Molecular effects of diethanolamine exposure on Calanus finmarchicus (Crustacea: Copepoda)

Potential toxic effects linked to taurine interactions with alkanolamines and diisopropylamine

Diisopropylamine (DIPA), aminomethyl propanol (AMP), amino ethoxy ethanol (AEE), diethanolamine (DEA), ethanolamine (EA), pyridine (PYR) and methyl diethanolamine (MDEA) are used for carbon capture and to sweeten sour gas, and are found in groundwater. They are also used in cosmetic products. Taurine is abundant in the body, with key biological functions linked to its charged SO groups. Interactions between SO and amines have not been studied, but can strongly affect the biological function of taurine. Fourier transform infrared spectroscopy indicates SO…HN hydrogen bonding between taurine and DIPA, AMP, AEE, DEA, EA and MDEA. These interactions induce the formation of hydrophobic amine-taurine clusters, thus decreasing amine miscibility in water, as revealed by light scattering. This effect is most marked for DIPA, leading to turbid mixtures indicative of micron-sized droplets. PYR and taurine likely interact via S…N bonding. This study offers insights regarding potential mechanisms of amine toxicity to humans.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1007/s43832-024-00146-1.

Effects of sulfate concentration on anaerobic treatment of wastewater containing monoethanolamine using an up-flow anaerobic sludge blanket reactor

Monoethanolamine (MEA), a toxic organic chemical, is widely used in industries and is found in their wastewater. Anaerobic MEA degradation is an appropriate strategy to reduce energy and cost for treatment. Industry wastewaters also contain sulfate, but information on the effects of sulfate on MEA degradation is limited. Here, an up-flow anaerobic sludge blanket (UASB) for MEA-containing wastewater treatment was operated under psychrophilic conditions (18-20 ºC) to investigate the effects of sulfate on the microbial characteristics of the retained sludge. To acclimatize the sludge, the proportion of MEA in the influent (containing sucrose, acetate, and propionate) was increased from 15% to 100% of total COD (1500 mg L^-1); sulfate was then added to the influent. The COD removal efficiency remained above 95% despite the increase in MEA and sulfate. However, granular sludge disintegration was observed when sulfate was increased from 20 to 330 mg L^-1. Batch tests revealed that propionate and acetate were produced as the metabolites of MEA degradation. In response to sulfate acclimation, methane-producing activities for propionate and hydrogen declined, while sulfate-reducing activities for MEA, propionate, and hydrogen increased. Accordingly, acclimation and changes in dominant microbial groups promoted the acetogenic reaction of propionate by sulfate reduction.

Oil-mediated oxidative-stress responses in a keystone zooplanktonic species, Calanus finmarchicus

The copepod Calanus finmarchicus is an ecologically important species in the North Atlantic, Norwegian and Barents seas. Accidental or continuous petroleum pollution from oil and gas production in these seas may pose a significant threat to this low trophic level keystone species. Responses related to oxidative stress, protein damage and lipid peroxidation were investigated in C. finmarchicus exposed to a water-accommodated fraction (WAF) of a naphthenic North Atlantic crude oil. The exposure concentration corresponded to 50% of the 96 h LC₅₀, and samples were obtained at 0, 24, 48, 72 and 96 h after exposure initiation. Gene expressions (superoxide dismutase, catalase, glutathione S-transferase, glutathione synthetase, heat shock protein 70 and 90, ubiquitin and cytochrome P-450 330A1), enzyme activities (superoxide dismutase, catalase, glutathione S-transferase) and concentrations of total glutathione and malondialdehyde were analyzed. Gene expression analyses showed no differences between controls and the exposed animals, however significantly higher glutathione S-transferase activity and malondialdehyde concentrations were found in the exposed group, suggests lipid peroxidation as main toxic effect.

First transcriptome of the copepod Gladioferens pectinatus subjected to chronic contaminant exposures

Contaminants are often at low concentrations in ecosystems and their effects on exposed organisms can occur over long periods of time and across multiple generations. Alterations to subcellular mechanistic pathways in response to exposure to contaminants can provide insights into mechanisms of toxicity that methods measuring higher levels of biological may miss. Analysis of the whole transcriptome can identify novel mechanisms of action leading to impacts in exposed biota. The aim of this study was to characterise how exposures to copper, benzophenone and diclofenac across multiple generations altered molecular expression pathways in the marine copepod Gladioferens pectinatus. Results of the study demonstrated differential gene expression was observed in cultures exposure to diclofenac (569), copper (449) and benzophenone (59). Pathways linked to stress, growth, cellular and metabolic processes were altered by exposure to all three contaminants with genes associated with oxidative stress and xenobiotic regulation also impacted. Protein kinase functioning, cytochrome P450, transcription, skeletal muscle contraction/relaxation, mitochondrial phosphate translocator, protein synthesis and mitochondrial methylation were all differentially expressed with all three chemicals. The results of the study also suggested that using dimethyl sulfoxide as a dispersant influenced the transcriptome and future research may want to investigate it's use in molecular studies. Data generated in this study provides a first look at transcriptomic response of G. pectinatus exposed to contaminants across multiple generations, future research is needed to validate the identified biomarkers and link these results to apical responses such as population growth to demonstrate the predictive capacity of molecular tools.

The genome of the European estuarine calanoid copepod Eurytemora affinis: Potential use in molecular ecotoxicology

In this study, we sequenced and assembled the genome of a European estuarine calanoid copepod using Oxford Nanopore PromethION and Illumina HiSeq 2500 platforms. The length of the assembled genome was 776.1 Mb with N50 = 474.9 kb (BUSCO 85.9%), and the genome consisted of 2473 contigs. A total of 18,014 genes were annotated and orthologous gene clusters were analyzed in comparison to other copepods. In addition, genome-wide identification of cytochrome P450s, glutathione S-transferases, and ATP-binding cassette transporters in E. affinis was performed to determine gene repertoire of these detoxification-related gene families. Results revealed the presence of species-specific gene inventories, indicating that these gene families have evolved through species-specific gene loss/expansion processes, possibly due to adaptation to different environmental stressors. Our study provides a new inventory of the European estuarine calanoid copepod E. affinis genome with emphasis on phase I, II, and III detoxification systems.

