Daphnia's Adaptive Molecular Responses to the Cyanobacterial Neurotoxin Anatoxin-α Are Maternally Transferred

Dietary exposure of the water flea Daphnia galeata to microcystin-LR

Harmful substances like the cyanotoxin microcystin-leucine-arginine (MC-LR) are commonly found in eutrophic freshwater environments, posing risks to aquatic organisms. The water flea, Daphnia, is a well-established model organism for environmental toxicology research. Nevertheless, there is currently insufficient research on the genes that respond to MC-LR in Daphnia galeata. This study aimed to gain insights into the notable genes that react significantly to MC-LR. In this study, we generated an extensive RNA-Seq sequences isolated from the D. galeata HK strain, Han River in Korea. This strain was nourished with a diet of the green microalga Chlorella vulgaris and treated with pure MC-LR at a concentration of 36 ug/L. The transcriptome profile in response to the MC-LR treatment was obtained and 336 differentially expressed genes were subjected to Gene Ontology (GO) and euKaryotic Orthologous Groups of proteins analyses. GO enrichment analysis showed that chemical stimulus, amino sugar metabolic and catabolic process, oxidative stress, and detoxification were highly enriched, in reverse, proteolysis and fucosylation were underpresented. Detoxification process related genes such as peroxidase-like, chorion, and thyroid peroxidase-like were enriched for eliminating or neutralizing MC_LR from an organism's body. Furthermore, functional protein classification revealed an upregulation of lipid and inorganic ion transport processes, while amino acid and carbohydrate transport processes were found to be downregulated. These findings offer insights into how organisms respond to ecotoxic stimuli, providing valuable information for understanding adaptation or defense pathways.

Cardio- and neuro-toxic effects of four parabens on Daphnia magna

Parabens can potentially disrupt the hormonal regulation of energy metabolism, leading to issues related to obesity, metabolic health, and the cardiovascular and nervous systems. However, the health effects of parabens have yielded conflicting research results. The impact of these substances on aquatic organisms, specifically their neuro- and cardio-toxic effects, has been insufficiently investigated. Hence, the primary goal of our research was to investigate and comprehensively assess the neuro- and cardio-toxic effects of four distinct parabens using the Daphnia magna model. After 48 h of exposure to various concentrations (0.1, 1, and 10 mg/L) of four parabens (methyl-, ethyl-, propyl-, and butyl-paraben), along with a solvent control, we conducted a series of physiological tests, behavioral observations, and gene transcription analyses, focusing on cardiomyopathy, serotonin, glutamate, dopamine, GABA, acetylcholine receptors, and ion flux. From a physiological perspective, the heart rate and thoracic limb activity of the exposed daphnids showed substantial time- and dose-dependent inhibitions. Notably, among the parabens tested, butylparaben exhibited the most potent inhibition, with significant alterations in cardiomyopathy-related gene transcription. In the context of neurotoxicity, all the parabens had a significant impact on gene expression, with methylparaben having the most pronounced effect. Additionally, significant changes were observed in parameters such as distance moved, the distance between individuals, and the extent of body contact among the daphnids. In summary, our findings indicate that each paraben has the capacity to induce neurobehavioral and cardiotoxic disorders in Daphnia magna. The effects of butylparaben on the cardiovascular and nervous systems were found to be the most pronounced. These discoveries showed the potential ecological implications of paraben exposure in aquatic ecosystems, particularly regarding the predator avoidance abilities of Daphnia magna.

A review on aquatic toxins - Do we really know it all regarding the environmental risk posed by phytoplankton neurotoxins?

