A novel biomarker for marine environmental pollution of pi-class glutathione S-transferase from Mytilus coruscus

Effects of elevated temperature and different crystal structures of TiO2 nanoparticles on the gut microbiota of mussel Mytilus coruscus

Coastal habitats are exposed to increasing pressure of nanopollutants commonly combined with warming due to the seasonal temperature cycles and global climate change. To investigate the toxicological effects of TiO2 nanoparticles (TiO2 NPs) and elevated temperature on the intestinal health of the mussels (Mytilus coruscus), the mussels were exposed to 0.1 mg/L TiO2 NPs with different crystal structures for 14 days at 20 °C and 28 °C, respectively. Compared to 20 °C, the agglomeration of TiO2 NPs was more serious at 28 °C. Exposure to TiO2 NPs led to elevated mortality of M. coruscus and modified the intestinal microbial community as shown by 16S rRNA sequence analysis. Exposure to TiO2 NPs changed the relative abundance of Bacteroidetes, Proteobacteria and Firmicutes. The relative abundances of putative mutualistic symbionts Tenericutes and Fusobacteria increased in the gut of M. coruscus exposed to anatase, which have contributed to the lower mortality in this group. LEfSe showed the combined stress of warming and TiO2 NPs increased the risk of M. coruscus being infected with potential pathogenic bacteria. This study emphasizes the toxicity differences between crystal structures of TiO2 NPs, and will provides an important reference for analyzing the physiological and ecological effects of nanomaterial pollution on bivalves under the background of global climate change.

The diverse functions of Mu-class Glutathione S-transferase HrGSTm1 during the development of Hyalomma rufipes with a focus on the detoxification metabolism of cyhalothrin

BACKGROUND

Glutathione S-transferases (GSTs) are a superfamily of multifunctional enzymes in living organisms with metabolic and detoxification functions, which can detoxify exogenous and endogenous compounds and thereby reduce the damage caused by toxic substances to the body. Ticks are obligate blood-sucking ectoparasites that can transmit various pathogens, and the characterization of tick-derived GSTs may help improve current understanding of the molecular mechanism of tick resistance to insecticides. In this study, a novel GST gene, named HrGSTm1, was identified from Hyalomma rufipes.

METHODS

Sequence analysis was performed by using bioinformatics techniques. A prokaryotic expression system was used to obtain the recombinant expression protein rHrGSTm1. Detection of spatiotemporal expression patterns of target genes and their response to the toxicity of cyhalothrin on female H. rufipes was performed by using a quantitative PCR platform. The optimal enzymological parameters of rHrGSTm1 using glutathione as substrate were calculated. The antioxidant capacity of the recombinant protein was evaluated by DPPH• (1,1-Diphenyl-2-picrylhydrazyl radical 2,2-Diphenyl-1-(2,4,6-trinitrophenyl) hydrazyl). Knockdown of the HrGSTm1 genes through RNA interference was used to analyze their effects on the physiological parameters of ticks. The changes in HrGSTm1 messenger RNA expression patterns under cypermethrin stress were analyzed.

RESULTS

The complementary DNA sequence of HrGSTm1 contained a 672-bp open reading frame, which potentially encoded 223 amino acids. The predicted molecular weight was 25.62 kDa, and the isoelectric point 8.22. HrGSTm1 is a Mu-class GST, belonging to the cytoplasmic GSTs with no signal peptide observed. The Vmax and Km of rHrGSTm1 were 3.367 ± 0.81 uM and 2.208 ± 0.76 uM, respectively, and its activities were dependent on different temperatures and pH conditions; the scavenging rate of rHrGSTm1 to DPPH• reached 76.4% at 1.25 mg/ml. Variable expressions of HrGSTm1 were observed under various treatment periods and in different tissues, with the highest appearing in eggs (analysis of variance [ANOVA], F(2, 9) = 279.9, P < 0.0001) and Malpighian tubules (ANOVA, F(3, 12) = 290.5, P < 0.0001). After knockdown of HrGSTm1, compared with the control group, the mortality in the treatment group was increased by 16.7%, the average oviposition rate decreased by 33.9%, the average engorged body weight decreased by 287.38 mg and egg weight decreased by 127.46 mg, although only the engorged body weight was significantly different (t-test, t(44) = 2.886, P = 0.006). After exposure to three sublethal concentrations (LC05, LC10, LC50) of cyhalothrin, the expression level of HrGSTm1 in the midgut, ovary and salivary gland was upregulated, whereas in Malpighian tubules, it showed a trend of upregulation at first and then downregulation, implying different functions during the detoxification in different tissues.

