Marine glutathione S-transferases

Assessment of Amphibola crenata as a bioindicator of estuarine trace element pollution using biochemical and physiological endpoints

To assess its utility as a bioindicator of estuarine contamination, Amphibola crenata, a pulmonate mud snail, was collected from 17 estuaries in New Zealand. Whole-body soft tissue trace element concentrations were measured via quadrupole inductively coupled plasma mass spectrophotometer (Q-ICP-MS) and were found to be significantly positively correlated with sediment trace element profiles for arsenic, copper and lead. Snails from polluted estuaries generally displayed higher ammonia excretion rates, elevated whole-body soft tissue catalase activity and lipid peroxidation compared to snails from reference sites. Across all sites haemolymph glucose was positively correlated with the tissue burdens of arsenic, copper, nickel and zinc, while haemolymph protein was negatively correlated with arsenic, cadmium and zinc soft tissue concentrations, indicative of altered energy metabolism associated with trace element contamination. Overall, sites were distinguishable by application of the array of measures employed. Our findings suggest that gastropods have significant value as bioindicators of estuarine health.

Naphthalene and phenanthrene affect differentially two glutathione S-transferases (GSTs) expression, GST activity, and glutathione content in white shrimp P. vannamei

Polycyclic aromatic hydrocarbons (PAHs) are persistent organic pollutants ubiquitous in coastal ecosystems. The white shrimp Penaeus vannamei naturally inhabits in coastal areas and is cultivated in farms located nearby the oceans. PAHs can damage shrimp health, endanger natural populations, and lower shrimp aquaculture productivity. However, crustaceans have enzymes capable of metabolizing organic xenobiotics as PAHs and to neutralize reactive oxygen species (ROS) produced during xenobiotics metabolism. An important superfamily of xenobiotic-metabolizing and antioxidant enzymes are glutathione S-transferases (GSTs). In white shrimp, some GSTs are known, but they have been scarcely studied in response to PAHs. In this study we report the molecular cloning and bioinformatic characterization of two novel nucleotide sequences corresponding to cytosolic GSTs belonging the Delta and Theta classes (GSTD and GSTT). Both proteins genes have tissue-specific patterns of expression under normal conditions, that do not necessarily relate to GST activity and glutathione content. The expression of the GSTD and GSTT, GST activity and glutathione content was analyzed in juvenile P. vannamei exposed to two PAHs, naphthalene (NAP) and phenanthrene (PHE) in sub-lethal concentrations for 96 h. GSTD expression was up-regulated by the two PAHs, while GSTT expression was only induced by NAP. In contrast, GST activity towards CDNB was only up-regulated by PHE, suggesting differential effects of PAHs at gene and protein level. On the other hand, lower reduced glutathione content (GSH) caused by PAHs indicates its utilization for detoxification or antioxidant defenses. However, the GSH/GSSG did not change by PAHs treatment, indicating that shrimp can maintain redox balance during short-term sub-lethal exposure to NAP and PHE. Despite the variations in the responses to NAP and PHE, all these results suggest that the GSTD and GSTT genes could be useful biomarkers for PAH exposure in P. vannamei.

Multistress Interplay: Time and Duration of Ocean Acidification Modulate the Toxicity of Mercury and Other Metals

The current understanding of multistress interplay assumes stresses occur in perfect synchrony, but this assumption is rarely met in the natural marine ecosystem. To understand the interplay between nonperfectly overlapped stresses in the ocean, we manipulated a multigenerational experiment (F0-F3) to explore how different temporal scenarios of ocean acidification will affect mercury toxicity in a marine copepod Pseudodiaptomus annandalei. We found that the scenario of past acidification aggravated mercury toxicity but current and persistent acidification mitigated its toxicity. We specifically performed a proteomics analysis for the copepods of F3. The results indicated that current and persistent acidification initiated the energy compensation for development and mercury efflux, whereas past acidification lacked the barrier of H+ and had dysfunction in the detoxification and efflux system, providing a mechanistic understanding of mercury toxicity under different acidification scenarios. Furthermore, we conducted a meta-analysis on marine animals, demonstrating that different acidification scenarios could alter the toxicity of several other metals, despite evidence from nonsynchronous scenarios remaining limited. Our study thus demonstrates that time and duration of ocean acidification modulate mercury toxicity in marine copepods and suggests that future studies should move beyond the oversimplified scenario of perfect synchrony in understanding multistress interaction.

Biochemical, molecular, and physiological assessments of crude oil dietary exposure in sub-adult red drum (Sciaenops ocellatus)

A 14-day exposure study in which sub-adult red drum (Sciaenops ocellatus) were fed a petroleum crude oil-treated pellet feed was conducted to assess the potential effects of ingesting an oil-contaminated food source. Though food consumption decreased, significant polycyclic aromatic hydrocarbons accumulated in the body and liver, which did not affect the body and liver's fatty acid composition. In the red drum given the crude oil-treated feed, a significant decrease in the RNA:DNA growth rate index was noted, while only subtle changes in body and liver lipid composition were seen. Differentially expressed gene analysis in the liver demonstrated a significant down-regulation of leptin and up-regulation of the aryl hydrocarbon receptor nuclear translocator-like protein 1. Gene ontology and Kyoto Encyclopedia of Genes and Genomes analyses indicated enrichment of terms and pathways associated with cholesterol biosynthesis and oxidative stress. Ingenuity Pathway Analysis further predicted activation of seven pathways associated with cholesterol biosynthesis. Measured oxidative stress biomarkers in the blood indicated decreased systemic antioxidants with increased lipid peroxidation. The results of this study suggest that dietary oil exposure alters the signaling of biological pathways critical in cholesterol biosynthesis and disruptions in systemic oxidative homeostasis.

Two novel glutathione S-transferase (GST) genes in the toxic marine dinoflagellate Alexandrium pacificum and their transcriptional responses to environmental contaminants

The present study identified two novel glutathione S-transferase (GST) genes from the toxic dinoflagellate Alexandrium pacificum and examined their molecular characteristics and transcriptional responses to algicides and environmental contaminants. Bioinformatic analysis revealed that both ApGSTs are cytosolic, belonging to the chi-like class (ApGST1) and an undefined class (ApGST2). The overall expression of ApGSTs showed similar patterns depending on the exposed contaminants, while they were differently regulated by polychlorinated biphenyl (PCB). Copper treatments (CuCl2 and CuSO4) did not significantly induce the expression of ApGSTs. The highest up-regulations of ApGST1 and ApGST2 were under 6-h treatments of 0.10 and 0.50 mg L-1 NaOCl. Interestingly, only ApGST1 increased significantly after 0.10, 0.50, and 1.00 mg L-1 of PCB exposure (6 h). Intracellular reactive oxygen species (ROS) increased considerably under NaOCl; however, it was not significantly higher in the PCB-treated cells. GST activity was increased by NaOCl and PCB treatments, but only PCB caused apoptosis. These results suggest that GSTs are involved in the first line of phase II detoxification, protecting dinoflagellate cells against oxidative damage.

Toxic effects of tire wear particles and the leachate on the Chinese mitten crab (Eriocheir sinensis)

Tire wear particles (TWPs) were considered as an important component of microplastic pollution in the aquatic environment. To understand the ecotoxicity of TWPs to crustacean, this study investigated toxic effects of TWPs and the leachate on the mitten crab Eriocheir sinensis and the accumulation of TWPs in the crabs. Although TWPs could be accumulated in various tissues (i.e., liver, gills and gut) of the crabs, exposure to TWPs or the leachate had no lethal effect on the crabs in this study. Lower concentrations of TWPs and the leachate exposure could stimulate the antioxidant defense system of the crabs, while higher concentrations could disrupt the stress defense system. In addition, the energy supply and metabolism of the crabs could also be affected by TWPs or the leachate. The transcriptomic profiles showed that the toxic mechanisms of TWPs and the leachate were not exactly the same. Similar to the results of biochemical analysis, several Gene Ontology (GO) terms and the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways related to oxidative stress and energy metabolism were significantly regulated by both TWPs and the leachate. However, TWPs could affect the expression of genes enriched in immune-related pathways, while the leachate regulated the enrichment of some other signaling pathways including FoxO signaling pathway, insulin signaling pathway, RIG-I-like receptor signaling pathway, NOD-like receptor signaling pathway, PPAR signaling pathway and neuroactive ligand-receptor interaction. Overall, our study could provide basic biological information for assessing the ecological risk of the TWP pollution in the aquatic environment and was useful to understand the potential toxic mechanisms of the TWPs and the leachate to crustaceans.

