Bioaccumulation and metabolomics responses in oysters Crassostrea hongkongensis impacted by different levels of metal pollution

Safe Production of Rice (Oryza sativa L.) in Arsenic-Contaminated Soil: a Remedial Strategy using Micro-Nanostructured Bone Biochar

This study investigated the effects of fine-sized pork bone biochar particles on remediating As-contaminated soil and alleviating associated phytotoxicity to rice in 50-day short-term and 120-day full-life-cycle pot experiments. The addition of micro-nanostructured pork bone biochar (BC) pyrolyzed at 400 and 600 °C (BC400 and BC600) significantly increased the As-treated shoot and root fresh weight by 24.4-77.6%, while simultaneously reducing tissue As accumulation by 26.7-64.1% and increasing soil As content by 17.1-27.1% as compared to As treatment. Microbial community analysis demonstrated that BC600 and BC400 treatments increased the proportion of plant growth-promoting microbes such as Ceratobasidium and Achromobacter by 33-81.6% in the roots and As adsorption-associated Bacillus by 1.15-1.59-fold in the rhizosphere soil. Metabolomic profiling suggests that BC and As coexposure triggered differentially expressed metabolites (DEMs) enriched in lipid, carbohydrate, and amino acid metabolic pathways, all of which could alleviate As-induced phytotoxicity and promote plant As tolerance. Importantly, the quality of As-treated rice grains was improved by the BC amendments. This study demonstrates the significant potential of BC for enhancing crop growth and minimizing the As-induced phytotoxicity to rice and provides a framework for a promising strategy for remediating heavy metal(loid)-contaminated soil while simultaneously promoting food safety.

Insights into the transcriptomic responses of silver-lipped pearl oysters Pinctada maxima exposed to a simulated large-scale seismic survey

BACKGROUND

The wild stocks of Pinctada maxima pearl oysters found off the coast of northern Australia are of critical importance for the sustainability of Australia's pearling industry. Locations inhabited by pearl oysters often have oil and gas reserves in the seafloor below and are therefore potentially subjected to seismic exploration surveys. The present study assessed the impact of a simulated commercial seismic survey on the transcriptome of pearl oysters. Animals were placed at seven distances (-1000, 0, 300, 500, 1000, 2000, and 6000 m) from the first of six operational seismic source sail lines. Vessel control groups were collected before the seismic survey started and exposed groups were collected after completion of six operational seismic sail lines (operated at varying distances over a four-day period). Samples from these groups were taken immediately and at 1, 3, and 6 months post-exposure. RNA-seq was used to identify candidate genes and pathways impacted by the seismic noise in pearl oyster mantle tissues. The quantified transcripts were compared using DESeq2 and pathway enrichment analysis was conducted using KEGG pathway, identifying differentially expressed genes and pathways associated with the seismic activity.

RESULTS

The study revealed the highest gene expression and pathway dysregulation after four days of exposure and a month post-exposure. However, this dysregulation diminished after three months, with only oysters at -1000 and 0 m displaying differential gene expression and pathway disruption six months post-exposure. Stress-induced responses were evident and impacted energy production, transcription, translation, and protein synthesis.

CONCLUSION

Seismic activity impacted the gene expression and pathways of pearl oysters at distances up to 2000 m from the source after four days of exposure, and at distances up to 1000 m from the source one-month post-exposure. At three- and six-months post-exposure, gene and pathway dysregulations were mostly observed in oysters located closest to the seismic source at 0 and - 1000 m. Overall, our results suggest that oysters successfully activated stress responses to mitigate damage and maintain cellular homeostasis and growth in response to seismic noise exposure.

Effects of single or combined exposure to tralopyril and ocean acidification on energy metabolism response and sex development in Pacific oysters (Crassostrea gigas)

The combined effects of the novel antifouling biocide tralopyril (TP) nitrile and ocean acidification (OA) on marine organisms are still not well understood, despite the increasing attention given to the toxic effects of emerging pollutants and OA on marine organisms in recent years. In this study, Crassostrea gigas (C. gigas) was exposed to TP, OA, and a combination of TP and OA for 21 days with a 14-day depuration. This study investigated the inter-tissue variability in energy metabolism responses and the impacts on gonadal development in C. gigas under both single and combined exposures to TP and OA. The results indicate that TP exposure and OA resulted in up-regulation of energy metabolism genes in the C. gigas, with tissues exhibiting enhanced aerobic metabolism. Furthermore, OA influences the sex determination of C. gigas, promoting the development of female individuals. Moreover, following depuration, C. gigas is able to restore normal energy metabolism and sexual development through the accumulation of suitable energy reserves. This study provides a valuable reference for the environmental and ecological risk assessment of TP, addressing the research gap in understanding the combined toxicity of TP and OA on aquatic organisms.

Understanding the variable metal concentrations in estuarine oysters Crassostrea hongkongensis: A biokinetic analysis

Understanding the metal concentrations in oysters is important because of its relevance to human health and biomonitoring. However, metal concentrations in oysters are highly variable in nature and not well explained by metal exposure. This study examined the metal contamination in farm oysters Crassostrea hongkongensis grown in Qinzhou Bay, south China. Cadmium (Cd), zinc (Zn), nickel (Ni), and copper (Cu) concentrations in the oysters varied between 7.9 and 72.2, 282-17003, 0.37-47.7 and 37-4012 μg g-1, respectively, showing large metal variability among different individuals. Oyster metal concentrations decreased with increasing body size and significantly higher levels were observed in wet season. Low salinity and slower oyster growth due to inferior growth conditions could be responsible for the elevated metal concentrations in the wet season. Biokinetic modeling showed that the coupling of ingestion rate and growth can cause 2.8-4.2 folds differences in the oyster Cd and Zn concentrations, respectively, suggesting the significant role of oyster bioenergetics in contributing to the metal variability. Modeling data revealed that Cd and Zn concentrations in oyster tissues reach maximum levels when oysters have their lowest growth efficiency. This suggests that any factors influencing the energy budget in oysters could simultaneously alter their metal concentrations, which might be the reason why oyster metal concentrations are so variable in the natural environment.

