Colicins B and Ia as novel counterselective agents in interspecies conjugal DNA transfers from colicin-sensitive Escherichia coli donors to other gram-negative recipient species.

Colicins are powerful counterselective agents in conjugal DNA transfers using colicin-sensitive Escherichia coli donor strains and colicin-resistant recipient species. We have constructed a high-level constitutive expression system for the bacteriocin and immunity genes of channel-forming colicins B and Ia to optimize production of these colicins as molecular biology reagents.