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Journal of Bacteriology, March 2007, p. 1946-1953, Vol. 189, No. 5
0021-9193/07/$08.00+0     doi:10.1128/JB.01451-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Localization of the Naturally Occurring Plasmid ColE1 at the Cell Pole

Center for Molecular Genetics and Division of Biological Sciences, University of California at San Diego, 9500 Gilman Drive, La Jolla, California 92093-0322

Received 13 September 2006/ Accepted 29 November 2006

The naturally occurring plasmid ColE1 was found to localize as a cluster in one or both of the cell poles of Escherichia coli. In addition to the polar localization of ColE1 in most cells, movement of the plasmid to the midcell position was observed in time-lapse studies. ColE1 could be displaced from its polar location by the p15A replicon, pBAD33, but not by plasmid RK2. The displacement of ColE1 by pBAD33 resulted in an almost random positioning of ColE1 foci in the cell and also in a loss of segregational stability, as evidenced by the large number of cells carrying pBAD33 with no visible ColE1 focus and as confirmed by ColE1 stability studies. The addition of the active partitioning systems of the F plasmid (sopABC) or RK2 (O_B1 incC korB) resulted in movement of the ColE1 replicon from the cell pole to within the nucleoid region. This repositioning did not result in destabilization but did result in an increase in the number of plasmid foci, most likely due to partial declustering. These results are consistent with the importance of par regions to the localization of plasmids to specific regions of the cell and demonstrate both localization and dynamic movement for a naturally occurring plasmid that does not encode a replication initiation protein or a partitioning system that is required for plasmid stability.

Published ahead of print on 8 December 2006.