CONCLUSIONS

In this study, a novel GST of the Mu-class was successfully isolated from H. rufipes and systematically subjected to bioinformatic analysis and recombination identification. The variation trend of HrGSTm1 expression level in different tissues suggests that the gene has different detoxification functions in different tissues. The potential function of this gene was analyzed to provide basic research for further investigation of its detoxification mechanism.

Insights into the Response in Digestive Gland of Mytilus coruscus under Heat Stress Using TMT-Based Proteomics

Ocean warming can cause injury and death in mussels and is believed to be one of the main reasons for extensive die-offs of mussel populations worldwide. However, the biological processes by which mussels respond to heat stress are still unclear. In this study, we conducted an analysis of enzyme activity and TMT-labelled based proteomic in the digestive gland tissue of Mytilus coruscus after exposure to high temperatures. Our results showed that the activities of superoxide dismutase, acid phosphatase, lactate dehydrogenase, and cellular content of lysozyme were significantly changed in response to heat stress. Furthermore, many differentially expressed proteins involved in nutrient digestion and absorption, p53, MAPK, apoptosis, and energy metabolism were activated post-heat stress. These results suggest that M. coruscus can respond to heat stress through the antioxidant system, the immune system, and anaerobic respiration. Additionally, M. coruscus may use fat, leucine, and isoleucine to meet energy requirements under high temperature stress via the TCA cycle pathway. These findings provide a useful reference for further exploration of the response mechanism to heat stress in marine mollusks.

Mytilus farming drives higher local bacterial diversity and facilitates the accumulation of aerobic anoxygenic photoheterotrophic related genera

Research to assess the impacts of mariculture on the microbiota of the surrounding environment is still inadequate. Here, we examined the effects of Mytilus coruscus farming on the diversity of bacterial community in surrounding seawater using field investigations and indoor simulations, focusing on the variation of members of aerobic anoxygenic photoheterotrophic (AAP) bacteria. In the field, Mytilus farming shaped bacterial community and significantly increased their diversity, including biomass, OTUs, Shannon, relative abundance, number of enriched species, as compared with the non-farming area. Higher abundance of AAP related genera was observed in the Mytilus farming seawater. Under the controlled condition, the presence of M. coruscus significantly shaped the bacterial community composition and caused species composition to become similar after 10 days. Furthermore, the presence of M. coruscus consistently strengthened local diversity in seawater bacterial community, with linkages to the recruitment of AAP members as well. In addition, the tissue-related composition of M. coruscus significantly differed from those in seawater. Our findings highlight a ecological importance of Mytilus farming, as process that shape surrounding water-cultured bacterial community and offer experimental evidence for the accumulation of AAP-related genera in aquaculture systems.

Effects of Ocean Acidification and Microplastics on Microflora Community Composition in the Digestive Tract of the Thick Shell Mussel Mytilus coruscus Through 16S RNA Gene Sequencing

Ocean acidification and microplastic pollution is a global environmental threat, this research evaluated the effects of ocean acidification and microplastics on mussel digestive tract microbial community. The 16S rRNA gene was sequenced to characterize the flora. Species diversity in the samples was assessed by clustering valid tags on 97% similarity. Bacteroidetes, Firmicutes and Proteobacteria were the three most abundant genera in the four groups, with Bacteroidetes showing the highest diversity. However, no differences in flora structure were evident under various treatments. Phylogenetic relationship analysis revealed Bacteroidetes and Firmicutes had the highest OTU diversity. The weighted UniFrac distance, principal coordinate analysis (PCoA), unweighted pair group method with arithmetic mean (UPGMA) cluster tree and analysis of molecular variance (AMOVA) evaluation results for all samples also showed that changes in pH and microplastics concentration did not significantly affect the microbial community structure in the mussel digestive tract. The results presented the no significant effects of ocean acidification and microplastics intake on mussel intestinal diversity.

