Molecular Genetic Analyses of the Role of the Major Acidic Phospholipids in Escherichia coli Cell Growth

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Two plans were enforced. They were resulted from the discovery that E. coli cells lacking the major acidic phospholipids were viable if it harbored a defective lpp allele.1) One is to clarify the lethality of acidic-phospholipid deficiency in the cells having wild type lpp allele. The proLpp expressed from a plasmid caused cell lysis in a pgsA lpp double mutant. The envelopes of the cells could not be separated into outer and inner membranes. In contrast, expression of a mutant Lpp lacking the C-terminal lysine residue (required for linking to peptidoglycan) did not cause lysis and allowed the clear separation of the outer and inner membranes. In pgsA mutants proLpp could not be modified by the addition of a diacylglyceryl moiety normally provided by phosphatidylglycerol and that this defect caused unmodified proLpp to The accumulation of unmodified wild type Lpp led to the linking to peptidoglycan, causing the inner membrane to be anomalously anchored to peptidoglycan and leading to cell lysis. This anomalous anchoring explains the non-viable phenotype of pgsA null mutants.2) The other is to clarify the reason for the temperature-sensitivity of the cells lacking the major acidic phospholipids. For this purpose we isolated 48 clones of temperature-resistant suppressor mutants and identified almost all the loci of suppressor mutations. They were revealed to have mutations in the genes responsible for rcs phosphorelay system (rcsC, rcsB, rcsF, yojN, and rcsA). An over-expression of a certain gene (s) under the control of rcs regulatory system might be responsible for the temperature-sensitivity.