Microcin plasmids: a group of extrachromosomal elements coding for low-molecular-weight antibiotics in Escherichia coli

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Abstract
Microcins are low MW compounds produced and excreted by Enterobacteriaceae. They inhibit the growth of a wide spectrum of microorganisms. Microcin-synthesizing transconjugants were obtained in 7 out of 8 experiments of conjugational transfer between wild-type microcinogenic strains of E. coli and E. coli strain BM21. The physical analysis of 1 of the transconjugant strains that acquired the ability to produce microcin 17 showed the presence of extrachromosomal DNA as a plasmid (pRYC17) of MW 36 .times. 106 (18.3 .mu.m length), which is absent in the microcin-cured derivative strain. pRYC17 was incompatible with plasmids of the IncFII group. Other suspected plasmids containing the information for the synthesis of microcins were not clearly classified. Strains producing microcins 93, 136 and 140 show a partial incompatibility with IncFIII group of plasmids.