Identification and characterization of Col plasmids from classical colicin E-producing strains

Abstract

A series of transformants were derived which carry the Col plasmids for 11 colicin E-producing strains of Escherichia coli isolated by Fredericq or Hamon. The ColE plasmids identified included 4 of type E1, 5 of type E2 and 2 of a type designated E4 by Horak 1975. Strain K317 carried a ColE7 plasmid and a 2.7-megadalton (Md) ColE2imm plasmid which confers immunity to colicin E2 but not the ability to produce colicin. Other plasmids identified in the colicinogenic isolates were a 3.4-Md ColN plasmid and a 1.3-Md Col plasmid of unknown type. The ColE1 plasmids all continued replicating in cultures treated with chloramphenicol. Strains carrying the ColE4 or ColE3-CA38 plasmid exhibited partial sensitivity to their own colicins and exhibited an unusual clearing-zone morphology when overlaid on stabs of colicin E2- or E7-producing strains. Except for ColE1-K53, ColE1-K47, ColE2-CA42 and ColE7-K317, all of the ColE plasmids were about 4.3 Md in size. ColE2-CA42 and ColE7-K317 are both about 3.9 Md and are the only 2 plasmids of the E2, E3, E4 and E7 types that did not yield a 0.39 Md DNA fragment as an EcoRI digestion product. The comparisons of the ColE plasmids suggest several structural and functional relationships among them.