Environmental organic contaminant body burdens and GC-MS based untargeted metabolomics in mediterranean mussels from Port Phillip Bay, Australia☆

Mussels were collected from four coastal sites around Port Phillip Bay, Australia in Mar and Apr 2021). Body burdens of Polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), and organochlorine pesticides (OCPs) were measured and the possible sources of toxicants discussed. In addition, a gas chromatography-mass spectrometry (GC-MS) based untargeted metabolomics analysis was performed using the mantle tissues of mussels. Correlations between the results of contaminant body burdens and metabolic variations were investigated. The results demonstrated that high accumulations of low-molecular-weight PAHs were found in mussels. High body burdens of PCBs and OCPs were only found at mussels from the site close to the river mouth. Some of the metabolic pathways were correlated with the accumulation of PAHs. No correlations were found between PCB and OCP accumulations and metabolic abundances. According to the food and environmental standards of the European Union (EU), the PAH, PCB, and OCP accumulation in mussels in this study are a serious food safety concern.

Differentiation and decreased genetic diversity in field contaminated oysters Crassostrea hongkongensis: Identification of selection signatures

The extent to which chemical contamination affects the population structure and genetic diversity of natural populations remains elusive. Here, we used the whole-genome resequencing and transcriptome to diagnose the effects of long-term exposure to multiple elevated chemical pollutants on the population differentiation and genetic diversity in oysters Crassostrea hongkongensis in a typically polluted Pearl River Estuary (PRE) of Southern China. Population structure revealed an obvious differentiation between the PRE oysters and those collected from a nearby clean Beihai (BH) individuals, while no significant differentiation was observed among individuals collected from the three pollution sites within PRE due to the high gene flow. The decreased genetic diversity in the PRE oysters reflected the long-term effects of chemical pollutants. Selective sweeps between BH and PRE oysters revealed that chemical defensome genes, including glutathione S-transferase, zinc transporter, were responsible for their differentiation, sharing common metabolic process of other pollutants. Combined with the genome-wide association analysis, 25 regions containing 77 genes were identified to be responsible for the direct selection regions of metals. Linkage disequilibrium blocks and haplotypes within these regions provided the biomarkers of permanent effects. Our results provide important insights to the genetic mechanisms underlying the rapid evolution under chemical contamination in marine bivalves.

Metabolomics-Based Investigation on the Metabolic Changes in Crassostrea gigas Experimentally Exposed to Galvanic Anodes

Cathodic protection is widely used to protect metal structures from corrosion in marine environments using sacrificial galvanic anodes. These anodes, either in Zinc, or preferentially nowadays in Al-Zn-In alloys, are expected to corrode instead of the metal structures. This leads to the release of dissolved species, Zn²⁺, Al³⁺, and In³⁺, and solid phases such as Al(OH)₃. Few studies have been conducted on their effects on marine organisms, and they concluded that further investigations are needed. We therefore evaluated the effects of Zn and Al-Zn-In anodes on oysters stabulated in tanks, under controlled conditions defined through a comparison with those prevailing in a given commercial seaport used as reference. We analyzed the entire metabolome of gills with a non-targeted metabolomic approach HRMS. A modelling study of the chemical species, corresponding to the degradation products of the anodes, likely to be present near the exposed oysters, was also included. We identified 16 and two metabolites modulated by Zn- and Al-Zn-In-anodes, respectively, that were involved in energy metabolism, osmoregulation, oxidative stress, lipid, nucleotide nucleoside and amino acid metabolisms, defense and signaling pathways. The combination of chemical modelling and metabolomic approach, used here for the first time, enlightened the influence of Zn present in the Al-Zn-In anodes.

The influence of temperature rise on the metabolic response of Ruditapes philippinarum clams to 17-α-ethinylestradiol

Untargeted Nuclear Magnetic Resonance metabolomics was employed to study the effects of warming conditions (17-21 °C) and exposure to 17-α-ethinylestradiol (EE2) on the polar metabolome of Ruditapes philippinarum clams, to identify metabolic markers for monitoring/prediction of deviant environmental conditions. Warming alone triggered changes in alanine/aspartate/glutamate, aromatic amino acids, taurine/hypotaurine and homarine/trigonelline pathways, as well as in energy metabolism, suggesting osmoregulatory adaptations and glycolytic/tricarboxylic acid (TCA) cycle activation, possibly accompanied to some extent by gluconeogenesis to preserve glycogen reserves. At 17 °C, the lowest EE2 concentration (5 ng/L) specifically engaged branched-chain and aromatic amino acids to activate the glycolysis/TCA cycle. Notably, a partial metabolic recovery was observed at 25 ng/L, whereas higher EE2 concentrations (125 and 625 ng/L) again induced significant metabolic disturbances. These included enhanced glycogen biosynthesis and increased lipid reserves, sustained by low-level glutathione-based antioxidative mechanisms that seemed active. At 21 °C, response to EE2 was notably weak at low/intermediate concentrations, becoming particularly significant at the highest EE2 concentration (625 ng/L), suggesting higher protection capacity of Ruditapes philippinarum clams under warming conditions. At 625 ng/L, disturbances in alanine/aspartate/glutamate and taurine/hypotaurine metabolisms were observed, with no evidence of enhanced carbohydrate/protein catabolism. This low energy function profile was accompanied by marked antioxidative mechanisms and choline compounds modulation for cell membrane protection/repair. These results help monitor clams´ response to temperature rise and EE2 exposure, paving the way for future effective guidance and prediction of environmental damaging effects.

Changes in metabolic profiles of amphipods Allorchestes compressa after acute exposures to copper, pyrene, and their mixtures

Amphipods are ideal indicators for biomonitoring and ecotoxicological studies of environmental contaminants because they are extensively distributed in aquatic environments, are easy to collect and are important in nutrient cycling. Marine amphipods (Allorchestes compressa) were exposed to two concentrations of copper and pyrene, and their mixtures, for 24 and 48 h. Changes in polar metabolites were assessed using Gas Chromatography Mass Spectrometry (GC-MS)-based untargeted metabolomics. Generally, limited metabolite changes were observed for copper and pyrene single exposures (eight and two significant metabolites, respectively), while 28 metabolites had changed following exposures to mixtures. Furthermore, changes were mainly observed after 24 h but had seemingly returned to control levels after 48 h. Multiple types of metabolites were affected including amino acids, Tricarboxylic acid (TCA) cycle intermediates, sugars, fatty acids, and hormones. This study highlights the sensitivity of metabolomics in assessing the impacts of low concentrations of chemicals compared to traditional ecotoxicological endpoints.

