Coordination of membrane synthesis with cell growth: localization of the Escherichia coli phospholipid synthesis enzyme PlsB responds to membrane abundance in a manner consistent with filamentation-mediated inhibition

Cell viability demands tight coordination between growth and the synthesis of new membrane. The mechanisms coordinating cell growth with membrane synthesis in any organism are unclear. In Escherichia coli, initiation of phospholipid synthesis by the glycerol-3-phosphate acyltransferase PlsB is regulated by cell growth via an unknown allosteric mechanism. Previous studies have established that PlsB assembles into enzymatically inactive, membrane-bound filaments when overexpressed. We propose that PlsB filamentation regulates PlsB activity and coordinates membrane synthesis with growth. Here, we test our hypothesis by observing the localization of fluorescently labelled PlsB using live-cell fluorescence microscopy. During growth, PlsB localizes as discrete foci, consistent with formation of inactive filaments. Reducing cellular membrane content eliminates PlsB foci and delocalizes PlsB into the cytoplasm. Restoring membrane synthesis causes PlsB foci to reform after a delay. These results are consistent with our hypothesis and suggest a model in which PlsB reversibly assembles into inactive filaments in response to phospholipid abundance. This mechanism establishes a negative feedback loop that controls initiation of phospholipid synthesis by PlsB and effectively coordinates membrane synthesis with growth.