De Novo Transcriptome Assembly and Gene Expression Profiling of the Copepod Calanus helgolandicus Feeding on the PUA-Producing Diatom Skeletonema marinoi

Diatoms are the dominant component of the marine phytoplankton. Several diatoms produce secondary metabolites, namely oxylipins, with teratogenic effects on their main predators, crustacean copepods. Our study reports the de novo assembled transcriptome of the calanoid copepod Calanus helgolandicus feeding on the oxylipin-producing diatom Skeletonema marinoi. Differential expression analysis was also performed between copepod females exposed to the diatom and the control flagellate Prorocentrum minimum, which does not produce oxylipins. Our results showed that transcripts involved in carbohydrate, amino acid, folate and methionine metabolism, embryogenesis, and response to stimulus were differentially expressed in the two conditions. Expression of 27 selected genes belonging to these functional categories was also analyzed by RT-qPCR in C. helgolandicus females exposed to a mixed solution of the oxylipins heptadienal and octadienal at the concentration of 10 µM, 15 µM, and 20 µM. The results confirmed differential expression analysis, with up-regulation of genes involved in stress response and down-regulation of genes associated with folate and methionine metabolism, embryogenesis, and signaling. Overall, we offer new insights on the mechanism of action of oxylipins on maternally-induced embryo abnormality. Our results may also help identify biomarker genes associated with diatom-related reproductive failure in the natural copepod population at sea.

Seasonal ecotoxicological monitoring of freshwater zooplankton in Bir Mcherga dam (Tunisia)

Dams represent large semi-closed reservoirs of pesticides and various organic and inorganic pollutants from agricultural and human activities, and their monitoring should receive special attention. This study evaluated the environmental health status of Bir Mcherga dam using zooplankton species. The dam has a capacity of 130 Mm³ and its waters are used for irrigation, water drinking supply, and fishery. Copepods and cladocerans (crustaceans) were collected in situ monthly between October and August 2012. Oxidative stress (CAT, MDA), neurotoxicity (AChE), and genotoxicity (micronucleus test) biomarkers were analyzed in two zooplankton species: Acanthocyclops robustus and Diaphanosoma mongolianum. High values of cells with a micronucleus were observed during summer. AChE activities were inhibited during early winter and summer. The high seasonal variability of CAT and MDA levels indicates that zooplankton is continuously exposed to different oxidative stresses. These results suggest that there is an obvious and continuous multi-faceted stress in Bir Mcherga reservoir and, consequently, an urgent monitoring of freshwater environments in Tunisia is needed, particularly those intended for human consumption and irrigation.

Effect of ocean acidification on the nutritional quality of marine phytoplankton for copepod reproduction

Phytoplankton are the oceans' principal source of polyunsaturated fatty acids that support the growth and reproduction of consumers such as copepods. Previous studies have demonstrated ocean acidification (OA) can change the availability of polyunsaturated fatty acids to consumer diets which may affect consumer reproduction. Two laboratory experiments were conducted to examine the effects of feeding high-pCO2-reared phytoplankton on copepod egg production, hatching success, and naupliar survival. Marine phytoplankton Rhodomonas salina, Skeletonema marinoi, Prorocentrum micans, and Isochrysis galbana were exponentially grown in semi-continuous cultures at present (control) (400 ppm CO2, pH~8.1) and future (1,000 ppm CO2, pH~7.8) conditions and provided to Acartia tonsa copepods over 4 consecutive days as either nitrogen-limited (Exp. I) or nitrogen-depleted (Exp. II) mixed assemblage of phytoplankton. The composition of FAs in the phytoplankton diet was affected by pCO2 concentration and nitrogen deficiency; the ratio of essential fatty acids to total polyunsaturated fatty acids decreased in phytoplankton grown under high pCO2 and the mass of total fatty acids increased under nitrogen depletion. Additionally, total concentrations of essential fatty acids and polyunsaturated fatty acids in the diet mixtures were less under the high-pCO2 compared to the control-pCO2 treatments. Median egg production, hatching success, and naupliar survival were 48-52%, 4-87%, and 9-100% lower, respectively, in females fed high-pCO2 than females fed low-pCO2 phytoplankton, but this decrease in reproductive success was less severe when fed N-depleted, but fatty acid-rich cells. This study demonstrates that the effects of OA on the nutritional quality of phytoplankton (i.e., their cellular fatty acid composition and quota) were modified by the level of nitrogen deficiency and the resulting negative reproductive response of marine primary consumers.

De novo transcriptome assembly and differential gene expression analysis of the calanoid copepod Acartia tonsa exposed to nickel nanoparticles

The calanoid copepod Acartia tonsa is a reference species in standardized ecotoxicology bioassay. Despite this interest, there is a lack of knowledge on molecular responses of A. tonsa to contaminants. We generated a de novo assembled transcriptome of A. tonsa exposed 4 days to 8.5 and 17 mg/L nickel nanoparticles (NiNPs), which have been shown to reduce egg hatching success and larval survival but had no effects on the adults. Aims of our study were to 1) improve the knowledge on the molecular responses of A. tonsa copepod and 2) increase the genomic resources of this copepod for further identification of potential biomarkers of NP exposure. The de novo assembled transcriptome of A. tonsa consisted of 53,619 unigenes, which were further annotated to nr, GO, KOG and KEGG databases. In particular, most unigenes were assigned to Metabolic and Cellular processes (34-45%) GO terms, and to Human disease (28%) and Organismal systems (23%) KEGG categories. Comparison among treatments showed that 373 unigenes were differentially expressed in A. tonsa exposed to NiNPs at 8.5 and 17 mg/L, with respect to control. Most of these genes were downregulated and took part in ribosome biogenesis, translation and protein turnover, thus suggesting that NiNPs could affect the copepod ribosome synthesis machinery and functioning. Overall, our study highlights the potential of toxicogenomic approach in gaining more mechanistic and functional information about the mode of action of emerging compounds on marine organisms, for biomarker discovering in crustaceans.