Gender-Specific Metabolic Responses of Crassostrea hongkongensis to Infection with Vibrio harveyi and Lipopolysaccharide

Gender differences in the hemocyte immune response of Hong Kong oyster Crassostrea hongkongensis to Vibrio harveyi and lipopolysaccharide (LPS) infection exist. To determine if a gender difference also exists, we use a ¹H NMR-based metabolomics method to investigate responses in C. hongkongensis hepatopancreas tissues to V. harveyi and LPS infection. Both infections induced pronounced gender- and immune-specific metabolic responses in hepatopancreas tissues. Responses are mainly presented in changes in substances involved in energy metabolism (decreased glucose, ATP, and AMP in males and increased ATP and AMP in LPS-infected females), oxidative stress (decreased glutathione in males and decreased tryptophan and phenylalanine and increased choline and proline in LPS-infected females), tricarboxylic acid (TCA) cycle (decreased α-ketoglutarate acid and increased fumarate in LPS-infected males, and decreased fumarate in LPS-infected females), and osmotic regulation (decreased trigonelline and increased taurine in V. harveyi-infected males and decreased betaine in V. harveyi-infected females). Results suggest that post-spawning-phase male oysters have a more significant energy metabolic response and greater ability to cope with oxidative stress than female oysters. We propose that the impact of oyster gender should be taken into consideration in the aftermath of oyster farming or oyster disease in natural seas.

Toxicological responses of juvenile Chinese shrimp Fenneropenaeus chinensis and swimming crab Portunus trituberculatus exposed to cadmium

Cadmium (Cd) is one of the typical metal pollutants in the Bohai Sea. To evaluate the acute toxicological effects of Cd on marine crustaceans, juvenile Fenneropenaeus chinensis and Portunus trituberculatus were exposed to Cd at environmentally relevant concentrations (5 and 50 μg/L) for 96 h. Cd accumulation, antioxidants and metabolite profiles were characterized to elucidate the responses of juvenile crustaceans to Cd stress. Significant Cd accumulation was observed in both juvenile crustaceans in 50 μg/L Cd-treated group. Results showed that Cd exposure induced hormesis based on the alterations of GSH, SOD and CAT activities (i.e. increased levels in the low concentration of Cd treatment and recovered levels in the high concentration of Cd treatment) in juvenile P. trituberculatus. Similarly, the responses of GSH contents presented hormesis pattern in Cd-treated juvenile F. chinensis. Na+-K+-ATPase contents were significantly elevated in 50 μg/L Cd-treated group. In addition, untargeted NMR-based metabolomics indicated Cd caused the disturbance in osmotic regulation and energy consumption in both juvenile F. chinensis and P. trituberculatus via different pathways. The immunotoxicity and movement disorder were uniquely demonstrated in juvenile P. trituberculatus after Cd exposure.

Highly Sensitive and Specific Responses of Oyster Hemocytes to Copper Exposure: Single-Cell Transcriptomic Analysis of Different Cell Populations

Oyster hemocytes are the primary vehicles transporting and detoxifying metals and are regarded as important cells for the occurrence of colored oysters due to copper (Cu) contamination. However, its heterogeneous responses under Cu exposure have not been studied. Single-cell transcriptome profiling (scRNA-seq) provides high-resolution visual insights into tissue dynamics and environmental responses. Here, we used scRNA-seq to study the responses of different cell populations of hemocytes under Cu exposure in an estuarine oyster Crassostrea hongkongensis. The 1900 population-specific Cu-responsive genes were identified in 12 clusters of hemocytes, which provided a more sensitive technique for examining Cu exposure. The granulocyte, semigranulocyte, and hyalinocyte had specific responses, while the granulocyte was the most important responsive cell type and displayed heterogeneity responses of its two subtypes. In one subtype, Cu was transported with metal transporters and chelated with Cu chaperons in the cytoplasm. Excess Cu disturbed oxidative phosphorylation and induced reactive oxygen species production. However, in the other subtype, endocytosis was mainly responsible for Cu internalization, which was sequestered in membrane-bound granules. Collectively, our results provided the first mRNA expression profile of hemocytes in oysters and revealed the heterogeneity responses under Cu exposure.

Pesticide mixture toxicity assessment through in situ and laboratory approaches using embryo-larval stages of the pacific oyster (Magallana gigas)

Worsened state of oysters in French Arcachon Bay, demand an investigation of possible causes. This study evaluated the effects of an environmentally relevant mixture of five common pesticides on the early-life stages of the Pacific oyster (Magallana gigas). Laboratory assays with artificial mixture and in situ transplantation were complementarily used to investigate a series of sublethal endpoints. The laboratory exposure revealed developmental toxicity at 0.32 μg/L, which corresponds to mixture concentrations in Arcachon Bay. Downregulation of some gene transcriptions was observed at environmental level. No difference in larvae development was revealed among the three sites in Arcachon Bay. This study was the first to evaluate locomotion of oyster larvae exposed in situ. Suspected poor water quality in the inner part of Arcachon Bay was reflected by impairment at the molecular level. In conclusion, current concentrations of the tested pesticides in Arcachon Bay hinder larval development and affect several biological functions.

Norethindrone causes cellular and hepatic injury in zebrafish by compromising the metabolic processes associated with antioxidant defence: Insights from metabolomics

Progestins, such as norethindrone (NET), have been increasingly detected in aquatic environments due to their extensive use for medical applications. While NET is notorious for its endocrine disrupting effects, it has been recently shown to cause cellular damage, suggesting its potential impacts on the body defence of organisms. Hence, we examined the histological features and antioxidant defence of zebrafish (Danio rerio) after exposing to NET (50 ng/L and 500 ng/L) for 72 days, followed by analysing its metabolome to explore whether NET disturbs the metabolic processes responsible for antioxidant defence. While acute mortality was not triggered, we found that antioxidant defence was substantially weakened by NET at 500 ng/L (i.e. reduced SOD and GSH levels) and hence liver injury was inflicted (i.e. elevated ALT and MDA levels), as manifested by vacuolization of liver tissues and reduced number of normal cells in the liver. Metabolomic analysis showed that the metabolic processes responsible for antioxidant defence were disrupted by NET (e.g. upregulation of nervonyl carnitine and chenodeoxycholic acid 3-sulfate; downregulation of homolanthionine and acevaltrate) and these changes can undermine antioxidant defence by suppressing Nrf2-ARE and NF-κB pathways that contribute to the synthesis of SOD and GSH. This study demonstrates how NET can compromise the body defence of aquatic organisms via metabolic disruption, suggesting that the impacts of progestins on their fitness are more detrimental than previously thought.

