtures in which CYL was present as a component decreased the level of this enzyme with nearly additive interactions in ANA-A + CYL. The quadruple mixture increased SOD level, with antagonistic interactions. Both single cyanobacterial metabolites, their binary and quadruple mixtures induced lipid peroxidation measured by MDA level and most of interactions in the binary mixtures were synergistic. The study suggested that antioxidative system of Daphnia magna responded to the tested metabolites and the real exposure to mixtures of these products may lead to various interactive effects with varied total toxicity.

Acute toxic effects of microcystin-LR on crayfish (Procambarus clarkii): Insights from antioxidant system, histopathology and intestinal flora

To study the toxic effects of microcystin-LR (MC-LR) on crayfish, adult male Procambarus clarkii were exposed to different concentrations of MC-LR for 96 h. In the meantime, the accumulation characteristics of MC-LR and the alternations of antioxidant system, histopathology and intestinal flora of P. clarkii were investigated. The results demonstrated that the hepatopancreas, gills and intestines of P. clarkii could effectively accumulate MC-LR. Antioxidant-related genes such as Mn-sod, cat, gst, gpx, mt and hsp70 showed different expression trends in different organs to respond to MC-LR-induced oxidative stress. MC-LR led to histological changes in the hepatopancreas, gills and intestines, thus affecting their corresponding physiological functions. Additionally, the abundances of bacterial phyla including Firmicutes and Planctomycetes and genera including Dysgonomonas, Brevundimonas and Anaerorhabdus in the intestine were significantly changed after MC-LR exposure, and the disruption of intestinal flora might further cause abnormal intestinal microbial metabolism and genetics in P. clarkii. This study provides novel mechanistic insights into the toxic impacts of microcystins on aquatic crustaceans. HIGHLIGHTS: • MC-LR was significantly accumulated in the hepatopancreas, gills and intestines of P. clarkii. • MC-LR induced the differential expression of antioxidant-related genes of P. clarkii. • MC-LR caused histological alterations in the hepatopancreas, gills and intestines of P. clarkii. • MC-LR affected the intestinal microbial composition and function of P. clarkii.

Toxicity and Starvation Induce Major Trophic Isotope Variation in Daphnia Individuals: A Diet Switch Experiment Using Eight Phytoplankton Species of Differing Nutritional Quality

Stable isotope values can express resource usage by organisms, but their precise interpretation is predicated using a controlled experiment-based validation process. Here, we develop a stable isotope tracking approach towards exploring resource shifts in a key primary consumer species Daphnia magna. We used a diet switch experiment and model fitting to quantify the stable carbon (δ¹³C) and nitrogen (δ¹⁵N) isotope turnover rates and discrimination factors for eight dietary sources of the plankton species that differ in their cellular organization (unicellular or filamentous), pigment and nutrient compositions (sterols and polyunsaturated fatty acids), and secondary metabolite production rates. We also conduct a starvation experiment. We evaluate nine tissue turnover models using Akaike's information criterion and estimate the repetitive trophic discrimination factors. Using the parameter estimates, we calculate the hourly stable isotope turnover rates. We report an exceedingly faster turnover value following dietary switching (72 to 96 h) and a measurable variation in trophic discrimination factors. The results show that toxic stress and the dietary quantity and quality induce trophic isotope variation in Daphnia individuals. This study provides insight into the physiological processes that underpin stable isotope patterns. We explicitly test multiple alternative dietary sources and fasting and discuss the parameters that are fundamental for field- and laboratory-based stable isotope studies.

Negative Effects of Cyanotoxins and Adaptative Responses of Daphnia

The plethora of cyanobacterial toxins are an enormous threat to whole ecosystems and humans. Due to eutrophication and increases in lake temperatures from global warming, changes in the distribution of cyanobacterial toxins and selection of few highly toxic species/ strains are likely. Globally, one of the most important grazers that controls cyanobacterial blooms is Daphnia, a freshwater model organism in ecology and (eco)toxicology. Daphnia-cyanobacteria interactions have been studied extensively, often focusing on the interference of filamentous cyanobacteria with Daphnia's filtering apparatus, or on different nutritional constraints (the lack of essential amino acids or lipids) and grazer toxicity. For a long time, this toxicity only referred to microcystins. Currently, the focus shifts toward other deleterious cyanotoxins. Still, less than 10% of the total scientific output deals with cyanotoxins that are not microcystins; although these other cyanotoxins can occur just as frequently and at similar concentrations as microcystins in surface water. This review discusses the effects of different cyanobacterial toxins (hepatotoxins, digestive inhibitors, neurotoxins, and cytotoxins) on Daphnia and provides an elaborate and up-to-date overview of specific responses and adaptations of Daphnia. Furthermore, scenarios of what we can expect for the future of Daphnia-cyanobacteria interactions are described by comprising anthropogenic threats that might further increase toxin stress in Daphnia.

