The dynamics of colicin E9 release from Escherichia coli in native conditions.

Colicin (Col) plasmid contains colicin encoding genes arranged in an operon controlled by an SOS inducible promoter. Therefore, any external stresses to the host cell can induce the expression of the downstream genes in the Col operon including a lysis gene. The lysis protein is involved in the extracellular release of colicin through lysis of the producer cells which causes a decline in culture turbidity. However, it is not yet known that E. coli cells with ColE9-J plasmid hold the same level of cell death at the population level following a set of induced conditions. In this study, using a mitomycin C sensitivity assay along with a live dead staining method of detection, we showed that the native pColE9-J plasmid which unusually carries an extended Col operon (ColE9) containing two lysis genes, did not confer a rapid decline in the culture turbidity following induction with mitomycin C. Interestingly a subset of the cells suffered perturbation of their outer membrane which was not observed from single lysis mutant (∆celE or ∆celI) cells. This observed heterogeneity in the ColE9 release leading to differential outer membrane perforation may bring a competitive advantage to these cells in a mixed population.