Evidence for unequal segregation of cytochromes at cell division inEscherichia coli

Cytochrome segregation at cell division was studied in an Escherichia coli mutant requiring δ-amino-laevulinic acid (δ-ALA) for cytochrome synthesis and oxidative growth. Approximately three generations after transfer to δ-ALA-deficient medium, two sub-populations of cells were distinguishable by their ampicillin sensitivity in a medium supporting growth only of cytochrome-containing cells. The sub-populations were separable on Percoll gradients: ampicillin-sensitive cells contained higher cytochrome concentrations than insensitive cells. The results support a model that describes localized growing zones of membrane, which are conserved in successive cell cycles.