Abstract
Benzotriazoles (BZTs) are ubiquitous aquatic contaminants used in a wide range of industrial and domestic applications from aircraft deicers to dishwasher tablets. Acute toxicity has been reported in aquatic organisms for some of the BZTs but their mode of action remains unknown. The objectives of this study were to evaluate the transcriptomic response of D. magna exposed to sublethal doses of 1H-benzotriazole (BTR), 5-methyl-1H-benzotriazole (5MeBTR) and 5-chloro-1H-benzotriazole (5ClBTR) using RNA-sequencing and quantitative real-time PCR. Cellular and life-history endpoints (survival, number of neonates, growth) were also investigated. Significant effects on the molting frequency were observed after 21-d exposure to 5MeBTR and 5ClBTR. No effects on molting frequency were observed for BTR but RNA-seq results indicated that this BZT induced the up-regulation of genes coding for cuticular proteins, which could have compensated the molting disruption. Molting in cladocerans is actively controlled by ecdysteroid hormones. Complementary short-term temporal analysis (4- and 8-d exposure) of the transcription of genes related to molting and hormone-mediated processes indicated that the three compounds had specific modes of action. BTR induced the transcription of genes involved in 20-hydroxyecdysone synthesis, which suggests pro-ecdysteroid properties. 5ClBTR exposure induced protein activity and transcriptional levels of chitinase enzymes, associated with an impact on ecdysteroid signaling pathways, which could explain the decrease in molt frequency. Finally, 5MeBTR seemed to increase molt frequency through epigenetic processes. Overall, results suggested that molting effects observed at the physiological level could be linked to endocrine regulation impacts of BZTs at the molecular level.
Highlights
Benzotriazoles (BZTs) are a family of high production volume (HPV) chemicals [1] that are used in a broad range of industrial, domestic, and commercial applications and products
The frequency of molting was not impacted by BTR but was significantly altered by both 5MeBTR and 5ClBTR. 5MeBTR significantly increased the molting frequency in D. magna after 21-d exposure to 2 mg/L compared to unexposed controls, whereas 5ClBTR chronic exposure resulted in a significant decreased number of molts in response to both concentrations of 2 μg/L and 2 mg/L (Fig 2)
5ClBTR seemed to induce an increase in the transcription of cyp18a1 with time, despite a lack of significance (Fig 6C). This enzyme is known to regulate the decline of 20HE titers in Daphnia before molting [109] and could explain the low transcription levels of ecr and usp observed in the present study (Fig 6A and 6B). These results suggest that the decreased molt frequency observed in response to 5ClBTR seemed to be the result of a perturbation of ecdysteroid signaling pathways rather than methyl farnesoate (MF)-mediated anti-ecdysteroid activities
Summary
Benzotriazoles (BZTs) are a family of high production volume (HPV) chemicals [1] that are used in a broad range of industrial, domestic, and commercial applications and products. Chemicalsubstanceschimiques.gc.ca/plan/indexeng.php, and the Strategic Technology Application of Genomics in the Environment (STAGE) program http://www.ec.gc.ca/scitech/default.asp?lang= En&n=BA7C049C-1.
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