Ecological and toxicological assessments of anthropogenic contaminants based on environmental metabolomics

There has long been a great concern with growing anthropogenic contaminants and their ecological and toxicological effects on living organisms and the surrounding environment for decades. Metabolomics, a functional readout of cellular activity, can capture organismal responses to various contaminant-related stressors, acquiring direct signatures to illustrate the environmental behaviours of anthropogenic contaminants better. This review entails the application of metabolomics to profile metabolic responses of environmental organisms, e.g. animals (rodents, fish, crustacean and earthworms) and microorganisms (bacteria, yeast and microalgae) to different anthropogenic contaminants, including heavy metals, nanomaterials, pesticides, pharmaceutical and personal products, persistent organic pollutants, and assesses their ecotoxicological impacts with regard to literature published in the recent five years. Contaminant-induced metabolism alteration and up/down-regulation of metabolic pathways are revealed in typical organisms. The obtained insights of variations in global metabolism provide a distinct understanding of how anthropogenic contaminants exert influences on specific metabolic pathways on living organisms. Thus with a novel ecotechnique of environmental metabolomics, risk assessments of anthropogenic contaminants are profoundly demonstrated.

Oyster copper levels in the northern South China Sea from 1989 to 2015: spatiotemporal trend detection and human health implications

Coastal heavy metal pollution has become an important topic for seafood safety and marine environmental protection. Unlike toxic heavy metals such as cadmium or chromium, copper is essential for oysters' growth but can inhibit their immune response to exotic stress when going above normal levels. Oysters with high copper levels can easily accumulate and transfer abnormal amounts of copper to upper trophic levels, and generate health risks for humans. This study investigated the spatiotemporal variability and health risk of copper levels in cultured oysters (Crassostrea rivularis) sampled from 23 harbors, bays, or estuaries along the northern South China Sea during 1989-2015. Overall, oyster copper concentrations in the study area ranged from 0.9 to 1897.0 μg/g wet weight with a mean of 210.0 (± 143.6) μg/g and a median of 89.3 μg/g. Although oyster copper levels in the southern China provinces of Guangdong, Guangxi, and Hainan showed an overall decrease during 1989-2015, they stayed relatively low since 1996 and increased slightly after 2010. Oyster copper levels in Guangdong were significantly higher than in Hainan and Guangxi. In Guangdong, oyster copper levels were highest in the Pearl River Estuary, followed by west Guangdong and east Guangdong. The health risk of copper exposure through oyster consumption increased in 2011-2015 compared with in 2006-2010. It is recommended that the human daily intake of cultured oysters in the study area should be reduced by half to minimize copper exposure. This study suggested that copper is one of the most important heavy metal contaminants in coastal and estuarine ecosystems of the northern South China Sea.

Integrated assessment of the acclimation capacity of the marine bivalve Crenomytilus grayanus under naturally highly contaminated conditions: Subcellular distribution of trace metals and structural alterations of nephrocytes

The aim of our work was to assess whether the cellular processes in the nephrocytes of the long-lived mussel Crenomytilus grayanus tend to acclimation or destruction under trace metal contamination. Mussels were collected from three sites in the north-western Pacific Ocean: reference site, upwelling site, and a site highly contaminated with trace metals. Concentration, subcellular distribution of trace metals (Cd, Cu, Zn, and Pb) in the mussel kidneys, and ultrastructural alterations of the nephrocytes were studied. To assess the total load of accumulated trace metals, the total concentration coefficient (∑СС) was determined. In the kidneys of the reference C. grayanus, trace metals were eliminated from cell metabolism mainly by lysosomal granules or residue bodies. Under high levels of contamination, the defense mechanisms of C. grayanus are practically suppressed (no metallothionein-like protein peak, decreased content of granules) by the total effect of accumulated pollutants that leads to the destruction of cellular structures. Under natural conditions (upwelling site), increased accumulation of trace metals in the mussel kidneys did not lead to an increase in the number or size of lysosomal granules. However, abnormal high Cd accumulation in the kidneys caused the synthesis of high levels of metallothionein-like proteins that sequester most of the studied trace metals. To quickly lower the metal levels in nephrocytes under these conditions, a unique long-term acclimatory response - apocrine-like secretion in nephrocytes, which provides rapid elimination of me-MTLP complexes from the cell arose. Thus, our integrated study of the subcellular distribution of trace metals and ultrastructural alterations in nephrocytes allowed us to characterize the features of the structural and functional alterations in mussel cells under the field conditions tested.

Production, characterization, evaluation and toxicity assessment of a Bacillus cereus UCP 1615 biosurfactant for marine oil spills bioremediation

In this study, Bacillus cereus was cultivated in a mineral medium composed of 2% frying oil and 0.12% peptone to produce a biosurfactant. The production was scaled up from flasks to 1.2-, 3.0- and 50-L bioreactors, where surface tension achieved 28.7, 27.5 and 32 mN/m and biosurfactant concentration 4.3, 4.6 and 4.7 g/L, respectively. The biosurfactant was characterized as anionic, while nuclear magnetic resonance, thin-layer chromatography and gas chromatography analyses revealed its lipopeptide nature. Toxicity tests showed survival rates of the fish Poecilia vivipara and the bivalve Anomalocardia brasiliana higher than 90% and 55%, respectively, thus suggesting the use of this biosurfactant in marine environment depollution. Moreover, the biosurfactant stimulated the growth of autochthonous microorganisms independently of the presence of motor oil in bioassays performed in seawater. These results demonstrate that the biosurfactant is biocompatible and has potential for industrial-scale production and application to bioremediation of oil spills-polluted marine environment.

