The separation and identification of the lipids of Rhodopseudomonas spheroides

Abstract

Detailed examination of the lipids of Rhodopseudomonas spheroides was undertaken since it was thought this might provide information on the biogenesis of the chromatophores. The phospholipids of purified chromatophores consist of phosphatidylethanolamine (35%), phosphatidylglycerol (34%) and phosphatidylcholine (23%); minor quantities of phosphatidic acid and of cardiolipin were also found. In addition, a sulpholipid was detected and also a new lipid containing ornithine. The relative proportions of the different phospholipids in chromatophores, in other subcellular fractions from pigmented micro-organisms and in fragments from cells grown under oxygen were similar. However, the 'aerobic fragments' contained much less ornithine lipid than the chromatophores. Comparison of the relative amounts of the different phospholipids in whole cells grown under oxygen, under air, or under semi-anaerobic conditions in the light showed no marked differences, the composition being similar to that found in chromatophores. It is concluded that there is no particular lipid specifically associated with chromatophores. Poly-$\beta $-hydroxybutyrate accounted for as much as 35% of the dry weight of cells grown under oxygen in the dark on malate-glutamate medium. It is necessary to remove this material before chromatography as it otherwise interferes with the separation.