Constant Neutral Loss Scanning for the Characterization of Bacterial Phospholipids Desorbed by Fast Atom Bombardment

Fast atom bombardment (FAB) of the lysed cells and crude lipid extracts of bacteria results In the selective desorption of phospholipids that are characteristic of bacterial species. In this paper, constant neutral loss (CNL) linked scanning of the magnetic and electric sector fields of a double focusing mass spectrometer Is evaluated as an approach to the analysis of bacteria cells that can provide greater selectivity for polar lipids and specificity for particular phospholipid classes. In the metastable time frame, neutral losses of phosphoryl-ethanolamlne, phosphorylglycerol, and other polar head groups are best obtained from protonated molecular Ions analyzed In the positive Ion mode. Selectivity Is Improved (relative to normal magnetic field scans) for phospholipids of a particular class In the presence of more abundant phospholipids and the background Ion signal characteristic of FAB mass spectra. In addition, CNL scans permit the observation of monomethyiphosphatidylethanolamine, a minor phospholipid present In a few bacteria, such as P. vulgaris, but indistinguishable In mass from fatty acid homologues of PE containing additional methylene groups. Since fatty acid content In bacterial lipids (and therefore the masses appearing In a particular spectrum) reflects growth conditions as well as species, the Identification of specific phospholipid classes by CNL scans provides a promising approach to the Identification and classification of bacteria.