Abstract
The cytoplasmic and outer membranes of a nonconditional chain-forming mutant, Escherichia coli PM61 envC, were separated by sucrose density gradient centrifugation. The phosphatidylglycerol/cardiolipin ratio in both membrane fractions was about one-third as high as in the parental strain P678. The increased level of cardiolipin in PM61 membranes is the result of an alteration of the polyglycerophosphatide cycle. It was found that the turnover rate of phosphatidylglycerol is more rapid in PM61 than in the parental strain but that its cardiolipin turnover is not significantly different. The envC mutation can be corrected phenotypically by increasing the osmolarity of the medium. In the presence of 0.6 M sucrose, the population of PM61 is composed of short rods, and the phosphatidylglycerol/cardiolipin ratio is shifted to that of the parent. The phosphatidylglycerol turns over more slowly, whereas the cardiolipin turns over more rapidly in both strains. Thus, the increase of external osmolarity acts on phospholipid metabolism as well as on an unknown step involved in the mechanism of cell division of the envC mutant.