In-Vivo NMR Spectroscopy: A Powerful and Complimentary Tool for Understanding Environmental Toxicity

Part review, part perspective, this article examines the applications and potential of in-vivo Nuclear Magnetic Resonance (NMR) for understanding environmental toxicity. In-vivo NMR can be applied in high field NMR spectrometers using either magic angle spinning based approaches, or flow systems. Solution-state NMR in combination with a flow system provides a low stress approach to monitor dissolved metabolites, while magic angle spinning NMR allows the detection of all components (solutions, gels and solids), albeit with additional stress caused by the rapid sample spinning. With in-vivo NMR it is possible to use the same organisms for control and exposure studies (controls are the same organisms prior to exposure inside the NMR). As such individual variability can be reduced while continual data collection over time provides the temporal resolution required to discern complex interconnected response pathways. When multidimensional NMR is combined with isotopic labelling, a wide range of metabolites can be identified in-vivo providing a unique window into the living metabolome that is highly complementary to more traditional metabolomics studies employing extracts, tissues, or biofluids.

Mortality and transcriptional effects of inorganic mercury in the marine copepod Calanus finmarchicus

Inorganic mercury (Hg) is highly toxic to organisms including crustaceans and displays multiple toxic modes of action (MoA). The main aim of this investigation was to assess the acute and sublethal toxicity mediated by mercury chloride (HgCl₂) in the marine copepod Calanus finmarchicus. A combination of short-term static studies to determine acute toxicity and a transcriptional investigation to characterize the sublethal MoA of HgCl₂ were conducted with an in-house continuous culture of C. finmarchicus. Transcriptional changes were determined by a custom 6.6 k C. finmarchicus Agilent oligonucleotide microarray and quantitative RT-PCR analysis. Data demonstrate that HgCl₂ produced a concentration- and time-dependent reduction in survival (NOEC_{48 h} = 6.9 μg/L [Hg²⁺] and LC₅₀ of 279, 73, 48, and 34 µg/L [Hg²⁺] after 24, 48, 72, and 96 h, respectively) and that exposure to sublethal concentrations of HgCl₂ (5 μg/L [Hg2⁺]) induced differential expression of 98 features (probes) on the microarray. Gene ontology (GO) and toxicological pathway analyses suggested that the main MOA were (1) uncoupling of mitochondrial oxidative phosphorylation (OXPHOS) and ATP production, (2) oxidative stress and macromolecular damage, (3) inactivation of cellular enzymes, (4) induction of cellular apoptosis and autophagocytosis, (5) over-excitation of glutamate receptors (neurotoxicity), (6) disruption of calcium homeostasis and signaling, and (7) modulation of nuclear receptor activity involved in vitamin D receptor signaling. Quantitative RT-PCR analysis verified that oligoarray performed reliably in terms of specificity and response, thus demonstrating that Hg²⁺ exerts multiple potential MoA in C. finmarchicus.

Acute hydrogen peroxide (H2O2) exposure does not cause oxidative stress in late-copepodite stage of Calanus finmarchicus

Use of hydrogen peroxide (H₂O₂) for removal of salmon lice in the aquaculture industry has created concern that non-target organisms might be affected during treatment scenarios. The aim of the present study was to examine the potential for H₂O₂ to produce oxidative stress and reduce survival in one of the most abundant zooplankton species in Norwegian coastal areas, the copepod Calanus finmarchicus. Copepods were subjected to two 96-hr tests: (1) acute toxicity test where mortality was determined and (2) treated copepods were exposed to concentrations below the No Observed Effect Concentration (0.75 mg/L) H₂O₂ and analyzed for antioxidant enzyme activities, as well as levels of glutathione (GSH) and malondialdehyde (MDA). Compared to available and comparable LC₅₀ values from the literature, our results suggest that C. finmarchicus is highly sensitive to H₂O₂. However, 96-hr exposure of C. finmarchicus to 0.75 mg H₂O₂/L did not significantly affect the antioxidant systems even though the concentration is just below the level where mortality is expected. Data suggest that aqueous H₂O₂ exposure did not cause cellular accumulation with associated oxidative stress, but rather produced acute effects on copepod surface (carapace). Further investigation is required to ensure that aqueous exposure during H₂O₂ treatment in salmon fish farms does not exert adverse effects on local non-target crustacean species and populations. In particular, studies on copepod developmental stages with a more permeable carapace are warranted.

The role of high-throughput screening in ecotoxicology and engineered nanomaterials

The field of environmental toxicology developed as a result of growing concerns about anthropogenic influences on the environment and how to ameliorate ecological impact. Many governmental bodies are beginning to emphasize prevention rather than mitigation when addressing novel products, leading to more of a focus on identifying potential toxicity prior to release. With the exponential advances in their development and sale, novel metamaterials and biotechnology are set to dramatically outpace the capabilities of current testing strategies. To address the need for a fast, cost-effective means of testing chemicals, high-throughput screening (HTS) is currently being used in toxicology and being adapted to ecotoxicology in projects such as ToxCast and Tox21. Despite the growth of research using HTS platforms, its role in ecotoxicology is still uncertain, particularly in how it should be applied in regulation. The aim of the present review is to discuss common test strategies used in designing HTS platforms, the current potential applications for ecotoxicological research, its role in regulatory policies, and its ability to address growing concerns such as engineered nanomaterials. Environ Toxicol Chem 2017;36:1704-1714. © 2017 SETAC.