Transcriptomic and Functional Analyses of Two Cadmium Hyper-Enriched Duckweed Strains Reveal Putative Cadmium Tolerance Mechanisms

Cadmium (Cd) is one of the most toxic metals in the environment and exerts deleterious effects on plant growth and production. Duckweed has been reported as a promising candidate for Cd phytoremediation. In this study, the growth, Cd enrichment, and antioxidant enzyme activity of duckweed were investigated. We found that both high-Cd-tolerance duckweed (HCD) and low-Cd-tolerance duckweed (LCD) strains exposed to Cd were hyper-enriched with Cd. To further explore the underlying molecular mechanisms, a genome-wide transcriptome analysis was performed. The results showed that the growth rate, chlorophyll content, and antioxidant enzyme activities of duckweed were significantly affected by Cd stress and differed between the two strains. In the genome-wide transcriptome analysis, the RNA-seq library generated 544,347,670 clean reads, and 1608 and 2045 differentially expressed genes were identified between HCD and LCD, respectively. The antioxidant system was significantly expressed during ribosomal biosynthesis in HCD but not in LCD. Fatty acid metabolism and ethanol production were significantly increased in LCD. Alpha-linolenic acid metabolism likely plays an important role in Cd detoxification in duckweed. These findings contribute to the understanding of Cd tolerance mechanisms in hyperaccumulator plants and lay the foundation for future phytoremediation studies.

Assessing the impact of terbium on Mytilus galloprovincialis: Metabolic and oxidative stress responses

The increasing demand for electric and electronic equipment has led to a rise in potentially hazardous electronic waste, including rare-earth elements (REEs), such as terbium (Tb), which have been already detected in aquatic systems. This study investigated the biochemical effects of anthropogenic Tb on mussels over a 28-day period. The mussels were exposed to different concentrations of Tb (0, 5, 10, 20, 40 μg/L), and biomarkers related to metabolism, oxidative stress, cellular damage, and neurotoxicity were evaluated. Bioaccumulation of Tb in the mussels' tissue increased with exposure concentrations, but the bioconcentration factor remained similar between treatments. Exposure to Tb enhanced glycogen consumption and decreased metabolic capacity which could be seen as a physiological adaptation to limit Tb accumulation. Antioxidant defenses and glutathione S-transferases showed a more complex dose-response, with enzymatic responses increasing until 10 μg/L but then returning to control levels at 20 μg/L. At 40 μg/L, enzymatic responses were also enhanced but to a lower extent than at 10 μg/L. The presence of Tb had clearly an inhibitory effect on biotransformation enzymes such as carboxylesterases in a dose-dependent manner. Likely, thanks to biochemical and physiological adaptations, no cellular damage or neurotoxicity was observed in any treatments, confirming the mussels' ability to tolerate Tb exposure. Nevertheless, prolonged exposure to these concentrations could lead to harmful consequences when facing other environmental stressors, such as misallocating energy resources for growth, reproduction, and defense mechanisms.

Glutathione S-transferase gene diversity and their regulation by Nrf2 in Chinese mitten crab (Eriocheir sinensis) during nitrite stress

Eriocheir sinensis is one of the most important economic aquatic products in China. However, nitrite pollution has become a serious threat to the healthy culture of E. sinensis. Glutathione S-transferase (GST) is an important phase II detoxification enzyme, which plays a leading role in the cellular detoxification of exogenous substances. In this study, we obtained 15 GST genes (designated as EsGST1-15) from E. sinensis, and their expression and regulation in E. sinensis under nitrite stress were studied. EsGST1-15 belonged to different GST subclasses. EsGST1, EsGST2, EsGST3, EsGST4, and EsGST5 belonged to Delta-class GSTs; EsGST6 and EsGST7 are Theta-class GSTs; EsGST8 is a mGST-3-class GST; EsGST9 belonged to mGST-1-class GSTs; EsGST10 and EsGST11 belonged to Sigma-class GSTs; EsGST12, EsGST13, and EsGST14 are Mu-class GSTs; EsGST15 is a Kappa-class GST. Tissue distribution experiments showed that EsGSTs were widely distributed in all detected tissues. The expression level of EsGST1-15 was significantly increased in the hepatopancreas under nitrite stress, indicating that EsGSTs were involved in the detoxification of E. sinensis under nitrite stress. Nuclear factor-erythroid 2 related factor 2 (Nrf2) is a transcription factor that can activate the expression of detoxification enzyme. We detected the expression of EsGST1-15 after interfering with EsNrf2 in the hepatopancreas of E. sinensis with or without nitrite stress. Results showed that EsGST1-15 were all regulated by EsNrf2 with or without nitrite stress. Our study provides new information about the diversity, expression, and regulation of GSTs in E. sinensis under nitrite stress.

Genome-wide identification glutathione-S-transferase gene superfamily in Daphnia pulex and its transcriptional response to nanoplastics

Glutathione S-transferases (GSTs) are key multifunctional phase II detoxification enzymes involved in the regulation of growth, development, and stress responses. However, the knowledge of GSTs in the model invertebrate organism Daphnia pulex at the genomic level remains limited. In the present study, 35 GST genes were identified in D. pulex (Dp-GST), belonging to eight subfamilies, with the sigma, mu, and delta/epsilon subfamilies constituting approximately 29 %, 20 %, and 20 % of the GST superfamily, respectively. Chromosome tandem duplication of genes within the same subfamily was observed, which may be the main force driving GST expansion in D. pulex. DpGST genes showed different expression patterns in response to nanoplastic exposure for 96 h and 21 days. Some homologous GST genes in D. pulex showed similar expression patterns in response to nanoplastic exposure, likely owing to their unique motifs. For example, motif 9 is found in all delta/epsilon GST genes, whereas motifs 1, 2, 3, 5, and 7 are highly conserved in sigma GST genes. The characterization of D. pulex GSTs extending the knowledge of GST-mediated environmental contaminants, especially nanoplastics.

pCO2-driven seawater acidification affects aqueous-phase copper toxicity in juvenile flounder Paralichthys olivaceus: Metal accumulation, antioxidant defenses and detoxification in livers

Ocean acidification potentially influences the biotoxicity of metals and the antioxidant defense systems of marine organisms. This study investigated how pCO₂-driven seawater acidification (SA) affected aqueous-phase copper (Cu) toxicity in the juvenile flounder Paralichthys olivaceus from the perspective of hepatic oxidative stress and damage to better understand the mechanisms underlying the biological effects produced by the two stressors. Fish were exposed to aqueous-phase Cu at relevant ambient and polluted concentrations (0, 5, 10, 50, 100 and 200 μg L^-1) at different pH levels (no SA: pH 8.10; moderate SA: pH 7.70, pCO₂ ∼1353.89 μatm; extreme SA: pH 7.30, pCO₂ ∼3471.27 μatm) for 28 days. A battery of biomarkers in the livers was examined to investigate their roles in antioxidant defense and detoxification in response to coexposure. Hepatic Cu accumulation (30.22-184.90 mg kg^-1) was positively correlated with Cu concentrations. The biomarkers responded adaptively to different redox states following SA and Cu exposure. In unacidified seawater, increases in Cu concentrations significantly induced hepatic lipid peroxidation (LPO, by up to 27.03 %), although compensatory responses in antioxidant defenses and detoxification were activated. Moderate SA helped maintain hepatic redox homeostasis and alleviated LPO through different defense strategies, depending on Cu concentrations. Under extreme SA, antioxidant-based defenses were activated to cope with oxidative stress at ambient-low Cu concentrations but failed to defend against Cu toxicity at polluted Cu levels, and LPO (by up to 63.90 %) was significantly induced. Additionally, thiols (GSH and MT) responded actively to cope with Cu toxicity under SA. SOD, CAT, EROD, and GST were also sensitively involved in defending against hepatic oxidative stress during coexposure. These findings highlight the notable interactive effects of SA and Cu and provide a basis for understanding antioxidant-based defenses in marine fish confronting environmental challenges.

Transcriptomics Analysis of the Toxicological Impact of Enrofloxacin in an Aquatic Environment on the Chinese Mitten Crab (Eriocheir sinensis)

Enrofloxacin is an important antimicrobial drug that is widely used in aquaculture. Enrofloxacin residues can have negative effects on aquatic environments and animals. The toxicological effects of different concentrations of enrofloxacin residues in cultured water on Chinese mitten crabs (Eriocheir sinensis) were compared. A histological analysis of the E. sinensis hepatopancreas demonstrated that the hepatopancreas was damaged by the different enrofloxacin residue concentrations. The hepatopancreas transcriptome results revealed that 1245 genes were upregulated and that 1298 genes were downregulated in the low-concentration enrofloxacin residue group. In the high-concentration enrofloxacin residue group, 380 genes were upregulated, and 529 genes were downregulated. The enrofloxacin residues led to differentially expressed genes related to the immune system and metabolic processes in the hepatopancreas of the Chinese mitten crab, such as the genes for alkaline phosphatase, NF-kappa B inhibitor alpha, alpha-amylase, and beta-galactosidase-like. The gene ontology terms "biological process" and "molecular function" were enriched in the carboxylic acid metabolic process, DNA replication, the synthesis of RNA primers, the transmembrane transporter activity, the hydrolase activity, and the oxidoreductase activity. A Kyoto Encyclopedia of Genes and Genomes pathway analysis determined that the immune and metabolic signal transduction pathways were significantly enriched. Furthermore, the nonspecific immune enzyme (alkaline phosphatase) and the metabolic enzyme system played a role in the enrofloxacin metabolism in the E. sinensis hepatopancreas. These findings helped us to further understand the basis of the toxicological effects of enrofloxacin residues on river crabs and provided valuable information for the better utilization of enrofloxacin in aquatic water environments.

