The fats of Escherichia coli during infancy and old age: regulation by global regulators, alarmones and lipid intermediates.

The fluidity and phase state of bacterial lipid bilayers commonly change in response to ambient environmental conditions to maintain the critical functions of the envelope as a semipermeable and selective boundary. A special, and intricate, set of alterations in membrane lipid metabolism is elicited by conditions causing growth arrest. Under such conditions, specific alterations in the membrane lipid-fatty acid composition are required for survival of the cell and, concurrently, the membrane lipids are suggested to serve as endogenous reserves providing carbon/energy for maintenance requirements. It appears that the global regulator FadR is required for both of these activities to be performed properly and that the FadR regulon is interconnected to the universal stress response of Escherichia coli. FadR, in conjunction with long-chain fatty acyl-CoA, long-chain acyl-ACP, ppGpp and cAMP, are key players in regulating the activities of enzymes and expression of genes involved in fatty acid and phospholipid metabolism in dividing and ageing E. coli cells.