Investigation of Partition Mechanism of High-Copy Number Bacterial Plasmids via Replication Incompatibility

Bacterial plasmids play important role in gene transport between cells both vertically and horizontally, and are also versatile tools for gene engineering. Their maintenance of inherence in the host cells is believed to depend on the delicate quantity control through the replication origin and the effective management of partition. Without active partition system, high-copy number plasmids are suggested to be distributed as multiple foci but randomly partitioned during cell division. Lack of the direct evidence, the detail mechanism and dynamics of plasmid location and partition in cell is unknown. Taking the advantage of temporary tolerance on the incompatibility of replication origin, two ColE1 derivative plasmids with different antibiotic resists and repressible replication origin are co-transformed and their distributions and motions are observed at single cell level simultaneously. Based on the nature of competition between plasmids, it also provides the opportunity to actually reveal a single plasmid translocation between multiple foci, which is affected by the nucleoids of the dividing cells. Also, the variance of the inhered number of copies for both of two plasmids from parent to daughter cells provides the insight of partition mechanism.