Evaluation of antioxidant capacity and digestive enzyme activities in Mytilus galloprovincialis exposed to nanoplastics under different patterns of hypoxia

In the marine environment, plastic pollution may occur simultaneously with hypoxia. However, current ecological risk assessments of nanoplastics have rarely considered the impact of additional environmental factors, such as hypoxia. In this study, we investigated the effect of polystyrene nanospheres (PS-NPs) on the digestive performance (antioxidant system and digestive enzymes) of mussels Mytilus galloprovincialis under different patterns of hypoxia (normoxia, constant hypoxia, and fluctuating hypoxia). The result showed that PS-NPs caused oxidative damage in the digestive glands of mussels, while all patterns of hypoxia exacerbated this oxidative damage. Activities of four digestive enzymes (α-amylase, cellulase, trypsin, and lipase) were examined. Among these, the activity of the α-amylase was inhibited by PS-NPs, and the inhibition was aggravated by all the hypoxia patterns. The cellulase activity and trypsin activity was enhanced by PS-NPs, and the increase was further stimulated by hypoxia. Lipase activity was not affected by PS-NPs alone, but significant inhibition was detected after the coexposure to PS-NPs and hypoxia. Conclusively, the combined stress of hypoxia and nanoplastics can significantly affect the digestive performance of mussels and may alter the mussel nutrient uptake strategy. Our work has provided new insight into the ecological risk assessment of plastics under global climate change.

Effects of atrazine and diuron on life parameters, antioxidant response, and multixenobiotic resistance in non-targeted marine zooplankton

Atrazine and diuron are among the most widely used antifoulant biocides in the world. Due to their persistence in the environment, they can induce adverse effects on non-targeted organisms. In this study, we investigated the chronic in vivo toxicity of atrazine and diuron with further assessments on oxidative stress responses (e.g., oxidative stress, antioxidant) and multixenobiotic resistance (MXR) function in the rotifer Brachionus koreanus, a non-targeted microzooplanktonic grazer at the primary level of the marine food chain. Although similar oxidative response was shown by both biocides, diuron induced stronger retardation on reproduction and population growth rates of B. koreanus while moderate effects were observed by atrazine. This higher toxicity of diuron was shown to be associated with its stronger inhibition of MXR conferred by P-glycoprotein and multidrug resistance proteins which play as a first line of defense by transporting various toxicants out of a cell. Our study provides new insight into non-targeted effects of biocides on marine zooplankton and mechanisms beyond their different degrees of toxicity.

Single-Cell Sequencing Reveals Types of Hepatopancreatic Cells and Haemocytes in Black Tiger Shrimp (Penaeus monodon) and Their Molecular Responses to Ammonia Stress

The cell types and developmental trajectories of shrimp cells based on the transcriptional level have not been established, and gene expression profile and function at the single-cell level is unclear. We aimed to use scRNA-seq to construct a single-cell resolution transcriptional map of hepatopancreas and haemocytes in shrimp to analyse the molecular mechanisms of the immune response to ammonia nitrogen stress. In the present study, seven cell clusters were successfully identified in each of the two tissues (haemocytes, Hem1-7; hepatopancreas, Hep1-7) based on specifically-expressed marker genes. The developmental starting points of haemocytes and hepatopancreatic cells were Hem2 and Hep1, respectively. We propose that Hem2 has oligopotent potential as the initiation site for haemocyte development and that Hem4 and Hem5, located at the end of development, are the most mature immune cell types in haemocytes. Hep5 and Hep6 were the developing terminal cells of hepatopancreas. The antioxidant system and proPO system of shrimp were activated under ammonia nitrogen stress. A large number of DEGs were involved in oxidative stress, detoxification metabolism, and immune defence. In particular, important response genes such as AMPs, proPO, and GST were not only marker genes for identifying cell groups but also played an important role in shrimp cell differentiation and functional plasticity. By successfully applying 10× Genomics based scRNA-seq to the study of shrimp, the single-cell transcriptional profiles of hepatopancreatic cells and haemocytes of shrimp innate immune responses under ammonia stress were constructed for the first time. This atlas of invertebrate hepatopancreatic cells and haemocytes at single-cell resolution identifies molecular events that underpin shrimp innate immune system responses to stress.

Moderate acidification mitigates the toxic effects of phenanthrene on the mitten crab Eriocheir sinensis

Freshwater acidification and phenanthrene may result in complex adverse effects on aquatic animals. Juvenile Chinese mitten crabs (Eriocheir sinensis) were exposed to different pH levels (7.8, 6.5, and 5.5) under phenanthrene (PHE) (0 (control) and 50 μg/L) conditions for 14 days. Antioxidant and transcriptomic responses were determined under stress conditions to evaluate the physiological adaptation of crabs. Under the control pH 7.8, PHE led to significantly reduced activities of superoxide dismutase (SOD), catalase (CAT), glutathione reductase (GR) and glutathione S-transferase (GST), but increased glutathione peroxidase (GSH-Px), 7-ethoxyresorufin-o-deethylase (EROD) activities, and malondialdehyde (MDA) levels. However, moderate acidification (pH 6.5) changed PHE effects by increasing antioxidant enzymes. Acidification generally reduced SOD, GPx, GST and EROD activities, but increased CAT, GR, MDA. Compared with pH7.8 group, pH7.8 × PHE and pH6.5 × PHE groups had 1148 and 1498 differentially expressed genes, respectively, with "Biological process" being the main category in the two experimental groups. pH7.8 × PHE treatment caused significant enrichment of disease and immune-related pathways, while under pH6.5 × PHE, more pathways related to metabolism, detoxification, environmental information processing, and energy supply were significantly enriched. Thus, PHE had a significant inhibitory effect on antioxidant performance in crabs, while moderate acidification (pH6.5) mitigated the toxic effects of PHE. Overall, moderate acidification has a positive effect on the defense against the negative effects of PHE in Chinese mitten crabs, and this study provides insights into the defense mechanism of crustaceans in response to combined stress of acidification and PHE.

Effects of particulate matter (PM2.5) on life history traits, oxidative stress, and defensome system in the marine copepod Tigriopus japonicus

Particulate matter (PM_2.5) generated in large cities creates new problems in marine ecosystems and may adversely affect its inhabitants. However, the mechanisms underlying the same remain unclear; hence, we investigated the effects of PM_2.5 on life history traits (e.g., mortality, development, and fecundity), cellular reactive oxygen species (ROS) levels, antioxidant enzyme (e.g., glutathione peroxidase [GPx], superoxide dismutase [SOD], and catalase [CAT]) activities, and the transcript levels of detoxification-related genes (cytochrome P450s [CYPs]) and antioxidant (glutathione S-transferases [GSTs]) in the copepod Tigriopus japonicus. Among the life history traits, developmental time was the only trait to significantly deviate (P < 0.05) in response to PM_2.5 (compared to that in the controls). Significant changes in ROS levels and antioxidant enzymatic activities (P < 0.05) in response to PM_2.5, suggested that PM_2.5 can induce oxidative stress, leading to adverse effects on the T. japonicus life history. In addition, PM_2.5 induced a differential regulation of various CYP and GST genes, particularly CYP307E1, GST-kappa, and GST-sigma were significantly upregulated (P < 0.05), suggesting that these genes likely play crucial roles in detoxification mechanisms and could be useful as reliable biomarkers for PM_2.5 toxicity. Overall, the results of this study provide new insights into the potential toxicity of PM_2.5.

Different patterns of hypoxia aggravate the toxicity of polystyrene nanoplastics in the mussels Mytilus galloprovincialis: Environmental risk assessment of plastics under global climate change

Hypoxia, largely triggered by anthropogenic activities and global climate change, exerts widespread and expanding stress on marine ecosystems. As an emerging contaminant, the influence of nanoplastics on marine organisms has also attracted attention in recent years. However, the impact of hypoxia on the risk assessments of nanoplastics is rarely considered. This study investigated the toxicity of PS-NPs (0, 0.5, and 5 mg/L) to the coastal mussels Mytilus galloprovincialis under different patterns of hypoxia (normoxia, constant hypoxia, and fluctuating hypoxia). The results showed that constant hypoxia might reduce the accumulation of PS-NPs in mussels by decreasing the standard metabolic rate. The impairment of PS-NPs on mussel immunity was also exacerbated by constant hypoxia. Fluctuating hypoxia did not affect the accumulation of PS-NPs, but aggravated the oxidative damage caused by PS-NPs. These findings emphasize the importance of environmental factors and their temporal variability in plastic risk assessment.