The Zebra Mussel (Dreissena polymorpha) as a Model Organism for Ecotoxicological Studies: A Prior 1H NMR Spectrum Interpretation of a Whole Body Extract for Metabolism Monitoring

The zebra mussel (Dreissena polymorpha) represents a useful reference organism for the ecotoxicological study of inland waters, especially for the characterization of the disturbances induced by human activities. A nuclear magnetic resonance (NMR)-based metabolomic approach was developed on this species. The investigation of its informative potential required the prior interpretation of a reference ¹H NMR spectrum of a lipid-free zebra mussel extract. After the extraction of polar metabolites from a pool of whole-body D. polymorpha powder, the resulting highly complex 1D ¹H NMR spectrum was interpreted and annotated through the analysis of the corresponding 2D homonuclear and heteronuclear NMR spectra. The spectrum interpretation was completed and validated by means of sample spiking with 24 commercial compounds. Among the 238 detected ¹H signals, 53% were assigned, resulting in the identification of 37 metabolites with certainty or high confidence, while 5 metabolites were only putatively identified. The description of such a reference spectrum and its annotation are expected to speed up future analyses and interpretations of NMR-based metabolomic studies on D. polymorpha and to facilitate further explorations of the impact of environmental changes on its physiological state, more particularly in the context of large-scale ecological and ecotoxicological studies.

Molecular responses of an estuarine oyster to multiple metal contamination in Southern China revealed by RNA-seq

The estuarine oysters Crassostrea hongkongensis hyper-accumulate many metals and survive under high levels of metal exposure. In the present study, three natural populations of oysters with various levels of accumulated metals (mainly Cu and Zn) were collected from Southern China. The morphological characteristics and metal concentrations revealed their phenotypic differentiation. Further transcripts sequences acquired from their gill tissues were analyzed and 44,801 genes (with effective reads) were obtained via de novo assembly. The principal component analysis (PCA) revealed that the gene expression patterns also displayed differentiation among the three populations. A total of 3,199 differentially expressed genes (DEGs) was identified in the contaminated oysters as compared to the 'clean' oysters, which were used to explain the molecular mechanisms of metal accumulation and toxicity. GO and KEGG enrichment analysis revealed that energy production and cytoskeleton metabolism-related genes were particularly enriched in the contaminated sites during chronic metal exposure. Besides, increasing expressions of Zn/Cu transporters and metallothionein may explain their high accumulation in contaminated populations. We showed that oysters with less metal accumulation tended to cope with metal stress actively, but severe contamination destroyed part of the normal function. Our study analyzed the gene expression patterns of C. hongkongensis in Southern China and demonstrated the phenotypic differentiation of oysters under chronical metal exposure in the field.

Functional responses of filter feeders increase with elevated metal contamination: Are these good or bad signs of environmental health?

Fast urbanization in coastal areas has increased the load of contaminants entering estuaries worldwide, threatening the diversity and provision of services by these important systems. Contamination causes structural changes in ecosystems, but the consequences for their functioning are still overlooked. Here we investigated filtration and biodeposition rates of the mussel Mytilaster solisianus across different concentrations of metals, nutrients and suspended material, and levels of urbanization. As expected, filtration rates increased with the number of particles in the water column. However, in areas with low particle concentration, filtering increased in mussels with higher metal concentrations (Cu/Zn/Ni), which were, in turn, related to high urbanization. Similarly, biodeposition rates were positively related to metal concentration in mussels. The increased functional responses observed here is likely a symptom of stress, caused by potential compensatory mechanisms to the energetic costs of cell maintenance and body detoxification of mussels, rather than an indication of healthy systems/organisms. CAPSULE: Increased functional responses of mussels can be a sign of environmental stress.

Influence of Human Activities on Broad-Scale Estuarine-Marine Habitats Using Omics-Based Approaches Applied to Marine Sediments

Rapid urban expansion and increased human activities have led to the progressive deterioration of many marine ecosystems. The diverse microbial communities that inhabit these ecosystems are believed to influence large-scale geochemical processes and, as such, analyzing their composition and functional metabolism can be a means to assessing an ecosystem’s resilience to physical and chemical perturbations, or at the very least provide baseline information and insight into future research needs. Here we show the utilization of organic and inorganic contaminant screening coupled with metabolomics and bacterial 16S rRNA gene sequencing to assess the microbial community structure of marine sediments and their functional metabolic output. The sediments collected from Moreton Bay (Queensland, Australia) contained low levels of organic and inorganic contaminants, typically below guideline levels. The sequencing dataset suggest that sulfur and nitrite reduction, dehalogenation, ammonia oxidation, and xylan degradation were the major metabolic functions. The community metabolites suggest a level of functional homogeneity down the 40-cm core depth sampled, with sediment habitat identified as a significant driver for metabolic differences. The communities present in river and sandy channel samples were found to be the most active, with the river habitats likely to be dominated by photoheterotrophs that utilized carbohydrates, fatty acids and alcohols as well as reduce nitrates to release atmospheric nitrogen and oxidize sulfur. Bioturbated mud habitats showed overlapping faunal activity between riverine and sandy ecosystems. Nitrogen-fixing bacteria and lignin-degrading bacteria were most abundant in the sandy channel and bioturbated mud, respectively. The use of omics-based approaches provide greater insight into the functional metabolism of these impacted habitats, extending beyond discrete monitoring to encompassing whole community profiling that represents true phenotypical outputs. Ongoing omics-based monitoring that focuses on more targeted pathway analyses is recommended in order to quantify the flux changes within these systems and establish variations from these baseline measurements.

Ecological risk of potentially toxic elements (PTEs) in sediments, seawater, wastewater, and benthic macroinvertebrates, Persian Gulf

In the current study, ecological risk of potentially toxic elements (PTEs) in sediments, seawater, wastewater, soft tissues and shell of a major fouling species Callista florida (C. florida) and soft tissue of rocky oyster, Saccostrea cucullata (S. cucullata) are investigated. For this purpose, 25 sediment samples, 24 seawater samples, 28 wastewater samples, and 100 bivalve samples were collected for PTEs analysis. Risk index (RI) and sediment quality guidelines along with calculated enrichment factors (EF) and PTEs profiles revealed that Musa Estuary is threatened by contamination, especially with respect to Hg, Cu, and Zn. The decreasing trend of average element enrichment factor is: Hg > Cu > Ni > Cd > Zn > Co > Cr > Mn > Fe > As > Pb > Mo > Sb. Among the investigated elements, Hg indicated the highest potential ecological risk factor in sediment (RI and EF are 1341.6 and 214.66 close to the industrial area). The Ficklin chart results demonstrated that seawater samples almost plot in regions with high metal load and pH values were the same. Mean concentrations of PTEs in water samples were 1.2 (for Cu) to 6565 (for Hg) times higher than world seawater. Regarding wastewater, pH values changed from very acidic to alkaline while PTEs load ranged from low to high load. In general, PTEs concentration in water samples was higher compared to those of the world seawater. Based on the results obtained in this biomonitoring study, elevated concentrations of Al, Fe, Cu, and Zn were found in soft tissue of C. florida and S. cucullata. Statistical analysis revealed significant differences in PTEs concentration between the two studied species. Generally, most PTEs concentration including Al, Co, Cr, Fe, Mn, Ni, Pb, and Sb in soft tissue fall between water and sediment samples i.e., sediment > biota > water.

