Identification of differentially expressed genes in the digestive gland of manila clam Ruditapes philippinarum exposed to BDE-47

Comparative transcriptome analysis reveals immunotoxicology induced by three organic UV filters in Manila clam (Ruditapes philippinarum)

Benzophenone-3 (BP-3), 4-methyl-benzylidene camphor (4-MBC) and 2-ethyl-hexyl-4-trimethoxycinnamate (EHMC) are commonly used organic ultraviolet (UV) filters and are frequently detected in water environments. In the present study, we studied the potential adverse impacts of UV filter exposures in Ruditapes philippinarum by investigating transcriptomic profiles and non-specific immune enzyme activities. Transcriptome analysis showed that more genes were differentially regulated in EHMC-treated group, and down-regulated genes (2009) were significantly more than up-regulated ones (410) at day 7. Function annotation revealed that pathways "immune system", "cell growth and death" and "infectious diseases" were significantly enriched. Generally, combined qPCR and biochemical analyses demonstrated that short-term exposure to low dose of UV filters could activate immune responses, whereas the immune system would be restrained after prolonged exposure. Taken together, the present study firstly demonstrated the immunotoxicology induced by BP-3, 4-MBC and EHMC on R. philippinarum, indicating their potential threats to the survival of marine bivalves.

Using meiobenthic taxa, nematofauna biological traits, and bacterial abundance to assess the effects of the polybrominated diphenyl ethers compound: Case study of tetrabromo diphenyl ether BDE-47

Trophic web structuring in aquatic sediments is dependent on the biological interactions between metazoans and microbial communities. The presence of pollutants in these biotas can therefore impact the meiofauna structure via the modification of the microbial communities. The current study examined in a laboratory bioassay the response of meiobenthic communities, particularly marine nematode taxa from the Bizerte Lagoon to the effect of the most detected polybrominated diphenyl ether in this aquatic environment, BDE-47. Four doses [D1 (2.5 ppb Dry weight (DW)), D2 (25 ppb DW), D3 (50 ppb DW), and D4 (100 ppb DW)] were gradually applied and sediment microcosms were incubated for 30 days in the presence or absence of meiofauna. Our results show that BDE-47-enriched sediments decreased the meiofaunal taxa and bacterial abundance. A lower taxonomic diversity of the nematodes' general structure was observed with all doses used. The numerical analysis of the two dimensional (2D) non-metric multidimensional scaling (nMDS) plots and the evolution of the relative abundances of each functional group of nematode genus assemblages revealed that the abundance of all biological traits was modified. Nevertheless, only three of the functional traits, adult length, feeding group, and amphid shape, showed a clear difference between the control and the treated microcosms. The similarity percentage analysis (SIMPER) revealed that the average dissimilarity between nematode genera communities and biological traits increased with BDE-47-enriched sediments. The nMDS second-stage ordination of inter-matrix rank correlations for matrices including genera and biological traits showed that the amphid shape was the functional trait closest to the generic distribution. Finally, the Principal Component Analysis (PCA) for the nematode biological traits and bacteria indicated a positive correlation of these microbes with the functional groups [1A, Cr, and ef], and a negative correlation only with the "cla"-type tail shape.

Ecotoxicity of polybrominated diphenyl ether (BDE-47) on a meiobenthic community with special emphasis on nematodes: Taxonomic and trophic diversity assessment

The response taxonomic and trophic of meiobenthic organisms, especially marine nematodes to polybrominated diphenyl ether (BDE-47) was studied using a community from Bizerte lagoon (Nord-East Tunisia). Four concentrations of BDE-47 [D1 (2.5 μg/kg dw), D2 (25 μg/kg dw), D3 (50 μg/kg dw), and D4 (100 μg/kg dw)] were applied, and responses were determined 30 days after exposure. Species abundance and all univariate indices were significantly affected in all treated microcosms compared to the control. The non-parametric cluster based on species abundance separated the nematode population into two groups: control + all treated microcosms. After grouping nematode species according to their trophic diversity, their abundance showed differential responses. The non-metric multi-dimensional scaling analysis and cumulative k-dominance based on the abundance of trophic groups abundances reflected significant separation between the control microcosm and each treatment condition. The correspondence analysis 2D plot generated from nematode species and trophic groups abundance showed the control microcosm was dominated by microvores, represented by two species of Terschellingia. However, when treated with the highest concentration of BDE-47, the community was occupied by the resistant trophic groups of facultative predators and epigrowth feeders represented by Metoncholaimus pristiurus and Paracomesoma dubium, respectively.

