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

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Two plans were enforced. The plans were resulted from the discovery that Escherichia coli cells lacking the major acidic phospholipids was 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. For this purpose we have constructed an lpp inducible system and examined the localization of proLPP protein in the membranes during its retarded growth after induction of lpp.2) The other is to clarify the reason for the temperature-sensitivity of the cells lacking the major acidic phospholipids. The temperature-sensitivity suggest that at temperatures above 40 the acidic phospholipid, phosphatidylglycerol, plays an indispensable role(s). For this purpose we have isolated 48 clones of temperature-resistant suppressor mutants and identified the loci of suppressor mutations. Half of the clones were revealed to have mutations in rcsC and rcsF genes. Introduction of rcsB mutation made the PG-deficient cells temperature-resistant. These suppressor analyses suggested that an over-expression of a certain gene(s) under the control of rcsC-rcsB regulatory system might be responsible for the temperature-sensitivity. However, introduction of cpsB mutation that interrupts capsular polysaccharide synthesis did not suppress the temperature-sensitivity of the PG-deficient cells. The result indicated that synthesis of capsular polysaccharide per se is not responsible for the temperature-sensitivity but that a certain gene(s) under the control of the regulatory system is responsible for the temperature-sensitivity of the PG-deficient cells.