Behavioral disturbances induced by cyanobacterial oligopeptides microginin-FR1, anabaenopeptin-A and microcystin-LR are associated with neuromotoric and cytotoxic changes in Brachionus calyciflorus

Aquatic animals are exposed to various cyanobacterial products released concomitantly to the environment by decaying blooms. Although there exist results on the toxicity of cyanobacterial extracts little is known on the influence of pure oligopeptides or their mixtures and elucidated mechanisms of behavioral toxicity in zooplanktonic organisms. Therefore, the aim of the present study was to assess the effects of single and mixed pure cyanobacterial oligopeptides: microginin FR-1 (MG-FR1), anabaenopeptin-A (ANA-A) and microcystin-LR (MC-LR) at various concentrations on the swimming behavior and catecholamine neurotransmitter activity, muscular F-actin structure, DNA nuclear content and cell viability of a model rotifer Brachionus calyciflorus. Swimming behavior was analyzed with the use of video digital analysis. Fluorescent microscopy imaging was used to analyze neuromotoric biomarkers in the whole organisms: neuromediator release (by staining with EC517 probe), muscle F-actin filaments (by staining with blue phalloidin dye). DNA content and cytotoxicity was also determined by Hoechst 34580 and propidium iodide double staining, respectively. The results showed that single oligopeptides inhibited all the tested endpoints. The binary mixtures induced synergistic interaction on swimming speed except for MG-FR1 +MC-LR which was nearly additive. Both binary and ternary mixtures also synergistically degraded F-actin and triggered cytotoxic effects visible in the whole organisms. Antagonistic inhibitory effects of all the binary mixtures were found on catecholamine neurotransmitter activity, however the ternary mixture induced additive toxicity. Antagonistic effects of both binary and ternary mixtures were also noted on nuclear DNA content. The results of the study suggest that both depression of neurotransmission and impairment of muscle F-actin structure in muscles may contribute to mechanisms of Brachionus swimming speed inhibition by the tested single cyanobacterial oligopeptides and their mixtures. The study also showed that natural exposure of rotifers to mixtures of these cyanobacterial metabolites may result in different level of interactive toxicity with antagonistic, additive synergistic effects depending on the variants and concentrations present in the environment.

Synergistic toxicity of some cyanobacterial oligopeptides to physiological activities of Daphnia magna (Crustacea)

Anabaenopeptins and microcystins are oligopeptides produced by bloom-forming cyanobacteria. We determined in vivo effects of anabaenopeptin-B (AN-B) and two variants of microcystins of different hydrophobicity (MC-LR and MC-LF) on the physiology of Daphnia magna. Heart rate, thoracic limb activity and post-abdominal claw activity were determined by digital video analysis and oxygen consumption by Oxygraph + system. EC50 calculation and isobole methodology for interactive effects of AN-B and MC-LR mixture were used. Daphnids' responses to all three oligopeptides were concentration- and time-dependent. MC-LF was the most potent inhibitor of heart rate, thoracic limb activity, post-abdominal claw activity and oxygen consumption. AN-B was more toxic than MC-LR toward oxygen consumption; it inhibited the movements of limbs and post-abdominal claw similarly to MC-LR, but did not inhibit heart rate. The strongest toxic effects were induced by the binary mixture of AN-B with MC-LR at the sum concentration equal to the concentration of the single compounds. First time direct synergistic toxic effects of the cyanopeptides on all the physiological parameters were found. The obtained results explain stronger disturbances in aquatic organisms caused by cyanobacterial cell contents than the individual cyanopeptides present even at higher concentrations. Other metabolites and their interactions need further studies.