Molecular cloning and oxidative-stress responses of a novel Phi class glutathione S-transferase (GSTF) gene in the freshwater algae Closterium ehrenbergii

Glutathione S-transferases (GSTs) belong to a family of enzymes involved in diverse biological processes, including detoxification and protection against oxidative damage. Here, we determined the full-length sequence (915 bp) of a novel Phi class cytosolic glutathione S-transferase (GSTF) gene from the green algae Closterium ehrenbergii. We examined the gene structure and expression patterns in response to metals and endocrine disrupting chemicals (EDCs). It was significantly upregulated by metals, but responded differently to EDCs. The highest up-regulation of CeGSTF was registered under 0.1 mg/L CuCl₂ and 0.01 mg/L CuSO₄ treatments. In a 72-h course experiment with treatment of 0.1 mg/L CuCl₂ , CeGSTF was dramatically induced at 6 h, and then gradually decreased with increasing exposure time. This was consistent with the increase in both GST activity and ROS production in copper-treated cells. These results suggest that CeGSTF may be involved in detoxification mechanisms associated with oxidative stress in green algae.

Assessment of the marine ecotoxic state in the Moroccan coastal area Anza-Taghazout following the installation of two wastewater treatment plants: a multibiomarker study using Mytilus galloprovincialis

The aim of the present study is the first to evaluate the ecotoxic state of the marine environment in Anza-Taghazout coasts (Morocco) after installation of two wastewater treatment plants using a natural population of marine bivalves Mytilus galloprovincialis. These coasts are exposed to many discharges generating, thus, different sources of pollutants. These pollutants can modulate the physiological responses of marine bivalves to environmental stress. In this context, a multibiomarker approach consisting of a battery of biomarker evaluation was used to assess the response of these species to stress. In the whole soft tissues of M. galloprovincialis, four biomarkers were evaluated as follows: acetylcholinesterase (AChE), glutathione S-transferase (GST), catalase (Cat), and malondialdehyde activity (MDA). In parallel, physico-chemical parameters were measured in the marine water of Anza-Taghazout within three selected sites: S₁ considered as "hotspot" located at Anza city; S₂ located near of Aourir city; and the third site, S₃ "reference" located in Imouran beach. Our results showed that activities of both glutathione S-transferase and catalase were higher in M. galloprovincialis collected from site S₁, but high values of malondialdehyde and acetylcholinesterase activities were observed successively at S₃ and S₂. Application of integrated biomarker response (IBR) index was suitable for classifying the stress response in the M. galloprovincialis but did not allow to evaluate the level of the xenobiotic exposure in the studied sites. The statistical results did not show any significant differences between the three studied sites, and therefore, S₁ has recently become clean due to the installation of two wastewater treatment plants.

Does acidification lead to impairments on oxidative status and survival of orange clownfish Amphiprion percula juveniles?

The nitrification process in recirculating aquaculture systems can reduce water pH. Fish can also be exposed to water acidification during transport, an important feature in the aquarium industry, as live fish can be kept in a closed environment for more than 24 h during overseas aerial transportation. Therefore, it is important to study the responses of fish to acidic environments. We investigated the impacts of acute exposure to decreasing pH levels in orange clownfish Amphiprion percula juveniles on their survival and oxidative stress status. Fish were exposed to pH 5, 6, 7, and 8 for 96 h. We observed a significant reduction in survival (85%) and protein damage as measured by P-SH (protein thiol) for fish maintained at pH 5. Despite no effects on survival or oxidative damage, fish exposed to pH 6 showed an increase in their antioxidant defense systems, demonstrating this pH level could not be suitable for them as well. Furthermore, there were no negative effects for fish kept at pH 7, compared to those maintained at pH 8 during this short-term evaluation.

The oxylipin messenger 1-octen-3-ol induced rapid responses in kelp Macrocystis pyrifera

Oxylipins are important oxygenated derivatives of fatty acids that regulate a variety of plant physiological and pathological processes in response to specific external challenges. A large body of evidence has indicated that algae can also produce a surprisingly diverse array of volatile oxylipins, yet little is known about the roles of volatile oxylipins as defense signals in macroalgae. In this study, the kelp Macrocystis pyrifera was treated by the oxylipin messenger 1-octen-3-ol and then a genome-wide gene expression profile and fatty acid spectrum analysis were performed. We found that M. pyrifera responded rapidly to the exposure of the oxylipin messenger 1-octen-3-ol. It regulated the expression levels of genes mainly involved in signal transduction, lipid metabolism, oxidation prevention, cell wall synthesis, photosynthesis, and development. Moreover, 1-octen-3-ol treatments decreased several types of total fatty acid contents and increased free fatty acid contents, especially for the C18 and C20 fatty acids. In addition, it decreased the content of indole-3-acetic acid, abscisic acid, and zeatin and increased the gibberellic acid content. Our findings demonstrated that 1-octen-3-ol is an available inducer for M. pyrifera, which is capable of rapidly upregulating kelp's defense response.

Cloning and expression of the ChGstα and ChGstκ genes in the gills of Crassostrea hongkongensis under nanoparticulate and ionic Zn stress

Nanoparticulate and ionic Zn have potential impacts on the detoxification systems of organisms, and Gst genes play key roles in the detoxification of xenobiotics. In this study, we cloned the ChGstα and ChGstκ genes of C. hongkongensis, and studied their expression in gills under nanoparticulate and ionic Zn stress. The results showed that the coding sequences of the ChGstα and ChGstκ genes were 684 and 675 bp, respectively, and had no signal peptide; ChGstα was cytoplasmic, while ChGstκ was mitochondrial. The two genes were expressed in all 8 tested samples, with the most abundant expression observed in hemocytes for ChGstα and digestive glands for ChGstκ. After ZnCl₂ or ZnoNP challenge, the expression of ChGstα decreased significantly in the ZnCl₂ groups, and its expression was higher in the ZnoNP groups than in the ZnCl₂ groups. The expression of ChGstκ was significantly decreased in the ZnCl₂ and ZnoNP groups, and its expression was higher in the ZnoNP groups than in the ZnCl₂ groups except at 3 h post metal Zn stress, which suggested that ChGstα and ChGstκ were more sensitive to ZnoNP than ZnCl₂.

Primary, secondary, and tertiary stress responses of juvenile seahorse Hippocampus reidi exposed to acute acid stress in brackish and seawater

Seahorse Hippocampus reidi is a vulnerable species, inhabiting estuarine and coastal waters. The safety of acidic environments for fish has been considered in terms of ocean acidification in nature and decreasing pH in intensive aquaculture systems. This study aimed to investigate the effects of acute exposition (96 h) of juvenile seahorses to different pH (5, 6, 7, and 8) in brackish (BW - salinity 11) or seawater (SW - salinity 33). For that, we studied the responses of cortisol, oxidative stress, and survival, thus covering primary, secondary, and tertiary stress responses. In SW, cortisol levels were not altered for fish maintained at pH 5 and 8. However, in BW, cortisol was higher for fish kept at pH 5. Regarding secondary stress responses, only GST activity increased with acidification in SW. However, acidification in BW caused biochemical alterations at enzymatic level (SOD, GST, GPx) and glutathione metabolism, accompanied by reduction of antioxidant capacity (TEAC) and increased lipid peroxidation (TBARS). Survival was always above 90% and it did not differ significantly among pH levels. Our results suggest that H. reidi juveniles are more vulnerable to acidic exposure in BW than in SW.

Effects of paralytic shellfish poisoning toxin-producing dinoflagellate Gymnodinium catenatum on the marine copepod Tigriopus japonicus

To understand how the marine copepod Tigriopus japonicus responds to the toxic marine dinoflagellate Gymnodinium catenatum, we assessed acute toxicity and investigated swimming behavior parameters (e.g., swimming speed, swimming path trajectory, and swimming distance) in response to G. catenatum exposure. In addition, the mRNA expression levels of detoxification-related genes (e.g., phase I cytochrome P450 [CYP] and phase II glutathione-S transferase [GST]) were measured in G. catenatum-exposed copepods. No significant change in survival was observed in response to G. catenatum, but swimming speed was significantly decreased (P < 0.05) at a high concentration of G. catenatum (600 cells/mL). Furthermore, the swimming distance was significantly decreased (P < 0.05) compared to that of the control at 600 cells/mL G. catenatum, while no significant change in swimming path trajectory was observed, suggesting that G. catenatum potentially has adverse effects on the swimming behavior of T. japonicus. In addition, the transcriptional regulation of T. japonicus CYPs and -GSTs were significantly upregulated and downregulated (P < 0.05), respectively, in response to G. catenatum. In particular, certain genes (e.g., CYPs [CYP307E1, CYP3041A1, and CYP3024A2] and GSTs [GST-kappa, GST-mu5, and GST-omega]) were significantly induced (P < 0.05) by G. catenatum, suggesting that these genes likely play a critical role in detoxification mechanisms and might be useful as potential molecular biomarkers in response to G. catenatum exposure. Overall, these results elucidate the potential impacts of the dinoflagellate G. catenatum on the swimming behavior and detoxification system of the marine copepod T. japonicus.

