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The effects of a wastewater effluent on population, transcriptomic and metabolomic markers in the freshwater amphipod Gammarus fossarum

Student thesis: Doctoral Thesis

  • Domenico Roberto Caputo
In order to prevent further deterioration of river quality in response to anthropogenic contaminants released into freshwaters through wastewater treatment plants (WWTPs), European countries, including Switzerland, financed important river monitoring plans. In addition, measures to improve the sewage treatment technologies were also proposed. Due to a central role in aquatic food
web and a marked sensitivity to xenobiotics, the amphipod Gammarus fossarum
has been defined as an ideal biomarker species for ecotoxicological risk
assessment. However, its genome has not yet been completely annotated and
attempts to monitor dysfunctions in invertebrates using biomarkers in fish species have produced inconsistent results. The present project was aimed to investigate the impact of a contaminant mixture released by a Swiss sewage effluent on the amphipod species Gammarus fossarum. In addition, the transcriptomic and metabolomic differences between male and female amphipods were also explored, in order to increase the knowledge on crustacean sexual biology. Firstly, the concentrations of 55 xenobiotics (pesticides and pharmaceuticals) commonly detected in river waters were measured up- and downstream of the WWTP, in both water samples and amphipods. An evaluation of the differences in the population structure between amphipods sampled above and below the effluent was conducted annually between September 2017 and 2018. A high-throughput sequencing of total RNA from G. fossarum was performed employing an Illumina HiSeq 2500 sequencing platform. The complete transcriptome of G. fossarum was assembled and annotated de novo and the changes in gene expression between G. fossarum sampled up- and downstream of the WWTP were investigated. In addition, the differentially expressed genes between male and female amphipods were also explored. Finally, an Ultra Performance Liquid Chromatography - Mass Spectrometry (UPLC-MS) platform was employed to investigate the metabolomic fingerprints in male and female G. fossarum sampled up- and downstream of the effluent. The differential “omics” analyses showed variations in general stress biomarkers, primary metabolism and mitochondrial metabolism in amphipods sampled at the downstream site. However, the toxic pressure did not cause observable abnormalities in amphipod population structures. The comparative analyses of male and female transcriptome and metabolome between animals sampled above and below the effluent showed that the genders may respond differently to anthropogenic pollutants in aquatic environments. Terms related to heart and circulatory processes, muscle system and cell differentiation were found when conducting a gene ontology (GO) analysis on the differentially expressed genes between males and females, suggesting that the sex distinction traits in hormonal system may act on a wide spectrum of molecular networks. Given the lack of molecular information on amphipod species, the data set collected in this project will be useful in future studies to develop new ecotoxicological biomarkers in amphipods.
Original languageEnglish
Awarding Institution
Thesis sponsors
  • Swiss Federal Institute of Aquatic Science and Technology
Award dateMay 2020


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