The snow alga Chlamydomonas nivalis is a typical microalgal species that can adapt and resist to natural habitats in the polar region and similar extreme environments. In response to various stress conditions, the change of lipid profile in cell membrane systems is known to play a vital role in cell survival and reproduction. In the present work, to elucidate the involvement of intracellular lipids in the molecular mechanism of cell response and adaptation to salt stress, C. nivalis was cultured and treated with different sodium chloride (NaCl) concentrations in different time courses. The ultra performance liquid chromatography/quadrupole-TOF-MS (UPLC/Q-TOF-MS)-based approach was developed for lipidomic profiling followed by multivariate statistical analysis including partial least squares discriminant analysis and orthogonal projection on latent structure discriminant analysis for data classification and potential biomarkers selection. Seven types and 35 kinds of polar lipid molecules were selected and identified as biomarkers, including monogalactosyldiacylglycerol, digalactosyldiacylglycerol, l, 2-diacylglyceryl-3-O-4 0 -(N,N,Ntrimethyl)-homoserine, phosphatidylglycerol, sulfoquinovosyl-diacylglycerol, phosphatidylethanolamine, and phosphatidylinositiol. Their functions in relation to the regulation of cell membrane stability, signal transduction and photosynthesis efficiency under salt stress are also discussed in this paper. This is the first study using UPLC/Q-TOF-MS-based lipidomic profiling with multivariate statistical analysis for lipid biomarkers discovery from microalgae in response to stress conditions.
IntroductionLipids, once simply regarded as structural components in cells, are now known to play a vital role in transcriptional and translational control, cellular signaling, cell-cell interactions, and act as indicators responding to changes in the environment where cells or organisms survive [1]. The lipid composition of microorganisms can exhibit considerable variations with a changing environment [2,3]. These changes may result in alteration of physical characteristics in their membranes which enable microorganisms to maintain membrane fluidity, integrity, and functionality in adaptation to environmental fluctuations [4]. However, the pathways regarding how the functional lipids change in cells in response to the multiple stress conditions are still not clear, especially at the lipidomic level.Typically, methods for intact lipid analysis involve total lipid extraction followed by thin-layer chromatography (TLC) separation of lipid classes, removal of TLC spots Abbreviations: CIJF JK , jack-knifed confidence interval; DGDG, digalactosyldiacylglycerol; DGTS, l, 2-diacylglyceryl-3-O-4 0 -(N,N,N-trimethyl)-homoserine; MGDG, monogalactosyldiacylglycerol; OPLS-DA, orthogonal projection on latent structure discriminant analysis; PE, phosphatidylethanolamine; PG, phosphatidylglycerol; PI, phosphatidylinositiol; PLS-DA, partial least squares discriminant analysis; RT, retention time; SQDG, sulfoquinovo...