Genes and environment - striking the fine balance between sophisticated biomonitoring and true functional environmental genomics

Current Status of Omics in Biological Quality Elements for Freshwater Biomonitoring

Freshwater ecosystems have been experiencing various forms of threats, mainly since the last century. The severity of this adverse scenario presents unprecedented challenges to human health, water supply, agriculture, forestry, ecological systems, and biodiversity, among other areas. Despite the progress made in various biomonitoring techniques tailored to specific countries and biotic communities, significant constraints exist, particularly in assessing and quantifying biodiversity and its interplay with detrimental factors. Incorporating modern techniques into biomonitoring methodologies presents a challenging topic with multiple perspectives and assertions. This review aims to present a comprehensive overview of the contemporary advancements in freshwater biomonitoring, specifically by utilizing omics methodologies such as genomics, metagenomics, transcriptomics, proteomics, metabolomics, and multi-omics. The present study aims to elucidate the rationale behind the imperative need for modernization in this field. This will be achieved by presenting case studies, examining the diverse range of organisms that have been studied, and evaluating the potential benefits and drawbacks associated with the utilization of these methodologies. The utilization of advanced high-throughput bioinformatics techniques represents a sophisticated approach that necessitates a significant departure from the conventional practices of contemporary freshwater biomonitoring. The significant contributions of omics techniques in the context of biological quality elements (BQEs) and their interpretations in ecological problems are crucial for biomonitoring programs. Such contributions are primarily attributed to the previously overlooked identification of interactions between different levels of biological organization and their responses, isolated and combined, to specific critical conditions.

Polyamide microplastic exposure elicits rapid, strong and genome-wide evolutionary response in the freshwater non-biting midge Chironomus riparius

Susceptibility to hazardous materials and contamination is largely determined by genetic make-up and evolutionary history of affected organisms. Yet evolutionary adaptation and microevolutionary processes triggered by contaminants are rarely considered in ecotoxicology. Using an evolve and resequencing approach, we investigated genome-wide responses of the midge C. riparius exposed to virgin polyamide microplastics (0-180 μm size range, at concentration 1 g kg^-1) during seven consecutive generations. The results were integrated to a parallel life-cycle experiment ran under the same exposure conditions. Emergence, life-cycle trait, showed first a substantial reduction in larval survival, followed by a rapid recovery within three generations. On the genomic level, we observed substantial selectively driven allele frequency changes (mean 0.566 ± 0.0879) within seven generations, associated with a mean selection coefficient of 0.322, indicating very strong selection pressure. Putative selection targets were mainly connected to oxidative stress in the microplastics exposed C. riparius population. This is the first multigenerational study on chironomids to provide evidence that upon exposure to polyamide microplastic there are changes on the genomic level, providing basis to rapid adaptation of aquatic organisms to microplastics.

Effects of polyvinyl chloride microplastics on reproduction, oxidative stress and reproduction and detoxification-related genes in Daphnia magna

The drastic increase of microplastics (MPs) in aquatic environment has become a serious threat to marine and freshwater ecosystems. However, little information is available regarding the potential detrimental effects of polyvinyl chloride microplastics (PVC-MPs) on aquatic organisms. This study investigated the changes of reproduction parameters, oxidative stress and the expression of reproduction and detoxification-related genes in Daphnia magna after exposed to 2 ± 1 and 50 ± 10 μm PVC-MPs. The results showed that chronic exposure to 2 ± 1 μm PVC-MPs prolonged days to the first brood, increased total number of broods per female and frequency of molting per adult, decreased offspring number at first brood and total number of offspring per female in D. magna. Moreover, 2 ± 1 μm PVC-MPs also disturbed the activities of SOD and CAT, increased GSH and MDA levels. The expression of Vtg, SOD, CAT, CYP314 and CYP360A8 genes also exhibited different response patterns depending on exposure time. Furthermore, 50 ± 10 μm PVC-MPs decreased offspring at first brood and Vtg mRNA level, increased the transcription levels and activities of SOD and CAT. These results suggest that the presence of PVC-MPs in aquatic environment may cause reproduction toxicity by disrupting the reproduction and detoxification-related genes expression and inducing oxidative stress in D. magna.

Microbial bioassays in environmental toxicity testing

Accidental spills and the misuse of chemicals may lead to current and legacy environmental contamination and pose concerns over possible (eco)toxicological secondary effects and risks toward non-target microbes and higher eukaryotes, including humans, in ecosystems. In the last decades, scientists and regulators have faced requests to thoroughly screen, prioritize and predict the possible deleterious effects of the huge numbers of existing and emerging xenobiotics, wastewaters and environmental samples on biological systems. In this context, it has become necessary to develop and validate (eco)toxicity bioassays based on microorganisms (e.g., bacteria, microalga, yeast, filamentous fungi, protozoa) as test-organisms whose data should be meaningful for environmental (micro)organisms that may be exposed to contaminated environments. These generally simple, fast and cost-effective bioassays may be preliminary and complementary to the more complex and long-term whole-organism animal-based traditional ecotoxicity tests. With the goal of highlighting the potential offered by microbial-based bioassays as non-animal alternatives in (eco)toxicity testing, the present chapter provides an overview of the current state-of-the art in the development and use of microbial toxicity bioassays through the examination of relatively recent examples with a diverse range of toxicity endpoints. It goes into the (eco)toxicological relevance of these bioassays, ranging from the more traditional microalga- and bacterial-based assays already accepted at regulatory level and commercially available to the more innovative microbial transcriptional profiling and gene expression bioassays, including some examples of biosensors.

Xenobiotic metabolism and transport in Caenorhabditis elegans

Caenorhabditis elegans has emerged as a major model in biomedical and environmental toxicology. Numerous papers on toxicology and pharmacology in C. elegans have been published, and this species has now been adopted by investigators in academic toxicology, pharmacology, and drug discovery labs. C. elegans has also attracted the interest of governmental regulatory agencies charged with evaluating the safety of chemicals. However, a major, fundamental aspect of toxicological science remains underdeveloped in C. elegans: xenobiotic metabolism and transport processes that are critical to understanding toxicokinetics and toxicodynamics, and extrapolation to other species. The aim of this review was to initially briefly describe the history and trajectory of the use of C. elegans in toxicological and pharmacological studies. Subsequently, physical barriers to chemical uptake and the role of the worm microbiome in xenobiotic transformation were described. Then a review of what is and is not known regarding the classic Phase I, Phase II, and Phase III processes was performed. In addition, the following were discussed (1) regulation of xenobiotic metabolism; (2) review of published toxicokinetics for specific chemicals; and (3) genetic diversity of these processes in C. elegans. Finally, worm xenobiotic transport and metabolism was placed in an evolutionary context; key areas for future research highlighted; and implications for extrapolating C. elegans toxicity results to other species discussed.

Benzo[a]pyrene and Caenorhabditis elegans: defining the genotoxic potential in an organism lacking the classical CYP1A1 pathway

Benzo[a]pyrene (BaP) is bioactivated in most organisms by the cytochrome P450 (CYP) enzymes, mainly CYP1A1, ultimately resulting in the reactive metabolite BaP-7,8-dihydrodiol-9,10-epoxide (BPDE) capable of covalently binding to DNA and forming adducts. This step has been defined as the key process in cancer initiation in humans. However, limited knowledge is available about the consequences of BaP exposure in organisms lacking this classical CYP1A1 pathway, one example is the model nematode Caenorhabditis elegans. The aim of this study was to define the genotoxic potential of BaP in C. elegans and to advance our understanding of xenobiotic processing in the absence of the CYP1A1 pathway. Exposure to high concentrations of BaP (0-40 µM) significantly affected life cycle endpoints of C. elegans, which were manifested by a reduced reproductive output and shortened life span. An optimised comet assay revealed that DNA damage increased in a dose-dependent manner; however, no bulky DNA adducts (dG-N²-BPDE) were observed by ³²P-postlabelling. Global transcriptomic analysis by RNA-Seq identified responsive transcript families, most prominently members of the cyp-35 and UDP-glucuronosyltransferases (UGTs) enzyme families, both of which are linked to xenobiotic metabolism. Strains harbouring mutations in the cyp-35A2 and cyp-35A3 genes were notably less prone to BaP-mediated toxicity, and BaP led to longevity in cyp-35A5 mutants. In summary, BaP induces transcriptional, genotoxic and phenotypic responses in C. elegans, despite the absence of the classical CYP1A1 bioactivation pathway. This provides first evidence that parallel pathways are implicated in BaP metabolism in C. elegans and this seems to be mediated via the cyp-35 pathway.

