Changes in the acyl lipid composition of photosynthetic bacteria grown under photosynthetic and non-photosynthetic conditions

Abstract

The acyl lipids and their constituent fatty acids were studied in the photosynthetic bacteria Rhodospirillum rubrum, Rhodopseudomonas capsulata and R. sphaeroides, which were grown under photosynthetic and non-photosynthetic conditions. The major lipids were phosphatidylethanolamine, phosphatidylglycerol and cardiolipin in each bacterium. The 2 Rhodopseudomonas spp. also contained significant quantities of phosphatidylcholine. Other acyl lipids accounted for less than 10% of the total. On changing growth conditions from non-photosynthetic to photosynthetic, a large increase in the relative proportion of phosphatidylglycerol was seen at the expense of phosphatidylethanolamine. In R. rubrum the fatty acids of the major phospholipids showed an increase in the proportion of palmitate and stearate and a decrease in palmitoleate and vaccenate on changing growth conditions to photosynthetic. In contrast, the exceptionally high levels (> 80%) of vaccenate in individual phospholipids of R. capsulata and R. sphaeroides were unaffected by changing growth conditions to photosynthetic. Analysis of lipids of chromatophores, isolated from the 3 bacteria, showed that these preparations were enriched in phosphatidylglycerol. The large increase in this phospholipid, seen during growth under photosynthetic conditions, appeared to be due to a proliferation of chromatophore membranes. Possible roles for acyl lipids in the formation and function of the photosynthetic apparatus of bacteria are discussed.