Aquatic toxins are potent natural toxins produced by certain cyanobacteria and marine algae species during harmful cyanobacterial and algal blooms (CyanoHABs and HABs, respectively). These harmful bloom events and the toxins produced during these events are a human and environmental health concern worldwide, with occurrence, frequency and severity of CyanoHABs and HABs being predicted to keep increasing due to ongoing climate change scenarios. These contexts, as well as human health consequences of some toxins produced during bloom events have been thoroughly reviewed before. Conversely, the wider picture that includes the non-human biota in the assessment of noxious effects of toxins is much less covered in the literature and barely covered by review works. Despite direct human exposure to aquatic toxins and related deleterious effects being responsible for the majority of the public attention to the blooms' problematic, it constitutes a very limited fraction of the real environmental risk posed by these toxins. The disruption of ecological and trophic interactions caused by these toxins in the aquatic biota building on deleterious effects they may induce in different species is paramount as a modulator of the overall magnitude of the environmental risk potentially involved, thus necessarily constraining the quality and efficiency of the management strategies that should be placed. In this way, this review aims at updating and consolidating current knowledge regarding the adverse effects of aquatic toxins, attempting to going beyond their main toxicity pathways in human and related models' health, i.e., also focusing on ecologically relevant model organisms. For conciseness and considering the severity in terms of documented human health risks as a reference, we restricted the detailed revision work to neurotoxic cyanotoxins and marine toxins. This comprehensive revision of the systemic effects of aquatic neurotoxins provides a broad overview of the exposure and the hazard that these compounds pose to human and environmental health. Regulatory approaches they are given worldwide, as well as (eco)toxicity data available were hence thoroughly reviewed. Critical research gaps were identified particularly regarding (i) the toxic effects other than those typical of the recognized disease/disorder each toxin causes following acute exposure in humans and also in other biota; and (ii) alternative detection tools capable of being early-warning signals for aquatic toxins occurrence and therefore provide better human and environmental safety insurance. Future directions on aquatic toxins research are discussed in face of the existent knowledge, with particular emphasis on the much-needed development and implementation of effective alternative (eco)toxicological biomarkers for these toxins. The wide-spanning approach followed herein will hopefully stimulate future research more broadly addressing the environmental hazardous potential of aquatic toxins.

Toxic Effects Produced by Anatoxin-a under Laboratory Conditions: A Review

The presence of cyanotoxins and its bioaccumulation in the food chain is an increasingly common problem worldwide. Despite the toxic effects produced by Anatoxin-a (ATX-a), this neurotoxin has been less studied compared to microcystins (MCs) and cylindrospermopsin (CYN). Studies conducted under laboratory conditions are of particular interest because these provide information which are directly related to the effects produced by the toxin. Currently, the World Health Organization (WHO) considers the ATX-a toxicological database inadequate to support the publication of a formal guideline reference value. Therefore, the aim of the present work is to compile all of the in vitro and in vivo toxicological studies performed so far and to identify potential data gaps. Results show that the number of reports is increasing in recent years. However, more in vitro studies are needed, mainly in standardized neuronal cell lines. Regarding in vivo studies, very few of them reflect conditions occurring in nature and further studies with longer periods of oral exposure would be of interest. Moreover, additional toxicological aspects of great interest such as mutagenicity, genotoxicity, immunotoxicity and alteration of hormonal balance need to be studied in depth.

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.

Reviewing Interspecies Interactions as a Driving Force Affecting the Community Structure in Lakes via Cyanotoxins

The escalating occurrence of toxic cyanobacterial blooms worldwide is a matter of concern. Global warming and eutrophication play a major role in the regularity of cyanobacterial blooms, which has noticeably shifted towards the predomination of toxic populations. Therefore, understanding the effects of cyanobacterial toxins in aquatic ecosystems and their advantages to the producers are of growing interest. In this paper, the current literature is critically reviewed to provide further insights into the ecological contribution of cyanotoxins in the variation of the lake community diversity and structure through interspecies interplay. The most commonly detected and studied cyanobacterial toxins, namely the microcystins, anatoxins, saxitoxins, cylindrospermopsins and β-N-methylamino-L-alanine, and their ecotoxicity on various trophic levels are discussed. This work addresses the environmental characterization of pure toxins, toxin-containing crude extracts and filtrates of single and mixed cultures in interspecies interactions by inducing different physiological and metabolic responses. More data on these interactions under natural conditions and laboratory-based studies using direct co-cultivation approaches will provide more substantial information on the consequences of cyanotoxins in the natural ecosystem. This review is beneficial for understanding cyanotoxin-mediated interspecies interactions, developing bloom mitigation technologies and robustly assessing the hazards posed by toxin-producing cyanobacteria to humans and other organisms.