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.

Antioxidant responses of the mussel Mytilus coruscus co-exposed to ocean acidification, hypoxia and warming

In the present study, the combined effects of pH, dissolved oxygen (DO) and temperature levels on the antioxidant responses of the mussel Mytilus coruscus were evaluated. Mussels were exposed to two pH (8.1, 7.7-acidification), two DO (6 mg L^-1, 2 mg L^-1-hypoxia) and two temperature levels (20 °C, 30 °C-warming) for 30 days. SOD, CAT, MDA, GPx, GSH, GST, TAOC, AKP, ACP, GPT, AST levels were measured in the gills of mussels. All tested biochemical parameters were altered by these three environmental stressors. Values for all the test parameters except GSH first increased and then decreased at various experimental treatments during days 15 and 30 as a result of acidification, hypoxia and warming. GSH content always increased with decreased pH, decreased DO and increased temperature. PCA showed a positive correlation among all the measured biochemical indexes. IBR results showed that M. coruscus were adversely affected by reduced pH, low DO and elevated temperature.

Is the Doce River elutriate or its water toxic to Astyanax lacustris (Teleostei: Characidae) three years after the Samarco mining dam collapse?

In 2015, after the Fundão dam failure, in Minas Gerais State, Brazil, around 50 million cubic meters of sludge from iron mining tailings were discharged into the Doce River. After the dam collapse, surpassing concentrations of metals were observed in the river sediment, which could be harmful to aquatic organisms, including the fishes. The present study aimed to evaluate the toxic effects of both elutriate and water, collected from the Doce River, on Astyanax lacustris three years after the dam failure. A bioassay was carried out through subchronic exposure to Doce River water (E0) and three elutriate concentrations (10, 50 and 100%). Biochemical analyses (CAT, GST, AChE), metal bioaccumulation assays and calculation of the integrated biomarker response index, version 2 (IBRv2) were performed. The outcomes uncovered deleterious consequences on organisms exposed to E0, with AChE inhibition and bioaccumulation of Fe and Mn in both liver and gills. IBRv2 values were more elevated in fishes exposed to E0 for all tissues. Thus, the elutriate was not harmful for the assessed fishes, since complexing agents presented in the sediment, such as goethite and hematite, may have triggered metals' chelation. In this scenario, the elutriate may have acted as a protective agent for the subjected organisms, unlike the Doce River waters, in which contaminants were proven to be hazardous for the aquatic biota.

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.

Microplastics impair digestive performance but show little effects on antioxidant activity in mussels under low pH conditions

In the marine environment, microplastic contamination and acidification may occur simultaneously, this study evaluated the effects of ocean acidification and microplastics on oxidative stress responses and digestive enzymes in mussels. The thick shell mussels Mytilus coruscus were exposed to four concentrations of polystyrene microspheres (diameter 2 μm, 0, 10, 10⁴ and 10⁶ particles/L) under two pH levels (7.7 and 8.1) for 14 days followed by a 7-day recovery acclimation. Throughout the experiment, we found that microplastics and ocean acidification exerted little oxidative stress to the digestive gland. Only catalase (CAT) and glutathione (GSH) showed a significant increase along with increased microplastics during the experiment, but recovered to the control levels once these stressors were removed. No significant effects of pH and microplastics on glutathione peroxidase (GPx) and superoxide dismutase (SOD) were observed. The responses of digestive enzymes to both stressors were more pronounced than antioxidant enzymes. During the experiment, pepsin (PES), trypsin (TRS), alpha-amylase (AMS) and lipase (LPS) were significantly inhibited under microplastics exposure and this inhibition was aggravated by acidification conditions. Only PES and AMS tended to recover during the recovery period. Lysozyme (LZM) increased significantly under microplastic exposure conditions, but acidification did not exacerbate this effect. Therefore, combined stress of microplastics and ocean acidification slightly impacts oxidative responses but significantly inhibits digestive enzymes in mussels.