First records of metal concentrations in the Pacific oyster (Crassostrea gigas) from a Southwest Atlantic estuary

The Pacific oyster (Crassostrea gigas) is one of the world's most widespread bivalves and a suitable species for biomonitoring metals in coastal environments. In the present research, wild individuals were collected from an Argentinian estuary and the coastal beaches nearby. The concentrations of eight metals (Cd, Cr, Cu, Fe, Mn, Ni, Pb and Zn) were quantified in the soft tissues of the Pacific oyster. Among the metals, Cu, Fe and Zn reached the highest concentrations in the soft tissues over the rest of the elements. The results showed the highest values to be estuary related, with the beach site achieving the lowest values. These results possibly lie on the impact of human activities surrounding the estuary, as well as streams and rivers that outflow within it. Higher Cu and Zn levels, both port related, were mainly found toward the outer estuary. On the other hand, high levels of Cr, Fe and Mn were found toward the inner zone of the estuary, an area with sewage sludge from the cities located on the margins of the BBE. Regarding the potential risk to public health, Cu and Zn levels found in C. gigas were above national and international safety guidelines in 100% and 11% of the samples, respectively.

Seasonal and spatial variations of biomarker responses of rock oysters in a coastal environment influenced by large estuary input

The present study assessed the spatial and temporal variations and the potential influences of the Pearl River discharge on trace metal bioaccumulation and biomarker responses in Hong Kong coastal waters. A suite of biomarkers including antioxidant defense, oxidative stress, metal detoxification, cellular response, neurotoxicity, and energy reserve were quantified in the rock oyster Saccostrea cucullata over spatial scale across the east and west of Hong Kong. We documented the elevated Cd, Cu and Zn concentrations in all western stations in the fall season, as a result of time-integrated accumulation during the peak discharge of the Pearl River Estuary (PRE) in summer. Lipid peroxidation and total glutathione corresponded well with the overall metal gradient and showed significant correlation with the tissue Cu bioaccumulation. The eastern station (Clear Water Bay) also exhibited high Cd and Cu concentrations with increased oxidative stress responses. In the spring, metal bioaccumulation in the oysters was reduced due to the weakened influence of PRE, with correspondingly less obvious biomarker responses. Our coupling measurements of biomarkers and tissue metal concentrations for the first time revealed that the large PRE could have latent and seasonal biological effects on the Hong Kong coastal biota. Sensitive biomarkers such as lipid peroxidation and glutathione responses might be good candidates for detecting the early biological responses in such sub-lethal contaminated environments.

Seasonal metabolic analysis of marine sediments collected from Moreton Bay in South East Queensland, Australia, using a multi-omics-based approach

Anthropogenic effects of urban density have altered natural ecosystems. Such changes include eutrophication of freshwater and adjoining coastal habitats, and increased levels of inorganic nutrients and pollutants into waterways. In Australia, these changes are intensified by large-scale ocean-atmospheric events, leading to considerable abiotic stress on the natural flora and fauna. Bacterial communities in marine sediments from Moreton Bay (South East Queensland, Australia) were examined in order to assess the impact of rainfall changes, chemical pollution, and subsequent abiotic stress on living organisms within a marine ecosystem. Sediments were collected during the wet and dry seasons and analyzed using bacterial metagenomics and community metabolomics techniques. Physicochemical data were also analyzed to account for biological variance that may be due to non-rainfall-based abiotic stresses. Wet-dry seasonality was the dominant control on bacterial community structure and metabolic function. Changes in the availability of nutrients, organic matter and light appeared to be the major seasonal stressors. In contrast, urban and industrial pollutants appeared to be minor stressors at the sites sampled. During the wet season, the bacterial community composition reflected organisms that utilize biogeochemical pathways with fast kinetics, such as aerobic metabolism, direct assimilation of inorganic compounds, and primary production. The transition to the dry season saw the bacterial community composition shift towards organisms that utilize more complex organic energy sources, such as carbohydrates and fatty acids, and anaerobic redox processes.

Trace metals in oysters: molecular and cellular mechanisms and ecotoxicological impacts

Oysters are important benthic bivalves in coastal and estuarine environments. They are widely farmed due to their rapid growth and taste; they are also widely applied in environmental monitoring of coastal pollution due to their accumulation of contaminants. Most importantly, oysters are among the few marine organisms that are considered to be hyper-accumulators of many toxic metals, such as cadmium, copper and zinc. As such, there is a tremendous call to study the interactions between metals and oysters, especially due to the increasing metal pollution in many coastal and estuarine waters. Over the past decades, many studies have focused on metal accumulation in oysters as well as the ecotoxicological effects of metals on oysters. In this review, we summarize the recent progress in our understanding of the molecular and cellular mechanisms of metal accumulation, sequestration and toxicity in oysters. Applications of modern technologies such as omics and nanoscale imaging have added significantly to our knowledge of metal biology in oysters. Variations between different metals also demonstrate the diversity of the interactions between oysters and metals. Despite this recent progress, however, there is a need for further study of the molecular mechanisms of metal uptake and toxicity as well as the joint effects of metal mixtures on oyster populations. Oysters have higher numbers of stress responsive genes than most animals, which may have been induced by gene duplication during the evolution of their intertidal environmental adaptations. The divergent expression of stress responsive genes may explain the different tolerances for metals among different species. These fundamental studies may eventually provide promising solutions for reducing toxic metal concentrations in oysters for safe consumption by humans. To conclude, the complexity of life history and metal chemistry of oysters coupled with emerging pollution and application of modern techniques represents an important and exciting research area in modern ecotoxicology.

