The lipids and fatty acid metabolism of photosynthetic bacteria

Abstract

1. (1) The major lipids of five strains of photosynthetic bacteria, Rhodopseudomonas spheroides, Rhodopseudomonas capsulata, Rhodopseudomonas palustris and Rhodopseuciomonas gelatinosa and Rhodospirillum rubrum were shown to be phosphatidyl glycerol, phosphatidyl choline, phosphatidyl ethanolamine, sulphoquinovosyl diglyceride, cardiolipin and an unidentified component, probably O-ornithyl phosphatidyl glycerol. The only lipids common to all five strains were phosphatidyl glycerol and phosphatidyl ethanolamine. 2. (2) In all cases, whether grown aerobically or anaerobically, the major fatty acids were n-hexadecanoic, 9-hexadecenoic and an 11-octadecenoic acid. Rhodospirillum rubrum and Rhodopseudomonas gelatinosa contain a small amount of 9-octadecenoic acid. 3. (3) Study of the biosynthesis of 11-octadecenoic acid under both dark aerobic and light anaerobic conditions showed saturated acids of a variety of chain lengths were utilised only after prior breakdown. This was demonstrated by the presence of randomised labelling in the 11-octadecenoic acid produced from specifically labelled saturated acids. The pathway of biosynthesis of the monoenoic acids is thus similar to that in non-photosynthetic anaerobic bacteria. 4. (4) Both oleic and linoleic acids were also utilised, apparently after β-oxidation. 5. (5) The only lipid common to all five bacteria, to green algae and plant chloroplasts is phosphatidyl glycerol.