High level of methylmercury exposure causes persisted toxicity in Nauphoeta cinerea

Methylmercury (MeHg⁺) is a neurotoxicant abundantly present in the environment. The long-term effects of MeHg⁺ have been investigated in rodents, yet data on the long-term or persisted toxicity of MeHg⁺ in invertebrates is scanty. Here, we examined the acute, intermediate, and chronic effects upon dietary administration of MeHg⁺ in nymphs of Nauphoeta cinerea. Besides, the potential reversibility of the toxic effects of MeHg⁺ after a detoxification period was evaluated. Nymphs were exposed to diets containing 0 (control), 2.5, 25, and 100 μg MeHg⁺/g of diet for 10, 30, and 90 days. Additional groups of nymphs were fed with the same dose of MeHg⁺ for 30 days and then were subjected to a detoxification period for 60 days. The nymphs exposed to 100 μg MeHg⁺/g succumbed to a high mortality rate, along with multiple biochemical (increase of reactive oxygen species production and glutathione S-transferase activity, as well as decrease in the acetylcholinesterase activity) and behavioral alterations. We observed delayed mortality rate and behavioral alterations in nymphs exposed to 100 μg MeHg⁺/g for 30 days and subsequently subjected to 60 days of detoxification. However, the biochemical alterations did not persist throughout the detoxification period. In conclusion, our results established the persistent toxic effect of MeHg⁺ even after a prolonged detoxification period and evidenced the use of N. cinerea as an alternative model to study the toxicity of MeHg⁺.

Simultaneous exposure to vinylcyclohexene and methylmercury in Drosophila melanogaster: biochemical and molecular analyses

Background

Exposure to vinylcyclohexene (VCH) and methylmercury (MeHg⁺) can induce oxidative stress and gene modulation. Several studies have been evaluating the effects of VCH and MeHg⁺, but little is known about interactive effects between them. This work aimed to assess the exposure and co-exposure effects of MeHg⁺ and VCH on oxidative stress and gene modulation in Drosophila melanogaster.

Methods

Reactive species production, glutathione S-transferase (GST) and acetylcholinesterase (AChE) activities were evaluated after exposure and co-exposure to VCH (1 mM) and MeHg⁺ (0.2 mM) for one or three days in the head and body (thorax and abdomen) of flies. The expression of genes related to redox state and inflammatory response was evaluated after exposure and co-exposure to VCH and MeHg⁺ for three days.

Results

Survival decreased only in flies co-exposed to VCH and MeHg⁺ for three days. All treatments increased total reactive species production after one day of exposure. However, no significant changes were observed in the head after three days of exposure. One day of exposure to VCH caused an increase in the head GST activity, whereas MeHg⁺ induced an increase after three days of exposure. Regarding the body, all treatments increased GST activity after one day of exposure, but only the flies exposed to MeHg⁺ presented an increase in GST activity after three days of exposure. Treatments did not alter AChE activity in the head. As for gene expression, there was a significant increase in the Relish transcription factor gene in the flies’ body, but Nrf2, Keap1, Jafrac1, TrxR1, and NF-κβ were not altered.

Conclusion

The results suggest that exposure to VCH and MeHg⁺ induce oxidative stress and activation of an inflammatory response in fruit flies.

