This study examined plasmid incompatibility among nine E colicin plasmids in Escherichia coli. Researchers used conjugation with the R64-11 mobilizing plasmid to introduce different colicin E plasmids into recipient cells already containing a colicin plasmid, then tested whether both plasmids stably coexisted through multiple generations by screening for colicin production. Most plasmid pairs were compatible and could replicate stably together. However, three groups of plasmids showed incompatibility: ColE3-CA38, ColE7-K317, and ColE8-J were mutually incompatible; ColE5-099 and ColE9-J were incompatible with each other; and ColE6-CT14 showed asymmetrical incompatibility with both ColE5-099 and ColE9-J, displacing them from cells while being unable to establish itself in cells already carrying these plasmids. Incompatibility between other pairs was symmetrical. These findings suggest that plasmids sharing incompatibility relationships likely share similar replication and copy number control mechanisms, consistent with their structural and functional similarities revealed by previous restriction mapping studies.

Key findings

• ColE3-CA38, ColE7-K317, and ColE8-J form a single incompatibility group, segregating when attempted to coexist in the same cell
• ColE5-099 and ColE9-J show symmetrical incompatibility with each other, despite their similar structural and functional maps
• ColE6-CT14 exhibits asymmetrical incompatibility with ColE5-099 and ColE9-J, displacing these plasmids from cells while unable to establish itself in their presence
• Most other E colicin plasmid pairs tested (E2, E4 combinations) were compatible and coexisted stably
• Plasmid incompatibility patterns indicate shared replication control mechanisms among related colicin plasmids