Metabolism of Phosphatidylglycerol, Phosphatidylethanolamine, and Cardiolipin of Bacillus stearothermophilus

Abstract

The total phospholipid content of Bacillus stearothermophilus was constant during exponential growth, increased during the transition from the exponential to stationary phase of growth, and then slowly increased during the stationary phase. The first increase was a result of an increase in phosphatidylethanolamine; the second was a result of an increase in cardiolipin. Cessation of aeration of an exponentially growing culture or suspension in a nongrowth medium resulted in an immediate reduction in the rate of total phospholipid and phosphatidylethanolamine synthesis and a quantitative conversion of phosphatidylglycerol to cardiolipin. Cardiolipin appeared to be synthesized by the direct conversion of two molecules of phosphatidylglycerol to cardiolipin. After a 20-min pulse of 32 P, phosphatidylglycerol showed the most rapid loss of 32 P followed by cardiolipin, whereas phosphatidylethanolamine did not lose 32 P. The loss of 32 P from the total lipid pool, phosphatidylglycerol, and cardiolipin was biphasic, with rapid loss during the first two bacterial doublings followed by a greatly reduced rate of loss. The major loss of 32 P from the total phospholipid pool appeared to be by breakdown of cardiolipin. The loss of 32 P from the lipid pool was energy dependent (i.e., did not occur under anaerobic conditions or in the absence of an energy source) and was dependent on some factor other than the concentration of cardiolipin in the cells. The apparent conversion of phosphatidylglycerol to cardiolipin was independent of energy metabolism. Chloramphenicol reduced the rate of turnover of both phosphatidylglycerol and cardiolipin. The rate of lipid synthesis (all phospholipid components) was constant for about 10 min after the addition of chloramphenicol but diminished markedly after 20 min. Turnover of 32 P incorporated into phospholipid during a 30-min period prior to the addition of chloramphenicol was more rapid after the removal of chloramphenicol than that of 32 P incorporated during a 30-min period in the presence of chloramphenicol.