Abstract
Mercury contamination in aquatic systems poses a serious environmental stress to phototrophic plankton. We used Euglena gracilis to gain an understanding of the physiochemical changes resulting from mercury stress across the transcriptome and metabolome. Using a combination of Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (FT-ICR-MS) and RNA-sequencing, we identified metabolomic and transcriptomic changes both within and outside cellular space after mercury exposure. Metabolic profiles of E. gracilis were less diverse after mercury exposure, highlighting an overall refinement of metabolites produced. Significant fold changes in cysteine, glutathione, and amino acid-based metabolites were significantly higher (p < 0.05) within the mercury exposed cells and in extracellular space than in untreated cultures. Using integrated omics analyses, a significant upregulation of transcripts and metabolites involved in amino acid synthesis, cellular responses to chemical stress, reactive oxygen species detoxification, and electron transport were identified. Together the enrichment of these pathways highlights mechanisms that E. gracilis harness to mitigate oxidative stress at sublethal concentrations of mercury exposure and give rise to new biomarkers of environmental stress in the widely distributed E. gracilis.
Highlights
Since the industrial revolution, anthropogenic activities have contributed to increased mercury (Hg) concentrations in the environment
A significant enrichment of transfrags, metabolites, and pathways corresponding to metabolism and amino acid synthesis was observed within E. gracilis cells after nonlethal exposure to Hg, suggesting that the production of amino acids aids E. gracilis in Hg tolerance
This study presents the integration of transcriptomics and metabolomics to gain comprehensive information regarding the cellular responses of E. gracilis to sublethal concentrations of Hg(II) exposure
Summary
Anthropogenic activities have contributed to increased mercury (Hg) concentrations in the environment. Despite environmental restrictions on emissions in 1950, legacy anthropogenic derived Hg still cycles around the world (Amos et al, 2013; Lepak et al, 2019). Oxidized Hg (Hg0) enters the atmosphere mainly because of combustion from smelting, manufacturing processes, and infrastructure development (Saiz-Lopez et al, 2018). Hg0 is globally dispersed, travelling in the atmosphere before being reduced to inorganic Hg (Hg (II)) and deposited to terrestrial and aquatic sources. Hg (II) contamination is a global issue that threatens neurological health in biota across aquatic and terrestrial systems. In microalgae low parts per million (ppm) concentrations of Hg (II) often results in increased plasma membrane permeability, chlorophyll degradation, reduced
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