While selenium (Se) has been demonstrated to be essential for the optimal growth of freshwater microalgae Chlamydomonas reinhardtii [1], exposure to elevated concentrations of selenite (Se[IV]) or selenate (Se[VI]), the two major aqueous forms of Se, induce cell toxicity[2]. In this study, Chlamydomonas reinhardtii (cc.1690) cells have been grown in the presence of Se[VI] at increasing concentrations of 20, 50, 100 and 150 μM. Se determination obtained using ICP-MS upon cell digestion revealed that the uptake of Se follows a linear pattern with Se amounts determined at 10.7 and 103.6 fg per cell for the 20 and 150 μM incubation, respectively. In order to gain further information on the protein-bound cell internalized Se, size-exclusion chromatography coupled to ICP-MS (SEC-ICP-MS) was employed. Results demonstrated that an average 41% ± 6% of the uptaken Se, for all incubation concentrations, is protein-bound, while the existence of a low intensity chromatographic peak adjacent to the elution time of inorganic Se suggests the incorporation of Se into smaller biomolecules such as Se-cysteine and/or Se-methionine. Mass spectra from the direct lipidomic analysis of cells, obtained using desorption ambient mass spectrometry (EASI-MS), demonstrated a higher degree of saturation for 2 classes of membrane lipids, i.e., phosphatidylglycerol (PG) and sulfoquinovosyl diacylglycerol (SQDG), suggesting that reorganization of cell membrane lipids is taking place upon cell interaction with increasing amounts of Se[VI].

[1] S. V. Novoselov, M. Rao, N. V. Onoshko, H. Zhi, G. V. Kryukov, Y. Xiang, D.P. Weeks, D.L. Hatfield, V.N. Gladyshev, Selenoproteins and selenocysteine insertion system in the model plant cell system, Chlamydomonas reinhardtii, EMBO J. 21 (2002) 3681–3693. https://doi.org/10.1093/emboj/cdf372.
[2] B. Vriens, R. Behra, A. Voegelin, A. Zupanic, L.H.E. Winkel, Selenium Uptake and Methylation by the Microalga Chlamydomonas reinhardtii, Environ. Sci. Technol. 50 (2016) 711–720. https://doi.org/10.1021/acs.est.5b04169.