Spatial control of bacterial division-site placement.

The site of cell division in bacterial cells is placed with high fidelity at a designated position, usually the midpoint of the cell. In normal cell division in Escherichia coli this is accomplished by the action of the Min proteins, which maintain a high concentration of a septation inhibitor near the ends of the cell, and a low concentration at midcell. This leaves the midcell site as the only available location for formation of the division septum. In other species, such as Bacillus subtilis, this general paradigm is maintained, although some of the proteins differ and the mechanisms used to localize the proteins vary. A second mechanism of negative regulation, the nucleoid-occlusion system, prevents septa forming over nucleoids. This system functions in Gram-negative and Gram-positive bacteria, and is especially important in cells that lack the Min system or in cells in which nucleoid replication or segregation are defective. Here, we review the latest findings on these two systems.