Different transcriptomic responses of two marine copepods, Tigriopus japonicus and Pseudodiaptomus annandalei, to a low dose of mercury chloride (HgCl2)

Mercury (Hg) pollution is a ubiquitous and serious concern in marine environments, but the response mechanisms of marine animals to Hg pollution (i.e., toxicity/tolerance) are poorly understood. To compare the global responses of two marine copepods (Tigriopus japonicus and Pseudodiaptomus annandalei), we analyzed whole transcriptomes using RNA-seq technology in response to Hg treatment (a nominal 10μg/L HgCl₂ in seawater) for 5h. Hg was strikingly accumulated in both copepods under treatment. The Hg concentration in P. annandalei was higher under metal exposure by approximately 1.4-fold compared with treated T. japonicus. Among transcriptomic data, 101 genes in T. japonicus and 18 genes in P. annandalei were differentially regulated in response to Hg exposure. The up-regulated genes in T. japonicus were concerned with stress, growth, and development, while the down-regulated ones were mainly related to immune response. In P. annandalei, most of the differentially expressed genes were up-regulated, and all were involved in stress response. Our work indicated that Hg exhibits endocrine-disrupting potential at the transcriptomic level in marine copepods. Overall, our study demonstrates the species-specific molecular responses of these two copepods to Hg pollution.

Exposure to crude oil micro-droplets causes reduced food uptake in copepods associated with alteration in their metabolic profiles

Acute oil spills and produced water discharges may cause exposure of filter-feeding pelagic organisms to micron-sized dispersed oil droplets. The dissolved oil components are expected to be the main driver for oil dispersion toxicity; however, very few studies have investigated the specific contribution of oil droplets to toxicity. In the present work, the contribution of oil micro-droplet toxicity in dispersions was isolated by comparing exposures to oil dispersions (water soluble fraction with droplets) to concurrent exposure to filtered dispersions (water-soluble fractions without droplets). Physical (coloration) and behavioral (feeding activity) as well as molecular (metabolite profiling) responses to oil exposures in the copepod Calanus finmarchicus were studied. At high dispersion concentrations (4.1-5.6mg oil/L), copepods displayed carapace discoloration and reduced swimming activity. Reduced feeding activity, measured as algae uptake, gut filling and fecal pellet production, was evident also for lower concentrations (0.08mg oil/L). Alterations in metabolic profiles were also observed following exposure to oil dispersions. The pattern of responses were similar between two comparable experiments with different oil types, suggesting responses to be non-oil type specific. Furthermore, oil micro-droplets appear to contribute to some of the observed effects triggering a starvation-type response, manifested as a reduction in metabolite (homarine, acetylcholine, creatine and lactate) concentrations in copepods. Our work clearly displays a relationship between crude oil micro-droplet exposure and reduced uptake of algae in copepods.

Spliced leader-based analyses reveal the effects of polycyclic aromatic hydrocarbons on gene expression in the copepod Pseudodiaptomus poplesia

Polycyclic aromatic hydrocarbons (PAHs) are a group of toxic and carcinogenic pollutants that can adversely affect the development, growth and reproduction of marine organisms including copepods. However, knowledge on the molecular mechanisms regulating the response to PAH exposure in marine planktonic copepods is limited. In this study, we investigated the survival and gene expression of the calanoid copepod Pseudodiaptomus poplesia upon exposure to two PAHs, 1, 2-dimethylnaphthalene (1, 2-NAPH) and pyrene. Acute toxicity responses resulted in 96-h LC₅₀ of 788.98μgL^-1 and 54.68μgL^-1 for 1, 2-NAPH and pyrene, respectively. Using the recently discovered copepod spliced leader as a primer, we constructed full-length cDNA libraries from copepods exposed to sublethal concentrations and revealed 289 unique genes of diverse functions, including stress response genes and novel genes previously undocumented for this species. Eighty-three gene families were specifically expressed in PAH exposure libraries. We further analyzed the expression of seven target genes by reverse transcription-quantitative PCR in a time-course test with three sublethal concentrations. These target genes have primary roles in detoxification, oxidative defense, and signal transduction, and include different forms of glutathione S-transferase (GST), glutathione peroxidases (GPX), peroxiredoxin (PRDX), methylmalonate-semialdehyde dehydrogenase (MSDH) and ras-related C3 botulinum toxin substrate (RAC1). Expression stability of seven candidate reference genes were evaluated and the two most stable ones (RPL15 and RPS20 for 1, 2-NAPH exposure, RPL15 and EF1D for pyrene exposure) were used to normalize the expression levels of the target genes. Significant upregulation was detected in GST-T, GST-DE, GPX4, PRDX6 and RAC1 upon 1, 2-NAPH exposure, and GST-DE and MSDH upon pyrene exposure. These results indicated that the oxidative stress was induced and that signal transduction might be affected by PAH exposure in P. poplesia. However, gene upregulation was followed by a reduction in expression level towards 96h, indicating a threshold value of exposure time that leads to depressed gene expression. Prolonged exposure may cause dysfunction of detoxification and antioxidant machinery in P. poplesia. The transcriptional responses of GST-T, GPX2 and GPX4 upon pyrene exposure were minimal. Our results reveal the different sensitivity of P. poplesia to two PAHs at both the individual and transcriptional levels. As the first attempt, this study proved that copepod spliced leader is useful for obtaining full-length cDNA in P. poplesia exposed to PAHs and provided a valuable gene resource for this non-model species. This approach can be applied to other calanoid copepods exposed to various stressors, particularly under field conditions.