Glutathione-S-transferase alpha-4 in Hippocampus abdominalis (big-belly seahorse): Molecular characterization, antioxidant properties, and its potent immune response

Glutathione-S-transferase (GST) is a key enzyme in the phase-II detoxification process and is a biomarker of oxidative stress. In this study, we analyzed the molecular, biochemical, and antioxidant properties of GST alpha-4 from Hippocampus abdominalis (HaGSTA-4). Also, the spatial and temporal expression of HaGSTA-4 upon immune challenge with abiotic and biotic stimulants were evaluated. The HaGSTA-4 ORF encodes 223 amino acids with a molecular weight of 25.7 kDa, and an estimated isoelectric point (pI) of 8.47. It consists of the GST_C superfamily and thioredoxin-like superfamily domain. The phylogenetic tree revealed that HaGSTA-4 is evolutionarily conserved with its GST alpha class counterparts. From pairwise alignment, the highest values of identity (78.5%) and similarity (85.7%) were with Parambassis ranga GSTA-4. Protein rHaGSTA-4 exhibited the highest conjugation activity towards 1-chloro-2,4-dinitrobenzene (CDNB) at pH 7 and 20 °C. A disk diffusion assay showed that rHaGSTA-4 significantly protects cells from the stress of exposure to ROS inducers such as CuSO₄, CdCl₂, and ZnCl₂. Furthermore, overexpressed HaGSTA-4 defended cells against oxidative stress caused by H₂O₂; evidence of selenium-independent peroxidase activity. From qPCR, the tissue-specific expression profile demonstrates that HaGSTA-4 is most highly expressed in the kidney, followed by the intestine and stomach, among fourteen different tissues extracted from healthy seahorses. The mRNA expression profile of HaGSTA-4 upon immune challenge varied depending on the tissue and the time after challenge. Altogether, this study suggests that HaGSTA-4 may be involved in protection against oxidative stress, in immune defense regulation, and xenobiotic metabolism.

Ecotoxicological effects of the azole antifungal agent clotrimazole on the macrophyte species Lemna minor and Lemna gibba

Pharmaceuticals are a large and diverse group of compounds used to treat, prevent and diagnose disease. Among these, a group that has been recently detected in the aquatic environment is that of the azole compounds, commonly used as antifungals. Clotrimazole (CLO) is a nonbiodegradable persistent azole compound, with broad-spectrum antifungal activity for which virtually no toxicological data are available, especially towards aquatic plants. The few existent data point to a documented interference with cytochrome P450 system of exposed organisms. Therefore, the aim of this paper was to evaluate the ecotoxicological effects of the fungicide CLO on two aquatic macrophyte species, namely, Lemna minor and Lemna gibba. To attain this purpose, an acute assay (96 h) was performed with both species being exposed to CLO, in a concentration range of 0 to 5 μg L^-1. The analyzed endpoints were levels of chlorophyll a and b, total, carotenoids, catalase (CAT) and glutathione -s-transferases activities (GSTs). In general, CLO exposure caused some minor alterations in L. minor and L. gibba pigment contents. Antioxidant enzymes exhibited a different pattern in both species, since the highest concentrations of CLO caused an increase on CAT activity, and a decrease on GSTs activity in L. minor, and the opposite in L. gibba, reflected by a decrease on CAT activity and an increase on GSTs activity in all tested concentrations. These results demonstrate that CLO exposure resulted in potential deleterious effects on macrophytes, namely with the involvement of the antioxidant defense mechanisms that were likely deployed to cope with pro-oxidative conditions established by CLO.

Differential responses of a pi-class glutathione S-transferase (CnGSTp) expression and antioxidant status between golden and brown noble scallops under pathogenic stress

Glutathione S-transferases (GSTs) play important roles in immunity by protecting organisms against the damage of reactive oxygen species (ROS). In this study, a pi-class GST cDNA sequence was first cloned from noble scallop Chlamys nobilis (named CnGSTp). The full length cDNA of CnGSTp was 922 bp, encoding a cytosolic protein of 202 amino acids residues, with predicted molecular masses of 23.1 kDa. Then an acute Vibrio Parahaemolyticus challenge experiment was conducted by using the Golden and Brown noble scallops with different total carotenoids content (TCC), and CnGSTp expression level, TCC and ROS level was separately determined. The results showed that ROS and CnGSTp expression levels were significantly up-regulate under Vibrio Parahaemolyticus challenge than the control group (P < 0.05). The Golden scallops showed significantly higher CnGSTp expression level and lower ROS level in hemocytes than the Brown ones (P < 0.05). Moreover, there is a significantly positive correlation between TCC and ROS in the Golden scallops. The present results revealed that CnGSTp plays important roles in immune response and carotenoids play assistant roles in antioxidant defense system under pathogenic stress in the noble scallop.

Temperature and hypoxia on oxidative stress responses in pacu Piaractus mesopotamicus

The aim of this study was to verify the effects of the interaction between different temperatures and levels of dissolved oxygen in the oxidative stress parameters of pacu juveniles. A total of 81 pacu juveniles (61.7 ± 9.1 g) were exposed to three temperatures (18, 23, and 28 °C), acclimated for a period of 30 days, and then submitted to three levels of dissolved oxygen: control or normoxia (7 mg L^-1); moderate hypoxia (4 mg L^-1); and severe hypoxia (2 mg L^-1) for 12 h. Glutathione-S-transferase (GST) activity, total antioxidant capacity against peroxyl radicals (ACAP), and protein thiol content (PSH) and LPO (lipid peroxidation) [measured by the TBARS] were measured in gill, liver, muscle and brain. The results indicated that the interaction between different temperatures and dissolved oxygen levels caused alterations in the antioxidant system and induced lipid and protein damage in pacu juveniles. In addition, the effects were organ specific. In conclusion, exposure to moderate and severe hypoxia affect oxidative stress parameters and have been shown to be organ-specific in pacu juveniles. The interaction between 23 °C and hypoxia caused greater disturbances in oxidative stress markers, such as PSH in the gills and liver and LPO in the muscle.

Antioxidative and neurotoxicity effects of acute and chronic exposure of the estuarine polychaete Hediste diversicolor to paracetamol

The presence of anthropogenic drugs in the aquatic ecosystems is a reality nowadays, and a large number of studies have been reporting their putative toxic effects on wildlife. However, the majority of the studies published so far uses standard organisms, whose probability of becoming in contact with drugs in real scenarios of contamination is at least, low. The use of autochthonous organisms in ecotoxicity testing is thus mandatory, and the present study aimed to assess the feasibility of assessing oxidative based stress responses (enzymatic defenses, such as catalase, glutathione-s-transferases, and lipid peroxidation; neurotoxicity as an indirect outcome of oxidizing conditions) on a polychaete species, Hediste diversicolor, after being acutely and chronically exposed to the widely employed drug paracetamol. H. diversicolor showed to be responsive to paracetamol exposure. Data obtained after acute exposure to paracetamol showed that no antioxidant adaptive response was established, but cholinesterasic activity was enhanced. On the contrary, long term exposure of H. diversicolor individuals to paracetamol resulted in clear pro-oxidative effects, with catalase and cholinesterase inhibition, and a significant reduction in the levels of lipoperoxidation. Considering that some of the tested levels (especially those of the chronic test) were already reported in the wild, the here-obtained results are of high environmental significance. In addition, chronic exposure regime yielded more significant results, with important modification of more parameters, suggesting that realistic conditions of exposure are more suited for an integrated assessment of toxicity of drugs in aquatic organisms.

Glutathione S-transferase (GST) genes from marine copepods Acartia tonsa: cDNA cloning and mRNA expression in response to 1,2-dimethylnaphthalene

The calanoid copepod, Acartia tonsa, is relatively sensitive to marine pollution. Glutathione S-transferase (GST) multifunctional enzyme, as a biomarker, play an important role in detoxification metabolism of exogenous substances. In the present study, GST-theta and GST-mu class homology genes (designated as AtGSTT1 and AtGSTM2) were identified and characterized from A. tonsa. The coding sequence of AtGSTT1 comprised 726 bp and encoded a putative protein of 241 amino acid residues. AtGSTM2 contained an open reading frame of 678 bp that encoded a putative 227 amino acid polypeptide. Both proteins contained a conserved GST-N domain and a GST-C domain. Structural analysis revealed the characteristic N-terminal G-site. Three-dimensional structure analysis showed that AtGSTT1 and AtGSTM2 have two typical domains of GST family: The βαβαββα topology structure at the N- terminus and the superhelical structure at the C- terminus. Subsequently, the expression levels of the two GST genes were detected in A. tonsa using real-time quantitative PCR after exposure to 1,2-dimethylnaphthalene (C2-NAPH) at different concentrations (0.574, 5.736 and 57.358 μg/L) for 24, 48, 72, and 96 h. AtGSTT1 mRNA expression was significantly up-regulated in a time-dependent manner and the highest mRNA expression occurred at 5.736 μg/L C2-NAPH exposure for 96 h. AtGSTM2 mRNA expression peaked at 72 h in 0.574 μg/L and 5.736 μg/L dose groups. The expression level of AtGSTM2 showed an increasing trend in a time-dependent manner at 57.358 μg/L of C2-NAPH. These results suggested that GST genes may play an important role in protecting A. tonsa from C2-NAPH pollution, and provide a theoretical basis for further study on the molecular mechanism of polycyclic aromatic hydrocarbon (PAHs) pollution on zooplankton.