Uniquely high turnover of nickel in contaminated oysters Crassostrea hongkongensis: Biokinetics and subcellular distribution

Despite the environmental concerns regarding nickel (Ni) especially in China, it has received little attention in aquatic animals due to its comparatively weak toxicity. In the present study, we explored the bioaccumulation, biokinetics, and subcellular distribution of Ni in an estuarine oyster Crassostrea hongkongensis. We demonstrated that Ni represented a new pattern of bioaccumulation in oysters characterized by rapid elimination and low dissolved uptake. The waterborne uptake rate constant and dietary assimilation efficiency were 0.036L/g/h and 28%, respectively, and dissolved uptake was the predominant exposure route. The efflux rate constant was positively related to tissue Ni concentration, with the highest efflux of 0.155d^-1. Such high elimination resulted in a high Ni turnover and steady-state condition reached rapidly, as shown with a 4-week waterborne exposure experiment at different Ni concentrations. Ni in oysters was mainly sequestered in metallothionein-like protein (MTLP), metal-rich granule, and cellular debris. MTLP was the most important binding fraction during accumulation and depuration, and played a dynamic role leading to rapid Ni elimination. Pre-exposure to Ni significantly reduced the dissolved uptake, probably accompanied by depressed filtration activity. Overall, the high turnover and regulation of Ni in oysters were achieved by enhanced efflux, suppressed uptake, and sequestration of most Ni into the detoxified pool.

A multi-omics based ecological analysis of coastal marine sediments from Gladstone, in Australia's Central Queensland, and Heron Island, a nearby fringing platform reef

The impact of anthropogenic factors arising from point and non-point pollution sources at a multi commodity marine port and its surrounding ecosystems were studied using sediment samples collected from a number of onshore (Gladstone Harbour and Facing Island) and offshore (Heron Island and Fitzroy Reefs) sites in Australia's Central Queensland. Sediment samples were analyzed for trace metals, organic carbon, polycyclic aromatic hydrocarbons (PAH), emerging chemicals of concern (ECC) and sterols. Similarly, the biological and biochemical interaction between the reef and its environment was analyzed by the multi-omic tools of next-generation sequencing characterization of the bacterial community and microbial community metabolic profiling. Overall, the trace elements were observed at the lower end of the Australian environmental guideline values at the offshore sites, while higher values were observed for the onshore locations Nickel and copper were observed above the high trigger value threshold at the onshore sites. The levels of PAH were below limits of detection across all sites. However, some of the ECC and sterols were observed at higher concentrations at both onshore and offshore locations, notably, the cholesterol family sterols and 17α-ethynylestradiol. Multi-omic analyses also indicated possible thermal and photo irradiation stressors on the bacterial communities at all the tested sites. The observed populations of γ-proteobacteria were found in combination with an increased pool of fatty acids that indicate fatty acid synthesis and utilisation of the intermediates of the shikimate pathways. This study demonstrates the value of applying a multi-omics approach for ecological assessments, in which a more detailed assessment of physical and chemical contaminants and their impact on the community bacterial biome is obtained.

Sex steroids and metabolic responses in mussels Mytilus galloprovincialis exposed to drospirenone

Drospirenone (DRO) is a synthetic progestin derived from 17α-spironolactone with a pharmacological mechanism of action similar to progesterone. Despite its wide use as pharmaceutical and consequent continuous release into the aquatic environment, DRO effects have been poorly investigated on aquatic biota. In order to unravel the toxicity mechanisms of DRO, mussels Mytilus galloprovincialis were exposed for 7 days to different concentrations of DRO, namely 20ng/L (Low; L), 200ng/L (Medium; M), 2000ng/L (High; H) and 10μg/L (Super High; SH) nominal doses. Following exposure, no significant effect was observed on gonad maturation of treated and untreated mussels. The levels of progesterone (P4) and testosterone (T) were measured in mantle/gonad tissues and no significant alteration detected after exposure. However, the application of a protonic nuclear magnetic resonance (¹H NMR)-based metabolomics approach enabled a comprehensive assessment of DRO effects in mussels. Specifically, ¹H NMR metabolic fingerprints of digestive glands of DRO treated mussel groups were clearly separated from each other and from controls through a principal component analysis (PCA). Moreover, a number of metabolites involved in different metabolic pathways were found to significantly change in DRO-exposed mussels compared to control, suggesting the occurrence of alterations in energy metabolism, amino acids metabolism, and glycerophospholipid metabolism. Overall, despite no changes in gonad maturation and steroids levels were recorded in mussels after DRO exposure, the metabolomics approach demonstrated its effectiveness and high sensitivity in elucidating DRO-induced metabolic disturbances in marine mussels, and thus its usefulness in the environmental risk assessment of pharmaceuticals.

Chronic effects of copper in oysters Crassostrea hongkongensis under different exposure regimes as shown by NMR-based metabolomics

Traditional metal toxicity tests on organisms have mainly focused on continuous exposure at a fixed concentration. However, organisms are more likely exposed to pollutants intermittently in estuarine environments that are significantly impacted by anthropogenic activity. The present study examined whether different copper (Cu) exposure regimes at an equivalent dose can induce different metabolomics effects on the oysters. An estuarine oyster Crassostrea hongkongensis was exposed to Cu continuously or intermittently at an equal dose (time × concentration) for 6 wk. Continuous exposure regimes included 2 doses of 3.3 μg/L for 24 h and 20 μg/L for 24 h, with corresponding equal doses of 2 intermittent exposure regimes of 20 μg/L for 4 h and 120 μg/L for 4 h, respectively. Time-course measurements suggested that Cu bioaccumulation was comparable at equal low doses between the continuous regime (3.3 μg/L for 24 h) and the intermittent regime (20 μg/L for 4 h), but there was considerable difference for the high dose under different regimes. Nuclear magnetic resonance (NMR)-based metabolomics suggested that continuous and intermittent Cu exposures led to similar metabolite variation pattern in gills at an equal high dose, including decreased amino acids (e.g., aspartate, glycine, isoleucine, leucine, lysine, phenylalanine, threonine, and valine), lower energy-related compounds (e.g., adenosine triphosphate/adenosine diphosphate, acetate, citrate, and glycogen), and altered osmolytes (e.g., homarine and taurine). These biomarkers indicated disturbance of osmotic regulation and energy metabolism induced by Cu exposure regardless of regime. In addition, the 4-h intermittent Cu exposure resulted in slightly fewer adverse effects compared with the corresponding equal-dose continuous exposure. Oysters appeared to recover during the intervals of Cu exposure. The results indicated that metabolomic effects induced by Cu were more dose dependent than the Cu exposure regime. Environ Toxicol Chem 2017;36:2428-2435. © 2017 SETAC.