Glutathione S-Transferase Regulation in Calanus finmarchicus Feeding on the Toxic Dinoflagellate Alexandrium fundyense

The effect of the dinoflagellate, Alexandrium fundyense, on relative expression of glutathione S-transferase (GST) transcripts was examined in the copepod Calanus finmarchicus. Adult females were fed for 5-days on one of three experimental diets: control (100% Rhodomonas spp.), low dose of A. fundyense (25% by volume, 75% Rhodomonas spp.), and high dose (100% A. fundyense). Relative expression of three GST genes was measured using RT-qPCR on days 0.5, 1, 2 and 5 in two independent experiments. Differential regulation was found for the Delta and the Sigma GSTs between 0.5 to 2 days, but not on day 5 in both experiments. The third GST, a microsomal, was not differentially expressed in either treatment or day. RT-qPCR results from the two experiments were similar, even though experimental females were collected from the Gulf of Maine on different dates and their reproductive output differed. In the second experiment, expression of 39 GSTs was determined on days 2 and 5 using RNA-Seq. Global gene expression analyses agreed with the RT-qPCR results. Furthermore, the RNA-Seq measurements indicated that only four GSTs were differentially expressed under the experimental conditions, and the response was small in amplitude. In summary, the A. fundyense diet led to a rapid and transient response in C. finmarchicus in three cytosolic GSTs, while a fourth GST (Omega I) was significantly up-regulated on day 5. Although there was some regulation of GSTs in response the toxic dinoflagellate, the tolerance to A. fundyense by C. finmarchicus is not dependent on the long-term up-regulation of specific GSTs.

Solar-Photocatalytic Degradation of Waste from CO2 Removal System Using Metal Doped TiO2 Photocatalysts: Effect of TiO2 Support

The wastewater containing the spent alkanolamines and its derivatives emerging from the natural gas industries into water has become a critical concern. In the present study, Titanium dioxides was used as photocatalysts to investigate for their efficiency for the photodegradation of Diisopropanolamine (DIPA) containing wastewater under the visible light irradiation. DIPA was used as a model alkanolamine while different commercially available TiO2 were tested for photodegradation of DIPA under the visible light source. The physico-chemical properties of the prepared photocatalysts were analyzed using different characterization techniques including X-ray diffraction (XRD), Raman spectroscopy and N2-physisorption (BET).

Individual and molecular level effects of produced water contaminants on nauplii and adult females of Calanus finmarchicus

In the Barents Sea region new petroleum fields are discovered yearly and extraction of petroleum products is expected to increase in the upcoming years. Despite enhanced technology and stricter governmental legislation, establishment of the petroleum industry in the Barents Sea may potentially introduce a new source of contamination to the area, as some discharges of produced water will be allowed. Whether the presence of produced water poses a risk to the Arctic marine life remains to be investigated. The aim of this study was to examine effects of exposure to several compounds found in produced water-a mixture of selected organic compounds (APW), radium-226 ((226)Ra), barium (Ba), and a scale inhibitor-on the copepod species Calanus finmarchicus. Experiments were performed using exposure concentrations at realistic levels based on those detected in the vicinity of known discharge points. The influence of lethal and sublethal effects on early life stages was determined and significantly lower survival in the APW exposure groups was found. In the Ba treatment the life stage development did not proceed to the same advanced stages as observed in the control (filtered sea water). The scale inhibitor and (226)Ra treatments showed no significant difference from control. In addition, adult females were exposed to APW, (226)Ra, and a mixture of the two. Both individual-level effects (egg production and feeding) and molecular-level effects (gene expression) were assessed. On the individual level endpoints, only treatments including APW produced an effect compared to control. However, on the molecular level the possibility that also (226)Ra induced toxicologically relevant effects cannot be ruled out.

The metabolic response of marine copepods to environmental warming and ocean acidification in the absence of food

Marine copepods are central to the productivity and biogeochemistry of marine ecosystems. Nevertheless, the direct and indirect effects of climate change on their metabolic functioning remain poorly understood. Here, we use metabolomics, the unbiased study of multiple low molecular weight organic metabolites, to examine how the physiology of Calanus spp. is affected by end-of-century global warming and ocean acidification scenarios. We report that the physiological stresses associated with incubation without food over a 5-day period greatly exceed those caused directly by seawater temperature or pH perturbations. This highlights the need to contextualise the results of climate change experiments by comparison to other, naturally occurring stressors such as food deprivation, which is being exacerbated by global warming. Protein and lipid metabolism were up-regulated in the food-deprived animals, with a novel class of taurine-containing lipids and the essential polyunsaturated fatty acids (PUFAs), eicosapentaenoic acid and docosahexaenoic acid, changing significantly over the duration of our experiment. Copepods derive these PUFAs by ingesting diatoms and flagellated microplankton respectively. Climate-driven changes in the productivity, phenology and composition of microplankton communities, and hence the availability of these fatty acids, therefore have the potential to influence the ability of copepods to survive starvation and other environmental stressors.

