Uncoupling of synthesis and release of cloacin DF13 and its immunity protein by Escherichia coli.

The synthesis of the bacteriocin cloacin DF13 and its release into the culture medium were genetically uncoupled by subcloning the gene encoding the bacteriocin release protein (BRP) from pCloDF13. The gene was cloned under the control of the IPTG-inducible lpp-lac promoter-operator system on the expression vector pINIIIA1, giving pJL1. A 4 kb DNA fragment of pJL1, containing the tandem lpp-lac promoter, the BRP gene and lacI (BRP cassette), was cloned into the pCloDF13 derivative plasmid pJN67, which encodes cloacin DF13 but not the release protein. Furthermore, the pCloDF13 immunity protein gene was subcloned downstream of the temperature-inducible PL promoter of the expression vector pPLc236, together with the BRP cassette. Growth, induction and excretion experiments with Escherichia coli cells harbouring the constructed plasmids revealed that: the BRP is the only pCloDF13-derived gene product responsible for the observed growth inhibition and apparent lysis of strongly induced cells. This growth inhibition and lysis can be prevented by Mg2+ ions added to the culture medium, and involves induction of phospholipase A activity. The expression of the BRP gene can be regulated by varying the IPTG concentration. A separately controlled and moderate induced BRP synthesis can be used to bring about the release of large amounts of cloacin DF13 under conditions that allow a strong induction of the bacteriocin and which do not result in lysis of cells. Preliminary results indicated that the BRP can stimulate the release of immunity protein in the absence of cloacin or cloacin fragments.