(182a) Lipidomic Profiling and Biomarker Discovery of the Snow Algae Chlamydomonas Nivalis by Salt Stress

Microalgae can respond quickly to the stress environments through a variety of molecular mechanisms for survival. Salinity is one of the most important factors in these harsh environments. Under extremely high salinity conditions, microalgae show various mechanisms, such as reducing osmotic stresses, protecting chloroplast functions and/or maintaining ion homeostasis, etc. The regulation of lipid biosynthesis in microalgae is considered a crucial pathway in resistant physiology to stress stimulus which, however, is still not fully understood.

In the present work, Chlamydomonas nivalis, the snow alga which is found in polar region and similar extreme environments, was used to as a model organism to investigate the mechanism of cell response and adaptation to salt stress on the lipidomic level. The 6-day culture of C. nivalis UTEX LB 2824 in Bold 1NV medium under autotrophic growth was stressed by NaCl with final concentrations of 0.25%, 0.50%, 1.00% for 1, 7, 15 h, respectively. Ten mg of dried biomass from each stressed culture was extracted with CHCl₃:CH₃OH:H₂O containing BHT to obtain the total lipids. All lipid samples were analyzed by a novel approach of UPLC/Q-TOF-MS-based lipidomic profiling coupled with multivariate statistical analysis for lipid biomarker discovery. 4,975 peaks of ions in ESI positive mode and 1,016 peaks of ions in ESI negative mode were presented in Based Peak Intensity (BPI) chromatograms. The data of both ESI modes were normalized and pareto-scaled followed by feeding to SIMCA-P⁺ V12.0 software to perform PLS-DA models, respectively. The samples were basically classified into three catalogues in PLS-DA score plots: 0.25%-NaCl/control, 0.5%-NaCl and 1%-NaCl group. 0.25%-NaCl group has insignificant difference with the control on lipid profile, but significantly different with 0.5%-NaCl and 1%-NaCl group. The time of NaCl stress had little effect on lipid profile. Three pairs of groups, control/0.5%-NaCl, control/1.0%-NaCl and 0.5%-NaCl/1.0%-NaCl, were analyzed separately by OPLS-DA models to select potential biomarkers. Twenty-six ions in ESI positive mode and nine ions in ESI negative mode were finally selected as lipid biomarkers and then identified by resolving the structure. All biomarkers are polar lipids and belong to seven types and thirty-five kinds, including three of MGDG, five of DGDG, sixteen of DGTS, two of PG, four of SQDG, four of PE and one of PI, which are in relation to the regulation of cell membrane stability, signal transduction and photosynthesis efficiency. These results demonstrated C. nivalis had developed a plethora of biochemical mechanisms by evolution to cope with salt stress: to synthesis new lipids from starting, digest the existing lipids completely or adjust their quantities and composition. This was the first report to demonstrate the lipid profile in microalgae corresponding to stress conditions by “lipidomics” technology, and the discovered lipid biomarkers with up- or down-regulation provided new insights into the explanation of the complex response pathways of microalgae to stress conditions on the lipidomic level.