Construction of a lethal mutation in the synthesis of the major acidic phospholipids of Escherichia coli

In order to determine if the major acidic phospholipids of Escherichia coli are essential to the organism, we constructed a null allele (pgsA30) of the pgsA gene thus rendering the organism incapable of synthesizing phosphatidylglycerol or cardiolipin. In strains carrying the pgsA30 allele cell viability, synthesis of gene product and the ability to synthesize the two major acidic phospholipids were dependent on the presence of a functional copy of the pgsA gene carried on a plasmid which was temperature-sensitive for replication. Growth ceased at the temperature restrictive for plasmid replication when the acidic phospholipid content dropped to about 10% of wild type levels which is slightly higher than the level reported in cells carrying the pgsA3 allele in a genetic background derived from strain SD12; the latter cells, which are capable of synthesizing low levels of acidic phospholipids, were previously shown to have no abnormal growth phenotype (Miyazaki, C., Kuroda, M., Ohta, A., and Shibuya, I. (1985) Proc. Natl. Acad. Sci. U. S. A. 82, 7530-7534). The pgsA30 allele, unlike the pgsA3 allele, could not support growth in strain SD12. Neither allele could support growth in two other independently derived strains of E. coli. Therefore, there is a direct dependence of cell viability on a functional pgsA gene product. Strain SD12 appears to contain a suppressor which allows cells with a reduced capability to synthesize acidic phospholipid (pgsA3 allele) to grow, but cannot support growth in cells with a complete lack of synthetic capability (pgsA30 allele).