Phospholipid molecular species of Bacteroides

The fatty acid composition, and types of polar lipid (PL) present, have been well-studied in Bacteroides. Nothing is known, however, of the detailed structures of individual phospholipid and molecular species. The aim of this study was to determine molecular weights and putative identities of individual phospholipid molecular species present in Bacteroides. Thirteen culture collection strains were harvested, washed and freeze-dried. Polar lipids were extracted and separated by conventional fast atom bombardment mass spectrometry (FAB MS). For each strain, hundreds of polar lipid peaks were seen. Nineteen major anions in the range m/z 209–299 were separated. The most intense of these was consistent with the expected presence of the C_15:0 anion. Other anions were attributable to saturated, mono-unsaturated, di-unsaturated, tri-unsaturated and hydroxy-carboxylate ions. Twenty-two major anion peaks were recorded in the range m/z 505–722. These were consistent with the presence of analogues of phosphatidic acid (PA), phosphatidylethanolamine (PE) and phosphatidylglycerol (PG). The most intense peaks included those consistent with the presence of PE(30:0), PG(29:1), PG(30:1), PG(28:1), PE(31:0), PE(OH-30:0), PG(31:1) and PE(OH-31:0). This combination of PL molecular species is unique to Bacteroides and has not been reported in other organisms so far examined.