Replacement of acidic phospholipids by acidic glycolipids in Pseudomonas diminuta

Abstract

PHOSPHOLIPIDS are characteristic components of the membranes of living cells, where in many cases they represent the major polar lipid components. The common phospholipids in Gram-negative bacteria are phosphatidylethanolamine, phosphatidylglycerol and diphosphatidylglycerol¹. Pseudomonas diminuta NCTC 8545, however, contains high proportions of glycolipids and relatively low proportions of phospholipids when grown on solid media or in submerged culture². The glycolipids are α-glucosyldiglyceride, α-glucuronosyldiglyceride and β-glucosyl (1→4)-α-glucuronosyldiglyceride³, and the phospholipids are phosphatidylglycerol³ and 6-phosphatidyl-α-glucosyldiglyceride⁴. It has been suggested that the acidic glycolipids (containing glucuronosyl residues) might behave as substitutes for acidic phospholipids in the membranes of this pseudomonad⁵. Here we describe studies on the lipid composition of P. diminuta grown in continuous culture in conditions of phosphate and magnesium limitation which support this suggestion. Moreover, in conditions of phosphate limitation the cells contain barely detectable amounts (0.3% of total polar lipids) of phospholipid, thereby suggesting that appreciable amounts of these compounds are not obligatory for the maintenance of membrane function.