Glutathione S-Transferase (GST) Gene Diversity in the Crustacean Calanus finmarchicus--Contributors to Cellular Detoxification

Detoxification is a fundamental cellular stress defense mechanism, which allows an organism to survive or even thrive in the presence of environmental toxins and/or pollutants. The glutathione S-transferase (GST) superfamily is a set of enzymes involved in the detoxification process. This highly diverse protein superfamily is characterized by multiple gene duplications, with over 40 GST genes reported in some insects. However, less is known about the GST superfamily in marine organisms, including crustaceans. The availability of two de novo transcriptomes for the copepod, Calanus finmarchicus, provided an opportunity for an in depth study of the GST superfamily in a marine crustacean. The transcriptomes were searched for putative GST-encoding transcripts using known GST proteins from three arthropods as queries. The identified transcripts were then translated into proteins, analyzed for structural domains, and annotated using reciprocal BLAST analysis. Mining the two transcriptomes yielded a total of 41 predicted GST proteins belonging to the cytosolic, mitochondrial or microsomal classes. Phylogenetic analysis of the cytosolic GSTs validated their annotation into six different subclasses. The predicted proteins are likely to represent the products of distinct genes, suggesting that the diversity of GSTs in C. finmarchicus exceeds or rivals that described for insects. Analysis of relative gene expression in different developmental stages indicated low levels of GST expression in embryos, and relatively high expression in late copepodites and adult females for several cytosolic GSTs. A diverse diet and complex life history are factors that might be driving the multiplicity of GSTs in C. finmarchicus, as this copepod is commonly exposed to a variety of natural toxins. Hence, diversity in detoxification pathway proteins may well be key to their survival.

Thermoluminescence as a complementary technique for the toxicological evaluation of chemicals in photosynthetic organisms

Thermoluminescence is a simple technique very useful for studying electron transfer reactions on photosystem II (standard thermoluminescence) or the level of lipid peroxidation in membranes (high temperature thermoluminescence) in photosynthetic organisms. Both techniques were used to investigate the effects produced on Chlorella vulgaris cells by six compounds: the chemical intermediates bromobenzene and diethanolamine, the antioxidant propyl gallate, the semiconductor indium nitrate, the pesticide sodium monofluoroacetate and the antimalarial drug chloroquine. Electron transfer activity of the photosystem II significantly decreased after the exposure of Chlorella cells to all the six chemicals used. Lipid peroxidation was slightly decreased by the antioxidant propyl gallate, not changed by indium nitrate and very potently stimulated by diethanolamine, chloroquine, sodium monofluoroacetate and bromobenzene. For five of the chemicals studied (not bromobenzene) there is a very good correlation between the cytotoxic effects in Chlorella cells measured by the algal growth inhibition test, and the inhibition of photosystem II activity. The results suggest that one very important effect of these chemicals in Chlorella cells is the inhibition of photosynthetic metabolism by the blocking of photosystem II functionality. In the case of sodium monofluoroacetate, diethanolamine and chloroquine this inhibition seems to be related with the induction of high level of lipid peroxidation in cells that may alter the stability of photosystem II. The results obtained by both techniques supply information that can be used as a supplement to the growth inhibition test and allows a more complete assessment of the effects of a chemical in photosynthetic organisms of aquatic ecosystems.

Acute and sub-lethal response to mercury in Arctic and boreal calanoid copepods

Acute lethal toxicity, expressed as LC50 values, is a widely used parameter in risk assessment of chemicals, and has been proposed as a tool to assess differences in species sensitivities to chemicals between climatic regions. Arctic Calanus glacialis and boreal Calanus finmarchicus were exposed to mercury (Hg(2+)) under natural environmental conditions including sea temperatures of 2° and 10°C, respectively. Acute lethal toxicity (96 h LC50) and sub-lethal molecular response (GST expression; in this article gene expression is used as a synonym of gene transcription, although it is acknowledged that gene expression is also regulated, e.g., at translation and protein stability level) were studied. The acute lethal toxicity was monitored for 96 h using seven different Hg concentrations. The sub-lethal experiment was set up on the basis of nominal LC50 values for each species using concentrations equivalent to 50, 5 and 0.5% of their 96 h LC50 value. No significant differences were found in acute lethal toxicity between the two species. The sub-lethal molecular response revealed large differences both in response time and the fold induction of GST, where the Arctic species responded both faster and with higher mRNA levels of GST after 48 h exposure. Under the natural exposure conditions applied in the present study, the Arctic species C. glacialis may potentially be more susceptible to mercury exposure on the sub-lethal level.

Insights into the transcriptome of the marine copepod Calanus helgolandicus feeding on the oxylipin-producing diatom Skeletonema marinoi

Diatoms dominate productive regions in the oceans and have traditionally been regarded as sustaining the marine food chain to top consumers and fisheries. However, many of these unicellular algae produce cytotoxic oxylipins that impair reproductive and developmental processes in their main grazers, crustacean copepods. The molecular mode of action of diatoms and diatom oxylipins on copepods is still unclear. In the present study we generated two Expressed Sequence Tags (ESTs) libraries of the copepod Calanus helgolandicus feeding on the oxylipin-producing diatom Skeletonema marinoi and the cryptophyte Rhodomonas baltica as a control, using suppression subtractive hybridization (SSH). Our aim was to investigate differences in the transcriptome between females fed toxic and non-toxic food and identify differentially expressed genes and biological processes targeted by this diatom. We produced 947 high quality ESTs from both libraries, 475 of which were functionally annotated and deposited in GenBank. Clustering and assembling of ESTs resulted in 376 unique transcripts, 200 of which were functionally annotated. Functional enirchment analysis between the two SSH libraries showed that ESTs belonging to biological processes such as response to stimuli, signal transduction, and protein folding were significantly over-expressed in the S. marinoi-fed C. helgolandicus compared to R. baltica-fed C. helgolandicus library. These findings were confirmed by RT-qPCR analysis. In summary, 2 days of feeding on S. marinoi activated a generalized Cellular Stress Response (CSR) in C. helgolandicus, by over-expressing genes of molecular chaperones and signal transduction pathways that protect the copepod from the immediate effects of the diatom diet. Our results provide insights into the response of copepods to a harmful diatom diet at the transcriptome level, supporting the hypothesis that diatom oxylipins elicit a stress response in the receiving organism. They also increase the genomic resources for this copepod species, whose importance could become ever more relevant for pelagic ecosystem functioning in European waters due to global warming.