The glutathione S-transferase genes in marine rotifers and copepods: Identification of GSTs and applications for ecotoxicological studies

Various xenobiotics are constantly being released and accumulated into the aquatic environments and consequently, the aquatic organisms are continuously being exposed to exogenous stressors. Among various xenobiotic detoxifying enzymes, Glutathione S-transferase (GST) is one of the major xenobiotic detoxifying enzyme which is widely distributed among living organisms and thus, understanding of the nature of GSTs is crucial. Previous studies have shown GST activity in response to various xenobiotics yet, full identification of GSTs in marine invertebrates is still limited. This review covers information on the importance of GSTs as a biomarker for emerging chemicals and their response to wide ranges of environmental pollutants as well as in-depth phylogenetic analysis of marine invertebrates, including recently identified GSTs belonging to rotifers (Brachionus spp.) and copepods (Tigriopus japonicus and Paracyclopina nana), with unique class-specific features of GSTs, as well as a new suggestion of GST evolutionary pathway.

Genomic insights into antioxidant activities of Pyruvatibacter mobilis CGMCC 1.15125T, a pyruvate-requiring bacterium isolated from the marine microalgae culture

Pyruvate is a well-known scavenger of reactive oxygen species (ROS) like hydrogen peroxide and could prevent cells from oxidative damage. A pyruvate-requiring marine bacterium, Pyruvatibacter mobilis CGMCC 1.15125^T (=KCTC 42509^T), was isolated from the culture broth of a photosynthetic marine microalga. Here we report the complete genome sequence of Pyruvatibacter mobilis, which contained a circular chromosome of 3,333,914 bp with a mean G + C content of 63.9%. Through genomic analysis, we revealed that strain CGMCC 1.15125^T encodes genes for some antioxidants like superoxide dismutase, glutathione, rubrerythrin and globin to relieve cellular oxidative stress, while pyruvate added to the medium may reduce extracellular ROS. The genome features of P. mobilis provide further insights into the antioxidant activities of bacteria surviving in oxygen-enriched habitats.

Effects of temperature changes on life parameters, oxidative stress, and antioxidant defense system in the monogonont marine rotifer Brachionus plicatilis

Global warming is a big concern for all organisms and many efforts have been made to reveal the potential effects of temperature elevation on aquatic organisms. However, limited studies on molecular mechanistic approaches on physiological effects due to temperature changes are available. Here, we investigated the effects of temperature changes on life parameters (e.g., population growth [total number of rotifers], and lifespan), oxidative stress levels and antioxidant activities (e.g., glutathione S-transferase [GST], catalase [CAT], superoxide dismutase [SOD]) with expression levels in the monogonont marine rotifer Brachionus plicatilis. The changes in temperatures led to significant reduction (P < 0.05) in lifespan, possibly due to significant decrease (P < 0.05) in antioxidant activities, reducing the potential to cope with significant elevation in the temperature-induced oxidative stress in B. plicatilis. To further assess the actual induction and clearance of reactive oxygen species (ROS), N-acetyl-L-cysteine was used to examine whether the temperature-induced oxidative stress could be successfully scavenged. Furthermore, expression patterns of the antioxidant-related genes (GSTs, SODs, and CATs) were down- or upregulated (P < 0.05) in response to different temperatures in B. plicatilis. Overall, these findings indicate that ROS-mediated oxidative stress led to cellular damage and antioxidant defense system, resulting in deleterious effects on life parameters in rotifer.

Two sigma and two mu class genes of glutathione S-transferase in the waterflea Daphnia pulex: Molecular characterization and transcriptional response to nanoplastic exposure

Two isoforms of Glutathione S-Transferase (GST) genes, belonging to mu (Dp-GSTm1 and Dp-GSTm2) and sigma (Dp-GSTs1 and Dp-GSTs2) classes, were cloned and characterised in the freshwater Daphnia pulex. No signal peptide was found in any of the four GST proteins, indicating that they were cytosolic GST. A highly conserved glutathione (GSH) binding site (G-site) occurred in the N-terminal sequence, and a substrate binding site (H-site), interacting non-specifically with the second hydrophobic substrate, was present in the C-terminal. A Tyr residue, for the stabilization of GSH, was found to be conserved in the analysed sequences. The secondary and tertiary structures indicated that these genes possess the typical cytosolic GST structure, including a conserved N-terminal domain with a βαβαββα motif. The μ loop (NVGPAPDYDR and NFIGAEWDR in Dp-GSTm1 and Dp-GSTm2, respectively) was identified between the βαβ (β1α1β2) and αββα motifs (α2β3β4α3) in the N-terminal domain. The expressions of Dp-GSTs1, Dp-GSTs2, and Dp-GSTm1 were higher in other age groups compared to the newly-born neonates (1 d); however, the expression of Dp-GSTm2 first increased and then decreased with age. Gene expression was significantly reduced by high concentration (1 and 2 mg/L) of 75 nm polystyrene nanoplastic. However, nanoplastic exposure at the predicted environmental concentration (1 μg/L) had a low effect. Exposure of mothers to nanoplastic (1 μg/L) elevated the Dp-GSTs2 level in their neonates. These results improve our understanding on the response of different types of Daphnid GST to environmental contaminants, especially nanoplastic.

Diversity of Glutathione S-Transferases (GSTs) in Cyanobacteria with Reference to Their Structures, Substrate Recognition and Catalytic Functions

Glutathione S-Transferases (GSTs) comprise a diverse group of protein superfamily involved in cellular detoxification of various harmful xenobiotics and endobiotics. Cyanobacteria, being the primordial photosynthetic prokaryotes, served as an origin for the evolution of GSTs with diversity in their structures, substrate recognition, and catalytic functions. This study analysed the diversity of GSTs in cyanobacteria for the first time. Based on the sequence alignment and phylogenetic tree analysis, 12 GST classes were identified, which are distributed variedly within cyanobacterial orders such as four in Pleurocapsales, eight in Chroococcales, seven in Oscillatoriales, five in Stigonematales, and nine in Nostocales. Detailed evolutionary analysis of cyanobacterial GSTs suggested that the order Pleurocapsales served as the ancestry for GST evolution. The analysis also identified a conserved motif S[GLNTARS][ADE]I[LAI] with signature residues, cysteine, serine, and tyrosine at the N-terminal end that serves as the initiating residue for detoxification. Alternatively, the grouping of cyanobacterial GSTs and their unique signature residues were located, which serve as a possible discriminating factor. The study also described the mode of glutathione binding between the identified cyanobacterial GST groups highlighting the differences among the GST classes. New GST sequence data may improve further our understanding on GST evolution and other possible divergences in cyanobacteria.

Differences in proteomic profile between two haemocyte types, granulocytes and hyalinocytes, of the flat oyster Ostrea edulis

Haemocytes play a dominant role in shellfish immunity, being considered the main defence effector cells in molluscs. These cells are known to be responsible for many functions, including chemotaxis, cellular recognition, attachment, aggregation, shell repair and nutrient transport and digestion. There are two basic cell types of bivalve haemocytes morphologically distinguishable, hyalinocytes and granulocytes; however, functional differences and specific abilities are poorly understood: granulocytes are believed to be more efficient in killing microorganisms, while hyalinocytes are thought to be more specialised in clotting and wound healing. A proteomic approach was implemented to find qualitative differences in the protein profile between granulocytes and hyalinocytes of the European flat oyster, Ostrea edulis, as a way to evaluate functional differences. Oyster haemolymph cells were differentially separated by Percoll® density gradient centrifugation. Granulocyte and hyalinocyte proteins were separated by 2D-PAGE and their protein profiles were analysed and compared with PD Quest software; the protein spots exclusive for each haemocyte type were excised from gels and analysed by MALDI-TOF/TOF with a combination of mass spectrometry (MS) and MS/MS for sequencing and protein identification. A total of 34 proteins were identified, 20 unique to granulocytes and 14 to hyalinocytes. The results suggested differences between the haemocyte types in signal transduction, apoptosis, oxidation reduction processes, cytoskeleton, phagocytosis and pathogen recognition. These results contribute to identify differential roles of each haemocyte type and to better understand the oyster immunity mechanisms, which should help to fight oyster diseases.

