Quantification of glycerophospholipids in Escherichia coli

Phosphatidic acid (PA), phosphatidylethanolamine (PE), phosphatidylglycerol (PG), and cardiolipin (CL) are the major glycerophospholipids in Escherichia coli. Each of these lipid classes contains numerous possible molecular species as defined by the total number of carbons and unsaturations in the acyl chains. The goal of this project is to quantify the total amount of each molecular species of PA, PE, PG, and CL in E. coli cells grown under different conditions. Wildtype E. coli was grown at 37°C and the lipids were extracted from cells in the presence of thirteen synthetic standards: three PE, PA, and PG and four CL standards. The samples were analyzed using normal phase liquid chromatography electrospray ionization mass spectrometry. Peak areas for the extracted ion current were recorded for each endogenous glycerophospholipid species and compared to its corresponding standard to determine the nmol of each molecular species of PE, PG, PA, and CL. The amount of each molecular species was summed to calculate the percent composition of PA, PE, PG, and CL in E. coli cells. The observed quantities, PE 79%, PG 19%, PA 1%, and CL 0.2%, are consistent with previous literature. In future experiments, the phospholipid composition in E. coli will be measured under various conditions, such as growing cells in different temperatures and under conditions that may alter acyl chain composition.