Visualization of membrane domains in Escherichia coli

Bacterial membrane and nucleoids were stained concurrently by the lipophilic styryl dye FM 4‐64 [N‐(3‐triethylammoniumpropyl)‐4‐(6‐(4‐(diethylamino)phenyl) hexatrienyl)pyridinium dibromide] and 4′,6‐diamidino‐2‐phenylindole (DAPI), respectively, and studied using fluorescence microscopy imaging. Observation of plasmolysed cells indicated that FM 4‐64 stained the inner membrane preferentially. In live Escherichia coli pbpB cells and filaments, prepared on wet agar slabs, an FM 4‐64 staining pattern developed in the form of dark bands. In dividing cells, the bands occurred mainly at the constriction sites and, in filaments, between partitioning nucleoids. The FM 4‐64 pattern of dark bands in filaments was abolished after inhibiting protein synthesis with chloramphenicol. It is proposed that the staining patterns reflect putative membrane domains formed by DNA–membrane interactions and have functional implications in cell division.