Response of a novel selenium-dependent glutathione peroxidase from thick shell mussel Mytilus coruscus exposed to lipopolysaccharide, copper and benzo[α]pyrene

Glutathione peroxidase (GPx) plays an important antioxidant role in cellular defense against environmental stress. In the present study, a novel selenium-dependent glutathione peroxidase termed McSeGPx firstly identified in thick shell mussel Mytilus coruscus. McSeGPx consists of 197 amino acid residues, characterized with one selenocysteine residue encoded by an opal stop codon TGA, one selenocysteine insertion sequence (SECIS) in the 3' untranslated region (UTR), two active site motifs and one signature sequence motif. McSeGPx transcripts were constitutively expressed in all examined tissues, and were significantly induced in gills and digestive glands with the stimulations of lipopolysaccharide (LPS), copper (Cu) and benzo[α]pyrene (B[α]P). Additionally, rough increases in McSeGPx activity were detected in both tissues under the challenge of LPS, Cu and B[α]P. Collectively, these results suggested that McSeGPx affiliate to selenocysteine dependent GPx (SeGPx) family and might play an important role in mediating the environmental stressors and antioxidant response in M. coruscus.

Short-Term Exposure of Mytilus coruscus to Decreased pH and Salinity Change Impacts Immune Parameters of Their Haemocytes

With the release of large amounts of CO₂, ocean acidification is intensifying and affecting aquatic organisms. In addition, salinity also plays an important role for marine organisms and fluctuates greatly in estuarine and coastal ecosystem, where ocean acidification frequently occurs. In present study, flow cytometry was used to investigate immune parameters of haemocytes in the thick shell mussel Mytilus coruscus exposed to different salinities (15, 25, and 35‰) and two pH levels (7.3 and 8.1). A 7-day in vivo and a 5-h in vitro experiments were performed. In both experiments, low pH had significant effects on all tested immune parameters. When exposed to decreased pH, total haemocyte count (THC), phagocytosis (Pha), esterase (Est), and lysosomal content (Lyso) were significantly decreased, whereas haemocyte mortality (HM) and reactive oxygen species (ROS) were increased. High salinity had no significant effects on the immune parameters of haemocytes as compared with low salinity. However, an interaction between pH and salinity was observed in both experiments for most tested haemocyte parameters. This study showed that high salinity, low salinity and low pH have negative and interactive effects on haemocytes of mussels. As a consequence, it can be expected that the combined effect of low pH and changed salinity will have more severe effects on mussel health than predicted by single exposure.

Molecular cloning and functional characterization of theta class glutathione S-transferase from Apostichopus japonicus

Glutathione S-transferases (GSTs) are the superfamily of multifunctional detoxification isoenzymes and play crucial roles in innate immunity. In the present study, a theta class GST homology was identified from A. japonicus (designated as AjGST-θ) by RACE approaches. The full-length cDNA of AjGST-θ was of 1013 bp encoded a cytosolic protein of 231 amino acids residues. Structural analysis revealed that AjGST-θ processed the characteristic N-terminal GSH-binding site (G-site) and the C-terminal hydrophobic substrate binding site (H-site). Multiple sequence alignment and phylogenetic analysis together supported that AjGST-θ belonged to a new member of theta class GST protein subfamily. Spatial expression analysis revealed that AjGST-θ was ubiquitously expressed in all examined tissues with the larger magnitude in intestine. The Vibrio splendidus challenge in vivo and LPS stimulation in vitro could both significantly up-regulate the mRNA expression of AjGST-θ when compared with control group. The recombinant protein was expressed in Escherichia coli and the purified AjGST-θ showed high activity with GST substrate. Meantime, disc diffusion assay showed that recombinant AjGST-θ protein could markedly improve bacterial growth under Cumene hydroperoxide exposure. More importantly, the recombinant AjGST-θ could effectively prevent primary coelomocytes apoptosis after LPS exposure. Our present findings suggested that AjGST-θ might play significantly roles in the modulation of immune response and protect cells from pathogens infection in A. japonicus.