Responses of antioxidant defenses in the clam Mactra veneriformis to 2,2',4,4'‑tetrabromodiphenyl ether exposure

Antioxidant enzymes play essential roles against oxidative stress caused by 2,2',4,4'-tetrabromodiphenyl ether (BDE-47), which is ubiquitous in marine environment and organisms. However, research on antioxidant responses to BDE-47 in marine bivalves is scarce. In this study, we identified the full-length cDNA of catalase (CAT), and glutathione peroxidase (GPx) in the clam Mactra veneriformis. Subsequently, the responses of CAT, GPx, and copper, zinc-superoxide dismutase (Cu, Zn-SOD) were investigated in the clams exposed to 0.1, 1, and 10 μg/L BDE-47 for 7 days, and then depurated in natural seawater for 3 days. MvCAT and MvGPx contained conserved sequences. The deduced amino acid sequences shared high similarity with CATs and GPxs in other mollusks. M. veneriformis accumulated BDE-47 in a dose-dependent manner and eliminated BDE-47 poorly. BDE-47 induced a time- and dose-dependent increase of malondialdehyde content. Both the dose and the duration had significant effect on mRNA expressions and activities of the three antioxidants. Cu, Zn-SOD responded to BDE-47 earlier than CAT and GPx. The antioxidant responses could recover after depuration. These results suggested that M. veneriformis could accumulate BDE-47 efficiently. Antioxidant enzymes were triggered to counter the oxidative stress generated by BDE-47. Cu, Zn-SOD acted as the first defense against oxidative stress, while CAT and GPx intervened later. This study is therefore helpful in understanding the antioxidant responses to PBDEs in marine bivalves.

Gene expression and genotoxicity in Manila clam (Ruditapes philippinarum) modulated by sediment contamination and lagoon dynamics in the Po river delta

The lagoons of the Po River delta are potentially exposed to complex mixtures of contaminants, nevertheless, there is a substantial lack of information about the biological effects of these contaminants in the Po delta lagoons. These environments are highly dynamic and the interactions between chemical and environmental stressors could prevent the proper identification of biological effects and their causes. In this study, we aimed to disentangle such interactions focusing on Manila clams, previously exposed to six lagoons of the Po delta, adopting three complementary tools: a) the detailed description via modelling techniques of lagoon dynamics for salinity and water temperature; b) the response sensitivity of a number of target genes (ahr, cyp4, ρ-gst, σ-gst, hsp22, hsp70, hsp90, ikb, dbh, ach, cat, Mn-sod, Cu/Zn-sod, cyp-a, flp, grx, TrxP) investigated in clam digestive glands by Real Time PCR; and c) the relevance of DNA adducts determined in clams as markers of exposure to genotoxic chemicals. The lagoons showed specific dynamics, and two of them (Marinetta and Canarin) could induce osmotic stress. A group of genes (ahr, cyp4, Mn-sod, σ-gst, hsp-22, cyp-a, TrxP) seemed to be associated with overall lagoon characteristics as may be described by salinity and its variations. Lagoon modelling and a second group of genes (hsp70, hsp90, cat, ikb, ach, grx, Cu/Zn-sod) also suggested that moderate increases of river discharge may imply worse exposure conditions. Oxidative stress seemed to be associated with such events but it was slightly evident also under normal exposure conditions. DNA adduct formation was mainly associated with overwhelmed antioxidant defences (e.g. low Cu/Zn-sod) or seemingly with their lack of response in due time. In Po delta lagoons, Manila clam can be affected by chemical and environmental factors which can contribute to induce oxidative stress, DNA adduct formation and, ultimately, to affect clam condition and health.

Toxicological effects of benzo(a)pyrene, DDT and their mixture on the green mussel Perna viridis revealed by proteomic and metabolomic approaches

Benzo(a)pyrene (BaP) and dichlorodiphenyltrichloroethane (DDT) are persistent organic pollutants and environmental estrogens (EEs) with known toxicity towards the green mussel, Perna viridis. In this study, the toxic effects of BaP (10 µg/L) and DDT (10 µg/L) and their mixture were assessed in green mussel gills with proteomic and metabolomic approaches. Metabolic responses indicated that BaP mainly caused disturbance in osmotic regulation by significantly decrease in branched chain amino acids, dimethylamine and dimethylglycine in gills of male green mussels after exposure for 7 days. DDT mainly caused disturbance in osmotic regulation and energy metabolism by differential alteration of betaine, dimethylamine, dimethylglycine, amino acids, and succinate in gills of male green mussels. However, the mixture of BaP and DDT didn't show obvious metabolite changes. Proteomic analysis showed different protein expression profiles between different treatment groups, which demonstrated that BaP, DDT and their mixture may have different modes of action. Proteomic responses revealed that BaP induced cell apoptosis, disturbance in protein digestion and energy metabolism in gills of green mussels, whereas DDT exposure altered proteins that were associated with oxidative stress, cytoskeleton and cell structure, protein digestion and energy metabolism. However, the mixture of BaP and DDT affected proteins related to the oxidative stress, cytoskeleton and cell structure, protein biosynthesis and modification, energy metabolism, growth and apoptosis.