Spatial distribution of high copy number plasmids in bacteria

Plasmids play essential roles in bacterial metabolism, evolution, and pathogenesis. The maintenance of plasmids is of great importance both scientifically and practically. In this mini-review, I look at the problem from a slightly different point of view and focus on the spatial distribution of high copy number plasmids, for which no active segregation mechanism has been identified. I review several distribution models and summarize the direct and indirect evidence in the literature, including the most recent progress on measuring the spatial distribution of high copy number plasmids using emerging super-resolution fluorescence microscopy. It is concluded that many open questions remain in the field and that in-depth studies on the spatial distribution of plasmids could shed light on the understanding of the maintenance of plasmids in bacteria.