Composition Analysis of Polar Lipids in Halobacteria with Mass Spectrometry

The structures of the polar lipids in halobacteria including their mutants were determined with ESI-MS and FAB-MS. The composition-analyses with ESI-MS gave the results fairly close to these with TLC analyses. The percentages of the composite polar lipids by the mass spectrometric analyses of Halobacterium salinarum S-9 were 20, 77, and 5% for glycolipid sulfate (S-TGD), methyl ester of phosphatidyl glycerophosphate (PGP-OMe), and phosphatidylglycerol (PG), respectively. The MS/MS analysis in the FAB-MS provided an analyzing tool for the structural elucidation of the functional groups in the lipids. Newly proposed methylation in the phosphate was investigated with stable isotope experiments. We found that the Australian halobacteria, Halorubrum sp. aus-1, mainly consist of an isolated glycolipid sulfate with two sugar parts of glucopyranoses. In relationship with the lipid-composition analysis, the chemotaxonomy of halobacteria was discussed. The methylation of the lipids was proved to be essentially independent of that in the photosensory protein of halobacteria on the basis of the wide distribution of the methylated lipids.