Molecular and cellular responses to short exposure to bisphenols A, F, and S and eluates of microplastics in C. elegans

Bisphenol F (BPF) and bisphenol S (BPS) have been developed as an alternative to bisphenol A (BPA), a well-known endocrine disruptor, leading to their detection in the aquatic environment. In this work, we used the animal model Caenorhabditis elegans to improve our understanding of their potential effects on the biota and the environment. Our findings demonstrated that, after 24 h exposure, all the bisphenols examined increased the number of apoptotic corpses and the expression of the detoxifying enzymes SOD-3 and GST-4, without affecting the ROS levels, while BPA and BPS significantly enhanced DNA fragmentation. Furthermore, similarly to BPA, BPF and BPS did not alter the lifespan through the activation of SEK-1 and SKN-1 pathways. Thus, this study raises the attention of the risks associated with exposure to BPA alternatives. We also examined the effects of microplastic (MP) eluates on C. elegans. Aqueous extracts of weathered microplastic samples, both at high and low degradation state and pellets, have been evaluated for their effects on lifespan, DNA fragmentation, germline apoptosis, and oxidative stress response. Overall, our findings showed that eluates of low degraded plastics exert a greater toxic effect on the nematode C. elegans compared with the aqueous sample of high degraded plastic fragments and pellets.

Multi-Level Gene Expression in Response to Environmental Stress in Aquatic Invertebrate Chironomids: Potential Applications in Water Quality Monitoring

In freshwater ecosystems, aquatic invertebrates are influenced continuously by both physical stress and xenobiotics. Chironomids (Diptera; Chironomidae), or non-biting midges, are the most diverse and abundant invertebrates in freshwater habitats. They are a fundamental link in food chains of aquatic ecosystems. Chironomid larvae tolerate stress factors in their environments via various physiological processes. At the molecular level, environmental pollutants induce multi-level gene responses in Chironomus that regulate cellular protection through the activation of defense processes. This paper reviews literature on the transcriptional responses of biomarker genes to environmental stress in chironomids at the molecular level, in studies conducted from 1991 to 2020 (120 selected literatures of 374 results with the keywords "Chironomus and gene expression" by PubMed search tool). According to these studies, transcriptional responses in chironomids vary depending on the type of stress factor and defensive responses associated with antioxidant activity, the endocrine system, detoxification, homeostasis and stress response, energy metabolism, ribosomal machinery, apoptosis, DNA repair, and epigenetics. These data could provide a comprehensive overview of how Chironomus species respond to pollutants in aquatic environments. Furthermore, the transcriptomic data could facilitate the development of genetic tools for water quality and environmental monitoring based on resident chironomid species.

Influence of pesticides and abiotic conditions on biochemical biomarkers in Aegla aff. longirostri (crustacea, anomura): Implications for conservation

Freshwater ecosystems are constantly threatened by the advance of agricultural activities. Abiotic variables (such as temperature, ammonia, and nitrite) and contaminants (e.g. pesticides) can potentially interact, increasing metabolism and the absorption of toxic substances, which can alter the ability of organisms to establish adequate stress responses. This study aimed to verify which pesticides were most frequently found and in the greatest quantities in low-order streams, and whether the combination of these pesticides with the abiotic variables altered the biological metabolism of aeglids. These freshwater crustaceans are important shredders that inhabit low-order streams and are sensitive to disturbances and/or abrupt environmental variations. The animals were exposed in situ in four streams (reference site and sites 1, 2, and 3). The reference site is a preserved stream with no apparent anthropogenic interference where aeglids still occur, while the other sites no longer exhibit populations of these animals and are influenced by agricultural activities. The exposure was performed bimonthly from November 2017 to September 2018 and lasted 96 h. Measured abiotic data and water samples were collected through all days of exposure. The analyzed biochemical parameters were acetylcholinesterase activity in muscle; and glutathione S-transferase, lipid peroxidation, protein carbonylation, non-protein thiols, antioxidant capacity against peroxides, and reactive oxygen species (ROS) in muscle, gills, and hepatopancreas. We found 24 active principles of pesticides, the most frequently being clomazone, atrazine, and propoxur. Bentazone was present at the highest amounts. The parameters evaluated in this study, including biochemical biomarkers and abiotic factors measured from the water, provided a separation of the months as a function of environmental conditions. There was a difference in activity and biomarker levels throughout the year within the same site and in some months between sites. The greater concentration or variety of pesticides associated with extreme abiotic (very high temperatures) data generated increased oxidative stress, with high levels of protein damage and considerable lipid damage in all tissues, as well as elevation in ROS, even with high levels of antioxidant capacity and non-protein thiols. With these data, we intend to warn about the risks of exposure to these environmental conditions by trying to contribute to the preservation of limnic fauna, especially aeglid crabs, because most species are under some degree of threat.

Analyzing Metabolomics Data for Environmental Health and Exposome Research

The exposome is the cumulative measure of environmental influences and associated biological responses across the life span, with critical relevance for understanding how exposures can impact human health. Metabolomics analysis of biological samples offers unique advantages for examining the exposome. Simultaneous analysis of external exposures, biological responses, and host susceptibility at a systems level can help establish links between external exposures and health outcomes. As metabolomics technologies continue to evolve for the study of the exposome, metabolomics ultimately will help provide valuable insights for exposure risk assessment, and disease prevention and management. Here, we discuss recent advances in metabolomics, and describe data processing protocols that can enable analysis of the exposome. This chapter focuses on using liquid chromatography-mass spectrometry (LC-MS)-based untargeted metabolomics for analysis of the exposome, including (1) preprocessing of untargeted metabolomics data, (2) identification of exposure chemicals and their metabolites, and (3) methods to establish associations between exposures and diseases.

Effect of phthalates on development, reproduction, fat metabolism and lifespan in Daphnia magna

Phthalates are used as plasticizers to increase durability, resistivity and flexibility of plastic materials. The commonly used phthalate, diethylhexyl phthalate (DEHP) is used in different plastic materials like food packaging, toys and medical devices. DEHP has been linked to different toxicities in humans as well as in animals, and as a consequence other phthalates, including dibutyl phthalate (DBP) and diethyl phthalate (DEP) are being introduced. The increased use of phthalates has resulted in contamination of aquatic ecosystem and it directly threatens the aquatic life. In this study, we analyzed the effects of three phthalates DEHP, DEP and DBP using freshwater organism Daphnia magna. Although, exposure of the three phthalates at 1 and 10 μM did not result any lethality and hatching delay, the chronic exposure for 14 days resulted in reduction of body length. There was enhanced fat accumulation on exposure to all the phthalates, as indicated by oil red O staining. qRT-PCR analysis of genes involved in fat metabolism suggests that the increase in fat content could be due to inhibition of absorption and catabolism of fatty acids. Reproduction analysis showed that DBP and DEP did not alter fecundity but surprisingly, DEHP at 1 μM increased reproduction by 1.5 fold compared to control group. Phthalates also showed negative effect on lifespan as DEP at 10 μM and DBP at both 1 and 10 μM significantly reduced the lifespan. Our data indicates that along with the banned phthalate DEHP, the other substitute phthalates DEP and DBP could also have detrimental effect on aquatic organisms.

Comparative analysis of transcriptomic responses to sub-lethal levels of six environmentally relevant pesticides in Saccharomyces cerevisiae

Accidental spills and misuse of pesticides may lead to current and/or legacy environmental contamination and may pose concerns regarding possible risks towards non-target microbes and higher eukaryotes in ecosystems. The present study was aimed at comparing transcriptomic responses to effects of sub-lethal levels of six environmentally relevant pesticide active substances in the Saccharomyces cerevisiae eukaryotic model. The insecticide carbofuran, the fungicide pyrimethanil and the herbicides alachlor, S-metolachlor, diuron and methyl(4-chloro-2-methylphenoxy)acetate were studied. Some are currently used agricultural pesticides, while others are under restricted utilization or banned in Europe and/or North America albeit being used in other geographical locations. In the present work transcriptional profiles representing genome-wide responses in a standardized yeast population upon 2 h of exposure to concentrations of each compound exerting equivalent toxic effects, i.e., inhibition of growth by 20% relative to the untreated control cells, were examined. Hierarchical clustering and Venn analyses of the datasets of differentially expressed genes pointed out transcriptional patterns distinguishable between the six active substances. Functional enrichment analyses allowed predicting mechanisms of pesticide toxicity and response to pesticide stress in the yeast model. In general, variations in transcript numbers of selected genes assessed by Real-Time quantitative reverse transcription polymerase chain reaction confirmed microarray data and correlated well with growth inhibitory effects. A possible biological relevance of mechanistic predictions arising from these comparative transcriptomic analyses is discussed in the context of better understanding potential modes of action and adverse side-effects of pesticides.

