Bacterial partitioning proteins affect the subcellular location of broad-host-range plasmid RK2

It has been demonstrated that plasmidsare not randomly distributed but are located symmetrically in mid-cell, or ¼, ¾ positions in bacterial cells. In this work we compared the localization of broad-host-range plasmidRK2 mini- replicons, which lack an active partitioning system, in Escherichia coli and Pseudomonas putidacells. In E. coli the location of the plasmidmini- repliconcluster was at the cell poles. In contrast, in Pseudomonascells, as a result of the interaction of chromosomally encoded ParB protein with RK2 centromere-like sequences, these mini-derivatives were localized in the proximity of mid-cell, or ¼, ¾ positions. The expression of the PseudomonasparAB genes in E. coli resulted in a positional change in the RK2 mini-derivative to the mid-cell or ¼, ¾ positions. Moreover, in a P. putida parAB mutant, both RK2 mini-derivatives and the entire RK2 plasmidexhibited disturbances of subcellular localization. These observations raise the possibility that in certain bacteria chromosomally encoded partitioning machinery could affect subcellular plasmidpositioning.