Metabolic Response to Altered Light Conditions in Genetically Modified Chlamydomonas reinhardtii by LAESI Mass Spectrometry with Ion Mobility Separation 
Denis Falconet1, Sylwia Stopka2, Bindesh Shrestha2,
Éric Maréchal1 and Akos Vertes2
1Laboratoire de Physiologie Cellulaire Végétale, UMR 5168, CEA-CNRS-INRA-Univ. Grenoble Alpes, Grenoble, France
2Department of Chemistry, W. M. Keck Institute for Proteomics Technology and Applications, The George Washington University, Washington, DC 20052, USA

The metabolic profiling of various microalga species and their genetic variants, grown in distinct environmental conditions and with different nutrient supplies has become critical to accelerate the exploration of phytoplankton. Laser ablation electrospray ionization (LAESI) combined with ion mobility separation (IMS) mass spectrometry (MS) has been used to detect changes in metabolites, lipids, and peptides from live Chlamydomonas. reinhardtii populations. The effect of light exposure was explored on the metabolomic and lipidomic profiles in genetically modified C. reinhardtii strains with defective photo-repair mechanism (impaired D1 protein) and with affected starch pathway. Lipids, such as triacylglycerol (TAG) and diacylglyceryl-N,N,N-trimethylhomoserine (DGTS) were monitored and quantified over a time period under altered light conditions. Over 200 ions related metabolites, e.g., arginine, cysteine, serine, palmitate, chlorophyll a, chlorophyll b, etc., were detected. The metabolite and lipid profiles at different light intensities for strains with defective D1 synthesis and starch pathway shutdown contained more than 30 glycerolipids, such as DGTS, monogalactosyldiacylglycerol (MGDG) and digalactosyldiacylglycerol (DGDG), as well as ~30 TAG species. Preliminary results were obtained over a 48-hour time period in light and dark conditions at 100 µmolm-2sec-1 light intensity for two mutants (cc4325 and cc4386). Compared to the wild-type, the strain with the affected starch pathway, i.e., with defective catalytic small subunit of ADP-glucose pyrophosphorylase (cc4325), showed higher lipid production at 24 and 48 hours under both light and dark conditions. The strain with the silenced REP 27 gene (cc4386), defective in the production of the D1 protein, exhibited a significantly reduced production in both metabolites and lipids under dark conditions.