Caenorhabditis elegans as an emerging model system in environmental epigenetics

The roundworm Caenorhabitis elegans has been an established model organism for the study of genetics and developmental biology, including studies of transcriptional regulation, since the 1970s. This model organism has continued to be used as a classical model system as the field of transcriptional regulation has expanded to include scientific advances in epigenetics and chromatin biology. In the last several decades, C. elegans has emerged as a powerful model for environmental toxicology, particularly for the study of chemical genotoxicity. Here, we outline the utility and applicability of C. elegans as a powerful model organism for mechanistic studies of environmental influences on the epigenome. Our goal in this article is to inform the field of environmental epigenetics of the strengths and limitations of the well-established C. elegans model organism as an emerging model for medium-throughput, in vivo exploration of the role of exogenous chemical stimuli in transcriptional regulation, developmental epigenetic reprogramming, and epigenetic memory and inheritance. As the field of environmental epigenetics matures, and research begins to map mechanisms underlying observed associations, new toolkits and model systems, particularly manipulable, scalable in vivo systems that accurately model human transcriptional regulatory circuits, will provide an essential experimental bridge between in vitro biochemical experiments and mammalian model systems. Environ. Mol. Mutagen. 59:560-575, 2018. © 2018 Wiley Periodicals, Inc.

Mode of action characterization for adverse effect of propranolol in Daphnia magna based on behavior and physiology monitoring and metabolite profiling

Studies are underway to gather information about the mode of action (MOA) of emerging pollutants that could guide practical environmental decision making. Previously, we showed that propranolol, an active pharmaceutical ingredient, had adverse effects on Daphnia magna that were similar to its pharmaceutical action. In order to characterize the mode of action of propranolol in D. magna, which is suspected to be organ-specific pharmaceutical action or baseline toxicity, we performed time-series monitoring of behavior along with heart rate measurements and nuclear magnetic resonance (NMR) based metabolite profiling. Principle component analysis (PCA) and hierarchical clustering were used to categorize the mode of action of propranolol among 5 chemicals with different modes of action. The findings showed that the mode of action of propranolol in D. magna is organ-specific and vastly different from those of narcotics, even though metabolite regulation is similar between narcotic and non-narcotic candidates. The method applied in this study seems applicable to rapid characterization of the MOA of other cardiovascular pharmaceutical ingredients.

An approach to the study of the immunity functions of bivalve haemocytes: Physiology and molecular aspects

The Mediterranean mussel Mytilus galloprovincialis is an ecologically and economically important species. It has been used in programs of monitoring of pollution, since it is sessile organism that is capable of accumulating pollutants in tissues through filter feeding. Due to an increase of pollutants in the environment, marine mussels present physiological alterations that compromise their innate immune system, which can latter lead to opportunistic diseases. The haemocytes are the cells in charge of the immune response in the Mediterranean mussel and in other mollusks. In this review, we summarize the physiological and genetic response capacity of these immune cells to the presence of xenobiotics, pathogens and the interplay. The identification of the basic mechanisms of immunity and their modulation in mussels can give important information for the possible utilization of this species as an invertebrate model for studies on innate immunity, future immunotoxicological studies, and predict changes in the community for the future.

Global Gene Expression Analysis of Cross-Protected Phenotype of Pectobacterium atrosepticum

The ability to adapt to adverse conditions permits many bacterial species to be virtually ubiquitous and survive in a variety of ecological niches. This ability is of particular importance for many plant pathogenic bacteria that should be able to exist, except for their host plants, in different environments e.g. soil, water, insect-vectors etc. Under some of these conditions, bacteria encounter absence of nutrients and persist, acquiring new properties related to resistance to a variety of stress factors (cross-protection). Although many studies describe the phenomenon of cross-protection and several regulatory components that induce the formation of resistant cells were elucidated, the global comparison of the physiology of cross-protected phenotype and growing cells has not been performed. In our study, we took advantage of RNA-Seq technology to gain better insights into the physiology of cross-protected cells on the example of a harmful phytopathogen, Pectobacterium atrosepticum (Pba) that causes crop losses all over the world. The success of this bacterium in plant colonization is related to both its virulence potential and ability to persist effectively under various stress conditions (including nutrient deprivation) retaining the ability to infect plants afterwards. In our previous studies, we showed Pba to be advanced in applying different adaptive strategies that led to manifestation of cell resistance to multiple stress factors. In the present study, we determined the period necessary for the formation of cross-protected Pba phenotype under starvation conditions, and compare the transcriptome profiles of non-adapted growing cells and of adapted cells after the cross-protective effect has reached the maximal level. The obtained data were verified using qRT-PCR. Genes that were expressed differentially (DEGs) in two cell types were classified into functional groups and categories using different approaches. As a result, we portrayed physiological features that distinguish cross-protected phenotype from the growing cells.

Copper at low levels impairs memory of adult zebrafish (Danio rerio) and affects swimming performance of larvae

Metal contamination at low levels is an important issue because it usually produces health and environmental effects, either positive or deleterious. Contamination of surface waters with copper (Cu) is a worldwide event, usually originated by mining, agricultural, industrial, commercial, and residential activities. Water quality criteria for Cu are variable among countries but allowed limits are generally in the μg/L range, which can disrupt several functions in the early life-stages of fish species. Behavioral and biochemical alterations after Cu exposure have also been described at concentrations close to the allowed limits. Aiming to search for the effects of Cu in the range of the allowed limits, larvae and adult zebrafish (Danio rerio) were exposed to different concentrations of dissolved Cu (nominally: 0, 5, 9, 20 and 60μg/L; measured: 0.4, 5.7, 7.2 16.6 and 42.3μg/L, respectively) for 96h. Larvae swimming and body length, and adult behavior and biochemical biomarkers (activity of glutathione-related enzymes in gills, muscle, and brain) were assessed after Cu exposure. Several effects were observed in fish exposed to 9μg/L nominal Cu, including increased larvae swimming distance and velocity, abolishment of adult inhibitory avoidance memory, and decreased glutathione S-transferase (GST) activity in gills of adult fish. At the highest Cu concentration tested (nominally: 60μg/L), body length of larvae, spatial memory of adults, and gill GST activity were decreased. Social behavior (aggressiveness and conspecific interaction), and glutathione reductase (GR) activity were not affected in adult zebrafish. Exposure to Cu, at concentrations close to the water quality criteria for this metal in fresh water, was able to alter larvae swimming performance and to induce detrimental effects on the behavior of adult zebrafish, thus indicating the need for further studies to reevaluate the currently allowed limits for Cu in fresh water.

The application of the comet assay to assess the genotoxicity of environmental pollutants in the nematode Caenorhabditis elegans

This study aimed to establish a protocol for cell dissociation from the nematode Caenorhabditis elegans (C. elegans) to assess the genotoxicity of the environmental pollutant benzo[a]pyrene (BaP) using the alkaline version of the single cell electrophoresis assay (comet assay). BaP genotoxicity was assessed in C. elegans (wild-type [WT]; N2, Bristol) after 48h exposure (0-40μM). Induction of comets by BaP was concentration-dependent up to 20μM; comet% tail DNA was ∼30% at 20μM BaP and ∼10% in controls. Similarly, BaP-induced DNA damage was evaluated in C. elegans mutant strains deficient in DNA repair. In xpa-1 and apn-1 mutants BaP-induced comet formation was diminished to WT background levels suggesting that the damage formed by BaP that is detected in the comet assay is not recognised in cells deficient in nucleotide and base excision repair, respectively. In summary, our study provides a protocol to evaluate DNA damage of environmental pollutants in whole nematodes using the comet assay.

