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The copepod Eurytemora affinis as a relevant species to assess estuarine sediment toxicity by combining sub-individual and individual endpoints: effects on gene expression and swimming behavior

ABSTRACT: Compared to freshwater ecosystems, the health status of estuarine waters remains little studied despite their importance for many species. They also represent a zone of interest for Human settlements that make them the final sink of pollution in both the water column and sediment. Once in sediments, pollutants could represent a threat to benthic as well as pelagic estuarine species through resuspension events. In the Seine estuary, the copepod Eurytemora affinis has been previously presented as a relevant species to assess resuspended sediment contamination through the use of fitness-related effects at the individual level. The aim of the present study was to use E. affinis copepods to assess estuarine sediment-derived elutriates toxicity using both a molecular (i.e. transcriptomics) and a behavioral approach. Two sites along the Seine estuary were sampled. They were both under anthropic pressures from the industrial-port activities or wastewater treatment plants (i.e. Tancarville) or agricultural pressure from freshwater affluent (i.e. Fatouville). The analysis of sediments used to prepare elutriates reveals that both sites have close contamination profiles. The transcriptomic analysis reveals that exposure to both sites triggers the dysregulation of genes involved in biological function as defense response, immunity, ecdysone pathway or neurotoxicity. This analysis also reveals a higher count of dysregulated genes in the Fatouville site compared to the Tancarville despite their close contamination profile. These results emphasize the sensitivity of this molecular approach to assess environmental matrix toxicity with E. affinis. The analysis of the swimming behavior of E. affinis did not highlight significant effects after both sites elutriate exposure. However, our strategy to assess E. affinis swimming behavior (i.e the combination of the DanioVision observation chamber and the EthoVision analysis software) allows the discrimination of basal swimming behavior in this species. Thus, it represents a promising standardized tool to assess copepods swimming behavior in ecotoxicological studies.

ORGANISM(S): Eurytemora affinis

PROVIDER: GSE235722 | GEO | 2024/09/30

REPOSITORIES: GEO

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Project description:Chemical contamination is a common threat to biota thriving in estuarine and coastal ecosystems. In particular, trace metals tend to accumulate and exert deleterious effects on small invertebrates such as zooplankton, which are essential trophic links between phytoplankton and higher-level consumers in aquatic food webs. Beyond the direct effects of the contamination, we hypothesized that metal exposure could also affect the zooplankton microbiota, which in turn might further impair host fitness. To assess this assumption, copepods (Eurytemora affinis) were sampled in the oligo-mesohaline zone of the Seine estuary and exposed to dissolved copper (25 µg.L-1) over a 72-hour time period. Copepod response to copper treatment was assessed by determining transcriptomic changes in E. affinis along with shifts in its microbiota. Unexpectedly, very few genes were differentially expressed in copper-treated copepods compared to controls, with most of the reported differences involving genes upregulated in males compared to females. In contrast, copper increased the taxonomic diversity indices of the microbiota and resulted in substantial compositional changes at both the phyla and genus levels. Phylogenetic reconstruction of the microbiota further suggested that copper mitigated phylogenetic relatedness of taxa at the basal tree structure of the phylogeny, whereas it strengthened it at the terminal branches. Increased terminal phylogenetic clustering in copper-treated copepods concurred with higher proportions of bacterial genera previously identified as copper resistant (e.g., Pseudomonas, Acinetobacter, and Alkanindiges) and a higher relative abundance of the copA gene encoding a periplasmic inducible multi-copper oxidase. Overall, these results revealed very contrasting responses of E. affinis and its microbiota to copper exposure. The enrichment in micro-organisms likely to perform copper sequestration and/or enzymatic transformation processes, underlines here the need to follow the microbial component during the evaluation of the vulnerability of the zooplankton to the metallic stress.

Project description:The abundance of bacterial (AOB) and archaeal (AOA) ammonia oxidisers, assessed using quantitative PCR measurements of their respective a-subunit of the ammonia monooxygenase (amoA) genes, and ammonia oxidation rates were measured in four contrasting coastal sediments in the Western English Channel. Sediment was sampled bimonthly from July 2008 to May 2011, and measurements of ammonia oxidiser abundance and activity compared to a range of environmental variables including salinity, temperature, water column nutrients and sediment carbon and nitrogen content. Despite a higher abundance of AOA amoA genes within all sediments, and at all time-points, rates of ammonia oxidation correlated with AOB and not AOA amoA gene abundance. Other than ammonia oxidation rate, sediment particle size was the only variable that correlated with the spatial and temporal patterns of AOB amoA gene abundance, implying a preference of the AOB for larger sediment particles. This is possibly due to deeper oxygen penetration into the sandier sediments, increasing the area available for ammonia oxidation to occur, higher concentrations of inhibitory sulphide with pore waters of muddier sediments or a combination of both oxygen and sulphide concentrations. Similar to many other temporal studies of nitrification within estuarine and coastal sediments, decreases in AOB amoA gene abundance were evident during summer and autumn, with maximum abundance and ammonia oxidation rates occurring in winter and early spring. The lack of correlation between AOA amoA gene abundance and ammonium oxidation rate suggests an alternative role for amoAÂ-carrying AOA within these sediments. Two color array (Cy3 and Cy5): the universal standard 20-mer oligo is printed to the slide with a 70-mer oligo (an archetype). Environmental DNA sequences (fluoresced with Cy3) within 15% of the 70-mer conjugated to a 20-mer oligo (fluoresced with Cy5) complementary to the universal standard will bind to the oligo probes on the array. Signal is the ratio of Cy3 to Cy5. Three replicate probes were printed for each archetype. Two replicate arrays were run on duplicate targets.

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The copepod Eurytemora affinis as a relevant species to assess estuarine sediment toxicity by combining sub-individual and individual endpoints: effects on gene expression and swimming behavior

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