A novel sigma class glutathione S-transferase gene in freshwater planarian Dugesia japonica: cloning, characterization and protective effects in herbicide glyphosate stress

As the top-selling herbicide in the world, glyphosate distributes widely in natural environment and its influence on the ecological security and human health has attracted more and more concern. Glutathione S-transferases (GSTs) are a well-characterized superfamily of isoenzymes for cellular defense against exogenous toxic substances and therefore protect organisms from injury. In this study, the complete cDNA sequence of GST gene (named as Dja-GST) in freshwater planarian Dugesia japonica was firstly cloned by means of RACE method. The full-length Dja-GST comprises of 706 nucleotides which encodes a polypeptide of 200 amino acids. Dja-GST has two representative GST domains at the N- and C-termini. The conservative GST-N domain includes G-site Y8, F9, R14, W39, K43, P52 and S64, while the variable GST-C domain contains H-site K104, V156, D159 and L161. Sequence analysis, phylogenetic tree reconstruction and multiple alignment collectively indicate that Dja-GST belongs to the Sigma class of GST superfamily. Also, GST gene expression profile, GST enzymatic activity and MDA content in response to glyphosate exposure were systematically investigated and the correlations among them were analyzed. The results suggest that glyphosate exposure modified the mRNA transcription and enzymatic activity of GST, as well as the MDA content in planarians, indicating that Dja-GST might play an important part in organisms defending against oxidative stress induced by glyphosate. This work lays a molecular foundation for further exploring the exact functions of Dja-GST and gives an important implication for evaluating the ecological environment effects of herbicide glyphosate.

Molecular characterization, expression and enzyme activity of three glutathione S-transferase genes from Eriocheir sinensis under pesticide stresses

Glutathione S-transferases (GSTs) are a multifunctional protein superfamily that can catalyze the detoxification processes in an organism. In the present study, we determined the structure and function of GSTs in Chinese mitten crab (Eriocheir sinensis) by gene cloning, expression, and enzyme activity in order to investigate the metabolic detoxification of GSTs in the hepatopancreas and muscles under three pesticide (trichlorfon, β-cypermethrin and avermectin) stresses. Multiple sequence alignment analysis showed that all the three Es-GST genes possessed N-terminal, and C-terminal domain as well as G-binding sites, while Es-GST2 and Es-GST3 contained Mu-type GST-specific Mu-loop structures. Phylogenetic tree analysis revealed that the three Es-GSTs belonged to the Mu-type GST of crustaceans. The quantitative real-time PCR revealed that the three Es-GSTS were expressed in 9 tissues of Eriocheir sinensis, with highest expression in hepatopancreas and muscle. The expression of the three Es-GSTS significantly increased in the hepatopancreas and muscle under the three pesticide stresses compared to the control group, and a steady increase in GST activity was observed. The study showed that the three Es-GSTs belong to the Mu-type GST of the crustaceans and might play an important role in the metabolic detoxification in Eriocheir sinensis.

Effects of common pharmaceutical drugs (paracetamol and acetylsalicylic acid) short term exposure on biomarkers of the mussel Mytilus spp

Pharmaceutical drugs in the wild may pose significant risks to non-target exposed organisms. This situation is even more troublesome for coastal marine or estuarine environments, located in the vicinity of large human conglomerates, for which the putative number of pollutants is extremely high, and the regime by which wild organisms are exposed is continuous. In addition, the number of studies addressing this issue is still scarce, despite evidences that show the potential contamination profiles and adverse biological effects in organisms from such areas. In this study, the ecotoxicity of common pharmaceutical drugs (namely paracetamol and acetylsalicylic acid) was assessed, by studying the susceptibility of the mussel species Mytilus spp to oxidative stress after being exposed for 96 h to increasing but ecologically relevant concentrations of the two mentioned pharmaceuticals (paracetamol: 0, 0.5, 5, 50, and 500 μg/L; acetylsalicylic acid: 0, 0.1, 1, 10, and 100 μg/L). The oxidative status in exposed organisms was analyzed by measuring oxidative stress biomarkers, namely catalase (CAT), glutathione-S-transferases (GSTs), and lipoperoxidation (LPO) levels, whose alteration was indicative of chemical exposure, in both digestive gland and gills of the organisms. In addition, the food uptake and the nutritional reserve status of exposed organisms were also assessed, by measuring the consumption of ingested food, and levels of tissue reserves of glycogen in gills and digestive gland. No significant alterations were observed in the assessed oxidative stress parameters so it was possible to hypothesize that the studied drugs may have probably exerted a limited alteration of antioxidant defenses and damage, which was reverted by the activation of defensive adaptive mechanisms. This set of data evidenced that the pro-oxidative metabolism that was already described for both drugs in other animal models, was not fully established in the exposed mussels. On the contrary, glycogen reserves were substantially changed after exposure to both toxicants, being possible to observe opposite responses caused by both drugs. Food uptake was not altered following exposure to the drugs. Further evaluations are thus required to conclude about both drugs ecotoxicity and other parameters, namely seasonality, which should be considered when performing ecotoxicology tests, especially with the selected species.

Transcriptomic response and hydrocarbon accumulation in the eastern oyster (Crassostrea virginica) exposed to crude oil

The adverse effect of crude oil on marine invertebrates is well known. To have a better understanding of its effects on marine invertebrates, Crassostrea virginica was exposed to different concentrations (50, 100 and 200 μg/L) of a mixture of super-light and light crude oil for two weeks, evaluating the transcriptomic response of the digestive gland using RNA-Seq and their accumulation in soft tissues. A total of 33,469,374 reads were assembled, which resulted in 61,356 genome assemblies ('Genes'). Trinotate was used for transcript annotation. At the end of this process, 86,409 transcripts were maintained, comprising a broad set of enzymes from xenobiotics metabolism, oxidative stress, stress and immune responses, and energetic metabolism. The enrichment analysis revealed a change in biological processes and molecular functions, finding from 100 to 200 μg/L. Moreover, the differential gene expression analysis showed a dose-dependent transcriptional response, generally up to 100 μg/L and in some cases up to 200 μg/L, which suggested that oysters' response decreased after 100 μg/L; the analysis of crude oil presence in soft tissues indicated that C. virginica is a suitable candidate for ecotoxicology. Finally, these results should contribute to expanding current genomic resources for C. virginica. Furthermore, they will help to develop new studies in aquatic toxicology focused on knowledge in depth of metabolic pathways, jointly with other approaches (such as proteomics) to allow obtaining a complete idea about the eastern oyster response to crude oil.

Biomarker-based assessment of the toxicity of the antifungal clotrimazol to the microcrustacean Daphnia magna

Among the vast list of xenobiotics that may promote harmful effects in aquatic ecosystems, pharmaceuticals are currently a prominent class due to their ability to persist in these environments and also due to the lack of information regarding their effects on the different components of the aquatic biota. Antifungals in particular, despite their massive use, are not extensively studied in environbmental terms. The main objective of this study was to characterize the toxicity of the antifungal clotrimazole to the aquatic organism Daphnia magna. To attain this purpose, the effects of this compound were measured, focusing on the determination of acute lethality, and quantification of biomarkers, such as neurotoxicity (soluble cholinesterases, ChEs); and oxidative stress and metabolism (such as catalase, CAT; and glutathione-S-transferases, GSTs). The toxicity assessment with biomarkers was based on animals exposed to concentrations similar to those already found in surface waters in order to increase the ecological relevance of the obtained data. The results showed that exposure to clotrimazole was able to induce significant increases in both CAT amd GSTs activities. ChE activity was not significantly altered after clotrimazol exposure. In view of the above, it is concluded that the drug studied caused adverse effects in terms of oxidative stress, at an ecological relevant levels, showing that the presence of clotrimazol in the wild is not innocuous.

First in vivo Evidence That Glutathione-S-Transferase Operates in Photo-Oxidative Stress in Cyanobacteria

Although glutathione (GSH) and GSH-dependent enzymes, such as glutathione transferases (GSTs), are thought to have been developed by cyanobacteria to cope with the reactive oxygen species (ROS) that they massively produced by their active photosynthesis, there had been no in vivo analysis of the role of GSTs in cyanobacteria so far. Consequently, we have analyzed two of the six GSTs of the model cyanobacterium Synechocystis PCC 6803, namely Sll1545 (to extend its in vitro study) and Slr0236 (because it is the best homolog to Sll1545). We report that Sll1545 is essential to cell growth in standard photo-autotrophic conditions, whereas Slr0236 is dispensable. Furthermore, both Sll1545 and Slr0236 operate in the protection against stresses triggered by high light, H₂O₂, menadione and methylene blue. The absence of Slr0236 and the depletion of Sll1545 decrease the tolerance to methylene blue in a cumulative way. Similarly, the combined absence of Slr0236 and depletion of Sll1545 decrease the resistance to high light. Attesting their sensitivity to high-light or methylene blue, these Δslr0236-sll1545 cells transiently accumulate ROS, and then reduced and oxidized glutathione in that order. In contrast, the absence of Slr0236 and the depletion of Sll1545 increase the tolerance to menadione in a cumulative way. This increased menadione resistance is due, at least in part, to the higher level of catalase and/or peroxidase activity of these mutants. Similarly, the increased H₂O₂ resistance of the Δslr0236-sll1545 cells is due, at least in part, to its higher level of peroxidase activity.