Transcriptional responses, metabolic activity and mouthpart deformities in natural populations of Chironomus riparius larvae exposed to environmental pollutants

Biomarkers are an important tool in laboratory assays that link exposure or effect of specific toxicants to key molecular and cellular events, but they have not been widely used in invertebrate populations exposed to complex mixtures of environmental contaminants in their natural habitats. The present study focused on a battery of biomarkers and their comparative analysis in natural populations of the benthic larvae of Chironomus riparius (Diptera), sampled in three differentially polluted rivers (the Con, Sar, and Louro in Galicia, Spain). In our study, some parameters were identified, such as hsp70 gene activity, GST enzymatic activity, total glycogen content and mouthpart deformities, which showed significant differences among populations from the three rivers that differed in the levels and types of sedimentary contaminants analyzed (metals, organic-chlorine pesticides, alkylphenols, pharmaceutical, and personal care products). In contrast to these sensitive biomarkers, other parameters showed no significant differences (hsc70 gene, EcR gene, P450 gene, RNA:DNA ratio, total protein content), and were stable even when comparing field and nonexposed laboratory populations. The hsp70 gene seems to be particularly sensitive to conditions of pollutant exposure, while its constitutive counterpart hsc70 showed invariable expression, suggesting that the hsc70/hsp70 ratio may be a potential indicator of polluted environments. Although further studies are required to understand the correlation between molecular responses and the ecological effects of pollutants on natural populations, the results provide new data about the biological responses to multiple-stressor environments. This field study adds new molecular endpoints, including gene expression, as suitable tools that, complementing other ecotoxicological parameters, may help to improve the methodologies of freshwater monitoring under the increasing burden of xenobiotics.

Low concentrations of dibromoacetic acid and N-nitrosodimethylamine induce several stimulatory effects in the invertebrate model Caenorhabditis elegans

Dibromoacetic acid (DBAA) and N-nitrosodimethylamine (NDMA) have natural and anthropogenic sources and are ubiquitously distributed in the environment. They are classified as toxic and carcinogenetic and various studies have addressed their effects on vertebrates. Furthermore, there is no information about the whole-organism effects at low concentrations or about their impact on invertebrates. Therefore, these compounds were studied with the model invertebrate Caenorhabditis elegans (C. elegans) at relatively low concentrations. Biological tests (life span, reproduction, body size, thermal stress resistance) as well as biochemical (pro- and antioxidative capacity and lipid peroxidation) and biomolecular assays (transcription of stress genes) were performed. None of the applied concentrations showed a toxic potential. Instead, they extended life span and increased the body length. Both xenobiotics did not cause oxidative stress or DNA damages, or acted as endocrine disruptors. The stimulatory effects on C. elegans were most likely not a result of an induced protective stress response. Instead, an 'energy saving mode', indicated by the reduced transcription of many stress response genes, could have provided additional resources for longevity and growth. Although both substances are potentially toxic at higher doses, the present study underlines the importance of testing lower concentrations and their impact on invertebrates.

A nutrigenomic approach to detect nutritional stress from gene expression in blood samples drawn from Steller sea lions

Gene expression profiles are increasingly being used as biomarkers to detect the physiological responses of a number of species to disease, nutrition, and other stressors. However, little attention has been given to using gene expression to assess the stressors and physiological status of marine mammals. We sought to develop and validate a nutrigenomic approach to quantify nutritional stress in Steller sea lions (Eumetopias jubatus). We subjected 4 female Steller sea lions to 3 feeding regimes over 70-day trials (unrestricted food intake, acute nutritional stress, and chronic nutritional stress), and drew blood samples from each animal at the end of each feeding regime. We then extracted the RNA of white blood cells and measured the response of 8 genes known to react to diet restriction in terrestrial mammals. Overall, we found that the genomic response of Steller sea lions experiencing nutritional stress was consistent with how terrestrial mammals respond to dietary restrictions. Our nutritionally stressed sea lions down-regulated some cellular processes involved in immune response and oxidative stress, and up-regulated pro-inflammatory responses and metabolic processes. Nutrigenomics appears to be a promising means to monitor nutritional status and contribute to mitigation measures needed to assist in the recovery of Steller sea lions and other at-risk species of marine mammals.

Molecular pathways associated with the intersex condition in rainbow darter (Etheostoma caeruleum) following exposures to municipal wastewater in the Grand River basin, ON, Canada. Part B

Rainbow darter (Etheostoma caeruleum; RBD) is a small benthic fish found in North America. This species is sensitive to sewage effluent, and intersex is found in up to 80% of males in near-field areas in the Grand River, Ontario, Canada. To learn more about the molecular signaling cascades associated with intersex, a developed customized oligonucleotide microarray (4×180 K) using next generation sequencing was developed to characterize the transcriptome in the gonad of male and female RBD. Gene expression profiling was performed in males and females from both a reference site and a polluted site. Males with and without intersex condition from the areas closest to effluent outfalls were compared to males and females from a reference site. Microarray analysis revealed that there was increased mRNA abundance for genes associated with oogenesis in intersex males (i.e. the presence of eggs within the testis), and a decrease in mRNA abundance for genes associated with spermatid development. In females exposed to effluent, cell processes related with hatching and ovulation were down-regulated, and genes involved in immune responses were increased in abundance. In the non-intersex males exposed to effluent, cell processes such as sperm cell adhesion were decreased at the transcript level relative to males from the reference site. Microarray analysis revealed that heat shock proteins (HSP) were significantly increased in non-intersex males exposed to effluent; however, HSPs were not differentially expressed in intersex males exposed to the effluent. Genes involved in sex differentiation (sox9, foxl2 and dmrt1) and reproduction (esr1, esrb, ar, vtg, cyp19a1 and cyp11a) were measured in males, females, and intersex individuals. Consistent with the intersex condition, many transcripts showed an intermediate expression level in intersex males when compared to phenotypic males and females. This study improves our knowledge regarding the molecular pathways that underlie the intersex condition and develops a suite of qPCR bioassays in RBD that are able to discriminate pollutant-exposed males without intersex from those males with intersex. Part A of this study reports on the effects of municipal wastewater effluents (MWWEs) on RBD in the Grand River and demonstrates that there are disruptions in higher level endpoints that include altered steroid levels. Here we develop a new tool for assessing and monitoring the intersex condition in RBD in polluted natural environments and begin to characterize gene networks that are associated with the condition.

Suitability of a Saccharomyces cerevisiae-based assay to assess the toxicity of pyrimethanil sprayed soils via surface runoff: comparison with standard aquatic and soil toxicity assays

The present study is aimed at evaluating whether a gene expression assay with the microbial eukaryotic model Saccharomyces cerevisiae could be used as a suitable warning tool for the rapid preliminary screening of potential toxic effects on organisms due to scenarios of soil and water contamination with pyrimethanil. The assay consisted of measuring changes in the expression of the selected pyrimethanil-responsive genes ARG3 and ARG5,6 in a standardized yeast population. Evaluation was held by assessing the toxicity of surface runoff, a major route of pesticide exposure in aquatic systems due to non-point-source pollution, which was simulated with a pyrimethanil formulation at a semifield scale mimicking worst-case scenarios of soil contamination (e.g. accident or improper disposal). Yeast cells 2-h exposure to the runoff samples led to a significant 2-fold increase in the expression of both indicator genes. These results were compared with those from assays with organisms relevant for the aquatic and soil compartments, namely the nematode Caenorhabditis elegans (reproduction), the freshwater cladoceran Daphnia magna (survival and reproduction), the benthic midge Chironomus riparius (growth), and the soil invertebrates Folsomia candida and Enchytraeus crypticus (survival and reproduction). Under the experimental conditions used to simulate accidental discharges into soil, runoff waters were highly toxic to the standard test organisms, except for C. elegans. Overall, results point out the usefulness of the yeast assay to provide a rapid preview of the toxicity level in preliminary screenings of environmental samples in situations of inadvertent high pesticide contamination. Advantages and limitations of this novel method are discussed.

Variation in variance means more than mean variations: what does variability tell us about population health status?

In environmental science, the variability of biological responses in natural or laboratory populations is a well known and documented phenomenon. However, while an extensive literature aims to explain and understand the origin of variability, few try to use it as a demonstration of the population's response facing a stress. We propose here a theoretical framework that explores various patterns of variability both within and among populations, and seeks methods useful in bioevaluation methodologies. We also introduce the concept of "ecotoxicological niche" to characterize the ability of a population to endure contamination.

