The relationship of intracytoplasmic membrane assembly to the cell division cycle in Rhodopseudomonas sphaeroides.

Discontinuous increases in the net accumulation of cellular phospholipid were previously observed during the synchronous growth of Rhodopseudomonas sphaeroides (Lueking, D. R., Fraley, R. T., and Kaplan, S. (1978) J. Biol. Chem. 253, 451-457). This pattern is shown to result from large increases in the rate of phospholipid synthesis, occurring just prior to cell division. The absence of detectable turnover of the phospholipid fraction suggests that the discontinuous accumulation of cellular phospholipid occurring during synchronous growth is directly attributable to the observed changes in the rate of phospholipid synthesis. Evidence is presented which suggests that different patterns of phospholipid synthesis (or insertion) are associated with the intracytoplasmic membrane system and the cytoplasmic and outer membranes. The previous observation that the proteinjphospholipid ratio of the intracytoplasmic membranes of R. sphaeroides underwent cyclical changes (40 to 50%) during synchronous growth has been confirmed by monitoring concomitant changes (1.1690 to 1.1790 g/ cm3) in the natural or intrinsic density of these membranes. Specific radioisotopic labeling of membrane protein and phospholipid components also verifies the changes in intracytoplasmic membrane composition observed during the cell cycle. It is proposed that the cyclical changes in intracytoplasmic membrane composition may serve as a means of regulating membrane-associated enzymes and modulating membrane synthesis during the cell cycle.