Effects of atrazine on life parameters, oxidative stress, and ecdysteroid biosynthetic pathway in the marine copepod Tigriopus japonicus

Atrazine is a widely used pesticide which acts as an endocrine disruptor in various organisms. The aim of this study was to investigate adverse effects of atrazine on life parameters, oxidative stress, and ecdysteroid biosynthetic pathway in the marine copepod Tigriopus japonicus. In T. japonicus, no mortality was shown in response to atrazine up to 20 mg/L in acute toxicity assessment. In nauplii, retardation in the growth and prolonged molting and metamorphosis resulted under chronic exposure of atrazine at 20 mg/L. In addition, body sizes of T. japonicus nauplii were significantly decreased (P < 0.01 in length and P < 0.001 in width) in response to 20 mg/L of atrazine. Furthermore, atrazine induced oxidative stress by the generation of reactive oxygen species at all concentrations compared to the control in the nauplii. Also, significant increase in glutathione-S transferase activity was observed in adult T. japonicus at low concentration of atrazine. To understand effects of atrazine on ecdysteroid biosynthetic pathway-involved genes (e.g., neverland, CYP307E1, CYP306A1, CYP302A1, CYP3022A1 [CYP315A1], CYP314A1, and CYP18D1) were examined with mRNA expressions of ecdysone receptor (EcR) and ultraspiracle (USP) in response to 20 mg/L atrazine in nauplii and adults. In the nauplii, these genes were significantly downregulated (P < 0.05) in response to atrazine, compared to the control but not in the adult T. japonicus. These results suggest that atrazine can interfere in vivo life parameters by oxidative stress-induced retrogression and ecdysteroid biosynthetic pathway in this species.

Genome-wide identification and expression of the entire 52 glutathione S-transferase (GST) subfamily genes in the Cu2+-exposed marine copepods Tigriopus japonicus and Paracyclopina nana

In this study, the entire glutathione S-transferases (GSTs), the major phase II detoxification enzyme, were identified in two marine copepod species Tigriopus japonicus and Paracyclopina nana. The genome-wide identification of GSTs in T. japonicus and P. nana resulted in 32 and 20 GSTs in total, respectively. Among the identified GSTs, two specific classes of GSTs, specifically sigma and delta/epsilon GSTs were the dominant form of cytosolic GSTs in T. japonicus, while delta/epsilon and mu classes were dominant cytosolic GSTs in P. nana. In addition, Membrane-Associated Proteins in Eicosanoid and Glutathione metabolism (MAPEG) family were found in relatively higher proportion compared to other classes. Moreover, sigma, delta/epsilon, and microsomal GSTs have shown to expand through tandem duplication. To validate the detoxification function of the identified GSTs, both copepods were exposed to copper (Cu²⁺) and the reactive oxygen species (ROS) level and GST activity were measured. With integration of phylogenetic analysis and xenobiotic-mediated GST mRNA expression patterns along with previous enzymatic activities, the functional divergence among species-specific GST genes was clearly observed. This study covers full identification of GST classes in two marine copepod species and their important role in marine environmental ecotoxicology.

Transcriptomic response of the Crassostrea virginica gonad after exposure to a water-accommodation fraction of hydrocarbons and the potential implications in reproduction

The Crassostrea virginica oyster has biological and economic importance in the Gulf of Mexico, an area with a high extraction and production of hydrocarbons. Exposure to hydrocarbons affects the reproductive processes in bivalves. In C. virginica, the effect of hydrocarbons on the gonad of the undifferentiated organism has not been evaluated to determine the possible damage during the maturation process. To evaluate this effect, RNA-seq data was generated from C. virginica gonads exposed to a 200 μg/L of hydrocarbons at different exposure times (7, 14 and 21 days) and a control treatment (without hydrocarbons). The analysis of the gonad transcriptome showed the negative effect of hydrocarbons on maturation, with a sub-expression of 22 genes involved in different stages of this process. Additionally, genes in the immune system were down-regulated, which may indicate that exposure to hydrocarbons causes immunosuppression in bivalves. A group of oxidative stress genes was also reduced. These data contribute to a better understanding of the effect of hydrocarbons on the reproductive process in bivalves and, at the same time, allow us to identify possible biomarkers associated with hydrocarbon contamination in the gonad of C. virginica.

Adverse effects of two pharmaceuticals acetaminophen and oxytetracycline on life cycle parameters, oxidative stress, and defensome system in the marine rotifer Brachionus rotundiformis

To investigate the adverse effect of two widely used pharmaceuticals, paracetamol (acetaminophen [APAP]) and oxytetracycline (OTC) on the marine rotifer Brachionus rotundiformis (B. rotundiformis), the animals were exposed to various environmentally-relevant concentrations. Up to date, acetaminophen and oxytetracycline have been considered as toxic, if used above threshold concentration, i.e. overdosed. However, this study demonstrated these two pharmaceuticals even at low concentration (i.e., μg/L scale) elicited oxidative stress through the generation of reactive oxygen species (ROS) along with the increased glutathione S-transferase activity, despite no-observed effect in in-vivo population growth. To validate the adverse effects of the two pharmaceuticals at relatively low concentrations, mRNA expression analysis was performed of the entire set of genes encoding 26 cytochrome P450s (CYPs) of phase I and 19 glutathione S-transferases (GSTs) of phase II of the rotifer B. rotundiformis. The mRNA expression analysis suggested specific genes CYP3045A2 and GSTσ1, GSTσ4, and GSTω1 take part in detoxification of APAP and OTC, resulting in no significant changes in the population growth and undetermined no observed effect concentration (NOEC) in the marine rotifer B. rotundiformis.

Molecular Cloning and Expression of MnGST-1 and MnGST-2 from Oriental River Prawn, Macrobrachium nipponense, in Response to Hypoxia and Reoxygenation

The glutathione-S-transferase (GST) superfamily includes seven classes, and different classes have different functions. GST superfamily members function in various processes including detoxification of xenobiotics, protection against oxidative damage, and intracellular transport of hormones, endogenous metabolites, and exogenous chemicals. Herein, to elucidate the tissue-specific expression pattern of GSTs in response to hypoxia stress, which induces cell death, we investigated the expression of GSTs in response to hypoxia and reoxygenation in oriental river prawn, Macrobrachium nipponense. Full-length cDNAs of two δ class GSTs were cloned from the hepatopancreas, and named MnGST-1 and MnGST-2 based on the established GST nomenclature system. Expression profiles of both GSTs in various tissues were different under acute and chronic experimental hypoxia stress conditions, suggesting that both respond strongly to hypoxia-induced oxidative stress. However, the intensity of responses to hypoxia and reoxygenation were different in different tissues. During acute hypoxia stress, MnGST-1 responds earlier than MnGST-2 in the hepatopancreas and gill, but more slowly in muscle. By contrast, during chronic hypoxia stress, MnGST-2 plays a more important role in the hepatopancreas and gill than MnGST-1.

Genome-wide identification of the entire 90 glutathione S-transferase (GST) subfamily genes in four rotifer Brachionus species and transcriptional modulation in response to endocrine disrupting chemicals

Genome-wide identification of glutathione S-transferase (GST), a major phase II detoxification enzyme, was investigated in four different aquatic model rotifer species Brachionus koreanus, B. plicatilis, B. rotundiformis, and B. calyciflorus. GSTs are ubiquitous antioxidant enzymes that play versatile function including cellular detoxification, stress alleviation, and production of the radical conjugates. Among the four rotifers, B. rotundiformis was found with the least number of GST genes (total 19 GST genes), whereas the other three species shared 23 to 24 GST genes. Among the identified GST genes, belonging to the cytosolic GST superfamily, the expansion of GST sigma classes mainly occurs through tandem duplication, resulting in tandem-arrayed gene clusters on the chromosomes. Overall, the number of genes discovered in this study was highest in the sigma class, zeta, alpha, and omega in descending order. With integration of phylogenetic analysis and xenobiotic-mediated GST mRNA expression patterns along with previous enzymatic activities, the functional divergence among species-specific GST genes was clearly observed. This study covers full identification of GST classes in three marine rotifer and one fresh-water rotifer species and their important role in marine environmental ecotoxicology.