Bacteriophage T5 growth in Escherichia coli containing PstI fragments of the colicin Ib plasmid.

PstI restriction fragments of the colicin Ib (ColIb) plasmid have been cloned into the Apr gene of the pBR322 vector. Colicin-producing clones (Col+) all contained two common PstI (L and U) fragments, 2000 and 800 bp long, respectively. All of these colicin producers were found to permit the normal growth of bacteriophage T5; the presence of the whole ColIb plasmid causes an abortive T5 or BF23 phage infection. None of the other clones selected for their inability to propagate T5 produced colicin. The clones (Abi+) that permitted only an abortive infection by T5 contained a single restriction fragment, O (1600 bp), which was not found in any of the colicin producers. Likewise, the specific fragments (L and U) found in the Col+ clones were not found in the Abi+ clones. These data are very hard to reconcile with the hypothesis of a colicin-induced cell deterioration after T5 phage infection.