Dynamics of protein phosphatase gene expression in Corbicula fluminea exposed to microcystin-LR and to toxic Microcystis aeruginosa cells

Integrating regular and transcriptomic analyses reveal resistance mechanisms in Corbicula fluminea (Müller, 1774) in response to toxic Microcystis aeruginosa exposure

The frequent occurrence of cyanobacterial blooms (CYBs) caused by toxic Microcystis aeruginosa poses a great threat to aquatic organisms. Although freshwater benthic bivalves have proven to be capable of uptake high levels of microcystins (MCs) due to their filter-feeding habits, there is a paucity of information concerning their systemic resistance mechanisms to MCs. In this study, the resistance mechanisms in Corbicula fluminea (O. F. Müller, 1774) in response to the exposure of toxic M. aeruginosa were explored through transcriptional analysis combined with histopathological and biochemical phenotypic analysis. Toxic M. aeruginosa exposure caused dose-dependent histological damage in the hepatopancreas. The conjugation reaction catalyzed by glutathione S-transferases was vulnerable to being activated by high concentrations of M. aeruginosa (10 ×10⁵ cells mL^-1). Additionally, reactive oxygen species scavenging processes mediated by superoxide dismutase and catalase were active in the initial stage of toxic M. aeruginosa exposure. The results of the integrated biomarker response index suggested that the biotransformation and antioxidant defense system in C. fluminea could be continuously activated after acute exposure to the high concentration of toxic M. aeruginosa. The eggNOG and GO analysis of the differentially expressed genes (DEGs) indicated that DEGs were significantly enriched in transporter activity, oxidant detoxification and response to oxidative stress categories, which were consistent with the alterations of biochemical indices. Besides, DEGs were significantly annotated in a few KEGG pathways involved in biotransformation (oxidation, cooxidation and conjugation) and immunoreaction (lysosome and phagosome responses), which could be responsible for the tolerance of C. fluminea to toxic M. aeruginosa. These findings improve our understanding of potential resistance mechanisms of freshwater bivalves to MCs.

Review on Cyanobacterial Studies in Portugal: Current Impacts and Research Needs

Cyanobacteria have long been associated with harmful effects on humans, animals and aquatic biota. Cyanotoxins are their most toxic metabolite. This review summarizes the current research, impacts and future needs in cyanobacterial studies undertaken in Portugal, the southernmost country of Europe, and with a recent multiplication of cyanotoxicity due to climate change events. Microcystins are still the most prevalent, studied and the only regulated cyanotoxins in Portuguese freshwater systems much like most European countries. With the development of some tools, particularly in molecular studies, the recent discovery of cylindrospermopsins, anatoxins and saxitoxins, both genes and toxins, in North and Center ecosystems of our country highlight current impacts that overall communities are facing with increased risks of exposure and uptake to cyanotoxins. Research needs encompass the expansion of studies at all aspects due to the uprising of these cyanotoxins and reinforces the urgent need of increasing the frequency of surveillance to achieve tangible effects of cyanotoxins in Portugal to ultimately implement regulations on cylindrospermopsins, anatoxins and saxitoxins worldwide.

Assessment of Lemna minor (duckweed) and Corbicula fluminea (freshwater clam) as potential indicators of contaminated aquatic ecosystems: responses to presence of psychoactive drug mixtures

The pharmaceutical products are emerging pollutants continuously released into the environment, because they cannot be effectively removed by the wastewater treatment plants. In recent years, questions have been raised concerning the environmental risks related to these pollutants. The goal of this research was to evaluate the responses in Lemna minor after 7 days and in Corbicula fluminea after differing durations (1, 3, 7, and 19 days) of exposure to the psychoactive drug mixture (valproic acid, citalopram, carbamazepine, cyamemazine, hydroxyzine, oxazepam, norfluoxetine, lorazepam, fluoxetine, and sertraline) in different concentrations (0, 0 + ethanol, drug concentration (DC) 1 = river water concentration, DC2 = effluent concentration, and DC3 = 10× effluent concentration). In this aim, growth parameters of L. minor, gluthathione S-transferase (GSTs), catalase (CAT), ethoxyresorufin-O-deethylase (EROD) and/or gene expressions (pi-gst, cat, cytochrome P450 4 (cyp4), multidrug resistant 1 (mdr1), and superoxide dismutase (sod)) were measured. GST activities increased significantly in L. minor exposed to DC3, but no changes were found in CAT activity. In C. fluminea, EROD activity was induced significantly in both gill and digestive gland tissues after 3 days' exposure to DC3, while a GST increase was observed only in digestive gland tissues, suggesting that these pharmaceuticals induced an oxidative effect. Gene expression analysis revealed transient transcriptomic responses of cyp4, sod, and mdr1 under drug concentrations 2 or 3 and no change of expression for the other genes (cat and pi-gst) or condition (environmental drug concentration) tested. Finally, the data reported in this study represent important ecotoxicological information, confirming that this enzyme family (cyp4, sod, and mdr1) may be considered as a sensible and early indicator of exposure to drugs and emphasizing the involvement of selected genes in detoxification pathways.