Defense Responses to Short-term Hypoxia and Seawater Acidification in the Thick Shell Mussel Mytilus coruscus

The rising anthropogenic atmospheric CO₂ results in the reduction of seawater pH, namely ocean acidification (OA). In East China Sea, the largest coastal hypoxic zone was observed in the world. This region is also strongly impacted by ocean acidification as receiving much nutrient from Changjiang and Qiantangjiang, and organisms can experience great short-term natural variability of DO and pH in this area. In order to evaluate the defense responses of marine mussels under this scenario, the thick shell mussel Mytilus coruscus were exposed to three pH/pCO₂ levels (7.3/2800 μatm, 7.7/1020 μatm, 8.1/376 μatm) at two dissolved oxygen concentrations (DO, 2.0, 6.0 mg L⁻¹) for 72 h. Results showed that byssus thread parameters, such as the number, diameter, attachment strength and plaque area were reduced by low DO, and shell-closing strength was significantly weaker under both hypoxia and low pH conditions. Expression patterns of genes related to mussel byssus protein (MBP) were affected by hypoxia. Generally, hypoxia reduced MBP1 and MBP7 expressions, but increased MBP13 expression. In conclusion, both hypoxia and low pH induced negative effects on mussel defense responses, with hypoxia being the main driver of change. In addition, significant interactive effects between pH and DO were observed on shell-closing strength. Therefore, the adverse effects induced by hypoxia on the defense of mussels may be aggravated by low pH in the natural environments.

Antioxidant response of the hard shelled mussel Mytilus coruscus exposed to reduced pH and oxygen concentration

Ocean acidification (OA) and hypoxic events are increasing worldwide problems, their interactive effects have not been well clarified, although their co-occurrence is prevalent. The East China Sea (the Yangtze River estuary area) suffers from not only coastal hypoxia but also pH fluctuation, representing an ideal study site to explore the combined effect of OA and hypoxia on marine bivalves. We experimentally evaluated the antioxidant response of the mussel Mytilus coruscus exposed to three pH levels (8.1, 7.7 and 7.3) at two dissolved oxygen (DO) levels (2.0mgL^-1 and 6.0mgL^-1) for 72h. Activities of superoxide dismutase, catalase, glutathione peroxidase, acid phosphatase, and alkaline phosphatase and levels of malondialdehyde were measured in gills and hemolymph. All enzymatic activities in hemolymph and gills followed a similar pattern throughout the experiment duration. Generally, low DO showed greater effects on enzyme activities than elevated CO₂. Significant interactions between DO, pH and time were only observed at superoxide dismutase and catalase in both tissues. PCA revealed positive relationships between most enzyme activities in both gills and hemolymph with the exception of alkaline phosphatase activity and the level of malondialdehyde in the hemolymph. Overall, our results suggested that decreased pH and low DO induced similar antioxidant responses in the hard shelled mussel, and showed an additive effect on most enzyme activities. The evaluation of multiple environmental stressors, a more realistic scenario than single ones, is crucial to predict the effect of future global changes on coastal species and our results supply some insights on the potential combined effects of reduced pH and DO on marine bivalves.

A novel biomarker for marine environmental pollution of HSP90 from Mytilus coruscus

Heat shock protein 90 (HSP90) is a conserved molecular chaperone contributing to cell cycle control, organism development and the proper regulation of cytosolic proteins. The full-length HSP90 cDNA of Mytilus coruscus (McHSP90, KT946644) was 2420bp, including an ORF of 2169bp encoding a polypeptide of 722 amino acids with predicted pI/MW 4.89/83.22kDa. BLASTp analysis and phylogenetic relationship strongly suggested McHSP90 was a member of HSP90 family, and it was highly conserved with other known HSP90, especially in the HSP90 family signatures, ATP/GTP-Binding sites and 'EEVD' motif. The mRNA of McHSP90 in haemolymph was upregulated in all treatments including Vibrio alginolyticus and Vibrio harveyi challenge, metals stresses (copper and cadmium) and 180 CST fuel exposure. All the results implied the expression of McHSP90 could be affected by Vibrio challenge and environmental stress, which might help us gain more insight into the molecular mechanism of HSP against adverse stresses in mollusca.