1H NMR-based metabolomics investigation on the effects of petrochemical contamination in posterior adductor muscles of caged mussel Mytilus galloprovincialis

Environmental metabolomics is a high-throughout approach that provides a snapshot of the metabolic status of an organism. In order to elucidate the biological effects of petrochemical contamination on aquatic invertebrates, mussels Mytilus galloprovincialis were caged at the "Augusta-Melilli-Priolo" petrochemical area and Brucoli (Sicily, south Italy), chosen as the reference site. After confirming the elevated concentrations of polycyclic aromatic hydrocarbons (PAHs) and mercury (Hg) in Augusta sediments in our previous work (Maisano et al., 2016a), herein an environmental metabolomics approach based on protonic nuclear magnetic resonance (¹H NMR), coupled with chemometrics, was applied on the mussel posterior adductor muscle (PAM), the main muscular system in bivalve molluscs. Amino acids, osmolytes, energy storage compounds, tricarboxylic acid cycle intermediates, and nucleotides, were found in PAM NMR spectra. Principal Component Analysis (PCA) indicated that mussels caged at the polluted site clustered separately from mussels from the control area, suggesting a clear differentiation between their metabolic profiles. Specifically, disorders in energy metabolism, alterations in amino acids metabolism, and disturbance in the osmoregulatory processes were observed in mussel PAM. Overall, findings from this work demonstrated the usefulness of applying an active biomonitoring strategy for environmental risk assessment, and the effectiveness of metabolomics in elucidating changes in metabolic pathways of aquatic organisms caged at sites differentially contaminated, and thus its suitability to be applied in ecotoxicological studies.

Copper-induced metabolic variation of oysters overwhelmed by salinity effects

In estuarine environments, Cu (copper) contamination is simultaneously coupled with salinity variation. In this study, ¹H NMR was applied to investigate the metabolic disturbance of estuarine oysters Crassostrea hongkongensis under both Cu and salinity stresses. Oysters were exposed to dissolved Cu (50 μg L^-1) at different salinities (10, 15 and 25 psu) for six weeks, and the Cu accumulation in the oyster tissues was higher at lowered salinity. Based on the NMR-metabolomics results, disturbances induced by Cu and salinity was mainly related to osmotic regulation, energy metabolism and glycerophospholipid metabolism, as indicated by the alteration of important metabolic biomarkers such as alanine, citrate, glucose, glycogen, betaine, taurine, hypotaurine and homarine in the gills. At lower salinity, oysters accumulated higher energy related compounds (e.g., glucose and glycogen) and amino acids (e.g., aspartate, dimethylglycine and lysine), with the enhancement of ATP/ADP production and accumulation of oxidizable amino acids catabolized from protein breakdown. With Cu exposure, the synthesis from glycine to dimethylglycine was observed to cope with severe osmotic stress, together with the elevation of lysine and homarine. The effects induced by Cu were much similar for each salinity treatment, but the combination of Cu and salinity turned out to be consistent with the singular salinity effects. Therefore, salinity played a dominant role in affecting the metabolites of oysters when combined with Cu exposure. This study indicated that salinity should be taken into consideration in order to predict the Cu toxicity in estuarine organisms.

A Community Multi-Omics Approach towards the Assessment of Surface Water Quality in an Urban River System

A multi-omics approach was applied to an urban river system (the Brisbane River (BR), Queensland, Australia) in order to investigate surface water quality and characterize the bacterial population with respect to water contaminants. To do this, bacterial metagenomic amplicon-sequencing using Illumina next-generation sequencing (NGS) of the V5-V6 hypervariable regions of the 16S rRNA gene and untargeted community metabolomics using gas chromatography coupled with mass spectrometry (GC-MS) were utilized. The multi-omics data, in combination with fecal indicator bacteria (FIB) counts, trace metal concentrations (by inductively coupled plasma mass spectrometry (ICP-MS)) and in-situ water quality measurements collected from various locations along the BR were then used to assess the health of the river ecosystem. Sites sampled represented the transition from less affected (upstream) to polluted (downstream) environments along the BR. Chemometric analysis of the combined datasets indicated a clear separation between the sampled environments. Burkholderiales and Cyanobacteria were common key factors for differentiation of pristine waters. Increased sugar alcohol and short-chain fatty acid production was observed by Actinomycetales and Rhodospirillaceae that are known to form biofilms in urban polluted and brackish waters. Results from this study indicate that a multi-omics approach enables a deep understanding of the health of an aquatic ecosystem, providing insight into the bacterial diversity present and the metabolic output of the population when exposed to environmental contaminants.

Relating metals with major cations in oyster Crassostrea hongkongensis: A novel approach to calibrate metals against salinity

Despite salinity has been well documented for its significant effects on the bioaccumulation of many trace elements in biomonitors, no calibration method has been proposed to reduce such influences. For the first time, the present study established a novel method to calibrate biomonitoring data against salinity. Relationships between trace element concentration in oyster Crassostrea hongkongensis and the biological proxy for salinity were quantified based on laboratory exposure experiments. The method was then verified by the biomonitoring data of Pearl River Estuary (PRE). Tissue concentrations of trace elements (Cu, Zn, Ag, Cd, Pb, Cr, As, Se, and Ni) and major cations (Na, Mg, K, and Ca) in oysters exposed at 4 salinities (5, 12, 20, and 28psu) and low concentrations for 6weeks were measured to establish such quantitative relationships. Tissue Na, Mg, and K could be the proxy for salinity, while Na was the best one. Negative correlations between tissue concentrations of trace elements and Na after exposure were observed for metal cations such as Cu, Zn, Ag, Cd, and Pb, while tissue As, Se, and Ni were positively correlated with Na. In PRE, salinity significantly influenced the bioaccumulation of trace elements even under the multifactor-affected field conditions. The calibration method applied to the biomonitoring of PRE was verified to be feasible, and effectively reduced the influences of salinity. Therefore, calibration against salinity could facilitate the interpretation, comparability, and analysis of biomonitoring data.