Changes in the expression of cyp35a family genes in the soil nematode Caenorhabditis elegans under controlled exposure to chlorpyrifos using passive dosing

In order to use sensitive molecular-level biomarkers for the evaluation of environmental risks, it is necessary to establish a quantitative dose-response relationship. Passive dosing is regarded as a promising new technique for maintaining a constant exposure condition of hydrophobic chemicals in the assay medium. The main goals of the present study were (1) to quantitatively compare gene expression results obtained using the passive dosing method and the conventional spiking method and (2) to investigate changes in gene expression with respect to the free concentration and exposure duration using passive dosing. Chlorpyrifos (CP), which is oxidized by the cytochrome P450 monooxygenases, was selected as a model chemical, and the expression of cytochrome P450 subfamily protein 35A gene series (cyp-35a1-5) was analyzed by quantitative real-time PCR on soil nematode Caenorhabditis elegans. Whereas the free concentration of CP rapidly decreased and the expression of cyp genes varied with the volume of exposure medium and the test duration when the spiking method was used, the free concentration in the assay medium was stable throughout the experiment when the passive dosing method was used. In addition, the level of gene expression increased with exposure time up to 8 h and with increasing CP concentration. The observed increased gene expression could be explained by increasing body residue concentration of CP with exposure time. In conclusion, quantitative dose-response relationships for gene expression biomarkers could be obtained for highly hydrophobic chemicals when the constant exposure condition is provided and the free concentration is used as the dose-metric.

Genetic basis for nitrate resistance in Desulfovibrio strains

Nitrate is an inhibitor of sulfate-reducing bacteria (SRB). In petroleum production sites, amendments of nitrate and nitrite are used to prevent SRB production of sulfide that causes souring of oil wells. A better understanding of nitrate stress responses in the model SRB, Desulfovibrio vulgaris Hildenborough and Desulfovibrio alaskensis G20, will strengthen predictions of environmental outcomes of nitrate application. Nitrate inhibition of SRB has historically been considered to result from the generation of small amounts of nitrite, to which SRB are quite sensitive. Here we explored the possibility that nitrate might inhibit SRB by a mechanism other than through nitrite inhibition. We found that nitrate-stressed D. vulgaris cultures grown in lactate-sulfate conditions eventually grew in the presence of high concentrations of nitrate, and their resistance continued through several subcultures. Nitrate consumption was not detected over the course of the experiment, suggesting adaptation to nitrate. With high-throughput genetic approaches employing TnLE-seq for D. vulgaris and a pooled mutant library of D. alaskensis, we determined the fitness of many transposon mutants of both organisms in nitrate stress conditions. We found that several mutants, including homologs present in both strains, had a greatly increased ability to grow in the presence of nitrate but not nitrite. The mutated genes conferring nitrate resistance included the gene encoding the putative Rex transcriptional regulator (DVU0916/Dde_2702), as well as a cluster of genes (DVU0251-DVU0245/Dde_0597-Dde_0605) that is poorly annotated. Follow-up studies with individual D. vulgaris transposon and deletion mutants confirmed high-throughput results. We conclude that, in D. vulgaris and D. alaskensis, nitrate resistance in wild-type cultures is likely conferred by spontaneous mutations. Furthermore, the mechanisms that confer nitrate resistance may be different from those that confer nitrite resistance.

Signal transduction disturbance related to hepatocarcinogenesis in mouse by prolonged exposure to Nanjing drinking water

Toxicogenomic approaches were used to investigate the potential hepatocarcinogenic effects on mice by oral exposure to Nanjing drinking water (NJDW). Changes in the hepatic transcriptome of 3 weeks male mice (Mus musculus) were monitored and dissected after oral exposure to NJDW for 90 days. No preneoplastic and neoplastic lesions were observed in the hepatic tissue by the end of NJDW exposure. However, total of 746 genes were changed transcriptionally. Thirty-one percent of differentially expressed genes (DEGs) were associated with the functional categories of cell cycle regulation, adhesion, growth, apoptosis, and signal transduction, which are closely implicated in tumorigenesis and progression. Interrogation of Kyoto Encyclopedia of Genes and Genomes revealed that 43 DEGs were mapped to several crucial signaling pathways implicated in the pathogenesis of hepatocellular carcinoma (HCC). In signal transduction network constructed via Genes2Networks software, Egfr, Akt1, Atf2, Ctnnb1, Hras, Mapk1, Smad2, and Ccnd1 were hubs. Direct gene-disease relationships obtained from Comparative Toxicogenomics Database and scientific literatures revealed that the hubs have direct mechanism or biomarker relationships with hepatocellular preneoplastic lesions or hepatocarcinogenesis. Therefore, prolonged intake of NJDW without employing any indoor water treatment strategy might predispose mouse to HCC. Furthermore, Egfr, Akt1, Ctnnb1, Hras, Mapk1, Smad2, and Ccnd1 were identified as promising biomarkers of the potential combined hepatocarcinogenicity.

Application of MicroResp™ for soil ecotoxicology

MicroResp™ is a miniaturised method for measuring substrate induced respiration (SIR) in soil. We modified the MicroResp™ method to develop a rapid tool for quantifying the ecotoxicological impact of contaminants. The method is based on reduction in SIR across a gradient of contaminant, allowing for determination of dose-response curves EC-values. Contaminants are mixed into soil samples at a range of concentrations; each sample is then dispensed into a column of eight wells in 96 well format (deep) plates. Moisture and glucose are added to the samples at levels to provide maximum response. Released CO₂ from the soils is then measured using colorimetric gel-traps, following the standard MicroResp™ methodology. Examination revealed that this method works over a range of soil types and is insensitive to minor variations in assay length (2-7 h), alteration of moisture content (±20 μL from optimum), and soil storage conditions (4 °C versus fresh).

Evolutionary concepts in ecotoxicology: tracing the genetic background of differential cadmium sensitivities in invertebrate lineages

In many toxicological and ecotoxicological studies and experimental setups, the investigator is mainly interested in traditional parameters such as toxicity data and effects of toxicants on molecular, cellular or physiological functions of individuals, species or statistical populations. It is clear, however, that such approaches focus on the phenotype level of animal species, whilst the genetic and evolutionary background of reactions to environmental toxicants may remain untold. In ecotoxicological risk assessment, moreover, species sensitivities towards pollutants are often regarded as random variables in a statistical approach. Beyond statistics, however, toxicant sensitivity of every species assumes a biological significance, especially if we consider that sensitivity traits have developed in lineages of species with common evolutionary roots. In this article, the genetic and evolutionary background of differential Cd sensitivities among invertebrate populations and species and their potential of adaptation to environmental Cd exposure will be highlighted. Important evolutionary and population genetic concepts such as genome structure and their importance for evolutionary adaptation, population structure of affected individuals, as well as micro and macroevolutionary mechanisms of Cd resistance in invertebrate lineages will be stressed by discussing examples of work from our own laboratory along with a review of relevant literature data and a brief discussion of open questions along with some perspectives for further research. Both, differences and similarities in Cd sensitivity traits of related invertebrate species can only be understood if we consider the underlying evolutionary processes and genetic (or epigenetic) mechanisms. Keeping in mind this perception can help us to better understand and interpret more precisely why the sensitivity of some species or species groups towards a certain toxicant (or metal) may be ranked in the lower or higher range of species sensitivity distributions. Hence, such a perspective will transcend a purely statistical view of the sensitivity distributions concept, and will enhance ecotoxicology in many respects.

