Evolution of microcin V and colicin Ia plasmids in Escherichia coli

Abstract

Survey results and genotypic characterization of Escherichia coli strains demonstrate that the bacteriocins colicin Ia and microcin V coassociate in a strain more often than would be expected by chance. When these two bacteriocins co-occur, they are encoded on the same conjugative plasmid. Plasmids encoding colicin Ia and microcin V are nonrandomly distributed with respect to the genomic background of the host strain. Characterization of microcin V and colicin Ia nucleotide variation, together with the backbone of plasmids encoding these bacteriocins, indicates that the association has evolved on multiple occasions and involves the movement of the microcin V operon, together with the genes iroNEDCB and iss, onto a nonrandom subset of colicin Ia plasmids. The fitness advantage conferred on cells encoding both colicin Ia and microcin V has yet to be determined.

FIG. 1.

Maximum-likelihood tree of the 36 Ia nucleotide sequence types detected in E. coli isolates from human and nonhuman vertebrates living in Australia. In each label, the first number is the ST and the number in parentheses is the number of times the ST was observed, followed by the genetic groups of E. coli in which the ST was detected and finally if the ST co-occurred with the microcin V operon in the same strain. Bootstrap values are based on 500 replicates.