Modulation of hepatic glutathione transferases isoenzymes in three bivalve species exposed to purified microcystin-LR and Microcystis extracts

This study compares the role of hepatic cytosolic glutathione transferases (cGST) isoforms of three different bivalve species to a Microcystis aeruginosa extract and purified MC-LR exposure (both at 150 μg MC-LR L^-1) for 24 h. Characterization and alterations of the cytosolic GST activities in Mytilus galloprovincialis, Ruditapes philippinarum and Corbicula fluminea were measured using four class-specific substrates and changes in individual GST isoforms expression were achieved by a subsequent two-dimensional electrophoresis analysis. Evaluation of cGST activity basal levels using the four class-specific substrates denoted quantitative differences between the three bivalves. Purified MC-LR did not induce any significant response from bivalves. On the other hand, cell extracts caused significant alterations according to bivalves and substrates. Among the three bivalves, only R. philippinarum showed a significant induction of cGST activity using generic 1-chloro-2,4-dinitrobenzene (CDNB) substrate. However, no significant alterations were detected in these clams by cell extracts using the other specific substrates. In contrast, C. fluminea revealed significant induction of cGST activity when using 3,4-dichloronitrobenzene (DCNB) and ethacrynic acid (EA). In M. galloprovincialis, cell extracts promoted a significant decrease of cGST activity when using EA substrate. Altered protein expression was quantitatively detected upon exposure to cell extracts for one spot in R. philippinarum and another for C. fluminea, both upregulated (2.0 and 8.5-fold, respectively) and identified as a sigma1-class GST in the case of the first. The results showed that the three bivalves presented specific adaptive biotransformation responses to MCs and other cyanobacteria compounds supported by the modulation of distinct cGST classes.

Proteomic and Real-Time PCR analyses of Saccharomyces cerevisiae VL3 exposed to microcystin-LR reveals a set of protein alterations transversal to several eukaryotic models

Some of the most common toxins present in freshwater, in particular microcystins (MCs), are produced by cyanobacteria. These toxins have a negative impact on human health, being associated with episodes of acute hepatotoxicity and being considered potentially carcinogenic to humans. To date the exact mechanisms of MC-induced toxicity and tumor promotion were not completely elucidated. To get new insights underlying microcystin-LR (MCLR) molecular mechanisms of toxicity we have performed the proteomic profiling using two-dimensional electrophoresis and MALDI-TOF/TOF of Saccharomyces cerevisiae cells exposed for 4 h-1 nM and 1 μM of MCLR, and compared them to the control (cells not exposed to MCLR). We identified 14 differentially expressed proteins. The identified proteins are involved in metabolism, genotoxicity, cytotoxicity and stress response. Furthermore, we evaluated the relative expression of yeast's PP1 and PP2A genes and also of genes from the Base Excision Repair (BER) DNA-repair system, and observed that three out of the five genes analyzed displayed dose-dependent responses. Overall, the different proteins and genes affected are related to oxidative stress and apoptosis, thus reinforcing that it is probably the main mechanism of MCLR toxicity transversal to several organisms, especially at lower doses. Notwithstanding these MCLR responsive proteins could be object of further studies to evaluate their suitability as biomarkers of exposure to the toxin.

Responses of cytochrome P450, GST, and MXR in the mollusk Corbicula fluminea to the exposure to hospital wastewater effluents

Pharmaceutical products are a major group of chemical compounds that are continuously released into the environment. The primary pathway of pharmaceuticals to the aquatic environment is the discharge of wastewater effluents. The Psychiatric hospital of Montpon (Dordogne, France) operates with its wastewater treatment plant. We first evaluated the presence and concentrations of 27 pharmaceuticals compounds in these effluents. All of the 27 compounds were detected in these wastewater effluents at concentrations ranging between 37,500 ng L(-1) (paracetamol) and 150 ng L(-1) (citalopram). The aim of the study was then to evaluate the exposure effects of the effluents on cytochrome P450, GST, and MXR responses in Corbicula fluminea gills and digestive glands. Experiments on clams exposed during 1, 3, 7 14, and 21 days revealed a strong and continuous overexpression of mdr1 (multidrug resistant 1) gene expression in gills and transitory variations in pi-gst expression and GST activity. EROD activity increased also transitory after 1 day in the digestive gland of exposed clams. These results indicated that in the effluent, some molecules have undergone metabolism of phase 1 and/or phase 2.

