Fast atom bombardment-mass spectrometry for bacterial chemotaxonomy: influence of culture age, growth temperature, gaseous environment and extraction technique

Phospholipid analogues of Porphyromonas gingivalis

Porphyromonas has lipids containing hydroxy acids and C16:0 and iso-C15:0 major monocarboxylic acids among others. Nothing is known of its individual phospholipid molecular species. The aim of this study was to determine molecular weights and putative identities of individual phospholipid molecular species extracted from Porphyromonas gingivalis (seven strains), P. asaccharolytica (one strain) and P. endodontalis (two strains). Cultures on Blood-Fastidious Anaerobe Agar were harvested, washed and freeze-dried. Phospholipids were extracted and separated by fast atom bombardment mass spectrometry (FAB MS) in negative-ion mode. Phospholipid classes were also separated by thin layer chromatography (TLC). The major anions in the range m/z 209-299 were consistent with the presence of the C13: 0, C15: 0, C16: 0 and C18: 3 mono-carboxylate anions. Major polar lipid anion peaks in the range m/z 618-961 were consistent with the presence of molecular species of phosphatidylethanolamine, phosphatidylglycerol and with unidentified lipid analogues. Porphyromonas gingivalis differed from comparison strains of other species by having major anions with m/z 932, 946 and 960. Unusually, a feline strain of P. gingivalis had a major peak of m/z 736. Selected anions were studied by tandem FAB MS which revealed that peaks with m/z 653 and 946 did not correspond to commonly occurring classes of polar lipids. They were however, glycerophosphates. It is concluded that the polar lipid analogue profiles obtained with Porphyromonas are quite different from those of the genera Prevotella and Bacteroides but reveal heterogeneity within P. gingivalis.

Phospholipid profiles in the oral yeast Candida

Individual molecular species of phospholipids can now be readily detected using fast atom-bombardment mass spectrometry (FAB MS). The aim was to obtain detailed information on individual molecular species of Candida phospholipids using FAB MS. Lipids were extracted from Candida isolates and prepared for FAB MS analysis in negative-ion mode. Each isolate yielded several hundred anion peaks. The major anion peaks consistent with the presence of phospholipids included those of mass/charge (m/z) 836, 743, 715, 744 and 834 tentatively identified as phosphatidylethanolamine PE(43:5), phosphatidylglycerol PG(34:3), PG(32:3), PE(36:1) and PE(43:5). Major peaks consistent with the presence of carboxylate anions were of m/z 241, 253, 255, 277, 279, 281, 283, and 307 putatively identified as C15:0, C16:1, C18:3, C18:2, C18:1, C18:0 and C20:2 which also support the putative identifications of phospholipids. Such phospholipid profiles differ from those published for other microorganisms analysed by FAB MS. Quantitative differences were observed between different candidal species. Candida albicans may be readily differentiated from C. glabrata on the basis of its carboxylate anions. Within species, there are quantitative differences in phospholipid profiles. Thus, Candida has a unique combination of phospholipid analogues with potential chemosystematic significance.