Sublethal exposure to crude oil enhances positive phototaxis in the calanoid copepod Calanus finmarchicus

We investigated the effects of exposure to sublethal concentrations of the water accommodated fraction (WAF) of fresh crude oil on phototactic behavior of the calanoid copepod Calanus finmarchicus (Gunnerus) copepodite stage 5 (C5). Exposure was conducted in closed bottle systems, and behavior was tested in a tailored setup. Exposure times were 24, 48, 72, and 96 h, and the chosen exposure concentration was 25% of the recorded LC50 value for the WAF (309 ± 32 μg/L total hydrocarbon, including 20.37 ± 0.51 μg/L total PAH). The exposure significantly increased the positive phototactic behavior of the copepods after 24 h exposure and a similar significant effect was observed for all exposure durations. Additionally, experiments were conducted with nonexposed copepods with low lipid reserves. The main effect of the exposure was a shift in the response to light toward a more positive phototaxis, similar to that observed in nonexposed C. finmarchicus with low lipid reserves. The observed change in phototactic behavior observed in these studies suggests that the depth distribution of this species could be altered following an oil spill. Thus, further research is warranted to determine the possible interactive effects of light and oil spill exposures on Calanus population dynamics under field conditions.

Environmental impacts of produced water and drilling waste discharges from the Norwegian offshore petroleum industry

Operational discharges of produced water and drill cuttings from offshore oil and gas platforms are a continuous source of contaminants to continental shelf ecosystems. This paper reviews recent research on the biological effects of such discharges with focus on the Norwegian Continental Shelf. The greatest concern is linked to effects of produced water. Alkylphenols (AP) and polyaromatic hydrocarbons (PAH) from produced water accumulate in cod and blue mussel caged near outlets, but are rapidly metabolized in cod. APs, naphtenic acids, and PAHs may disturb reproductive functions, and affect several chemical, biochemical and genetic biomarkers. Toxic concentrations seem restricted to <2 km distance. At the peak of discharge of oil-contaminated cuttings fauna disturbance was found at more than 5 km from some platforms, but is now seldom detected beyond 500 m. Water-based cuttings may seriously affect biomarkers in filter feeding bivalves, and cause elevated sediment oxygen consumption and mortality in benthic fauna. Effects levels occur within 0.5-1 km distance. The stress is mainly physical. The risk of widespread, long term impact from the operational discharges on populations and the ecosystem is presently considered low, but this cannot be verified from the published literature.

Choline and betaine intakes are associated with reduced risk of nasopharyngeal carcinoma in adults: a case-control study

Background:

Intakes of choline and betaine have been inversely related to the risk of various neoplasms, but scant data exist on nasopharyngeal carcinoma (NPC). We examined the association between consumption of choline and betaine and risk of NPC.

Methods:

We conducted a case–control study with 600 incident NPC patients and 600 controls 1 : 1 matched by age, sex and household type in Guangdong, China. Dietary intake was assessed by a food frequency questionnaire through face-to-face interview.

Results:

Intakes of total choline, betaine and choline+betaine were inversely related to NPC after adjustment for various lifestyle and dietary factors (all P-trend <0.001). Adjusted odds ratios (95% CI) for quartile 4 (vs quartile 1) were 0.42 (0.29, 0.61) for total choline, 0.50 (0.35, 0.72) for betaine and 0.44 (0.30, 0.64) for betaine+total choline. Regarding various sources of choline, lower NPC risk was associated with greater intakes of choline from phosphatidylcholine, free choline, glycerophosphocholine and phosphocholine, but not sphingomyelin.

Conclusion:

These findings are consistent with a beneficial effect of choline and betaine intakes on carcinogenesis.

Gene expression patterns and stress response in marine copepods

Aquatic organisms are constantly exposed to both physical (e.g. temperature and salinity variations) and chemical (e.g. endocrine disruptor chemicals, heavy metals, hydrocarbons, diatom toxins, and other toxicants) stressors which they react to by activating a series of defense mechanisms. This paper reviews the literature on the defense systems, including detoxification enzymes and proteins (e.g. glutathione S-transferases, heat shock proteins, superoxide dismutase and catalase), studied in copepods at the molecular level. The data indicate high inter- and intra-species variability in copepod response, depending on the type of stressor tested, the concentration and exposure time, and the enzyme isoform studied. Ongoing -omics approaches will allow the identification of new genes which will give a more comprehensive overview of how copepods respond to specific stressors in laboratory and/or field conditions and the effects of these responses on higher trophic levels.

Molecular evidence of the toxic effects of diatom diets on gene expression patterns in copepods

BACKGROUND

Diatoms are dominant photosynthetic organisms in the world's oceans and are considered essential in the transfer of energy through marine food chains. However, these unicellular plants at times produce secondary metabolites such as polyunsaturated aldehydes and other products deriving from the oxidation of fatty acids that are collectively termed oxylipins. These cytotoxic compounds are responsible for growth inhibition and teratogenic activity, potentially sabotaging future generations of grazers by inducing poor recruitment in marine organisms such as crustacean copepods.

PRINCIPAL FINDINGS

Here we show that two days of feeding on a strong oxylipin-producing diatom (Skeletonema marinoi) is sufficient to inhibit a series of genes involved in aldehyde detoxification, apoptosis, cytoskeleton structure and stress response in the copepod Calanus helgolandicus. Of the 18 transcripts analyzed by RT-qPCR at least 50% were strongly down-regulated (aldehyde dehydrogenase 9, 8 and 6, cellular apoptosis susceptibility and inhibitor of apoptosis IAP proteins, heat shock protein 40, alpha- and beta-tubulins) compared to animals fed on a weak oxylipin-producing diet (Chaetoceros socialis) which showed no changes in gene expression profiles.