Upregulation of biotransformation genes in gills of oyster Crassostrea brasiliana exposed in situ to urban effluents, Florianópolis Bay, Southern Brazil

The release of untreated sanitary sewage, combined with unplanned urban growth, are major factors contributing to degradation of coastal ecosystems in developing countries, including Brazil. Sanitary sewage is a complex mixture of chemicals that can negatively affect aquatic organisms. The use of molecular biomarkers can help to understand and to monitor the biological effects elicited by contaminants. The aim of this study was to evaluate changes in transcript levels of genes related to xenobiotic biotransformation in the gills of oysters Crassostrea brasiliana transplanted and kept for 24h at three areas potentially contaminated by sanitary sewage (Bücheller river, BUC; Biguaçu river, BIG; and Ratones island, RAT), one farming area (Sambaqui beach, SAM) and at one reference site (Forte beach, FOR) in the North Bay of Santa Catarina Island (Florianópolis, Brazil). Transcript levels of four cytochrome P450 isoforms (CYP2AU1, CYP3A-like, CYP356A1-like and CYP20A1-like), three glutathione S-transferase (GST alpha-like, GST pi-like and GST microsomal 3-like) and one sulfotransferase gene (SULT-like) were evaluated by means of quantitative reverse transcription PCR (qRT-PCR). Chemical analysis of the sediment from each site were performed and revealed the presence of aliphatic and polycyclic aromatic hydrocarbons, linear alkylbenzenes and fecal sterols in the contaminated areas (BUC and BIG). Water quality analysis showed that these sites had the highest levels of fecal coliforms and other parameters evidencing the presence of urban sewage discharges. Among the results for gene transcription, CYP2AU1 and SULT-like levels were upregulated by 20 and 50-fold, respectively, in the oysters kept for 24h at the most contaminated site (BUC), suggesting a role of these genes in the detoxification of organic pollutants. These data reinforce that gills possibly have an important role in xenobiotic metabolism and highlight the use of C. brasiliana as a sentinel for monitoring environmental contamination in coastal regions.

Transcriptome response to copper heavy metal stress in hard-shelled mussel (Mytilus coruscus)

The hard-shelled mussel (Mytilus coruscus) has considerably one of the most economically important marine shellfish worldwide and considered as a good invertebrate model for ecotoxicity study for a long time. In the present study, we used Illumina sequencing technology (HiSeq2000) to sequence, assemble and annotate the transcriptome of the hard-shelled mussel which challenged with copper pollution. A total of 21,723,913 paired-end clean reads (NCBI SRA database SRX1411195) were generated from HiSeq2000 sequencer and 96,403 contigs (with N50 = 1118 bp) were obtained after de novo assembling with Trinity software. Digital gene expression analysis reveals 1156 unigenes are upregulated and 1681 unigenes are downregulated when challenged with copper. By KEGG pathway enrichment analysis, we found that unigenes in four KEGG pathways (aminoacyl-tRNA biosynthesis, apoptosis, DNA replication and mismatch repair) show significant differential expressed between control and copper treated groups. We hope that the gill transcriptome in copper treated hard-shelled mussel can give useful information to understand how mussel handles with heavy metal stress at molecular level.

Effect of pH and temperature on antioxidant responses of the thick shell mussel Mytilus coruscus

This study evaluated the combined effects of seawater pH decrease and temperature increase on the activity of antioxidant enzymes in the thick shell mussel Mytilus coruscus, an ecological and economic bivalve species widely distributed along the East China Sea. Mussels were exposed to three pH levels (8.1, 7.7 and 7.3) and two temperatures (25 °C and 30 °C) for 14 days. Activities of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPX), glutathione (GSH), acid phosphatase (ACP), alkaline phosphatase (AKP) and glutamic-pyruvic transaminase (GPT) were measured in gills and digestive glands after 1, 3, 7 and 14 days of exposure. All enzymatic activities were significantly impacted by pH, temperature. Enzymatic activities at the high temperature were significantly higher than those at the low temperature, and the mussels exposed to pH 7.3 showed significantly higher activities than those under higher pH condition for all enzymes except ACP. There was no interaction between temperature and pH in two third of the measured activities suggesting similar mode of action for both drivers. Interaction was only consistently significant for GPX. PCA revealed positive relationships between the measured biochemical indicators in both gills and digestive glands. Overall, our results suggest that decreased pH and increased temperature induce a similar anti-oxidative response in the thick shell mussel.