Increased production of colicin E1 in stationary phase

The synthesis of colicin E1 is known to be regulated by the SOS response, anaerobiosis, and catabolite repression. The expression of cea-lacZ fusions was also found to be stimulated when cells reached stationary phase. This increase in expression was determined to be due to depletion of nutrients from the medium, since the addition of fresh medium reversed the effect. Expression of the fusion increased when cells were starved in 10 mM MgSO4 and when they were grown in conditioned medium in which cells had been grown previously. The stimulation of expression occurred when the cea-lacZ fusion was present in single-copy as well as in multicopy plasmids. Finally, the data were consistent with this increase being independent of the SOS response, anaerobiosis, catabolite repression, and integration host factor as well as the stationary-phase regulators encoded by rpoS and lrp.