Response of Lumbriculus variegatus transcriptome and metabolites to model chemical contaminants

Assessment of the underlying molecular events leading to xenobiotic toxicity is challenging especially when techniques are applied in isolation. We examined transcriptional and metabolic changes in Lumbriculus variegatus exposed to benzo(a)pyrene (B(a)P), cadmium (Cd) or pentachlorophenol (PCP) by DNA microarrays (7422 ESTs) and gas chromatography-mass spectrometry (GC-MS), respectively. In addition, the DNA damage response of worms exposed to B(a)P was assessed by a capillary electrophoresis laser induced fluorescence (CE-LIF) immunoassay. We found elevated expression of oxidative stress responsive genes, which correlated positively with the changes in antioxidant vitamin precursors including alpha-tocopherol and cholecalciferol. Other genes with strong differential expressions were mostly involved in actin related processes and proteolysis, despite an apparent delayed Cd response. Phosphates, sugars and fatty acids were effectively reduced and suggested that chemical treatments may have interfered with energy metabolism. The increased amount of B(a)P diol-epoxide (BPDE)-DNA adducts in exposed worms appeared to correlate with the variability in uridine, inosine and xanthine, which are key components of nucleoside metabolism. This suggests that DNA damage was imminent or peaked within 6h. The results conformed to transcriptional changes in B(a)P exposed worms and compliment other approaches to elucidate underlying molecular changes.

Transcript expression patterns illuminate the mechanistic background of hormesis in caenorhabditis elegans maupas

The animal model Caenorhabditis elegans was employed to study polyphenol- and humic substances-induced hormetic changes in lifespan. A detailed insight into the underlying mechanism of hormesis was uncovered by applying whole genome DNA microarray experimentation over a range of quercetin (Q), tannic acid (TA), and humic substances (HuminFeed(®), HF) concentrations. The transcriptional response to all exposures followed a non-linear mode which highlighted differential signaling and metabolic pathways. While low Q concentrations regulated processes improving the health of the nematodes, higher concentrations extended lifespan and modulated substantially the global transcriptional response. Over-represented transcripts were notably part of the biotransformation process: enhanced catabolism of toxic intermediates possibly contributes to the lifespan extension. The regulation of transcription, Dauer entry, and nucleosome suggests the presence of distinct exposure dependent differences in transcription and signaling pathways. TA- and HF-mediated transcript expression patterns were overall similar to each other, but changed across the concentration range indicating that their transcriptional dynamics are complex and cannot be attributed to a simple adaptive response. In contrast, Q-mediated hormesis was well aligned to fit the definition of an adaptive response. Simple molecules are more likely to induce an adaptive response than more complex molecules.

Transcription profiling in environmental diagnostics: health assessments in Columbia River basin steelhead (Oncorhynchus mykiss)

The health condition of out-migrating juvenile salmonids can influence migration success. Physical damage, pathogenic infection, contaminant exposure, and immune system status can affect survival probability. The present study is part of a wider investigation of out-migration success in juvenile steelhead (Oncorhynchus mykiss) and focuses on the application of molecular profiling to assess sublethal effects of environmental stressors in field-collected fish. We used a suite of genes in O. mykiss to specifically assess responses that could be directly related to steelhead health condition during out-migration. These biomarkers were used on juvenile steelhead captured in the Snake River, a tributary of the Columbia River, in Washington, USA, and were applied on gill and anterior head kidney tissue to assess immune system responses, pathogen-defense (NRAMP, Mx, CXC), general stress (HSP70), metal-binding (metallothionein-A), and xenobiotic metabolism (Cyp1a1) utilizing quantitative polymerase chain reaction (PCR) technology. Upon capture, fish were ranked according to visual external physical conditions into good, fair, poor, and bad categories; gills and kidney tissues were then dissected and preserved for gene analyses. Transcription responses were tissue-specific for gill and anterior head kidney with less significant responses in gill tissue than in kidney. Significant differences between the condition ranks were attributed to NRAMP, MX, CXC, and Cyp1a1 responses. Gene profiling correlated gene expression with pathogen presence, and results indicated that gene profiling can be a useful tool for identifying specific pathogen types responsible for disease. Principal component analysis (PCA) further correlated these responses with specific health condition categories, strongly differentiating good, poor, and bad condition ranks. We conclude that molecular profiling is an informative and useful tool that could be applied to indicate and monitor numerous population-level parameters of management interest.

Toxic effects of engineered nanoparticles in the marine environment: model organisms and molecular approaches

Engineered nanoparticles (ENPs) have been produced by nano-biotech companies in recent decades to generate innovative goods in various fields, including agriculture, electronics, biomedicine, manufacturing, pharmaceuticals and cosmetics. The nano-scale size of the particles can confer novel and significantly improved physical, chemical and biological properties to scientific phenomena and processes. As their applications to science and technology expand, the need to understand the putative noxious effects of ENPs on humans and ecosystems is becoming increasingly important. ENPs are emerging as a new class of pollutants with eco-toxicological impacts on marine ecosystems because the particles can end up in waterways and reach the sea. Recent laboratory studies in invertebrates and fishes suggest that exposure to ENPs could have harmful effects. Because there is not much data available for gauging the effects of ENPs on marine wildlife, the ultimate ecotoxicological impacts of chronic exposure to ENPs should be investigated further using laboratory tests and field studies. We propose the use of model organisms to understand the molecular pathways involved in the mechanisms that may be affected by exposure to ENPs. Sensitive and innovative molecular methods will provide information regarding the hazards of ENPs that may exist in the marine environment. Model organisms that have not been conventionally used for risk assessment and the development of eco-toxicogenomic approaches will result in an improved understanding of the mechanistic modes of action of contaminating ENPs in the marine environment.

Hepatic proteome changes in Solea senegalensis exposed to contaminated estuarine sediments: a laboratory and in situ survey

Assessing toxicity of contaminated estuarine sediments poses a challenge to ecotoxicologists due to the complex geochemical nature of sediments and to the combination of multiple classes of toxicants. Juvenile Senegalese soles were exposed for 14 days in the laboratory and in situ (field) to sediments from three sites (a reference plus two contaminated) of a Portuguese estuary. Sediment characterization confirmed the combination of metals, polycyclic aromatic hydrocarbons and organochlorines in the two contaminated sediments. Changes in liver cytosolic protein regulation patterns were determined by a combination of two-dimensional electrophoresis with de novo sequencing by tandem mass spectrometry. From the forty-one cytosolic proteins found to be deregulated, nineteen were able to be identified, taking part in multiple cellular processes such as anti-oxidative defence, energy production, proteolysis and contaminant catabolism (especially oxidoreductase enzymes). Besides a clear distinction between animals exposed to the reference and contaminated sediments, differences were also observed between laboratory- and in situ-tested fish. Soles exposed in the laboratory to the contaminated sediments failed to induce, or even markedly down-regulated, many proteins, with the exception of a peroxiredoxin (an anti-oxidant enzyme) and a few others, when compared to reference fish. In situ exposure to the contaminated sediments revealed significant up-regulation of basal metabolism-related enzymes, comparatively to the reference condition. Down-regulation of basal metabolism enzymes, related to energy production and gene transcription, in fish exposed in the laboratory to the contaminated sediments, may be linked to sediment-bound contaminants and likely compromised the organisms' ability to deploy adequate responses against insult.

The Epigenetic Repertoire of Daphnia magna Includes Modified Histones

Daphnids are fresh water microcrustaceans, many of which follow a cyclically parthenogenetic life cycle. Daphnia species have been well studied in the context of ecology, toxicology, and evolution, but their epigenetics remain largely unexamined even though sex determination, the production of sexual females and males, and distinct adult morphological phenotypes, are determined epigenetically. Here, we report on the characterization of histone modifications in Daphnia. We show that a number of histone H3 and H4 modifications are present in Daphnia embryos and histone H3 dimethylated at lysine 4 (H3K4me2) is present nonuniformly in the nucleus in a cell cycle-dependent manner. In addition, this histone modification, while present in blastula and gastrula cells as well as the somatic cells of adults, is absent or reduced in oocytes and nurse cells. Thus, the epigenetic repertoire of Daphnia includes modified histones and as these epigenetic forces act on a genetically homogeneous clonal population Daphnia offers an exceptional tool to investigate the mechanism and role of epigenetics in the life cycle and development of an ecologically important species.

