Selenate uptake by Chlamydomonas reinhardtii Algal Cells, its Transformation and its Effect on Membrane Lipid Profiles

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.