CONCLUSIONS

Our results provide molecular evidence of the toxic effects of strong oxylipin-producing diatoms on grazers, showing that primary defense systems that should be activated to protect copepods against toxic algae can be inhibited. On the other hand other classical detoxification genes (glutathione S-transferase, superoxide dismutase, catalase, cytochrome P450) were not affected possibly due to short exposure times. Given the importance of diatom blooms in nutrient-rich aquatic environments these results offer a plausible explanation for the inefficient use of a potentially valuable food resource, the spring diatom bloom, by some copepod species.

Observing copepods through a genomic lens

Background

Copepods outnumber every other multicellular animal group. They are critical components of the world's freshwater and marine ecosystems, sensitive indicators of local and global climate change, key ecosystem service providers, parasites and predators of economically important aquatic animals and potential vectors of waterborne disease. Copepods sustain the world fisheries that nourish and support human populations. Although genomic tools have transformed many areas of biological and biomedical research, their power to elucidate aspects of the biology, behavior and ecology of copepods has only recently begun to be exploited.

Discussion

The extraordinary biological and ecological diversity of the subclass Copepoda provides both unique advantages for addressing key problems in aquatic systems and formidable challenges for developing a focused genomics strategy. This article provides an overview of genomic studies of copepods and discusses strategies for using genomics tools to address key questions at levels extending from individuals to ecosystems. Genomics can, for instance, help to decipher patterns of genome evolution such as those that occur during transitions from free living to symbiotic and parasitic lifestyles and can assist in the identification of genetic mechanisms and accompanying physiological changes associated with adaptation to new or physiologically challenging environments. The adaptive significance of the diversity in genome size and unique mechanisms of genome reorganization during development could similarly be explored. Genome-wide and EST studies of parasitic copepods of salmon and large EST studies of selected free-living copepods have demonstrated the potential utility of modern genomics approaches for the study of copepods and have generated resources such as EST libraries, shotgun genome sequences, BAC libraries, genome maps and inbred lines that will be invaluable in assisting further efforts to provide genomics tools for copepods.

Summary

Genomics research on copepods is needed to extend our exploration and characterization of their fundamental biological traits, so that we can better understand how copepods function and interact in diverse environments. Availability of large scale genomics resources will also open doors to a wide range of systems biology type studies that view the organism as the fundamental system in which to address key questions in ecology and evolution.

Cu/Zn- and Mn-superoxide dismutase (SOD) from the copepod Tigriopus japonicus: molecular cloning and expression in response to environmental pollutants

Superoxide dismutase (SOD) is an important antioxidant enzyme which catalyzes conversion of superoxide to oxygen and hydrogen peroxide in aerobic organisms. Here, we cloned and sequenced the full-length cDNA and genomic DNA of two SODs from the copepod, Tigriopus japonicus: copper/zinc SOD (TJ-Cu/Zn-SOD) and manganese SOD (TJ-Mn-SOD). To define whether TJ-Mn-SOD is a cytosolic or a mitochondrial protein, a phylogenetic analysis was performed. The genomic structure of both TJ-SOD genes was determined with the promoter region sequences. In order to investigate their potential role in response to environmental pollutants, T. japonicus were treated with heavy metal (copper, zinc, and silver; 0, 10, 25, 50, and 100 μg L(-1)) and industrial chemicals (benzo[α]pyrene, 4-nonylphenol, and tributyltin; 0, 1, 5, 10, and 20 μg L(-1)) for 96 h. Subsequently, the TJ-Cu/Zn-SOD and TJ-Mn-SOD mRNA level was measured with quantitative real-time RT-PCR along with total SOD activity. The deduced amino acid residues of TJ-Cu/Zn-SOD and TJ-Mn-SOD possessed evolutionary conserved domains that are required for metal binding and Cu/ZnSOD-conserved signature sequences. The phylogenetic analysis revealed that TJ-Mn-SOD was closely clustered to mitochondrial Mn-SOD of another copepod, Lepeophtheirus salmonis. TJ-Cu/Zn-SOD gene had four exons and three introns, while the TJ-Mn-SOD gene consisted of two exons interrupted by one intron. In the 5'-flanking region of TJ-Cu/Zn-SOD and TJ-Mn-SOD, we observed several transcription regulatory elements such as p53, XRE, MRE, and ERE-half sites. In the response to heavy metals, Cu, Zn, and Ag, both TJ-Cu/Zn-SOD and TJ-Mn-SOD transcript levels along with enzyme levels were significantly increased at high concentrations (50 μg L(-1) and 100 μg L(-1)). Particularly, in the Cu- and Ag-exposed group, the expression of TJ-Mn-SOD mRNA was regulated more sensitively than the TJ-Cu/Zn-SOD mRNA level, indicating that the chemical susceptibility would be not correlated with the form of chemicals. B[a]P treatment showed a significant increase in the expression of both TJ-SODs mRNA level and enzyme level from 5 μg L(-1) concentration, while TBT decreased its expression at high concentrations (10 μg L(-1) and 20 μg L(-1)). 4-NP increased both TJ-SODs mRNA level at 1 μg L(-1) concentration, and then inhibited its expression from 5 μg L(-1) concentration to a lower level than the control. This finding suggests that TJ-Cu/Zn-SOD and TJ-Mn-SOD would be an inducible gene upon exposure to heavy metals and B[α]P, and could be used as a potential biomarker for the risk assessment of these environmental pollutants. This is the first report to elucidate response of SOD to environmental pollutants in copepods. Therefore, this study would give a clue to better understand the mode of action of antioxidant genes and enzymes under oxidative stress in marine invertebrates.