Reference genes for qPCR assays in toxic metal and salinity stress in two flatworm model organisms

The flatworm species Schmidtea mediterranea and Macrostomum lignano have become new and innovative model organisms in stem cell, regeneration and tissue homeostasis research. Because of their unique stem cell system, (lab) technical advantages and their phylogenetic position within the Metazoa, they are also ideal candidate model organisms for toxicity assays. As stress and biomarker screenings are often performed at the transcriptional level, the aim of this study was to establish a set of reference genes for qPCR experiments for these two model organisms in different stress situations. We examined the transcriptional stability of nine potential reference genes (actb, tubb, ck2, cox4, cys, rpl13, gapdh, gm2ap, plscr1) to assess those that are most stable during altered stress conditions (exposure to carcinogenic metals and salinity stress). The gene expression stability was evaluated by means of geNorm and NormFinder algorithms. Sets of best reference genes in these analyses varied between different stress situations, although gm2ap and actb were stably transcribed during all tested combinations. In order to demonstrate the impact of bad normalisation, the stress-specific gene hsp90 was normalised to different sets of reference genes. In contrast to the normalisation according to GeNorm and NormFinder, normalisation of hsp90 in Macrostomum lignano during cadmium stress did not show a significant difference when normalised to only gapdh. On the other hand an increase of variability was noticed when normalised to all nine tested reference genes together. Testing appropriate reference genes is therefore strongly advisable in every new experimental condition.

Effects of cadmium chloride and nonylphenol on the expression of StAR-related lipid transfer domain containing protein (START1) gene in aquatic midge, Chironomus riparius

We identified and characterized a partial cDNA of StAR-related lipid transfer domain containing protein gene from Chironomus riparius (CrSTART1) having homology with human MLN64 and Drosophila melanogaster START1 (DmSTART1) and evaluated the effects of cadmium chloride (Cd) and nonylphenol (NP) on its expression. Pfam analysis identified the presence of two StAR-related lipid transfer (START) domains in CrSTART1 having several conserved amino acid residues, characteristic of the MLN64 and DmSTART1. The mRNA expression of CrSTART1 was observed in all developmental stages. The modulation in the mRNA expression of CrSTART1 was investigated after exposure to different concentrations Cd (0, 2, 10, and 20 mg/L) and NP (0, 10, 50, and 100 μg/L) for different time intervals in fourth instar larvae of C. riparius. Significant downregulation of CrSTART1 mRNA was observed after exposure to 2, 10 and 20 mg/L of Cd for 24, 48 and 72 h. Significant upregulation of CrSTART1 was observed after exposure to 10 and 50 μg/L of NP for 24, and 48 h period. At 100 μg/L of NP significant upregulation of CrSTART1 was observed after 12 h and downregulated after 24, 48 and 72 h.

Can the integration of multiple biomarkers and sediment geochemistry aid solving the complexity of sediment risk assessment? A case study with a benthic fish

Surveying toxicity of complex geochemical media as aquatic sediments often yields results that are either difficult to interpret or even contradictory to acknowledged theory. Multi-level biomarkers were investigated in a benthic fish exposed to estuarine sediments through laboratory and in situ bioassays, to evaluate their employment either in ecological risk assessment or in more mechanistic approaches to assess sediment-bound toxicity. Biomarkers reflecting lesions (such as genotoxicity or histopathology), regardless of their low or absent specificity to contaminants, are efficient in segregating exposure to contaminated from uncontaminated sediments even when classical biomarkers like CYP1A and metallothionein induction are inconclusive. Conversely, proteomics and gene transcription analyses provided information on the mechanics of toxicity and aided explaining response variation as a function of metabolic imbalance and impairment of defences against insult. In situ bioassays, although less expedite and more affected by confounding factors, produced data better correlated to overall sediment contamination.

Transcriptional responses underlying the hormetic and detrimental effects of the plant secondary metabolite gossypol on the generalist herbivore Helicoverpa armigera

BACKGROUND

Hormesis is a biphasic biological response characterized by the stimulatory effect at relatively low amounts of chemical compounds which are otherwise detrimental at higher concentrations. A hormetic response in larval growth rates has been observed in cotton-feeding insects in response to increasing concentrations of gossypol, a toxic metabolite found in the pigment glands of some plants in the family Malvaceae. We investigated the developmental effect of gossypol in the cotton bollworm, Helicoverpa armigera, an important heliothine pest species, by exposing larvae to different doses of this metabolite in their diet. In addition, we sought to determine the underlying transcriptional responses to different gossypol doses.

RESULTS

Larval weight gain, pupal weight and larval development time were measured in feeding experiments and a hormetic response was seen for the first two characters. On the basis of net larval weight gain responses to gossypol, three concentrations (0%, 0.016% and 0.16%) were selected for transcript profiling in the gut and the rest of the body in a two-color double reference design microarray experiment. Hormesis could be observed at the transcript level, since at the low gossypol dose, genes involved in energy acquisition such as β-fructofuranosidases were up-regulated in the gut, and genes involved in cell adhesion were down-regulated in the body. Genes with products predicted to be integral to the membrane or associated with the proteasome core complex were significantly affected by the detrimental dose treatment in the body. Oxidoreductase activity-related genes were observed to be significantly altered in both tissues at the highest gossypol dose.

CONCLUSIONS

This study represents the first transcriptional profiling approach investigating the effects of different concentrations of gossypol in a lepidopteran species. H. armigera's transcriptional response to gossypol feeding is tissue- and dose-dependent and involves diverse detoxifying mechanisms not only to alleviate direct effects of gossypol but also indirect damage such as pH disturbance and oxygen radical formation. Genes discovered through this transcriptional approach may be additional candidates for understanding gossypol detoxification and coping with gossypol-induced stress. In a generalist herbivore that has evolved transcriptionally-regulated responses to a variety of different plant compounds, hormesis may be due to a lower induction threshold of growth-promoting, stress-coping responses and a higher induction threshold of detoxification pathways that are costly and cause collateral damage to the cell.

An estrogen-responsive plasma protein expression signature in Atlantic cod (Gadus morhua) revealed by SELDI-TOF MS

Compound-specific protein expression signatures (PESs) can be revealed by proteomic techniques. The SELDI-TOF MS approach is advantageous due to its simplicity and high-throughput capacity, however, there are concerns regarding the reproducibility of this method. The aim of this study was to define an estrogen-responsive PES in plasma of Atlantic cod (Gadus morhua) using the SELDI-TOF MS technique. Protein expression analysis of male cod exposed to 17β-estradiol (E₂) showed that 27 plasma peaks were differentially expressed following exposure. The reproducibility of this result was evaluated by reanalyzing the samples six months later, and a significant change in expression was confirmed for 13 of the 27 peaks detected in the first analysis. The performance of the reproducible E₂-responsive PES, constituting these 13 peaks, was then tested on samples from juvenile cod exposed to 4-nonylphenol, North Sea oil, or North Sea oil spiked with alkylphenols. Principal component analysis revealed that nonylphenol-exposed cod could be separated from unexposed cod based on the E₂-responsive PES, indicating that the PES can be used to assess estrogenic exposure of both juvenile and adult specimens of cod. A targeted antibody-assisted SELDI-TOF MS approach was carried out in an attempt to identify the E₂-responsive peaks. Results indicated that 2 peaks were fragments of the well-known biomarkers VTG and/or ZRP. In this study, the SELDI-TOF MS technology has shown its potential for defining compound-specific PESs in fish. Nevertheless, thorough validation of reproducibility, specificity and sensitivity of a PES is required before it can be applied in environmental monitoring.

Transcriptomic analyses in a benthic fish exposed to contaminated estuarine sediments through laboratory and in situ bioassays

The transcription of contaminant response-related genes was investigated in juvenile Senegalese soles exposed to sediments from three distinct sites (a reference plus two contaminated) of a Portuguese estuary (the Sado, W Portugal) through simultaneous 28-day laboratory and in situ bioassays. Transcription of cytochrome P450 1A (CYP1A), metallothionein 1 (MT1), glutathione peroxidase (GPx), catalase (CAT), caspase 3 (CASP3) and 90 kDa heat-shock protein alpha (HSP90AA) was surveyed in the liver by real-time PCR. CASP3 transcription analysis was complemented by surveying apoptosis through the TUNEL reaction. After 14 days of exposure, relative transcription was either reduced or decreased in fish exposed to the contaminated sediments, revealing a disturbance stress phase during which animals failed to respond to insult. After 28 days of exposure all genes' transcription responded to contamination but laboratory and in situ assays depicted distinct patterns of regulation. Although sediments revealed a combination of organic and inorganic toxicants, transcription of the CYP1A gene was consistently correlated to organic contaminants. Metallothionein regulation was found correlated to metallic and organic xenobiotic contamination in the laboratory and in situ, respectively. The transcription of oxidative stress-related genes can be a good indicator of general stress but caution is mandatory when interpreting the results since regulation may be influenced by multiple factors. As for MT1, HSP90 up-regulation has potential to be a good indicator for total contamination, as well as the CASP3 gene, even though hepatocyte apoptosis depicted values inconsistent with sediment contamination, showing that programmed cell death did not directly depend on caspase transcription alone.

