Phospholipid interconversions in Mycoplasma capricolum.
Mycoplasma capricolum cells increase their phospholipid content by incorporating exogenous phospholipids from the growth medium. Growing the cells in media with increasing serum concentrations resulted in a massive incorporation of phosphatidylcholine and sphingomyelin (up to about 50% of total phospholipids) into the cell membrane. The incorporation of the exogenous phospholipids had essentially no effect on the rate of cell growth and did not decrease the overall phospholipid biosynthesis of the cells. Thus, the ratio of phospholipid to protein in membranes from cells grown with 5% horse serum was 0.5 (mumol/mg) compared to 0.3 (mumol/mg) in cells grown without serum, and the relative content of charged polar lipids was apparently decreased. The consequence of the incorporation of exogenous phosphatidylcholine was an alteration in the relative amount of the major end-products of the de novo phospholipid biosynthesis; a marked increase in the ratio of diphosphatidylglycerol to phosphatidylglycerol was observed. The possibility that the increase in the ratio of diphosphatidylglycerol to phosphatidylglycerol is part of a control mechanism to maintain a mixture of bilayer and non-bilayer lipids is discussed.