Dual stable isotopes enhance lipidomic studies in bacterial model organism Enterococcus faecalis

Dual stable isotope probes of deuterium oxide and ¹³C fatty acid were demonstrated to probe the lipid biosynthesis cycle of a Gram-positive bacterium Enterococcus faecalis. As external nutrients and carbon sources often interact with metabolic processes, the use of dual-labeled isotope pools allowed for the simultaneous investigation of both exogenous nutrient incorporation or modification and de novo biosynthesis. Deuterium was utilized to trace de novo fatty acid biosynthesis through solvent-mediated proton transfer during elongation of the carbon chain while ¹³C-fatty acids were utilized to trace exogenous nutrient metabolism and modification through lipid synthesis. Ultra-high-performance liquid chromatography high-resolution mass spectrometry identified 30 lipid species which incorporated deuterium and/or ¹³C fatty acid into the membrane. Additionally, MS² fragments of isolated lipids identified acyl tail position confirming enzymatic activity of PlsY in the incorporation of the ¹³C fatty acid into membrane lipids.