Analysis of the Elodea nuttallii Transcriptome in Response to Mercury and Cadmium Pollution: Development of Sensitive Tools for Rapid Ecotoxicological Testing

Abstract

Toxic metals polluting aquatic ecosystems are taken up by inhabitants and accumulate in the food web, affecting species at all trophic levels. It is therefore important to have good tools to assess the level of risk represented by toxic metals in the environment. Macrophytes are potential organisms for the identification of metal-responsive biomarkers but are still underrepresented in ecotoxicology. In the present study, we used next-generation sequencing to investigate the transcriptomic response of Elodea nuttallii exposed to enhanced concentrations of Hg and Cd. We de novo assembled more than 60 000 contigs, of which we found 170 to be regulated dose-dependently by Hg and 212 by Cd. Functional analysis showed that these genes were notably related to energy and metal homeostasis. Expression analysis using nCounter of a subset of genes showed that the gene expression pattern was able to assess toxic metal exposure in complex environmental samples and was more sensitive than other end points (e.g., bioaccumulation, photosynthesis, etc.). In conclusion, we demonstrate the feasibility of using gene expression signatures for the assessment of environmental contamination, using an organism without previous genetic information. This is of interest to ecotoxicology in a wider sense given the possibility to develop specific and sensitive bioassays.

Transcriptomic responses of the endangered freshwater mussel Margaritifera margaritifera to trace metal contamination in the Dronne River, France

“…In this aim, we conducted a large-scale and without a priori RNA-Seq-based approach. RNA-Seq technology offers the opportunity for ecotoxicologists to investigate the effects of contaminants on transcriptome-wide response in non-model but environmentally relevant species (Regier et al 2013;Uren Webster et al 2013) for which molecular information are limited such as M. margaritifera (González et al 2015). Gene expression profiling using RNA-seq could play a key role in identifying new biomarkers of exposure and adverse effects and in discovering new toxicity pathways (Connon et al 2012;Gonzalez and Pierron 2015).…”

Mercury Resistance and Removal Mechanisms of Pseudomonas sp. Isolated Mercury-contaminated Site in Taiwan

“…There were 3 genes encoding the sugar transporter (namely, sugar ABC transporter periplasmic protein, MFS transporter, rhizopinebinding protein). Similarly, the up-regulation of sugar-catabolizing enzymes was observed in Elodea nuttallii (Regier et al, 2013) treated with Hg. The other genes encoded proteins for diverse biological function.…”

“…Hg pollution using Illumina sequencing (Regier et al, 2013), indicating that Illumina sequencing was a sensitive tool for rapid ecotoxicological testing.…”

Towards Mechanistic Understanding of Mercury Availability and Toxicity to Aquatic Primary Producers

“…[32] Whole transcriptome response of E. nut tallii exposed to increasing HgCl 2 concentrations from ca.1 nM to 5 µM revealed up-regulation of proteins (e.g. chaperones) known for their stress response function.…”

“…[19] The hypothesis of Hg uptake via high affinity Cu transporters was further supported by transcriptomic analysis revealing decrease of EnCOPT1 gene expression at increasing Hg II concentrations. [32] Thus the possible involvement of Hg 2+ binding to membrane transporters, is not as straightforward as for other metals. [15,33] Similarly to other trace metals, the above-mentioned processes at the biotamedium interface can be influenced by: [33] (i) the characteristics of the cell wall and biological membrane; (ii) the reactivity of the species towards the biological membranes; (iii) the water quality parameters, such as pH and water hardness; (iv) the presence and concentrations of micronutrients and toxic trace metals; (v) the presence of different ligands of natural (e.g.…”