Transcriptional profiling in Saccharomyces cerevisiae relevant for predicting alachlor mechanisms of toxicity

Alachlor has been a commonly applied herbicide and is a substance of ecotoxicological concern. The present study aims to identify molecular biomarkers in the eukaryotic model Saccharomyces cerevisiae that can be used to predict potential cytotoxic effects of alachlor, while providing new mechanistic clues with possible relevance for experimentally less accessible eukaryotes. It focuses on genome-wide expression profiling in a yeast population in response to two exposure scenarios exerting effects from slight to moderate magnitude at phenotypic level. In particular, 100 and 264 genes, respectively, were found as differentially expressed on a 2-h exposure of yeast cells to the lowest observed effect concentration (110 mg/L) and the 20% inhibitory concentration (200 mg/L) of alachlor, in comparison with cells not exposed to the herbicide. The datasets of alachlor-responsive genes showed functional enrichment in diverse metabolic, transmembrane transport, cell defense, and detoxification categories. In general, the modifications in transcript levels of selected candidate biomarkers, assessed by quantitative reverse transcriptase polymerase chain reaction, confirmed the microarray data and varied consistently with the growth inhibitory effects of alachlor. Approximately 16% of the proteins encoded by alachlor-differentially expressed genes were found to share significant homology with proteins from ecologically relevant eukaryotic species. The biological relevance of these results is discussed in relation to new insights into the potential adverse effects of alachlor in health of organisms from ecosystems, particularly in worst-case situations such as accidental spills or careless storage, usage, and disposal.

Global DNA methylation in earthworms: a candidate biomarker of epigenetic risks related to the presence of metals/metalloids in terrestrial environments

In this work, possible relationships between global DNA methylation and metal/metalloid concentrations in earthworms have been explored. Direct correlation was observed between soil and tissue As, Se, Sb, Zn, Cu, Mn, Ag, Co, Hg, Pb (p< 0.05). Speciation results obtained for As and Hg hint at the capability of earthworms for conversion of inorganic element forms present in soil to methylated species. Inverse correlation was observed between the percentage of methylated DNA cytosines and total tissue As, As + Hg, As + Hg + Se + Sb (β = -0.8456, p = 0.071; β = -0.9406, p = 0.017; β = -0.9526, p = 0.012 respectively), as well as inorganic As + Hg (β = -0.8807, p = 0.049). It was concluded that earthworms would be particularly helpful as bioindicators of elements undergoing in vivo methylation and might also be used to assess the related risk of epigenetic changes in DNA methylation.

Changes in gene transcription and whole organism responses in larval fathead minnow (Pimephales promelas) following short-term exposure to the synthetic pyrethroid bifenthrin

The combination of molecular and whole-organism endpoints in ecotoxicology provides valuable information about the ecological relevance of sublethal stressor effects in aquatic ecosystems such as those caused by the use of insecticides and translocation of their residues into surface waters. This study contributes knowledge about the sublethal effects of a common use insecticide, the synthetic pyrethroid bifenthrin, on larval fathead minnow (Pimephales promelas). Transcriptomic responses, assessed by quantitative real-time PCR, combined with individual effects on swimming performance were used to estimate the ecological relevance of insecticide impacts. Significant transcriptomic responses were observed at 0.07 μg L(-1) bifenthrin (lowest observed effect concentration, LOEC) but mostly followed a biphasic rather than a linear dose-response with increasing concentration. Transcript patterns for genes involved in detoxification, neuromuscular function and energy metabolism were linked to an impairment of swimming performance at ≥0.14 μg L(-1) bifenthrin. With increasing treatment concentration, a significant down-regulation was observed for genes coding for cyp3a, aspartoacylase, and creatine kinase, whereas metallothionein was up-regulated. Additionally, bifenthrin induced endocrine responses as evident from a significant up-regulation of vitellogenin and down-regulation of insuline-like growth factor transcripts. Recovery occurred after 6 days and was dependent on the magnitude of the initial stress. During the recovery period, down-regulation of vitellogenin was observed at lowest exposure concentrations. The data presented here emphasize that links can be made between gene transcription changes and behavioral responses which is of great value for the evaluation and interpretation of biomarker responses.

Comparative effects of butyl benzyl phthalate (BBP) and di(2-ethylhexyl) phthalate (DEHP) on the aquatic larvae of Chironomus riparius based on gene expression assays related to the endocrine system, the stress response and ribosomes

In this work, the effects of butyl benzyl phthalate (BBP) and di(2-ethylhexyl) phthalate (DEHP), two of the most extensively used phthalates, were studied in Chironomus riparius under acute short-term treatments, to compare their relative toxicities and identify genes sensitive to exposure. The ecotoxicity of these phthalates was assessed by analysis of the alterations in gene expression profiles of selected inducible and constitutive genes related to the endocrine system, the cellular stress response and the ribosomal machinery. Fourth instar larvae, a model system in aquatic toxicology, were experimentally exposed to five increasing concentrations (0.01, 0.1, 1, 10, and 100mg/L) of DEHP and BBP for 24h. Gene expression was analysed by the changes in levels of transcripts, using RT-PCR techniques with specific gene probes. The exposures to DEHP or BBP were able to rapidly induce the hsp70 gene in a concentration-dependent manner, whereas the cognate form hsc70 was not altered by either of these chemicals. Transcription of ribosomal RNA as a measure of cell viability, quantified by the levels of ITS2, was not affected by DEHP, but was slightly, yet significantly, downregulated by BBP at the highest concentrations tested. Finally, as these phthalates are classified as endocrine disruptor chemicals (EDCs), their potential effect on the ecdysone endocrine system was studied by analysing the two genes, EcR and usp, of the heterodimeric ecdysone receptor complex. It was found that BBP provoked the overexpression of the EcR gene, with significant increases from exposures of 0.1mg/L and above, while DEHP significantly decreased the activity of this gene at the highest concentration. These data are relevant as they show for the first time the ability of phthalates to interfere with endocrine marker genes in invertebrates, demonstrating their potential capacity to alter the ecdysone signalling pathway. Overall, the study clearly shows a differential gene-toxin interaction for these two phthalates and adds novel genomic tools for biomonitoring environmental xenobiotics in insects.

Physiology and mRNA expression in rainbow trout (Oncorhynchus mykiss) after long-term exposure to the new antifoulant medetomidine

Medetomidine is under evaluation for use as an antifouling agent, and its effects on non-target aquatic organisms are therefore of interest. In this study, rainbow trout was exposed to low (0.5 and 5.0nM) concentrations of medetomidine for up to 54 days. Recently we have reported on effects on paleness and melanophore aggregation of medetomidine in these fish. Here, specific growth rates were investigated together with a broad set of physiological parameters including plasma levels of growth hormone (GH), insulin-like growth factor-I (IGF-I) and leptin, glucose and haemoglobin (Hb), hematocrit (Ht), condition factor, liver and heart somatic indexes (LSI, HSI). Hepatic enzyme activities of CYP1A (EROD activity), glutathione S-transferases (GST) and glutathione reductase (GR) were also measured. Additionally, hepatic mRNA expression was analysed through microarray and quantitative PCR in fish sampled after 31 days of exposure. Medetomidine at both concentrations significantly lowered blood glucose levels and the higher concentration significantly reduced the LSI. The mRNA expression analysis revealed few differentially expressed genes in the liver and the false discovery rate was high. Taken together, the results suggest that medetomidine at investigated concentrations could interfere with carbohydrate metabolism of exposed fish but without any clear consequences for growth.

Microarray analyses of shrimp immune responses

Shrimp aquaculture is one of the major foodproducing industries in the world. However, it is being impacted by several problems including diseases, antibiotic use, and environmental factors. The extent of the effects of these problems in the immune system of the shrimp at the molecular level is just beginning to be understood. Here, we review the gene expression profile of shrimp in response to some of these problems using the high-throughput microarray analysis, including white spot syndrome virus, yellow head virus, Vibrio spp., peptidoglycan, oxytetracycline, oxolinic acid, salinity, and temperature.