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

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Abstract
A series of transformants have been derived which carry the Col plasmids from 11 E-colicin-producing strains isolated by Fredericq or Hamon. The ColE plasmids identified included four of type E1, five of type E2, and two of a type designated E4 by Horak (Zentralbl. Bakteriol. Parasitenkd. Infektionskr. Hyg. Abt. 1 Orig. Reihe A 233:58-63, 1975). Strain K317 was shown to carry 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 found to be about 4.3 Md in size. ColE2-CA42 and ColE7-K317 are both about 3.9 Md and are the only two plasmids of the E2, E3, E4, and E7 types that did not yield a 0.39-Md deoxyribonucleic acid fragment as an EcoRI digestion product. The comparisons of the ColE plasmids suggest several structural and functional relationships among them.