2787
Anal. Chem. IQ88, 60,2787-2791
Constant Neutral Loss Scanning for the Characterization of Bacterial Phospholipids Desorbed by Fast Atom Bombardment D. N. Reller, C. M. Murphy, and R. J. Cotter* Department of Pharmacology and Molecular Sciences, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205
Catherine Fenselau University of Maryland Baltimore County, Baltimore, Maryland 21228
0 . M. Uy The Johns Hopkins University Applied Physics Laboratory, Laurel, Maryland 20707
Fast atom bombardment (FAB) of the lysed cells and crude llpld extracts of bacterla results In the selective desorption of phorphoupkk that are characteristic of bacterlal specks. I n thk paper, constant neutral loss (CNL) llnked scarmlng of the magnetk and electrlc sector flekls of a double focuslng mass spectrometer Is evaluated as an approach to the analysls of bacterla cells that can provlde greater selectlvlty for polar llplds and speclflclty for partlcular phosphollpld classes. I n the metastable t h e frame, neutral losses of phosphorylethanolamlne, phosphorylglycerol, and other polar head groups are be8t obtalned from protonated molecular Ions analyzed In the posltlve Ion mode. SelectlvHy Is Improved (relathre to normal magnetk fleld scans) for phosphollplds of a partlcular class In the presence of more abundant phosphollpMs and the background Ion dgnal characteristk of FAB m a s spectra. I n addklon, CNL scans penntl the observation of momnnethy@hoaphattklylethanolamhre,a mhror pbsphoUpkl prewnt In a few bacterla, such as P. vu&8f/s, but lndlstlngulshabk In mass from fatty acld homologues of PE contalnIng addltlonal methylene groups. Slnce fatty acld content In bacterial lipids (and therefore the masses appearlng In a particular spectrum) reflects growth condltlons as well as specks, the ldenttflcatlon of specllc phosphollpld classes by CNL scans provlcks a promlskrg approach to the klentllicatlon and cladlcatlon of bacterla.
Membrane lipids are important biomarkers that can be used to differentiate bacteria from one another (1-3). We have found that desorption mass spectrometry techniques selectively ionize polar membrane lipids directly from lysed bacteria to provide mass spectra that are characteristic of Gram stain and species (4, 5). Both phospholipids and glycolipids are selectively desorbed by these techniques. The most common phospholipids contain two fatty acids, a glycerolphosphate core, and a polar head group which determines the phospholipid class (Scheme I). The variable portions of phospholipids (the head group and the fatty acids) are both found in distribution patterns that are chemotaxonomicallysignificant. Thus, one approach to characterizing bacteria involves the chromatographic analysis of fatty acids extracted from bacteria cultured and harvested under standard conditions (6). Fatty acids are identified by retention times and their distribution is determined from the relative peak areas. While there are limits to the range of fatty acids that a given species will produce, the fatty acid distribution itself can vary significantly in the same species grown on different media, at different 0003-2700/88/0380-2787$01.50/0
Scheme I -CO-O-CH,
I
L/ JJ
CO-0-CH
I
CH, 0-t-0 R
R -CHiCH