Glutathione Transferases Responses Induced by Microcystin-LR in the Gills and Hepatopancreas of the Clam Venerupis philippinarum

A multi-method approach was employed to compare the responses of Glutatione Transferases (GSTs) in the gills and hepatopancreas of Venerupis philippinarum to microcystins (MCs) toxicity. In this way, using the cytosolic fraction, the enzymatic activity of GSTs, superoxide dismutase (SOD), serine/threonine protein phosphatases (PPP2) along with the gene expression levels of four GST isoforms (pi, mu, sigma1, sigma2) were investigated in both organs of the clams exposed for 24 h to 10, 50 and 100 μg L⁻¹ of MC-LR. Cytosolic GSTs (cGSTs) from both organs of the high dose exposed clams were purified by glutathione-agarose affinity chromatography, characterized kinetically and the changes in the expression of cGSTs of the gills identified using a proteomic approach. MC-LR caused an increase in GST enzyme activity, involved in conjugation reactions, in both gills and hepatopancreas (100 μg L⁻¹ exposure). SOD activity, an indicator of oxidative stress, showed significantly elevated levels in the hepatopancreas only (50 and 100 μg L⁻¹ exposure). No significant changes were found in PPP2 activity, the main target of MCs, for both organs. Transcription responses revealed an up-regulation of sigma2 in the hepatopancreas at the high dose, but no significant changes were detected in the gills. Kinetic analysis evidenced differences between gills of exposed and non-exposed extracts. Using proteomics, qualitative and quantitative differences were found between the basal and inducible cGSTs. Overall, results suggest a distinct role of GST system in counteracting MCs toxicity between the gills and the hepatopancreas of V. philippinarum, revealing different roles between GST isoforms within and among both organs.

Transcriptional responses of glutathione transferase genes in Ruditapes philippinarum exposed to microcystin-LR

Glutathione Transferases (GSTs) are phase II detoxification enzymes known to be involved in the molecular response against microcystins (MCs) induced toxicity. However, the individual role of the several GST isoforms in the MC detoxification process is still unknown. In this study, the time-dependent changes on gene expression of several GST isoforms (pi, mu, sigma 1, sigma 2) in parallel with enzymatic activity of total GST were investigated in gills and hepatopancreas of the bivalve Ruditapes philippinarum exposed to pure MC-LR (10 and 100 µg/L). No significant changes in GST enzyme activities were found on both organs. In contrast, MC-LR affected the transcriptional activities of these detoxification enzymes both in gills and hepatopancreas. GST transcriptional changes in gills promoted by MC-LR were characterized by an early (12 h) induction of mu and sigma 1 transcripts. On the other hand, the GST transcriptional changes in hepatopancreas were characterized by a later induction (48 h) of mu transcript, but also by an early inhibition (6 h) of the four transcripts. The different transcription patterns obtained for the tested GST isoforms in this study highlight the potential divergent physiological roles played by these isoenzymes during the detoxification of MC-LR.

A cantilever biosensor-based assay for toxin-producing cyanobacteria Microcystis aeruginosa using 16S rRNA

Monitoring of cyanotoxins in source waters is currently done through toxin-targeting assays which suffer from low sensitivity due to poor antibody avidity. We present a biosensor-based method as an alternative for detecting toxin-producing cyanobacteria M. aeruginosa via species-selective region of 16S rRNA at concentrations as low as 50 cells/mL, and over a five-log dynamic range. The cantilever biosensor was immobilized with a 27-base DNA strand that is complementary to the target variable region of 16S rRNA of M. aeruginosa. The cantilever sensor detects mass-changes through shifts in its resonant frequency. Increase in the biosensor's effective mass, caused by hybridization of target strand with the biosensor-immobilized complementary strand, showed consistent and proportional frequency shift to M. aeruginosa concentrations. The sensor hybridization response was verified in situ by two techniques: (a) presence of duplex DNA structure postdetection via fluorescence measurements, and (b) secondary hybridization of nanogold-labeled DNA strands to the captured 16S rRNA strands. The biosensor-based assay, conducted in a flow format (∼ 0.5 mL/min), is relatively short, and requires a postextraction analysis time of less than two hours. The two-step detection protocol (primary and secondary hybridization) is less prone to false negatives, and the technique as a whole can potentially provide an early warning for toxin presence in source waters.