Most bacteria divide quite precisely and their daughter cells are often the same size. The reason for this accuracy is not really known, but it must be important because it is such a frequent phenomenon. This requires good measuring sticks, systems that calculate distance from the ends and restrict the formation of the division site to the middle of a dividing cell. In Escherichia coli, two systems are known to help contribute to midcell positioning of the division machinery: nucleoid occlusion, which prevents the scaffold protein FtsZ from forming rings over nucleoids, and the Min system. Even with the help of these mechanisms, the question of how a bacterium finds its center so precisely is still enigmatic.
Click "source" to read more.