Metabolomics characterizes low-molecular-weight molecules involved in different biochemical reactions and provides an integrated assessment of the physiological state of an organism. By using liquid chromatography-mass spectrometry targeted metabolomics, we examined the response of green alga Chlamydomonas reinhardtii to sublethal concentrations of inorganic mercury (IHg) and monomethylmercury (MeHg). We quantified the changes in the levels of 93 metabolites preselected based on the disturbed metabolic pathways obtained in a previous transcriptomics study. Metabolites are downstream products of the gene transcription; hence, metabolite quantification provided information about the biochemical status of the algal cells exposed to Hg compounds. The results showed that the alga adjusts its metabolism during 2 h exposure to 5 × 10^-9 and 5 × 10^-8 mol L^-1 IHg and MeHg by increasing the level of various metabolites involved in amino acid and nucleotide metabolism, photorespiration, and tricarboxylic acid (TCA) cycle, as well as the metabolism of fatty acids, carbohydrates, and antioxidants. Most of the metabolic perturbations in the alga were common for IHg and MeHg treatments. However, the exposure to IHg resulted in more pronounced perturbations in the fatty acid and TCA metabolism as compared with the exposure to MeHg. The observed metabolic perturbations were generally consistent with our previously published transcriptomics results for C. reinhardtii exposed to the comparable level of IHg and MeHg. The results highlight the potential of metabolomics for toxicity evaluation, especially to detect effects at an early stage of exposure prior to their physiological appearance.

Mechanistic understanding of the interaction of copper-based nanomaterials with crops is crucial for exploring their application in precision agriculture and their implications on plant health. We investigated the biological response of soybean (Glycine max) plants to the foliar application of copper hydroxide nanowires (CNWs) at realistic exposure concentrations. A commercial copper based-fungicide (Kocide), dissolved copper ions, and untreated controls were used for comparison to identify unique features at physiological, cellular, and molecular levels. After 32 d of exposure to CNW (0.36, 1.8, and 9 mg CNW/plant), the newly developed tissues accumulated significantly high levels of Cu (18-60 μg/g) compared to Kocide (10 μg/g); however, the rate of Cu translocation from the site of CNW treatment to other tissues was slower compared to other Cu treatments. Like Kocide, CNW exposure at medium and high doses altered Co, Mn, Zn, and Fe accumulation in the tissues and enhanced photosynthetic activities. The proteomic and metabolomic analyses of leaves from CNW-treated soybean plants suggest a dose-dependent response, resulting in the activation of major biological processes, including photosynthesis, energy production, fatty acid metabolism, lignin biosynthesis, and carbohydrate metabolism. In contrast to CNW treatments, Kocide exposure resulted in increased oxidative stress response and amino acid metabolism activation.

Silver nanoparticles (AgNPs) are one of the most used engineered nanomaterials. Despite progress in assessing their environmental implications, knowledge gaps exist concerning the metabolic perturbations induced by AgNPs on phytoplankton, essential organisms in global biogeochemical cycles and food-web dynamics. We combine targeted metabolomics, biouptake and physiological response studies to elucidate metabolic perturbations in alga Poterioochromonas malhamensis induced by AgNPs and dissolved Ag. We show time-dependent perturbation of the metabolism of amino acids, nucleotides, fatty acids, tricarboxylic acids, photosynthesis and photorespiration by both Ag-treatments. The results suggest that dissolved Ag ions released by AgNPs are the major toxicity driver; however, AgNPs internalized in food vacuoles contributed to the perturbation of amino acid metabolism, TCA cycle and oxidative stress. The metabolic perturbations corroborate the observed physiological responses. We highlight the potential of metabolomics as a tool for understanding the molecular basis for these metabolic and physiological changes, and for early detection of stress.