The present study has as its objective to understand the biosynthesis, regulation, and function of membrane phospholipids in Escherichia coli. Three specific goals for the current year have been: 1) Characterization of membranes isolated from mutants defective in phosphatidylserine (PS)-synthetase. 2. Isolation of second-step mutants defective in phosphatidylglycerophosphate (PGP) synthetase containing 10 times less phosphatidylglycerol and cardiolipin than normal cells. 3. Characterization of mutants lacking diglyceride kinase. The finding that a very precise lipid composition is essential for cell division and growth of E. coli suggests that putative inhibitors of these metabolic reactions would be novel antibiotics.